Feb 18/19 Disco/Obs

[SLPressure]

35/19

30.27

Sunny with some thin high clouds.

National Harbor

[high risk]

2 minutes ago, WxUSAF said:

@Bob Chill, totally agree on the soundings.    Razor thin line between 2”/hr or sleet that can peel the paint off your car. Hopefully @high risk agrees with @psuhoffman that it can be a little aggressive with warm layers at times.

        I'll agree with that, but while I might delay its timeline for the transition by an hour, I don't know that I'd bet against it for much longer.    If it is an hour, though, I hope that we get 2"/hour rates during that period.....

 

[blueberryfaygo]

5 minutes ago, Weather Will said:

Just looked at the 3K NAM 18Z forecast over Arkansas late this afternoon.  For what it is worth it appears to be under forecasting the intensity of the snow this afternoon there and the rain/snow line is farther south than it was forecasted even a few hours out....hopefully that extrapolates to something meaningful for us.

We need more of this!

[high risk]

Still some pretty decent difference between the GFS/GFSpara and the NAM for the late day/overnight precip.    GFS is a big hit of ice during that period for most of the metro, but it still seems to be an outlier.   Even the wetter para keeps its ice threat further southeast.

[Bob Chill]

6 minutes ago, high risk said:

        I'll agree with that, but while I might delay its timeline for the transition by an hour, I don't know that I'd bet against it for much longer.    If it is an hour, though, I hope that we get 2"/hour rates during that period.....

 

Agree. My yard has been through a number of these dicy ptype storms. Nearly every single on flipped right on time or sooner. I cant remember the specific dates but the only times I've been surprised with more snow and less sleet than expected were a couple heavy dumpers. 

Of course the greatest reverse sleet bust of all time (imo only) was in Feb 2014 when a west track primary was all snow with a hp out in the atlantic just pumping southerlies in the mids. I think I got like 7" all snow with just a touch of sleet and drizzle on the tail. @WinterWxLuvr loved that storm. So did Ji if you can believe it

[WinterWxLuvr]

1 minute ago, Deck Pic said:

In terms of forecasting, I'm pretty much hugging the euro at this point, other than it may be a little dry.  I don''t have any confidence in the American models right now.  There is way too much disparity between  Hi res/Lo Res, Para/OP

Interesting. Was thinking pretty much the same things. I know models are constructed differently but this close you would expect a little more consensus 

[Eskimo Joe]

10 minutes ago, WxUSAF said:

@Bob Chill, totally agree on the soundings.    Razor thin line between 2”/hr or sleet that can peel the paint off your car. Hopefully @high risk agrees with @psuhoffman that it can be a little aggressive with warm layers at times.

12z RAOB from IAD tomorrow will be very interesting. If it's colder, then we're golden everywhere.

[WinterWxLuvr]

Just now, Bob Chill said:

Agree. My yard has been through a number of these dicy ptype storms. Nearly every single on flipped right on time or sooner. I can remember the specific dates but the only times I've been surprised with more snow and less sleet than expected were a couple heavy dumpers. 

Of course the greatest reverse sleet bust of all time (imo only) was in Feb 2014 when a west track primary was all snow with a hp out in the atlantic just pumping southerlies in the mids. I think I got like 7" all snow with just a touch of sleet and drizzle on the tail. @WinterWxLuvr loved that storm. So did Ji if you can believe it

If memory serves that was a 20” snow here.

[mappy]

Just now, Bob Chill said:

Agree. My yard has been through a number of these dicy ptype storms. Nearly every single on flipped right on time or sooner. I can remember the specific dates but the only times I've been surprised with more snow and less sleet than expected were a couple heavy dumpers. 

Of course the greatest reverse sleet bust of all time (imo only) was in Feb 2014 when a west track primary was all snow with a hp out in the atlantic just pumping southerlies in the mids. I think I got like 7" all snow with just a touch of sleet and drizzle on the tail. @WinterWxLuvr loved that storm. So did Ji if you can believe it

Was that the mid month, one? Was two parts, I think?

[EHoffman]

1 minute ago, Bob Chill said:

So did Ji if you can believe it

I believed everything you wrote up until this

[WinterWxLuvr]

Just now, Eskimo Joe said:

12z RAOB from IAD tomorrow will be very interesting. If it's colder, then we're golden everywhere.

