732
FXUS02 KWBC 101900
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
300 PM EDT SAT MAY 10 2025
VALID 12Z TUE MAY 13 2025 - 12Z SAT MAY 17 2025
...EXCESSIVE RAIN/FLOODING THREAT FOR THE MID-ATLANTIC/APPALACHIANS
AND NORTHERN ROCKIES/PLAINS SPRING STORM INTO TUESDAY/WEDNESDAY...
..GENERAL OVERVIEW
A DEEPLY MOIST CLOSED LOW/SYSTEM MEANDERING OVER THE SOUTH FOR THE
NEXT COUPLE OF DAYS REMAINS SLATED TO SLOWLY WEAKEN AND GRADUALLY
LIFT NORTHEASTWARD TUESDAY/WEDNESDAY TO SHIFT HEAVY RAIN/FLOODING
MAIN IMPACTS OVER THE MID-ATLANTIC/SOUTH-CENTRAL APPALACHIANS.
OUT WEST, A POTENT TROUGH WITH EMBEDDED CLOSED UPPER LOW WILL MOVE
STAEDILY INLAND FROM THE WEST COAST TO AFFECT THE INTERMOUNTAIN
WEST WITH COLDER TEMPERATURES, WITH HEAVY MOUNTAIN SNOWS ONWARD TO
THE NORTH-CENTRAL ROCKIES. DOWNSTREAM ACTIVITY WILL BE ENHANCED BY
NORTH-CENTRAL PLAINS CYCLOGENESIS AND WELL-DEFINED WRAP-BACK
MOISTURE FEED. LEAD MOISTURE/INSTABILITY INFLUX UP THROUGH THE
PLAINS ALSO OFFERS A THREAT FOR HEAVIER CONVECTIVE RAINS UP THROUGH
THE NORTHERN HIGH PLAINS/PLAINS THAT OFFER LOCAL RUNOFF ISSUES.
VERY WARM AND DRY CONDITIONS ARE EXPECTED FOR THE PLAINS THROUGH
MIDWEEK WITH AN UPPER RIDGE EXTENDING NORTH ACROSS THE UPPER
MIDWEST, WITH A COLD FRONT SLOWLY APPROACHING FROM THE WEST TO
BRING 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 GUIDANCE 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. INCORPORATED MORE ENSMEBLE MEAN GUIDANCE
AND WPC CONTINUITY INTO LONGER TIME FRAMES AMID SLOWLY GROWING
MODEL SPREAD. THIS PLAN OVERALL MAINTAINS VERY GOOD WPC PRODUCT
CONTINUITY IN LINE WITH LATEST/STILL SUPPORTING 12 UTC GUIDANCE.
..WEATHER/HAZARDS HIGHLIGHTS
THE SLOW MOVING OCCLUDED SURFACE LOW AND ASSOCIATED UPPER LOW WILL
RESULT IN A STRONG NORTHWARD INFLUX OF DEEP MOISTURE 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 TUESDAY (DAY 4) WILL LIKELY RESULT IN HIGHER
RAINFALL TOTALS ACROSS CENTRAL/EASTERN NORTH CAROLINA NORTHWARD TO
CENTRAL AND WESTERN VIRGINIA. GIVEN LOW-MID LEVEL SOUTHEASTERLY
FLOW DIRECTED TOWARDS THE BLUE RIDGE, SOME ENHANCED RAINFALL TOTALS
WILL BE POSSIBLE HERE AND THE LATEST MODEL GUIDANCE DEPICTS THIS
SCENARIO WELL. SOME CELLS WITH HOURLY RAINFALL RATES IN EXCESS OF
AN INCH ARE LIKELY, AND THEREFORE A SLIGHT RISK AREA HAS BEEN
INTRODUCED FOR DAY 4. WHILE THE SYSTEM WILL SLOWLY WEAKEN AND MOISTURE
CONVERGENCE LESSENS GOING INTO WEDNESDAY (DAY 5), THE UPPER LOW PATTERN
REMAINS QUITE FAVORABLE FOR THIS TIME OF YEAR, SO INTRODUCED A WPC
ERO MARGINAL RISK THREAT AREA THE CENTRAL MID-ATLANTIC.
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 NEXT WEEK WITH SOME OF THE HIGHER RANGES
PICKING UP ENHANCED LATE SEASON SNOWFALL, POSSIBLY OVER A FOOT IN
SOME CASES ACROSS SOUTHWESTERN MONTANA. AS THE SYSTEM PROGRESSES
EAST, MODERATE TO HEAVY RAINFALL MAY DEVELOP TO THE NORTHWEST OF A
SURFACE LOW OVER THE DAKOTAS, AND GIVEN THE POTENTIAL FOR SOME 1-2
INCH RAINFALL TOTALS ON WEDNESDAY, A MARGINAL RISK AREA IS SHOWN FOR
THE DAY 5 PERIOD.
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 MIDDLE 80S
TO LOWER 90S, WHICH IS AT LEAST 20 DEGREES ABOVE AVERAGE FOR THIS
TIME OF YEAR 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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