738
FXUS02 KWBC 011953
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
252 PM EST THU DEC 01 2022
VALID 12Z SUN DEC 04 2022 - 12Z THU DEC 08 2022
...BELOW NORMAL TEMPERATURES OVER THE WEST WITH RAIN/MOUNTAIN SNOW
GENERALLY TRENDING LIGHTER...
...HEAVY RAINFALL POTENTIAL FOR PORTIONS OF THE EASTERN AND
CENTRAL U.S. NEXT WEEK...
..OVERVIEW
EXPECT A MAJORITY OF THE LOWER 48 TO SEE FAST FLOW ALOFT BETWEEN A
MEAN LOW OVER CENTRAL CANADA AND A RIDGE OVER THE GULF OF MEXICO.
GUIDANCE HAS TRENDED TOWARDS A POSITIVELY-TILTED UPPER-LEVEL
TROUGH PERSISTING OVER THE EASTERN PACIFIC AND WESTERN U.S. WITH
ONLY A GRADUAL EASTWARD DRIFT DURING THE EARLY-MID WEEK TIME
FRAME. AN UPSTREAM RIDGE SHOULD MOVE INTO THE NORTHWEST
U.S./WESTERN CANADA BY MIDWEEK OR SO, FOLLOWED BY A SHORTWAVE
TROUGH APPROACHING THE PACIFIC NORTHWEST NEXT THURSDAY. THIS
PATTERN SHOULD PROMOTE BELOW NORMAL TEMPERATURES OVER MOST OF THE
WEST AND NORTHERN PLAINS ON MOST DAYS, WHILE THE RAIN AND MOUNTAIN
SNOW AFFECTING SOME PARTS OF THE WEST SHOULD STEADILY DECREASE IN
COVERAGE AND INTENSITY WITH TIME. ON THE OTHER HAND IT LOOKS TO
BE A FAVORABLE SETUP FOR HEAVY RAINFALL OVER PORTIONS OF THE
EAST-CENTRAL U.S. EARLY NEXT WEEK AS MULTIPLE MOISTURE SOURCES
INTERACT WITH A COUPLE FRONTS. THE FAR SOUTHERN TIER STATES SHOULD
SEE MOSTLY ABOVE NORMAL TEMPERATURES.
..GUIDANCE AND PREDICTABILITY ASSESSMENT
WHILE THE LARGE-SCALE PATTERN TENDED TO REMAIN RELATIVELY
CONSISTENT ACROSS THE GUIDANCE, SIGNIFICANT DIFFERENCES IN THE
MORE FINE SCALE DETAILS RUN-TO-RUN CONTINUE TO PROVE CHALLENGING.
THE MAIN FEATURES TO ACCOUNT FOR WERE A POSITIVELY-TILTED
UPPER-LEVEL TROUGH PROGRESSING SLOWLY OVER THE EASTERN PACIFIC
ALONG THE WEST COAST AND SHORTWAVES MOVING THROUGH SOUTHERN
CANADA/THE NORTHERN U.S. IN THE NORTHERN STREAM. THE WPC FORECAST
FOLLOWED A GENERAL TREND OF INCORPORATING MAINLY THE DETERMINISTIC
GUIDANCE EARLY IN THE PERIOD TO BLENDING IN MORE OF THE ENSEMBLE
MEANS LATER TO HOPEFULLY BEST CAPTURE THE BROADER PATTERN WHILE
ACCOUNTING FOR SMALL-SCALE SHORTWAVE ENERGY THAT PROVED TO HAVE AN
IMPACT ON THE EVOLUTION OF SYSTEMS AT THE SURFACE. EARLY IN THE
PERIOD, THE LARGE-SCALE FLOW WAS GENERALLY CONSISTENT ACROSS THE
GUIDANCE EXCEPT FOR SUBTLE DIFFERENCES IN STRENGTH OF THE CLOSED
LOW OFF THE WEST COAST AND THE TIMING OF SHORTWAVE ENERGY IN THE
NORTHERN STREAM OVER SOUTH-CENTRAL CANADA. BOTH THE 06Z GFS AND
00Z EURO WERE TRENDING TOWARDS AGREEMENT ON THE TIMING OF THIS
FEATURE WHILE THE 00Z CMC/UKMET WERE MORE PROGRESSIVE. THE WPC
FORECAST INCORPORATED EACH PIECE OF GUIDANCE WITH AN EMPHASIS
TOWARDS THE 06Z GFS AND 00Z EURO AS TO NOT INTRODUCE TOO MUCH OF A
BIMODAL PHASING OF THE FLOW.
