548
FXUS02 KWBC 191859 AAC
PMDEPD
EXTENDED FORECAST DISCUSSION...UPDATED
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
259 PM EDT TUE MAR 19 2024
VALID 12Z FRI MAR 22 2024 - 12Z TUE MAR 26 2024
***LATE SEASON WINTER STORM BECOMING MORE LIKELY FOR THE DAKOTAS
AND INTO PORTIONS OF THE UPPER MIDWEST***
..GENERAL OVERVIEW
A SPLIT UPPER LEVEL FLOW PATTERN IS FORECAST TO INITIALLY BE IN
PLACE ACROSS THE CONTINENTAL U.S. FOR THE END OF THE WEEK, WITH A
SHORTWAVE TROUGH CROSSING THE GULF COAST REGION AND THEN TRACKING
OFF THE EAST COAST, AND BROAD CYCLONIC FLOW ACROSS THE NORTH-
CENTRAL STATES. THE SOUTHERN SHORTWAVE IS EXPECTED TO PRODUCE A
SURFACE LOW OVER THE NORTHERN GULF, AND THEN THE LOW TRACKS OFF
THE SOUTHEAST COAST GOING INTO THE WEEKEND. LOOKING AHEAD TO THE
SUNDAY TO TUESDAY TIME PERIOD, A PATTERN CHANGE EVOLVES ACROSS THE
WESTERN HALF OF THE U.S. AS A LARGER SYNOPTIC SCALE TROUGH
DEVELOPS ACROSS THE INTERMOUNTAIN WEST AND ROCKIES. THIS WILL LEAD
TO SURFACE CYCLOGENESIS ACROSS THE CENTRAL PLAINS AND MIDWEST
BRINGING A LATE SEASON WINTER STORM TO PARTS OF THE NORTHERN
PLAINS, AND STRONG THUNDERSTORMS ACROSS PORTIONS OF THE SOUTH.
..GUIDANCE/PREDICTABILITY ASSESSMENT
THE FOCUS FOR THE EARLY PART OF THE PERIOD REMAINS ON THE SOUTHERN
STREAM WITH A SHORTWAVE PASSING OVER THE SOUTHEAST LEADING TO
SURFACE LOW DEVELOPMENT IN THE GULF, SUBSEQUENTLY PROGRESSING TO
THE NORTHEAST ORIENTED ALONG THE SOUTHEASTERN ATLANTIC COAST.
GUIDANCE DIFFERENCES QUICKLY ARRISE IN THE DOWNSTREAM TRACK AND
SPEED OF THE SYSTEM, WITH THE GFS ON THE FASTER SIDE OF THE
ENVELOPE AS A LEAD SHORTWAVE TAKES THE LOW QUICKLY NORTHWARD ALONG
THE COAST, CLEARING THE EAST COAST AND HEADING INTO CANADA BY
SUNDAY MORNING. THE OTHER GUIDANCE, BOTH DETERMINSTIC AND ENSEMBLE
MEANS, IS GENERALLY SLOWER WITH THE LOW, BRINGING IT UP ALONG THE
CAROLINAS SATURDAY EVENING AND SHIFING INTO THE ATLANTIC INTO
SUNDAY. HOWEVER, THE SUITE OF MACHINE LEARNING MODELS DOES SHOW
SOME SUPPORT FOR A FASTER LOW, SUPPORTING A SOLUTION MORE SIMILAR
TO THE GFS. THIS WILL HAVE IMPLICATIONS FOR THE EXTENT AND AMOUNT
OF PRECIPITATION ALONG THE EAST COAST THIS WEEKEND, WITH THE SLOWER
SOLUTIONS ALLOWING FOR MUCH MORE WIDESPREAD, HEAVIER RAIN EXTENDING
NORTHEASTWARD ALONG THE COAST, PERHAPS AS FAR NORTH AS NEW ENGLAND,
WHILE THE GFS WOULD SUGGEST THE COVERAGE AND DURATION OF RAINFALL
WILL BE LESS. OTHERWISE, ATTENTION THEN TURNS TOWARDS THE WESTERN
U.S. AS A LARGER-SCALE AMPLIFYING TROUGH DIGS IN THE WEST, WHICH
WITH EASTWARD PROGRESSION LEADS TO EVENTUAL LEE-CYCLOGENESIS OVER
THE PLAINS AND THE DEVELOPMENT OF A STORM SYSTEM IN THE CENTRAL
U.S. THE GUIDANCE SHOWS GOOD AGREEMENT OVERALL ON THIS GENERAL
PATTERN, HOWEVER NOTED SMALLER-SCALE SPECIFICS IN INDIVIDUAL
SHORTWAVE TIMING AND THE PROGRESSION OF THE TROUGH WILL HAVE
DOWNSTREAM IMPACTS ON EVENTUAL PRECIPITATION POTENTIAL, AND THE
PLACEMENT OF THE TRANSITION ZONE OF RAIN AND SNOW, THOUGH
CONFIDENCE IN A BROAD ZONE OF BOTH HEAVY RAIN ON THE WARM SIDE OF
THE SYSTEM AND THE POTENTIAL FOR A WINTER STORM ON THE COLDER SIDE
REMAINS HIGH. THE UPDATED WPF FORECAST FOLLOWED AN INITIAL
COMPOSITE BLEND OF THE DETERMINSTIC GUIDANCE, FAVORING THE 00Z
ECMWF AND 06Z GFS, EVOLVING TO INCLUDE MORE CONTRIBUTION FROM THE
ENSEMLE MEANS AS SMALLER-SCALE DIFFERENCES NATURALLY INCREASE LATER
INTO THE FORECAST PERIOD.
