361
FXUS02 KWBC 022048
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
347 PM EST FRI DEC 02 2022
VALID 12Z MON DEC 05 2022 - 12Z FRI DEC 09 2022
...HEAVY RAIN BECOMING MORE LIKELY FROM THE CENTRAL PLAINS TO THE
MID-SOUTH EARLY-MID NEXT WEEK...
19Z UPDATE: THE 12Z MODEL GUIDANCE SUITE HAS VERY GOOD SYNOPTIC
SCALE AGREEMENT THROUGH ABOUT WEDNESDAY MORNING WITH THE BROAD
CYCLONIC FLOW ALOFT OVER THE NORTH-CENTRAL U.S., THE TROUGH MOVING
IN ACROSS THE WEST COAST, AND THE UPPER RIDGE OVER THE GULF OF
MEXICO. HOWEVER, FORECAST CONFIDENCE DROPS OFF CONSIDERABLY BY
DAY 7 (FRIDAY) AS MODELS STRUGGLE WITH TIMING AND EVOLUTION OF
SHORTWAVE PERTURBATIONS ACROSS THE WESTERN U.S., AND THE POTENTIAL
FOR PHASING BETWEEN NORTHERN/SOUTHERN STREAM FLOW LATE IN THE
PERIOD. 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. THE QPF FORECAST WAS DERIVED FROM
A ROUGHLY 75% NBM/12% GFS/12% ECMWF BLEND, AND QPF WAS SLIGHTLY
INCREASED FROM THE BLEND ACROSS PORTIONS OF CENTRAL AND NORTHERN
MONTANA TO BETTER ACCOUNT FOR LIGHT QPF IN UPSLOPE FLOW BEHIND A
STRONG COLD FRONT. THE POTENTIAL EXISTS FOR 2-4 INCHES OF
RAINFALL ACROSS PORTIONS OF ARKANSAS AND INTO TENNESSEE AS
MOISTURE IS LIFTED OVER A QUASI-STATIONARY FRONTAL BOUNDARY. THE
PREVIOUS FORECAST DISCUSSION IS APPENDED BELOW FOR REFERENCE.
/HAMRICK
--------------------------
..GUIDANCE AND PREDICTABILITY ASSESSMENT
THE WPC MEDIUM RANGE PRODUCT SUITE WAS PRIMARILY 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 MONDAY.
THE LARGER SCALE UPPER FLOW PATTERN EVOLUTION REMAINS GENERALLY
COMPATIBLE IN GUIDANCE WELL INTO MEDIUM RANGE TIME SCALES AND
OFFERS SOME COMMON TREND FOR A SLOWER SOUTHERN STREAM SOLUTION IN
RECENT GUIDANCE INCLUDING THE LATEST 00 UTC RUNS. HOWEVER,
EMBEDDED SYSTEM TIMING/SURFACE FEATURE FOCUS AND RUN TO RUN
CONTINUITY ISSUES BUILD IN A SENSITIVE PATTERN WITH UNCERTAIN
MULTI-STREAM SYSTEM INTERACTIONS. THE 12 UTC ECMWF ENSEMBLES WERE
NOT AVAILABLE FOR THIS FORECAST PACKAGE DUE TO A TECHNICAL ISSUE,
BUT THE 12 UTC NAEFS MEAN THAT INCLUDES INPUT FROM BOTH GEFS AND
CANADIAN ENSEMBLES DOES SEEM TO PROVIDE A DECENT FORECAST BASIS
TUESDAY-NEXT FRIDAY WITH AND EXTENDING FROM A GENERAL COMPOSITE OF
VARIED MODEL GUIDANCE IN A PATTERN WITH LESS THAN STELLAR
CONTINUITY WITH LOCAL SPECIFICS. ACCORDINGLY, FELT COMPELLED TO
ONLY BROADLY IMPLY THREAT AREAS AND TARGETED A BLEND OF NBM QPF
WITH SOME WPC CONTINUITY TO SOFTEN RUN TO RUN VARIANCE AND LOCAL
FOCUS.
..PATTERN OVERVIEW AND WEATHER/HAZARD HIGHLIGHTS
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 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 NEXT WEEK PRIOR TO LATER WEEK EJECTION INTO THE
FLOW. 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 AROUND THURSDAY TO RENEW
PRECIPITATION INTO THE REGION. 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 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 MID-LATER NEXT WEEK.
SCHICHTEL
- HEAVY RAIN ACROSS PORTIONS OF THE LOWER MISSISSIPPI VALLEY, AND
THE SOUTHERN PLAINS, WED-THU, DEC
7-DEC 8.
- HEAVY RAIN ACROSS PORTIONS OF THE CENTRAL APPALACHIANS, THE
TENNESSEE VALLEY, AND THE OHIO
VALLEY, MON-TUE, DEC 5-DEC 6.
- HEAVY RAIN ACROSS PORTIONS OF THE NORTHEAST, TUE, DEC 6.
- HEAVY SNOW ACROSS PORTIONS OF THE PACIFIC NORTHWEST, THU, DEC 8.
- HEAVY SNOW ACROSS PORTIONS OF THE CENTRAL ROCKIES, AND THE
NORTHERN ROCKIES, MON, DEC 5.
- MUCH BELOW NORMAL TEMPERATURES ACROSS PORTIONS OF CALIFORNIA,
AND THE NORTHERN GREAT BASIN,
WED-THU, DEC 7-DEC 8.
- MUCH BELOW NORMAL TEMPERATURES ACROSS PORTIONS OF THE UPPER
MISSISSIPPI VALLEY, AND THE NORTHERN
PLAINS, MON-WED, DEC 5-DEC 7.
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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