April Feed

April 2021 Weather Recap: Above Average Temperatures, Below Average Rainfall.

 

 Pink blossoms new york city

April 2021 featured ten days with highs of 70° or warmer, the first time April reported this many since 2010, and just the tenth time overall.   (The average number of such days in April is six.)  This above average number of warm days resulted in the month's average high being 2.5 degrees milder than average (its average low was 0.7 degrees above average).  Of the ten Aprils with ten or more highs of 70° or warmer, just four rank among the ten mildest Aprils.  This April ranked 22nd (out of 153). 

 

Chart - aprils with 10+ 70-deg highs
 

The month's  coldest temperature was 28° (on 4/2), which was the coldest reading in April in five years.  And although this April was significantly milder than April 2020 (which was 2.7 degrees colder than average), its coldest temperature was eight degrees colder.  The warmest reading was 85°, which is close to what the warmest reading in April has averaged since 2000 (last April was an exception, with a mildest reading of just 68°).   This reading came five weeks after the year's first reading in the 80s (82° on 3/26), and it was the warmest reading since Sept. 5.  

 

The month's warmest reading was on 4/28, but the most above-average period of the month was the seven days between April 4 and 10, when temperatures were eight degrees above average (high/low of 68°/49°).  In total, the month had twelve days that were five degrees or more above average, and five that were five degrees or more below average.  

 

Another highlight of the month occurred on 4/8 when the humidity dropped to 7% during the afternoon - the second lowest level this century.  Finally, April's rainfall of 2.69" was nearly two inches below average.  All but 0.05" fell between 4/11 and 4/30.

 

Here are April recaps of the past five years:

2020

2019

2018

2017

2016

 Park avenue in the spring


How "Back-Door" Cold Fronts Impact New York's Springtime Weather

 

Back door cold front

 

For the most part, cold fronts move from west to east in the Northeast, but, occasionally, chilly air arrives from the opposite direction.  When it does, this occurrence is known as a "back-door" cold front.   Because such a front's winds usually come in from the ocean, this type of front is often associated with overcast skies (sometimes with drizzle); its east-northeasterly winds bring damp and chilly air. 

These incursions of chilly air that come from the opposite direction occur mostly in the springtime, when their cooling effect is enhanced by the wintertime water temperature of the Atlantic Ocean.  In terms of geographic reach, these fronts mostly impact New York City, the Jersey shore, and New England; only occasionally do they extend as far inland as Philadelphia, Baltimore, or DC.

What follows are 40 instances of the more impressive back-door fronts that have come down from the cold Atlantic.  As you'll read, six of the years had two notable back-door fronts.

 

East to west

June 4, 1895 - Winds shifted from the southwest to northeast during the afternoon, breaking a five-day heat wave (its record highs on June 1, 2 and 3 are still standing).  Between 3PM and 8PM, the temperature dropped from 91° to 64°.  The following day would be overcast, with temperatures stuck in the 60s. 

April 25, 1915 - This date experienced, perhaps, the greatest temperature swings of any in New York's weather history.  After the temperature soared from 47° shortly after midnight to 91° at 3:00 PM, winds shifted to the east-northeast, and the temperature plunged to 52° by midnight.  This was the result of a strong warm front moving through for about ten hours (9 AM-7 PM), then being displaced by a back door cold front.  No rain was produced by the passage of these fronts.  Two days later, a similar scenario unfolded.  After reaching 92° shortly before 4:30 on 4/27, a back-door front moved through a few hours later, and the temperature dropped to 54° by midnight.

April 1, 1917 - In the span of just eight hours, the temperature plummeted from 83° to 44° as a back-door cold front moved through and winds shifted from the southwest to the northeast.  This was the warmest reading of the month, with the next reading in the 80s not occurring for another seven weeks.

March 19, 1918 - After a balmy high of 76° was reached at 3:00 PM (a record for the date that still stands), the wind shifted from the southwest to the northeast, and the temperature dropped like a rock, and was half that reading by midnight.

