241
FXUS02 KWBC 091857
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
257 PM EDT THU MAY 9 2024
VALID 12Z SUN MAY 12 2024 - 12Z THU MAY 16 2024
...EXCESSIVE RAINFALL/FLOODING THREAT FOR THE SOUTHERN PLAINS,
GULF COAST AND SOUTHEAST...
..GUIDANCE/PREDICTABILITY ASSESSMENT
THE LATEST MODELS AND ENSEMBLES SHOW REASONABLY GOOD AGREEMENT THAT
BY THE START OF THE PERIOD ON SUNDAY, THE PATTERN SHOULD TREND MORE
PROGRESSIVE FEATURING A SERIES OF TROUGHS/SHORTWAVES MIGRATING FROM
THE CENTRAL TO EASTERN U.S. AS UPPER LEVEL RIDGING TRIES TO BUILD
BACK IN OVER THE WEST. THERE WAS GOOD ENOUGH AGREEMENT IN THE
GUIDANCE FOR A GENERAL BLEND OF THE DETERMINISTIC GUIDANCE THE
FIRST HALF OF THE PERIOD AS TROUGHING SHIFTS OUT OF THE NORTHEAST
AND ANOTHER POTENT SHORTWAVE MOVES THROUGH THE CENTRAL PLAINS TO
LOWER/MIDDLE MISSISSIPPI VALLEY. BY DAY 6/WEDNESDAY, THERE ARE SOME
TIMING DIFFERENCES WITH THIS SHORTWAVE AS IT SHIFTS INTO THE MID-
SOUTH AND SOUTHEAST WHICH HAS CRITICAL IMPLICATIONS ON RESULTING
QPF ACROSS THIS REGION. THERE ARE ALSO SOME MORE NOTICEABLE
DIFFERENCES WITH AN AMPLIFYING SHORTWAVE FROM CENTRAL CANADA INTO
THE PLAINS, AND HOW STRONG RIDGING BUILDS BACK IN ACROSS THE WEST.
OVER THE PAST COUPLE OF GUIDANCE RUNS, THE CMC REMAINS THE
STRONGEST WITH THAT RIDGE, WHILE THE GFS AND ECMWF (TO VARYING
DEGREES) ARE A LITTLE WEAKER DUE TO STRONGER SHORTWAVE ENERGY
BRITISH COLUMBIA NEXT THURSDAY. THERE IS A LOT OF RUN TO RUN
INCONSISTENCIES BETWEEN MODELS TOO, SO IT SEEMS PRUDENT AT THIS
POINT THE BLEND TRENDS INCREASINGLY MORE TOWARDS THE ENSEMBLE MEANS
LATE IN THE PERIOD TO MITIGATE/SMOOTH THESE UNCERTAINTIES. DID
CONTINUE TO INCLUDE SOME ECMWF JUST FOR A LITTLE EXTRA SYSTEM
DEFINITION. THE APPROACH MAINTAINED GOOD CONTINUITY WITH THE
PREVIOUS WPC FORECAST AS WELL.
..WEATHER/HAZARDS HIGHLIGHTS
A GENERAL SPLIT FLOW PATTERN WILL PERSIST OVER THE LOWER 48 STATES
INTO NEXT WEEK. THIS PATTERN WILL BE HIGHLIGHTED BY AN AMPLIFIED
SOUTHERN STREAM UPPER TROUGH SLATED TO EJECT SLOWLY BUT STEADILY EAST-
NORTHEASTWARD FROM THE SOUTHWEST SUNDAY AND THROUGH THE MID-
SOUTH/SOUTH TO OFFSHORE THE MID-ATLANTIC/EAST COAST NEXT THURSDAY.
THIS SYSTEM AND ASSOCIATED LEAD WAVY FRONT WILL INCREASINGLY TAP
AND FEED INLAND A RETURN OF DEEP GULF MOISTURE AND INSTABILITY
UNDER FAVORABLE UPPER TROUGH AND RIGHT ENTRANCE REGION UPPER JET
SUPPORT TO FUEL A POTENTIALLY SIGNIFICANT HEAVY RAINFALL AND
RUNOFF/FLOODING PERIOD. THE WPC DAY 4/SUNDAY EXCESSIVE RAINFALL
OUTLOOK (ERO) DEPICTS A MARGINAL RISK AREA SPREAD SOUTH/SOUTHEASTWARD
FROM THE CENTRAL-SOUTHERN PLAINS TO THE LOWER MISSISSIPPI VALLEY.
WITHIN THIS, A SLIGHT RISK AREA REMAINS IN PLACE FOR SOUTHEAST
TEXAS INTO LOUISIANA GIVEN MOIST SOIL/STREAMFLOW SENSITIVITIES
FROM RECENT HEAVY RAINFALL. THE OVERALL RISK SHOULD SHIFT EAST ON DAY
5/MONDAY AS HIGHLIGHTED BY THE ERO WITH A MARGINAL RISK ACROSS THE
MIDDLE/LOWER MISSISSIPPI VALLEY INTO THE GULF COAST/SOUTHEAST. AN
EXPANSIVE SLIGHT RISK EXISTS FROM SOUTHEAST TEXAS INTO THE FLORIDA
PANHANDLE. HEAVY RAIN AND A THREAT OF RUNOFF ISSUES IS ALSO
EXPECTED TO SPREAD ACROSS THE SOUTHEAST THROUGH NEXT MIDWEEK AND
POSSIBLY BUILD BACK INTO THE SOUTHERN/CENTRAL PLAINS AS ADDITIONAL
SHORTWAVE ENERGY MOVES INTO THE REGION.
MEANWHILE, SEVERAL AMPLIFIED UPPER TROUGHS AND SURFACE SYSTEMS ARE
SET TO WORK OVER THE NORTHERN TIER OF THE NATION FROM THE
NORTHWEST AND NORTH- CENTRAL U.S. THROUGH THE NORTHEAST AND FOCUS
MAINLY MODEST MOISTURE AND PRECIPITATION.
SANTORELLI/SCHICHTEL
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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