731
FXUS02 KWBC 131906
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
205 PM EST WED DEC 13 2023
VALID 12Z SAT DEC 16 2023 - 12Z WED DEC 20 2023
...A WET PATTERN IS LIKELY OVER THE SOUTH/SOUTHEAST AND
POTENTIALLY UP THE EAST COAST THIS WEEKEND INTO NEXT WEEK...
..OVERVIEW
A SOUTHERN STREAM UPPER LOW TRAVERSING THE SOUTH-CENTRAL TO
SOUTHEASTERN U.S. INTERACTING WITH NORTHERN STREAM ENERGY THIS
WEEKEND INTO EARLY NEXT WEEK WILL PROVIDE SUPPORT FOR A SURFACE
LOW TO STRENGTHEN AND SPREAD WIDESPREAD HEAVY RAINFALL ACROSS
FLORIDA ON SATURDAY. HEAVY RAIN MAY SPREAD UP THE EAST COAST INTO
EARLY NEXT WEEK, BUT ITS PLACEMENT REMAINS QUITE UNCERTAIN GIVEN
MODEL DIFFERENCES IN THE UPPER LEVELS AND THE SURFACE LOW TRACK.
BEHIND THESE FEATURES, DRY UPPER RIDGING WILL BUILD INTO THE
INTERIOR WEST AHEAD OF A MEAN EASTERN PACIFIC TROUGH AXIS THAT
SHOULD PUSH PERIODIC PRECIPITATION INTO THE WEST COAST STATES.
..GUIDANCE/PREDICTABILITY ASSESSMENT
THERE IS FAIRLY GOOD AGREEMENT ON THE TWO STREAMS OF ENERGY ACROSS
THE MIDWEST AND THE SOUTH, THE INTERACTION OF WHICH SHOULD INDUCE
CYCLOGENESIS ACROSS THE SOUTHEAST GULF OF MEXICO ON SATURDAY WHICH
TRACKS ACROSS FLORIDA INTO SUNDAY. THERE REMAINS HOWEVER A LOT OF
UNCERTAINTY IN THE DETAILS OF THIS INTERACTION, AND ALSO WITH
ADDITIONAL WEAKER ENERGY IN THE GULF. THE MODELS STRUGGLE RUN TO
RUN AND MODEL TO MODEL ON THE INTERACTION BETWEEN THESE THREE
FEATURES WHICH HAVE HUGE IMPLICATIONS FOR EXACT SURFACE LOW
TRACK/PLACEMENT AND HEAVY RAINFALL POTENTIAL ACROSS THE SOUTHEAST
AND INTO THE MID-ATLANTIC AND THE NORTHEAST AS WELL. BASED ON THE
12Z GUIDANCE FOR TODAY THOUGH, THERE DOES SEEM TO BE SOME TREND
TOWARDS A SURFACE LOW TRACK CLOSER TO THE COAST (OR POSSIBLY EVEN
INLAND) ACROSS THE SOUTHEAST AND MID-ATLANTIC. BY MONDAY-TUESDAY,
ADDITIONAL ENERGY DROPPING IN FROM THE MIDWEST LOOKS TO REINFORCE
SOME KIND OF TROUGHING STILL OFF THE SOUTHEAST COAST, WITH SOME
SUPPORT FOR SURFACE LOW PRESSURE TO LINGER OFF THE COAST INTO NEXT
WEEK. THE 06Z GFS FAVORED THIS SOLUTION MOST, BUT ITS NEW 12Z RUN
TODAY BACKED OFF ON THIS IDEA. THE CMC AND ECMWF SHOW THE LOW
RACING NORTHWARD UP THE EAST COAST. THE VARIOUS ENSEMBLE GUIDANCE
OFFERS A LOT OF SPREAD ALL THE WAY UP THE EAST COAST, BUT BOTH THE
EC AND GEFS MEANS DO SUPPORT SOME SORT OF WEAK AREA OF LOW
PRESSURE LINGERING OFF THE COAST. THE WPC FORECAST FOR TODAY
TRENDED MOSTLY TOWARDS THE ENSEMBLE MEANS THE SECOND HALF OF THE
PERIOD, WITH SOME BLENDING OF THE PREVIOUS SHIFT CONTINUITY TOO,
BUT THIS IS A VERY LOW CONFIDENCE FORECAST AND HIGHLY DEPENDING ON
EXACT STREAM/ENERGY INTERACTIONS WHICH COULD TAKE UNTIL THE SHORT
RANGE PERIOD TO FULLY RESOLVE.
OUT WEST, THERE IS A LOT OF UNCERTAINTY WITH TROUGHING OFF THE
WEST COAST, BUT THE 12Z GUIDANCE FOR TODAY DOES SHOW BETTER
SUPPORT FOR A CUT OFF UPPER LOW DEEPENING AS IT MOVES TOWARDS THE
CALIFORNIA COAST MID-NEXT WEEK. LOTS OF QUESTIONS STILL ON
PLACEMENT OF THIS FEATURE AND EFFECTS ON HEAVY RAINFALL POTENTIAL
ACROSS PARTS OF CALIFORNIA AS WELL.