UNCERTAINTY IN THE FORECAST BEGAN TO INCREASE SIGNIFICANTLY DURING
THE MIDDLE OF THE FORECAST PERIOD IN TERMS OF THE EVOLUTION OF
BOTH THE WESTERN TROUGH AND ENERGY IN THE NORTHERN STREAM. THIS
UNCERTAINTY WAS HIGHLIGHTED BY THE RAPIDLY INCREASING DIVERGENCE
IN THE SOLUTIONS OF THE INDIVIDUAL GEFS AND ECENS ENSEMBLE
MEMBERS. THE LATEST FEW RUNS OF THE GFS WAVERED BACK AND FORTH
BETWEEN RETAINING A CLOSED LOW, BUT FELL IN LINE WITH THE OTHER
GUIDANCE BY 06Z IN DEPICTING AN OPEN WAVE. THE WPC FORECAST
CONTINUED WITH A BLEND OF THE LATEST DETERMINISTIC GUIDANCE WHILE
GRADUALLY INCORPORATING THE 06Z GEFS AND 00Z ECENS MEANS AS TO NOT
PUT TOO MUCH EMPHASIS ON ANY ONE SOLUTION GIVEN THE SMALLER SCALE
DISAGREEMENT. THE TROUGH IN THE WEST HAS TRENDED A BIT SLOWER
COMPARED TO THE PRIOR WPC FORECAST.
A SIMILAR PATTERN OF SIGNIFICANT RUN-TO-RUN UNCERTAINTY CONTINUED
LATE INTO THE FORECAST PERIOD. THE PREVIOUS 11/30 00Z GFS/ECMWF
RUNS WERE SIGNIFICANTLY DIFFERENT FROM EACHOTHER. THE GFS WAS MUCH
MORE PROGRESSIVE WITH THE TROUGH ALONG THE WEST COAST, DEPICTING
IT MOVING EAST QUICKLY AND BLENDING INTO THE LARGE-SCALE FLOW. ON
THE OTHER HAND, THE LATEST 00Z GFS HAD A CLOSED LOW OFF THE COAST.
THE ECMWF DEMONSTRATED A BIT MORE CONSISTENCY RUN-TO-RUN WITH A
LESS PROGRESSIVE OPEN WAVE, AND THE CMC ALSO HAD A SIMILAR
SOLUTION. GIVEN THE GFS DID TREND THIS WAY BY 06Z, FELT CONFIDENT
ENOUGH TO CONTINUE WITH A GENERAL BLEND OF EACH OF THE
DETERMINISTIC GUIDANCE AND MEANS WHICH RESULTED IN AN UPDATED
FORECAST THAT REMAINED RELATIVELY SIMILAR TO THE PRIOR FORECAST
DESPITE THE LINGERING CONSISTENCY ISSUES. THE 06Z GFS AND 00Z
ECWMF INDICATE THIS TROUGH FINALLY MOVES INTO THE SOUTHWEST BY THE
END OF THE PERIOD, WHILE THE 00Z CMC WAS MUCH LESS PROGRESSIVE AND
AN OUTLIER. COMPLETED THE WPC FORECAST PERIOD WITH A BLEND OF THE
06Z GFS AND 00Z ECMWF ALONG WITH THE GEFS AND ECENS MEANS, WITH
THE DETERMINISTIC GUIDANCE HELPING TO BETTER DEPICT THE TREND OF A
DEEPER TROUGH MOVING INTO THE SOUTHWEST THAN THE PRIOR WPC
FORECAST. USE OF THE MEANS HELPED TO CONTINUE TO ACCOUNT FOR
SIGNIFICANT DIFFERENCES IN THE TIMING OF SHORTWAVE ENERGY MOVING
THROUGH SOUTHERN CANADA AND THE NORTHERN U.S. WITH NO CLEAR
EVIDENCE OF A DOMINANT SOLUTION OR PATTERN TO FOLLOW.