..WEATHER/HAZARDS HIGHLIGHTS
THERE ARE STILL SOME UNCERTAINTIES IN THE EXPECTED MESOSCALE
EVOLUTION OF THE LOW DEVELOPING IN THE VICINITY OF THE SOUTHEAST
U.S. COAST ON FRIDAY, WITH MODEL GUIDANCE VARIED REGARDING
PLACEMENT OF HEAVIEST QPF AXES. HOWEVER, IT DOES APPEAR MORE
LIKELY THAT HEAVIER RAIN COULD FALL MORE INLAND COMPARED TO
EARLIER FORECASTS, AND THE MARGINAL RISK PLANNED FOR DAY 4 NOW
ENCOMPASSES MOST OF FLORIDA AND EXTENDING NORTH TO CENTRAL NORTH
CAROLINA. A SLIGHT RISK AREA COULD EVENTUALLY BE NEEDED NEAR THE
COASTAL CAROLINAS AND EVEN PARTS OF SOUTH FLORIDA, BUT OVERALL
FORECAST CONFIDENCE IS NOT YET HIGH ENOUGH IN EXACT PLACEMENT. FOR
THE DAY 5 PERIOD SATURDAY, THE CORE OF HEAVIEST RAINFALL LIFTS
NORTHEAST AND THE BEST PROSPECTS FOR HEAVIER RAINFALL WOULD BE FROM
EASTERN NORTH CAROLINA TO THE DELMARVA AND INTO COASTAL NEW JERSEY,
ALTHOUGH GUIDANCE CONTINUES TO TREND FURTHER INLAND. THE HIGHEST
UNCERTAINTY IS WITH NORTHWARD EXTENT, WITH GREATER CONFIDENCE FOR
HEAVIER TOTALS IN THE MID-ATLANTIC, AND THEN POTENTIALLY INTO
SOUTHERN NEW ENGLAND. THEREFORE, THE EXISTING DAY 5 MARGINAL RISK
HAS BEEN EXTENDED NORTHEASTWARD TO ENCOMPASS MORE OF THE DELMARVA
AND NEW JERSEY. IF GUIDANCE CONTINUES TO SUPPORT THIS TREND, A
SLIGHT RISK MAY EVENTUALLY BE NEEDED HERE AS WELL, AS THERE IS AN
INDICATION THAT A FEW INCHES OF RAINFALL IS NOT OUT OF THE
QUESTION. THE COMBINATION OF THE ATLANTIC LOW AS WELL AS A NORTHERN
STREAM WAVE LOOK TO ALSO BRING SNOW, POTENTIALLY HEAVY AT TIMES,
INTO THE INTERIOR NORTHEAST THIS WEEKEND. IN THE WEST, THERE IS A
MARGINAL RISK PLANNED BOTH DAYS FOR COASTAL PORTIONS OF
NORTHWESTERN CALIFORNIA AND SOUTHWESTERN OREGON WITH MOISTURE FLUX
FROM THE PACIFIC PRODUCING 1-3 INCHES OF QPF OVER THIS TIME PERIOD.
ATTENTION THEN TURNS TO THE CENTRAL U.S. AS A POTENTIALLY STRONG
SURFACE LOW DEVELOPS IN THE LEE OF THE ROCKIES AND THEN TRACKS
TOWARDS THE MIDWEST BY MONDAY MORNING. THERE IS AN UPWARD TREND
FOR SNOWFALL ACCUMULATIONS FROM EASTERN MONTANA INTO THE DAKOTAS,
MINNESOTA, AND INTO WISCONSIN, AS THIS REGION WILL LIKELY BE ON
THE COLDER SIDE OF THE LOW WITH A DEFORMATION ZONE LIKELY
DEVELOPING, AND PRODUCING BANDS OF HEAVIER WET SNOW WITH GUSTY
WINDS. MULTIPLE ROUNDS OF SHOWERS AND THUNDERSTORMS, SOME OF WHICH
COULD BE STRONG TO SEVERE, CAN BE EXPECTED IN THE WARM SECTOR OF
THE LOW FROM TEXAS TO THE OHIO VALLEY. SNOW SHOWERS ARE ALSO
EXPECTED TO CONTINUE ACROSS MANY OF THE WESTERN U.S. MOUNTAIN
RANGES WITH THE UPPER TROUGH BUILDING IN.
THERE WILL LIKELY BE A STARK TEMPERATURE CONTRAST FROM THE CENTRAL
PLAINS/MIDWEST TO THE CANADIAN BORDER LATE IN THE WEEK. WINTER-
LIKE READINGS WILL CONTINUE ACROSS MONTANA, NORTH DAKOTA, AND INTO
NORTHERN MINNESOTA WITH A STRONG ARCTIC HIGH SITUATED OVER CENTRAL
CANADA PROVIDING COLD NORTHERLY FLOW. EVEN COLDER TEMPERATURES ARE
POSSIBLE FROM MONTANA TO THE CENTRAL PLAINS BY NEXT MONDAY BEHIND
THE STRONG COLD FRONT WITH SUBFREEZING HIGH TEMPERATURES FOR
MONTANA AND MOST OF THE DAKOTAS. MEANWHILE, A PLEASANT WARM-UP IS
LIKELY AHEAD OF THE DEVELOPING STORM SYSTEM FROM THE DEEP SOUTH TO
THE OHIO VALLEY.
PUTNAM/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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