839
FXUS02 KWBC 021855
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
255 PM EDT THU MAY 2 2024
VALID 12Z SUN MAY 05 2024 - 12Z THU MAY 09 2024
...HEAVY RAIN WILL CONTINUE IN THE SOUTH-CENTRAL U.S. INTO
SUNDAY WITH INCREASING RAINFALL ACROSS THE NORTHERN
PLAINS/MISSISSIPPI VALLEY ON MONDAY...
..OVERVIEW
AN UPPER LOW THAT IS STRONG FOR THIS TIME OF YEAR IS FORECAST TO
MOVE THROUGH THE WEST EARLY NEXT WEEK AND TRACK EAST INTO THE
PLAINS AND MIDWEST AS THE WEEK PROGRESSES. THIS WILL SUPPORT
COOLER THAN NORMAL TEMPERATURES, GUSTY WINDS, AND PRECIPITATION
INCLUDING HIGHER ELEVATION SNOW IN THE WEST EARLY IN THE WEEK. RAIN
THAT COULD BE LOCALLY HEAVY THEN SHIFTS INTO THE NORTHERN PLAINS
TO MIDWEST. FARTHER SOUTH, A SUBTROPICAL JET COMING INTO THE SOUTH-
CENTRAL U.S. AND THE WESTERN SIDE OF A FRONT STALLING WILL LEAD TO
RAIN AND THUNDERSTORMS IN THE SOUTHERN HALF OF THE PLAINS AND
MISSISSIPPI VALLEY INTO SUNDAY, POTENTIALLY IN SOME AREAS THAT HAVE
RECEIVED AMPLE RAINFALL RECENTLY AND/OR WILL DURING THE SHORT
RANGE PERIOD. THEN MEAN UPPER RIDGING WILL LEAD TO WARMING
TEMPERATURES IN MUCH OF THE CENTRAL AND EASTERN U.S. NEXT WEEK.
..GUIDANCE/PREDICTABILITY ASSESSMENT
RECENT MODEL GUIDANCE, INCLUDING THE NEWER 12Z CYCLE, CONTINUES TO
SHOW REASONABLY GOOD AGREEMENT WITH AN UPPER LOW COMING THROUGH
THE GREAT BASIN AS THE PERIOD BEGINS SUNDAY SHIFTING EAST MONDAY
AND PIVOTING NORTHWARD BEFORE SLOWING OVER THE NORTHERN PLAINS. A
STRONG SURFACE LOW (THAT MODELS SHOW COULD BREAK LOW PRESSURE
RECORDS FOR MAY) WILL ACCOMPANY IT. MODEL SPREAD WAS WELL WITHIN
TYPICAL RANGES THROUGH ABOUT MONDAY-TUESDAY, THOUGH THE DETAILS OF
EXACT STRENGTH AND TRACK AND QPF REMAIN UNCERTAIN. A MODEL BLEND
FAVORING THE DETERMINISTIC GUIDANCE CONTINUED TO WORK WELL FOR THE
FIRST FEW DAYS OF THE FORECAST.
BY MIDWEEK, MODEL SPREAD INCREASES AS THE UPPER LOW GETS TRAPPED
BETWEEN RIDGING TO ITS EAST AND AN UPPER HIGH TO ITS NORTH IN A
BLOCKIER PATTERN, WITH SOME GUIDANCE WANTING TO HOLD THE UPPER
LOW BACK LONGER THAN OTHERS. THERE IS ALSO ADDITIONAL ENERGY WHICH
DROPS INTO THE WEST THIS PERIOD TOO, WHICH MAY COMPLICATE THE
PATTERN. THE ECMWF (BOTH 00Z AND 12Z RUNS) ARE STRONGEST WITH
HOLDING THE NORTHERN PLAINS LOW BACK. GIVEN THE MODEL VARIABILITY,
TRANSITIONED FAIRLY QUICKLY TOWARD A 60/40 ENSEMBLE MEAN TO
DETERMINISTIC GUIDANCE BLEND LATE PERIOD. THIS MAINTAINED GOOD
CONTINUITY WITH THE PREVIOUS WPC FORECAST AS WELL.
