NWS-Philly update on evolving system - could get here earlier, as we've been talking about and I expect them to raise accumulations if the rest of the 12Z models come in anywhere close to the GFS, especially the Euro, whose output last night was similar to today's GFS.
MID MORNING UPDATE...
BASED ON TRENDS IN THE LATEST GUIDANCE,
RADAR AND SURFACE
OBSERVATIONS, THE SNOW LOOKS TO COME IN FASTER. THE WORDING IN THE
WINTER HEADLINES WERE UPDATED TO ACCOUNT FOR THE EARLIER ARRIVAL
OF THE SNOW. A SPS WAS ISSUED FOR SOUTH OF PHILLY AS WE ARE
PARTICULARLY CONCERNED WITH THE SNOW STARTING DURING THE
AFTERNOON/EVENING COMMUTE. ONCE THE SNOW STARTS, IT WON`T TAKE
LONG FOR IT TO BECOME MODERATE TO EVEN LOCALLY HEAVY IN INTENSITY.
THERE IS A POTENTIAL FOR RATES TO APPROACH 1"/
HR IN THE DELMARVA
AND SOUTHERN-MOST PART OF NJ AT THE TAIL END OF RUSH HOUR.
EXPECT ADDITIONAL REFINEMENTS TO THE SNOWFALL FORECAST FOR THIS
EVENT SOMETIME THIS AFTERNOON AFTER MOST OF THE 12Z GUIDANCE COMES
IN. WE`LL STILL HAVE TO
WATCH HOW FAR THAT TIGHT PRECIP
GRADIENT
ON THE NORTHERN EDGE OF THE STORM SHIFTS. WE`LL ALSO TRY TO
PINPOINT THE AREA THAT HAS THE BEST CHANCE TO SEE
MESOSCALE SNOW
BANDING THROUGHOUT THE EVENT WHICH WILL
LIKELY BE NOT TOO FAR NORTH
OF THE RAIN/SLEET-SNOW LINE. WE WOULD INCREASE SNOWFALL AMOUNTS IF
CONFIDENCE IN THE PLACEMENT, DURATION AND INTENSITY OF THIS
MESOSCALE FEATURE IS SUFFICIENTLY HIGH. THERE IS A POTENTIAL TO
SEE SNOWFALL RATES OF 2-3" PER HOUR AND PERHAPS THUNDERSNOW
UNDERNEATH THIS BAND. LOOKING AT THE 00Z/06Z GUIDANCE LAST NIGHT,
THIS BAND COULD SET UP ROUGHLY AS FAR SOUTH AS THE EASTERN SHOWER
OF MD-
C DE TO AS FAR NORTH AS THE NORTHERN SUBURBS OF PHILLY/
CENTRAL NJ.
IT SHOULD BE NOTED THAT THE SNOW WILL BE PARTICULARLY HEAVY/WET
WITH THIS EVENT AS MODEL SOUNDINGS SHOWS A DEEP RIMING LAYER. THIS
HAS TO BE FACTORED INTO THE POTENTIAL IMPACTS FROM A SOCIETAL
PERSPECTIVE AND SNOW RATIOS FROM A FORECAST PERSPECTIVE.
POWER
OUTAGES COULD BE EXTENSIVE AT THE
HEIGHT OF THE STORM WHERE THERE
ARE
BLIZZARD WARNINGS DUE TO THE HEAVY WET SNOW AND STRONG WINDS.
ADDITIONALLY, EXTENSIVE
POWER OUTAGES ARE
LIKELY NEAR THE COAST
(WHERE THE STRONGEST WINDS RESIDE ON SATURDAY) EVEN IF THEY SWITCH
OVER TO RAIN. WE`LL ALSO HAVE TO CONSIDER EXPANDING THE
BLIZZARD
WARNINGS A TAD SOUTHEAST OF THE CURRENT ONE. WITH REGARDS TO SNOW
RATIOS, THEY WILL BE LESS THAN THE TYPICAL 10:1 DURING THE MIDDLE
OF THE EVENT DUE TO THE RIMING FACTOR AND POTENTIAL FOR MIXING.
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