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March 3-4, 2019 Snow Discussion and Obs


WxUSAF
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10 minutes ago, C.A.P.E. said:

Ha maybe! I know very little about the physics of the HRRR. What I do know its it is prone to dramatic shifts over a few runs, and it is next to useless beyond 3-4 hours. So  I guess what I am saying is, I wouldn't worry about that particular model.

There are enough subtle changes in the more reliable guidance over the past 2-3 model cycles to put up some caution flags though. Just for a "quick and dirty" look, check out the snow map over last 3 runs of the GFS on TT. Don't look at the amounts, just the trend. It now has all the significant snow focused more NW, as expected in this setup. I said yesterday I thought the ICON looked pretty reasonable, and it has pretty much held.

I noticed that. Snow maps are pretty useless on the southern edge as much of that was actually showing sleet. And that was fluctuating from run to run depending on precip being shown. So though it looked as if we were maybe getting a shift southward of the snowfall in fact that was nothing more then it just showing an increase of qpf totals. If you actually looked at the soundings you could see there has been a shift in the temp profile northward run over run, more so to the east then the west. 

Right now the battle ground in my mind between mostly conversational snow and/or sleet and shovelable snow is probably just north of DC running east through Balt. Now how that adjusts will probably be determined by what amount of heating we do in fact see on the ground as well as what dews are looking like when the precip does move in. If we do see a spike in temps and/or dews then we can probably shift that battleground northward as we will see deeper low level warmth that needs to initially be overcome. That lends less time where the temp profile will support snow before the warm nose pops in over top. Conversely less heating/lower dews and you can shift the battle ground south. 

At this time I am liking the potential for 10-15 miles N/W of the cities especially the favored locations around the PA line. Seeing a general increase on projected qpf and tend to believe we will continue to see that increase. Thinking at this time there is a decent shot we see some 10"+ reports somewhere up in that favored local as I would not be surprised if we see some 10-1 to 12-1 ratios as we see some good lift through the DGZ at times in that region. The only limiting factor will be ground temps in that case. Keep the temps around freezing for the majority of the event and they may be golden.

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2 minutes ago, mappy said:

34/26  starting warm and hoping to cool quickly is the worst. 

We're ok.  We should cool quickly once precip. starts. If we were in the low 40's now it would be a tougher situation. Hopefully we sent rise too much this morning whicjmh I dont think will happen. Temp should go right to 30-31 once we're snowing and fully saturated.

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5 minutes ago, WxUSAF said:

Nothing would really surprise me for us. All snow, nearly all rain, mix.  Think we see some accumulation, but big bust potential on both sides.

Hoping for the best. You are much farther west than me though, so you are in a bit of a better spot.

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5 minutes ago, WxUSAF said:

Nothing would really surprise me for us. All snow, nearly all rain, mix.  Think we see some accumulation, but big bust potential on both sides.

Our back yards seem to have fallen on the right side of the equation this winter. Fingers crossed we do it again today. :)

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1 minute ago, HighStakes said:

We're ok.  We should cool quickly once precip. starts. If we were in the low 40's now it would be a tougher situation. Hopefully we sent rise too much this morning whicjmh I dont think will happen. Temp should go right to 30-31 once we're snowing and fully saturated.

Thanks. This years marginal events haven’t leaned in my favor so I’m hesitate to be excited about the higher totals. My version of PSUs fringe worry I suppose lol

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12Z IAD sounding shows a decent dry layer just above the sfc, dewpoints a few degrees lower than the 6z NAM forecast fwiw. Makes me feel a little better about my 39/29 pws reading knowing there is some drier air just above the surface.

-------------------------------------------------------------------------------
LEV PRES  HGHT  TEMP  DEWP  RH  DD   WETB DIR SPD THETA THE-V THE-W THE-E   W
     mb     m     C     C    %   C     C  deg knt   K     K     K     K    g/kg
-------------------------------------------------------------------------------
SFC 1010    98   4.2  -2.8  60  7.0   1.4  10   7 276.6 277.1 274.0 285.1  3.07
  1 1000   169   3.4  -5.6  52  9.0   0.1  10   8 276.5 277.0 273.2 283.6  2.51
  2  944   633  -0.7  -7.7  59  7.0  -3.1 358  11 277.0 277.4 273.1 283.3  2.26
  3  925   795  -1.7  -6.5  70  4.8  -3.4 340   7 277.6 278.0 273.8 284.7  2.54
  4  896  1048  -3.7  -5.6  87  1.9  -4.4 258  11 278.0 278.5 274.5 285.9  2.81
  5  872  1263  -2.1  -2.6  96  0.5  -2.3 231  18 281.9 282.5 277.7 292.0  3.62
  6  850  1466  -2.7  -3.0  98  0.3  -2.9 235  20 283.3 283.9 278.4 293.5  3.60
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Snow maps are bad among the southern edge not just because of sleet but also how they calculate. So let’s take a spot along 95 for example. It’s 34 degrees and during the period gets .3 qpf. The model calculates that 50% of what falls will be snow, half’s the .3 and says 1.5”. But a half rain/snow mix at 34 degrees isn’t going to be 1.5” it’s white rain. That’s another example of why those things are awful right along the rain snow line. 

They are ok to glance at just to see trends quickly from run to run but you have to actually look at the soundings if you want to make a real forecast. 

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8 minutes ago, psuhoffman said:

32/22 here. 

Went to my friend's house in gamber/finksburg. No snow left on the ground. Bare as can be. Actually there was no snowcover left south of Walmart. 

The fact that we held some snow cover bodes well. Our temps are running quite a bit cooler than the rest of the forum this morning .

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9 minutes ago, Scraff said:

Our back yards seem to have fallen on the right side of the equation this winter. Fingers crossed we do it again today. :)

If this was our last hope in a bad winter I’d be more stressed, but I’m already over climo and it’s March.  I’ll just let it play out and hope to pad stats.

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5 minutes ago, WxUSAF said:

If this was our last hope in a bad winter I’d be more stressed, but I’m already over climo and it’s March.  I’ll just let it play out and hope to pad stats.

We still got a shot at something on Friday. Would be nice to have some good looks at 12z and 18z to hold us over if it does just rain. Holding steady at 39.

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The 06Z Euro has the 2m temp at 34 at 00Z at DCA,  The 11Z HRRR has it at 39.  I've not been a big fan of the HRRR. My question to my friends at EMC,  are there any verification of the HRRR 2m temps and is there a high bias?  oops I showed teh 23Z but the 00Z has the same temp.

 

Mar_3_hrrr_2019.png

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