950
FXUS02 KWBC 111906
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
205 PM EST MON DEC 11 2023
VALID 12Z THU DEC 14 2023 - 12Z MON DEC 18 2023
..AN EMERGING WET PATTERN OVER THE SOUTH/SOUTHEAST
..OVERVIEW
A SOUTHERN STREAM UPPER LOW TRAVERSING THE SOUTHERN U.S. DURING
THE MEDIUM RANGE PERIOD WILL BE A PRIMARY DRIVER OF THE SENSIBLE
WEATHER, INCLUDING RAIN AND SNOW IN THE SOUTHERN PLAINS LATE THIS
WEEK, WITH RAIN POTENTIALLY SPREADING INTO THE SOUTHEAST INTO THE
WEEKEND AND EARLY NEXT WEEK THOUGH WITH MORE UNCERTAINTY AS MODELS
STRUGGLE TO AGREE ON A POSSIBLE GULF SURFACE LOW FORMING. AHEAD OF
THIS POSSIBILITY, MOIST EASTERLY FLOW INTO SOUTHERN FLORIDA COULD
CAUSE LOCALIZED HEAVY RAIN. FAIRLY PROGRESSIVE MID-UPPER FLOW IN
THE NORTHERN STREAM IS LIKELY WITH A SERIES OF SHALLOW TROUGHS
MOVING THROUGH THE NORTH-CENTRAL AND NORTHEASTERN U.S., WHILE MEAN
RIDGING BUILDS IN THE WEST AHEAD OF EASTERN PACIFIC TROUGHING.
..GUIDANCE/PREDICTABILITY ASSESSMENT
THE LATEST GUIDANCE CONTINUES TO FAVOR A DOMINANT SOUTHERN STREAM
SYSTEM THAT SPREAD SEVERAL INCHES OF MOISTURE FROM TEXAS TO THE
SOUTHEAST STATES ALBEIT WITH INCREASING MODEL SPREAD. AS
PREVIOUSLY NOTED, THE UKMET IS THE FIRST TO DIVERGE FROM CONSENSUS
WITH THE SLOWER UPPER LOW TRACK AND THERE ARE VARYING DEGREES OF
POTENTIAL INTERACTION WITH A NORTHERN STREAM SHORTWAVE UPSTREAM
THAT SHOULD MOVE NEAR THE U.S./CANADIAN BORDER THURSDAY-FRIDAY AND
THEN POTENTIALLY DIVE SOUTHEASTWARD INTO THE EAST-CENTRAL U.S.
THE STRENGTH AND TRACK OF THIS SHORTWAVE WILL HAVE IMPLICATIONS
DOWNSTREAM. NAMELY, THE GFS/GEFS SUITE LATELY HAS BEEN
INTERACTING/COMBINING THE PREEXISTING SOUTHERN STREAM UPPER LOW
AND THIS SHORTWAVE, WHICH FORMS AN EAST-CENTRAL U.S. TROUGH THAT
SUPPORTS A STRONG AND FASTER MOVING SURFACE LOW IN THE GULF AND
PROGRESSING NORTHEASTWARD. THIS IS OPPOSED TO THE REMAINING
MAJORITY THAT KEEPS THE NORTHERN STREAM SHORTWAVE PROGRESSIVE AND
NORTH OF THE SOUTHERN STREAM UPPER LOW. WITHOUT THE PHASING OF
THESE FEATURES, THE SOUTHERN STREAM UPPER LOW WILL BE SLOWER AND
THE ONLY DYNAMICAL SUPPORT FOR SURFACE LOW PRESSURE, SO THE
SURFACE LOW FORMS/STRENGTHENS LATER AND STAYS MORE SUPPRESSED. WPC
HAS BEEN GENERALLY FAVORING THE MORE SUPPRESSED AND SLOWER TRACK
GIVEN IT IS THE LARGER CLUSTER WITH MULTIPLE MODEL SUITES (THE
ECMWF AND CMC). ENSEMBLE MEMBERS TEND TO FAVOR WITH THEIR
OPERATIONAL RUNS BUT DO SHOW A LOT OF SPREAD.
ELSEWHERE, UPPER RIDGING SEEMS WELL PREDICTED IN THE WEST BEHIND
THESE FEATURES AND AHEAD OF LARGE SCALE EASTERN PACIFIC TROUGHING.
THE TIMING OF THE TROUGHING EDGING TOWARD THE WEST COAST EARLY
NEXT WEEK STILL SHOWS SOME SPREAD BUT NOTHING TOO EGREGIOUS FOR
THE DAYS 6-7 TIMEFRAME. WPC MAINTAINED CONTINUITY BY LEANING
TOWARD THE CMC, ECWMF AND GFS INITIALLY BEFORE DECREASING
INCLUSION OF THE GFS WHILE BOOSTING THE EC ENSEMBLE AND GEFS MEANS
FOR THE MIDDLE AND LATTER PERIODS.
