272
FXUS02 KWBC 120701
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
200 AM EST MON DEC 12 2022
VALID 12Z THU DEC 15 2022 - 12Z MON DEC 19 2022
...HEAVY SNOW THREAT SHIFTS INTO THE INTERIOR NORTHEAST THURSDAY
AND FRIDAY, WITH HEAVY RAIN POSSIBLE ACROSS COASTAL LOCATIONS...
..OVERVIEW
A DEEP UPPER LEVEL LOW (THE SAME ONE RESPONSIBLE FOR A NORTHERN
PLAINS WINTER STORM IN THE SHORT RANGE) WILL BE IN PLACE OVER THE
MIDWEST BY THE START OF THE PERIOD ON THURSDAY WITH A COLD FRONT
AT THE SURFACE SPREADING MODERATE TO HEAVY RAINFALL INTO EASTERN
PORTIONS OF THE U.S.. COASTAL LOW DEVELOPMENT LOOKS LIKELY BY
EARLY FRIDAY OFF THE MID-ATLANTIC COAST BRINGING A THREAT FOR
HEAVY SNOWFALL TO PORTIONS OF THE CENTRAL APPALACHIANS AND
INTERIOR NORTHEAST AS IT LIFTS NORTH, WITH SOME ACCUMULATING LAKE
EFFECT SNOWFALL ON THE BACKSIDE OF THE SYSTEM AS WELL. THE PRIMARY
UPPER SYSTEM SHOULD SHIFT NORTH AND WEAKEN AS IT INTERACTS WITH
ANOTHER SYSTEM DROPPING INTO CENTRAL CANADA. WEAK SHORTWAVE ENERGY
LOOKS TO ROTATE AROUND THESE SYSTEMS THROUGH THE U.S. THIS WEEKEND
(WITH SOME ENTERING THE WEST COAST AS WELL), EVENTUALLY RESULTING
IN MEAN TROUGHING AND BELOW NORMAL TEMPERATURES ACROSS MUCH OF THE
CONUS BY EARLY NEXT WEEK.
..GUIDANCE/PREDICTABILITY ASSESSMENT
MODELS SHOW FAIRLY GOOD AGREEMENT WITH THE UPPER LOW IN PLACE OVER
THE MIDWEST ON THURSDAY BUT STRUGGLE THEREAFTER ON THE DETAILS OF
VARIOUS PIECES OF SHORTWAVE ENERGY ROUNDING THE BASE. THERE IS
ALSO INCREASING CONFIDENCE ON A SURFACE LOW ORIGINATING OVER THE
SOUTHEAST TO LIVE ALONG THE EAST COAST AS A NOR'EASTER WITH MODEL
GUIDANCE CONTINUING TO SHOW RELATIVELY GOOD CONSENSUS FOR TRACK
AND TIMING. BY THIS WEEKEND, THERE ARE ALSO BIGGER QUESTIONS AND
DIFFERENCES REGARDING HOW THE MAIN UPPER LOW INTERACTS WITH
POSSIBLE ENERGY TO THE NORTH. THROUGH THE 12/18Z DEC 11 RUNS, THE
ECMWF AND UKMET BOTH SHOW MORE PHASING OF THESE TWO SYSTEMS DUE TO
A STRONGER CANADIAN SHORTWAVE, BUT THE GFS AND CMC ARE SLOWER AND
MORE ELONGATED WITH THE UPPER LOW AS IT MOVES OVER THE GREAT
LAKES. MODELS DISAGREE WITH HOW/WHEN TO GET THERE, BUT THERE IS
SOME CONSENSUS FOR ANOTHER UPPER LOW TO BECOME ANCHORED OVER
CENTRAL CANADA ALLOWING FOR MEAN TROUGHING ACROSS MUCH OF THE
CONUS BY EARLY NEXT WEEK. THERE REMAINS A LOT OF UNCERTAINTY OUT
WEST STILL TOO AS ENERGY OR AN UPPER LOW TRIES TO UNDERCUT A RIDGE
IN THE GULF OF ALASKA. A QUICK LOOK AT THE NEW 00Z RUNS (AVAILABLE
AFTER FORECAST GENERATION) SHOWS CONTINUED UNCERTAINTIES AND WILD
VARIATION IN THE DETAILS ACROSS THE BOARD.
DESPITE THE UNCERTAINTIES AS EARLY AS DAY 4, A GENERAL MODEL BLEND
SUFFICED THROUGH DAY 4. BY DAY 5, THE UKMET WAS REMOVED FROM THE
BLEND AS IT TOOK THE UPPER MIDWEST LOW TOO NORTH TOO QUICKLY. A
QUICK TRANSITION TO THE ENSEMBLE MEANS SEEMED PRUDENT THE LAST
HALF OF THE PERIOD WITH A LOT OF FORECAST UNCERTAINTY MID TO LATE
PERIOD. DID BLEND IN SMALLER AMOUNTS OF THE ECMWF AND GFS THROUGH
7 THOUGH JUST FOR SOME ADDED SYSTEM DEFINITION. THIS MAINTAINED
GOOD AGREEMENT WITH THE PREVIOUS WPC FORECAST THROUGH DAY 6.
