723
FXUS02 KWBC 171822
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
222 PM EDT WED APR 17 2024
VALID 12Z SAT APR 20 2024 - 12Z WED APR 24 2024
..OVERVIEW
THE PATTERN DURING THE MEDIUM RANGE PERIOD WILL CONTINUE TO
TRANSITION TO MORE PROGRESSIVE FLOW BY THIS WEEKEND AS AN OMEGA
BLOCK OVER THE NORTHEAST PACIFIC INTO WESTERN NORTH AMERICA AND THE
NORTHERN U.S. TIER BEGINS TO BREAK DOWN. ENERGY FROM THE WEST SIDE
OF A DEEP UPPER LOW INITIALLY OVER SOUTHEAST CANADA ON SATURDAY
WILL INTERACT WITH ANOTHER SHORTWAVE INTO THE SOUTHERN PLAINS,
INCREASING THE HEAVY RAIN THREAT ON SATURDAY ESPECIALLY ACROSS MUCH
OF TEXAS, THEN CONTINUING TO A LESSER EXTENT INTO SUNDAY ACROSS
THE SOUTHEAST. SECONDARY ENERGY EJECTING FROM AN UPPER LOW/TROUGH
OVER THE NORTHEAST PACIFIC WILL SKIRT THE NORTHERN TIER AND MOVE
THROUGH THE GREAT LAKES INTO THE NORTHEAST EARLY NEXT WEEK.
TROUGHING GENERALLY WILL GET REESTABLISHED OVER THE WEST COAST BY
NEXT TUESDAY-WEDNESDAY.
..GUIDANCE/PREDICTABILITY ASSESSMENT
THE LATEST GUIDANCE SHOWS VERY GOOD AGREEMENT ACROSS THE CONUS
THROUGH MUCH OF THE PERIOD (SATURDAY-WEDNESDAY). THERE ARE SOME
TIMING DIFFERENCES WITH SHORTWAVE TROUGHING THROUGH THE SOUTHEAST
SUNDAY-MONDAY AND AGAIN WITH THE NEXT SHORTWAVE THROUGH THE GREAT
LAKES/NORTHEAST TUESDAY-WEDNESDAY. THESE DETAILS CREATE SOME
UNCERTAINTY IN THE EVENTUALLY (GENERALLY LIGHT) PRECIPITATION
PATTERN ACROSS THE SOUTHEAST AND NORTHEAST EARLY NEXT WEEK.
GENERALLY FAVORED THE MODEL/ENSEMBLE CONSENSUS FOR NOW. THERE IS
MORE UNCERTAINTY LATE PERIOD WITH THE EVOLUTION OF A DEEP CLOSED
LOW OVER THE GULF OF ALASKA WHICH MAY SPLIT INTO TWO FACTIONS --
THE SOUTHERN PART LIKELY HEADED TOWARDS THE WEST COAST BY NEXT WED.
THE GFS/GEFS WERE QUICKER THAN THE ECMWF/ECMWF ENSEMBLES (WHICH
HAD SUPPORT FROM THE AIFS-ECMWF). FAVORED A MIDDLE-GROUND TO SLOWER
SOLUTION THAN A STRAIGHT CONSENSUS.
THE WPC FORECAST USED A BLEND OF THE 06Z GFS/GEFS AND 00Z
ECMWF/CMC THIS MORNING WITH MORE WEIGHT TOWARD THE ECMWF BY THE END
OF THE FORECAST PERIOD.
..WEATHER/HAZARDS HIGHLIGHTS
SHORTWAVE ENERGY INTO THE SOUTHERN PLAINS INTERACTING WITH A SLOW-
MOVING FRONTAL BOUNDARY AND ANOMALOUS MOISTURE/INSTABILITY WILL
INCREASE THE THREAT FOR HEAVY TO EXCESSIVE RAINFALL ACROSS MUCH OF
THE SOUTHERN PLAINS INTO THE LOWER MISSISSIPPI VALLEY ON SATURDAY.
A SLIGHT RISK CONTINUES ON THE DAY 4 EXCESSIVE RAINFALL OUTLOOK
(SAT-SUN MORNING) ACROSS CENTRAL TO NORTHEAST TEXAS. RAINFALL WILL
CONTINUE INTO THE SOUTHEAST/CAROLINAS ON SUNDAY AS THE FRONT SLOWLY
SINKS THROUGH THAT REGION, THOUGH AMOUNTS OVERALL LOOK TO BE LOWER
THAN ON DAY 4. THIS IS DEPICTED AS A MARGINAL RISK ON THE DAY 5
ERO. THE NEXT SHORTWAVE THROUGH THE NORTHERN PLAINS-GREAT LAKES-
NORTHEAST WILL BE ACCOMPANIED BY SOME GENERALLY LIGHT RAIN EARLY
NEXT WEEK.
THE UPPER TROUGH OVER THE NORTHERN TIER STATES AND EVENTUALLY INTO
THE EAST WILL SUPPORT BELOW NORMAL TEMPERATURES (WITH GREATER
ANOMALIES FOR HIGHS THAN LOWS) FOR MOST AREAS EAST OF THE ROCKIES
EXCEPT FLORIDA BY NEXT WEEKEND. ABOVE NORMAL TEMPERATURES ACROSS
THE SOUTHWEST SHOULD GRADUALLY EXPAND NORTHWARD UNDERNEATH A
BUILDING WESTERN U.S. RIDGE AND PROGRESS EASTWARD INTO THE ROCKIES
EARLY NEXT WEEK. NORTHERN PARTS OF THE WEST MAY STAY NEAR NORMAL
DUE TO THE UPPER SHORTWAVE/COLD FRONT CROSSING THE REGION NEXT
WEEK.
FRACASSO/SANTORELLI
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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