..WEATHER/HAZARDS HIGHLIGHTS
AMPLE MOISTURE ADVECTING NORTHWARD IN CONJUNCTION WITH A SOUTHERN
STREAM UPPER LOW TRAVERSING FROM THE SOUTHWEST TO THE
SOUTH-CENTRAL STATES WILL HELP SPREAD RAIN FROM TEXAS, ACROSS THE
GULF COAST AND TO THE SOUTHEAST LATER THIS WEEK AND INTO EARLY
NEXT WEEK. DYNAMIC SUPPORT, ABUNDANT MOISTURE AND THE PRESENCE OF
SOME INSTABILITY SHOULD SUPPORT PERIODS OF MODERATE OR HEAVY
RAINFALL ACROSS THE SOUTHERN PLAINS, GULF COAST AND PORTIONS OF
THE SOUTHEAST. MARGINAL RISKS FOR EXCESSIVE RAINFALL WERE ALREADY
IN EFFECT THROUGH FRIDAY WERE SOME FLOODING RISK SEEMS POSSIBLE.
ONLY MINOR ADJUSTMENTS WERE NEEDED TO REFLECT THE LATEST TRENDS
AND WPC FORECAST. PORTIONS OF NEW MEXICO, THE SOUTHERN HIGH PLAINS
AND SOUTHERN ROCKIES, WHICH WILL BE ON THE WEST/NORTHWEST SIDE OF
THE PRECIPITATION SHIELD WILL LIKELY HAVE SNOW.
MEANWHILE ON THURSDAY, MOIST EASTERLY FLOW WILL LIKELY PERSIST
INTO SOUTHEASTERN FLORIDA WITH SOME INSTABILITY IN PLACE, SO A
MARGINAL RISK PERSISTS FOR THAT AREA FROM WEDNESDAY/DAY 3,
ESPECIALLY FOR THE SENSITIVE URBAN CORRIDOR. BY FRIDAY AND BEYOND,
CONFIDENCE WITH THE EXTENT OF PRECIPITATION RAPIDLY LOWERS AS
MODEL GUIDANCE DIVERGES. SOME MODEL GUIDANCE SHOWS WIDESPREAD
HEAVY RAIN OVER FLORIDA AND THE SOUTHEAST BY LATE WEEK, BUT THE
MORE FAVORED/LARGER CLUSTER OF GUIDANCE MAINTAINS A FOCUS FOR
HEAVY RAINFALL IN THE SOUTHERN PART OF THE STATE (OR EVEN PERHAPS
FULLY SOUTH OF FLORIDA) TO THE SOUTH OF HIGH PRESSURE AT THE
SURFACE. WPC MAINTAINS A MARGINAL RISK TO ACCOUNT FOR THE
POTENTIAL FOR POOLING MOISTURE. HIGH UNCERTAINTY PERSISTS IN
REGARDS TO HOW FAR NORTH THE PRECIPITATION COULD SPREAD ACROSS THE
SOUTHEAST.
ELSEWHERE, MAINLY DRY CONDITIONS ARE FORECAST THROUGH LATE WEEK,
OTHER THAN SOME LIGHT SHOWERS IN THE UPPER MIDWEST/UPPER GREAT
LAKES AND SOME PACIFIC NORTHWEST PRECIPITATION. BY EARLY NEXT
WEEK, EASTERN PACIFIC UPPER TROUGHING COULD SNEAK ENERGY INTO
CALIFORNIA AND SPREAD PRECIPITATION THERE, BUT THERE REMAINS
UNCERTAINTY IN TIMING WHEN THIS WILL OCCUR WHICH AFFECTS THE
PRECIPITATION AMOUNTS. THE INTERIOR WEST IS FORECAST TO STAY DRY.
A VAST PORTION OF THE NORTHERN STATES EAST OF THE ROCKY MOUNTAINS
ARE FORECAST TO HAVE ABOVE SEASONAL NORMAL TEMPERATURES THROUGH
THE EXTENDED PERIOD WITH BROAD COVERAGE OF PLUS 10F OR GREATER
ANOMALIES. SOME OF THE WARMEST VALUES WILL BE IN THE 15 TO 25F
RANGE AND FOCUSED IN THE VICINITY OF THE DAKOTAS AND UPPER MIDWEST
THROUGH SATURDAY. MEAN RIDGING ALOFT OVER THE WEST WILL FAVOR
MODERATELY ABOVE NORMAL TEMPERATURES AND A VERY GRADUAL WARMING
TREND WITH TIME. IN CONTRAST, CLOUDS/PRECIPITATION DURING THE
LATTER HALF OF THE WEEK WILL PRODUCE CHILLY HIGHS OVER THE
SOUTHERN HIGH PLAINS DURING THE LATTER PART OF THE WEEK.
TEMPERATURES THERE SHOULD REBOUND CLOSER TO NORMAL NEXT WEEKEND.
AREAS NEAR THE EAST COAST SHOULD SEE A DAY OR SO OF BELOW NORMAL
HIGHS THURSDAY AS STRONG AND COOL HIGH PRESSURE BUILDS IN BEHIND A
COLD FRONT. HIGHS OVER NORTHERN PARTS OF THE EAST SHOULD TREND
ABOVE NORMAL FRIDAY INTO THE WEEKEND WHILE THE SOUTH STAYS NEAR
NORMAL (BUT WITH FLORIDA ABOVE NORMAL FOR LOWS DUE TO PERSISTENT
CLOUDS/RAINFALL).
CAMPBELL/TATE
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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