May 23, 1925 - After the high reached 91°, winds shifted from the southwest to northeast late in the afternoon, and by midnight the temperature had fallen to 59°; the temperature on the afternoon of 5/24 was only in the upper 40s.

July 1, 1933 - After a high in the low 90s, a severe thunderstorm from 8:30-10:30 PM dumped 2.17" of rain.  During the storm the temperature dropped from 88° to 72°, where it stayed for much of the next 24 hours.  And on 7/3, afternoon temperatures got no higher than the mid-60s.  

March 27, 1939 - Today's high/low of 73°/39° followed one of 72°/39° three days earlier.  However, while the low on 3/24 was in the pre-dawn hours, the low today was at midnight after winds shifted to the northeast in the PM hours.  And the following day had temperatures in a narrow range of 35°-40°.

April 25, 1939 - After rising from 53° at 4:00 AM to 86° for a few hours in the early afternoon, winds shifted to the northeast mid-afternoon and the temperature dropped back to 52° by 11:00 PM.  And then three days later the high would be only 46° (20 degrees below average).

July 4, 1941 - Just two days after a torrid high/low of 98°/78°, and winds out of the southwest, today was rainy, foggy and cool, with winds from out of the northeast, and a high/low of just 64°/62°.  Today's high would be July 4th's coolest until 1978.

 

Reverse
  

March 22, 1945 - In the midst of the very mild second half of March, today was an outlier as the high reached only 40° (the low was a seasonable 35°).  Winds were out of the northeast, skies were overcast and light showers fell throughout the day. 

April 13, 1955 - A chilly high of 46° came just two days after a high of 84°.  Skies were overcast and winds were from the northeast.

July 6, 1956 - Although yesterday was cool (high/low of 66°/58°), today was even cooler as the high/low was just 61°/57° under gray skies and winds from out of the northeast.  These two unseasonably cool days followed consecutive days in the 90s.

June 1, 1959 - Today's chilly high of 64°, under mostly overcast skies, followed a five-day warm spell at the end of May that had highs averaging 87°.  Today's conditions were the result of a back-door cold front that moved in from New England last night. 

April 30, 1962 - After three days of summer-like warmth (highs of 91°-89°-80°), and winds from out of the southwest, winds shifted to the northeast after midnight and daytime temperatures were only in the mid-40s. 

April 19, 1964 - The day after the high reached 86°, a "back-door" cold front moved through, and by mid-afternoon the temperature dropped into the mid-50s.  (And on 4/21 the high would be just 44°.)

May 5, 1965 - The day after the high reached 90°, today's was 62°.  Winds came from a north-northeast-easterly direction.

April 28, 1966  - It was a dreary, raw, and damp day, with light rain in the morning.  With a high/low of only 42°/39°, today had the coldest mean temperature of the month.  On 4/26 the mercury dropped from 73° late in the afternoon, to 49° by midnight.  Then the high/low the next two days was 52°/40° and 42°/39°.  Winds were from out of the north-northeast.

April 20, 1972 - The temperature at 4:00 PM was quite chilly, at 43°, a drop of 32 degrees since midnight, and forty-three degrees from yesterday afternoon's 4:00 PM reading of 86°.  This was a result of winds shifting to the northeast from dawn to dusk.

May 24, 1975 - Today's high of 93° (the Saturday of Memorial Day weekend) was the year's first reading in the 90s.  However, the heat was short lived as a cold front from the northeast moved through during the evening, dropping the temperature to 61° by midnight, and into the upper 50s by the following afternoon. 

 

Overcast

Aug. 11, 1979 - The day after a high of 95°, today's temperatures in the afternoon were only in the mid-60s after the wind shifted to the northeast during the morning.  The next day was equally cool (after a chilly AM low of 57°) - and  a wet one, as 1.68" of rain fell; this was on top of 0.87" of rain that fell the night of 8/11. 

