504
FXUS02 KWBC 100701
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
200 AM EST SUN DEC 10 2023
VALID 12Z WED DEC 13 2023 - 12Z SUN DEC 17 2023
..PATTERN OVERVIEW AND GUIDANCE/PREDICTABILITY ASSESSMENT
THE 18 UTC GFS AND 12 UTC ECMWF/CANADIAN/UKMET SOLUTIONS SEEM
REASONABLY WELL CLUSTERED WEDNESDAY INTO THURSDAY FOR MUCH OF THE
COUNTRY AND VICINITY. THIS IS EVIDENT IN A PATTERN WITH A
DEVELOPING AND SEPARATING SOUTHERN STREAM CLOSED LOW DIGGING INTO
THE SOUTHWEST, WELL DETACHED FROM A SERIES OF SYSTEMS RIDING MORE
PROGRESSIVELY FROM THE PACIFIC INLAND THROUGH SOUTHERN CANADA AND
THE U.S. NORTHERN TIER WITHIN NORTHERN STREAM FLOWS. A MODEL
COMPOSITE COUPLED WITH THE 01 UTC NATIONAL BLEND OF MODELS
MAINTAINS GREAT WPC PRODUCT CONTINUITY IN THIS PERIOD WITH AT
LEAST AVERAGE PREDICTABILITY. LATEST 12 UTC GUIDANCE STAYS MAINLY
IN LINE.
HOWEVER, THE MODELS THEN INCREASINGLY SHOW LESS THAN STELLAR MODEL
TO MODEL AND RUN CYCLE TO RUN CYCLE CONTINUITY ISSUES LATER WEEK
INTO NEXT WEEKEND WITH THE BULK OF THE DIFFERENCES/QPF ASSOCIATED
WITH THE POTENTIALLY WET DOWNSTREAM EJECTION OF THE AFOREMENTIONED
SOUTHWEST SOUTHERN STREAM SYSTEM AND THE EXTENT OF PHASING WITH
NORTHERN STREAM ENERGIES. THIS LEADS TO SIGNIFICANT VARIANCE WITH
THE POTENTIAL DEVELOPMENT AND AREAL EXTENT OF GULF OF MEXICO THEN
SOUTHEAST COAST/VICINITY COASTAL LOW GENESIS AND ASSOCIATED
MOISTURE FUELING RAINFALL PATTERN. THE 12 UTC ECMWF SHOWED
STREAM/SYSTEM PHASING FRIDAY, BUT THE ASSOCIATED NORTHERN STREAM
SYSTEM OFFERS TIMING ISSUES THAT OFTEN PORTEND QUITE UNCERTAIN
PHASING. THE NEWER 00 UTC ECMWF HAS FLIPPED AWAY FROM PHASING. THE
18 UTC GFS WAITED UNTIL SATURDAY TO OFFER SOME SYSTEM PHASING, BUT
IS ALSO THE MOST EARNEST OF THE MODELS TO DEVELOP LEADING
ACTIVITY/QPF OVER THE EASTERN GULF/FLORIDA THIS WEEK THAT LEADS
INTO A MORE SIGNIFICANT LOW UP THE EASTERN SEABOARD NEXT WEEKEND.
THE NEWER 00 UTC GFS OFFERS VERY DIFFERENT SYSTEM INTERACTIONS,
SHOWING ENHANCED SENSITIVITY AND LOWERING FORECAST CONFIDENCE. THE
12 UTC AND NOW 00 UTC CANADIAN RUNS MAINTAIN A SEPARATED SOUTHERN
STREAM SYSTEM THAT EVENTUALLY LEADS INTO VERY DEEP COASTAL LOW
DEVELOPMENT OFF FLORIDA/SOUTHEAST. PREFERENCE IS TO DISCOUNT LESS
LIKELY STREAM PHASING SCENARIOS THAT RELY ON UNCERTAIN SHORTWAVE
INTERACTIONS AT MEDIUM RANGE TIME SCALES UNTIL A MORE COMMON
GUIDANCE SIGNAL IS ESTABLISHED. THE 12 UTC AND NEWER 00 UTC
CANADIAN RUNS CERTAINLY OFFERS A ROBUST OPTION, BUT INSTEAD
PREFER, GIVEN GROWING UNCERTAINTIES IN THE FLOW, A BROAD COMPOSITE
OF MORE COMPATIBLE GEFS/ECMWF/NAEFS/CANADIAN ENSEMBLE MEANS THAT
GENERALLY MAINTAINS SPLIT FLOW WITH FOCUS ON THE MORE PREDICTABLE
EMBEDDED SYSTEMS. 01 UTC NATIONAL BLEND OF MODEL QPF ALSO SEEMS A
REASONABLE BASELINE FOR THIS PATTERN.
