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Feb 8th-9th Obs/Discussion Thread


mappy

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DPs 33-35 for the whole event in DC.  Not cold. 

 

yes...pretty ugly.,.I think we might be able to discern something by 9-10 pm or so.....not going to sweat DCA too much, but would like to be down to 36-37 IMBY...GFS has me at 39 at midnight...that would be problematic, but I don't buy it..44/28 now...I think we are in pretty good shape if we get decent rates...We aren't going to be 36 and 0.5 mi viz at 3 am

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yes...pretty ugly.,.I think we might be able to discern something by 9-10 pm or so.....not going to sweat DCA too much, but would like to be down to 36-37 IMBY...GFS has me at 39 at midnight...that would be problematic, but I don't buy it..44/28 now...I think we are in pretty good shape if we get decent rates...We aren't going to be 36 and 0.5 mi viz at 3 am

It's not really all that different than the 12Z run-- just mostly warmer in the first phase through 12Z as you pointed out. This isn't one of those deals where we have to wait until waking up in the morning to figure out whether it's right. The rain/snow transition we can watch start to happen before bedtime. 

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PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION

NWS WEATHER PREDICTION CENTER COLLEGE PARK MD

340 PM EST MON FEB 08 2016

VALID 00Z TUE FEB 09 2016 - 00Z FRI FEB 12 2016

DAYS 1 THROUGH 3...

...MID ATLANTIC/OH VALLEY/SOUTHERN APPALACHIANS...

A COMPLEX LOW PRESSURE SYSTEM FORMING OFF THE MID ATLANTIC COAST

WILL FOCUS MOISTURE AND LIFT ALONG A SURFACE TROUGH EXTENDING BACK

ACROSS NORTHERN MID ATLANTIC STATES DURING DAY 1. THERE IS SOME

SPREAD IN THE GUIDANCE CONCERNING HOW THE THERMAL FIELDS SET UP

ALONG THE TROUGH...AND MODEL SOUNDINGS INDICATE THIS EVENT COULD

HAVE SOME ELEVATION DEPENDENCIES WITH IT. BASED ON THE

SPREAD...AND THE POTENTIAL FOR BOUNDARY LAYER TEMPERATURE ISSUES

AND ELEVATION ISSUES...THE THERMAL PORTION OF THE FORECAST WAS

BASED ON A 12Z NAM/GFS/09Z SREF MEAN BLEND. THE WPC QPF WAS BASED

ON THE MOST RECENT WPC QPF

DAY 1...

SURFACE LOW PRESSURE IS EXPECTED TO SPINS UP ON A LOW LEVEL

BOUNDARY EXTENDING FROM FILLING LOW PRESSURE OVER THE LOWER GREAT

LAKES TO A POSITION OFF THE SOUTHERN DELMARVA COAST BEFORE 09/12Z.

THE SURFACE LOW AND TROUGH BECOMES THE FOCUS FOR LOW LEVEL INFLOW

AHEAD OF A SHORT WAVE CROSSING THE OH AND TN VALLEY. MODEL

SOUNDINGS SHOWED STEEPENING MID LEVEL LAPSE RATES (APPROACHING 8.0

C/KM) AFTER 09/06Z...AND THE STRONG MID LEVEL LIFT IS EXPECTED TO

INITIATE A BLOOM OF PRECIPITATION WITH THE SHORT WAVE AND

DEVELOPING SURFACE WAVE.

THE BOUNDARY LAYER IS INITIALLY WARM AHEAD OF THE MID LEVEL AND

SURFACE SYSTEMS...AND A LOW LEVEL EASTERLY FLOW AHEAD OF THE

TROUGH AND SURFACE WAVE WILL CONTINUE TO KEEP THE BOUNDARY LAYER

WARM THROUGH AT LEAST 09/06Z. EVAPORATIVE COOLING OCCURS WHEN THE

COLUMN SATURATES..AND THE INITIAL AREA OF RAIN WILL BEGIN TO

TRANSITION TO SNOW BETWEEN 09/06Z AND 09/12Z. SOUTH AND EAST OF

THE FALL LINE...THE BOUNDARY LAYER MAY REMAIN WARM ENOUGH FOR THE

SNOW TO DEVELOP LATER IN THE BEST LIFT...AND SHOULD RESULT IN LESS

ACCUMULATION. CLOSER TO THE FALL LINE...THE EVENT BECOMES MORE

ELEVATION DRIVEN... AS THE INITIALLY WARM BOUNDARY IS OVERCOME BY

THE COOLING IN THE SATURATED COLUMN. THIS IS SHOWN WELL BY THE 12Z

NAM...WHICH INDICATES THAT RIMING COULD BE ENOUGH OF A FACTOR FOR

LOWER SNOW TO LIQUID RATIOS CLOSE TO THE FALL LINE.

A SHARP SNOWFALL GRADIENT IS EXPECTED ACROSS NORTHERN AND EASTERN

MD/NORTHERN VA...WHERE RIMING AND PRECIPITATION PHASE PROBLEMS ARE

EXPECTED. THE AXIS OF HIGHEST SNOWFALL SHOULD LIE FROM NORTHERN WV

ACROSS NORTHERN MD AND EASTERN VA INTO SOUTHEAST PA/NORTHERN

DE/SOUTHWEST...WHERE THE BEST COMBINATION OF MOISTURE AND LIFT IS

EXPECTED. IN THIS AXIS...4 TO 8 INCHES OF SNOWFALL IS

EXPECTED...AND THIS IS SUPPORTED BY BOTH THE ECMWF ENSEMBLES AND

09Z SREF OUTPUT. GIVEN THE STEEP MID LEVEL LAPSE RATES...THUNDER

IS POSSIBLE IN THIS BAND...AND THE CONVECTIVE ASPECT COULD RESULT

IN HIGHER SNOWFALL AMOUNTS. THE BEST LIFT EXISTS BETWEEN 09/12Z

AND 09/18Z FROM WEST TO EAST...AFTER WHICH TIME LIGHT SNOW OR

MIXED PRECIPITATION IS POSSIBLE.

