514
FXUS02 KWBC 100700
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
200 AM EST SAT DEC 10 2022
VALID 12Z TUE DEC 13 2022 - 12Z SAT DEC 17 2022
...MAJOR STORM SYSTEM TO BRING HEAVY SNOW/BLIZZARD CONDITIONS TO
NORTHERN-CENTRAL PLAINS WITH A HEAVY RAIN/SEVERE WEATHER THREAT
FOR SOUTHERN AREAS NEXT WEEK...
..OVERVIEW
A MAJOR STORM SYSTEM WILL BE EXITING THE ROCKIES BY THE START OF
THE PERIOD ON TUESDAY, WITH HIGH CONFIDENCE FOR A DEEP LOW
PRESSURE SYSTEM TO EMERGE INTO THE PLAINS. THIS SYSTEM SHOULD
BRING A WIDE ARRAY OF HAZARDS INCLUDING HEAVY RAIN/SEVERE WEATHER
TO THE SOUTH AND HEAVY SNOW/BLIZZARD CONDITIONS ACROSS PARTS OF
THE NORTH-CENTRAL PLAINS AND INTO THE UPPER MIDWEST AROUND MIDWEEK
WITH SOME CHANCE OF FREEZING RAIN FOR SOME AS WELL. THIS STORM
SYSTEM SHOULD TRACK STEADILY EASTWARD BRINGING A HEAVY RAIN THREAT
TO PARTS OF THE SOUTHEAST AND MID-ATLANTIC (WITH SOME MORE
UNCERTAIN SNOW POTENTIAL FARTHER NORTH) LATER NEXT WEEK.
..GUIDANCE/PREDICTABILITY ASSESSMENT
THROUGH AROUND MIDWEEK, MODEL GUIDANCE HAS BEEN AND CONTINUES TO
BE WELL CLUSTERED FOR THE OVERALL PATTERN SETUP INVOLVING A
VIGOROUS SURFACE LOW CONSOLIDATING IN THE CENTRAL PLAINS AND
SHIFTING TOWARD THE MIDWEST. THERE REMAIN SOME WIGGLES IN THE
TIMING OF THE SURFACE LOW TRACK AND ITS ASSOCIATED FRONTS, WITH
RECENT CMC RUNS ON THE FASTER SIDE AND UKMET RUNS A LITTLE SLOWER.
AFTER WEDNESDAY/DAY 4, RECENT RUNS OF THE GFS HAVE BEEN A VERY
NOTABLE OUTLIER WITH WANTING TO WEAKEN AND ELONGATE THE UPPER LOW
WITH AN OVERALL MUCH LESS AMPLIFIED PATTERN LATER NEXT WEEK. THE
REMAINDER OF THE MODELS, WITH SUPPORT FROM THE ENSEMBLE MEANS
(INCLUDING THE GEFS) STILL SHOW A DISTINCT UPPER LOW PROGRESSING
INTO THE OHIO VALLEY AND EVENTUALLY THE NORTHEAST. THE GFS WAS NOT
INCLUDED IN TONIGHTS BLEND PAST DAY 4 AT ALL. THERE IS ALSO PLENTY
OF UNCERTAINTY STILL ON A POTENTIAL COASTAL LOW/NOR'EASTER
DEVELOPMENT OFF THE MID-ATLANTIC COAST BY FRIDAY. THE CMC
(INCLUDING THE NEW 00Z RUN) IS SIGNIFICANTLY FASTER WITH THE LOW
COMPARED TO THE ECMWF, BUT BOTH TAKE A SIMILAR TRACK. THE GFS IS
SHUNTED WELL TO THE SOUTH. THE ENSEMBLE MEANS AGAIN SUPPORT LOW
DEVELOPMENT MOST CONSISTENT WITH THE ECMWF. WHILE THE GUIDANCE IS
SHOWING BETTER AGREEMENT ON A LOW DEVELOPMENT, THE EXACT TRACK
REMAINS HIGHLY UNCERTAIN AT THIS TIME AND WOULD HAVE HUGE
IMPLICATIONS FOR ANY KIND OF WINTRY WEATHER ACROSS THE NORTHEAST
LATER IN THE PERIOD.
OUT WEST, AN UPPER LOW DROPS SOUTH OFF THE WEST COAST, AND AS
EARLY AS DAY 3, THERE'S A LOT OF UNCERTAINTY. THE ECMWF AND CMC
ARE DEEPER AND MAINTAIN A LOW WELL OFF THE COAST, WHILE THE GFS
AND UKMET (GFS FASTER) DROP IT DOWN ALONG THE COAST. THE GFS SPINS
IT NEAR THE COAST AND EVENTUALLY OFFSHORE. LOTS OF UNCERTAINTY
THERE LENDED TO FAVORING THE ENSEMBLE MEANS.