..WEATHER/HAZARDS HIGHLIGHTS
ACCORDINGLY AND OVERALL, CHANCES FOR PRECIPITATION SHOULD INCREASE
ACROSS THE SOUTHERN PLAINS BY MIDWEEK AS AN UPPER LOW SETTLES OVER
THE SOUTHWEST/FOUR CORNERS AND THE INLAND RETURN OF GULF MOISTURE
INTERACTS WITH A WAVY LEAD FRONT. SOME OF THIS PRECIPITATION MAY
BE SNOW FROM THE SOUTHERN ROCKIES/HIGH PLAINS, WITH TYPICAL
ELEVATION/COVERAGE UNCERTAINTY. DETAILS OF PRECIPITATION
COVERAGE/AMOUNTS/TYPE WILL DEPEND ON THE UPPER LOW TRACK, WHICH AT
THIS TIME GUIDANCE SUGGESTS COULD BE ANYWHERE OVER THE CENTRAL OR
SOUTHERN PLAINS. IN THE CASE OF BOTH SNOW AND RAIN AREAS, SOME
TOTALS COULD BE LOCALLY HEAVY. MOST OF THE SOUTHERN HIGH PLAINS
REGION HAS FAIRLY DRY ANTECEDENT CONDITIONS AND SHORT-TERM
RAINFALL RATES DO NOT APPEAR TO BE HIGH ENOUGH TO MERIT
SIGNIFICANT RUNOFF CONCERNS. HOWEVER, INTRODUCED A WPC EXCESSIVE
RAINFALL "MARGINAL THREAT AREA OVER THE VICINITY OF THE TEXAS HILL
COUNTRY FOR DAY 5/FRIDAY GIVEN FAVORABLE SOUTHEAST UPSLOPE FLOW
LONGEVITY.
ACROSS FLORIDA, EXPECT EASTERLY FLOW TO SET UP SOUTH OF STRONG
EASTERN U.S. HIGH PRESSURE WHILE MOISTURE AND INSTABILITY INCREASE
FOR MIDWEEK AND BEYOND. THE DAY 4/WEDNESDAY AND DAY 5/THURSDAY
EXCESSIVE RAINFALL OUTLOOK MAINTAINS A MARGINAL RISK AREA FOR
SOUTHEASTERN FLORIDA GIVEN THESE INGREDIENTS FOR HEAVY RAINFALL
ARE IN PLACE ACROSS THE SENSITIVE URBAN CORRIDOR. THERE IS STILL
UNCERTAINTY OVER THE MAGNITUDE AND NORTHWARD EXTENT OF
INSTABILITY/DEEP MOISTURE THOUGH. THE SENSIBLE WEATHER FORECAST
OVER A BROADER PORTION OF THE SOUTH/EAST BECOMES INCREASINGLY
UNCERTAIN TOWARD NEXT FRIDAY-SATURDAY, GIVEN THE COMBINED SPREAD
FOR UPPER LEVEL TROUGHING EXPECTED TO REACH THE CENTRAL U.S.
(ANCHORED BY THE EMERGING WESTERN UPPER LOW BUT POSSIBLY
CONTAINING ENERGY APPROACHING FROM THE NORTHWEST) AND SOUTHERN
STREAM IMPULSES ALOFT ALONG WITH HOW THESE FEATURES MAY INFLUENCE
THE SURFACE PATTERN. THE MOST LIKELY SCENARIO WOULD HAVE SOME
RAINFALL EXTENDING EAST THROUGH THE MISSISSIPPI VALLEY AND BY THE
WEEKEND LIFTING NORTHWARD OVER THE SOUTHEAST, BUT WITH LOWER
TOTALS/COVERAGE THAN DEPICTED IN SOME RECENT GFS/GEFS RUNS.
OVER THE WEST, A WEAKENING FRONT MAY BRING SOME LIGHT
PRECIPITATION TO THE PACIFIC NORTHWEST AROUND MIDWEEK OR SO, WITH
ONLY LIGHT/SCATTERED ACTIVITY EXTENDING FARTHER INLAND BY
THURSDAY. INCREASING PRECIPITATION CHANCES ARE LESS LIKELY NOW FOR
CALIFORNIA NEXT WEEKEND AS AN EASTERN PACIFIC LOW PRESSURE SYSTEM
HOLDS MORE OFF THE COAST.
THE MOST ANOMALOUS TEMPERATURES DURING THE PERIOD WILL BE OF THE
WARM VARIETY ACROSS THE NORTHERN PLAINS AND UPPER MIDWEST FROM
WEDNESDAY ONWARD. MORE MODERATE WARMTH SHOULD ALSO EXTEND INTO THE
NORTHERN HALF TO TWO-THIRDS OF THE EAST LATER IN THE WEEK. EXPECT
DECENT COVERAGE OF TEMPERATURES 10F OR MORE ABOVE NORMAL AND
PORTIONS OF THE DAKOTAS INTO UPPER MIDWEST MAY BE 15-25F ABOVE
NORMAL THURSDAY INTO EARLY FRIDAY. MEANWHILE CLOUDS/PRECIPITATION
OVER AND NEAR THE SOUTHERN HIGH PLAINS MID-LATE WEEK WILL SUPPORT
A FAIRLY NARROW TEMPERATURE RANGE (ABOVE NORMAL LOWS, BELOW NORMAL
DAYTIME HIGHS). MUCH OF THE WEST WILL LIKELY SEE NEAR TO SLIGHTLY
ABOVE NORMAL TEMPERATURES DURING THE PERIOD.
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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