bluewave

Steep surface to 500mb lapse rates in place for severe storms.

The forecast will come down to what happens with the low pressure system on Sunday. The EPS keeps it going far enough to our east so that we get into a deep SW flow at the end of the month. The OP Euro cuts it off east of New England with more of an onshore influence. If we can can get into a strong SW flow, then 80s will be possible.

Looks like an early round of showers next few hours. Then we’ll see how much we can destabilize going into the afternoon. The latest HRRR has a line of strong to potentially severe convection this afternoon.

Our next big temperature drop of the spring. From late March into early April it was 80s to 20s in 7 days. Now places like Newark will drop from 78° to the mid 30s in just 2 days. TEMPERATURE (F) YESTERDAY MAXIMUM 78 245 PM 91 1941 64 14 56 MINIMUM 48 550 AM 34 1953 45 3 42 AVERAGE 63 54 9 49

Yeah, not thinking that we see a repeat of last year. That was the first time the May monthly minimum temperature was lower than April. Quite a swing to warmer after that to the 2nd warmest summer behind 2010 near the coast. Monthly Lowest Min Temperature for NY CITY CENTRAL PARK, NY Click column heading to sort ascending, click again to sort descending. Year Apr May Season 1891 29 32 29 1874 20 33 20 2020 36 34 34 1947 33 35 33 1880 26 35 26 https://www.ncdc.noaa.gov/cag/divisional/time-series/3004/tavg/3/8/1895-2021?base_prd=true&begbaseyear=1981&endbaseyear=2010 201006 - 201008 75.2°F 126 3.5°F 202006 - 202008 74.4°F 125 2.7°F 201606 - 201608 74.2°F 124 2.5°F 200506 - 200508 73.9°F 123 2.2°F 201106 - 201108 73.9°F 123 2.2°F 199906 - 199908 73.7°F 121 2.0°F 201206 - 201208 73.4°F 120 1.7°F 201806 - 201808 73.4°F 120 1.7°F 201906 - 201908 73.2°F 118 1.5°F 201506 - 201508 73.1°F 117 1.4°F 194906 - 194908 73.0°F 116 1.3°F 200606 - 200608 73.0°F 116 1.3°F 200206 - 200208 72.9°F 114 1.2°F 201306 - 201308 72.9°F 114 1.2°F

Very active pattern for late April coming up. Severe threat Wednesday and big temperature drop to near freezing Thursday. Then a warm up followed by a slow moving coastal on Sunday.

The latest forecast soundings have some of the steepest surface to 500 mb lapse rates that we have seen in April. Looks like the potential for a severe squall line Wednesday afternoon,. Pretty impressive severe signal for April.

This will be the first time that we have 15 and 30 year climate normals with an update. So the annual average snowfall will be very high if we get a 15 year average. So it will be interesting to see all the new normals when they are released soon. https://www.ncei.noaa.gov/news/Upcoming-NOAA-2020-Climate-Normals Calculating the New Climate Normals Palecki emphasized that NOAA’s Normals are rather complicated sets of calculations, not just simple averages. These calculations fill in missing data using surrounding weather stations and ensure that daily Normals match monthly Normals. They also remedy discrepancies that might arise when stations change locations. In this next round of Climate Normals, new things will be added—including several small changes to how NCEI calculates them. “Our main methodologies have not changed since the last Normals cycle,” Palecki said. “But minor improvements have been made in how we round numbers, calculate percentiles, count the numbers of days exceeding thresholds, and format output.” Also, for the first time, this updated batch of Normals will include 15-year Normals for those needing a climatology representing a period closer to today. NOAA will also release high spatial resolution monthly Normals data for the conterminous U.S., as well as develop new tools and methods to access the data

+1 to +2 is the new normal. So we need a +3 to +4 monthly departure to seem warm. That’s what we got back in March with a top 5 monthly high temperature reaching 84° at Newark. So this would translate into 90°+ in April to have a similar warm feel.

It’s actually been a warmer than average April so far with numerous 70° days. But the cool downs after each warm up have created a cooler perception. We make another run on 70° before the sharp cold front on Wednesday. This is when strong to locally severe convection will be possible across the region. Then another sharp cool down into the 30s with a freeze just N and W of NYC. This is followed by another rebound in temperatures with a coastal storm possible on Sunday. Longer range may come down to the typhoon interaction with the mid and higher latitude pattern. The OP GFS and EPS are hinting that the SE Ridge will try to flex near the end of the month. So that may be the next chance to reach 80° if the models don’t shift before then. KEWR GFSX MOS GUIDANCE 4/19/2021 0000 UTC FHR 24| 36 48| 60 72| 84 96|108 120|132 144|156 168|180 192 MON 19| TUE 20| WED 21| THU 22| FRI 23| SAT 24| SUN 25| MON 26 CLIMO X/N 67| 50 71| 52 58| 33 56| 39 65| 47 69| 51 66| 51 70 45 64 SE ridge builds near end of April?

