596
FXUS02 KWBC 110708
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
207 AM EST SUN DEC 11 2022
VALID 12Z WED DEC 14 2022 - 12Z SUN DEC 18 2022
...MAJOR STORM SYSTEM WILL CONTINUE TO BRING POSSIBLY HEAVY SNOW
INTO PARTS OF THE UPPER MIDWEST WITH A HEAVY RAIN/SEVERE WEATHER
THREAT FOR SOUTHERN AREAS NEXT WEEK...
..OVERVIEW
A DEEP UPPER LEVEL LOW WILL BE IN PLACE OVER THE CENTRAL PLAINS BY
THE START OF THE PERIOD WEDNESDAY AND IS EXPECTED TO TRACK
STEADILY EASTWARD INTO THE NORTHEAST BY THIS WEEKEND. THE
ASSOCIATED SURFACE LOW PRESSURE SYSTEM SHOULD WEAKEN OVER THE
MIDWEST LATER THIS WEEK IN FAVOR OF A NEW DEVELOPING COASTAL LOW
OFF THE MID-ATLANTIC COAST. THIS SYSTEM WILL CONTINUE TO BRING
MODERATE TO HEAVY SNOWFALL ACROSS PORTIONS OF THE NORTHERN PLAINS,
UPPER MIDWEST, AND GREAT LAKES THROUGH THURSDAY, WITH INCREASING
CONFIDENCE FOR SOME HEAVY SNOWFALL TO IMPACT INTERIOR PORTIONS OF
THE NORTHEAST AS WELL BY FRIDAY-SATURDAY. TO THE SOUTH, A HEAVY
RAIN THREAT WILL CONTINUE ACROSS THE SOUTHEAST AND THE
EASTERN/COASTAL MID-ATLANTIC AND NORTHEAST AS WELL. OTHERWISE, A
COUPLE OF WEAKER SHORTWAVES FROM CANADA SHOULD DROP IN AND ALONG
WITH TROUGHING INTO THE WESTERN U.S. EARLY NEXT WEEK, THIS SHOULD
MAINTAIN MEAN TROUGHING SUPPORTING BELOW NORMAL TEMPERATURES
ACROSS MUCH OF THE CONUS.
..GUIDANCE/PREDICTABILITY ASSESSMENT
T PERIOD BEGINS WITH GOOD ENOUGH AGREEMENT ON THE UPPER LOW
PLACEMENT/SYSTEM TIMING FOR A GENERAL MODEL BLEND (WEIGHTED
TOWARDS THE ECMWF/CMC) THROUGH DAY 4. UKMET WAS FASTER THAN THE
BETTER CONSENSUS AND WAS NOT INCLUDED. AFTER DAY 4, HOWEVER, MODEL
GUIDANCE BEGINS TO DIVERGE RATHER QUICKLY ACROSS THE BOARD. THE
GFS CONTINUES TO BE MORE ELONGATED WITH THE UPPER LOW OVER THE
MIDWEST LATE IN THE WEEK AND HAS AN OVERALL SLIGHTLY LESS
AMPLIFIED PATTERN (THOUGH IT DOES LOOK BETTER THAN IT DID IN
PREVIOUS RUNS). THIS ALLOWS FOR A MUCH QUICKER AND MORE OFFSHORE
COASTAL LOW/POSSIBLE NOR'EASTER OFF THE NORTHEAST COAST NEXT
WEEKEND. THERE ARE SOME TIMING DIFFERENCES BETWEEN THE ECMWF AND
CMC BUT OVERALL, THOSE MODELS CONTINUE TO BE MOST IN LINE WITH THE
ENSEMBLE MEANS. OUT WEST, THERE'S ALSO CONSIDERABLE DIFFERENCES IN
A SHORTWAVE DROPPING INTO THE NORTHERN TIER WITH THE GFS MUCH MORE
BULLISH WITH THIS AND WANTING TO DROP A CLOSED LOW ACROSS THE
WESTERN U.S.. THE OTHER MODELS AND ENSEMBLES SUGGEST A WEAKER MORE
PROGRESSIVE NORTHERN STREAM SHORTWAVE WITH A DEEPER CLOSED UPPER
LOW INITIALLY WELL OFF THE WEST COAST AND SLOWLY DRIFTING EASTWARD
INTO THE WESTERN U.S. BY THE END OF THE PERIOD. A QUICK LOOK AT
THE NEW 00Z GUIDANCE (AVAILABLE AFTER FORECAST GENERATION TIME)
SHOWS EVEN MORE UNCERTAINTY BOTH ACROSS THE EAST AND THE WEST.