March 29, 1985 - This was the third day in a row with exceedingly mild temperatures, and today was the warmest of the three with a high of 82°.  Then a back-door cold front moved through after dark, and by midnight the temperature was down to 55°, on its way to down to 46° by daybreak on the 30th (but still well above average).  

April 19, 1985 - After the temperature soared to 88°, a back-door cold front moved through during the evening, and the temperature was down to 51° the next morning.  Then the cool air retreated on the 21st, and after two more days with highs in the 80s, winds backed around and came from the east late in the afternoon on the 22nd, cooling the temperature down to 53° by midnight.  

March 30, 1989 - After the wind shifted to the northeast, the temperature fell all day, from 76° to 50°; the next day the high/low was 50°/41°, which wasn't far from seasonable, but it was quite a cool-down from 3/29's high of 82°.

March 14, 1990 - One day after Central Park recorded its earliest 80-degree reading on record, the warm front that delivered this extraordinary warmth retreated south of the area, as winds shifted to the northeast, and by afternoon, under a bank of clouds and fog, temperatures tumbled into the mid-40s, forty degrees colder than yesterday. 

May 23-25, 1992 - It was a Jekyl & Hyde Memorial Day weekend.  Saturday had mid-summer conditions, with a high of 92°.  Then a big change came on Sunday as a strong cold front pushed through in early afternoon, and temperatures plummeted from the low 80s to 45° by midnight.  Monday felt more like October, with overcast skies and a high of just 61°. 

April 12, 1996 - The high reached 80°, and then winds shifted to the northeast late in the afternoon, dropping the temperature to 55° by midnight, and 45° by daybreak on the 13th.

May 10, 2000 - After three days with highs in the 90s, winds shifted from the southwest to the east, bringing in much cooler air, and by daybreak today, the temperature was in the mid-50s, where it stayed for the rest of the day.  

June 12, 2000 - One month after a back-door cold front cooled down a hot spell, it was replicated today, with late afternoon temperatures in the upper 50s, and winds coming from the east-northeast 24 hours after temperatures were in the low 90s.

 

Northeasterly winds
 

April 16, 2003 - After peaking at 88°, winds shifted to the northeast and by midnight the temperature was down to 51°.  And on the 17th temperatures slowly fell all day, and it was 36° at midnight.  Winds remained out of the east-northeast for the next six days.

May 14, 2004 - The day after the high reached 86°, the temperature was only in the low 60s in the early afternoon.  However, the wind shifted later in the day and temperatures were back into the mid-80s on 5/15.

April 20, 2006 - Today's high of 83° was the warmest reading of the month.  A back-door cold front moved through during the evening, and by midnight the mercury had fallen to the mid-50s, and the mercury was mostly in the 50s for much of the next day, and stuck in the 40s on 4/22 as a developing nor'easter moved up the coast .

April 29, 2009 - The day after the high reached 90° (and dropped 25 degrees by midnight as winds shifted to the north-northeast), the temperature was in the mid-50s by daybreak.

July 19, 2012 - After yesterday's extreme heat (high of 100°) and humidity, today's high, under mostly overcast skies, was just 76°.  Never before has there been such a drop-off in temperature the day following a reading in the triple digits.  The next day the temperature was around 70° during the afternoon. 

May 28, 2014 - One day after a sultry high of 86°, today was overcast, with afternoon temperatures only in the upper 50s.  The back-door cold front passed through after 10 PM, and the temperature quickly dropped into the low 60s, then gradually falling into the 50s by daybreak, where it stayed for the rest of the day. 

June 1, 2015 - After a week of temperatures in the summery mid-80s today, was 30 degrees colder, with periods of rain, drizzle and fog.  Today's high in the 50s was chillier than any day in May - the first time this has ever occurred.  And tomorrow would have similar conditions. 

May 20, 2017 - An early, three-day heat wave came to an end last night after a shift in wind direction.  Today's afternoon temperatures were in the low 60s, which was about 30° cooler than the highs of  the previous three days.

