669
FXUS02 KWBC 290701
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
200 AM EST TUE NOV 29 2022
VALID 12Z FRI DEC 02 2022 - 12Z TUE DEC 06 2022
...WET/SNOWY CONDITIONS ACROSS THE WEST WITH BELOW NORMAL
TEMPERATURES...
..OVERVIEW
GUIDANCE SHOWS PROGRESSIVE WEST-SOUTHWESTERLY MEAN FLOW ALOFT OVER
MOST OF THE LOWER 48, BETWEEN A RIDGE OVER THE GULF OF MEXICO AND
AN UPPER LOW THAT DROPS FROM NORTHERN INTO CENTRAL CANADA. MEAN
TROUGHING THAT BECOMES ESTABLISHED NEAR THE WEST COAST MID-LATE
WEEK SHOULD FINALLY PUSH INLAND EARLY NEXT WEEK. THIS PATTERN
WILL LIKELY LEAD TO BELOW NORMAL DAYTIME TEMPERATURES OVER MOST
AREAS TO THE WEST OF THE ROCKIES, AS WELL AS A COUPLE EPISODES OF
WELL BELOW NORMAL TEMPERATURES OVER THE NORTHERN PLAINS. EXPECT
SOME AREAS IN THE WEST TO SEE SIGNIFICANT RAIN AND HIGHER
ELEVATION SNOW. SHORTWAVES EJECTING FROM THE WEST COAST MEAN
TROUGH COULD GENERATE A COUPLE VIGOROUS SYSTEMS TO THE EAST OF THE
ROCKIES, PRODUCING SNOW OVER THE NORTHERN TIER AND PLAYING A ROLE
IN A DEVELOPING AREA OF POTENTIALLY SIGNIFICANT RAINFALL OVER THE
EAST-CENTRAL U.S.
..GUIDANCE AND PREDICTABILITY ASSESSMENT
AMONG THE 12Z/18Z GUIDANCE, GFS RUNS WERE A BIT ON THE FASTER SIDE
OF THE SPREAD (THOUGH NOT TO AN EXTREME DEGREE) FOR THE LEADING
SHORTWAVE EJECTING FROM THE WEST WHILE THE CMC WAS ON THE SLOW
SIDE VERSUS OTHER MODELS/ENSEMBLES TO A GREATER DEGREE. THIS LEFT
THE GFS/ECMWF/UKMET AS THE BEST CLUSTER FOR THIS FEATURE. OVER
THE PAST DAY, THE MODELS HAVE TRENDED NOTICEABLY STRONGER FOR THE
SURFACE LOW THAT TRACKS ACROSS THE NORTH-CENTRAL PLAINS INTO THE
UPPER GREAT LAKES FRIDAY-SATURDAY. IN THE 00Z CYCLE BOTH THE GFS
AND CMC HAVE TRENDED FAVORABLY TOWARD THE AVERAGE OF PREVIOUS
GUIDANCE. FOR THE NEXT SYSTEM DROPPING DOWN TOWARD THE WEST COAST
LATE WEEK THROUGH THE WEEKEND, THE GFS/ECMWF HAVE CONVERGED ON AN
UPPER LOW TRACK THAT REACHES THE COAST NEAR OR JUST SOUTH OF THE
OREGON/CALIFORNIA BORDER. UKMET RUNS HAVE BEEN A BIT NORTH OF
THAT. THE 12Z CMC BECAME NOTICEABLY FLAT WITH THE TROUGH (WHICH
HAS BEEN A TENDENCY OF THE MODEL AND ITS ENSEMBLES OVER RECENT
DAYS) WHILE THE NEW 00Z RUN HAS ADJUSTED MUCH CLOSER TO CONSENSUS.
MINUS THE EARLIER CMC/CMCENS RUNS, THERE HAS BEEN BETTER THAN
AVERAGE CLUSTERING AS THE SECOND UPPER FEATURE OPENS UP AND MOVES
THROUGH THE WEST, ULTIMATELY SUPPORTING A WELL-DEFINED SURFACE
SYSTEM REACHING THE MIDWEST/OHIO VALLEY/GREAT LAKES AREA BY DAY 7
NEXT TUESDAY. A MODEL/ENSEMBLE AVERAGE LOOKS GOOD FOR THE INITIAL
REPRESENTATION OF THIS SYSTEM GIVEN TYPICAL PREDICTABILITY THAT
FAR OUT IN TIME. FINALLY, GUIDANCE AGREES THAT THE SHAPE AND
PROGRESSION OF THE UPSTREAM RIDGE SHOULD ENCOURAGE THE NEXT BUNDLE
OF DIGGING SHORTWAVE ENERGY TO TAKE A FARTHER EAST TRAJECTORY INTO
THE WESTERN U.S. EARLY NEXT WEEK, WITH TYPICAL SPREAD AND
VARIABILITY FOR SPECIFICS. THIS TRAILING ENERGY MAY HAVE SOME
INFLUENCE ON THE EAST-CENTRAL U.S. SYSTEM.
WITH THE 12Z CMC COMPARING POORLY TO OTHER GUIDANCE IN MULTIPLE
WAYS, THE UPDATED FORECAST BLEND EMPHASIZED THE 18Z GFS AND 12Z
ECMWF/UKMET FOR ABOUT THE FIRST HALF OF THE FORECAST AND THEN
TRANSITIONED TO A COMBINATION OF THE GFS/ECMWF AND THEIR ENSEMBLE
MEANS.