THE WPC BLEND FOR TONIGHT RELIED HEAVILY ON THE ECMWF WHICH SEEMED
THE MOST STABLE AND AGREEABLE TO THE BETTER MODEL ENSEMBLE
CONSENSUS. DAYS 3 AND 4 WAS ABLE TO INCORPORATE SMALLER AMOUNTS OF
THE CMC AND GFS, BUT AFTER THAT, USED INCREASING PARTS OF THE
ENSEMBLE MEANS WITH THE ECMWF GIVEN THE ISSUES ADDRESSED ABOVE
WITH THE CMC AND GFS. THE UKMET WAS TOO DIFFERENT ACROSS THE EAST
PACIFIC EARLY IN THE PERIOD TO FAVOR NOT USING IT AT ALL IN THE
BLEND. THIS APPROACH MAINTAINED GOOD CONTINUITY WITH THE PREVIOUS
SHIFT AS WELL. ANY ONE MODEL SOLUTION SEEMED PLAUSIBLE (SOME MORE
THAN OTHERS), BUT WITH NO CLEAR TREND, KEEPING WITH WPC CONTINUITY
SEEMED SAFER AT THIS POINT.
..WEATHER/HAZARD HIGHLIGHTS
AS THE UPPER TROUGH EMERGES INTO THE PLAINS AND A SURFACE LOW
CONSOLIDATES AND DEEPENS, DEEP AMPLE MOISTURE WILL SPREAD AHEAD OF
A COLD FRONT TO PRODUCE SIGNIFICANT RAINFALL ACROSS THE
LOWER/MIDDLE MISSISSIPPI VALLEY INTO THE TENNESSEE
VALLEY/APPALACHIANS AND VICINITY, STEADILY SHIFTING EAST WITH
TIME. THE LATEST WPC EXPERIMENTAL EXCESSIVE RAINFALL OUTLOOKS SHOW
SLIGHT RISKS ACROSS EASTERN ARKANSAS, FAR WEST TENNESSEE, AND
SOUTHEAST MISSOURI ON TUESDAY, WITH THE SLIGHT SHIFTING EAST INTO
THE TENNESSEE VALLEY/SOUTHERN APPALACHIANS AND NORTHERN PARTS OF
THE SOUTHEAST WHERE STREAM FLOWS AND SOIL MOISTURE ARE ABOVE
NORMAL. THE STORM PREDICTION CENTER CONTINUES TO MONITOR AND
HIGHLIGHT THE POTENTIAL FOR STRONG TO SEVERE CONVECTION ACROSS THE
LOWER MISSISSIPPI VALLEY AND CENTRAL GULF COAST TUESDAY AND
WEDNESDAY AS WELL. ON THE BACKSIDE OF THE LOW, COLD TEMPERATURES
AND WRAP-BACK MOISTURE WILL SUPPORT SIGNIFICANT SNOW/WINDS IN THE
NORTHERN PLAINS/UPPER MIDWEST AS SHOWN BY STEADILY INCREASING WPC
WINTER WEATHER OUTLOOK PROBABILITIES, WITH SOME MIXED
PRECIP/FREEZING RAIN POTENTIAL IN THE TRANSITION ZONE AND ALSO
ALONG THE EASTERN EDGE OF THE PRECIP SHIELD NEAR/NORTH OF THE WARM
FRONT. BY THE LATTER HALF OF THE WEEK, CURRENT FORECASTS SHOW
PRECIPITATION IS LIKELY TO SPREAD ACROSS THE EAST COAST ALONG AND
AHEAD OF THE FRONTAL SYSTEM, WITH POTENTIAL FOR WINTRY WEATHER
SPREADING ACROSS THE GREAT LAKES REGION AND NORTHEAST. BUT
PRECIPITATION TYPES AND AREAS OF HEAVIEST PRECIPITATION HAVE A
GREAT DEAL OF UNCERTAINTY ESPECIALLY CONSIDERING POSSIBLE COASTAL
LOW DEVELOPMENT OFF THE MID-ATLANTIC COAST LATE WEEK.
THE WEST SHOULD SEE BELOW NORMAL CONDITIONS THROUGH THE PERIOD,
WITH THE MOST WIDESPREAD READINGS OF AT LEAST 10-15F BELOW NORMAL
FOR HIGH TEMPERATURES AS THE DEEP UPPER TROUGH CROSSES THE REGION
FOR THE FIRST HALF OF NEXT WEEK. SOME OF THIS COLDER AIR SHOULD
SPILL INTO THE HIGH PLAINS BY NEXT TUESDAY-THURSDAY BEHIND THE
EXPECTED PLAINS STORM. ON THE OTHER HAND, SOUTHERN/EASTERN AREAS
WILL BE NEAR TO ABOVE NORMAL FOR TEMPERATURES. ANOMALIES WILL BE
GREATEST FOR MORNING LOWS, WITH SOME PLUS 15-25F ANOMALIES ACROSS
THE SOUTHERN TIER THROUGH THURSDAY. HIGHS ARE FORECAST TO BE
AROUND 10-15F ABOVE NORMAL FOR THE CENTRAL AND THEN EAST-CENTRAL
U.S., LOCALLY HIGHER AHEAD OF THE STORM SYSTEM. MUCH OF THE
COUNTRY LOOKS TO BE NEAR OR BELOW NORMAL BY NEXT FRIDAY AND
SATURDAY AFTER THE COLD FRONTAL PASSAGE AS HIGH PRESSURE
OVERSPREADS MUCH OF THE COUNTRY.
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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