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Weekend Storm Discussion Part II, 2/18-2/19


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Agree fully. Yeah, I never remember NWS putting amounts out this far ahead. Maybe a mention in the AFD but that's different than the public forecast.

I think the standard procedure is ~24 hours out. Maybe 36 hours at the outside. If the GFS and Euro also show potential for warning level snow, I'm sure they mention it in the AFD.

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I think the standard procedure is ~24 hours out. Maybe 36 hours at the outside. If the GFS and Euro also show potential for warning level snow, I'm sure they mention it in the AFD.

From LWX

A Winter Storm Watch is issued when there is the potential for significant and hazardous winter weather within 48 hours. It does not mean that significant and hazardous winter weather will occur...it only means it is possible.

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IT IS EVIDENT THAT THE STORM SYSTEM WILL DEEPEN OFFSHORE WITH A

SOLID SWATH OF PRECIPITATION AND BACKING LOW LEVEL FLOW.

PRECIPITATION IS EXPECTED TO BEGIN AS A RAIN/SNOW MIX OVER THE

COASTAL LOCALES AND WEST TO THE MAJOR METRO AREAS OF WASHINGTON

D.C/BALTIMORE. ALL SNOW IS ANTICIPATED FOR THE HIGHER ELEVATIONS

WEST OF THE METRO TO THE ALLEGHENY FRONT. DYNAMIC COOLING AND

BACKING FLOW TO THE NORTH WILL COOL THE COLUMN AND CHANGE THE MIXED

PRECIPITATION TO ALL SNOW EAST THROUGH THE METRO AND COASTAL LOCALES

LATER SUNDAY AFTERNOON INTO SUNDAY NIGHT WITH THE SYSTEM PULLING

AWAY THEREAFTER. IT IS MUCH TOO EARLY TO TELL HOW MUCH SNOW WILL

FALL AND WHERE. IT DOES APPEAR THAT AT LEAST A LIGHT TO MODERATE

ACCUMULATION COULD BE POSSIBLE. WAITING FOR MORE CONSISTENT GUIDANCE

BEFORE MAKING THAT DECISION. STAY TUNED.http://forecast.weather.gov/product.php?site=NWS&issuedby=lwx&product=AFD&format=CI&version=1&glossary=1&highlight=off

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I think the NWS is right on for now. If the other 12z runs are similarly cold as the NAM, they might switch that "rain or snow" to just "snow", but they don't need to be putting amounts out yet. This is still 48hrs+ away. Accumulation totals would probably be added in tomorrow's afternoon update. Perhaps they put out a HWO or something like that this afternoon if the Euro and GFS also show potential warning-level snows.

Only heros put out amounts that early and you know what happens to them. We'll probably put up an initial accumulation map after seeing the euro but with the euro and 00Z gGEm showing almost a miss. Why would anyone jump the gun. The 09Z SERF plume diagram is all over the place with amounts. I'd show an annotated version but am doing a CWG post today so I've got to hold off.

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funny how nobody trusts the NAM 48 hours and its a short range model. When do you trust it...3 minutes before the first flake?

it's usually pretty good about 6 hours after the fact. seriously.. it's a travesty of a model in most instances. it has its strengths tho.. like keeping people occurpied until the gfs.

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Since Wes can't post it...here's the info from the 9z SREF plumes:

BWI: mean snow 0.25", max 0.8", min 0".

DCA: mean snow 0.44", max 1.03", min 0"

IAD: mean snow 0.4", max 1.01", min 0"

RIC: mean snow 0.61", max 1.03", min 0"

Still a lot of members with rain for RIC. The mean is biased low by the rainers. None look like misses for RIC. Still a couple members were complete misses for the DC-Balt stations.

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Looks a little error laden.

Really? At 48 hours looks pretty darn similar to the NAM, I think...

It looks pretty realistic and normal, and honestly, while folks may want to "lock" onto a solution, that just doesn't happen with systems like this when they have such a GOM tap. Grossly too much latent energy available here, and the final solution of this system will move around like this since the GFS/NAM/GEM/UK/and ECMWF will all be dependent upon the activation of sub-grid convective schemes and how they develop that DMC...which is not necessarily something that will be well handled by the deterministic guidance.

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It looks pretty realistic and normal, and honestly, while folks may want to "lock" onto a solution, that just doesn't happen with systems when they have such a GOM tap. Grossly too much latent energy available here, and the final solution of this system will move around like this since the GFS/NAM/GEM/UK/and ECMWF will all be dependent upon sub-grid convective schemes and how they develop that DMC...which is not necessarily something that will be well handled by the guidance.

This thing is going to have a ton of convection. Southern stream systems always do.

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It looks pretty realistic and normal, and honestly, while folks may want to "lock" onto a solution, that just doesn't happen with systems like this when they have such a GOM tap. Grossly too much latent energy available here, and the final solution of this system will move around like this since the GFS/NAM/GEM/UK/and ECMWF will all be dependent upon the activation of sub-grid convective schemes and how they develop that DMC...which is not necessarily something that will be well handled by the deterministic guidance.

How the convective schemes handle the convection will play a big role in where the models put their lows and that convection may or may not be in the wrong spot. That's the big rub.

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How the convective schemes handle the convection will play a big role in where the models put their lows and that convection may or may not be in the wrong spot. That's the big rub.

Yeah agreed, I will probably give more consideration to the convective environment here the next day, it is going to be crucial. SPC outlooks will also be worth reading.

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