Nov. 4, 2017 - The day after temperatures were in the mid-70s, the temperature at daybreak today was nearly 30 degrees chillier, the result of a shift in the wind direction; afternoon temperatures were twenty degrees cooler.  On the positive side, skies were mostly clear.

April 8, 2019 - After peaking at 79° at 4 PM, winds shifted from west to northeast, and by midnight the temperature was down to 49°.

October 3, 2019 - The day after the mercury soared to 93° (the first reading in the 90s in October since 1941), winds shifted overnight to a northeasterly direction, and temperatures this afternoon were only in the mid-50s.  Light showers and drizzle fell throughout the day.

 

Overcast Skies_Brooklyn Bridge_RedHanded_StockF

 

 

 

 

 


A Taste of Summer: The Year's First High of 80+

 First
Since 1980, the average date of the first reading of 80° or warmer is April 21 (a month later than the average date of the first reading of 70°+).  This is about a week earlier than 1900-1979, and two weeks earlier than the 1869-1899 period.  It's happened as early as March 13 (in 1990) and as late as June 7 (in 1924).  1918, 1927, and 2010 had their first reading of 80+ occur on the same date as each year's first high in the 90s. 

 

The average high temperature on the day before the first 80+ reading has been 70°, on the day of the first 80+, it's been 83°, and the high on the day following has averaged 74°. 

 

About one-third of the years have had a day of 80° or warmer on the day following the first 80+, but 16 years didn't have their second high of 80°+ for four weeks or more.  The greatest number of days to elapse before the second 80+ reading was 57 in 1928 (April 6-June 1).  The most recent lengthy hiatus was 41 days in 2013 (April 10-May 20).

 

Eight years have had their first 80+ high in March.  The first time it happened was in 1921, the most recent occurrence was 100 years later, in 2021.  Meanwhile, a first 80+ in June has occurred just once (1924).

 

Chart - earliest and latest first 80

 

On the day with the first high of 80° or warmer, the diurnal variation has averaged 27 degrees (this compares to a 14-degree variation for any day of the year).  The  greatest variation was 43 degrees in 1929, when the high/low was 89°/46°.   The smallest variation was 16 degrees in 1908 (81°/65°).

 

Chart - greatest diurnal variation on day of first 80
 

The chilliest low on the day of  the first 80+ reading was 43° in 1936 and, again, in 1990.  The warmest low was 68° in 1898.  The chilliest day-before high was 49°, in 1977.  The chilliest day-after high was 50° in 1921, and 51° in 1939.

 

29 years (about once every five years) had a warmer reading on the day after the first 80+ reading.  The warmest day-after reading was 93° in 1988.   The last time the day-after was warmer was in 2009, when the  high was 92° (the first 80+ reading that year was 88°).  The warmest day-before reading was 79°, which has happened in four years, most recently in 1955.  (And ten other years had a day-before high of 78°.)

 

April 19 is the date that's had the most first 80+ occurrences - in ten years.  And it's happened in seven years on April 25.   The most consecutive years to have the first 80+ occur in May is six, from 1873-1878. 

 

There have been six pairs of years in which the date of the first 80+ was the same:

> April 18, in 2015 and 2016

> April 15, in 2002 and 2003

> April 19, in 1972 and 1973

> April 26, in 1969 and 1970

> May 16, 1931 and 1932 (and in 1933, the date was 5/15)

> April 19, in 1914 and 1915

 

There have been fiver pairs of years in which the dates of the first 80+ were at opposite ends of the early/late spectrum.

> 1997 - May 19/ 1998 - March 27

> 1988 - May 23/ 1989 - March 28

> 1984 - May 23/1985 - March 29

> 1945 - March 20/ 1946 - May 25

> 1920 - May 28/ 1921 - March 21

 

Finally, measurable rain has fallen on the day of the first 80+ reading in 20% of the years (similar to the day of the first reading of 70+).  The biggest rainfall on this date was 0.67" in 1984 (May 23) as afternoon thunderstorms moved in after the temperature peaked at 81°; the second most was 0.60" in 1951 (4/29).

