584
FXUS02 KWBC 160704
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
203 AM EST SAT DEC 16 2023
VALID 12Z TUE DEC 19 2023 - 12Z SAT DEC 23 2023
...EMERGING PRECIPITATION THREAT TO FOCUS INTO CALIFORNIA AND THE
SOUTHWEST NEXT WEEK...
..OVERVIEW
A CLOSED UPPER TROUGH/LOW REMAINS SLATED TO DIG SOUTHWARD OFF THE
WEST COAST NEXT WEEK. FEATURE PROXIMITY MAY BRING PERIODS OF
MOISTURE ENHANCED PRECIPITATION ONSHORE AND THEN INCREASINGLY
INLAND HEADING INTO NEXT WEEKEND AS IT SLOWLY TURNS TOWARDS
SOUTHERN CA AND THE SOUTHWEST.
..GUIDANCE/PREDICTABILITY ASSESSMENT
THE WPC MEDIUM RANGE PRODUCT SUITE WAS PRIMARILY DERIVED FOR
TUESDAY INTO THURSDAY 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 TO PROVIDE SUFFICIENT DETAIL CONSISTENT WITH A
PATTERN WITH SEEMINGLY ABOVE NORMAL PREDICTABILITY. THE 12 UTC
CANADIAN WAS A MORE PROGRESSIVE FLOW OUTLIER, BUT THE NEWER 00 UTC
RUN HAS COME BACK INTO THE FOLD. OPTED TO SWITCH TO A COMPOSITE OF
THE GFS/ECMWF AND THEIR ENSEMBLE MEANS LATER WEEK INTO NEXT
WEEKEND TO MAINTAIN AS MUCH DETAIL AS FEASIBLE ALBEIT IN A PERIOD
OF SLOWLY GROWING FORECAST SPREAD.
..WEATHER/HAZARDS HIGHLIGHTS
EXPECT LINGERING WRAPBACK SNOWS IN COLD POST-FRONTAL FLOW TO THE
LEE OF THE LOWER GREAT LAKES AND MORE BROADLY ACROSS ESPECALLY
FAVORED TERRAIN/MOUNTAINS OF THE NORTHEAST INTO TUESDAY IN THE
WAKE OF THE EXIT OF A DEEP COASTAL STORM, SECONDARY LOW GENESIS
AND DEEP TROUGHING ALOFT.
OUT WEST...PRECIPITATION CHANCES WILL BE INCREASING NEXT WEEK DOWN
ACROSS THE WEST COAST, ESPECIALLY AS A PLUME OF DEEPENED MOISTURE
IS CHANNELED AROUND A CLOSED UPPER TROUGH/SURFACE SYSTEM DIGGING
SOUTHWARD OVER THE EASTERN PACIFIC. RAIN AMOUNTS AND RATES COULD
BE SUFFICIENT TO CAUSE SOME LOCAL FLOODING CONCERNS, ESPECIALLY
GIVEN SOME INSTABILITY COULD REACH COASTAL AREAS. A MAIN FOCUS OF
A FUELING ATMOSPHERIC RIVER IS EXPECTED TO GRADUALLY SHIFT
SOUTHWARD THROUGH CALIFORNIA NEXT WEEK AS THE MAIN LOW DIGS THEN
EVENTUALLY SHIFTS EASTWARD TOWARD SOUTHERN CALIFORNIA/BAJA AND THE
SOUTHWEST. MARGINAL RISKS OF EXCESSIVE RAINFALL ARE PLANNED FOR
TUESDAY AND WEDNESDAY FROM NORTHERN TO CENTRAL COASTAL CALIFORNIA.
ORGANIZED ENHANCED ACTIVITY WILL WORK INTO SOUTHERN CALIFIRNIA AND
THE SOUTHWEST LATER NEXT WEEK/WEEKEND WITH MAIN SYSTEM SLOW
APPROACH. HIGHER ELEVATION SNOWS ARE ALSO EXPECTED ALONG/INLAND
FROM THE WEST COAST. MEANWHILE, SYSTEM/ENERGY DOWNSTREAM
PROPAGATION MAY ALSO GENERATE AN EMERGING WET PATTERN FROM THE
SOUTH-CENTRAL TO EAST-CENTRAL U.S. GIVEN EVENTUAL GULF OF MEXICO
RETURN MOISTURE INFLOW RESPONSE.
ADDITIONALLY, THERE IS ALSO A GROWING GUIDANCE SIGNAL SHOWING THAT
RENEWED UPPER SHORTWAVE TROUGH AND SURFACE SYSTEM PROGRESSION INTO
THE PACIFIC NORTHWEST MAY ALLOW FOR A BURST OF MODERATE
PRECIPITATION AGAIN BY NEXT WEEKEND.
TEMPERATURES WILL TREND DOWNWARDS OVER THE EAST THROUGH THE REST
OF THE WEEK IN THE WAKE OF THE DEEP LEAD STORM. ABOVE AVERAGE
TEMPERATURES ARE MEANWHILE EXPECTED TO PERSIST ACROSS THE WEST AND
SPREAD INTO THE CENTRAL U.S. FOR THE SECOND HALF OF NEXT WEEK.
TEMPERATURES IN THE SOUTHEAST WILL LIKELY REMAIN BELOW AVERAGE
EARLY-MID NEXT WEEK AS A COLD FRONT PASSES THROUGH AND HIGH
PRESSURE BUILDS INTO THE REGION. FROST AND FREEZE CONDITIONS MAY
EXTEND INTO PARTS OF NORTH FLORIDA.
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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