bluewave

The latest Euro brings the warm front through around 7-8 am in Sunday with some rain. Then it has breaks of sun and areas south of the warm front make it into the 70s. It has a round of late afternoon and evening convection as the atmosphere destabilizes behind the front.

Yeah, that was the conclusion of a recent study.

We are pretty much rewriting SST and air temperature climo following such a -AO winter. Notice how much warmer the Western Atlantic is now compared to 2010 and 2011. Those were the last two winters with such a -AO and peak values dipping below -5. There is supposed to be a cold pool off the East Coast after such a -AO winter. But instead, there are near record warm SSTs to our east. The blocking pattern this month so far is linking up with the WAR and boosting heights over the NE. So the average temperature during the first week of April was much warmer than the past years with a low max temperature under 40°. It also resulted in the near record low single digit RH values and highs that keep beating guidance. 4-6-21 4-6-11 4-6-10

This is the first time since at least 1950 that NYC had a warmer than average first week of April with a high temperature under 40°. All the other years were around 10° colder for the first week of April. So like we saw over the winter, this south based blocking pattern is creating new and unusual weather patterns for us. Time Series Summary for NY CITY CENTRAL PARK, NY Click column heading to sort ascending, click again to sort descending. Rank Ending Date Lowest Max Temperature Apr 1 to Apr 7 Avg Temperature + Departure 1 1982-04-07 30 41.1 -7.9 2 1975-04-07 37 40.4 -8-6 3 2003-04-07 38 40.6 -8.4 4 2021-04-07 39 51.0 +2.0 - 1995-04-07 39 43.2 -5.8

The dry conditions are allowing the high temperatures to beat guidance. Pretty impressive diurnal range especially in areas that radiated last night. So the warm departure for the day was mostly driven by the high temperature. CLIMATE REPORT NATIONAL WEATHER SERVICE NEW YORK, NY 446 PM EDT WED APR 07 2021 ................................... ...THE ISLIP NY CLIMATE SUMMARY FOR APRIL 7 2021... VALID TODAY AS OF 0400 PM LOCAL TIME. CLIMATE NORMAL PERIOD 1981 TO 2010 CLIMATE RECORD PERIOD 1963 TO 2021 WEATHER ITEM OBSERVED TIME RECORD YEAR NORMAL DEPARTURE LAST VALUE (LST) VALUE VALUE FROM YEAR NORMAL ................................................................... TEMPERATURE (F) TODAY MAXIMUM 68 153 PM 85 2010 55 13 64 MINIMUM 40 519 AM 23 1982 38 2 44 AVERAGE 54 46 8 54

The April forecast looks like a continuation of the winter south based blocking theme with spring wavelengths. This week the south based blocking allowed highs around 70°. Looks like our first chances for heavier rain will come on Sunday. Next week appears generally cooler than this week as the -AO and +PNA gets stronger. But the south based blocking should allow enough ridging near the East Coast. This will keep the coolest temperature departures to our west which has been a frequent theme. Perhaps more rain chances for the gardening interests.

JFK made it down to 10%. March and April typically have our lowest relative humidity readings of the year. It will be interesting to see if anyone can find the relative humidity during the July 1936 dust bowl heatwave.

Ridiculous AO and NAO volatility since February.

I believe the all-time lowest relative humidity at Newark is 5% on 3-30-07 Newark/Liberty MOSUNNY 71 3 7 https://www.wunderground.com/history/daily/us/nj/newark/KEWR/date/2007-3-30 5:51 PM 68 F -5 F 5 %

First time the relative humidity at Newark dropped under 10% since 2012. Newark Liberty SUNNY 69 8 9 https://mesonet.agron.iastate.edu/plotting/auto/?_wait=no&q=157&network=NJ_ASOS&station=EWR&year=2021&var=min_rh&dir=below&thres=0&dpi=100&_fmt=png

The relative humidity is running under the current model forecasts. The HRRR has the RH levels dropping to 10-15% in some spots this afternoon. So it will be interesting to see if any stations can record a rare single digit relative humidity reading.

Next several days look warm and dry with highs making another run on 70° today.Then it appears that the high over the region providing the dry and warm conditions will shift east by Friday. So more of a backdoor onshore flow developing. Main question is where the front will stall out. That will determine where the best rainfall potential sets up. Dry and warm N to NW flow next several days High moves east by Friday allowing more onshore flow with a backdoor nearby

Yeah, JFK can have some of the warmest area temperatures on dry offshore flow days. JFK and EWR both made it to 70°. Our area was far enough SW of the storm east of New England. Looks like the blocking ridge should keep most rain west of the area this week. Then it appears that the ridge eventually weakens by the weekend allowing better rain chances.

The warm spots may make a run on 70° today as these dry and windy downslope days often beat guidance. KEWR GFS MOS GUIDANCE 4/05/2021 0000 UTC DT /APR 5 /APR 6 /APR 7 / HR 06 09 12 15 18 21 00 03 06 09 12 15 18 21 00 03 06 09 12 18 00 X/N 68 44 66 46 67 TMP 50 47 49 58 64 67 61 55 49 46 50 57 62 64 60 55 50 48 51 64 61 DPT 27 27 28 27 26 25 27 29 29 28 29 25 22 23 26 30 32 33 35 34 37 CLD CL CL FW FW FW CL SC BK CL CL CL CL FW FW FW FW CL CL FW SC BK WDR 31 27 31 32 31 30 30 31 31 28 31 32 31 32 32 33 30 36 35 34 11 WSP 07 07 13 15 17 18 16 12 06 05 08 11 13 10 09 04 03 02 04 06 06

It’s one of the quirks of our warming climate. The average first 80° day has moved one month earlier up at Newark from April 28th in 1970 to March 31st in 2021. But the average first 90° day has remained nearly unchanged from May 19th in 1970 to May 21st in 2020. So record early 90°+ heat like April 2002 remains rare. The fall is reversed. Later last 90° day while the last 80° day is mostly unchanged.

