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February 12-13 Storm IV, Model Discussion


stormtracker

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Very good points.  "Flirting" with the dry slot is sort of analogous to flirting with a supermodel.  You can easily get burned, but IF all goes well, it also can result in the night of your life :)  On a more serious level, you *need* to be near it to attain the potential instability aloft, *but* cannot be too far into it (dry slot extending to far down in the atmosphere) where you have no moisture reaching the -10C, which often times is approximated ~700 mb give or take 50 or so mb.  So ideally, you want to see some drying above 700 mb, but not down to or (especially) below 700 mb.  In the absence of CI, as you noted, CSI can play out, and do so (often times) farther w-nw-n of the dry slot where the static stability aloft is still weakening, yet not as much so (certainly not to the degree that would support upright convection).

You are now my favorite met with that analogy.  

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NWS seems to believe it's going to look more like last night's Euro given current obs...

 

A COMPARISON OF 12Z/18Z RAOBS TO INITIALIZATION OF THE 12Z MODELS
AND THEIR 6-H FORECASTS INDICATE THE GFS/NAM WERE TOO FLAT WITH THE
LOW-LEVEL THERMAL TROUGH ON THE EASTERN SIDE OF THE APPALACHIANS AND
DOWNSTREAM THERMAL RIDGE TOWARD THE SOUTHEAST COAST. SATELLITE WATER
VAPOR LOOP INDICATED THE NRN STREAM SHORTWAVE TROUGH WAS ALREADY
CLOSING OVER ERN NE-KS...WHICH WAS EARLIER/FASTER THAN MOST OF THE
12Z GUIDANCE HAD INDICATED. THESE ERRORS PROVIDE EVIDENCE TOWARD A
MORE WESTWARD TRACK OF THE COASTAL LOW...CLOSER TO THE PAST FEW RUNS
OF THE ECMWF. THE LOW TRACKING RIGHT UP THE COASTLINE WOULD SHIFT
THE AXIS OF HEAVIEST SNOWFALL TOWARD THE BLUE RIDGE AND I-81
CORRIDOR...WHERE ISOLATED TOTALS OF UP TO 20 INCHES ARE POSSIBLE AT
THE HIGHER ELEVATIONS. FCST SNOWFALL TOTALS WERE INCREASED TO
10-14 INCHES FROM THE FAR WRN SUBURBS OF DC AND BALTIMORE BACK WEST
TO THE POTOMAC HIGHLANDS. THIS WESTWARD TRACK WOULD ALSO YIELD MORE
MIXING WITH SLEET/RAIN FOR THE I-95 CORRIDOR. THE TRANSITION IS
EXPECTED TO OCCUR LATE TNGT IN SRN MD AND THU MRNG NEAR I-95. ALL
RAIN OR RAIN/IP MIX EXPECTED TO CONTINUE INTO THU AFTN FOR THESE
AREAS.

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The only things I can think of that could ruin a 10"+ event in DC is:

1. If the dry slot is more assertive, pushing best snow making/bands NW of DC.

2. The "steamroll" stays separate of the incoming negative-tilt, and then it begins to accelerate due to its convective process. This would limit the amount of time some of the great bands can stay over any one location.

That's about it, as far as I can see...

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The only things I can think of that could ruin a 10"+ event in DC is:

1. If the dry slot is more assertive, pushing best snow making/bands NW of DC.

2. The "steamroll" stays separate of the incoming negative-tilt, and then it begins to accelerate due to its convective process. This would limit the amount of time some of the great bands can stay over any one location.

That's about it, as far as I can see...

What about the last night Euro type solution with a lot of mixing tomorrow?  I know that's not the prime time for precip, but wouldn't that also kill the size (or existence) of the back-end thumping?

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The only things I can think of that could ruin a 10"+ event in DC is:

1. If the dry slot is more assertive, pushing best snow making/bands NW of DC.

2. The "steamroll" stays separate of the incoming negative-tilt, and then it begins to accelerate due to its convective process. This would limit the amount of time some of the great bands can stay over any one location.

That's about it, as far as I can see...

 

mixing early?

