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The Weekend Rule? Saturday 2/17 - The Icon Storm


DDweatherman
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4 minutes ago, stormtracker said:

They snatched back the Warning to the west.  Poor Ji.   Don't despair, we'll get upgraded after midnight when the storm is just about over.

Leesburg is not in eastern Loudoun so i consider myself under a warning

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56 minutes ago, MillvilleWx said:

2072046756_Snowforecast.thumb.PNG.361fd8641a2b47e14792d372face208b.PNG

 

Rough snow forecast outline (Medium Confidence):

Zone A: 6-10"

Zone B: 3-5" w/ stripe of 5-6" within the 85H frontogen band that sets up from NoVA through SoMD. The potential does include the DC metro, but best chance for highest totals will lie on the edge and outside the beltway. Uncertainty for Southern DE due to thermals

Zone C: 4-6" in the Catoctins and adjacent terrain 

Zone D: 4-6" w/ max of 7" elevation areas above 650ft. This is tricky depending on 7H frontogenesis placement

Most of region: 2-5" fairly widespread. Higher totals within the Parrs ridge area from NW MoCo through western HoCo into the Carroll/Frederick border (Clarksburg/Damascus/Mount Airy). 1-2" for areas south of Zone B

I'll try to fine tune this forecast with the new 12z data set. Might be bumping totals a bit

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35 minutes ago, osfan24 said:

3k looks really good. Both NAMs look good with precip. What's the deal with Kuchera? 12:1-15:1 rates are what I thought we were expecting? I would expect the clown maps to be throwing out 6-8+, not actually giving us less than 10:1 rates.

Surface temps.  Kuchera uses the warmest temp below h5 as a significant part of the calculation.  Looking at soundings a lot of the area is right at 32 during the snowfall.  First of all, that is a little warmer than I expected for a NS wave at night with the thermal boundary south of us!  That said, so long as temps get below freezing so there isn't actually a lot of compaction as the snow hits the ground (at night there shouldn't be so long as temps are BELOW 32, gonna be close unfortunately) IMO the temps in the DGZ and through most of the column are more important.  There is good saturation and lift in the DGZ so we should have near optimal snow growth.  The column is cold until near the ground so there is nothing to ruin the integrity of the flakes.  So long as the ground temps can be 30-31 and not 32-33 I think we will get higher ratios.  12-1 maybe.  Places a little further north in the region that also get under good banding could see 15-1.  But again this depends totally on ground temps not actually being 32-33.  I was NOT expecting that...at night, north of the thermal boundary in a NS wave...under heavy precip, we should NOT have surface temp issues in mid February!  But its going to be close...1 or 2 degrees as the surface will make all the difference here between getting low ratios due to ground compaction/melt and getting high ratios because every other level is good.  

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3 minutes ago, Ji said:

Leesburg is not in eastern Loudoun so i consider myself under a warning

Technically it is but we are both close enough, I think if you walked to the old West Park golf course that is considered the start of western loudoun up by you and if i walked a few feet to my west I would be in western loudoun. So close enough i suppose.

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Just now, aldie 22 said:

Technically it is but we are both close enough, I think if you walked to the old West Park golf course that is considered the start of western loudoun up by you and if i walked a few feet to my west I would be in western loudoun. So close enough i suppose.

i mean our neighborhood backs to route 15 until you and Dave johnson moved out! Poor Dave!

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Western loudoun is either/both higher elevation and less populated than eastern loudoun, so it makes sense they hedged with a warning there. 

It's also a saturday morning, so that's probably why they went with a WWA east loudoun even though they're forecasting for 3-5" locally up to 7" imby. Had it been a weekday, they would have gone with a warning. 

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1 minute ago, Terpeast said:

Western loudoun is either/both higher elevation and less populated than eastern loudoun, so it makes sense they hedged with a warning there. 

It's also a saturday morning, so that's probably why they went with a WWA east loudoun even though they're forecasting for 3-5" locally up to 7" imby. Had it been a weekday, they would have gone with a warning. 

I don’t see this hitting warning levels in most spots, so the advisory makes sense. The 7” thing is a stretch IMO and probably mainly for the highest parts of Parrs ridge.

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Instead of wrangling over digital ratios, just use your memory. Imo, because of the start temps in the closer burbs, I don't see how my yard clocks over 10:1 in total without instability or fronto luck (impossible to predict).

Euro has been steady with qpf for a while. It doesn't blow that too often this close with a fairly simple wave. So .40qpf seems like a good # there. 10:1 max avg would lay down an honest 3.5-4". Seems like a fair take but we all have our own way

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3 minutes ago, WxMan1 said:

Lots of dark blues on the 3km NAM on TT, almost from the get-go. All that snow falls within a 4-5 hour period. Definitely some near zero to negative theta lapse rates.

I'm surprised how tempered the posts are considering how good the 3k looked.  I'm kind of stoked for this.

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3 minutes ago, nw baltimore wx said:

I'm surprised how tempered the posts are considering how good the 3k looked.  I'm kind of stoked for this.

I’d be even more stoked if it wasn’t super late at night. Might stay up till 3am or so.

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8 minutes ago, Bob Chill said:

Instead of wrangling over digital ratios, just use your memory. Imo, because of the start temps in the closer burbs, I don't see how my yard clocks over 10:1 in total without instability or fronto luck (impossible to predict).

Euro has been steady with qpf for a while. It doesn't blow that too often this close with a fairly simple wave. So .40qpf seems like a good # there. 10:1 max avg would lay down an honest 3.5-4". Seems like a fair take but we all have our own way

That's my wag. I called for 2-4" dc/balt metros and 4-7" far N&W, and don't see any reason to change that. I'd love to get 5" out of this, though! 

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