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Saint Patrick's Day Snow Event II

stormtracker

By stormtracker,
in Mid Atlantic

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WxMan1

WxMan1

Posted
Posted

This sounds great and thanks for the detailed summary

 

No problem guys.  A lot of this is info you already know.  It's a shame that as of now the product can't be as robust as it *could* be.  It's also a shame that the SREF, even the parallel SREF (which has been in parallel for a while now), continues to have issues with some of these winter storm cases (i.e. the wet/cold bias we sometimes see around here).  But it's getting better, and will continue to do so.  

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ers-wxman1

ers-wxman1

Posted
Posted

I can tell you that one of the improvements we hope to make at WPC is to limit the percent weight of the SREF members. Right now, WPC's automated PWPF product (probability of winter precipitation forecast) is a 33 multi-member ensemble, with the "mode" being the WPC winter weather forecaster's deterministic snowfall (and ice) forecast based on the preferred model blend(s) over a particular region. Now, all 21 SREF members are included, along with 7 operational runs, and 5 GEFS members. That's a 33 member system, HOWEVER, 64% of which (21/33) are based on the SREF -- 7 NMB members (which go into the NAM), 7 NMM members (GFS), and 7 EM/WRF members (RAP). The problem is, when the NCEP models, particularly the NAM and SREF, are not the preferred runs for a particular winter storm, the "spread" among the mode (which again is the winter weather desk's deterministic forecast) is going to widen toward that SREF output.

What we want to do going into next season is to not make the PWPF so "SREF heavy". In doing so, we're going to incorporate some (perhaps half) of the ECMWF ensemble members. One may be asking the question right now, "how come you (WPC) haven't done that already?" Well, it's a matter of resolution. Right now, we are getting the EC members at a full degree resolution, or 111 km. That's a pretty course resolution -- the kind that will make a NW flow clipper event bleed east of the Appalachians into the DC area. Why are we getting the ECMWF members at such a low resolution currently? I think the main reason is computational -- being able to get the data and process it in our system in a timely manner. However with the new supercomputer (part of the Sandy suppliment), that's going to change, as we hope to have 0.5 degree resolution ECMWF ensemble data by next season (closer to 54.5 km).

So, we are getting there folks, gradually. In the meantime, keep in mind a couple of things, at least from our (WPC's) perspective:

1) Those google-earth background probability graphics you see (i.e. our "automated" PWPF) for the time being will remain 64% SREF weighted. Translation: when the SREF is not preferred -- especially when the other operational NCEP runs are not preferred (NAM and GFS), you will get a fairly large (too large) distribution with those snowfall and ice probabilities.

2) WPC in the meantime still has the ability to manually edit the "final" 10, 40, and 70 percent probabilities for the 4, 8, and 12" snowfall probabilities, as well as for the 0.25" of ice. So, when we see such a huge disparity with the WPC's manual winter weather output vs. the automated PWPF, it is because we did not buy into the SREF output (and possibly NAM and/or GFS as well). A great example of this is with the 03/03 event: when the WPC winter weather forecaster had the highest snowfall axis along the mid Atlantic region (our area), while the SREF was pointing toward NYC and SNE. So, in this case, the automated PWPF looked AWFUL, with higher probs of 4, 6, and even 8 inches stretching from SNE all the way down into central VA. Again, we'll get there...

Awesome stuff. We will reciprocate the changes next winter for our prob forecasts

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AlexD

AlexD

Posted
Posted

I know not many people care about SBY, but I have been impressed with the SREFS here in Salisbury for predicted snowfall with this storm. They haven't been the best this year but this has been the highest totals it's shown all winter for here.

attachicon.gifsref.jpg

wouldnt it be deliciously ironic if this turns out to be our biggest storm of the year? Of all the storms this year I honestly think not one has exceeded 4" here, despite several forecasts of much higher amounts..
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Deck Pic

Deck Pic

Posted
Posted

Lol yes. It's kinda annoying. I'm out trying to get a feel for it and you'd think it was awful going by the commentary here.

 

we get around 0.5" (compared to 0.75" last run) in the 3z to 15z window, which is more in line with other guidance (though on the high end),...the outcome is becoming a little more clear...and hopefully remains that way through the euro...I'd like to see the euro bump up to 0.35 or 0.4" during that period, but I have that feeling that we are going to stay up and not be too happy....

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CAPE

CAPE

Posted
Posted

Lol yes. It's kinda annoying. I'm out trying to get a feel for it and you'd think it was awful going by the commentary here.

