584
FXUS02 KWBC 181800
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
200 PM EDT MON MAR 18 2024
VALID 12Z THU MAR 21 2024 - 12Z MON MAR 25 2024
...LATE SEASON WINTER STORM POSSIBLE ACROSS PORTIONS OF THE
NORTHERN PLAINS/UPPER MIDWEST SUNDAY-MONDAY...
..GENERAL OVERVIEW
A SPLIT UPPER LEVEL FLOW PATTERN IS FORECAST TO BE IN PLACE ACROSS
THE CONTINENTAL U.S. FOR THE END OF THE WEEK, WITH A SHORTWAVE
TROUGH CROSSING THE GULF COAST REGION AND BROAD CYCLONIC FLOW
ACROSS THE NORTH-CENTRAL STATES. THE SOUTHERN SHORTWAVE IS
EXPECTED TO SPUR SURFACE CYCLOGENESIS OVER THE NORTHERN GULF AND
THEN THE LOW TRACKS OFF THE SOUTHEAST COAST GOING INTO THE WEEKEND.
LOOKING AHEAD TO SUNDAY AND NEXT MONDAY, A LARGER SYNOPTIC SCALE
TROUGH LIKELY DEVELOPS ACROSS THE WESTERN U.S. WITH AN ORGANIZED
LOW PRESSURE SYSTEM DEVELOPING OVER THE PLAINS BRINGING A POTENTIAL
LATE SEASON WINTER STORM TO PARTS OF THE NORTHERN PLAINS.
..GUIDANCE/PREDICTABILITY ASSESSMENT
THE LATEST MODEL GUIDANCE CONTINUES TO SHOW REASONABLY GOOD
AGREEMENT ON THE LARGE SCALE, BUT DEFINITELY SOME NOTICEABLE
DIFFERENCES STILL IN THE DETAILS, TIMING, AND AMPLITUDE OF
INDIVIDUAL SYSTEMS. THERE CONTINUE TO BE SOME AMPLITUDE DIFFERENCES
WITH THE SOUTHEAST/GULF COAST LOW, WITH THE GFS ON THE STRONGER
SIDE OF THE GUIDANCE, BRINGING THE LOW FARTHER UP THE EAST COAST.
ENSEMBLE MEANS AND OTHER OPERATIONAL MODELS SUGGEST A CUTOFF UPPER
LOW OFF THE SOUTHEAST DEVELOPS WITH A WEAKER SURFACE LOW REFLECTION
AND MORE EASTERLY/OFFSHORE TRACK.
BY SATURDAY, THE GFS (INCLUDING THE NEW 12Z RUN TODAY) IS NOTABLY
SLOWER THAN THE REST OF THE GUIDANCE WITH THE UPPER LOW/SHORTWAVE
INTO THE NORTHWEST. THE CMC IS ALSO FASTER WITH IT BY SUNDAY-MONDAY
AS IT AMPLIFIES OVER THE FOUR CORNERS REGION.
THE WPC FORECAST BLEND FOR TODAY USED A BLEND OF THE OPERATIONAL
GUIDANCE FOR DAYS 3 AND 4. AFTER 5, REMOVED THE GFS FROM THE BLEND
DUE TO ITS ISSUES NOTED ABOVE AND BLENDED THE ENSEMBLE MEANS WITH
THE ECMWF THROUGH DAY 7. OVERALL, THIS MAINTAINED GOOD CONTINUITY
WITH THE PREVIOUS WPC FORECAST.
..WEATHER/HAZARDS HIGHLIGHTS
WITH THE LOW BEGINNING TO DEVELOP OVER THE GULF THURSDAY INTO
FRIDAY, AN AXIS OF GREATER MOISTURE FLUX NEAR THE COAST MAY RESULT
IN HEAVIER LOCAL DOWNPOURS FROM SOUTHEAST TEXAS TO SOUTHERN
LOUISIANA, WHERE AN ERO MARGINAL RISK AREA REMAINS IN PLACE FOR
THE DAY 4 PERIOD. WHILE THE GREATEST RAINFALL TOTALS ARE FORECAST
TO REMAIN OFFSHORE OVER THE NORTHERN GULF, ACTIVITY WILL GRADUALLY
PROGRESS TOWARD THE FLORIDA PENINSULA ON FRIDAY, WITH POTENTIAL FOR
SOME LOCALIZED HEAVY RAINFALL ACROSS PORTIONS OF SOUTHERN FLORIDA
WHERE A DAY 5 MARGINAL RISK AREA IS HIGHLIGHTED. THE EVENTUAL
EVOLUTION AND TRACK OF THE SURFACE LOW OFF THE SOUTHEAST COAST AND
POSSIBLY UP OFF THE EAST COAST FRIDAY INTO NEXT WEEKEND REMAINS
QUITE UNCERTAIN IN GUIDANCE, BUT CURRENTLY SEEMS TO FAVOR ENHANCED
RAINS UP THROUGH THE COASTAL CAROLINAS, WHERE A SECOND DAY 5
MARGINAL RISK AREA WAS PLACED. ADDITIONAL RAINFALL AND ENHANCED
WINDS NEAR THE COASTAL MID-ATLANTIC AND NORTHEAST ARE POSSIBLE IN
GRADIENT FLOW BETWEEN THE WESTERN ATLANTIC COASTAL LOW AND AMBIENT
HIGH PRESSURE WEDGED INLAND OVER THE REGION.
MEANWHILE, MULTIPLE ROUNDS OF MAINLY LIGHT SNOW ARE FORECAST WITH
A HEAVIER SNOW FOCUS FOR FAVORED TERRAIN OF WESTERN MONTANA AND
NORTHERN IDAHO, AND ALSO THE CANADIAN ROCKIES. ENHANCED RAINS ARE
EXPECTED TO SPREAD FROM THE PACIFIC NORTHWEST DOWN ACROSS
CALIFORNIA BY FRIDAY AND INTO SATURDAY AS THE NEXT STORM SYSTEM
MOVES INTO THE REGION, WITH TERRAIN FOCUSING HEAVY SNOWS FOR THE
CENTRAL AND NORTHERN SIERRA. ACTIVITY SHOULD ALSO PROGRESS INLAND
ACROSS THE NORTH-CENTRAL GREAT BASIN AND THE NORTHERN
ROCKIES/PLAINS, THEN PROBABLY THE UPPER MIDWEST INTO NEXT WEEKEND.
GUIDANCE CONTINUES TO SHOW POTENTIAL FOR A LATE SEASON WINTER STORM
ON THE NORTHWEST SIDE OF A DEVELOPING SURFACE LOW ACROSS THE
DAKOTAS AND INTO MINNESOTA TOWARDS THE END OF THE FORECAST PERIOD
LATE SUNDAY INTO MONDAY.
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. ABOVE NORMAL TEMPERATURES
ACROSS THE INTERMOUNTAIN WEST MIDWEEK ARE EXPECTED TO COOL DOWN TO
BELOW AVERAGE LEVELS WITH THE UPPER TROUGH DEVELOPING LATE IN THE
FORECAST PERIOD. EVEN COLDER TEMPERATURES ARE POSSIBLE FROM
MONTANA TO THE CENTRAL PLAINS BY NEXT MONDAY BEHIND A STRONG COLD
FRONT WITH SUBFREEZING HIGH TEMPERATURES FOR MONTANA AND MOST OF
THE DAKOTAS.
SANTORELLI/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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