..WEATHER/HAZARD HIGHLIGHTS
LOW PRESSURE NEAR THE WEST COAST THROUGH SUNDAY SHOULD PRODUCE
SOME ENHANCED RAIN AND MOUNTAIN SNOW ALONG FAVORED TERRAIN OF THE
SIERRA NEVADA. SOME OF THE MOISTURE FROM THIS SYSTEM WILL ALSO
EXTEND INTO THE GREAT BASIN AND CENTRAL/NORTHERN ROCKIES WITH SOME
LOCALLY HEAVIER SNOW POSSIBLE THERE AS WELL. MOIST SOUTHERN
STREAM PACIFIC FLOW ALOFT AHEAD OF THIS SYSTEM MAY CONTINUE TO
PRODUCE SOME RAINFALL OVER PARTS OF SOUTHERN ARIZONA AND NEW
MEXICO THROUGH SUNDAY. RAINFALL AMOUNTS HAVE TRENDED A BIT DRIER,
BUT GIVEN RAINFALL PRIOR TO THE START OF THE PERIOD, AN ISOLATED
INSTANCE OR TWO OF FLASH FLOODING REMAIN POSSIBLE. THE SOUTHERN
HALF OF THE WEST SHOULD TREND DRIER EARLY NEXT WEEK AS THE WEST
COAST SYSTEM OPENS UP BEFORE THE SYSTEM BEGINS TO MOVE INTO THE
SOUTHWEST THURSDAY. ANOTHER FRONTAL SYSTEM APPROACHING THE
NORTHWEST MAY BRING AN INCREASE OF PRECIPITATION BY NEXT THURSDAY
AS WELL.
FARTHER EAST, A FRONT SETTLING NEAR THE GULF COAST ON SUNDAY IS
FORECAST TO RETURN NORTHWARD AS A WARM FRONT EARLY NEXT WEEK WHILE
A SYSTEM (CURRENTLY EXPECTED TO BE OF MODERATE STRENGTH) EMERGES
FROM THE PLAINS WITH A TRAILING COLD FRONT. WEST-SOUTHWESTERLY
UPPER LEVEL FLOW OF MOISTURE FROM THE PACIFIC AND A GRADUAL
INCREASE OF LOW LEVEL GULF INFLOW MAY INTERACT WITH THE FRONTS TO
PRODUCE AREAS OF HEAVY RAINFALL OVER THE EAST-CENTRAL U.S. EARLY
NEXT WEEK. CURRENTLY THE SIGNAL IS FAVORABLE ENOUGH TO DEPICT A
SLIGHT RISK AREA ON THE EXPERIMENTAL DAY 5 EXCESSIVE RAINFALL
OUTLOOK (VALID MONDAY-MONDAY NIGHT) CENTERED PRIMARILY OVER MOST
OF TENNESSEE AND SOUTHERN KENTUCKY. FAIRLY WET GROUND CONDITIONS
WILL MAKE THIS AREA SENSITIVE TO SIGNIFICANT RAINFALL AS WELL.
RAINFALL COULD PERSIST OVER PARTS OF THE SOUTH-CENTRAL U.S.
THROUGH AT LEAST MIDWEEK IF THE WAVY FRONT CROSSING THE REGION IS
SLOW ENOUGH. ANY SNOW SHOULD BE CONFINED TO FAR NORTHERN
LATITUDES OF THE EAST.
