069
FXUS02 KWBC 100654
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
254 AM EDT SAT MAY 10 2025
VALID 12Z TUE MAY 13 2025 - 12Z SAT MAY 17 2025
...EARLY SEASON HEAT FOR THE DAKOTAS AND HEAVY RAIN FOR THE MID-
ATLANTIC REGION ON TUESDAY...
..GENERAL OVERVIEW
A SLOW MOVING AND WELL DEFINED UPPER LOW DEVELOPING OVER THE
INTERIOR SOUTHEAST U.S. GOING INTO EARLY-MIDDLE PART OF NEXT WEEK
WILL MAKE WEATHER HEADLINES WITH PERIODS OF HEAVY RAINFALL FROM THE
CAROLINAS 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
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 FOR THE MIDDLE OF THE WEEK.
THE CMC AND UKMET ARE QUICKER TO LIFT THE SURFACE LOW FROM THE
DAKOTAS TO MANITOBA AND WESTERN QUEBEC WHEN COMPARED TO THE
GFS/ECMWF BY LATE THURSDAY INTO FRIDAY, AND THE MACHINE LEARNING
GUIDANCE IS ALSO SPLIT ON THE LOCATION OF THIS LOW AS IT EXITS THE
DAKOTAS. LOOKING AHEAD TO NEXT SATURDAY, THE GUIDANCE BEGINS TO
DIFFER MORE SUBSTANTIALLY ACROSS THE WESTERN U.S. AS A SECOND UPPER
TROUGH LIKELY DEVELOPS. THE ECMWF/GFS ARE STILL RELATIVELY CLOSE
WITH THE TROUGH/CLOSED LOW OVER THE GREAT LAKES REGION BY THIS
TIME, WHILE THE CMC IS WEAKER AND MUCH MORE PROGRESSIVE. THE WPC
FRONT/PRESSURES RELIED MORE ON THE GFS/ECMWF/ENSEMBLE MEANS BY THE
FRIDAY-SATURDAY TIME PERIOD, WITH ABOUT HALF MEANS BY SATURDAY.
..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. THE SYSTEM WEAKENS FURTHER AND MOISTURE
CONVERGENCE LESSENS GOING INTO WEDNESDAY (DAY 5), SO NO RISK AREAS
ARE CURRENTLY WARRANTED FOR THAT TIME.
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 PLANNED
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
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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