327
FXUS02 KWBC 170648
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
248 AM EDT SUN MAR 17 2024
VALID 12Z WED MAR 20 2024 - 12Z SUN MAR 24 2024
..GENERAL OVERVIEW
THE BLOCKY UPPER LEVEL PATTERN WITH THE UPPER HIGH OVER THE PACIFIC
NORTHWEST AND THE UPPER LOW OVER THE DESERT SOUTHWEST EARLY IN THE
WEEK IS EXPECTED TO BREAK DOWN, WHILE THE TROUGH OVER THE NORTHEAST
U.S. SHOULD GRADUALLY LIFT OUT SOME AND RESULT IN MORE OF A ZONAL
FLOW PATTERN ACROSS MOST OF THE NATION. A SOUTHERN STREAM SHORTWAVE
TROUGH ORIGINATING FROM THE CLOSED UPPER LOW OVER THE SOUTHWEST
WILL LIKELY SUSTAIN A WEAK SURFACE LOW OVER THE GULF THAT WILL
INCREASE CHANCES FOR SHOWERS AND STORMS FROM SOUTHERN TEXAS TO
FLORIDA. AN UPPER TROUGH IS EXPECTED TO REACH THE PACIFIC NORTHWEST
NEXT WEEKEND AND BRING A RESULT TO MORE UNSETTLED CONDITIONS.
..GUIDANCE/PREDICTABILITY ASSESSMENT
THE 00Z MODEL GUIDANCE SUITE IS IN REASONABLY GOOD AGREEMENT ON THE
SYNOPTIC SCALE FOR START THE FORECAST PERIOD WEDNESDAY, BUT TIMING
DIFFERENCES ARE MORE APPARENT BY THURSDAY WITH SHORTWAVES TRACKING
EAST ACROSS THE ROCKIES AND THEN THE NORTHERN PLAINS IN A MORE
ZONAL FLOW PATTERN. THERE IS BETTER OVERALL AGREEMENT IN THE
SOUTHERN STREAM SHORTWAVE CROSSING THE SOUTH-CENTRAL U.S., BUT
UNCERTAINTY AS TO WHERE THE CORRESPONDING SURFACE LOW DEVELOPS OVER
THE GULF BY LATE IN THE WEEK.
THE FORECAST GETS TRICKY GOING INTO NEXT WEEKEND FOR THE EAST COAST
REGARDING THE LIKELY EVOLUTION OF AN OFFSHORE SURFACE LOW. AT THE
TIME OF FRONTS/PRESSURES COMPOSITION, BOTH THE 12Z/18Z RUNS OF THE
GFS WERE OUTLIER SOLUTIONS WITH THE VERY PROGRESSIVE AND NORTHWARD
TRACK OF THE SURFACE LOW, EVEN COMPARED TO THE GEFS MEAN WHICH IS
MUCH MORE SUPPRESSED AND CLOSER TO THE ECMWF AND ECENS GUIDANCE.
THE 00Z GFS MAINTAINS THE HIGHLY PROGRESSIVE AND AMPLIFIED
SOLUTION AS WELL. THE 00Z CMC ALSO TAKES THE LOW MORE TOWARDS THE
NORTH, BUT NOT NEARLY TO THE SAME DEGREE AS THE GFS. THE MACHINE
LEARNING GUIDANCE FROM THE ECMWF ALSO DOES NOT FAVOR A GFS
SCENARIO, SO A NON-GFS BLEND WAS USED FOR THE SECOND HALF OF THE
FORECAST PERIOD WITH OVERALL BELOW AVERAGE CONFIDENCE.
THE WPC FORECAST INCORPORATED A GENERAL DETERMINISTIC MODEL BLEND
FOR WEDNESDAY, WITH SLIGHTLY MORE WEIGHTING APPLIED TO THE ECMWF
AND CMC. AFTER THAT, THERE WAS A GRADUAL INCREASE IN THE USE OF THE
ENSEMBLE MEANS TO ABOUT 50-60 PERCENT OF THE BLEND BY NEXT
SUNDAY.
..WEATHER/HAZARDS HIGHLIGHTS
THERE WILL LIKELY BE AN INCREASE IN SHOWERS AND SOME THUNDERSTORMS
ACROSS PORTIONS OF TEXAS AND OKLAHOMA ON WEDNESDAY WITH WARM AIR
ADVECTION FROM THE WESTERN GULF AND LIFT FROM A FRONTAL BOUNDARY.
IT CURRENTLY DOES NOT APPEAR THAT THE CONVECTION WOULD BE
WIDESPREAD NOR HEAVY ENOUGH TO WARRANT ANY MARGINAL RISKS AREAS AT
THIS TIME, ALTHOUGH TRENDS WILL CONTINUE TO BE MONITORED. WITH THE
LOW BEGINNING TO DEVELOP OVER THE WESTERN GULF ON THURSDAY, AN AXIS
OF GREATER MOISTURE FLUX NEAR THE COAST MAY RESULT IN HEAVIER
RAINFALL TOTALS ON THE ORDER OF 1 TO 2 INCHES FROM SOUTHEAST TEXAS
TO SOUTHERN LOUISIANA, WHERE A MARGINAL RISK AREA IS PLANNED. THE
GREATEST RAINFALL TOTALS WILL LIKELY REMAIN OFFSHORE.
FARTHER TO THE NORTH FROM MONTANA TO THE UPPER MIDWEST, MULTIPLE
ROUNDS OF MAINLY LIGHT SNOW ARE FORECAST, AND HEAVIER SNOW FOR THE
HIGHER TERRAIN OF WESTERN MONTANA AND NORTHERN IDAHO. HEAVIER RAIN
IS ALSO EXPECTED TO MAKE A RETURN TO MUCH OF CALIFORNIA BY FRIDAY
AND INTO SATURDAY AS THE NEXT STORM SYSTEM MOVES INTO THE REGION,
AND HEAVY SNOW FOR THE CENTRAL AND NORTHERN SIERRA. FOR THE EASTERN
U.S., THE EVENTUAL EVOLUTION AND TRACK OF THE SURFACE LOW OFF THE
SOUTHEAST COAST WILL PLAY A ROLE IN HOW MUCH RAIN AND WIND COASTAL
PORTIONS OF THE CAROLINAS WILL GET, AND FOR NOW IT APPEARS THE
WORST WEATHER CONDITIONS SHOULD REMAIN OFFSHORE.
THERE WILL LIKELY BE A STARK TEMPERATURE CONTRAST FROM THE CENTRAL
PLAINS/MIDWEST TO THE CANADIAN BORDER. WINTER-LIKE READINGS WILL
CONTINUE ACROSS NORTHERN 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
NORTHWESTERN U.S. MIDWEEK ARE EXPECTED TO COOL DOWN TO NEAR OR
SLIGHTLY BELOW AVERAGE LEVELS WITH THE UPPER RIDGE BREAKING DOWN
AND A UPPER TROUGH DEVELOPING NEAR THE WEST COAST LATE IN THE
FORECAST PERIOD. ELSEWHERE, TEMPERATURES SHOULD GENERALLY BE WITHIN
10 DEGREES OF LATE MARCH AVERAGES FOR MOST LOCATIONS.
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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