It looks like the typhoon will track very slowly near the Philippines the next several days. So it may be another week before it can recurve back out into the Pacific and potentially cause a wave break. The main player right now is the record block over Western North America buckling the flow.

Model forecasts indicating a very impressive cold frontal passage on Wednesday. Temperatures quickly rise into the low 70s ahead of the front. The forecast soundings indicate near record surface to 500 mb lapse rates. So severe convection looks possible. This is followed by a quick temperature drop to near freezing just N and W of NYC Thursday morning. Lapse rates remain steep to above 700mb so 50+ mph gusts will be possible behind the cold front.

It may be related to the slowing AMOC and warmer waters east of New England. More ridging east of New England since 2015 has resulted in frequent summer SSE to SSW flow. There was a stronger ridge over the Plains from 2010 to 2013 with a dominant SW to W flow.

The 90° degree day stats seem more like a wind direction issue since the airports are all on the water. Much more humid heat since 2015. The big onshore flow component has resulted in fewer 90° days at EWR and JFK. But since LGA is on the North Shore of Queens, the S to SE flow hasn’t impacted their recent 90° day counts. So they have had some of their highest 90° totals on record since 2015. Same story for Harrison, NJ which is more inland from Newark airport and doesn’t get the bay breeze. Time Series Summary for LAGUARDIA AIRPORT, NY - Jan through Dec Click column heading to sort ascending, click again to sort descending. Rank Year Number of Days Max Temperature >= 90 Missing Count 1 2010 48 0 2 2018 38 0 3 2002 35 0 4 2020 34 0 - 1991 34 0 5 2016 32 0 6 1983 31 0 7 2005 30 0 - 1953 30 0 Time Series Summary for HARRISON, NJ - Jan through Dec Click column heading to sort ascending, click again to sort descending. Rank Year Number of Days Max Temperature >= 90 Missing Count 1 2010 50 30 2 2018 47 0 - 2002 47 8 3 2005 41 9 4 2016 40 0 5 2020 39 0 - 2019 39 0 6 2012 35 21 7 2015 32 0 8 2011 31 30 9 2006 30 4 Time Series Summary for NEWARK LIBERTY INTL AP, NJ - Jan through Dec Click column heading to sort ascending, click again to sort descending. Rank Year Number of Days Max Temperature >= 90 Missing Count 1 2010 54 0 2 1993 49 0 3 1988 43 0 4 2002 41 0 - 1991 41 0 5 2016 40 0 - 1983 40 0 - 1959 40 0 6 1994 39 0 - 1944 39 0 7 2005 37 0 - 1987 37 0 8 2018 36 0 - 1949 36 0 9 2015 35 0 Time Series Summary for JFK INTERNATIONAL AIRPORT, NY - Jan through Dec Click column heading to sort ascending, click again to sort descending. Rank Year Number of Days Max Temperature >= 90 Missing Count 1 2010 32 0 2 1983 26 0 3 2002 21 0 4 1971 18 0 - 1949 18 0 5 2005 17 0 - 1991 17 0 6 2012 16 0 - 1959 16 3 - 1955 16 2 7 2016 15 0 - 1995 15 0 - 1961 15 0 8 1999 14 0 - 1988 14 0 - 1966 14 0 - 1952 14 0

Plows were out at around 700 ft in NE CT.

Doesn’t take long for above normal temperatures to return again. Next chance of 70° on Tuesday. Then another cool down with lows in the 30s for next Thursday. KEWR GFSX MOS GUIDANCE 4/16/2021 0000 UTC FHR 24| 36 48| 60 72| 84 96|108 120|132 144|156 168|180 192 FRI 16| SAT 17| SUN 18| MON 19| TUE 20| WED 21| THU 22| FRI 23 CLIMO X/N 55| 41 58| 42 61| 45 64| 47 68| 51 65| 37 59| 45 66 44 63

Heaviest rain at ISP since the end of October. 2021-04-15 1.80 2020-10-29 1.24 2020-10-30 0.58

