754
FXUS02 KWBC 211902
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
300 PM 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 WARM UPPER
RIDGE WILL SHIFT VERY SLOWLY EASTWARD OVER THE PLAINS BEFORE
NUDGING TOWARD THE MISSISSIPPI VALLEY/MIDWEST BY THE WEEKEND.
MEANWHILE, FAIRLY AMPLIFIED TROUGHS WILL BE ANCHORED ALONG BOTH
THE WEST AND THE EAST COASTS, RESULTING IN LITTLE OVERALL MOTION
TO THE ENTIRE SYNOPTIC PATTERN ACROSS THE U.S. A NOTABLE TREND
SHOWN BY THE DETERMINISTIC MODEL RUNS SINCE YESTERDAY IS THE
INTRODUCTION OF THE IDEA OF A DEEPER CLOSED LOW FORMING BETWEEN
THE GREAT LAKES AND NEW ENGLAND NEAR THE SOUTHERN END OF AN
AMPLIFIED TROUGH. THE PRESENCE OF THIS UPPER LOW WOULD ENHANCE
THE FRONTAL CHARACTERISTICS ALONG THE EAST COAST AND THEREBY
INCREASE THE CHANCE OF INTERACTION WITH ANOTHER UPPER LOW THAT IS
FORECAST TO FORM IN THE VICINITY OF THE SOUTHEAST/FLORIDA LATE
THIS WEEK. UNCERTAINTY REMAINS 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 TWO UPPER
LOWS (OR THE MERGER OF THE TWO) TO PUSH ONSHORE FROM THE EAST
COAST OF FLORIDA TO THE SOUTHEAST AND POSSIBLY FARTHER UP THE EAST
COAST AS WE HEAD INTO THE MEMORIAL DAY WEEKEND.
ALONG THE WEST COAST, MODELS HAVE SETTLED INTO THE IDEA OF A
CLOSED LOW MOVING SLOWLY ACROSS CALIFORNIA FOR THE LATTER HALF OF
NEXT WEEK. THE NEXT UPPER TROUGH IS FORECAST TO REACH THE PACIFIC
NORTHWEST BY THE MEMORIAL DAY WEEKEND WITH QUITE A BIT OF
UNCERTAINTY IN ITS DEPTH.
A COMPOSITE BLEND WAS USED TO COMPOSE THE WPC FORECAST PACKAGE
BASED ON 40% FROM THE 00Z ECMWF/EC MEAN, 20% FROM THE 00Z CMC/CMC
MEAN, WITH THE REMAINING PORTIONS BASED MAINLY ON THE 06Z GEFS
MEAN. THIS OVERALL SOLUTION MAINTAINS BROADLY GOOD WPC PRODUCT
CONTINUITY.
..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. MEANWHILE, WITH THE MODELS TRENDING TOWARD THE
SCENARIO OF A DEEPER UPPER LOW BETWEEN THE GREAT LAKES AND NEW
ENGLAND, DETERMINISTIC GUIDANCE IS NOW INDICATING THE POSSIBILITY
OF A SLUG OF HEAVY RAIN ACROSS NORTHERN NEW ENGLAND BY THURSDAY ON
THE SOUTHEASTERN PERIPHERY OF THE DEEPENING UPPER LOW. SINCE
MODELS HAVE NOT YET SETTLED INTO A STABLE SOLUTION REGARDING THIS
UPPER LOW, NO FLASH FLOODING RISK AREAS HAVE BEEN PROPOSED AT THIS
POINT.
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.
KONG/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
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page