THE HYDROMETEOROLOGICAL PREDICTION CENTER

CAMP SPRINGS, MD

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PROBABILISTIC HEAVY SNOW AND ICE DISCUSSION

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PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
410 PM EST FRI NOV 30 2007

VALID 00Z SAT DEC 01 2007 - 00Z TUE DEC 04 2007

DAY 1 THROUGH 3...

LARGE SYSTEM FROM ROCKIES TO MIDWEST...
COPIOUS PACIFIC MOISTURE AND SHRTWV ENERGY LIFTING NEWD ACROSS
MEXICO WILL RESULT IN HVY SNOW ACROSS THE FAVORED TERRAIN OF THE
CNTRL ROCKIES ON D1. HVST AMTS OF 1-2 FEET OR MORE ARE LIKELY
ACROSS THE WRN CO MTNS. A STRONG WARM ADV PATTERN WILL PRECEDE A
DEVELOPING CIRCULATION OVER THE PLAINS AS THIS MOISTURE AND ENERGY
PROGRESS INTO THE PLAINS. THIS WILL TOUCH OFF A PERIOD OF
FREEZING/FROZEN PCPN THAT WILL SPREAD RAPIDLY NORTH AND NORTHEAST
FROM KS TO THE UPPER GREAT LAKES REGION. USED A BLEND OF THE
COLDER NAM AND WARMER GFS PTYPE ALGORITHMS TO FAVOR A THREAT FOR
SIGNIFICANT ICING FROM NRN KS...ERN NE AND IA TO NWRN IL AND WRN
WI...THOUGH PCPN MAY BEGIN AS SNOW/SLEET IN THIS REGION. WITH THE
TRACK OF THE SFC LOW ACROSS IA AND WI TO NRN LOWER MI...PCPN
SHOULD REMAIN MAINLY SNOW WITH SIGNIFICANT AMTS UP TO 12 INCHES
POSSIBLE FROM CNTRL/NERN MN TO WRN UPPER MI. GENERALLY FOLLOWED
THE 12Z GFS SYNOPTIC PATTERN AND QPF AMTS ON DAYS 1 AND 2 IN THIS
REGION.

NORTHEAST...
THE MIDWEST SYSTEM WILL BEGIN TO AFFECT PA/NY EARLY SUN AS WARM
ADV SPARKS PCPN. COLD AIR WILL BE FIRMLY IN PLACE AS A STRONG
POLAR SFC HIGH OVER THE ERN SEABOARD SLOWLY WEAKENS. NAM/GFS
SUPPORT LEADING EDGE OF THE PCPN TO BEGIN AS A PERIOD OF SNOW WITH
SEVERAL INCHES POSSIBLE ESPECIALLY THRU NRN PA AND ADJACENT PARTS
OF NY. WARMING 85H TEMPS WITH SUBFREEZING BL TEMPS WILL ALLOW FOR
A PERIOD OF FREEZING RAIN AND SOME SLEET DURING SUNDAY OVER PA TO
SPREAD NORTHEAST WITH TIME INTO PORTIONS OF NY AND PERHAPS SRN NEW
ENG. AREAS FROM CNTRL PA TO CNTRL AND INTERIOR SERN NY APPEAR TO
HAVE THE BEST THREAT FOR .25 INCH PLUS ICING AMTS. A TRIPLE POINT
LOW IS FCST BY ALL GUIDANCE TO FORM JUST SOUTH OF NEW ENG AROUND
12Z/MON....AS THE ORIGINAL CIRC REACHES LAKE ONTARIO. THIS SHOULD
HELP SHUT OFF THE WARM INFLOW INTO NEW ENG AND PROVIDE A SETUP FOR
HVY SNOW AS THE COASTAL CIRCULATION RAPIDLY INTENSIFIES OVER THE
GULF OF MAINE....AS INDICATED BY THE 12Z GFS/ECMWF AT 00Z/04.
STRONG ATLC INFLOW IN RESPONSE TO THE COASTAL DEVELOPMENT...ALONG
WITH RESIDUAL MOISTURE FROM THE MIDWEST SYSTEM SHOULD COMBINE TO
BRING HVY SNOW ESPECIALLY TO CNTRL/NRN NEW ENG WITH SOME 12 INCH
PLUS AMTS POSSIBLE OVER THE TERRAIN OF VT/NH AND WRN MAINE. WITH
THE LOW TRACKING CLOSE TO THE COAST...BL TEMPS ARE LIKELY TO WARM
SUFFICIENTLY FOR A CHANGE TO RAIN ACROSS COASTAL SRN NEW
ENG....AND A MIXTURE INLAND. ARCTIC AIR SURGING ACROSS THE GTLKS
IN THE NWLY FLOW ON MON SHOULD HELP TO IGNITE BANDS OF LAKE EFFECT
SNOW...AND SOME UPSLOPE SNOW ALONG THE WRN SLOPES OF THE
APPALACHIANS.

NORTHWEST...
HEIGHTS ARE FCST TO RISE TREMENDOUSLY OVER THE NW DURING THE NEXT
3 DAYS....WITH DEEP ONSHORE FLOW INCREASING INTO THE REGION.
DURING SAT...A NRN STREAM SHRTWV WILL BRING LIGHTER SNOW WITH VERY
LOW SNOW LEVELS INTO WA/OR. WARM ADV INCREASES THEREAFTER..AND
AN OFFSHORE CIRCULATION WILL STRENGTHEN AND SEND A PLUME OF
MOISTURE AND SEVERAL IMPULSES INTO THE NW ON DAYS 2 AND 3. HVST
SNOW IS LIKELY ACROSS THE CASCADES ON D2 BEFORE SNOW LEVELS RISE
SUBSTANTIALLY. 1-2 FOOT PLUS AMTS ARE POSSIBLE THRU THE WA
CASCADES...WHILE SNOW SHOULD CONTINUE INTO D3 INTO THE MTNS OF NRN
ID AND NWRN MT WITH A FOOT OR MORE LIKELY.

HEDGE






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