725
FXUS02 KWBC 230700
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
300 AM EDT TUE MAY 23 2023
VALID 12Z FRI MAY 26 2023 - 12Z TUE MAY 30 2023
...WATCHING COASTAL FRONT/LOW FOR THE POSSIBILITY OF BRINGING
HEAVY RAIN TO THE EASTERN SEABOARD...
..PATTERN OVERVIEW AND GUIDANCE/PREDICTABILITY ASSESSMENT
GUIDANCE GENERALLY AGREES THAT A WARMING UPPER RIDGE WILL SHIFT
VERY SLOWLY EASTWARD OVER THE PLAINS BEFORE NUDGING TOWARD THE
MISSISSIPPI VALLEY/MIDWEST BY THE WEEKEND. MEANWHILE, AMPLIFIED
TROUGHS MAY PROVE TOUGH TO DISLODGE ALONG BOTH THE WEST AND THE
EAST COASTS, RESULTING IN LITTLE OVERALL MOTION TO THE ENTIRE
SYNOPTIC PATTERN ACROSS THE U.S. THROUGH EARLY NEXT WEEK. WITHIN
THIS BLOCKY PATTERN, THERE HAVE BEEN CONSIDERABLE DIFFERENCES FROM
MODEL TO MODEL AND RUN TO RUN OVER THE PAST COUPLE OF DAYS.
UPSTREAM OF THE RIDGE OVER THE WEST-CENTRAL U.S., DIFFERENCES
LINGER LATE WEEK INTO THE WEEKEND WITH THE POTENTIAL/POSITIONING
FOR A LOW TO CLOSE OFF WITHIN THE MEAN TROUGH, BUT THE AXES OF THE
TROUGH ARE GENERALLY SIMILAR. FORECAST SPREAD INCREASES FROM THE
WEEKEND INTO EARLY NEXT WEEK, BUT RUN TO RUN CONTINUITY HAS
IMPROVED TO A DEGREE COMPARED TO THE PAST FEW DAYS. WHILE
PREDICTABILITY IS STILL ONLY BELOW TO NEAR AVERAGE WITH EMBEDDED
SYSTEMS, THE LARGER SCALE PATTERN WITH LINGERING CHANNELED
MOISTURE BETWEEN THE UPPER TROUGH AND DOWNSTREAM UPPER RIDGE
SHOULD FAVOR A PROTRACTED WET AND UNSETTLED PERIOD. QUITE A BIT OF
THIS WIDESPREAD CONVECTIVE ACTIVITY WILL ALSO SPILL OVER THE
ROCKIES AND DIG INTO THE PLAINS AS AIDED BY EJECTING IMPULSES AND
OVERALL FAVORABLE UPPER DIFFLUENCE AND INSTABILITY.
DOWNSTREAM OF THE RIDGE OVER THE EAST, TWO MAIN FORECAST CAMPS
HAVE EMERGED IN GUIDANCE. RECENT RUNS OF THE CANADIAN/NAVGEM AND
CANADIAN ENSEMBLES ALLOW UPPER TROUGH/LOW ENERGY TO LINGER INTO
THE HOLIDAY WEEKEND OVER THE NORTHEAST AND EVENTUALLY INTERACT
MORE WITH THE SOUTHEAST CLOSED UPPER TROUGH TO SUBSEQUENTLY AFFECT
THE EVOLUTION OF A WEATHER FOCUSING COASTAL LOW. THIS IS IN STARK
CONTRAST TO RECENT RUNS OF THE GFS/ECMWF/UKMET AND GEFS/ECMWF
ENSEMBLES EJECTS INTO THE CANADIAN MARITIMES FRIDAY AND HOLDS A
SLOW MOVING CLOSED UPPER LOW BACK IN SEPARATED SOUTHERN STREAM
FLOW OVER THE SOUTHEAST/SOUTHERN MID-ATLANTIC. THE PERISTENCE OF
THIS FEATURE WOULD FAVOR A SURFACE LOW NEAR THE SOUTHEAST COAST
AND DIRECT MOISTURE INTO THE MID-ATLANTIC REGION THAT COULD BE
LONG-LASTING THROUGH THE HOLDIDAY WEEKEND. RAINFALL AMOUNTS ARE
TRENDING UPWARDS AND CREEPING INLAND. THIS EVOLUTION MAKES IT LESS
LIKELY AN ASSOCIATED SURFACE LOW WILL HAVE TROPICAL
CHARACTERISTICS AS PER NHC, AND THIS IS CONSISTENT WITH THE
CYCLONE PHASE SPACE DIAGRAMS FROM MULTIPLE MODELS SHOWING AN
ASYMMETRIC COLD-CORE LOW. A SEPARATE SURFACE LOW THAT THE NATIONAL
HURRICANE CENTER IS TRACKING FOR ANY POSSIBLE TROPICAL/SUBTROPICAL
DEVELOPMENT LOOKS TO EJECT FROM THE BAHAMAS NORTH AND NORTHEAST
AWAY FROM THE LOWER 48 BY THURSDAY-FRIDAY.