..WEATHER/HAZARDS HIGHLIGHTS
AMPLE MOISTURE WITH PRECIPITABLE WATER VALUES LIKELY WELL OVER THE
90TH PERCENTILE WILL BE IN PLACE ACROSS FLORIDA AS THE SOUTHERN
STREAM UPPER LOW ENHANCES LIFT AND DEVELOPS A SURFACE LOW. THESE
FACTORS WILL LEAD TO WIDESPREAD HEAVY RAINFALL OF 2-4 INCHES WITH
LOCALLY HIGHER AMOUNTS LIKELY. A SLIGHT RISK CONTINUES ON DAY
4/SATURDAY IN THE EXCESSIVE RAINFALL OUTLOOK, AS RAINFALL OF THIS
MAGNITUDE WITH SOME HIGH RAIN RATES COULD CAUSE INSTANCES OF FLASH
FLOODING. HEAVY RAIN AND FLOODING MAY BE A CONCERN FOR THE LOWER
MISSISSIPPI VALLEY AS WELL ON SATURDAY IN THE VICINITY OF ANOTHER
FRONTAL SYSTEM. A MARGINAL RISK CONTINUES TO COVER THIS POTENTIAL
AS RECENT MODELS HAVE TRENDED UP WITH RAINFALL ONSHORE, THOUGH
THERE IS STILL A CHANCE THAT MOST COULD FALL OFFSHORE IN THE
CENTRAL GULF. BY SUNDAY, INCREASING MODEL SPREAD MAKES RAINFALL
TOTALS AND PLACEMENT VERY UNCERTAIN. THE WPC PRECIPITATION
FORECAST IS REFLECTIVE OF THE MODEL PREFERENCE FOR A LOW MOVING
NORTHEASTWARD INTO THE FAR WESTERN ATLANTIC, FOCUSING RAINFALL
FROM GEORGIA INTO THE CAROLINAS AND THE MID-ATLANTIC BUT THE
LATEST 12Z GUIDANCE SHOWS BETTER SUPPORT FOR HEAVIER RAINFALL EVEN
FARTHER INLAND. FOR THE DAY 5 ERO, THERE WAS ENOUGH AGREEMENT (AND
SUPPORT FROM WFOS ILM, MHX, AND AKQ) FOR A SLIGHT RISK ACROSS FAR
EASTERN NORTH CAROLINA TO SOUTHEAST VIRGINIA. A MARGINAL RISK
SURROUNDS THIS EXTENDING FROM NORTHEAST FLORIDA, ACROSS MUCH OF
THE SOUTHEAST, AND INTO THE EASTERN MID-ATLANTIC REGION WHERE THE
INLAND EXTENT FOR HEAVY RAIN IMPACTS ARE MUCH MORE UNCERTAIN.
HEAVY RAIN COULD ALSO SPREAD INTO THE THE NORTHEAST ON MONDAY
DEPENDING ON THE SURFACE LOW TRACK, WITH MODELS AS OF NOW SHOWING
SOME AGREEMENT ON THIS POTENTIAL ACROSS EASTERN NEW ENGLAND.
PRECIPITATION CHANCES WILL BE INCREASING OVER THE WEEKEND FOR
CALIFORNIA AS SHORTWAVE ENERGY SUPPORTING A POSSIBLE ATMOSPHERIC
RIVER APPROACHES. RAIN AMOUNTS AND RATES ON SUNDAY COULD BE
SUFFICIENT TO CAUSE SOME FLOODING CONCERNS, ESPECIALLY GIVEN SOME
INSTABILITY COULD REACH COASTAL AREAS, SO A MARGINAL RISK IS IN
PLACE IN THE ERO. PRECIPITATION LOOKS TO PERSIST ACROSS CALIFORNIA
AND REACH THE PACIFIC NORTHWEST INTO MONDAY-TUESDAY, INCLUDING
SOME HIGHER ELEVATION SNOW, THOUGH CONFIDENCE IN THE DETAILS
REMAINS SOMEWHAT LOW. THE INTERIOR WEST TO THE PLAINS WILL BE THE
DRY SPOT OVER THE LOWER 48 THROUGH THE FIRST HALF OF NEXT WEEK.
THE NORTHERN TWO-THIRDS OF THE LOWER 48 SHOULD SEE NEAR TO ABOVE
NORMAL TEMPERATURES THIS WEEKEND INTO EARLY NEXT WEEK, WITH
TEMPERATURES 10-20F ABOVE AVERAGE PERIODICALLY AFFECTING THE
NORTHERN/CENTRAL HIGH PLAINS INTO THE UPPER MIDWEST. THE WEST CAN
ALSO EXPECT GENERALLY ABOVE NORMAL TEMPERATURES UNDERNEATH UPPER
RIDGING. COOLER THAN NORMAL TEMPERATURES WILL BE LIMITED TO THE
SOUTHERN PLAINS (IN TERMS OF HIGHS) EASTWARD INTO THE SOUTHEAST
THIS WEEKEND, MODERATING CLOSER TO NORMAL BY EARLY NEXT WEEK,
THOUGH FLORIDA COULD STILL SEE BELOW NORMAL HIGHS BEHIND MULTIPLE
FRONTAL PASSAGES.
SANTORELLI/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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