Nice to see the table turned once in a while. Most of the time with winter events its the N MD and VA hill folk that set the tone for model discussion. This one may suck for them, but looks pretty decent for many that have seen much less snow this winter.

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BTRWx

BTRWx

Posted
Posted

That is what we do now. Plus the highlighting of the most likely

wow, I honestly did not notice the size differences, they all do seem a bit small, imo. Can the middle "most likely" map be enlarged?

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Deck Pic

Deck Pic

Posted
Posted

Another good run in the books.

Ratios are tricky. They could start 0:1 if the surface doesn't cool as quick as modeled (probable). I would think 10-12:1 during the 2am-6am perio. Dc looks good for 3-4 or so imo.

 

I'm punting any accumulation before 11-12 here..what you thinking?

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mitchnick

mitchnick

Posted
Posted

we get around 0.5" (compared to 0.75" last run) in the 3z to 15z window, which is more in line with other guidance (though on the high end),...the outcome is becoming a little more clear...and hopefully remains that way through the euro...I'd like to see the euro bump up to 0.35 or 0.4" during that period, but I have that feeling that we are going to stay up and not be too happy....

verbatim, DCA would be at or below freezing at the start of precip....the ground's another matter

http://68.226.77.253/text/NAM80km/NAM_Kdca.txt

 

BWI

http://68.226.77.253/text/NAM80km/NAM_Kbwi.txt

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BTRWx

BTRWx

Posted
Posted

wouldnt it be deliciously ironic if this turns out to be our biggest storm of the year? Of all the storms this year I honestly think not one has exceeded 4" here, despite several forecasts of much higher amounts..

That is what I was expecting with the last snowstorm, but maybe this one will go our way.

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snowdude

snowdude

Posted
Posted

wouldnt it be deliciously ironic if this turns out to be our biggest storm of the year? Of all the storms this year I honestly think not one has exceeded 4" here, despite several forecasts of much higher amounts..

Yeah it would be. We've had several 1-3 and 2-4 events. Time for a bigger one! haha

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ers-wxman1

ers-wxman1

Posted
Posted

I hear ya ers...I'm thinking we'll all be working off a better starting point, at the very least.

:)

I think what we have done in collaboration thus far has been a success and I'm proud to be a part of the work being done. Looking forward to the changes and additions next winter. We plan to expand these for ice accumulations and might even research the Sperry/Piltz Ice damage assessment

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Ian

Ian

Posted
Posted

With publicly available products, the clearer the better. IMO suggestions like these could help to prevent confusion/spread of misinformation.

That's my main interest and not to bash LWX or anyone else. Sometimes I wonder of they don't like me over there. I am mostly vocal with disagreements rather than the 85% awesome. ;)

And thanks to wxman1 for the details.

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Bob Chill

Bob Chill

Posted
Posted

I'm punting any accumulation before 11-12 here..what you thinking?

Smart. I feel the same way. If the rates are heavy enough at 34-35* could get going on mulch and grass earlier but that's a big wildcard and not something worth guessing about now.

We'll have a much better gauge on bl temps tomorrow aft/eve. It does look like most of the precip will fall as snow this time compared to 3/3. I like snowTV either way.

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MillvilleWx

MillvilleWx

Posted
Posted

verbatim, DCA would be at or below freezing at the start of precip....the ground's another matter

http://68.226.77.253/text/NAM80km/NAM_Kdca.txt

 

BWI

http://68.226.77.253/text/NAM80km/NAM_Kbwi.txt

 

That's a pretty good run for BWI. That period between hour 30-36 will be when the best goods are delivered. Decent 700 mb VV in combination with the thermal profiles throughout could yield a good 3-6" snowfall for the storm. The VV numbers shown lead me to suspect there will be some interesting banding around the area during the storms height between 2-8am. Ratios of 10:1 can be achieved based off that data. Thanks Mitch

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Bob Chill

Bob Chill

Posted
Posted

I think DCA will get mid 40s at the least tomorrow. GFS mos is like 47,

Yea, it's an important consideration. With low dews and cold mid levels it can drop quick shortly after onset but if it starts before temps drop to close to 40 it will be a frustrating start from an accum standpoint

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Deck Pic

Deck Pic

Posted
Posted

I think DCA will get mid 40s at the least tomorrow. GFS mos is like 47,

 

I think upper 40s sounds about right...I bet me and you don't hit freezing until midnight.....but of course at 33-34 at night if we get 0.75mi viz or less we should stick on measuring surfaces at somewhat crappy ratios.....so I guess we could start to get some accumulation by 10pm or so, but I'm not counting on it....

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