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February 19-20th Threat - STORM MODE


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2 minutes ago, psuhoffman said:

The issue with the NAM's are where they set up the best banding.  They push the best fronto banding north of our area.  Even north of my area.  After an initial short thump around 7am it focuses the best banding up in PA.  You can see the cooling from the heavy band in the morning at 700 mp and then once that lifts north with only lighter rates the WAA takes over and without heavy rates to mix the column we torch at the mid levels.  That is how this works.  If we stay under heavy banding like the GFS/FV3/GEM/RGEM/HRDRPS/ICON suggest the flip will be delayed a couple hours plus combined with more qpf and we get those 4-8" numbers NWS is pimping.  But if the NAM's are right that the best lift and banding ends up to our north in PA, this will be very disappointing to most in here IMO.  I am NOT saying I think the NAM is right here...but the NAM progression of this would be a quick 1-3" followed by ice across most of our area.  That would probably be considered a fail by most in here considering what the official NWS forecast is right now!

Usually safe to bet against the NAM. If one of the globals jumps on with it, that's more concerning.

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1 minute ago, psuhoffman said:

The issue with the NAM's are where they set up the best banding.  They push the best fronto banding north of our area.  Even north of my area.  After an initial short thump around 7am it focuses the best banding up in PA.  You can see the cooling from the heavy band in the morning at 700 mp and then once that lifts north with only lighter rates the WAA takes over and without heavy rates to mix the column we torch at the mid levels.  That is how this works.  If we stay under heavy banding like the GFS/FV3/GEM/RGEM/HRDRPS/ICON suggest the flip will be delayed a couple hours plus combined with more qpf and we get those 4-8" numbers NWS is pimping.  But if the NAM's are right that the best lift and banding ends up to our north in PA, this will be very disappointing to most in here IMO.  I am NOT saying I think the NAM is right here...but the NAM progression of this would be a quick 1-3" followed by ice across most of our area.  That would probably be considered a fail by most in here considering what the official NWS forecast is right now!

It's certainly possible the 3k NAM is right for several reasons:

1.) the jet streak was well sampled by the the RAOBs out of New York this morning.

2.) we've seen the last minute north trend all winter, this could be it.

3.) ian is coming back from vacation in time for the "storm" so this thing is falling apart just in time for him to get back in town

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5 minutes ago, Ji said:

the NAM being dry...what happened to this  model? 

It's not dry...its just shifting the best forcing NORTHWEST of us...its aiming that stj moisture plume across PA instead of our area.  Lets see what the other guidance does today before deciding were in trouble.  

IF...if if if...everything else moves towards the NAM then I agree we are in trouble if people expect the 4"+ snowfall totals around here.  But as of last night the NAM was pretty much on its own with that look.  Sometimes the NAM is onto something...and often the NAM is just off on a tangent smoking some bad mojo.  

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Just now, psuhoffman said:

It's not dry...its just shifting the best forcing NORTHWEST of us...its aiming that stj moisture plume across PA instead of our area.  Lets see what the other guidance does today before deciding were in trouble.  

IF...if if if...everything else moves towards the NAM then I agree we are in trouble if people expect the 4"+ snowfall totals around here.  But as of last night the NAM was pretty much on its own with that look.  Sometimes the NAM is onto something...and often the NAM is just off on a tangent smoking some bad mojo.  

the NAM has been shifting north since yesterday. 

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5 minutes ago, MN Transplant said:

I know it isn't worth using as a forecasting tool, but as an example of how we at the DC latitude could potentially maximize this storm is the 12z extended HRRR.  The sleet line approaches at 15z after 2-3" like the NAM, but then the precipitation ramps up in intensity and effectively "beats back" the mix line so that we end up with 6-7" by 19z.

THIS THIS THIS...  people need to focus on where the best banding sets up.  It's that simple.  We have seen this type setup over and over.  Wherever those intense bands set up during the mid morning to mid-day will delay the flip to sleet as the intense rates and vv's will help to mix out the warm layers for a time.  That extra 2 hours (along with a LOT of qpf in those 2 hours) makes all the difference.  The guidance can't agree on where that banding sets up.  Euro kind of splits into two areas...one south of DC early and one north of DC later.  GFS and RGEM like to crush DC.  ICON and HRDRPS likes MD.  NAM is way up over PA.  But that banding feature is the key to who gets good snow and where is left kind of disappointed by all this imo.   

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2 minutes ago, mappy said:

the NAM has been shifting north since yesterday. 

It has actually been pretty consistently north for 2 days...it had that one great 0z run that went south and NAMd DC and MD and got everyone excited...but it had been north before that and went right back at 6z and has only been shifting further north every run since.  Everything else has kind of been shifting north (except the euro which has been rock solid steady) also...but is still way way south of the NAM.  Interesting model war.  Unfortunately this is kind of the exact situation the NAM was designed for.  Still doesn't make it right.  I suppose the high res Canadian SHOULD be able to handle this kind of thing also.  

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25 minutes ago, WxUSAF said:

A euro/3k NAM blend is usually a good forecast in a CAD situation like this. That’s where I’d lean.

Me too!  I also like the idea of the heavier precip focusing a little to our north because as the low lifts to north west of the mountains temps will warm across Kentucky and western WV setting up a frontal boundary to focus the precipitation.  That's what the NAM and Euro seem to be doing.  Heck no one likes to look at the SREF.  It has a mean of 3 inches over DC because it has members that fringe us to the north but also have a four 5 inch plus members to balance it out.  its mean is pretty much in the Euro, NAM camp.  The other caveat is for the snow changeover go with the fastest model but at the surface relay on the slowest one to warm the temps. 