..WEATHER/HAZARDS HIGHLIGHTS
AS THE UPPER LOW TRACKS INTO AND THROUGH THE WEST, WIDESPREAD
PRECIPITATION IS LIKELY. THE HIGHER ELEVATIONS OF THE SIERRA
NEVADA, NORTH INTO THE CASCADES, AND EAST INTO THE INTERMOUNTAIN
WEST/ROCKIES WILL SEE SOME MAY SNOW. THE TROUGH/LOW ALOFT AND
FRONTAL BOUNDARIES COULD ALSO PRODUCE SOME HIGH WINDS ACROSS THE
GREAT BASIN TO ROCKIES TO HIGH PLAINS. PRECIPITATION IS FORECAST TO
MOVE STEADILY EASTWARD THROUGH EARLY NEXT WEEK, REACHING THE
NORTHERN PLAINS TO MIDWEST MONDAY AND TUESDAY. RAINFALL ON THE WEST
SIDE OF THE STRONG SURFACE LOW COULD BE HEAVY ACROSS EASTERN
MONTANA INTO THE DAKOTAS GIVEN STRONG UPPER-LEVEL SUPPORT FOR LIFT.
HOWEVER, THIS REGION IS NOT PARTICULARLY SENSITIVE TO FLOODING
CONCERNS, AND INSTABILITY SHOULD BE LIMITED WRAPPING AROUND THE
LOW. THUS A MARGINAL RISK IS IN PLACE IN THE DAY 5/MONDAY ERO FOR
THIS AREA GIVEN THE POTENTIAL FOR UNUSUALLY HEAVY RAIN BUT WITHOUT
WIDESPREAD SIGNIFICANT FLOODING IMPACTS. THE MARGINAL RISK EXTENDS
SOUTHEAST INTO THE UPPER/MIDDLE MISSISSIPPI VALLEY, WHERE MORE
INSTABILITY WILL BE IN PLACE FOR HIGHER RAIN RATES, BUT STORMS WILL
LIKELY BE FASTER-MOVING. THE STORM PREDICTION CENTER ALSO HAS
PORTIONS OF THE PLAINS DELINEATED WITH POTENTIAL FOR SEVERE WEATHER
ON MONDAY. RAINFALL IS FORECAST TO SHIFT EAST INTO THE GREAT LAKES
AND OHIO VALLEY TUESDAY-WEDNESDAY.
FARTHER SOUTH, THE SUBTROPICAL JET LOOKS TO BE ACTIVE COMING INTO
THE SOUTH-CENTRAL U.S. SUNDAY, FOCUSING CONVECTION IN A MOIST AND
UNSTABLE ENVIRONMENT. MANY AREAS IN THE SOUTH-CENTRAL U.S. WILL
HAVE QUITE SATURATED ANTECEDENT CONDITIONS BECAUSE OF RECENT AND
UPCOMING SHORT RANGE EVENTS, SO THIS WILL BE A FACTOR FOR FLOODING
AS WELL. THOUGH THERE IS STILL SOME VARIABILITY, MODELS SEEM TO BE
CONVERGING ON A POSITION FOR HEAVIER RAINFALL IN EASTERN OKLAHOMA
AND VICINITY, SO THE ERO FOR DAY 4/SUNDAY INCLUDES AN EMBEDDED SLIGHT
RISK WITHIN THE BROADER SOUTH-CENTRAL U.S. MARGINAL FOR THAT AREA.
FORTUNATELY INTO THE WORKWEEK, RAIN CHANCES SHOULD LESSEN FOR
THOSE WATERLOGGED AREAS. THE EASTERN SEABOARD CAN ALSO EXPECT SOME
RAIN ON SUNDAY, WITH PERHAPS A NONZERO CHANCE OF LOCALLY HEAVY
RAIN, THOUGH ANTECEDENT CONDITIONS ARE MUCH DRIER ACROSS THE MID-
ATLANTIC INTO THE NORTHEAST.
MUCH COOLER THAN AVERAGE TEMPERATURES BY AROUND 15-25 DEGREES FOR
HIGHS WILL BE PRESENT IN THE WEST ON SUNDAY UNDERNEATH THE UPPER
LOW. THE ANOMALOUSLY COOL TEMPERATURES SHOULD MODERATE SOMEWHAT AS
THE WEEK PROGRESSES, BUT SPREAD INTO THE NORTHERN HIGH PLAINS AFTER
A WARM DAY ON SUNDAY. BUT FARTHER SOUTHEAST, MEAN UPPER RIDGING
WILL CAUSE WARM TEMPERATURES TO SPREAD ACROSS THE SOUTH-CENTRAL
AND EAST-CENTRAL U.S. INTO THE EASTERN SEABOARD. 90S ARE FORECAST
TO BECOME MORE WIDESPREAD ACROSS THE SOUTHERN TIER, WITH
TEMPERATURES OVER 100F (AND EVEN HIGHER HEAT INDICES) INTO
SOUTHWEST TEXAS AND THE POSSIBILITY FOR THE FIRST EXCESSIVE HEAT
DAYS OF THE YEAR.
SANTORELLI/TATE
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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