091
FXUS02 KWBC 211909
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
309 PM EDT SUN APR 21 2024
VALID 12Z WED APR 24 2024 - 12Z SUN APR 28 2024
...LOW PRESSURE SYSTEMS IN THE CENTRAL U.S. SHOULD LEAD TO SEVERE
WEATHER AND HEAVY RAIN FOR THE LATTER PART OF THE WEEK...
..OVERVIEW
DURING THE FORECAST PERIOD FROM MIDWEEK INTO NEXT WEEKEND, ROUNDS
OF UPPER TROUGHING AND SURFACE LOWS WILL LEAD TO A WET PATTERN FOR
THE WESTERN AND CENTRAL U.S., INCLUDING POTENTIALLY SEVERE
THUNDERSTORMS AND HEAVY RAIN ACROSS THE PLAINS AND MISSISSIPPI
VALLEY AND SPRINGTIME SNOW FOR THE HIGHER ELEVATIONS OF THE
INTERMOUNTAIN WEST. MEANWHILE IN THE EAST, SOME UPPER TROUGHING
WILL PUSH THROUGH A COLD FRONT OR TWO ON WEDNESDAY AND CAUSE SOME
RAIN/SNOW BEFORE SURFACE HIGH PRESSURE BEHIND DRIES OUT THE REGION.
THESE FEATURES WILL LEAD TO BELOW NORMAL TEMPERATURES IN THE
NORTHEASTERN QUADRANT OF THE COUNTRY WEDNESDAY-FRIDAY BEFORE
WARMING NEXT WEEKEND.
..GUIDANCE/PREDICTABILITY ASSESSMENT
FOR WEDNESDAY-FRIDAY IN THE EAST, THE MAIN FEATURE OF NOTE WILL BE
A TROUGH PUSHING THROUGH WITH AN EMBEDDED UPPER LOW. FORTUNATELY
MODELS HAVE CONVERGED BETTER WITH THE TIMING AND DEPTH OF THIS
FEATURE, AS RECENT GFS RUNS HAVE TRANSITIONED TO A LESS AMPLIFIED
AND FASTER FEATURE. THUS THERE WAS LESS QPF (INCLUDING SNOW)
LINGERING IN THE NORTHEAST COMPARED TO THE PREVIOUS FORECAST.
IN THE WESTERN TO CENTRAL U.S., THERE ARE MULTIPLE UPPER-LEVEL AND
SURFACE FEATURES OF CONCERN. SOUTHERN STREAM TROUGHING PUSHING
FROM THE EASTERN PACIFIC ACROSS CALIFORNIA INTO THE FOUR CORNERS
STATES AND THEN NORTHEASTWARD INTO THE CENTRAL PLAINS AND UPPER
MIDWEST LATE WEEK SHOWS REASONABLE AGREEMENT. THE ASSOCIATED
SURFACE LOW TRACK IS ALSO IN OKAY ALIGNMENT, WITH THE ENSEMBLE
MEANS IN BETWEEN THE SLIGHTLY FARTHER NORTHWEST 00Z ECMWF/CMC AND
SLIGHTLY FARTHER SOUTHEAST GFS RUNS, WITHIN TYPICAL SPREAD FOR THE
MEDIUM RANGE PERIOD.
MORE MODEL DIFFERENCES ARISE WITH SECONDARY ENERGY/TROUGHING
DIVING INTO THE WEST FRIDAY INTO THE WEEKEND. THOUGH THE 00Z/06Z
OPERATIONAL GFS AND 00Z ECMWF LOOKED PRETTY AGREEABLE WITH EACH
OTHER WITH A DEEP AND WEST TROUGH AXIS, THE FULL SUITE OF GUIDANCE
SUGGESTED THAT THESE WERE TOO AMPLIFIED. ENSEMBLE MEANS WERE LESS
AMPLIFIED, AND LOOKING AT THE INDIVIDUAL MEMBERS SHOWED THAT THESE
DETERMINISTIC MODELS WERE BOTH DEEPER THAN MOST IF NOT ALL THE
MEMBERS. ADDITIONALLY, THE AVAILABLE AI/MACHINE LEARNING MODELS
SHOWED A LESS AMPLIFIED AND FARTHER EAST TROUGH AXIS. THE CMC WAS
MORE REASONABLE WITH THE TROUGH POSITION. THE 12Z MODELS
FORTUNATELY HAVE COME IN WITH A FASTER AND SHALLOWER TROUGH AS
EXPECTED. UPSTREAM ACROSS THE NORTHEAST PACIFIC, 12Z MODELS ARE
ALSO MORE AGREEABLE IN INDICATING AN UPPER LOW BY NEXT SUNDAY AFTER
A LOT OF SPREAD IN THE 00Z/06Z RUNS.
THUS THE WPC FORECAST BEGAN WITH A BLEND OF THE DETERMINISTIC
GUIDANCE, AND TRANSITIONED TO A BLEND FAVORING THE ENSEMBLE MEANS
OVER HALF BY THE LATE PERIOD, WHILE REDUCING THE DETERMINISTIC
COMPONENTS ESPECIALLY FROM THE ECMWF AND GFS.