EXPECT BELOW NORMAL HIGH TEMPERATURES TO PERSIST OVER MUCH OF THE
WEST THROUGH THE SUNDAY-THURSDAY PERIOD, WITH MOST LOCATIONS 5-15F
BELOW NORMAL. THE NORTHERN PLAINS WILL BE BELOW NORMAL AS WELL,
WITH MONDAY-WEDNESDAY HAVING THE COLDEST HIGHS OF AT LEAST 15-20F
BELOW NORMAL AND LOWS THAT MAY DIP INTO THE NEGATIVE TEENS. THE
SOUTHERN TIER WILL TEND TO SEE ABOVE NORMAL TEMPERATURES, AND
ESPECIALLY FOR MORNING LOWS THAT COULD BE UP TO 20-25F ABOVE
NORMAL EARLY-MID WEEK. A FEW DAILY RECORDS FOR WARM LOWS MAY BE
POSSIBLE. SYSTEM PROGRESSION SHOULD BRING VARIABLE TEMPERATURES
TO THE NORTHERN HALF OF THE EAST.
PUTNAM/RAUSCH
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
HAZARDS:
- HEAVY RAIN ACROSS PORTIONS OF THE MIDDLE MISSISSIPPI VALLEY, THE
LOWER MISSISSIPPI VALLEY, AND THE SOUTHERN PLAINS, WED-THU, DEC
7-DEC 8.
- HEAVY RAIN ACROSS PORTIONS OF THE LOWER MISSISSIPPI VALLEY, THE
TENNESSEE VALLEY, THE MIDDLE MISSISSIPPI VALLEY, THE MID-ATLANTIC,
THE SOUTHERN APPALACHIANS, THE SOUTHEAST, AND THE OHIO VALLEY,
MON-TUE, DEC 5-DEC 6.
- HEAVY RAIN ACROSS PORTIONS OF THE NORTHEAST, TUE-WED, DEC 6-DEC
7.
- HEAVY SNOW ACROSS PORTIONS OF THE CENTRAL GREAT BASIN, THE
NORTHERN ROCKIES, THE CENTRAL ROCKIES, CALIFORNIA, THE NORTHERN
GREAT BASIN, AND THE SOUTHWEST, SUN, DEC 4.
- HEAVY SNOW ACROSS PORTIONS OF THE SOUTHERN ROCKIES, THE CENTRAL
ROCKIES, AND THE CENTRAL GREAT BASIN, MON, DEC 5.
- MUCH BELOW NORMAL TEMPERATURES ACROSS PORTIONS OF THE CENTRAL
GREAT BASIN, CALIFORNIA, AND THE NORTHERN GREAT BASIN, TUE-THU,
DEC 6-DEC 8.
- MUCH BELOW NORMAL TEMPERATURES ACROSS PORTIONS OF THE NORTHERN
ROCKIES AND THE NORTHERN GREAT BASIN, SUN-TUE, DEC 4-DEC 6.
- MUCH BELOW NORMAL TEMPERATURES ACROSS PORTIONS OF THE UPPER
MISSISSIPPI VALLEY, THE NORTHERN PLAINS, AND THE NORTHERN ROCKIES,
MON-WED, DEC 5-DEC 7.
- HEAVY PRECIPITATION ACROSS PORTIONS OF MAINLAND ALASKA, SUN-TUE,
DEC 4-DEC 6.
- HEAVY PRECIPITATION ACROSS PORTIONS OF THE ALASKA PANHANDLE AND
MAINLAND ALASKA, TUE-WED, DEC 6-DEC 7.
- HEAVY SNOW ACROSS PORTIONS OF MAINLAND ALASKA, SUN-MON, DEC
4-DEC 5.
- FREEZING RAIN ACROSS PORTIONS OF NORTHERN MAINLAND ALASKA,
SUN-MON, DEC 4-DEC 5.
- HIGH WINDS ACROSS PORTIONS OF MAINLAND ALASKA, SUN-TUE, DEC
4-DEC 6.
- HIGH WINDS ACROSS PORTIONS OF THE ALEUTIANS, SUN-MON, DEC 4-DEC
5.
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
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page