279
FXUS02 KWBC 161842
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
142 PM 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 COMING INLAND ACROSS SOUTHERN CALIFORNIA OR
FAR NORTHERN MEXICO AROUND NEXT SATURDAY. THIS LIKELY WILL BRING
PERIODS OF ENHANCED PRECIPITATION ONSHORE ACROSS CALIFORNIA AND
THEN INCREASINGLY INLAND HEADING INTO NEXT WEEKEND. MEANWHILE, A
DEEP UPPER LOW/TROUGH OVER THE EAST COAST WILL CUT OFF ANOTHER LOW
WHICH LIFTS NORTH WELL OFF THE EAST COAST NEXT WEEK. IN BETWEEN
THE WESTERN AND EASTERN FEATURES, UPPER RIDING WILL BUILD ACROSS
THE CENTRAL INTO EASTERN U.S..
..GUIDANCE/PREDICTABILITY ASSESSMENT
OUTSIDE OF THE 00Z UKMET, THE REMAINDER OF THE MODELS AND
ENSEMBLES SHOWED FAIRLY GOOD CLUSTERING FOR THE UPPER LOW WHICH
LIFTS WELL OFF THE EAST COAST MID TO LATER NEXT WEEK. THE UKMET
SEEMED MUCH TOO CLOSE TO THE COAST AND WAS NOT INCLUDED IN THE
BLEND TODAY. IN THE WEST, THE OUTLIER FOR THE DEEP LOW DROPPING
SOUTHWARD ALONG THE COAST WAS THE 06Z GFS WHICH SHIFTED NOTICEABLY
WESTWARD WITH THE LOW PLACEMENT, RESULTING IN BEING SLOWER TO
BRING PRECIPITATION ONSHORE ACROSS CENTRAL AND SOUTHERN
CALIFORNIA. INTERESTING TO NOTE THOUGH THAT THE 12Z GFS CAME IN
JUST SLIGHTLY EAST OF IT'S 06Z POSITION, WHILE THE 12Z ECMWF WAS
SLIGHTLY WEST, AND THE UKMET AND CMC ARE STILL CLOSEST TO THE
COAST. SO THERE REMAINS SOME RUN TO RUN VARIABILITY AND WOBBLE
WITH THIS LOW.
THROUGH THE 00Z/06Z GUIDANCE, THE WPC FORECAST LEANED MORE HEAVILY
ON THE ECMWF AND THE CMC EARLY IN THE PERIOD DUE TO THE GFS
CONCERNS OFF THE WEST COAST. BY DAY 5, AND ESPECIALLY BEYOND, USED
INCREASINGLY MORE OF THE ENSEMBLE MEANS AS OVERALL SPREAD
GENERALLY INCREASED. THIS APPROACH MAINTAINS GOOD CONTINUITY WITH
THE PREVIOUS WPC FORECAST AS WELL.
..WEATHER/HAZARDS HIGHLIGHTS
EXPECT LINGERING WRAP BACK SNOWS IN COLD POST-FRONTAL FLOW TO THE
LEE OF THE LOWER GREAT LAKES AND MORE BROADLY ACROSS ESPECIALLY
FAVORED TERRAIN/MOUNTAINS OF THE NORTHEAST INTO TUESDAY IN THE
WAKE OF THE DEEP COASTAL STORM, SECONDARY LOW GENESIS AND DEEP
TROUGHING ALOFT.
OUT WEST...PRECIPITATION CHANCES WILL BE INCREASING NEXT WEEK DOWN
ACROSS THE WEST COAST, AS A PLUME OF DEEPENED MOISTURE IS
CHANNELED AROUND A CLOSED UPPER TROUGH/SURFACE SYSTEM DIGGING
SOUTHWARD OVER THE EASTERN PACIFIC. TIMING AND EXACT AMOUNTS
REMAIN IN QUESTION ARE ARE DEPENDING ON HOW CLOSE TO THE COAST THE
UPPER LOW ACTUALLY TRACKS, HOWEVER RAIN AMOUNTS AND RATES COULD
STILL BE SUFFICIENT TO CAUSE SOME LOCAL FLOODING CONCERNS,
ESPECIALLY GIVEN SOME INSTABILITY COULD REACH COASTAL AREAS. THE
MAIN FOCUS OF THE 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 CONTINUE FOR TUESDAY AND WEDNESDAY FROM NORTHERN TO
CENTRAL COASTAL CALIFORNIA. ORGANIZED ENHANCED ACTIVITY WILL WORK
INTO SOUTHERN CALIFORNIA 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 ALONG THE EAST COAST MAY BEGIN MODERATELY BELOW
NORMAL ON TUESDAY IN THE WAKE OF THE DEEP LEAD STORM, WITH FROST
AND FREEZE CONDITIONS EXTENDING INTO PARTS OF NORTHERN FLORIDA
TUESDAY/WEDNESDAY. CONDITIONS SHOULD TREND WARMER AND BACK TOWARDS
NORMAL FOR THE REST OF NEXT WEEK/WEEKEND THOUGH. 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.
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, 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
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page