384
FXUS02 KWBC 090658
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
258 AM 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
AN 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 ACROSS 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
THE 00Z MODEL GUIDANCE SUITE FEATURES VERY GOOD SYNOPTIC SCALE
AGREEMENT, WITH A MULTI-DETERMINISTIC MODEL BLEND SUFFICING AS A
STARTING POINT IN THE FORECAST PROCESS. THE LATEST CMC RUN IS NOW
IN BETTER ALIGNMENT WITH THE MODEL CONSENSUS COMPARED TO THE 12Z
RUN THAT WAS DISPLACED TO THE EAST WITH THE WESTERN U.S. TROUGH. BY
THURSDAY, THE CMC BECOMES MORE AMPLIFIED WITH THE UPPER TROUGH NEAR
THE EAST COAST, AND STRONGER WITH THE CLOSED LOW NEAR NORTH DAKOTA
GOING INTO FRIDAY. THE 00Z GFS TRENDED LESS AMPLIFIED WITH THE
TROUGH AXIS NEAR THE CALIFORNIA COAST COMPARED TO ITS 18Z RUN FOR
THE END OF THE WEEK. THE GFS/ECMWF SOLUTIONS WERE GENERALLY CLOSER
TO THE AIFS GUIDANCE WITH THE FRONT AND LOW PRESSURE SYSTEM ACROSS
THE NORTH-CENTRAL U.S., SO THE SECOND HALF OF THE FORECAST PERIOD
WAS HEDGED MORE IN THAT DIRECTION, WITH THE ENSEMBLE MEANS
INCREASED TO ABOUT HALF BY FRIDAY.
..WEATHER/HAZARDS HIGHLIGHTS
THE SLOW MOVING OCCLUDED SURFACE LOW AND ASSOCIATED UPPER LOW WILL
RESULT IN A STRONG INFLUX OF DEEP MOISTURE FROM THE WESTERN
ATLANTIC AND RESULT IN MULTIPLE 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 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) AS THE MOISTURE PLUME SLOWLY WORKS ITS WAY NORTH
WHILE PROBABLY WEAKENING SOME.
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 NORTHERN ROCKIES GOING
INTO THE MIDDLE OF THE WEEK WITH SOME OF THE HIGHER RANGES PICKING
UP SEVERAL INCHES OF 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
NOT EXPECTED TO BE HEAVY ENOUGH TO WARRANT ANY EXCESSIVE RAINFALL
RISK AREAS AT THIS TIME.
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
CONDITIONS ARE FORECAST FOR THE INTERMOUNTAIN WEST WITH THE UPPER
TROUGH MOVING IN, WITH HIGHS RUNNING 10-20 DEGREES BELOW MID-MAY
AVERAGES IN SOME CASES.
HAMRICK
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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