12z tomorrow? By then ground obs ought to tell us what we need to know.

[gymengineer]

I think he’s referring to the 2/21/2015 event? The 2/2014 2-parter was a coastal storm. 

[midatlanticweather]

Just now, Deck Pic said:

In terms of forecasting, I'm pretty much hugging the euro at this point, other than it may be a little dry.  I don''t have any confidence in the American models right now.  There is way too much disparity between  Hi res/Lo Res, Para/OP

This has been a tough winter with models and a lot of strange behaviors. Very happy that systems are spotted ahead of time, but final placements of bands of snow and warm layers seem last minute. I expect the typical northward trends, but they have been in both directions this year. I thought this was going to be a bit less complicated. But so many variables, and there are good reasons for the challenges, but we really are the battle ground for this year. I guess we always are. Makes it fun and exhausting at the same time. This is probably banter 

[Bob Chill]

1 minute ago, mappy said:

Was that the mid month, one? Was two parts, I think?

It was a single storm iirc and was on the tail of a snow heater in that wild progressive pattern. None of us really drilled down on it leading in. We were kinda burned out from other storms and this one had literally no high pressure to our north. All return flow from the arctic high sliding off the coast. 99.9% of those storms would be a mix and mess everywhere at best. It was such a legit airmass we capitalized when we really shouldnt have. Thats as much as this old guy can remember 

[blueberryfaygo]

   The GFS gives the Baltimore-dc corridor 5 inches in the 6 hours leading up to the change over.. if you can believe that it stays all snow up to or around 18Z, then this would be a legit event.  Should be fun to watch... Although we are not seeing the big totals from last couple of days.. this quick hitter warning criteria type event should be very impactful and fun to watch!

 

[high risk]

6 minutes ago, Bob Chill said:

Agree. My yard has been through a number of these dicy ptype storms. Nearly every single on flipped right on time or sooner. I cant remember the specific dates but the only times I've been surprised with more snow and less sleet than expected were a couple heavy dumpers. 

Of course the greatest reverse sleet bust of all time (imo only) was in Feb 2014 when a west track primary was all snow with a hp out in the atlantic just pumping southerlies in the mids. I think I got like 7" all snow with just a touch of sleet and drizzle on the tail. @WinterWxLuvr loved that storm. So did Ji if you can believe it

       I remember that storm really well.    That was an incredible thump - the precip arrived like a wall of white.

[Eskimo Joe]

4 minutes ago, WinterWxLuvr said:

12z tomorrow? By then ground obs ought to tell us what we need to know.

When the 12z sounding is release tomorrow, we'll be able to see if there's a significant intrusion of warm air starting, or if things are colder and perhaps we have a better chance at a prolonged front end thump of snow. Normally, I'd look towards RNK, but as you said the event will probably be underway by then so that data won't be as useful.

[Bob Chill]

2 minutes ago, gymengineer said:

I think he’s referring to the 2/21/2015 event? The 2/2014 2-parter was a coastal storm. 

Def could have been 2015. Makes sense coming in a week after the VDay supersquall. We tracked fails all season up until that arctic front. The storm was so unconventional we didnt take it as serious as we usually do iirc

[midatlanticweather]

Just now, Bob Chill said:

It was a single storm iirc and was on the tail of a snow heater in that wild progressive pattern. None of us really drilled down on it leading in. We were kinda burned out from other storms and this one had literally no high pressure to our north. All return flow from the arctic high sliding off the coast. 99.9% of those storms would be a mix and mess everywhere at best. It was such a legit airmass we capitalized when we really shouldnt have. Thats as much as this old guy can remember 

I remember something like this and then the ULL ended up giving many some excitement but missed my backyard. Was also an inland runner and unexpected that it would stay snow. 

[Bob Chill]

Just now, high risk said:

       I remember that storm really well.    That was an incredible thump - the precip arrived like a wall of white.

It may have been feb 2015. Those 2 febs are blended together in my mind like a corrupt hard drive. So similar at times it was uncanny. Even though the pattern in both feb 14&15 was not ideal at all, our area could not have maximized it any better. Prob once in a lifetime pattern/snow. I wont root for a raging +ao/nao ever. But man, some fond fond memories of that stretch. I remember literally getting sick and tired of tracking in mid Mar 2014. First and last for me. Lol

[blueberryfaygo]

3 minutes ago, Eskimo Joe said:

When the 12z sounding is release tomorrow, we'll be able to see if there's a significant intrusion of warm air starting, or if things are colder and perhaps we have a better chance at a prolonged front end thump of snow. Normally, I'd look towards RNK, but as you said the event will probably be underway by then so that data won't be as useful.

