486
FXUS02 KWBC 211900 AAC
PMDEPD
EXTENDED FORECAST DISCUSSION...UPDATED
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
300 PM EDT THU MAR 21 2024
VALID 12Z SUN MAR 24 2024 - 12Z THU MAR 28 2024
...LATE SEASON WINTER STORM FOR THE DAKOTAS AND INTO MINNESOTA AND
WISCONSIN SUNDAY AND INTO MONDAY...
...HEAVY RAIN THREAT ACROSS THE DEEP SOUTH THROUGH EARLY NEXT
WEEK...
..GENERAL OVERVIEW
A STRONG LOW PRESSURE SYSTEM IS FORECAST TO INTENSIFY AND TRACK
ACROSS THE CENTRAL PLAINS TO THE UPPER MIDWEST, AND WILL LIKELY
BRING HEAVY SNOW FROM THE NORTHERN PLAINS INTO THE UPPER MIDWEST
THROUGH EARLY NEXT WEEK. ON THE WARM SIDE OF THE SYSTEM, HEAVY RAIN
ASSOCIATED WITH STRONG THUNDERSTORMS AHEAD OF A RELATIVELY POTENT
COLD FRONT WILL LIKELY LEAD TO FLOODING ISSUES ACROSS THE DEEP
SOUTH THROUGH EARLY NEXT WEEK. A SECOND SURFACE LOW IS FORECAST TO
DEVELOP OVER THE SOUTHEAST U.S. BY NEXT THURSDAY AND RESULT IN
RENEWED PROSPECTS FOR ADDITIONAL ENHANCED RAINFALL SPREADING UP THE
EAST COAST. MEANWHILE, A LOW PRESSURE SYSTEM FROM THE PACIFIC IS
FORECAST TO MOVE INTO THE NORTHWESTERN U.S., BRINGING ADDITIONAL
RAIN AND MOUNTAIN SNOW INTO THE REGION THROUGH MID-WEEK.
..GUIDANCE/PREDICTABILITY ASSESSMENT
THE 06Z AND 12Z MODEL GUIDANCE GENERALLY HAVE HALTED THE WESTWARD
MODEL TREND OF PLACING A TROUGH/STATIONARY FRONT ACROSS THE UPPER
MIDWEST EARLY NEXT WEEK AHEAD OF THE INTENSIFYING LOW PRESSURE
SYSTEM OVER THE CENTRAL PLAINS. THIS FRONT WILL LIKELY BE INSTRUMENTAL
IN PLACING AND ORIENTING AN AXIS OF HEAVIEST SNOWFALL ASSOCIATED
WITH THIS WINTER WEATHER EVENT ACROSS THE NORTHERN U.S. MODELS HAVE
ALSO COME INTO BETTER AGREEMENT WITH THE FORWARD SPEED OF THE LOW
PRESSURE SYSTEM, WITH THE GFS SLOWING DOWN VERSUS THE ECMWF
SPEEDING UP THE LOW, BOLSTERING CONFIDENCE THAT THE ACTUAL TRACK OF
THE LOW WILL BE SOMEWHERE BETWEEN THOSE TWO MODEL SOLUTIONS.
FARTHER SOUTH, THERE ARE NOTICEABLE MODEL DISCREPANCIES ON THE
HEAVY RAIN AREA ACROSS THE DEEP SOUTH EARLY NEXT WEEK, WITH THE
GFS/GEFS KEEPING THE HEAVIEST RAINFALL FARTHER NORTH THAN THE
ECMWF CLUSTER. THIS DISCREPANCY IS LIKELY DUE TO THE GFS' RECENT
TREND OF DEVELOPING A NEW LOW PRESSURE WAVE UPSTREAM ACROSS THE
SOUTHERN PLAINS TOWARD THE MID-MISSISSIPPI VALLEY ON TUESDAY IN
RESPONSE TO A SLOWER PROGRESSION OF THE WINTER STORM UP NORTH AND
THE RESULTING MORE AMPLIFIED UPPER-AIR PATTERN. THE ECMWF-AI MODEL
ALSO HAS SHOWN THIS TENDENCY WHILE THE ECMWF AND CMC ARE KEEPING
THIS SOUTHERN STREAM DEVELOPMENT MINIMAL AND PROGRESSIVE.
THE WPC FORECAST BLEND FAVORED A COMBINATION OF THESE TWO
EXTREMES, WITH THE QPF BASED ON THE FARTHER SOUTH SOLUTIONS FROM
THE ECMWF EARLY NEXT WEEK WHILE THE PMSL AND 500 MB MAPS ARE BASED
ON 40% FROM 00Z EC/EC MEAN, 25% FROM 00Z GFS/GEFS, 15% FROM THE
06Z GEFS/GFS, AND 20% FROM THE 00Z CMC.
