443
FXUS02 KWBC 091905
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
305 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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