064
FXUS02 KWBC 091830
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
230 PM EDT FRI MAY 9 2025
VALID 12Z MON MAY 12 2025 - 12Z FRI MAY 16 2025
..MULTI-DAY SOUTHEAST U.S. HEAVY RAINFALL/FLOODING THREAT
..GENERAL OVERVIEW
A SLOW MOVING AND WELL DEFINED UPPER LOW DEVELOPING OVER THE
INTERIOR SOUTHEAST U.S. GOING INTO EARLY NEXT WEEK WILL MAKE
WEATHER HEADLINES WITH PERIODS OF HEAVY RAINFALL FROM FLORIDA TO
THE MID-ATLANTIC THROUGH WEDNESDAY. OUT WEST, A POTENT TROUGH WITH
EMBEDDED CLOSED UPPER LOW WILL MOVE INLAND AND AFFECT THE WEST
COAST AND INTERMOUNTAIN WEST WITH COLDER TEMPERATURES AND MOUNTAIN
SNOW INLAND TO THE ROCKIES. VERY WARM AND DRY CONDITIONS ARE
EXPECTED ACROSS THE PLAINS THROUGH MIDWEEK WITH AN UPPER RIDGE
EXTENDING NORTH ACROSS THE UPPER MIDWEST, WITH A COLD FRONT SLOWLY
APPROACHING FROM THE WEST AND BRINGING A RETURN TO MORE SEASONAL
CONDITIONS BY THE END OF THE WEEK.
..GUIDANCE/PREDICTABILITY ASSESSMENT
RECENT MODEL AND ENSEMBLE GUIDANCE HAS BEEN IN OVERALL VERY GOOD
SYNOPTIC SCALE AGREEMENT THROUGH MEDIUM RANGE TIME SCALES, ALBEIT
WITH LINGERING SMALLER SCALE SYSTEM SPECIFIC VARIANCES THAT HAVE
VARIED FROM RUN TO RUN. A MULTI-DETERMINISTIC MODEL BLEND COUPLED
WITH WPC CONTINUITY AND THE NATIONAL BLEND OF MODELS SEEMS TO OFFER
A SOLID FORECAST AND THREAT MESSAGING STARTING POINT, WITH THE
COMPOSITE TENDING TO MITIGATE DIFFERENCES AS CONSISTENT WITH
INDIVIDUAL PREDICTABILITY.
..WEATHER/HAZARDS HIGHLIGHTS
THE SLOW MOVING OCCLUDED SURFACE LOW AND ASSOCIATED UPPER LOW WILL
RESULT IN A STRONG INFLUX OF DEEP MOISTURE FROM THE GULF AND WESTERN
ATLANTIC AND RESULT IN MULTIPLE SUSTAINED ROUNDS OF MODERATE TO
HEAVY RAINFALL EXTENDING FROM NORTHERN FLORIDA TO THE MID-ATLANTIC
REGION. IN PARTICULAR, ENHANCED MOISTURE FLUX WITH UPSLOPE
COMPONENT ACROSS THE SOUTHERN APPALACHIANS ON MONDAY (DAY 4) WILL
LIKELY RESULT IN HIGHER RAINFALL TOTALS ACROSS WESTERN SC/NC, AND
THERE IS THE POTENTIAL THAT A MODERATE RISK AREA MAY BE NEEDED AS
THIS EVENT ENTERS THE SHORT RANGE FORECAST PERIOD. HOWEVER, FOR THE
TIME BEING, A SLIGHT RISK AREA STILL REMAINS VALID FROM
SOUTHWESTERN VIRGINIA TO THE NORTHERN FLORIDA PENINSULA, AND A
MARGINAL RISK AREA ACROSS MUCH OF NORTH CAROLINA INTO THE MID-
ATLANTIC FOR TUESDAY (DAY 5), LINGERING INTO WEDNESDAY, AS THE
MOISTURE PLUME SLOWLY WORKS ITS WAY NORTH WHILE SLOWLY WEAKENING.
OUT WEST, RAIN AND HIGHER ELEVATION SNOWS WILL BECOME MORE
WIDESPREAD INTO NEXT WEEK WITH THE AMPLIFIED UPPER LOW PASSING
THROUGH. THIS ESPECIALLY HOLDS TRUE FOR THE SIERRA EARLY AND INTO
THE NORTHERN ROCKIES GOING INTO THE MIDDLE OF NEXT WEEK WITH SOME
OF THE HIGHER RANGES PICKING UP ENHANCED LATE SEASON SNOWFALL. AS
THE SYSTEM PROGRESSES EAST, MODERATE TO LOCALLY HEAVY RAINFALL MAY
DEVELOP ON THE NORTH AND WEST SIDE OF A SURFACE LOW OVER THE NORTH-
CENTRAL PLAINS, BUT FOR THE MOST PART NOT EXPECTED TO BE HEAVY
ENOUGH TO WARRANT ANY EXCESSIVE RAINFALL RISK AREAS AT THIS TIME,
BUT WILL BE MONITORED.
AN EARLY SEASON HEATWAVE IS LIKELY ACROSS THE DAKOTAS AND INTO
MINNESOTA EARLY IN THE WEEK AS THIS REGION WILL BE IN THE WARM
SECTOR OF A DEVELOPING SURFACE LOW. TEMPERATURES WILL BE THE
WARMEST OF THE SEASON THUS FAR WITH HIGHS REACHING THE UPPER 80S TO
POTENTIALLY MIDDLE 90S, AND EASILY SETTING SOME DAILY RECORD HIGHS.
IT WILL ALSO BE HOT ACROSS MUCH OF TEXAS WITH SOME 100+ DEGREE
READINGS EXPECTED NEAR THE RIO GRANDE. WARMER TEMPERATURES ARE ALSO
COMING TO MUCH OF THE EASTERN U.S. BY THE END OF THE WEEK, WITH
HUMIDITY LEVELS ALSO INCREASING. IN CONTRAST, UNSEASONABLY COOL
AND UNSETTLED CONDITIONS ARE FORECAST FOR THE INTERMOUNTAIN WEST
WITH THE AMPLIFIED UPPER TROUGH MOVING IN, WITH HIGHS RUNNING
10-20 DEGREES BELOW MID-MAY AVERAGES IN SOME CASES.
HAMRICK/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 FORECAST (QPF), EXCESSIVE RAINFALL
OUTLOOK (ERO), WINTER WEATHER OUTLOOK (WWO) PROBABILITIES, HEAT
INDICES, AND KEY MESSAGES CAN BE ACCESSED FROM:
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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