The south based blocking has been the real deal since early December. We can see how it has resulted in a drier pattern for New England. We’ll probably have to wait for it to weaken a bit to get more significant rain chances again here. But the rains eventually end up arriving even if they get pushed back a little from earlier forecasts.

Looks like we are headed for a pattern when the warmest days top out in the 60s. Some days that get more onshore flow and clouds may only make it to the 50s. The blocking has corrected further south in the most recent model runs. So the lows get forced by well to our south. The NW to NE flow prevents us from making a run on 80s like late March for a while. Our next chance at any significant rains will have to wait for the block to weaken a bit. Funny how we are seeing a spring version of the winter south based blocking pattern. KEWR GFSX MOS GUIDANCE 4/04/2021 0000 UTC FHR 24| 36 48| 60 72| 84 96|108 120|132 144|156 168|180 192 SUN 04| MON 05| TUE 06| WED 07| THU 08| FRI 09| SAT 10| SUN 11 CLIMO X/N 61| 43 67| 43 66| 44 65| 48 61| 47 59| 46 56| 42 59 40 59 New run blocking pressing further south Old run more low pressure near the Northeast

Tough to keep the 60s away for long this time of year. KEWR GFSX MOS GUIDANCE 4/03/2021 1200 UTC FHR 24 36| 48 60| 72 84| 96 108|120 132|144 156|168 180|192 SUN 04| MON 05| TUE 06| WED 07| THU 08| FRI 09| SAT 10|SUN CLIMO N/X 38 59| 41 66| 43 62| 46 63| 47 64| 47 59| 46 63| 48 40 59

Yeah, the low humidity season usually peaks in March and April here. Things should gradually moisten back up going into next week. Then it looks like our next chance of significant rain again in about a week. We saw this in March when we went from very dry to wet again. The main take away is that dry patterns don’t have much staying power in our new wetter climate. https://mesonet.agron.iastate.edu/plotting/auto/?_wait=no&q=157&network=NJ_ASOS&station=EWR&year=2020&var=min_rh&dir=below&thres=20&dpi=100&_fmt=png

Looks like another low dewpoint and low relative humidity special today. Dewpoints are forecast to drop to near 0 with temperatures getting back above 50°. We make a run on 60° tomorrow and get back into the 60s on Monday. So it’s tough to maintain the record cold of the last few days very long. KEWR GFS MOS GUIDANCE 4/03/2021 0600 UTC DT /APR 3 /APR 4 /APR 5 / HR 12 15 18 21 00 03 06 09 12 15 18 21 00 03 06 09 12 15 18 00 06 X/N 55 38 58 40 65 TMP 36 44 52 55 51 46 42 40 44 49 55 56 53 48 44 42 46 56 62 58 50 DPT 9 3 3 5 11 17 21 25 29 31 31 29 29 30 29 28 29 28 27 30 32

This is only the 3rd April since 1990 with a NYC high temperature below 40°. The other 2 years were 2003 and 1995. It was also the first -14 daily temperature departure in NYC since November 18th. Time Series Summary for NY CITY CENTRAL PARK, NY - Month of Apr Click column heading to sort ascending, click again to sort descending. Year Lowest Max Temperature Missing Count 2021 39 28 2020 46 0 2019 45 0 2018 43 0 2017 48 0 2016 43 0 2015 43 0 2014 47 0 2013 43 0 2012 52 0 2011 44 0 2010 52 0 2009 48 0 2008 50 0 2007 41 0 2006 47 0 2005 50 0 2004 43 0 2003 37 0 2002 45 0 2001 43 0 2000 43 0 1999 46 0 1998 48 0 1997 42 0 1996 40 0 1995 39 0 1994 53 0 1993 41 0 1992 45 0 1991 46 0 1990 46 0

Outside of the unusual cold today and tomorrow, I don’t think anyone is forecasting dreary and cold for the whole month. The models have the blocking shifting from Greenland back to Canada over the next few weeks. So we trade in Greenland blocking for more +PNA blocking as the month progresses. We could easily get 60s like the models show coming up. Highs to our north will probably mean plenty of NW to NE flow. Maybe a low will eventually try to cut off underneath leading to several days of more easterly flow and rains. Northeastern New Jersey... Newark, NJ Ptcldy Sunny Mocldy Sunny Sunny Ptcldy Ptcldy /42 29/55 39/62 42/65 42/66 46/66 49/65 /00 00/00 10/10 10/00 00/10 20/20 20/30

Record cold today at LGA and EWR only a week after the record 80s heat last Friday.

This made the top 5 for greatest spring 7day temperature drops. https://mesonet.agron.iastate.edu/plotting/auto/?_wait=no&q=169&network=NJ_ASOS&zstation=EWR&hours=162&month=spring&dir=cool&dpi=100&_fmt=png

Updated for March 2021. 3....2021...LGA.....9...JFK....10.....BDR....8