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Tuesday 1/7/20 Disco snow event


MountainGeek
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.SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/...
Moving into tomorrow, a compact shortwave will approach from the
OH/TN Valleys, bringing a period of snow to the region. While
the shortwave itself won't be large in areal extent, it will be
a sharp feature, with a very short wavelength (which will lead 
to strong lift in the zone of differential cyclonic vorticity
advection in advance of the wave). Given the short wavelength
and the rapid movement of the shortwave, the areal extent of
the precipitation is expected to be small, but the precipitation
may be rather intense. Expect that snow at least reaches
moderate intensity in most locations, and brief bursts of heavy
snow can't be ruled out. Guidance has progressively trended
heavier with the QPF over the last few model runs, and some
models indicate 1 hourly QPF values in excess of one tenth of 
an inch will be possible across central Virginia late tomorrow 
morning. As a result, we've upped snow totals and raised Winter 
Weather Advisories across southwestern portions of the forecast 
area.

 

 

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What a nice look tomorrow for good old Torchanuary. Can’t wait for the OBS thread. Should be rocking! Any chance this gets here earlier so schools don’t even open? Inquiring for some teenage daughters...
 

Meh. Who we kidding!? It’s the DMV.  They’re probably closing as I type. :lol:

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I literally can’t recall a single event where the snow depth map was the best verifying forecast product.  Yes 10:1 isn’t always good. Kuchera seems to be in the right sort of ballpark if there’s any precip type or temp issues. Tomorrow isn’t THAT marginal unless you want to take your spotter reports from on the asphalt of the beltway.

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21 minutes ago, Bob Chill said:

This has to be the top end run that set expectations too high that results in people getting 1-2" and being pissed off. lol. It's engraved in the script. 

I think we're at the peak.  We back down a little from him to set the expectations right.  If I get a sloppy inch of snow, I'm lucky.  

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59 minutes ago, jewell2188 said:

We have seen time and time again, NWS is always playing catch up 

They have plenty of time to make adjustments. They are doing a decent job so far imo. 00z runs on guidance will be the biggest time frame for areas to the NE. SW portion of the CWA is a slam dunk WWA. 

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My gut says dc gets good snow tv but blanked on tha accum department. McLean on NW and Rockville points west see 1-2. Hagerstown cashes in. Winchester down to snowshoe and valley gets the goods on this setup.

Eitherway nice to be in the game. I’ve seen signs of PNA perhaps flipping and PAC jet finally slowing down a bit

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8 minutes ago, WxUSAF said:

I literally can’t recall a single event where the snow depth map was the best verifying forecast product.  Yes 10:1 isn’t always good. Kuchera seems to be in the right sort of ballpark if there’s any precip type or temp issues. Tomorrow isn’t THAT marginal unless you want to take your spotter reports from on the asphalt of the beltway.

I feel like this is a tough call with the temperatures because if this thing really thumps, then it could drag down colder air and also it will just be easier to accumulate. Might really come down to how heavy the rates get. Get the rates, get a few inches. Don't get the rates, get white rain.

Agree on the snow depth maps. I find them totally useless except for when white rain is the expectation.

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7 minutes ago, WxUSAF said:

I literally can’t recall a single event where the snow depth map was the best verifying forecast product.  Yes 10:1 isn’t always good. Kuchera seems to be in the right sort of ballpark if there’s any precip type or temp issues. Tomorrow isn’t THAT marginal unless you want to take your spotter reports from on the asphalt of the beltway.

 

       I'd respectfully argue that it's way better than 10:1 maps in any sort of sleet or  mixed events or in a daytime event with lousy rates or super warm ground.    It fails in the events with it knows that that the temps are marginal and cuts amounts that can stick, but in the real world the rates overcome the marginal temps.

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4 minutes ago, osfan24 said:

I feel like this is a tough call with the temperatures because if this thing really thumps, then it could drag down colder air and also it will just be easier to accumulate. Might really come down to how heavy the rates get. Get the rates, get a few inches. Don't get the rates, get white rain.

Agree on the snow depth maps. I find them totally useless except for when white rain is the expectation.

If the NAM is right, it's.a 4-hr long beatdown.  Probably not right, but all the guidance today seems to suggest at least 1-2 hours of solid rates.  It's early January fercrissakes.  Yes, near-surface temps are a bit warm, but the column is perfectly cold.  

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1 minute ago, high risk said:

 

       I'd respectfully argue that it's way better than 10:1 maps in any sort of sleet or  mixed events or in a daytime event with lousy rates or super warm ground.    It fails in the events with it knows that that the temps are marginal and cuts amounts that can stick, but in the real world the rates overcome the marginal temps.

Yes, if it's a largely sleet event maybe.  

 

I don't have the photographic memory for T-2" events that @psuhoffman has, but I recall some slop storm from the last couple years that looked super marginal on temps.  10:1 was like 2-4", but the snow depth maps were all like 0.1-1".  I was hedging pretty hard on the snow depth maps, and the spotter reports ended up mostly like 1-2".  Which I think was pretty close to Kuchera.  Kuchera seems like a pretty good call in a marginal snow or rain scenario.  Sleet does complicate a bit.  

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2 minutes ago, WxUSAF said:

Yes, if it's a largely sleet event maybe.  

 

I don't have the photographic memory for T-2" events that @psuhoffman has, but I recall some slop storm from the last couple years that looked super marginal on temps.  10:1 was like 2-4", but the snow depth maps were all like 0.1-1".  I was hedging pretty hard on the snow depth maps, and the spotter reports ended up mostly like 1-2".  Which I think was pretty close to Kuchera.  Kuchera seems like a pretty good call in a marginal snow or rain scenario.  Sleet does complicate a bit.  

 

          I like what I've seen from the Kuchera plots.

          I'll admit that it drives me nuts when it's going to be an all sleet or a white rain event, and people post the 10:1 maps screaming "The GFS/NAM/whatever is predicting 14" here.  LOL."      The models are NOT doing that.      Any sleet or snow gets tallied together into a liquid amount, and then the web sites slap on a generic ratio that makes a product with already severe limitations 5x worse.

       

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9 minutes ago, high risk said:

 

       I'd respectfully argue that it's way better than 10:1 maps in any sort of sleet or  mixed events or in a daytime event with lousy rates or super warm ground.    It fails in the events with it knows that that the temps are marginal and cuts amounts that can stick, but in the real world the rates overcome the marginal temps.

In marginal events or events with sleet, the 10:1 maps are usually awful as well. I tend to take the middle ground between the two unless it's a true white rain event.

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Just now, SnowGolfBro said:

Going to be a tough call for the schools.  If this does materialize and thump it would likely happen in the noon to 6pm window.  Commuttageddon redux not impossible lol

I would be shocked if there are not early dismissals. There have been for much, much less threatening events.

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