  80 plus

 

 


Spring Awakening - The Year's First High Temperature in the 70s

70+

 

So far this century, the average date for the first reading of 70° or warmer in Central Park has been March 19 (and in the past five years it's been March 5).  This is four weeks earlier than what the average date was during 1869-1899; and during the 20th century this first occurrence was at the end of March.  The earliest date for a 70+ reading has been Jan. 6, which happened in 2007 (joining two other "first 70s" in January, in 1932 and 1950); the latest date is May 9, which happened in 1875 (and it's happened in May in five other years, the last time being in 1940).

 

Chart - earliest first 70s

Chart - latest first 70

 

The average high temperature on the day of the first 70+ has been 74°; the average low on that day, 48° (this diurnal variation of 24 degrees is much wider than the typical daily variation of 15 degrees).  The average high of the day before the first 70+ is 60°; the average high on the day following the first 70+ day  is 66°. 

 

11 years' first 70+ reading also served as those years' first 80°+ reading, with the most recent occurrence being in 2003.  And in 1927 the year's first 70+ served not only as the first 80+, but as the year's first reading in the 90s.  Meanwhile, 15 other years had their first 80+ come the day after the first 70+ (the last time this happened was in 2013).

 Chart - warmest first 70s

 

Back-to-back years with very early dates for the first 70+ are 1949 (Feb. 15) and 1950 (Jan. 26), and 2017 (Feb. 21) and 2018 (Feb. 24).  And there have been two periods of three consecutive years with very late dates: 1883 (May 3), 1884 (May 2) and 1885 (April 21); and 1875 (May 9), 1876 (May 6) and 1877 (April 23).

 

The greatest difference in high temperature between the day before and the day of the first 70+ is +34 degrees, in March 1935 (from 43° to 77°), and +33 degrees in April 2001 (from 45° to 78°).  And the biggest decline on the day after occurred in March 1934, -35 degrees (from 71° to 36°), and -34 degrees in Feb. 1874 (from 72° to 38°).  Lastly, the biggest increase on the day after is +14 degrees in 1902 (from 70° to 84°).

 

Chart - biggest temp diff day before first 70

 Chart - biggest temp drop after first 70

The greatest diurnal variation on the day of the first 70+ is 42 degrees, with a high/low on March 13, 1990 of 85°/43°.  The coldest reading to occur on the day of the first reading of 70+ is 30° on March 18, 1934.  It came after the high of 71° was reached and a cold front moved thru mid-afternoon.  (This is the also the only time a reading of 32° or colder occurred on the same day as the first 70°+.)

 

After a reading of 70°+, the average number of days before the next reading of 70°+ has been 11, with the greatest hiatus being 80 days in 1932 (when the first 70+ was on 1/14).  Not surprisingly, the most days to elapse before the next 70+ high have occurred in Jan/Feb -  with the average hiatus being 43 days.  In about one-third of the years, the first 70°+ was followed the very next day by another high of 70+, with the longest streak being eight days, in April 1896 (including highs of 87°, 88° and 90°).  The longest streak in the years since 1900 has been six, set in April 1952.  

 

Spring awakening
 

 

An early first 70+ isn't predictive of a hot summer as some very hot summers had their first 70+ at a late date.  This includes the year with the second hottest summer, 1966, which didn't see its first 70+ until April 25.  And the fifth and sixth hottest summers, in 1983 and 1993, didn't have their first 70+ until April 25 and April 19, respectively.

 

About 20% of the dates of the first 70+ reported measurable rain; two-thirds of these years had amounts less than 0.10".  (By contrast, 40% of the days with the first 60+ reading had rain.)  Just one date had more than an inch, on April 6, 1937.  On that day, 1.02" of rain fell before dawn and ushered in mild air (the high reached 72°).

