682
FXUS02 KWBC 111859
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
159 PM 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 AND POSSIBLY THE NORTHEAST WITH A
HEAVY RAIN/SEVERE WEATHER THREAT FOR SOUTHERN AREAS AROUND
MIDWEEK...
..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
NEAR 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 NOTABLE SNOWFALL TO IMPACT INTERIOR PORTIONS
OF THE NORTHEAST AS WELL BY THURSDAY-SATURDAY. TO THE SOUTH, A
HEAVY RAIN THREAT WILL CONTINUE ACROSS THE SOUTHEAST WEDNESDAY
BEFORE SPREADING NORTHWARD INTO THE EASTERN/COASTAL MID-ATLANTIC
AND NORTHEAST AS THE LIKELY NOR'EASTER TRACKS NORTH. THE OVERALL
PATTERN CALMS DOWN BY NEXT WEEKEND, AS LOWER AMPLITUDE TROUGHING
MAY LINGER ACROSS THE NORTHEASTERN U.S. LEADING TO SOME LAKE
EFFECT SNOW, WHICH COMBINED WITH UNCERTAIN TROUGHING IN THE WEST
WILL LEAD TO BELOW NORMAL TEMPERATURES ACROSS MUCH OF THE CONUS.
..GUIDANCE/PREDICTABILITY ASSESSMENT
THERE REMAINS GOOD AGREEMENT AS THE PERIOD BEGINS WEDNESDAY FOR
THE PRESENCE OF AN UPPER LOW AND SURFACE LOW PRESSURE SYSTEM OVER
THE NORTH-CENTRAL PLAINS WITH GRADUAL MOVEMENT EAST-NORTHEASTWARD
THROUGH THE LATTER HALF OF THE WEEK. AROUND FRIDAY INTO NEXT
WEEKEND, TODAY'S 00Z/06Z MODEL CYCLE GENERALLY INDICATED SLOWER
MOVEMENT OF THOSE FEATURES COMPARED TO YESTERDAY'S MODELS AND THE
WPC FORECAST. THIS WOULD LINGER LOW PRESSURE LONGER ACROSS THE
GREAT LAKES TO NORTHEAST FOR POTENTIALLY HIGHER SNOW TOTALS, SHOWN
IN THIS FORECAST WITH OVERALL HIGHER PROBABILITIES IN THE DAYS 5-6
WINTER WEATHER OUTLOOK. RECENT GFS RUNS GENERALLY HAD THE UPPER
LOW AMONG THE SLOWEST TO ELONGATE AND MOVE, BUT WERE SUPPORTED BY
THE CMC AND GEFS/EC ENSEMBLE MEANS. REGARDLESS, RECENT MODELS
CONTINUE TO SHOW ANOTHER SURFACE LOW IS LIKELY TO ORIGINATE ACROSS
THE SOUTHEAST AND THEN MOVE ALONG THE EAST COAST AS A NOR'EASTER,
WITH REASONABLY GOOD MODEL AGREEMENT AND A TRACK/TIMING SIMILAR TO
CONTINUITY.
THE PATTERN ACROSS THE PACIFIC AND WESTERN NORTH AMERICA SHOWS
CONSIDERABLE DIFFERENCES FROM MODEL TO MODEL AND RUN TO RUN. AN
UPPER LOW MEANDERING OVER THE EASTERN PACIFIC MAY WEAKEN LATER
THIS WEEK AS IT IS INFLUENCED BY AN UPPER HIGH NEAR BRITISH
COLUMBIA AND PERHAPS TRACK EAST TOWARD THE CONUS. MEANWHILE
NORTHERN STREAM ENERGY COULD SPILL INTO THE WEST SIDE OF THE
CENTRAL U.S. UPPER LOW AND INFLUENCE THE PATTERN ACROSS THE
WESTERN/CENTRAL U.S. DEPENDING ON HOW IT EVOLVES. ALL THESE
INTERACTIONS OF FEATURES REMAIN QUITE UNCERTAIN AT THIS TIME. THE
WPC FORECAST UTILIZED A MULTI-MODEL DETERMINISTIC BLEND EARLY IN
THE FORECAST PERIOD BUT WITH INCREASING PROPORTIONS OF THE
ENSEMBLE MEANS TO OVER HALF BY DAY 7 AMID INCREASING UNCERTAINTY.
..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 FROM THE CENTRAL GULF COAST INTO PARTS OF
THE SOUTHEAST/TENNESSEE VALLEY/SOUTHERN APPALACHIANS, WITH
NORTHERN AREAS SENSITIVE TO FLOODING BECAUSE OF ABOVE NORMAL
STREAMFLOWS AND SOIL MOISTURE WHILE SOUTHERN AREAS COULD HAVE
HIGHER RAIN RATES DUE TO MORE INSTABILITY. 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 CONTINUING 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. THEN THERE IS INCREASING CONFIDENCE FOR SURFACE
LOW DEVELOPMENT TRACKING ALONG/NEAR THE EAST COAST THURSDAY INTO
THE WEEKEND. EVEN SMALL SHIFTS IN THIS LOW TRACK COULD CAUSE
DIFFERENCES PARTICULARLY WITH PRECIPITATION TYPES IN THE EAST, SO
THE FORECAST WILL CONTINUE TO BE REFINED. AT THIS POINT, IT LOOKS
LIKE COASTAL AREAS OF THE MID-ATLANTIC AND NORTHEAST MAY STAY RAIN
WHILE INTERIOR AREAS COULD SEE SEVERAL INCHES OF SNOW. AS THE
SYSTEM EXITS THE EAST NEXT WEEKEND, SOME LIGHT LAKE EFFECT SNOW
SHOWERS MAY CONTINUE 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 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 GENERALLY
10-20F BELOW NORMAL FOR HIGH TEMPERATURES WILL BE ACROSS MUCH OF
THE WEST AND INTO THE NORTHERN PLAINS.
TATE/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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