GIVEN THIS, IT SEEMED SAFEST TO LEAN INCREASINGLY MORE ON THE
ENSEMBLE MEANS BEYOND DAY 5, WITH SOME INCLUSION OF THE ECMWF AND
CMC FOR BETTER SYSTEM DEFINITION. THIS ALSO MAINTAINED GOOD
CONTINUITY WITH THE PREVIOUS WPC FORECAST.
..WEATHER/HAZARD HIGHLIGHTS
DEEP AMPLE MOISTURE WILL CONTINUE TO STREAM NORTHWARD AHEAD OF THE
UPPER LOW OVER THE CENTRAL U.S. TO FUEL HEAVY TO EXCESSIVE
RAINFALL INTO THE DEEP SOUTH AND EVENTUALLY UP THE EAST COAST. THE
LATEST DAY 4 WPC EXPERIMENTAL EXCESSIVE RAINFALL OUTLOOK
HIGHLIGHTS A SLIGHT RISK OVER PARTS OF THE TENNESSEE
VALLEY/SOUTHERN APPALACHIANS AND NORTHERN PARTS OF THE SOUTHEAST
WHERE ABOVE NORMAL STREAMFLOWS AND SOIL MOISTURE COULD ENHANCE
FLOODING POTENTIAL. THE STORM PREDICTION CENTER ALSO CONTINUES TO
MONITOR AND HIGHLIGHT THE POTENTIAL FOR STRONG TO SEVERE
CONVECTION ACROSS THE CENTRAL GULF COAST ON WEDNESDAY. ON THE
BACKSIDE OF THE SURFACE LOW, COLD TEMPERATURES AND WRAP-BACK
MOISTURE WILL CONTINUE TO SUPPORT MODERATE TO HEAVY SNOWFALL
ACROSS PARTS OF THE NORTHERN PLAINS INTO THE UPPER MIDWEST AND
GREAT LAKES WITH SOME MIXED PRECIPITATION/FREEZING RAIN POTENTIAL
IN THE TRANSITION ZONE AS WELL AS ALONG THE EASTERN EDGE OF THE
PRECIP SHIELD NEAR/NORTH OF THE WARM FRONT. THERE IS INCREASING
CONFIDENCE FOR COASTAL LOW DEVELOPMENT OFF THE MID-ATLANTIC COAST
AROUND NEXT FRIDAY, WITH SOME INCREASING POTENTIAL FOR MODEST
SNOWFALL ACROSS INTERIOR NEW ENGLAND. AS THE SYSTEM EXITS THE EAST
NEXT WEEKEND, SOME LIGHT LAKE EFFECT SNOW SHOWERS MAY CONTINUE
DOWNWIND OF THE LOWER LAKES. NEXT WEEKEND SHOULD FEATURE MAINLY
LIGHT PRECIPITATION UNDERNEATH OF THE LINGERING UPPER SYSTEM OVER
THE NORTHEAST, AS WELL AS SOME LIGHTER PRECIPITATION MOVING INTO
CALIFORNIA AND THE SOUTHWEST ASSOCIATED WITH THE UPPER SHORTWAVE.
ABOVE NORMAL TEMPERATURES WILL FEATURE 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 READING OF GENERALLY
10-20F BELOW NORMAL FOR HIGH TEMPERATURES WILL BE ACROSS MUCH OF
THE WEST AND INTO THE NORTHERN PLAINS.
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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