 

And, finally, some more interesting occurrences:

> In 2018, after a high of 78° on Feb. 21 (the warmest reading ever in Jan/Feb), more than seven weeks passed before the mercury rose above the low 60s.

> In 1998 the first 70+ reading was 83°, and it was the first of five days in a row in the 80s - at the end of March (March 27-31), when the average high is in the mid-50s. 

> The first high of 70+ in 1988, 76° on 3/24, came just two days after a low of 17°

> The day of 1980's first 70+ followed a big rainstorm of 3.42" the day before.

> In 1967, a week after the first 70+, on March 11, there was a week of harsh winter conditions, with an average high/low of only 31°/20°, including a reading of 8° on 3/19; and three snowfalls produced 15.4" of snow. 

> 1947's first 70+ on 4/6 was the day after nearly two inches of rain fell. 

> In 1929 the first 70+ came three days after a low of 12°.  (In 2009 a low of 12° in March came four days before the year's first 70+.)

> In 1874, two days after a high of 72° on Feb. 23, 7.5" of snow fell. 

 

Springtime in central park

 

To read an analysis about the first readings of 60+ each year, double click here.

 

 

 


April 2020 Weather Review: First Cooler Than Average Month of the Year

April 2020

 

April was 2.7 degrees below average, making it the first month this year to be chillier than average.  It was also the fourth chilliest April of the past 40 years.  Even more interesting, this was the first April since 1940 with no highs of 70° or warmer (after three such days in March).  In the years since 2000 the warmest reading in April has averaged 85°, but this April's mildest reading was just 68°.  Despite this cool warmest reading, the nights weren't as cold as might be expected as the coldest reading, 36°, was three degrees milder than a typical April's coldest temperature.  The 32-degree difference between the month's coldest and warmest readings was 20 degrees less than the average difference between the two extremes - the smallest gap of any April on record.

 

The last sixteen days of the month all had below average mean temperatures, the longest below average streak since March 2018's streak of 22 days.  These 16 days were seven degrees below average (seven of the days were ten or more degrees below average).  Before this streak started April had been two degrees milder than average (with April 4-8 seven above average).

 

Although it was the fourth coldest April of the past 40 years, it ranked 63rd among all Aprils going back to 1869.  This was due to the fact that Aprils before 1940 were much chillier.  (Six of the eight Aprils with no high readings of 70° or warmer occurred between 1873-1884.)

 

Cool-ish

 

Although April's rainfall, at 4.49", was an average amount, it was enough to make it the rainiest month so far this year.  The month also had the year's biggest rainstorm - 1.92" on 4/13 (the day after Easter).

 

A typical April is 10 to 11 degrees warmer than March, but April 2020 was just 2.4 degrees milder - the third closest of any year.  Additionally, April's mildest reading was nine degrees cooler than March's (68° vs. 77°) and its mildest low temperature was one degree cooler than March's (53° vs. 54°).

 

Chart - closest april-march temp
 

2020 is just the seventh year in which April, March and February had more precipitation than the month preceding it. This year April had 4.49"; March, 3.78"; February 2.54"; and January 1.93".

Chart - first 4 months of rain

 

Here are April recaps of previous years:

2019

2018

2017

2016

 

     


April 2019 Weather Recap

April 2019As we headed into the last week of April it appeared the month had a good chance of becoming either the fifth, sixth or seventh mildest April on record.  But when the last five days of the month averaged five degrees cooler than average, it ended up as the 13th mildest, 2.5 degrees above average (still a noteworthy achievement as it was milder than 138 other Aprils).  Perhaps a bigger highlight was the month's 18 days with measurable precipitation, the most since May 2012.  This was also the most days of precipitation of any April.  However, despite the frequent rainfall, the 4.55" that was measured was just an average amount.  Despite being only average, this amount was enough to make April the wettest month so far this year. 

