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12/20-12/21 Moderate/Intense Clipper Event?


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The good news for ORD is that they shouldn't have any dry air issues to deal with. It's currently 16/11.

The bad news for ORD is that the 12z NAM (fwiw) has the 546 thickness line pass through for the last half of the event. Even if ORD manages to get 0.30" of liquid (an optimistic projection to begin with), at least 0.10" of this could be non-snow. The more I follow these events, it makes you realize that snow is not an easy process; many things need to go right. For example, you'd think we wouldn't have precip-type issues with such an antecedent cold airmass in place and good snowcover in the midwest for mid-Dec...

2" sounds like a good target. Some area might see more given the weenie nuggets Izzi dropped and the banding seen out west. Not too worried about mixing cutting down the action here outside poor ratios and meager back end freezing drizzle.

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The good news for ORD is that they shouldn't have any dry air issues to deal with. It's currently 16/11.

The bad news for ORD is that the 12z NAM (fwiw) has the 546 thickness line pass through for the last half of the event. Even if ORD manages to get 0.30" of liquid (an optimistic projection to begin with), at least 0.10" of this could be non-snow. The more I follow these events, it makes you realize that snow is not an easy process; many things need to go right. For example, you'd think we wouldn't have precip-type issues with such an antecedent cold airmass in place and good snowcover in the midwest for mid-Dec...

850's at ORD are -4C at 12Z. The event is over by then. There will be no mixing during the main event. Freezing drizzle or snow grains after the snow is done due to drying above 800mb is possible, but a bonafide mixing scenario is not going to happen. Using 1000-500mb thicknesses in this situation is tricky, as mid-level thicknesses are pretty high due to WAA aloft, but never get that close to... or over 0C.

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The good news for ORD is that they shouldn't have any dry air issues to deal with. It's currently 16/11.

The bad news for ORD is that the 12z NAM (fwiw) has the 546 thickness line pass through for the last half of the event. Even if ORD manages to get 0.30" of liquid (an optimistic projection to begin with), at least 0.10" of this could be non-snow. The more I follow these events, it makes you realize that snow is not an easy process; many things need to go right. For example, you'd think we wouldn't have precip-type issues with such an antecedent cold airmass in place and good snowcover in the midwest for mid-Dec...

Well if you put stock into the 12z NAM (and the soundings), it's pretty much all snow for ORD. Thickness only gets to 543, but that's after all of the precip has passed. The profiles are favorable for all snow IMO.

http://68.226.77.253/text/NAM212/NAM212_KORD.txt

http://68.226.77.253/text/NAMSFC/NAM_KORD.txt

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Well if you put stock into the 12z NAM (and the soundings), it's pretty much all snow for ORD. Thickness only gets to 543, but that's after all of the precip has passed. The profiles are favorable for all snow IMO.

http://68.226.77.253...NAM212_KORD.txt

http://68.226.77.253...FC/NAM_KORD.txt

Yeah, agree...thanks ChicagoWx (and alek and csnavy). I should have been a bit clearer: even if the precip is done by then, the surface temp and/or Td will probably rise to the mid 30s after the event at ORD, which would melt off some of the snow that falls. The storm certainly has an intense baroclinic zone...it has definitely been interesting to follow from a meteorological standpoint. Good luck to all.

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'

Yeah, agree...thanks ChicagoWx (and alek and csnavy). I should have been a bit clearer: even if the precip is done by then, the surface temp and/or Td will probably rise to the mid 30s after the event at ORD, which would melt off some of the snow that falls. The storm certainly has an intense baroclinic zone...it has definitely been interesting to follow from a meteorological standpoint. Good luck to all.

We're just not getting a lot out of this one anyways, if we lose 1/2" of our 2" to melting so be it. Ground temps are pretty cold though and it will be dark, so i'm not that worried.

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In Bloomington, MN for holiday visits. Snowing lightly here for thirty minutes or so with a dusting on the paved surfaces so far. Trends look decent to our south and west.

Looking to get on the sleds today at last weekend's hot spot over in Shakopee. Wouldn't mind today's hot spot being over the Bank. Going to be a hell of a story line playing out there. Pack loss last night makes a closer game more palatable for Bears.

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The good news for ORD is that they shouldn't have any dry air issues to deal with. It's currently 16/11.

The bad news for ORD is that the 12z NAM (fwiw) has the 546 thickness line pass through for the last half of the event. Even if ORD manages to get 0.30" of liquid (an optimistic projection to begin with), at least 0.10" of this could be non-snow. The more I follow these events, it makes you realize that snow is not an easy process; many things need to go right. For example, you'd think we wouldn't have precip-type issues with such an antecedent cold airmass in place and good snowcover in the midwest for mid-Dec...

I hate to say it, but this is not a very informed post. Sounding data tells the story (not the 546 thickness line), and you can't infer column saturation from a single surface observation.

I just checked the sounding forecasts for ORD from about 20Z this afternoon through 12Z Tuesday. The sounding clearly supports an all snow event. Moreover, the output from the 12Z NAM is a liquid equivalent of 0.39". This should be easily 3-4" if taken verbatim. I don't see any mixing issues at ORD.

And the forecast from the NAM also shows ORD getting up to 33F tomorrow at the most, so I don't think the snow is going anywhere once it falls. It will, however, make it easier to keep runways clear.

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I hate to say it, but this is not a very informed post. Sounding data tells the story (not the 546 thickness line), and you can't infer column saturation from a single surface observation.

I just checked the sounding forecasts for ORD from about 20Z this afternoon through 12Z Tuesday. The sounding clearly supports an all snow event. Moreover, the output from the 12Z NAM is a liquid equivalent of 0.39". This should be easily 3-4" if taken verbatim. I don't see any mixing issues at ORD.

And the forecast from the NAM also shows ORD getting up to 33F tomorrow at the most, so I don't think the snow is going anywhere once it falls. It will, however, make it easier to keep runways clear.

Fair enough...I appreciate the explanation. :)

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AREA FORECAST DISCUSSION

NATIONAL WEATHER SERVICE QUAD CITIES IA IL

1019 AM CST MON DEC 20 2010

UPDATE

..MAJOR REVISIONS TO THE OVERALL FCST

12Z UA DATA COMBINED WITH RADAR/SFC OBS SHOW THE SNOW BREAKING OUT

MUCH SOONER THAN EXPECTED. COMBINATION OF RUC TRENDS AND INCOMING

WRF INDICATE THE 290K CONDENSATION PRESSURE DEFICITS AND 290K

OMEGA DEPICT REASONABLY WELL WHAT IS CURRENTLY GOING. WAA

STRENGTHENS THE OMEGA BY LATE MORNING AND INTO THE AFTERNOON. THE

STRONGEST FORCING IS CURRENTLY ROUGHLY ON A KALO TO KEWANEE LINE

AND WILL SLOWLY SHIFT TO THE NORTH/EAST.

THUS HAVE EXPANDED THE CURRENTLY HEADLINES AND HAVE MADE THEM

EFFECTIVE IMMEDIATELY. IT APPEARS THAT 2 TO NEARLY 4 INCHES MAY

OCCUR BY SUNSET WITH ANOTHER INCH OR TWO POSSIBLE OVERNIGHT. FCST

SOUNDINGS IN THE SOUTH GET TO AROUND FREEZING SO A RASN MIX IS

POSSIBLE IN THE SOUTHERN THIRD OR SO OF THE CWFA.

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