Then we can look at the 6z sounding

[gymengineer]

1 minute ago, Bob Chill said:

Def could have been 2015. Makes sense coming in a week after the VDay supersquall. We tracked fails all season up until that arctic front. The storm was so unconventional we didnt take it as serious as we usually do iirc

Yup, the high at IAD was 15F and 19F on the 2 days leading up to the event (2/19/15 and 2/20/15). Superb airmass that the models just didn’t have a good handle for and hence our great positive bust here in the suburbs. 

[adelphi_sky]

34F/14.9 Blue skies.

[CAPE]

6 minutes ago, blueberryfaygo said:

   The GFS gives the Baltimore-dc corridor 5 inches in the 6 hours leading up to the change over.. if you can believe that it stays all snow up to or around 18Z, then this would be a legit event.  Should be fun to watch... Although we are not seeing the big totals from last couple of days.. this quick hitter warning criteria type event should be very impactful and fun to watch!

 

Dude.. SLEET.

[CAPE]

Interesting tidbits from Mount Holly AFD-

The ultimate evolution of the first southern-stream perturbation will be what is responsible for our winter weather late tonight and Thursday. A strong anticyclonic upper-level jet streak will combine with midlevel differential cyclonic vorticity advection to aid in intensifying surface low pressure from the northern Gulf of Mexico tonight to the Mid-Atlantic coast Thursday afternoon. Intense warm advection atop a low-level baroclinic zone will aid in widespread precipitation to the north and northeast of the developing low. Meanwhile, a strong surface high will remain in southeast Canada, providing cold onshore flow for the northern Mid-Atlantic preceding the storm. Models are, as usual, too moist with the predecessor boundary-layer environment, with dew points a good 6-10+ degrees lower than model consensus today. This will be important in two ways. First, it is likely that low-level saturation requirements will delay precipitation onset in our CWA, with snow not likely to get going in earnest until near or just after daybreak. Second, models are likely too warm at the surface, especially during the main "thump" of precipitation during the morning hours. Sided with colder guidance here.

With models trending slightly northward with the warm-nose influence on precipitation type on Thursday, our inclination was to be a little less aggressive than consensus in this regard. No question that the strength of warm advection will be intense, likely leading to a veritable sleet storm in a good chunk of the area as the event unfolds during the day. However, there has been a tendency for higher-res guidance to be a little too aggressive in shunting the warm nose to the north this season. Of course, there has also been a tendency for northwest shifts in the snow/sleet/freezing rain geographical distributions within 24 hours of the event (playing out once again with today`s guidance). It will be quite interesting to see how the 00z solutions play out, as run-to-run variability has been diminishing confidence in the forecast for this event considerably.

[BristowWx]

90% of VA under a warning.  That’s a rare look 

[blueberryfaygo]

4 minutes ago, Bob Chill said:

Def could have been 2015. Makes sense coming in a week after the VDay supersquall. We tracked fails all season up until that arctic front. The storm was so unconventional we didnt take it as serious as we usually do iirc

mid February 2015 featured a very cold stretch of  record breaking temperatures for our region.. hands down the coldest stretch we have ever seen

[Bob Chill]

My first and only call for my area is 3-4" of snow and a bunch of sleet. Once it shuts off I'm thinking 5" total of frozen stuff. Sleet will pummel and compact for sure. My plan is to measure snow at the beginning of the flip, clear the table, then measure sleet. Roads will be the worst they've been since Jan 16. Jan 19 was 11" in my yard but iirc the roads were fine. Not to mention snow distribution was all over the place so road impacts varied by the mile. Tomorrow will be a different story. 

[H2O]

34.6/17. Gotta get the bottoms to drop out now the sun is down and before clouds roll in

[blueberryfaygo]

2 minutes ago, CAPE said:

Dude.. SLEET.

The sounding at 18Z for Baltimore county says that it is just about ready to sleet.. that tells me that the 850s hold on until just about then (per the model)