 

The five chilly days at the end of the month were immediately preceded by a two-week period with above average temperatures (six degrees above average); this was the longest streak of above average days since one of eighteen days in late December/early January.  This mild streak included the year's first reading in the 80s - 80° on 4/19, which was Good Friday (just the fifth Good Friday with a high in the 80s); Easter Sunday cooled down to a high of 66°.  The month's coldest reading, 33°, occurred on 4/1.  (Since 2000 April's warmest temperature has averaged 85°, its coldest reading has averaged 33°.)

 

Finally, 2019's mild April came a year after the coldest April in 40 years (which followed the second mildest April on record).  Despite the disparity between the two years, April 2018's warmest temperature was two degrees above this year's (82° vs. 80°) while its coldest reading was just one degree lower (32°).

 

W4th street blossoms

Here are recaps of previous Aprils:

2018

2017

2016

 


Best & Worst Weather Conditions During Mets Home Openers

Mr. met

 

It seems fitting that the Mets first home opener in 1962, a season in which they lost 120 games, ranks as one of its worst, with cold temperatures, wind and drizzle.  And how perfect was it that the weather was glorious the year they won their first home opener in 1968?  The charts below focus on the best weather conditions in years the Mets won their home openers, while the worst weather is grouped into games lost and games won.  (But does it really matter what the weather is, just as long as the home team wins?)      

 

 Chart - best and worst mets home openers

 

To read about weather and outcome of every Mets home opener since 1962, double click here.

 

Tom seaver

 

 


April 2018 Weather Recap - Chilly, Snowy, Rainy

Rainy day in new york

 

Like four of the past five months, April was colder than average.  (February, the mildest on record, was the outlier.)  This was the chilliest April since 1975, 3.5 degrees below average.  Eight days had mean temperatures ten degrees or more colder than average (and half of the month's days were five degrees or more below average).  Just three days had highs of 70°+, the fewest since April 2000.  Two of them were back-to-back: 82° and 77° on 4/13 and 4/14.  Earlier that week the month's coldest temperature, 32°, was posted on consecutive days, on-par with what the coldest reading is during a typical April (33°).  However, the number of days with highs chillier than 50° (nine) and lows in the 30s (sixteen) was well above average (three and five days, respectively). 

 

April was also a wet month, with 5.78" of precipitation measured, making it the third month in a row to receive more than five inches (5.83" fell in February, 5.17" in March).  The last time this occurred was August-October 2011.  More than half of the month's precipitation fell during a rainstorm on 4/15-16 that dropped 3.29", the biggest deluge since April 30, 2014.  Finally, Easter, which fell on 4/1, was sunny and pleasant, with a high of 60°.  However, 5.5" of snow fell the next morning (forcing postponement of the Yankees' home opener).  This was the biggest snowfall in April since 1982.

 

Snow on yankees home opener

 

April 2018 was just one of three Aprils since 1970 to have an average temperature below 50.0 degrees (coming in at 49.5).  Before 1970, however, April temperatures this cool were much more common, with half of the Aprils between 1869 and 1969 being that chilly.  Therefore, when compared to all Aprils, this April ranks as 44th coolest overall.  Finally, March and April 2018 combined were the coldest first two months of meteorological spring since 1984, and the third coldest in the years since 1970.

 

For recaps of the past two Aprils double-click here: April 2017 and April 2016 

 

 Apr 22 st lukes garden

 

 

 

 

 


April 2017 Recap: Second Mildest April, Featuring Second Warmest Easter

BlossomsWith four days in the 80s and no truly cold days (the chilliest was five degrees below average), April 2017 became the second mildest April on record (4.2 degrees above average), pushing April 1941 to third place (57.2° vs 56.9°).  This was a rebound from March, which was 3.3 degrees colder than average.  April's coldest low was 37° on 4/1, which was only three degrees colder than average.  This was the "mildest coldest" reading since April 2010 (the mildest April on record).  The warmest reading of the month, 87°, occurred on Easter Sunday (4/16), which was the second warmest temperature every experienced during the holiday. 

