bluewave

27° With sleet here in SW Suffolk.

This winter is really doing its own thing. The big snowstorm in December came before the lowest AO reading of the month. No measurable snowfall through most of January with the AO dropping below -3 several times. Then we had the snowiest first week of February in NYC just before the -AO dropped below -5. So there have been a number of competing influences on our pattern.

We are back to 20 days or more of 1”+ snow cover like 16-17 and 17-18. But still well behind the 50+ day years like 10-11, 13-14, and 14-15. I can still remember the snow piles that looked like a mini mountain range near the LB Boardwalk in 2011. Time Series Summary for NY CITY CENTRAL PARK, NY Click column heading to sort ascending, click again to sort descending. Ending Date Number of Days Snow Depth >= 1 Oct 1 to Apr 30 Missing Count 2021-04-30 20 77 2020-04-30 2 0 2019-04-30 12 0 2018-04-30 20 0 2017-04-30 20 0 2016-04-30 11 0 2015-04-30 55 0 2014-04-30 59 0 2013-04-30 11 0 2012-04-30 3 0 2011-04-30 57 0 2010-04-30 25 0

Yeah, the strongest Arctic outbreaks in recent years have been to our west around the Plains. You can see how the Plains are warming more slowly than other parts of the country. The record Atlantic SSTs and SE Ridge have been a dominant force in our weather.

NYC has finally made it to 10+ consecutive days with at least 1” of snow cover. This is a first since 2016. But it’s tough to compete with years like 10-11, 13-14, and 14-15. 2010 to 2021 longest snow cover >= 1 Number of Consecutive Days Snow Depth >= 1 for NY CITY CENTRAL PARK, NY Click column heading to sort ascending, click again to sort descending. Rank Run Length Ending Date 1 53 2011-02-17 2 50 2015-03-14 3 48 2014-03-10 4 12 2010-02-21 5 11 2021-02-11 6 10 2016-02-01

Area Forecast Discussion...UPDATED National Weather Service Fort Worth TX 239 PM CST Fri Feb 12 2021 ...New Long Term... .SHORT TERM... /Issued 1133 AM CST Fri Feb 12 2021/ /Through Saturday/ Key Messages (now through Saturday): (1) Isolated bands of lake effect snow have developed near some of the lakes across North Texas. Some of these snow bands may result in localized reductions in visibility to less than one mile, and quick snow accumulations of up to one-half inch. LONG TERM... /NEW/ /Saturday evening onward/ Key Messages: (1) A historic winter storm is poised to impact North and Central Texas, with impacts beginning as early as Saturday morning, continuing through Monday. (2) Extremely cold temperatures, rivaling the December 1989 Arctic Outbreak, are forecast on Sunday and into Monday, with prolonged much below normal temperatures expected to continue through next week. (3) Major impacts resulting in severe stress to the region`s infrastructure (particularly power, water, and highways) are likely. Regional travel will be crippled for days. (4) Additional frozen precipitation will be possible toward the middle of next week, though confidence is low in the details at this time. Perhaps the most serious threat from this winter storm will be the cold temperatures. High temperatures will likely remain in the teens across the entire CWA on Monday. Combined with strong and gusty northerly winds, wind chill factors during the day will likely hover near 0 F. With the expected snowpack by Monday night, and the Arctic high building farther south, temperatures will plunge into the lower single digits across the region, with subzero temperatures likely north and west of the Dallas/Fort Worth Metropolitan Area. These will be some of the coldest temperatures in the region since the December 1989 Arctic Outbreak. Wind chill factors will likely be subzero across the region. Given that the region is highly unaccustomed to temperatures this low, significant impacts to the region`s infrastructure are expected. In the December 1989 Arctic Outbreak, there were numerous instances of water pipes (both exposed and buried) bursting as they froze in the extreme cold. In addition, the power grid is likely to approach record demand levels given the duration of the cold in addition to the magnitude. It cannot be stressed enough that this cold will be very dangerous. With the icy road conditions, if one were to become stuck attempting to travel, the cold temperatures would pose a serious threat to one`s life. Persons are urged to remain home and off the roads, and if one must venture out, to include necessary items to survive in extremely cold weather as it could be some time before someone were able to rescue you.

That’s for sure. Our winters have alternated between blocking or the SE Ridge. Once we lose the blocking, the SE Ridge returns. Even when we did have the strong blocking this winter, several of our snowstorms were more tucked in than usual. Probably related to the record SSTs off the East Coast forcing the baroclinic zone closer to the coast. So we seem to have the SSTs and MJO amping the SE Ridge. It takes some extreme type of blocking to suppress the SE Ridge enough.

Sure, it will be quite a temperature drop for them after reaching 85° earlier in the month. Climatological Data for Austin Area, TX (ThreadEx) - February 2021 Click column heading to sort ascending, click again to sort descending. Date Max Temperature Min Temperature Avg Temperature Avg Temperature Departure HDD CDD Precipitation Snowfall Snow Depth 2021-02-01 67 41 54.0 1.3 11 0 0.00 0.0 0 2021-02-02 69 40 54.5 1.7 10 0 0.00 0.0 M 2021-02-03 77 45 61.0 8.0 4 0 0.00 0.0 M 2021-02-04 85 55 70.0 16.9 0 5 0.00 0.0 0 2021-02-05 61 44 52.5 -0.8 12 0 0.06 0.0 0 2021-02-06 75 48 61.5 8.1 3 0 0.00 0.0 0 2021-02-07 70 40 55.0 1.5 10 0 0.00 0.0 0 2021-02-08 76 51 63.5 9.8 1 0 0.00 0.0 0 2021-02-09 64 46 55.0 1.1 10 0 T 0.0 0 2021-02-10 46 37 41.5 -12.5 23 0 0.04 M M 2021-02-11 37 31 34.0 -20.2 31 0 0.45 0.0 0

The last time they dropped below 10° was 1989. Time Series Summary for Austin-Bergstrom Airport Area, TX (ThreadEx) - Jan through Dec Click column heading to sort ascending, click again to sort descending. Rank Year Lowest Min Temperature Missing Count 1 1949 -5 2 2 1989 6 0 3 1951 8 1 4 2010 10 0 5 1983 11 0 - 1964 11 0

NYC is at the 23rd longest streak under 50° days at 41 days.

