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Feb 21/22 PDIII Junior Model/Forecast Discussion


WxUSAF

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A question that has a lot to do with impact, but hasn't been analyzed much yet: Is the GFS or NAM going to be closer with surface temps? As WxUSAF pointed out, there's a huge difference in surface temps between the two models at 0Z tonight, and that difference continues all the way through the night. The GFS verbatim already has teens (!) into the area by 1 am, and is likely too cold. But is the NAM too warm by a significant amount?

Edited to add: I'm not implying anything about precip type-- just looking at how cold it's going to be overnight, which will have a large impact on road conditions, etc.

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/feb-22-pa-event-folks-in-dca-bwi-and-far-northern-va-need-to-calm-down/

:lol:

His prediction:

For DCA I would be surprised if they saw an 1" but from 495 N and W and N and E... and NORTH of I-66.... snow could accumulate 1-2" ...in NW VA about 3" ( west of Rte 15) FOR MARYLAND...6" by the PA Border and into Gettysburrg Harrisburrg York Janover Lancaster.... 3" in Frederick east to Cockeysville to Havre De Grace

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WWA issued.

WINTER WEATHER ADVISORY IN EFFECT FROM 9 PM THIS EVENING TO 7 AM EST TUESDAY... THE NATIONAL WEATHER SERVICE IN BALTIMORE MD/WASHINGTON HAS ISSUED A WINTER WEATHER ADVISORY FOR SNOW AND SLEET... WHICH IS IN EFFECT FROM 9 PM THIS EVENING TO 7 AM EST TUESDAY.

* PRECIPITATION TYPE... WINTRY MIX CHANGING OVER TO SNOW.

* ACCUMULATIONS... 2 TO 5 INCHES OF SNOW.

* TIMING... WINTRY MIX WILL BEGIN LATE THIS EVENING... THEN CHANGE OVER TO ALL SNOW AFTER MIDNIGHT... AND CONTINUE REST OF THE OVERNIGHT.

* TEMPERATURES... TEMPERATURES IN THE MID 30S THIS EVENING... DROPPING TO THE UPPER 20S BY TUESDAY MORNING.

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WWA:

...WINTER WEATHER ADVISORY IN EFFECT FROM 9 PM THIS EVENING TO 7 AM EST TUESDAY...

THE NATIONAL WEATHER SERVICE IN BALTIMORE MD/WASHINGTON HAS ISSUED A WINTER WEATHER ADVISORY FOR SNOW AND SLEET... WHICH IS IN EFFECT FROM 9 PM THIS EVENING TO 7 AM EST TUESDAY.

* PRECIPITATION TYPE...WINTRY MIX CHANGING OVER TO SNOW.

* ACCUMULATIONS...2 TO 5 INCHES OF SNOW.

* TIMING...WINTRY MIX WILL BEGIN LATE THIS EVENING...THEN CHANGE OVER TO ALL SNOW AFTER MIDNIGHT... AND CONTINUE REST OF THE OVERNIGHT.

* TEMPERATURES...TEMPERATURES IN THE MID 30S THIS EVENING... DROPPING TO THE UPPER 20S BY TUESDAY MORNING.

* WINDS...NORTH-NORTHEAST 10 TO 15 MPH. GUSTS TO 20 MPH.

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His prediction:

For DCA I would be surprised if they saw an 1" but from 495 N and W and N and E... and NORTH of I-66.... snow could accumulate 1-2" ...in NW VA about 3" ( west of Rte 15) FOR MARYLAND...6" by the PA Border and into Gettysburrg Harrisburrg York Janover Lancaster.... 3" in Frederick east to Cockeysville to Havre De Grace

Oh, that Davey Tolleris!

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URGENT - WINTER WEATHER MESSAGE

NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC

1157 AM EST MON FEB 21 2011

MDZ003>007-501-502-VAZ028-WVZ050>053-055-501>504-220100-

/O.UPG.KLWX.WS.A.0004.110222T0200Z-110222T1200Z/

/O.NEW.KLWX.WS.W.0004.110222T0000Z-110222T1200Z/

WASHINGTON-FREDERICK MD-CARROLL-NORTHERN BALTIMORE-HARFORD-

EXTREME WESTERN ALLEGANY-CENTRAL AND EASTERN ALLEGANY-

FREDERICK VA-HAMPSHIRE-MORGAN-BERKELEY-JEFFERSON-HARDY-

WESTERN GRANT-EASTERN GRANT-WESTERN MINERAL-EASTERN MINERAL-

INCLUDING THE CITIES OF...HAGERSTOWN...FREDERICK...WESTMINSTER...

FROSTBURG...CUMBERLAND...WINCHESTER...MARTINSBURG...

CHARLES TOWN...MOOREFIELD...BAYARD...MOUNT STORM...PETERSBURG...

ELK GARDEN...KEYSER...FORT ASHBY

1157 AM EST MON FEB 21 2011

...WINTER STORM WARNING IN EFFECT FROM 7 PM THIS EVENING TO 7 AM

EST TUESDAY...