..WEATHER/HAZARD HIGHLIGHTS
A LEADING WAVY FRONT PUSHING INTO THE WEST LATE THIS WEEK SHOULD
BRING SOME TERRAIN-ENHANCED RAINFALL TO PARTS OF THE SOUTHERN HALF
OF CALIFORNIA AS WELL AS SOME SNOW TO PORTIONS OF THE GREAT BASIN
AND CENTRAL ROCKIES. TRAILING LOW PRESSURE DRIFTING SOUTHEAST
TOWARD THE CENTRAL WEST COAST INTO THE WEEKEND WILL LIKELY SPREAD
LOCALLY MODERATE TO HEAVY RAIN AND HIGHER ELEVATION SNOW INTO THE
PACIFIC NORTHWEST AND THEN CALIFORNIA, WITH SOME OF MOISTURE ALSO
EXTENDING INTO THE GREAT BASIN/CENTRAL ROCKIES. MEANWHILE, FLOW
ALOFT AHEAD OF BOTH SYSTEMS MAY CARRY IN SOME ADDED MOISTURE FROM
THE EASTERN PACIFIC, LEADING TO AREAS OF RAINFALL ACROSS ARIZONA
AND NEW MEXICO. SOME OF THIS ACTIVITY COULD BE ON THE LOCALLY
MODERATE TO HEAVY SIDE BUT CONFIDENCE IS LOW IN THE DETAILS AT
THIS TIME. THE SOUTHERN HALF OF THE WEST SHOULD TREND DRIER BY
NEXT MONDAY OR TUESDAY AS UPPER TROUGHING MOVES FARTHER INLAND BUT
SOME PRECIPITATION MAY PERSIST OVER THE NORTHWEST/ROCKIES. THESE
SYSTEMS MAY PRODUCE GUSTY WINDS OVER SOME AREAS.
AREAS EAST OF THE ROCKIES SHOULD SEE A FAIRLY ACTIVE PATTERN AS
FEATURES EJECT FROM THE WEST. LATEST TRENDS HAVE BEEN FOR A
STRONGER SYSTEM TO TRACK FROM THE NORTH-CENTRAL PLAINS THROUGH THE
UPPER GREAT LAKES AROUND THE END OF THE WEEK, PRODUCING A BAND OF
SNOW ACROSS THE NORTHERN TIER AND A BRIEF PERIOD OF STRONG WINDS.
FARTHER SOUTH, SOME LIGHT RAIN MAY INITIALLY ACCOMPANY THE
TRAILING FRONT AS IT PUSHES INTO THE EASTERN U.S. HOWEVER THE
FRONT SHOULD STALL AND THEN RETURN NORTHWARD AS A WARM FRONT AHEAD
OF THE NEXT SYSTEM EMERGING OVER THE PLAINS/MIDWEST, SERVING AS A
FOCUS FOR INCREASING RAINFALL OVER THE MIDDLE LATITUDES OF THE
EAST-CENTRAL U.S. SUNDAY ONWARD. BOTH LOW LEVEL FLOW FROM THE
GULF AND THE WEST-SOUTHWESTERLY FLOW ALOFT SHOULD CONTRIBUTE
MOISTURE FOR THIS EVENT THAT COULD PRODUCE AREAS OF MODERATE TO
HEAVY RAINFALL. SOME RAIN MAY EXTEND BACK INTO THE PLAINS AS
WELL. THE AFOREMENTIONED TRAILING SYSTEM MAY PRODUCE ANOTHER AREA
OF SNOW ACROSS THE NORTHERN TIER EARLY NEXT WEEK, WITH TOTALS AND
WIND STRENGTH DEPENDENT ON THE ULTIMATE DEPTH OF THE SYSTEM.
MUCH OF THE WEST SHOULD SEE BELOW NORMAL HIGH TEMPERATURES FROM
LATE THIS WEEK INTO EARLY NEXT WEEK, WITH MOST LOCATIONS 5-15F
BELOW NORMAL. THERE MAY BE A FEW ISOLATED DAILY RECORDS FOR COLD
MORNING LOWS/DAYTIME HIGHS NEAR THE WEST COAST LATE THIS WEEK. THE
NORTHERN PLAINS SHOULD SEE A COUPLE SEPARATE EPISODES OF COLDER
READINGS. THE FIRST WILL FEATURE HIGHS 15-30F BELOW NORMAL ON
FRIDAY MAINLY OVER MONTANA INTO NORTH DAKOTA. THE NEXT PUSH OF
SIMILARLY COLD ANOMALIES SHOULD EXPAND ACROSS A LARGER PORTION OF
THE NORTHERN PLAINS NEXT MONDAY-TUESDAY. SOUTHERN/EASTERN AREAS
WILL TEND TO SEE NEAR TO ABOVE NORMAL TEMPERATURES ASIDE FROM A
COOL START TO THE DAY OVER THE EAST ON FRIDAY, WITH VARIOUS AREAS
OF PLUS 10-15F ANOMALIES LIKELY DURING THE WEEKEND INTO EARLY NEXT
WEEK. THE SOUTHERN TIER SHOULD SEE MULTIPLE DAYS OF PLUS 15-25F
ANOMALIES FOR MORNING LOWS. ALSO THE CENTRAL PLAINS MAY SEE HIGHS
UP TO 10-20F ABOVE NORMAL ON FRIDAY.
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
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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