381
FXUS02 KWBC 210700
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
300 AM EDT SUN MAY 21 2023
VALID 12Z WED MAY 24 2023 - 12Z SUN MAY 28 2023
...WATCHING COASTAL FRONT/LOW FOR THE POSSIBILITY OF BRINGING
HEAVY RAIN TO THE SOUTHEAST/FLORIDA...
..PATTERN OVERVIEW AND GUIDANCE/PREDICTABILITY ASSESSMENT
MODELS AND ENSEMBLES REMAIN IN DECENT AGREEMENT THAT A WARMING
UPPER RIDGE NEXT WEEK WILL SHIFT SLOWLY EASTWARD OVER THE PLAINS
BEFORE NUDGING INTO THE MISSISSIPPI VALLEY/MIDWEST, WITH THE
ENTIRE PATTERN THEN BARELY MOVING THROUGH LATER NEXT WEEK.
EARLY-MID NEXT WEEK WILL ALSO SEE AN UPSTREAM UPPER TROUGH FORM
OVER THE NORTHWEST AS A NORTHEAST U.S. UPPER TROUGH LIFTS INTO THE
CANADIAN MARITIMES. ENERGIES SEPARATING FROM BOTH OF THESE UPPER
TROUGHS MAY AMPLIFY THE UPPER-AIR PATTERN TOWARD THE END OF NEXT
WEEK, WITH THE POSSIBILITY OF A CLOSED LOW DEVELOPING NEAR
CALIFORNIA, AND A BROADER TROUGH/CLOSED LOW DEVELOPING OVER THE
SOUTHEAST/FLORIDA.
MEANWHILE, NEAR AND JUST OFF THE SOUTHEAST AND INTO FLORIDA,
ENSEMBLE MEANS CONTINUE TO SUPPORT AN UPPER TROUGH/LOW TO LINGER
OVER THE VICINITY LATER WEEK AND INTO NEXT WEEKEND. GIVEN WARM
SEA-SURFACE TEMPERATURES ALONG THE GULF STREAM AND THE PRESENCE OF
A LINGERING FRONT, SOME OF THE DETERMINISTIC GUIDANCE HAS
OCCASIONALLY SPUN UP A TROPICAL SYSTEM OFF THE COAST OF THE
SOUTHEASTERN U.S. AND TRACKED IT TOWARD THE COAST BY THE MEMORIAL
DAY WEEKEND. THERE IS ALSO THE POSSIBILITY FOR ANOTHER PIECE OF
VORTICITY TO BREAK OFF OVER THE NORTHEAST AND THEN INTERACT WITH
WHAT MAY BE PRESENT FROM FLORIDA TO OFF THE SOUTHEAST U.S. COAST.
NEEDLESS TO SAY, UNCERTAINTY IS TOO HIGH TO PROVIDE THE SPECIFICS
AT THIS POINT. NONETHELESS, THERE APPEARS TO BE A HIGHER THAN
NORMAL CHANCE FOR THE HEAVY RAIN ASSOCIATED WITH THE SYSTEM TO
PUSH ONSHORE FROM THE EAST COAST OF FLORIDA TO THE SOUTHEAST AND
POSSIBILITY FARTHER UP THE EAST COAST AS WE HEAD CLOSER TO THE
MEMORIAL DAY WEEKEND.
OVERALL, THE WPC MEDIUM RANGE PRODUCT SUITE WAS PRIMARILY DERIVED
FROM A COMPOSITE BLEND OF SEEMINGLY BEST CLUSTERED AND REASONABLY
RUN TO RUN CONSISTENT GUIDANCE OF THE 18 UTC GFS/GEFS, 12 UTC
ECMWF/UKMET AND A COMPATIBLE 01 UTC NATIONAL BLEND OF MODELS (NBM)
FOR MID-LATER THIS WEEK IN A PATTERN WITH SEEMINGLY NEAR AVERAGE
PREDICTABILITY AND DECENT WPC PRODUCT CONTINUITY. SWITCHED
GUIDANCE PREFERENCE TO A BLEND OF BROADLY COMPATIBLE BLEND OF THE
GEFS/ECMWF ENSEMBLE MEANS AND NBM BY NEXT WEEKEND AMID MORE
RAPIDLY GROWING FORECAST SPREAD AND UNCERTAINTY.
..WEATHER/HAZARDS HIGHLIGHTS
IT REMAINS THE CASE THAT A SLOW-MOVING AND SOUTHERN STREAM
SEPARATED UPPER TROUGH OVER SOUTHEAST FOR MUCH OF NEXT WEEK WILL
BROADLY FAVOR PERIODS OF HEAVY MARITIME RAINS, BUT ALSO ONSHORE
FROM MAINLY ATLANTIC COASTAL PORTIONS OF THE SOUTHEAST/FLORIDA AS
SURFACE FRONTAL LOWS ROTATE IN PROXIMITY TO TAP DEEPENED POOLED
MOISTURE. DETAILS REMAIN UNCERTAIN AND THE NHC IS ADDITIONALLY
MONITORING POTENTIAL FOR ANY NON-FRONTAL LOW DEVELOPMENTS WITH
DEEPER TROPICAL MOISTURE. STRONG ONSHORE FLOW COULD BE EXPECTED TO
SET UP NORTH OF ANY OF THESE SURFACE LOWS WITH SUFFICIENT
DEVELOPMENT. OTHERWISE, THE AFOREMENTIONED MAIN UPPER RIDGE
POSITION SLOW TRANSLATION SHOULD SUPPORT SUMMERTIME TEMPERATURES
WITH VALUES UPWARDS TO 15-20 DEGREES ABOVE NORMAL INTO LATER WEEK
THAT SHOULD SPREAD SLOWLY EAST WITH TIME ACROSS THE NORTH-CENTRAL
U.S. TO THE MIDWEST INTO LATER NEXT WEEK. THE HEAT MAY BE TEMPERED
LOCALLY BY SCATTERED AND POTENTIALLY STRONG THUNDERSTORM ACTIVITY
BOTH WITH EJECTION OF IMPULSES FROM THE WEST AND WITH INTERACTION
WITH NORTHERN STREAM SYSTEM/FRONTAL APPROACHES FROM SOUTHERN
CANADA. LOCALLY HEAVY THUNDERSTORM ACTIVITY MAY ALSO FOCUS HEAVY
LOCAL DOWNPOURS DOWN OVER THE SOUTHERN PLAINS AS WELL WITH
MOISTURE/INSTABILITY POOLING WITH SOUTHERN STREAM IMPULSES. ABOVE
TO MUCH ABOVE NORMAL OVERNIGHT TEMPERATURES AND A PATTERN FAVORING
SCATTERED TO WIDESPREAD SHOWERS AND THUNDERSTORMS ARE ALSO
EXPECTED TO LINGER ALL NEXT WEEK OVER MUCH OF INTERIOR WEST
THROUGH THE ROCKIES IN MOISTENED FLOW CHANNELED BETWEEN WEST COAST
UPPER TROUGHING AND THE DOWNSTREAM CENTRAL U.S. UPPER RIDGE, WITH
DETAILS/LOCAL FOCUS DEPENDENT ON THE ULTIMATE SHAPE OF THE STILL
QUITE UNCERTAIN LATER WEEK UPPER TROUGH POSITION.
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, EXPERIMENTAL EXCESSIVE RAINFALL
OUTLOOK, WINTER WEATHER OUTLOOK PROBABILITIES AND HEAT INDICES 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
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