..WEATHER/HAZARDS HIGHLIGHTS
THE UPPER TROUGH AND COLD FRONT PASSING THROUGH THE NORTHEAST
WEDNESDAY WILL BE ACCOMPANIED BY WIDESPREAD LIGHT TO MODERATE RAIN
ALONG WITH HIGH ELEVATION SNOW FOR PORTIONS OF NORTHERN NEW
ENGLAND. FARTHER WEST, WARM AIR ADVECTION ACROSS THE SOUTH-CENTRAL
U.S. WILL BRING A RETURN TO SCATTERED SHOWERS AND STORMS ACROSS
THIS REGION, WITH SOME POTENTIAL FOR ENHANCED RAIN TOTALS. RECENT
MODELS INDICATE THE AXIS OF HEAVIEST RAIN (1-2 INCHES) CROSSING
FROM NORTHEAST OKLAHOMA INTO NORTHWEST ARKANSAS. HOWEVER, DID NOT
FEEL THERE WAS ENOUGH RUN-TO-RUN CONSISTENCY IN PLACEMENT NOR
CONFIDENCE IN IMPACTS TO DELINEATE AN EXCESSIVE RAINFALL OUTLOOK
FOR DAY 4/WEDNESDAY. MORE WIDESPREAD SHOWERS AND STORMS ARE THEN
EXPECTED TO DEVELOP ACROSS PORTIONS OF KANSAS, NEBRASKA, IOWA, AND
MISSOURI GOING INTO THURSDAY (DAY 5) AS MOISTURE AND ELEVATED
INSTABILITY INCREASE WITH SURFACE LOW PRESSURE SYSTEM DEVELOPMENT
ACROSS THE CENTRAL PLAINS. A MARGINAL RISK AREA IN THE ERO SEEMS
PRUDENT AND THERE WERE MINIMAL CHANGES TO THE PREVIOUS ISSUANCE.
THE STORM PREDICTION CENTER IS ALSO WATCHING FOR SEVERE WEATHER
AHEAD OF THE DRYLINE WITH THE LOW PRESSURE SYSTEM, WITH OUTLOOKS
FOR PARTS OF THE SOUTHERN HALF OF THE PLAINS ON THURSDAY AND PARTS
OF THE CENTRAL PLAINS AND MISSISSIPPI VALLEY ON FRIDAY. ON THE
BACKSIDE OF THE DRYLINE, CONDITIONS WILL BE FAVORABLE FOR FIRE
DEVELOPMENT IN THE SOUTHERN HIGH PLAINS THURSDAY-FRIDAY. BY LATE
WEEK INTO THE WEEKEND, SHOWERS AND STORMS SHOULD PROGRESS INTO THE
OHIO VALLEY AND GREAT LAKES AND PORTIONS OF THE EASTERN SEABOARD,
WHILE ALSO BEING RENEWED IN THE PLAINS/MISSISSIPPI VALLEY.
MULTIPLE ROUNDS OF ENERGY MOVING THROUGH THE WEST WILL HELP TO
PRODUCE PRECIPITATION CHANCES THERE. WITH COOLER AIR IN PLACE GIVEN
UPPER TROUGHING, SNOW WILL BE POSSIBLE ACROSS THE HIGHER
ELEVATIONS INCLUDING THE CASCADES/SIERRA NEVADA ACROSS PARTS OF THE
INTERMOUNTAIN WEST INTO THE NORTHERN/CENTRAL ROCKIES.
MUCH OF THE WEST SHOULD HAVE ABOVE NORMAL TEMPERATURES ON
WEDNESDAY, BEFORE RETURNING TO NEAR OR SLIGHTLY BELOW NORMAL LEVELS
FOR MUCH OF THE WEST COAST AND INTERMOUNTAIN WEST TO CLOSE OUT THE
WEEK, AS THE MEAN UPPER TROUGH ENCOMPASSES THE REGION. WARMER
TEMPERATURES AND INCREASING HUMIDITY ARE FORECAST FOR THE
CENTRAL/SOUTHERN PLAINS BY FRIDAY AND BEYOND AS THE UPPER RIDGE
AXIS BUILDS BACK, AND SOUTHERLY FLOW FROM THE WESTERN GULF ADVECTS
MOISTURE NORTHWARD AHEAD OF THE DEVELOPING SURFACE LOW. THIS
SPREADS NORTHEASTWARD TO INCLUDE THE OHIO VALLEY AND THE
APPALACHIANS, WITH MORE WIDESPREAD ABOVE NORMAL READINGS FOR
OVERNIGHT LOWS (+10 TO +20 DEGREES) WITH CONDITIONS MORE TYPICAL OF
MAY OR EARLY JUNE BY NEXT WEEKEND. HIGHS COULD GET OVER 100
DEGREES FOR PORTIONS OF SOUTHERN TEXAS BY SATURDAY.
TATE/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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