This was the first time that Newark had 4 days reach 70° April 1-14 but not get above 72°. Time Series Summary for NEWARK LIBERTY INTL AP, NJ Click column heading to sort ascending, click again to sort descending. Rank Ending Date Number of Days Max Temperature >= 70 Apr 1 to Apr 14 Maximum Temperature 1 1945-04-14 8 84 2 2010-04-14 7 92 - 1981-04-14 7 80 3 1991-04-14 5 88 4 2021-04-14 4 72 - 2019-04-14 4 80 - 2017-04-14 4 84 - 2014-04-14 4 83 - 2011-04-14 4 87 - 2005-04-14 4 78 - 2002-04-14 4 77 - 1967-04-14 4 83 - 1955-04-14 4 84 - 1954-04-14 4 78

I don’t think anyone will be surprised by December having the biggest CONUS monthly temperature increase. Looks like September will follow in 2nd place. The few areas of cooling wound up near the Plains. Matches the pattern of where the most impressive Arctic outbreaks have occurred like we saw in February.

While we are still in a blocky pattern, the warm spots will make a run on 70° today. Looks like several cooler days coming up before the next 70° chance early next week. So some warmer days in the mix even with the -AO +PNA -EPO pattern. Beyond the next 10 days, we would need to see more of a SE Ridge for an 80° chance near the end of April. Still outside the effective range of the guidance. Euro highs today Next run on 70° possible early next week Blocking pattern in the means next 10 days

The warm spots could sneak in a 70° tomorrow. Then we cool down for several days. Looks like we could make another run on 70° in about a week. Shows how challenging it is to sustain below normal temperatures for more a than a few days at a time. KEWR GFSX MOS GUIDANCE 4/13/2021 1200 UTC FHR 24 36| 48 60| 72 84| 96 108|120 132|144 156|168 180|192 WED 14| THU 15| FRI 16| SAT 17| SUN 18| MON 19| TUE 20|WED CLIMO N/X 49 68| 52 55| 42 57| 42 59| 45 64| 47 67| 46 68| 48 43 62 TMP 55 60| 53 48| 43 51| 45 54| 50 57| 51 59| 51 61| 51 DPT 41 46| 46 41| 34 29| 33 31| 36 37| 37 31| 37 40| 38 CLD PC OV| OV OV| OV OV| PC OV| PC OV| PC PC| PC OV| OV

While the La Niña didn’t have the expected influence on our winter pattern, the tropics are looking more Niño-like. The very strong MJO has resulted in a significant WWB. Today we saw the biggest SOI drop of the year so far. So does this just get us back to ENSO neutral or is another El Niño beginning? It will probably come down to whether a follow up WWB emerges in May. ENSO neutral vs El Niño could have an influence on summer hurricanes and temperatures. The ENSO forecast models are currently in the spring forecast barrier period. Daily SOI 2021 103 1009.79 1010.95 -25.60 Very strong WWB pattern

2010 is always a tough act to follow since it was so much warmer than all the other summers. While last summer was our 2nd warmest, it was almost a full degree cooler than 2010. The spring of 2010 was warm throughout with our last April 90s. NY Coastal climate division 4 https://www.ncdc.noaa.gov/cag/divisional/time-series/3004/tavg/3/5/1895-2021?base_prd=true&begbaseyear=1981&endbaseyear=2010 201006 - 201008 75.2°F 126 3.5°F 202006 - 202008 74.4°F 125 2.7°F 201606 - 201608 74.2°F 124 2.5°F 200506 - 200508 73.9°F 123 2.2°F 201106 - 201108 73.9°F 123 2.2°F 199906 - 199908 73.7°F 121 2.0°F 201206 - 201208 73.4°F 120 1.7°F 201806 - 201808 73.4°F 120 1.7°F 201906 - 201908 73.2°F 118 1.5°F 201506 - 201508 73.1°F 117 1.4°F 194906 - 194908 73.0°F 116 1.3°F 200606 - 200608 73.0°F 116 1.3°F

We trade in warmer and drier blocking for cooler and wetter. Better chances for rain starting today. The pattern usually ends up with closed lows this time of year with strong blocking. So one closed low moves through the next several days followed by another on Thursday. The ensembles are hinting at the Eastern Trough lingering into late April.

The elevated convection will be nice change on Sunday following the 3rd driest start to April on record. Time Series Summary for NY CITY CENTRAL PARK, NY Click column heading to sort ascending, click again to sort descending. Rank Ending Date Total Precipitation Apr 1 to Apr 10 Missing Count 1 1881-04-10 0.00 0 2 1900-04-10 0.01 0 3 2021-04-10 0.04 1 4 1909-04-10 0.05 0 5 1963-04-10 0.06 0