235
FXUS02 KWBC 031858
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
157 PM EST SAT DEC 3 2022
VALID 12Z TUE DEC 6 2022 - 12Z SAT DEC 10 2022
...HEAVY RAIN BECOMING MORE LIKELY FROM THE SOUTH-CENTRAL PLAINS
TO THE MID-SOUTH/TENNESSEE VALLEY EARLY-MID NEXT WEEK...
19Z UPDATE: THE 12Z MODEL GUIDANCE SUITE HAS VERY GOOD SYNOPTIC
SCALE AGREEMENT THROUGH WEDNESDAY EVENING WITH THE BROAD CYCLONIC
FLOW ALOFT OVER THE NORTH-CENTRAL U.S., THE TROUGH MOVING ACROSS
THE INTERMOUNTAIN WEST, AND THE BUILDING UPPER RIDGE OVER THE GULF
OF MEXICO. FORECAST CONFIDENCE HAS IMPROVED SOME FOR THE END OF
THE WEEK, BUT THERE ARE STILL SOME NOTEWORTHY DIFFERENCES WITH THE
TIMING AND DEGREE OF AMPLIFICATION WITH THE NEXT BIG TROUGH
DEVELOPING OVER THE WEST COAST AND THEN THE INTERMOUNTAIN WEST TO
CLOSE OUT THE WORK WEEK AND BEYOND. THE WPC FORECAST WAS
PRIMARILY DERIVED FROM A MULTI-DETERMINISTIC BLEND THROUGH
WEDNESDAY, AND THEN INCREASED USE OF THE ENSEMBLE MEANS ALONG WITH
SOME PREVIOUS WPC CONTINUITY GOING INTO THE END OF THE WEEK AND
INTO SATURDAY. THE QPF FORECAST WAS DERIVED FROM A ROUGHLY 75%
NBM/12% GFS/12% ECMWF BLEND FOR MOST OF THE U.S., WITH SOME MANUAL
ADJUSTMENTS ACROSS CALIFORNIA AND ALSO TO SLIGHTLY NARROW THE AXIS
OF HEAVIEST QPF ACROSS THE MID-SOUTH. THE POTENTIAL EXISTS FOR 3
TO 5 INCHES OF RAINFALL FROM EASTERN OKLAHOMA TO WESTERN TENNESSEE
AS MOISTURE IS LIFTED OVER A QUASI-STATIONARY FRONTAL BOUNDARY,
AND A SLIGHT RISK OF EXCESSIVE RAINFALL WAS INTRODUCED FOR THE DAY
5 PERIOD ACROSS NORTHEASTERN OKLAHOMA INTO NORTH-CENTRAL ARKANSAS.
THE PREVIOUS FORECAST DISCUSSION IS APPENDED BELOW FOR REFERENCE.
/HAMRICK
-----------------
..GUIDANCE AND PREDICTABILITY ASSESSMENT
THE LATEST WPC MEDIUM RANGE PRODUCT SUITE WAS MAINLY DERIVED FROM
A COMPOSITE OF REASONABLY WELL CLUSTERED GUIDANCE FROM THE 18 UTC
GFS AND 12 UTC ECMWF/UKMET/CANADIAN MODELS ALONG WITH WPC
CONTINUITY AND THE 1 UTC NATIONAL BLEND OF MODELS VALID TUESDAY
INTO WEDNESDAY. THE LARGER SCALE UPPER FLOW PATTERN EVOLUTION
REMAINS GENERALLY COMPATIBLE IN GUIDANCE FOR MUCH OF NEXT WEEK
INCLUDING THE LATEST 00 UTC MODEL RUNS. HOWEVER, SMALLER SCALE
EMBEDDED SYSTEM FOCUS AND RUN TO RUN CONTINUITY ISSUES REMAIN
EVIDENT IN THIS SENSITIVE PATTERN WITH UNCERTAIN MULTI-STREAM
SYSTEM INTERACTIONS. ACCORDINGLY, TRANSITIONED TO USAGE OF A BLEND
OF COMPATIBLE GEFS/NAEFS/ECMWF ENSEMBLE MEANS LATER WEDNESDAY
THROUGH NEXT SATURDAY. THERE IS A GROWING SIGNAL FOR HEAVY RAINS
FROM THE SOUTH-CENTRAL PLAINS TO THE MID-SOUTH EARLY-MID NEXT
WEEK, BUT WAS HESITANT TO ISSUE ANY EXPERIMENTAL ERO "SLIGHT" RISK
AREAS DUE TO UNCERTAINTIES WITH LOCAL MAIN QPF FOCUS. FOR QPF,
TARGETED A BLEND TO THE 1 UTC NBM WITH LIMITED INCORPORATION OF
WPC CONTINUITY TO SOFTEN RUN TO RUN VARIANCE.
..PATTERN OVERVIEW AND WEATHER/HAZARD HIGHLIGHTS
IT REMAINS THE CASE THAT MUCH OF THE LOWER 48 WILL EXPERIENCE
PROGRESSIVE FLOW ALOFT TO CHANNEL BETWEEN A MEAN CLOSED LOW/TROUGH
OVER CENTRAL CANADA AND A RIDGE OVER THE GULF OF MEXICO NEXT WEEK.
NORTHERN STREAM SHORTWAVE AROUND THE CANADIAN VORTEX MAY FAVOR
SOME PERIODS OF SNOW FROM THE MIDWEST TO THE NORTHEAST. GUIDANCE
SHOWS 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 NEXT WEEK PRIOR TO LATER WEEK EJECTION
INTO THE FLOW. AN UPSTREAM RIDGE SHOULD MOVE INTO THE NORTHWEST
U.S./WESTERN CANADA BY MIDWEEK, FOLLOWED BY A POTENTIALLY VIGOROUS
SHORTWAVE TROUGH DIGGING INTO THE PACIFIC NORTHWEST
THURSDAY/FRIDAY TO RENEW PRECIPITATION INTO THE REGION, WITH AMPLE
SYSTEM ENERGIES WORKING OVER AN UNSETTLED WEST INTO NEXT WEEKEND.
THIS PATTERN SHOULD PROMOTE BELOW NORMAL TEMPERATURES OVER MOST OF
THE WEST AND NORTH-CENTRAL STATES ON MOST DAYS, WITH RAIN AND
MOUNTAIN SNOW AFFECTING SOME PARTS OF THE WEST. THE PATTERN ALSO
LOOKS TO OFFER A FAVORABLE SETUP FOR SOME HEAVIER RAINFALL OVER
PORTIONS OF THE EAST-CENTRAL U.S. NEXT WEEK AS MULTIPLE LEAD
MOISTURE SOURCES UNCERTAINLY INTERACT WITH A COUPLE FRONTS,
PERHAPS WITH A FOCUS FROM SOUTH-CENTRAL PLAINS TO THE MID-SOUTH
ONWARD ACROSS THE TENNESSEE VALLEY TO THE SOUTHERN APPALACHIANS. A
MAINLY DOMINANT NORTHERN STREAM FLOW AND ASSOCIATED SETTLING OF
COLDER AIR TO THE NORTH OF THESE FRONTS MAY ALSO PROVIDE A
POSSIBILITY FOR AN OVERRUNNING SWATH OF SNOW/ICE/FREEZING RAIN ON
THE NORTH SIDE OF THE RAIN SHIELDS, PERHAPS FROM THE SOUTH-CENTRAL
PLAINS THROUGH THE OHIO VALLEY STATES TO THE INTERIOR NORTHEAST
MID-LATER NEXT WEEK.
SCHICHTEL
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
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page