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February 19-20th Threat - STORM MODE


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34 minutes ago, psuhoffman said:

It's really hard to use the GFS in these situations because its lack of resolution really forces you to assume a lot about the details.  But the GFS blasts our area with some heavy precip between 11am and 3pm.  At 18z the column is still cold enough for snow across northern MD...barely.  By 0z its toast.  But how long it can hold on with mixing of the warm layer with those heavy rates would determine our fate.  If we can hold on an extra hour or two during that band (not a crazy idea given the typical mixing and dynamic cooling in such bands) the GFS implies a really good thump up here.  

 

          we CAN see the in-between hours for the GFS on the mag.ncep.noaa.gov site which has the full hourly output.    You'll see that the changeover is well before 00z, but as has been noted, the GFS is well-known for being way too fast in breaking down inversions and warming the low levels

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1 hour ago, psuhoffman said:

It's really hard to use the GFS in these situations because its lack of resolution really forces you to assume a lot about the details.  But the GFS blasts our area with some heavy precip between 11am and 3pm.  At 18z the column is still cold enough for snow across northern MD...barely.  By 0z its toast.  But how long it can hold on with mixing of the warm layer with those heavy rates would determine our fate.  If we can hold on an extra hour or two during that band (not a crazy idea given the typical mixing and dynamic cooling in such bands) the GFS implies a really good thump up here.  

@HighStakes

It totally depends on the banding.  Think of the similar events to this...Feb 2007 (NOT the VD storm the second one), December 2013, Feb 2015 had some similarities too... the area's that get under the heavy bands will hold the column longer.  The VV's and heavy precip will help to mix out the mid level warm layer from WAA for a time.  If we get under that banding we will get thumped.  If we don't...the mid level warmth will race north and its congrats PA.  We know the drill.  I have no idea where that banding will set up.  No one does.  We can all make educated guesses.   But the idea of a duel max is gaining some traction imo today.  Even the guidance that hits our area pretty good "sees" the banding associated with the jet streak up over PA its just not killing the STJ WAA moisture plume into our area as much and is hitting that band up there less.  Figuring out those kind of details are above my pay grade though.  

So my goalposts from 2 days ago are still in the same place LOL...

Notice even the guidance that thumps us still has some enhancement up in central PA associated with the jet streak?  Its just the NAM is going nuts with that and killing the WAA/STJ moisture feed south of it.  The other guidance has more of a duel max idea hinted at between those two areas.  That is a much better result for us.  

Good and detailed analysis.   Personally, I'm taking the prerogative of using the model that gives me the most snow in my backyard.  For now, with my limited analysis, that shall be the GFS.  The dominant precipitation type gives mby snow from hour 24 to hour 33.  The QPF is about 0.7... with heavy wet snow and ratio of 8:1 (YAG) I'm hoping for 5" to 6".

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Interesting observation from Mount Holly. Maybe models underdoing the initial banding lifting north, especially eastern edge? Or maybe it means nothing.

 

...930 AM Update: No changes made yet to the forecast for this
period, as we are waiting to see more of the 12Z guidance.
However, it is interesting to note that the current
precipitation shield extends further east (across the Carolinas)
than what the models had depicted. I am not sure this will
result in any significant changes for our area as models already
had the precip extending across our region by late tomorrow. We
will have a complete update on this system with the 4 PM update.
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1 minute ago, snowdude said:

Interesting observation from Mount Holly. Maybe models underdoing the initial banding lifting north, especially eastern edge? Or maybe it means nothing.

 


...930 AM Update: No changes made yet to the forecast for this
period, as we are waiting to see more of the 12Z guidance.
However, it is interesting to note that the current
precipitation shield extends further east (across the Carolinas)
than what the models had depicted. I am not sure this will
result in any significant changes for our area as models already
had the precip extending across our region by late tomorrow. We
will have a complete update on this system with the 4 PM update.

Would this mean an earlier start or heavier precip at the start due to increased banding?  If it meant something?

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4 minutes ago, snowdude said:

Interesting observation from Mount Holly. Maybe models underdoing the initial banding lifting north, especially eastern edge? Or maybe it means nothing.

 


...930 AM Update: No changes made yet to the forecast for this
period, as we are waiting to see more of the 12Z guidance.
However, it is interesting to note that the current
precipitation shield extends further east (across the Carolinas)
than what the models had depicted. I am not sure this will
result in any significant changes for our area as models already
had the precip extending across our region by late tomorrow. We
will have a complete update on this system with the 4 PM update.

Yes there is a decided eastern move but looks like lifting north is starting. 1040 still west of us and that’s a good sign for cold not substantially being east of us come crunch time and then see what effect it has on changeover 

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