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Just now, psuhoffman said:

It has actually been pretty consistently north for 2 days...it had that one great 0z run that went south and NAMd DC and MD and got everyone excited...but it had been north before that and went right back at 6z and has only been shifting further north every run since.  Everything else has kind of been shifting north (except the euro which has been rock solid steady) also...but is still way way south of the NAM.  Interesting model war.  Unfortunately this is kind of the exact situation the NAM was designed for.  Still doesn't make it right.  I suppose the high res Canadian SHOULD be able to handle this kind of thing also.  

I sorta hope the 12z NAM is not correct, 2" of snow followed by a bunch of sleet before the flip, sounds awful. 

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Just now, mappy said:

I sorta hope the 12z NAM is not correct, 2" of snow followed by a bunch of sleet before the flip, sounds awful. 

Of course down here, we're hoping the GFS is correct with the snow part, but it's pretty bad with CAD vs NAM.  NAM is probably more reliable in this situation.   I never expected more than 2-4 anyway, so I'm unmoved by the last few NAM runs.  

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If we're being honest with ourselves we should count ourselves lucky that we even have a shot at a few inches with no major cold air before or after this storm and a low track like this. That high pressure is saving us from a 40 degree rain storm. You gotta take what you can get in a winter like this. It's part of the mess of living in this region. Gotta get used to it if you're going to stay here lol. 

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My thinking aligns with Hoffman’s in that for those outside these bands tossed north by a warm front, there are most certainly going to be winners and losers. @Amped made a great post yesterday talking about this. Precip driven by an adjoined warm front and WAR feature will have a less than perfectly uniform QPF distribution and in the case of our warm nose nudging north quickly at h7, there will be discrepancies in snow that could loom large (2” vs 6” in a 25-30 mile range).

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1 minute ago, psuhoffman said:

NWS must be weighting the GFS/FV3 a LOT in its forecast... only way those bullish numbers make a lot of sense.  

Possible although you could sort of justify a widespread 4-6” swath using the euro with a little smidgen of gfs blend. They came down from yesterday when they had a lot of 6-8” which seems really unlikely IMO.

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1 minute ago, psuhoffman said:

NWS must be weighting the GFS/FV3 a LOT in its forecast... only way those bullish numbers make a lot of sense.  

Last Model Diagnostic Discussion from WPC last night indicated the NAM is the furthest north with the expected QPF maxima compared to other guidance, but is within the general ensemble spread, so it was maintained. The overall pattern evolution is a weighted average of all models, so no disclaimers made given the trends of last nights runs. 

If anyone wants a link to the discussions, here's where to find them. https://www.wpc.ncep.noaa.gov/discussions/hpcdiscussions.php?disc=pmdhmd 

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NWS must be weighting the GFS/FV3 a LOT in its forecast... only way those bullish numbers make a lot of sense.  

 

Didn’t the 06z EURO justify a widespread 4-6” swath?

 

Anyways, it’s almost obs time given that I’m probably 16 hours from first flakes or so.

 

41/32 with high clouds. Sun not struggling to get through though.

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Just now, MillvilleWx said:

Last Model Diagnostic Discussion from WPC last night indicated the NAM is the furthest north with the expected QPF maxima compared to other guidance, but is within the general ensemble spread, so it was maintained. The overall pattern evolution is a weighted average of all models, so no disclaimers made given the trends of last nights runs. 

If anyone wants a link to the discussions, here's where to find them. https://www.wpc.ncep.noaa.gov/discussions/hpcdiscussions.php?disc=pmdhmd 

When I was a lead forecaster in college, we were always taught to read the NCEP diagnostic disco first before looking at anything else...either obs or models.  You learn so much through that one product.

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2 minutes ago, WxUSAF said:

Possible although you could sort of justify a widespread 4-6” swath using the euro with a little smidgen of gfs blend. They came down from yesterday when they had a lot of 6-8” which seems really unlikely IMO.

That's probably what they and WPC went within during collaboration because it does fit their forecast. I refrained from making a final call on this storm because of any minor adjustments in the placement and strength of any synoptic features will cause significant shifts in the snow maxima and final distribution of sleet/freezing rain. I want to see all guidance before making any final calls today. Probably will not happen until the evening for me since I work and I'm going to be crazy busy today. 

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5 minutes ago, psuhoffman said:

ICON is another beatdown across the area... kind of has the euro idea of two heavy bands but is even thumpier with both...  first band crushes DC and northern VA early morning...second band crushes MD late morning to mid-day.  Everyone wins.  

Hoff, agreed. The consistency shown in the modeling by the ICON and FV3 bullseyeing NVA to the M/D has been worth watching. 

I personally liked having the GFS and RGEM south, and set my look on a compromise of the camps to bring a favorable solution to most of our sub. 

it would appear that models have some leverage to that double banded solution that the Euro has started to key in on. That’s what I’ll be watching for the rest of the 12z suite. 

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11 minutes ago, psuhoffman said:

NWS must be weighting the GFS/FV3 a LOT in its forecast... only way those bullish numbers make a lot of sense.  

I know I'm biased since I work there, but one thing I like to look at is the trend in the WPC probabilistic guidance. What looked like a bar of 4" here in the urban corridor from yesterday's PWPF is now closer to 2-3". 4-6" here in central-northern AA feels like a pipe dream. If this were deal or no deal, I'd sign up for 4" right now, but instinctively I think 2-3" would be more realistic. In fact, I think there's a better chance of 1-2" of snow before sleet here than 3-4". Hope I'm wrong. 

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