866
FXUS02 KWBC 170710
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
209 AM EST SUN DEC 17 2023
VALID 12Z WED DEC 20 2023 - 12Z SUN DEC 24 2023
...EMERGING PRECIPITATION THREAT FOR SOUTHERN CALIFORNIA AND THE
SOUTHWEST...
..OVERVIEW
A CLOSED UPPER TROUGH/LOW WILL DIG SOUTHWARD OFF CALIFORNIA
MID-LATE WEEK BEFORE EJECTING INLAND ACROSS SOUTHERN
CALIFORNIA/NORTHERN MEXICO AND THE SOUTHWEST NEXT WEEKEND. THIS
WILL BRING PERIODS OF ENHANCED PRECIPITATION INTO SOUTHERN
CALIFORNIA, THE SOUTHWEST. MEANWHILE, A DEEP UPPER LOW/TROUGH OVER
THE EAST COAST MIDWEEK WILL CUT OFF ANOTHER LOW OFF THE EAST COAST
INTO LATER WEEK, ACTING MAINLY AS A MARITIME THREAT. IN BETWEEN
THE WESTERN AND EASTERN FEATURES, WARMING UPPER RIDING WILL
POSITION OVER THE CENTRAL INTO EAST-CENTRAL U.S..
..GUIDANCE/PREDICTABILITY ASSESSMENT
THE WPC MEDIUM RANGE PRODUCT SUITE WAS PRIMARILY DERIVED FOR
WEDNESDAY INTO FRIDAY FROM A COMPOSITE BLEND OF BEST CLUSTERED
GUIDANCE FROM THE 18 UTC GFS AND 12 UTC ECMWF/UKMET ALONG WITH
COMPATIBLE INPUT FROM THE 01 UTC NATIONAL BLEND OF MODELS (NBM)
AND WPC CONTINUITY IN AN EFFORT TO PROVIDE SUFFICIENT DETAIL
CONSISTENT WITH A PATTERN WITH SEEMINGLY ABOVE NORMAL
PREDICTABILITY. THE 12 UTC CANADIAN SOLUTION OFFERS AN OUTLIER
SOLUTION WHOSE CLOSER HELD ATLANTIC CLOSED LOW PROXIMITY ALLOWS
FOR MUCH WETTER PATTERN FOR NEW ENGLAND MID-LATE WEEK, BUT THE
NEWER 00 UTC RUN HAS TRENDED STRONGLY TOWARD THE GUIDANCE
COMPOSITE. PREFER A COMPOSITE OF THE GFS/ECMWF AND GEFS/ECMWF
ENSEMBLE MEANS BY NEXT WEEKEND FOR THE BEST DETAIL AS FEASIBLE IN
A PERIOD WITH SLOWLY GROWING FORECAST SPREAD.
..WEATHER/HAZARDS HIGHLIGHTS
LOCALLY ENHANCED RAIN CHANCES WILL SHIFT SOUTHWARD ACROSS
CALIFORNIA THIS WEEK AS A PLUME OF DEEPENED MOISTURE IS CHANNELED
AROUND A CLOSED UPPER TROUGH/SURFACE SYSTEM DUG OVER THE EASTERN
PACIFIC. RAIN AMOUNTS AND RATES MAY BE SUFFICIENT FOR SOME LOCAL
FLOODING CONCERNS, ESPECIALLY GIVEN SOME INSTABILITY COULD REACH
COASTAL AREAS. THE WPC EXCESSIVE RAINFALL OUTLOOK (ERO) OFFERS
MARGINAL RISKS FOR WEDNESDAY INTO THURSDAY FROM CENTRAL TO
SOUTHERN COASTAL CALIFORNIA. ORGANIZED RAINS AND TERRAIN/MOUNTAIN
FOCUSING SNOWS SET TO WORK INLAND THROUGH THE SIERRA AND WITH SOME
THREAT FROM THE SOUTHWEST ACROSS THE SOUTH-CENTRAL GREAT
BASIN/ROCKIES FOR THE HOLIDAY WEEKEND WITH SLOW SYSTEM APPROACH.
MEANWHILE, SYSTEM/ENERGY DOWNSTREAM PROPAGATION MAY ALSO GENERATE
AN EMERGING WET PATTERN FROM THE SOUTH-CENTRAL PLAINS WITH SYSTEM
GENESIS AND WITH MORE UNCERTAINTY TO THE EAST GIVEN RETURN
MOISTURE INFLOW SIGNAL IN GUIDANCE. THIS COULD INCLUDE SOME
NORTHERN TIER WINTRY PRECIPITATION. MEANWHILE UPSTREAM, UPPER
SHORTWAVE TROUGH AND SURFACE SYSTEM PROGRESSION INTO THE NORTHWEST
SHOULD SUPPORT PERIODS OF ENHANCED PRECIPITATION FRIDAY INTO THE
WEEKEND.
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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