913
FXUS02 KWBC 221900
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
300 PM EDT MON MAY 22 2023
VALID 12Z THU MAY 25 2023 - 12Z MON MAY 29 2023
...WATCHING COASTAL FRONT/LOW FOR THE POSSIBILITY OF BRINGING
HEAVY RAIN TO THE EASTERN SEABOARD...
..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. 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. FIRST, THE 00Z/06Z MODEL CYCLE TRENDED TOWARD A
DIFFERENT EVOLUTION OF ENERGY WITHIN THE EASTERN TROUGH COMPARED
TO PREVIOUS CYCLES. NAMELY, AT THE START OF THE PERIOD
THURSDAY-FRIDAY, AN UPPER LOW PRESENT OVER SOUTHEASTERN CANADA NOW
LOOKS TO SHIFT NORTHEAST AWAY FROM THE FORECAST DOMAIN (THOUGH
WITH VARIED TIMING--GFS SUITE FASTER). BUT WEAKER ENERGIES WEST OF
THIS LOW MAY DIVE SOUTH AND ARE THE ONES TO SPIN UP AN UPPER LOW
IN THE SOUTHEAST BY THE WEEKEND AND LINGERING INTO EARLY NEXT
WEEK--AT LEAST THIS IS WHAT THE BULK OF MORE RECENT GUIDANCE HAS.
IN PREVIOUS MODEL CYCLES THE ORIGINAL SOUTHEASTERN CANADA LOW
SEEMED TO BE THE ONE TO LINGER OVER THE NORTHEAST AND POSSIBLY
DIRECT MOISTURE THERE. CMC RUNS FROM 00Z AND THE NEWER 12Z RUN
MAINTAIN THIS ORIGINAL LOW LONGER, BUT THE GFS/ECMWF/UKMET ARE
SHOWING THIS NEWER TREND. IF THIS UPPER LOW FORMS AND SPINS OVER
THE SOUTHEAST, THIS COULD PRODUCE A SURFACE LOW NEAR THE SOUTHEAST
COAST AND DIRECT MOISTURE INTO THE MID-ATLANTIC REGION THAT COULD
BE LONG-LASTING LATE THIS WEEK INTO EARLY NEXT WEEK. THE WPC
FORECAST TRENDED UP WITH QPF IN THE MID-ATLANTIC REGION THOUGH NOT
AS HIGH AS SOME MODEL GUIDANCE, GIVEN THIS MODEL TREND IS PRETTY
NEW. THIS EVOLUTION MAKES IT LESS LIKELY AN ASSOCIATED SURFACE LOW
WILL HAVE ANY TROPICAL CHARACTERISTICS, AND THIS IS CONSISTENT
WITH THE CYCLONE PHASE SPACE DIAGRAMS FROM MULTIPLE MODELS SHOWING
AN ASYMMETRIC COLD-CORE LOW. THE 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.
WITH THE UPPER LOW POTENTIALLY SETTING UP OVER THE SOUTHEAST, THE
RIDGE TO ITS WEST MAY BREAK OFF AN UPPER HIGH TO THE LOW'S NORTH
EARLY NEXT WEEK.
MEANWHILE IN THE WEST, THERE ARE SOME DIFFERENCES LATE WEEK WITH
THE POTENTIAL FOR A LOW TO CLOSE OFF WITHIN THE TROUGH OR NOT, BUT
THE AXES OF THE TROUGH ARE GENERALLY SIMILAR. BY THIS WEEKEND AND
BEYOND THOUGH, MODELS DIVERGE QUITE A BIT AS DIFFERENCES IN ENERGY
TRACKING OUT FROM THE GULF OF ALASKA LEADING TO HORRENDOUS RUN TO
RUN CONTINUITY AND PREDICTABILITY. IN GENERAL THOUGH, ADDITIONAL
TROUGHING IS LIKELY OVER THE WEST, AS SHOWN BY THE MORE AGREEABLE
ENSEMBLE MEANS, WITH SOME UNSETTLED WEATHER CONTINUING. DID THINK
THE 00Z ECMWF MAY HAVE BEEN AN OUTLIER BY EARLY NEXT WEEK WITH
HOLDING A STRONG UPPER LOW OFFSHORE, AND THE 12Z ECMWF HAS TRENDED
AWAY FROM THAT SOLUTION AND CLOSER TO OTHER MODELS/ENSEMBLES.
GIVEN THESE MODEL DIFFERENCES, THE WPC FORECAST UTILIZED A
MULTI-MODEL MAINLY DETERMINISTIC BLEND EARLY IN THE PERIOD, BUT
TRANSITIONED FAIRLY QUICKLY TO AN ENSEMBLE MEAN-HEAVY BLEND BY
DAYS 6-7 CONSIDERING THE INCREASING MODEL SPREAD AND UNCERTAINTY.
THE INCOMING 12Z MODEL CYCLE IS GENERALLY FOLLOWING THE 00Z/06Z
MODEL TRENDS IN THE EAST BY SHOWING A SOUTHEAST UPPER LOW, ADDING
A BIT OF CONFIDENCE IN THIS PATTERN, BUT PREFER TO SEE ANOTHER
MODEL CYCLE OR TWO BEFORE FEELING COMFORTABLE WITH TOO MANY
FORECAST CHANGES.
..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
RECENT FORECAST KEEPS HEAVY RAINFALL OFFSHORE OF THE CAROLINAS ON
THURSDAY WITH SOME POTENTIAL FOR HEAVY AMOUNTS TO REACH THE NORTH
CAROLINA COAST ON FRIDAY. THEN AMPLE MOISTURE MAY BE 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 15-20 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 CENTRAL TO SOUTHERN ROCKIES/PLAINS
AS WELL WITH MOISTURE/INSTABILITY POOLING AHEAD OF A GENERAL
DRYLINE PATTERN 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 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 INTRODUCE LARGE MARGINAL
RISKS IN THE DAYS 4-5 (THURSDAY-FRIDAY) ERO 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.
TATE/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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