The other thing is how much warmer strong -AO patterns have become. This is only the 4th year with with a -1 AO or lower for all 3 winter months DJF. I believe Don had a great post a while back on the warming -AO patterns. This winter so far through February 10th is the warmest on the list. NYC average temperature for a -1 or lower AO for each individual month Dec, Jan, and Feb Dec 1 to Feb 10 average temperature NYC 20-21....36.4° 09-10....33.7° 76-77...26.0° 69-70°...30.1°

It’s tough to make comparisons to before the super El Niño in 15-16 since winters have been so much warmer.

Those old version GFS maps will become collectors items when the v16 goes operational on St Patrick’s Day. Still wish I kept a few old DGEX forecast maps.

The models lost the single digits lows for NYC a while ago. So the coldest temperatures will dump into the Plains. Probably related to the very strong MJO 7 pattern. But NYC still has a shot to drop below 20°. New run Old run

The strongest blocking of the whole winter was within the last few days. Looks like it gets weaker and becomes more east based going forward. You can see the shift on the long range models.

Looks like one of the greatest AO rises from -5 that we have seen coming up.

1.8” of fluffy powder here in SW Suffolk.

Only the 16 year since 1950 that NYC went 40 days without reaching 50°. Number of Consecutive Days Max Temperature < 50 for NY CITY CENTRAL PARK, NY Click column heading to sort ascending, click again to sort descending. Rank Run Length Ending Date 1 77 1969-03-15 2 65 1977-02-10 3 63 2015-03-08 4 54 1971-02-11 5 50 1981-02-01 6 47 2004-02-20 - 47 1985-02-18 - 47 1970-01-28 7 46 1968-03-07 8 44 2007-03-01 - 44 1996-01-17 - 44 1978-03-11 - 44 1956-02-07 9 43 2001-01-29 10 42 2011-02-13 11 40 2021-02-11

Yeah, those areas will be closer to the path of the current record breaking high pressure when it drops south. https://forecast.weather.gov/product.php?site=NWS&issuedby=FWD&product=AFD&format=CI&version=1&glossary=0 The freezer door will then be propped open on Sunday as mid level ridging amplifies over the Northwest U.S. and our polar low over Southern Canada pivots eastward allowing a chunk of arctic air to spread southward through the Plains. A 1050 mb high will surge southward behind a strong cold front but ahead of a compact shortwave ejecting out of the southwest U.S. This will set the stage for some exceptionally cold air to spread into North Texas over the latter half of the weekend into early next week. We`re becoming increasingly concerned for a prolonged cold spell with actual air temperatures falling into the single digits to near 0 across parts of the region by Monday. While the GFS is currently the coldest guidance, other global guidance and ensemble members indicate 850 mb temps falling into the -12 to -17 degree range which would be in the coldest 10% of temperatures in our observed sounding data. In addition, a pool of moisture will reside across much of East Texas and should quickly surge northwestward into the region as strong forcing overspreads North Texas late Sunday into Monday. With column temperatures as cold as currently forecast, widespread moderate to heavy snow would be expected to develop as the shortwave spreads across the Southern Plains. The current forecast will reflect these trends with all snow by late Sunday night and continuing into Monday. While it`s a little early to pin down exact accumulations, as of now, it appears that widespread snowfall amounts of 2 to 4 inches will be possible over a large area of the region. Column temperatures would be cold enough to support higher snowfall ratios than we typically see which could result in significantly heaftier snow totals. North winds 15 to 25 mph could also result in significant reductions to visibility during the snow. This will be a fast moving system, but definitely has the potential for significant impacts to travel and infrastructure across the region. Extremely cold weather will continue into the middle of next week. It should be stressed that this bout of extreme cold may have significant impact to infrastructure over the latter part of the weekend into early next week. Exposed pipes are likely to burst in the prolonged cold. Preparations should be made now to protect exposed pipes or other infrastructure sensitive to the cold. Plans should be made for pets and people.

The record Arctic high that slips south will provide plenty of CAD and low level Arctic air. But ice will be an issue with more amplified systems. We may need to get to within 2-3 days of each event to know how amped up they are going to be. Less amped is better if you want more snow and less ice.

It works in our favor for weak systems like tomorrow. So we get a nice light snow event. But MJO 7 with too amped a system can present ice issues.

Tough to bet against the SE Ridge helping us out in an amplified MJO 7 pattern. New run Old run

Looks like our first -5 AO reading during a La Niña February. The other 3 Februaries were El Niño years. 2-14-10...-5.132....2-6-10....-5.205....Niño 3.4....+1.5 2-5-78.....-5.291....................................................+0.7 2-13-69....-5.285...................................................+1.1

This big a swing from the exact date last year is unprecedented. The +AO almost made it to +6. Just ridiculous volatility for two consecutive Februaries. 2020 2 9 5.765 2020 2 10 5.910