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PROBABILISTIC HEAVY SNOW AND ICING DISCUSSIONNWS WEATHER PREDICTION CENTER COLLEGE PARK MD340 PM EST MON FEB 08 2016VALID 00Z TUE FEB 09 2016 - 00Z FRI FEB 12 2016DAYS 1 THROUGH 3......MID ATLANTIC/OH VALLEY/SOUTHERN APPALACHIANS...A COMPLEX LOW PRESSURE SYSTEM FORMING OFF THE MID ATLANTIC COASTWILL FOCUS MOISTURE AND LIFT ALONG A SURFACE TROUGH EXTENDING BACKACROSS NORTHERN MID ATLANTIC STATES DURING DAY 1. THERE IS SOMESPREAD IN THE GUIDANCE CONCERNING HOW THE THERMAL FIELDS SET UPALONG THE TROUGH...AND MODEL SOUNDINGS INDICATE THIS EVENT COULDHAVE SOME ELEVATION DEPENDENCIES WITH IT. BASED ON THESPREAD...AND THE POTENTIAL FOR BOUNDARY LAYER TEMPERATURE ISSUESAND ELEVATION ISSUES...THE THERMAL PORTION OF THE FORECAST WASBASED ON A 12Z NAM/GFS/09Z SREF MEAN BLEND. THE WPC QPF WAS BASEDON THE MOST RECENT WPC QPFDAY 1...SURFACE LOW PRESSURE IS EXPECTED TO SPINS UP ON A LOW LEVELBOUNDARY EXTENDING FROM FILLING LOW PRESSURE OVER THE LOWER GREATLAKES TO A POSITION OFF THE SOUTHERN DELMARVA COAST BEFORE 09/12Z.THE SURFACE LOW AND TROUGH BECOMES THE FOCUS FOR LOW LEVEL INFLOWAHEAD OF A SHORT WAVE CROSSING THE OH AND TN VALLEY. MODELSOUNDINGS SHOWED STEEPENING MID LEVEL LAPSE RATES (APPROACHING 8.0C/KM) AFTER 09/06Z...AND THE STRONG MID LEVEL LIFT IS EXPECTED TOINITIATE A BLOOM OF PRECIPITATION WITH THE SHORT WAVE ANDDEVELOPING SURFACE WAVE.THE BOUNDARY LAYER IS INITIALLY WARM AHEAD OF THE MID LEVEL ANDSURFACE SYSTEMS...AND A LOW LEVEL EASTERLY FLOW AHEAD OF THETROUGH AND SURFACE WAVE WILL CONTINUE TO KEEP THE BOUNDARY LAYERWARM THROUGH AT LEAST 09/06Z. EVAPORATIVE COOLING OCCURS WHEN THECOLUMN SATURATES..AND THE INITIAL AREA OF RAIN WILL BEGIN TOTRANSITION TO SNOW BETWEEN 09/06Z AND 09/12Z. SOUTH AND EAST OFTHE FALL LINE...THE BOUNDARY LAYER MAY REMAIN WARM ENOUGH FOR THESNOW TO DEVELOP LATER IN THE BEST LIFT...AND SHOULD RESULT IN LESSACCUMULATION. CLOSER TO THE FALL LINE...THE EVENT BECOMES MOREELEVATION DRIVEN... AS THE INITIALLY WARM BOUNDARY IS OVERCOME BYTHE COOLING IN THE SATURATED COLUMN. THIS IS SHOWN WELL BY THE 12ZNAM...WHICH INDICATES THAT RIMING COULD BE ENOUGH OF A FACTOR FORLOWER SNOW TO LIQUID RATIOS CLOSE TO THE FALL LINE.A SHARP SNOWFALL GRADIENT IS EXPECTED ACROSS NORTHERN AND EASTERNMD/NORTHERN VA...WHERE RIMING AND PRECIPITATION PHASE PROBLEMS AREEXPECTED. THE AXIS OF HIGHEST SNOWFALL SHOULD LIE FROM NORTHERN WVACROSS NORTHERN MD AND EASTERN VA INTO SOUTHEAST PA/NORTHERNDE/SOUTHWEST...WHERE THE BEST COMBINATION OF MOISTURE AND LIFT ISEXPECTED. IN THIS AXIS...4 TO 8 INCHES OF SNOWFALL ISEXPECTED...AND THIS IS SUPPORTED BY BOTH THE ECMWF ENSEMBLES AND09Z SREF OUTPUT. GIVEN THE STEEP MID LEVEL LAPSE RATES...THUNDERIS POSSIBLE IN THIS BAND...AND THE CONVECTIVE ASPECT COULD RESULTIN HIGHER SNOWFALL AMOUNTS. THE BEST LIFT EXISTS BETWEEN 09/12ZAND 09/18Z FROM WEST TO EAST...AFTER WHICH TIME LIGHT SNOW ORMIXED PRECIPITATION IS POSSIBLE.

 

 

 

There is no forecast for 4-8" anywhere in VA.. wonder what they mean by this.

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You're more optimistic than I am. Maybe we'll get lucky and get under a convective band.

Sent from my iPhone using Tapatalk

 

rates are really what it is all about...GFS doesn't get us into good stuff until later overnight which is partly why temps are elevated...I feel pretty good about at least 2"...I'd put at least 2" at 60%

 

This seems about right for your backyard

 

At least cartopper - 90%

At least 1" - 75%

At least 2" - 60%

At least 3" - 45%

At least 4" - 25%

5"+ - 15%

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