OVERALL, THE WPC MEDIUM RANGE PRODUCT SUITE WAS PRIMARILY DERIVED
FROM A COMPOSITE BLEND OF BEST CLUSTERED GUIDANCE OF THE 18 UTC
GFS/GEFS MEAN, 12 UTC ECMWF/UKMET/ECMWF ENSEMBLE MEAN AND A
COMPATIBLE 01 UTC NATIONAL BLEND OF MODELS (NBM) THROUGH THE
FORECAST PERIOD IN A PATTERN WITH BELOW AVERAGE PREDICTABILITY.
DESPITE UNCERTAINTIES, THIS SOLUTION OFFERS A REASONABLY GOOD
MATCH WITH WPC PRODUCT CONTINUITY FOR MUCH OF THE LOWER 48 AND
FITS BEST WITH LATEST NHC/WPC OFFSHORE SYSTEM COLLABORATIONS AND
EXPECTATIONS. THE 00 UTC GUIDANCE CYCLE MAINTAINED PRIOR TRENDS.
..WEATHER/HAZARDS HIGHLIGHTS
SHOWERS AND STORMS ARE LIKELY OVER FLORIDA LATE THIS WEEK WITH THE
POTENTIAL FOR A DEVELOPING SURFACE LOW SYSTEM. RAIN MAY SPREAD UP
PARTS OF THE EASTERN SEABOARD DEPENDENT ON THE LOW TRACK. THE
LATEST FORECAST OFFERS INCREASING POTENTIAL FOR HEAVY AMOUNTS TO
REACH THE COASTAL CAROLINAS BY FRIDAY, THEN LINGERING. THE WPC
EXPERIMENTAL DAY 4/5 EXCESSIVE RAINFALL OUTLOOK (ERO) PLANS TO ADD
A "MARGINAL" RISK AREA TO ADDRESS. THEN AMPLE MOISTURE MAY BE
FURTHER DIRECTED INTO THE MID-ATLANTIC THIS WEEKEND ON THE
EAST/NORTH SIDES OF THE POTENTIAL SOUTHEAST UPPER LOW FORMING.
AMOUNTS AND PLACEMENT REMAIN UNCERTAIN AT THIS POINT THOUGH. BEACH
HAZARDS FOR THE UPCOMING MEMORIAL DAY WEEKEND MAY NOT BE RULED OUT
EITHER CONSIDERING THIS PATTERN, WITH POTENTIAL FOR GUSTY WINDS
AND UNSETTLED MARITIME CONDITIONS. SHOWERS AND STORMS MAY FORM
FARTHER INLAND ACROSS THE TENNESSEE VALLEY AND VICINITY TOO. WITH
THE UPPER TROUGH/LOW AND THE POTENTIAL CLOUDINESS AND RAIN
CHANCES, TEMPERATURES ARE LIKELY TO BE COOLER THAN NORMAL ON
AVERAGE DURING THE PERIOD ACROSS MUCH OF THE EAST.
OTHERWISE, THE AFOREMENTIONED MAIN UPPER RIDGE POSITION SLOW
TRANSLATION SHOULD SUPPORT SUMMERTIME TEMPERATURES WITH VALUES
UPWARDS TO 10-15 DEGREES ABOVE NORMAL INTO LATE WEEK THAT SHOULD
PROVE SLOW TO SPREAD SLOWLY EAST WITH TIME ACROSS THE
NORTH-CENTRAL U.S. TO THE MIDWEST. 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 ROCKIES AND HIGH PLAINS AS WELL WITH
MOISTURE/INSTABILITY POOLING AHEAD OF A GENERAL DRYLINE PATTERN
WITH SOUTHERN STREAM IMPULSES UNDER FAVORABLE UPPER DIFFLUENCE AND
INSTABILITY. ABOVE TO MUCH ABOVE NORMAL OVERNIGHT TEMPERATURES AND
A PATTERN FAVORING SCATTERED TO WIDESPREAD SHOWERS AND
THUNDERSTORMS ARE ALSO EXPECTED TO LINGER ALL 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. SINCE MOISTURE LEVELS WILL BE ABOVE AVERAGE AND
MOISTURE SHOULD BE POOLING AHEAD OF SLOW-MOVING FRONTS/BOUNDARIES,
PLAN TO MAINTAIN AND EXTEND BROAD "MARGINAL" RISKS FOR THE NEW
DAYS 4-5 (FRIDAY-SATURDAY) ERO PERIODS ACROSS MUCH OF THE HIGH
PLAINS AND BACK TOWARD THE NORTHERN ROCKIES FOR SOME POTENTIAL FOR
FLASH FLOODING WITH SOME DOWNPOURS OF HEAVY RAIN THAT COULD BE
SLOW-MOVING. THE DETAILS AND LOCAL FOCUS WILL BE DEPENDENT ON THE
ULTIMATE SHAPE OF THE STILL QUITE UNCERTAIN LATER WEEK UPPER
TROUGH POSITIONS AND FLOW INTERACTIONS.
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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