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february 20-21st winter storm


earthlight

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Mt Holly 808PM

THE NAM TROUNCED THE GFS WITH ITS COLDER 850MB TEMPS UPSTREAM OF

OUR CWA OFF THE 00Z SOUNDINGS. BOTH MODELS DID OK AT 925MB WITH

THE HANDLING OF UPSTREAM TEMPS. THE RUB REMAINS THAT THE WARM AIR

IS COMING IN ABOVE 850MB AND THE BEST WE CAN GLEAN FROM THIS IS A

GREATER SLEET POTENTIAL. ON THE OTHER HAND THE NAM`S FORECAST

800MB TEMPS ARE SHOWING THE SNOW/NOT SNOW LINE PRETTY WELL. UPSHOT

FOR THIS UPDATE WE ARE USING THE NAM`S THERMAL FIELDS.

AS FOR QPF THE GFS AND EURO ARE SHOWING THE LEADING EDGE OF THE

SNOW PRETTY WELL, BUT MEASURABLE IS MATCHING THE NAM BETTER THAN

EITHER AT 00Z. THERE REMAINS A PRETTY BIG DIFFERENCE IN THE

CENTRAL PART OF OUR CWA BETWEEN THE NAM AND GFS. WE ALL KNOW THAT

QPF IS NEVER NUMBER ONE OF MODELING STRENGTH AND OUR COURSE OF

LEAST REGRET IS TO LEAN TOWARD A MODELING CONSENSUS AVERAGE.

TEMPS ARE HOLDING UP OK FROM PHL/I95 SOUTHEAST HIGHER THAN STAT

GUIDANCE, BUT COLDER POCKETS CLOSER TO STAT GUIDANCE ARE

OCCURRING IN THE NW PART OF OUR CWA.

TO DRAW SOME CONCLUSIONS FROM ALL OF THIS, WE WILL BE EXPANDING

THE ADVYS FARTHER TO THE SE INCLUDING THE PHL NW SUBURBS AND

MERCER COUNTY AS WELL AS MONMOUTH COUNTY. FOR THE FORMER PAIR, THE

COMBINATION OF THOSE 800MB TEMPS AND SUBFREEZING TEMPS DO MAKE A

WINDOW FOR FREEZING RAIN IN THE MORNING FOR A COUPLE OF HOURS.

CONFIDENCE IS NOT 100 PERCENT, BUT ENOUGH IS THERE WITH BOTH THE

GFS AND NAM OFF THE 18Z RUN TO FORCE OUR HAND. IN MONMOUTH COUNTY

(INLAND) ITS THE SNOWIER WEST TO EAST ORIENTATION OF THE SNOW/NOT

SNOW LINE. OVERALL IN NORTHERN NEW JERSEY WE UPPED ACCUMS

SLIGHTLY. MIN TEMPS ARE STILL REASONABLE AND VERY LITTLE

ADJUSTMENT WAS DONE.

GFS/ECMWF QPF VALUES (WE LEANED A BIT TOWARD HIGHER VALUES BECAUSE

OF THE GOOD LOWER LEVEL FRONTOGENESIS AND LOW EPV VALUES ALOFT,

BUT DID NOT GO OVER THE TOP BECAUSE OF A WEAK AND PROGRESSIVE

TROWAL AND LACK OF ANY SIGNIFICANT MID LEVEL DRY SLOT) ALONG WITH

FORECAST RATIOS (NOT TERRIBLY HIGH BECAUSE OF GOOD WINDS BELOW THE

SNOW GROWTH REGION AND SOME MIXING) YIELD VALUES THAT RESEMBLE

WHAT OUR COLLEAGUES AT THE NATIONAL CENTER WERE THINKING REGARDING

ACCUMULATIONS, AND THAT HAS RESULTED IN AN EXPANSION OF THE

ADVISORY SOUTHWARD AND AN UPGRADE TO A WARNING OVER CARBON AND

MONROE COUNTIES. TEMPERATURES TONIGHT ARE A GUIDANCE/CONTINUITY

BLEND, AND WE TRIED TO KEEP THE PREVIOUS FORECAST`S INDICATION OF

SOME WARMING (ESPECIALLY SOUTH) AFTER MIDNIGHT.-- End Changed Discussion --

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straight out of the swfe play book. This thing may be over by the time the morning commute comes around

i don't agree---i think 15z is a good end time in the city and northeast of there..which is past the morning commute. you have to remember that this is being squashed southeast by the pv--which is why models have that extended band of heavier lift near the thermal gradient. this isn't a swfe by nature, which is in and out with a change to drizzle at the end.

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i don't agree---i think 15z is a good end time in the city and northeast of there..which is past the morning commute. you have to remember that this is being squashed southeast by the pv--which is why models have that extended band of heavier lift near the thermal gradient. this isn't a swfe by nature, which is in and out with a change to drizzle at the end.

I think we'll get a good 8 - 12 hours - making an end time between 8 and 12

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I don't see how this is a SWFE. We're not warming in the mid-levels, and there really is no southerly flow. It's being squashed SE by the PV. We are getting some of the moisture via frontogenesis from the storm's interaction with the PV.

Yup, exactly my point. It is being driven by warm air advection in the mid levels, to an extent, but then it starts being squashed southeast by the polar vortex as you mentioned. it's more about the thermal gradient and the frontogenic lift than anything.

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