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You guys would probably like the SPC WRF.

 

Pretty much agree with HM. Just watch the DS that is going to want to zoom in to the NW, but come to a halt very near DC I think. Second is any WCB type convection robbing this thing..but I agree it doesn't seem to be a March 2013 deal there..at least now. Just have to watch that the WCB  omega bomb precip doesn't peal NE.

 

Sort of worry near I-95 about DS and mixing, but 10-15 miles means everything.

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NWS seems to believe it's going to look more like last night's Euro given current obs...

 

A COMPARISON OF 12Z/18Z RAOBS TO INITIALIZATION OF THE 12Z MODELS

AND THEIR 6-H FORECASTS INDICATE THE GFS/NAM WERE TOO FLAT WITH THE

LOW-LEVEL THERMAL TROUGH ON THE EASTERN SIDE OF THE APPALACHIANS AND

DOWNSTREAM THERMAL RIDGE TOWARD THE SOUTHEAST COAST. SATELLITE WATER

VAPOR LOOP INDICATED THE NRN STREAM SHORTWAVE TROUGH WAS ALREADY

CLOSING OVER ERN NE-KS...WHICH WAS EARLIER/FASTER THAN MOST OF THE

12Z GUIDANCE HAD INDICATED. THESE ERRORS PROVIDE EVIDENCE TOWARD A

MORE WESTWARD TRACK OF THE COASTAL LOW...CLOSER TO THE PAST FEW RUNS

OF THE ECMWF. THE LOW TRACKING RIGHT UP THE COASTLINE WOULD SHIFT

THE AXIS OF HEAVIEST SNOWFALL TOWARD THE BLUE RIDGE AND I-81

CORRIDOR...WHERE ISOLATED TOTALS OF UP TO 20 INCHES ARE POSSIBLE AT

THE HIGHER ELEVATIONS. FCST SNOWFALL TOTALS WERE INCREASED TO

10-14 INCHES FROM THE FAR WRN SUBURBS OF DC AND BALTIMORE BACK WEST

TO THE POTOMAC HIGHLANDS. THIS WESTWARD TRACK WOULD ALSO YIELD MORE

MIXING WITH SLEET/RAIN FOR THE I-95 CORRIDOR. THE TRANSITION IS

EXPECTED TO OCCUR LATE TNGT IN SRN MD AND THU MRNG NEAR I-95. ALL

RAIN OR RAIN/IP MIX EXPECTED TO CONTINUE INTO THU AFTN FOR THESE

AREAS.

Shenandoah Valley will be buried :snowing:

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zwyts, euro sees on its own with the far West track, all short term high res mods are east of it, not sure why NWS is using euro as a crutch.

 

??  The euro gives me and you 6" by dawn...every model has mixing issues...There are hundreds of posts discussing this storm...if people cant follow along, I dont know what to tell you

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They actually say change to rain

 

The discussion almost looks like it is from yesterdays model runs. They think the models are too far east and are favoring a more west track, maybe they are still scared from March's bust. The 4-8 inches for DC or 7-12 in MoCo still could verify, it'll just be on the very high end at 8 inches.... but yeah, I'm surprised they didn't go with a 6-10 or 6-12 for DC.

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zwyts, euro sees on its own with the far West track, all short term high res mods are east of it, not sure why NWS is using euro as a crutch.

If you recall, their reasoning was discussed in here the last few days. The Euro was coming farther west because it was phasing earlier. They are now showing that phasing happening when the Euro said it would, hence why they are buying it's 850 track. Believe me, I hope they are wrong and we still get our major front end thump. Truthfully, I think we will.  :snowing:

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You guys would probably like the SPC WRF.

 

Pretty much agree with HM. Just watch the DS that is going to want to zoom in to the NW, but come to a halt very near DC I think. Second is any WCB type convection robbing this thing..but I agree it doesn't seem to be a March 2013 deal there..at least now. Just have to watch that the WCB  omega bomb precip doesn't peal NE.

 

Sort of worry near I-95 about DS and mixing, but 10-15 miles means everything.

 

just for clarification what is DS?

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