THE NATIONAL WEATHER SERVICE IN BALTIMORE MD/WASHINGTON HAS

ISSUED A WINTER STORM WARNING FOR SNOW AND SLEET...WHICH

IS IN EFFECT FROM 7 PM THIS EVENING TO 7 AM EST TUESDAY. THE

WINTER STORM WATCH IS NO LONGER IN EFFECT.

* PRECIPITATION TYPE...BRIEF PERIOD OF SLEET...THEN SNOW WHICH

WILL BE HEAVY AT TIMES.

* ACCUMULATIONS...5 TO 7 INCHES OF SNOW.

* TIMING...WINTRY MIX WILL BEGIN EARLY THIS EVENING...THEN CHANGE

OVER TO ALL SNOW BY LATE THIS EVENING... AND CONTINUE OVERNIGHT.

THE HEAVIEST SNOWFALL IS EXPECTED BETWEEN MIDNIGHT AND 6AM.

* TEMPERATURES...TEMPERATURES IN THE LOWER 30S THIS EVENING...

DROPPING TO THE MID 20S BY TUESDAY MORNING.

* WINDS...NORTH-NORTHEAST 10 TO 15 MPH. GUSTS TO AROUND 20 MPH.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

A WINTER STORM WATCH MEANS THERE IS A POTENTIAL FOR SIGNIFICANT

SNOW AND SLEET ACCUMULATIONS THAT MAY IMPACT TRAVEL. CONTINUE TO

MONITOR THE LATEST FORECASTS.

&&

PRECAUTIONARY/PREPAREDNESS ACTIONS...

A WINTER STORM WARNING MEANS SIGNIFICANT AMOUNTS OF SNOW...

SLEET...AND ICE ARE EXPECTED OR OCCURRING. STRONG WINDS ARE ALSO

POSSIBLE. THIS WILL MAKE TRAVEL VERY HAZARDOUS OR IMPOSSIBLE.

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FWIW 12z UKIE

At 12 hrs... IAD- DCA north are below 0c at the 850 level. Freezing line (aka 32 line) just about on top of that, perhaps a few more miles north.

At 18 hrs... Freezing line (aka 32 line) SOUTH of EZF. I would argue BWI/IAD/DCA are in the upper 20s at this time. 850s are COLD, -5 to -7 at IAD/BWI/DCA/HGR/FDK

At 24 hrs... 850s are bascially same... perhaps a few tenths of a degree colder. Freezing line (aka 32 line) down by KRIC... N VA/DC/MD in the 20s

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FWIW 12z UKIE

At 12 hrs... IAD- DCA north are below 0c at the 850 level. Freezing line (aka 32 line) just about on top of that, perhaps a few more miles north.

At 18 hrs... Freezing line (aka 32 line) SOUTH of EZF. I would argue BWI/IAD/DCA are in the upper 20s at this time. 850s are COLD, -5 to -7 at IAD/BWI/DCA/HGR/FDK

At 24 hrs... 850s are bascially same... perhaps a few tenths of a degree colder. Freezing line (aka 32 line) down by KRIC... N VA/DC/MD in the 20s

It's that 12-18hr period that's critical. Whether it's snow or sleet in that period depends on that warm layer around 800mb. I'd trust the NAM and GFS more then the Ukie.

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That's pretty reasonable by LWX. I think Clarke and Loudon counties in VA and Montogomery, Howard, S. Baltimore and Baltimore City could have been included in the warning...but I suppose they could wait for the 18 and 00z runs to change.

yep

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All this DT talk... gave me the inkling that I might find something fun in his blog. I was not disappointed. Thanks Ian et al for the good laugh. I'll reserve anything else for after the storm verifies.

I'll just go ahead and put this here since it stands out in his blog (posted just under 24 hours ago):

We have a interesting situation developing with regard to the potential for some winter weather over portions of Pennsylvania and New Jersey and rumors… totally unfounded and irrational rumors …. that there some sort of significant snow coming for Northern Virginia and Maryland.

At first I thought this sort of wretched winter weather forecasting was coming from the usual sources— Herny M of accu weather but it has brought to my attention that for some incomprehensible reason that THE WEATHER CHANNEL also talking about some sort of accumulating snow over far Northern Virginia and Maryland including the DC and Baltimore metro areas.

That portion of the forecast… is crap. The real problem is that temperatures are way too warm for any sort of winter precipitation for any portion of the northwest VA as well as DCA / Baltimore metro areas or even as far north has the Pennsylvania Maryland border. Those areas are to warm at the surface …they are too warm in the Middle levels of atmosphere and they are two warm in the the upper levels of the atmosphere.

Link: http://www.wxrisk.co...d-to-calm-down/

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It's that 12-18hr period that's critical. Whether it's snow or sleet in that period depends on that warm layer around 800mb. I'd trust the NAM and GFS more then the Ukie.

True. I can't seem to get the precip map at 18. At 24... there is a large area of 0.175-0.25 QPF across the LWX area, which is snow

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