 

 

Interestingly, despite it being the second mildest overall, eight other Aprils had warmer average highs than April 2017.  However, this April was the mildest of them all in terms of average low, even ahead of New York's mildest April (2010) by a comfortable margin.

 

10 Mildest Aprils

 

Other observations of interest:

  • The four 80-degree days were the most since April 2009, when there were also four (the most for any April is five, which happened in four years:  2002, 1985, 1962 and 1941).  This years summery high temperatures occurred on 4/11 (80°), 4/16 (87°), 4/28 (85°) and 4/29 (85°).

 

80degrees

 

  • Although there were two days in the mid-80s at the end of April, the most extended period of above average temperatures occurred from 4/10 thru 4/17 when temperatures were 13 degrees above average.
  • Although Easter Sunday had the warmest high temperature, the day with the warmest mean temperature (average of the high and low) was 4/29, which had a high/low of 85/64, 1.5 degrees degrees warmer than Easter (87/59).
  • The month's two biggest rainstorms produced nearly identical amounts - 1.21" in the pre-dawn hours of 4/4, and 1.25" on the night of 4/25 into the early AM hours of the 26th.
  • Finally, for what it's worth, the warmest and coldest readings of April 2005 were the same as April 2017 (87/37), but 2015 is ranked as 14th mildest.

 

Springtime sky on west fourth st 

 

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Days With Desert-Like Humidty

Weather_hot_sun

 

In April of 2016 New York experienced eleven days in a row with clear or sunny skies (4/12-22).  In addition to this abundance of blue skies, the streak was also characterized by extremely low humidity.  While typical late afternoon humidity levels in April are generally between 45% and 50%, during these eleven days it was mostly between 15% and 20%.  And at 5 PM on 4/20 it fell to 9%.  Since 2000, only one other day has had a humidity level that was lower - March 31, 2007, which reported 6% humidity late in the afternoon.  April 2016's streak of arid days was the inspiration for this post, which looks at hourly and monthly relative humidity reported in Central Park since 2000, with a focus on extremely low levels, which for the purposes of this analysis is 25% or lower.          

 

  • Since 2000 5% of the days have had at least one hour with a relative humidity of 25% or lower (about 19 days/year).  The number of such days ranged from six in 2000 to 32 in 2010.  When I began this project I guessed that January and February might have the most days with the lowest humidity, but it turns out that two-thirds of the these days occurred in March or April.

 

Humidity Bar Chart

 

  • February, March and April have the lowest humidity, while September has the highest (followed closely by June).
  • Not only were the two years with the lowest average humidity consecutive (2015, 2014), so were the years with highest average humidity (2003, 2004).  And while the year with lowest humidity had significantly lower than average precipitation, the second driest was well above average.  In fact, the total precipitation for the year with the highest humidity was very similar to this second driest year (58.56" vs. 57.79").

 

Dust

 

  • During a typical day, the lowest and highest humidity levels occur about nine hours apart, with the highest occurring around daybreak (averaging 72%), and lowest levels during mid-afternoon, averaging in the mid-50s.

 

HumidityMonthly

 

  • There have been nearly 40 days with at least one hour of humidity at 15% or lower (thru the first week of April 2021).  All were in March or April, until 2018 when the humidity fell below 15% twice in May and once in November.  The lowest humidity to occur in the other months has been 16%, and it's happened on four dates: Feb. 26, 2014; May 3 and May 13 in 2007, and Sept. 11, 2001.
  • The months with the least and most precipitation don't always have corresponding low and high average humidity.  For example, the most humid October and February had only 1.18" and 1.66" of precipitation, respectively.  The months with the least humidity don't have outliers quite that extreme, but the driest June and January had more than four inches of precipitation, which is close to average.
  • In this century, months in the years 2000-2004 tended to have the highest average humidity while those with the lowest were clustered in the years since 2010.

 

Chart - lowest humidity


  



 

   

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