928
FXUS02 KWBC 031848
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
148 PM EST SUN DEC 03 2023
VALID 12Z WED DEC 06 2023 - 12Z SUN DEC 10 2023
..PATTERN OVERVIEW
IT REMAINS THE CASE THA AN AMPLIFIED UPPER RIDGE IS EXPECTED TO BE
IN PLACE ACROSS THE CENTRAL U.S. FOR THE MIDDLE OF THE WEEK, ALONG
WITH A DEPARTING UPPER TROUGH ALONG THE EAST COAST. THE RIDGE
AXIS IS THEN EXPECTED TO FLATTEN OUT WITH A QUASI-ZONAL FLOW
PATTERN COMMENCING FOR A BRIEF TIME ACROSS THE CENTRAL AND WESTERN
U.S. ON THURSDAY. PACIFIC SHORTWAVE ENERGY REACHING THE WEST
COAST THURSDAY NIGHT WILL HELP BUILD AN UPPER TROUGH ACROSS THE
WESTERN U.S. TO CLOSE OUT THE WORK WEEK, AND THIS WILL NOW MORE
RAPIDLY EJECT EASTWARD ACROSS THE PLAINS AND SPUR SURFACE
CYCLOGENESIS INTO THE WEEKEND ACROSS THE CENTRAL TO EAST CENTRAL
U.S.. THIS WILL LIKELY RESULT IN A WELL ORGANIZED STORM SYSTEM
WITH INCREASING AND ENHANCING RAIN AND STORM CHANCES ACROSS THE
BROAD REGION WITH FRONTAL SYSTEM ADVANCE/FOCUS, WITH WRAPPING
WINTRY PRECIPITATION NORTHWEST OF THE MAIN SURFACE LOW TRACK.
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
MODEL AND ENSEMBLE SOLUTIONS SEEM OVERALL REASONABLY WELL
CLUSTERED INTO MID-LATE WEEK IN A PATTERN WITH SEEMINGLY ABOVE
NORMAL PREDICTABILITY. ACCORDINGLY, THE WPC MEDIUM RANGE PRODUCT
SUITE WAS PRIMARILY DERIVED FROM A COMPOSITE OF THE BEST CLUSTERED
06 UTC GFS AND 00 UTC ECMWF/UKMET/CANADIAN MODELS ALONG WITH THE
COMPATIBLE 13 UTC NATIONAL BLEND OF MODELS (NBM) AND WPC
CONTINUITY FOR BEST DETAIL. NEWER 12 UTC GUIDANCE REMAINS MAINLY
IN LINE AND MULTI-CENTER ENSEMBLE SUPPORT REMAINS VERY GOOD IN
THIS PERIOD. FORECAST SPREAD INCREASES STEADILY HEADING INTO NEXT
WEEKEND, LEANING A SWITCH IN PREFERENCE TO A BLEND OF BEST
COMPATIBLE 06 UTC GEFS/00 UTC ECMWF ENSEMBLE MEANS IN AN EFFORT TO
MITIGATE VARIANCE CONSISTENT WITH PREDICTABILITY. WPC PRODUCT
CONTINUITY HAS TRENDED TOWARD PROGRESSION ACROSS THE LOWER 48 AND
VICINITY AT THESE LONG TIME FRAMES.
..WEATHER/HAZARDS HIGHLIGHTS
THERE CONTINUES TO BE SOME GOOD NEWS TO REPORT ACROSS THE PACIFIC
NORTHWEST WITH AN ABATEMENT IN THE ATMOSPHERIC RIVER AND LESSER
RAINFALL TOTALS GOING INTO WEDNESDAY AND THROUGH THE REMAINDER OF
THE WEEK. THERE IS STILL A MARGINAL RISK AREA OF EXCESSIVE
RAINFALL FROM EXTREME NORTHWEST CALIFORNIA TO THE OREGON COASTAL
RANGES AND THE WESTERN OREGON CASCADES ON DAY 4 (WEDNESDAY) WITH
LOCALLY 1 TO 2 INCHES OF RAINFALL EXPECTED, BUT THIS IS A
NOTEWORTHY IMPROVEMENT COMPARED TO THE MUCH HEAVIER RAINFALL
EXPECTED DURING THE SHORT TERM FORECAST PERIOD. EVEN THOUGH
RAINFALL TOTALS ARE EXPECTED TO BE LIGHTER, THE GROUNDS WILL BE
QUITE SATURATED BY THIS TIME WITH ELEVATED CREEKS AND RIVERS, SO
THERE MAY STILL BE SOME INSTANCES OF MINOR FLOODING FOR THOSE
AREAS. LOOKING AHEAD TO DAY 5 (THURSDAY), FURTHER IMPROVEMENT IS
EXPECTED FOR THIS REGION AND THEREFORE NO RISK AREAS ARE CURRENTLY
WARRANTED AT THIS TIME.
A SWINGING OF A NOW MODERATELY AMPLIFIED WESTERN U.S. TROUGH BY
THE END OF THE WEEK WILL BRING MOISTURE ACROSS THE INTERMOUNTAIN
WEST AND THE ROCKIES, WITH MODERATE TO HEAVY SNOW FOR
PARTICULARILY THE HIGHER ELEVATIONS AND POSSIBLE SPILLING A BIT
INTO THE ADJACENT HIGH PLAINS WITH SYSTEM PROGRESSION. FARTHER
SOUTH IN THE WARM SECTOR OF THE LOW, INCREASING COVERAGE OF
SHOWERS AND THUNDERSTORMS CAN BE EXPECTED FROM THE CENTRAL GULF
COAST TO THE OHIO VALLEY, ALONG WITH BREEZY TO WINDY CONDITIONS.
THIS ACTIVITY LOOKS TO BECOME QUITE EXPANSIVE OVER NEXT WEEKEND
OVER THE EAST-CENTRAL U.S. AND COULD RESULT IN RUNOFF ISSUES OVER
TIME.
PLEASANTLY MILD CONDITIONS FOR EARLY DECEMBER ARE EXPECTED FROM
THE CENTRAL PLAINS TO THE DAKOTAS AND MONTANA ON WEDNESDAY AND
INTO THURSDAY, WITH TEMPERATURES RUNNING 20 TO 30 DEGREES ABOVE
AVERAGE IN MANY CASES. THE MILD CONDITIONS THEN REACH THE MIDWEST
BY FRIDAY AND MUCH OF THE EASTERN U.S. FOR THE WEEKEND WITH
WIDESPREAD 10-20 DEGREE ABOVE AVERAGE TEMPERATURES LIKELY, WITH
GRADUALLY COOLING TEMPERATURES ACROSS THE PLAINS. COLDER WEATHER
ENVELOPS MUCH OF THE INTERIOR WEST AND ROCKIES BY THE WEEKEND IN
RESPONSE TO THE UPPER TROUGH/LOW AND INCREASED CLOUD COVER AND
PRECIPITATION.
HAMRICK/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 FORECAST, EXCESSIVE RAINFALL OUTLOOK,
WINTER WEATHER OUTLOOK PROBABILITIES, HEAT INDICES AND KEY
MESSAGES 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
HTTPS://WWW.WPC.NCEP.NOAA.GOV/#PAGE=OVW
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