..WEATHER/HAZARD HIGHLIGHTS
DEEP/AMPLE MOISTURE WILL CONTINUE TO STREAM NORTHWARD AHEAD OF THE
UPPER LOW OVER THE CENTRAL U.S. TO FUEL MODERATE TO HEAVY RAINFALL
INTO THE EASTERN U.S. THURSDAY AND FRIDAY. THE LIKELY DEVELOPMENT
OF A NOR'EASTER OFF THE MID-ATLANTIC COAST BRINGS A THREAT FOR
WINTRY WEATHER AND POTENTIALLY HEAVY SNOWFALL ACROSS INTERIOR
PORTIONS OF THE NORTHEAST AND MID-ATLANTIC, WITH EVEN SOME
ICE/SLEET POTENTIAL CLOSER IN TOWARDS THE I-95 CORRIDOR EARLY
THURSDAY BEFORE THE WARM AIR MOVES IN AND CHANGES THE
PRECIPITATION TO RAIN. THERE REMAINS PLENTY OF UNCERTAINTY IN THE
DETAILS OF THIS SYSTEM, AND EVEN SMALL SHIFTS IN THIS LOW TRACK
COULD CAUSE DIFFERENCES IN PRECIPITATION TYPES/AMOUNTS ACROSS THE
EAST. ELSEWHERE, LINGERING WRAP-BACK MOISTURE ON THE BACKSIDE OF
THE MAIN UPPER LOW WILL CONTINUE TO SUPPORT SOME LIGHT SNOWFALL
ACCUMULATIONS ACROSS THE UPPER MIDWEST, AND ESPECIALLY DOWNWIND OF
THE GREAT LAKES. THERE MAY ALSO BE SOME LIGHT PRECIPITATION MOVING
INTO CALIFORNIA AND THE SOUTHWEST NEXT WEEKEND, WHILE GULF
MOISTURE RETURN COULD PRODUCE SOME SHOWERS OVER THE
WESTERN-CENTRAL GULF COAST.
ABOVE NORMAL TEMPERATURES ARE EXPECTED AHEAD OF THE COLD FRONT AS
IT SLIDES THROUGH THE EAST LATER THIS WEEK BUT BY FRIDAY AND
ESPECIALLY NEXT WEEKEND, MUCH OF THE CONUS SHOULD BE NEAR OR BELOW
NORMAL. THE GREATEST AND MOST WIDESPREAD READINGS OF BELOW NORMAL
TEMPERATURES WILL BE ACROSS MUCH OF THE WEST AND INTO THE NORTHERN
PLAINS, TRENDING COLDER WITH TIME. BY SUNDAY AND MONDAY, DAYTIME
TEMPERATURES ACROSS THE NORTHERN PLAINS COULD BE AS MUCH AS 20 TO
30+ DEGREES BELOW NORMAL, EQUATING TO WIDESPREAD SINGLE DIGIT
TEMPERATURES WITH SOME BELOW ZERO READINGS ACROSS EASTERN MONTANA
AND NORTH DAKOTA.
SANTORELLI
ADDITIONAL 3-7 DAY HAZARD INFORMATION CAN BE FOUND ON THE WPC
MEDIUM RANGE HAZARDS OUTLOOK CHART AT:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
WPC MEDIUM RANGE 500MB HEIGHTS, SURFACE SYSTEMS, WEATHER GRIDS,
QUANTITATIVE PRECIPITATION, EXPERIMENTAL EXCESSIVE RAINFALL
OUTLOOK, WINTER WEATHER OUTLOOK PROBABILITIES AND HEAT INDICES ARE
AT:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/MEDR/5DAYFCST500_WBG.GIF
HTTPS://WWW.WPC.NCEP.NOAA.GOV/MEDR/5DAYFCST_WBG_CONUS.GIF
HTTPS://WWW.WPC.NCEP.NOAA.GOV/5KM_GRIDS/5KM_GRIDSBODY.HTML
HTTPS://WWW.WPC.NCEP.NOAA.GOV/QPF/DAY4-7.SHTML
HTTPS://WWW.WPC.NCEP.NOAA.GOV/#PAGE=ERO
HTTPS://WWW.WPC.NCEP.NOAA.GOV/WWD/PWPF_D47/PWPF_MEDR.PHP?DAY=4
HTTPS://WWW.WPC.NCEP.NOAA.GOV/HEAT_INDEX.SHTML
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