GaWx

85.2 at 1:54 PM. Highest I saw yesterday 84.7.

12Z SV AI Weathernext: DC up to ~7” 10:1 from ~5” 10:1 prior 3 runs; probably ~~5” Kuchera up from ~~4” prior 3 runs

It’s 84.2 here at 1:50PM! At 1 PM, it had already hit 83, just 1F below the daily record high. There are gusty warm SW winds. Edit: 84.7 at 2:36PM!

GFS seems to have a bit of a too heavy QPF bias in general. Not for all cases by any means but averaged out, which would fit the definition of a bias. Any other opinions on this?

Teleconnections have been steady for Feb 22-23 with MJO phase 3 (coldest Feb phase for La Niña on avg), strong -EPO/-WPO/-PNA/+NAO, and near neutral AO.

6Z SV AI-Weathernext 10:1 mean (see below) as well as the 0Z and 18Z have been consistent on going with ~5” for DC: perhaps that would imply ~4” Kuchera, which seems to be a reasonable possibility at this stage (significant event if it verifies)

I wonder if the GFS is once again way overdoing the qpf like it did for the 1/25 storm. Some runs had 3”+ of qpf at ATL just a few days in advance but they ended up with only 0.85”. If so, it would likely gradually reduce it from run to run.

The 18Z GFS suite surpringly pretty much held close to the 12Z. Also, the 18Z Euro suites (regular and AI) all got snowier.

@donsutherland1has done some excellent analyses showing that a -PNA in Feb, especially second half, isn’t negatively correlated to the chance for a big NYC snowstorm. I decided to just look specifically at -ENSO NYC Feb 5”+ snowstorms since 1950 and found that the NYC median was a very weak -PNA (essentially neutral) for the entire Feb during -ENSO: 19 NYC 5”+ Feb Nina or cold neutral: PNA 2/1/57 -1.2 2/7/67 +0.7 2/19/72 -0.5 2/23-4/72 -0.5 2/8/74 -0.2 2/12/75 -0.8 2/7/79 -1.1 2/19/79 -0.1 2/5-6/85 -0.8 2/2-3/96 +0.7 2/16/96 -0.4 2/22/01 +0.4 2/12/06 +1.7 2/22/08 +0.7 2/8-9/13 +0.4 2/3/14 -1.1 2/13-14/14 -1.0 2/9/17 +0.7 2/1/21 0.0 Median -0.2 Mean -0.1 Range +1.7 to -1.2 So, this suggests that during -ENSO throughout Feb that a -PNA doesn’t hurt significant snow chances at NYC. That being said, the last few 0Z GEFS PNA progs have been going with ~-1.2 for the crucial period, Feb 21-22. If -1.2 were to verify, that would be at/near the lowest PNAs for a Feb La Niña 5”+ NYC snowstorm since 1950, which are -1.2 for 2/1/57, -1.1 for 2/7/79, -1.1 for 2/3/14, and -1.0 for 2/13-14/14. ————— Aside: I want to also mention that I had already done a similar study for DC although I used a lower threshold for there due to lower snow climo, 3”, which like for NYC resulted in a sample of 19 storms. Here are those DC results, which are a bit more +PNA favored for -ENSO during Feb: Median +0.3 Mean +0.2 Range +1.7 to -1.1 ————— So, NYC has done better than DC during -ENSO Febs when there was a -PNA. In other words, unlike NYC, DC has done a little better with +PNAs than -PNAs.

Indeed, the SV AI-Weathernext has been terrible because it’s been all over the place, especially for an ensemble mean! The heaviest I’ve posted was this one, the 6Z 2/17 run giving DC ~10” and ~12” for its Mid-Atlantic max centered over C DE: Compare that to the latest (today’s 6Z): DC ~3” with none of the Mid-Atlantic >4”:

In case it wasn’t posted, here’s the SV 6Z AI-Weathernext ens: averaging 3” for this area based on 10:1

1. Note that the 2/22-23 snowstorm threat period remains mainly in phase 3, the coldest phase on avg during La Niña Febs. 2. When I calculate avg temperatures associated with each phase, I’m not assuming any lag. So, during La Niña, phase 3 was coldest on avg in Feb and phase 7 was coldest on avg in Mar, each with no lag. But also keep in mind that these are merely averages being the coldest along with spreads that cover MB to MA. For example: 1) For the coldest La Niña phase in Feb on avg, phase 3: Avg -107/73 days = -1.5, which is 4F colder than the La Niña Feb phase average of +2.5 and has easily averaged the coldest phase. Breakdown of the 18 different Feb La Nina phase 3 periods: wide range but more B/MB (7) than A/MA (5) MB: 1 B: 6 N: 6 A: 3 MA: 2 ————— 2) For the coldest La Niña phase in Mar on avg, phase 7: Avg -135/81 days = -1.7, which is 2.4F colder than the La Niña Mar average of +0.7 and has averaged the coldest phase. Breakdown of the 18 different Mar La Nina phase 7 periods: wide range but more B/MB (8) than A/MA (6) MB: 2 B: 6 N: 4 A: 3 MA: 3

What NorthHills said. In addition, dewpoints are relatively high (mid 50s). So, even with clear skies, the high RH (70%+) isn’t conducive for strong radiational cooling as the water vapor acts as a blanket (kind of what you were speculating).

As posted earlier, MJO phase 3 is a plus based on it having been the coldest phase on avg in Feb during La Niña. However, the GEFS progged strong -PNA presents a challenge to getting a significant snow per daily PNAs since 1950. For the 19 DC 3”+ snowstorms during the 40 La Nina or cold neutral Febs since 1950, here were the daily PNAs: 2/11/25 +0.9 2/25-6/14 +0.5 2/13/14 -1.1 2/12/06 +1.7 2/8/97 +0.5 2/16/96 -0.4 2/2/96 +0.7 2/4/95 +1.6 2/24/86 +0.3 2/22/86 -0.4 2/4/75 -0.3 2/8/74 -0.2 2/19/72 -0.5 2/17/72 -0.7 2/2/72 -1.1 2/17/67 +0.3 2/7/67 +0.7 2/13/60 +0.2 2/7/51 +0.3 Median +0.3 Mean +0.2 Highest +1.7 Lowest -1.1 Feb 8th GEFS PNA for 2/22-3: ~-1.2 So, should the PNA verify close to this GEFS run and there be 3”+, this would be near the lowest PNA for a DC Feb 3”+ snowstorm during La Niña since 1950. Thus, for a better shot at 3”+, I’d rather the PNA trend less negative.

Nobody should ever have faith in any model. But Weathernext was pretty good for some storms this winter.