..WEATHER/HAZARDS HIGHLIGHTS
ON SUNDAY, A MARGINAL RISK AREA FOR EXCESSIVE RAINFALL IS ADJUSTED
NORTHEASTWARD FROM EASTERN NEBRASKA TO IOWA IN ANTICIPATION OF SOME
CONVECTIVE RAINFALL LATER ON SUNDAY AHEAD OF A WARM FRONT
ASSOCIATED WITH THE INTENSIFYING SURFACE LOW OVER THE CENTRAL
PLAINS. THE LOW WILL LIKELY TRACK TOWARDS THE UPPER MIDWEST BY
MONDAY MORNING AND BECOME THE DRIVER FOR A BIG LATE SEASON WINTER
STORM. THERE CONTINUES TO BE AN UPWARD TREND FOR SIGNIFICANT
SNOWFALL ACCUMULATIONS (8"+) ACROSS NORTHERN SOUTH DAKOTA, SOUTHERN
NORTH DAKOTA, CENTRAL MINNESOTA, AND NORTHWESTERN WISCONSIN, AS
THIS REGION WILL BE ON THE COLDER SIDE OF THE LOW WITH A
DEFORMATION ZONE DEVELOPING, AND PRODUCING BANDS OF HEAVIER WET
SNOW WITH GUSTY WINDS. THERE MAY ALSO BE A SWATH OF POTENTIALLY
IMPACTFUL MIXED PRECIPITATION, INCLUDING SOME FREEZING RAIN, MOST
LIKELY TO THE SOUTHEAST OF THE HEAVY SNOW SWATH FROM EASTERN
NEBRASKA TO NORTHWEST IOWA AND INTO SOUTHERN MINNESOTA.
TIMING/TRACK UNCERTAINTY MAY CHANGE THE EVENTUAL LOCATION OF THE
IMPACTFUL WINTER WEATHER, BUT THE RISK FOR DISRUPTIONS TO DAILY
LIFE AND HAZARDOUS TRAVEL IS LIKELY.
MULTIPLE ROUNDS OF SHOWERS AND THUNDERSTORMS, SOME OF WHICH COULD BE
STRONG TO SEVERE, CAN BE EXPECTED IN THE WARM SECTOR OF THE SYSTEM,
BEGINNING FROM THE SOUTHERN PLAINS SUNDAY, AND THEN SPREADING EASTWARD
TO THE DEEP SOUTH ON MONDAY WHERE A SLIGHT RISK AREA HAS BEEN INDRODUCED
FOR DAY 5 BASED ON THE LATEST QPF GUIDANCE. THERE ARE STILL QUESTION
MARKS ON THE NORTH-SOUTH PLACEMENT OF THE HEAVY RAINFALL AHEAD OF THE
FRONT AS THE SYSTEM PROGRESSES EASTWARD, EVEN THOUGH THE KINEMATIC
ENVIRONMENT WILL BE MORE FAVORABLE FOR POTENTIAL SEVERE WEATHER.
NONETHELESS, A QUASI- LINEAR CONVECTIVE SYSTEM (QLCS) IS EVIDENT ON
THE LATEST GFS AND ECMWF RUNS. THE STORMY WEATHER THEN REACHES THE
FLORIDA PANHANDLE AND PORTIONS OF ALABAMA AND GEORGIA ON TUESDAY
WITH A SECONDARY LOW LIKELY DEVELOPING OVER THE NORTHERN GULF.
IN TERMS OF TEMPERATURES, IT WILL FEEL MORE LIKE JANUARY ACROSS THE
WESTERN HIGH PLAINS FROM WESTERN KANSAS TO MONTANA AND THE DAKOTAS IN
THE WAKE OF THE STRONG COLD FRONT. HIGHS WILL ONLY BE IN THE 20S AND
30S FOR THESE AREAS ON MONDAY, BUT A MODERATING TREND WILL COMMENCE
GOING INTO THE MIDDLE OF THE WEEK, EVEN THOUGH MONTANA AND NORTH DAKOTA
WILL STILL REMAIN CHILLY BY LATE MARCH STANDARDS. WARMER WEATHER LIKELY
MAKES A RETURN TO MUCH OF THE SOUTH-CENTRAL U.S. BY NEXT WEDNESDAY AND
THURSDAY.
KONG/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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