601
FXUS02 KWBC 191801
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
101 PM EST THU DEC 19 2024
VALID 12Z SUN DEC 22 2024 - 12Z THU DEC 26 2024
...HEAVY PRECIPITATION/WINDY PATTERN FOCUS FOR THE PACIFIC
NORTHWEST/NORTHERN CALIFORNIA THIS WEEKEND INTO THE HOLIDAYS...
..OVERVIEW
A MODERATELY AMPLIFIED FLOW PATTERN OVER THE CONUS IS EXPECTED TO
BE IN PLACE BY THE START OF THE MEDIUM RANGE PERIOD ON SUNDAY WITH
DEEP TROUGHING OVER THE EAST AND MEAN RIDGING OVER THE WESTERN TO
CENTRAL U.S.. A SERIES OF DYNAMIC SHORTWAVES ORIGINATING FROM
AMPLIFIED EAST PACIFIC TROUGHING WILL PUSH INTO/THROUGH THE MEAN
RIDGE OUT WEST, BRINGING A COUPLE OF ATMOSPHERIC RIVERS AND HEAVY
RAIN/MOUNTAIN SNOWS TO PARTS OF THE WEST COAST WELL INTO THE
UPCOMING HOLIDAY WEEK. CURRENT FORECASTS SHOW EASTWARD PROGRESS OF
A LEADING SHORTWAVE THROUGH THE NORTHERN PLAINS AND ONWARD BY EARLY
NEXT WEEK TO HELP PUSH THE EASTERN U.S. UPPER TROUGH EASTWARD WITH
A RETURN TO A MORE PROGRESSIVE, BUT POTENTIALLY STILL ACTIVE FLOW.
..GUIDANCE/PREDICTABILITY ASSESSMENT
MODEL FORECAST CLUSTERING AND PREDICTABILITY SEEM MUCH BETTER THAN
AVERAGE FOR BOTH THE LARGER SCALE FLOW EVOLUTION AND MANY EMBEDDED
SYSTEMS DAYS 3-7. A PREFERRED COMPOSITE OF THE 06 UTC GFS AND 00
UTC ECMWF/UKMET/CANADIAN MODELS WAS USED FOR WPC PRODUCT CREATION
FOR DAYS 3-7. IT SHOULD BE NOTED THAT RECENTLY THE DAYSHIFT
AVAILABLE MODEL SOLUTIONS INITIALIZED AT 00/06 UTC HAVE BEEN
SLIGHTLY BETTER CLUSTERED THAN THEIR RESPECTIVE OVERNIGHT VERSIONS.
IN EITHER CASE A MODEL COMPOSITE HAS RECENTLY SEEMED CONSISTENT
WITH WPC AND GUIDANCE CONTINUITY ALONG WITH THE 13 UTC NATIONAL
BLEND OF MODELS. THERE IS ALSO GOOD MULTI-MODEL ENSEMBLE AND
MACHINE LEARNING MODEL SUPPORT. THIS BLEND PROCESS TENDS TO
MITIGATE LINGERING SMALLER SCALE MODEL VARIANCES AS CONSISTENT WITH
INDIVIDUAL SYSTEM UNCERTAINTIES. LATEST INFORMATION FROM THE NEWER
12 UTC GUIDANCE SUITE SO FAR REMAINS WELL IN LINE WITH THIS
OVERALL FORECAST PLAN.
..WEATHER/HAZARDS HIGHLIGHTS
IT GENERALLY REMAINS THE CASE THAT A SERIES OF WEAK-MODERATE
ATMOSPHERIC RIVERS WILL BE ONGOING BY THIS WEEKEND INTO THE WEST
BRINGING A PROLONGED PERIOD OF WINDY AND GENERALLY UNSETTLED
CONDITIONS ALONG THE WEST COAST. FOR SUNDAY, GUIDANCE CONTINUES TO
SHOW SOME RAINFALL, BUT RAINFALL RATES MAY NOT BE HIGH ENOUGH TO
CAUSE ANY WIDESPREAD HAZARDS. BY MONDAY HOWEVER, A CORE AXIS OF
THE EASTERN PACIFIC TROUGH SHOULD PUSH EAST WITH AN INCREASE IN THE
MOISTURE AND HEAVY RAIN/MOUNTAIN SNOW POTENTIAL. MOISTURE AND
INSTABILITY WITH THIS AR LOOKS MORE SUFFICIENT FOR AT LEAST A
MARGINAL RISK ON THE WPC EXCESSIVE RAINFALL OUTLOOK FOR DAY
5/MONDAY, WITH THIS TYPE OF TO ENHANCED ACTIVITY SLATED TO
PERIODICALLY CONTINUE INTO THE HOLIDAYS, WITH CUMULATIVE IMPACT
POTENTIAL TO MONITOR. MODEL QPFS CONTINUE TO SUGGEST ENHANCED
RAINFALL POSSIBLE OVER THE PACIFIC NORTHWEST, BUT ESPECIALLY FOR
PARTS OF NORTHWEST CALIFORNIA, WITH ACCUMULATING AND POSSIBLE HEAVY
SNOW FOCUS IN THE HIGHER TERRAIN OF THE CASCADES AND THE SIERRA,
THEN WORKING INLAND ACROSS MAINLY THE NORTHWEST AND THE NORTH-
CENTRAL INTERMOUNTAIN WEST/ROCKIES.
FARTHER EAST, THE LEADING SHORTWAVE AND FRONTAL LOW INTO THE
NORTHERN PLAINS WILL SPREAD SOME WEAK RAIN OR SNOW ACROSS PORTIONS
OF THE UPPER MIDWEST AND THE GREAT LAKES INTO MONDAY. THE SOUTHERN
STREAM SYSTEM MAY CLOSE, WITH MODERATE CYCLOGENESIS/FRONTOGENESIS
LEADING TO SOME PRECIPITATION DEVELOPMENT ACROSS THE PLAINS INTO
THE MIDWEST NEXT WEEK, BUT WITH LINGERING SPECIFICS UNCERTAINTY.
A DEPARTING SURFACE HIGH OVER THE EAST WILL CONTINUE MUCH BELOW
NORMAL TEMPERATURES THROUGH MONDAY, WITH MODERATION THEREAFTER.
ABOVE NORMAL TEMPERATURES WILL EXPAND FROM THE WEST INTO THE PLAINS
AND MIDWEST THROUGH THE PERIOD. DAYTIME HIGHS IN SOME LOCATIONS
COULD BE 10 TO 20 DEGREES ABOVE NORMAL.
SANTORELLI/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 (QPF), EXCESSIVE RAINFALL
OUTLOOK (ERO), WINTER WEATHER OUTLOOK (WWO) PROBABILITIES, HEAT
INDICES, AND KEY MESSAGES CAN BE ACCESSED FROM:
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
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page