616
FXUS02 KWBC 301844
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
244 PM EDT WED OCT 30 2024
VALID 12Z SAT NOV 02 2024 - 12Z WED NOV 06 2024
...MULTI-DAY HEAVY RAIN/FLOODING THREAT FROM THE SOUTHERN PLAINS
TO THE MID-MISSISSIPPI VALLEY THIS WEEKEND INTO EARLY NEXT WEEK...
19Z UPDATE: THE 12Z MODEL GUIDANCE SUITE FEATURES GOOD OVERALL
AGREEMENT ACROSS THE CONTINENTAL U.S. GOING INTO NEXT WEEKEND,
GIVEN A MORE AMPLIFIED UPPER FLOW PATTERN EVOLVING WITH A DEEP
WESTERN U.S. TROUGH AND A BUILDING RIDGE AXIS EAST OF THE
MISSISSIPPI RIVER. THIS WILL RESULT IN A PRONOUNCED TEMPERATURE
DICHOTOMY ACROSS THE COUNTRY, WITH HIGHS RUNNING UP TO 20 DEGREES
ABOVE EARLY NOVEMBER AVERAGES ACROSS THE OHIO VALLEY EARLY NEXT
WEEK, AND 15 DEGREES BELOW AVERAGE FOR PORTIONS OF THE
INTERMOUNTAIN WEST. WITH RESPECT TO THE DAY 4 AND 5 EXCESSIVE
RAINFALL OUTLOOKS, NO MAJOR CHANGES WERE NEEDED FOR THIS UPDATE,
WITH SLIGHT RISK AREAS MAINTAINED FOR THE CENTRAL PLAINS. GOING
INTO MONDAY, MORE NOTICEABLE DIFFERENCES EMERGE WITH THE NEXT
TROUGH APPROACHING THE PACIFIC NORTHWEST COAST, WITH THE ECMWF
FASTER WITH THE TROUGH PROGRESSION. TOWARDS THE END OF THE PERIOD,
THE MODELS STILL HAVE GREAT AGREEMENT WITH THE RIDGE NEAR THE EAST
COAST, BUT VARY MORE ACROSS THE NORTH- CENTRAL U.S. AS THE MAIN
TROUGH BEGINS LIFTING OUT AND THE SECOND ONE FROM THE PACIFIC
NORTHWEST MOVES INLAND. THE ENSEMBLE MEANS WERE GRADUALLY INCREASED
TO ABOUT 40% BY NEXT WEDNESDAY. THE PREVIOUS FORECAST DISCUSSION
IS APPENDED BELOW FOR REFERENCE. /HAMRICK
-----------------------------
..GENERAL OVERVIEW
AN EMERGING EXCESSIVE RAINFALL EVENT IS EXPECTED TO DEVELOP IN
EARNEST BY THE WEEKEND INTO EARLY NEXT WEEK OVER THE SOUTH-
CENTRAL U.S. WITH RETURN GULF OF MEXICO INFLOW IN A DEEPENING
MOISTURE CHANNEL BETWEEN A EAST/SOUTHEAST UPPER RIDGE AND SLOW
APPROACH OF AMPLIFIED UPPER TROUGH/LOW ENERGY AND FRONT FROM THE
WEST. TOWARDS THAT END, AFOREMENTIONED UPSTREAM UPPER TROUGH ENERGY
WILL DIG SHARPLY ACROSS THE WESTERN U.S. THIS WEEKEND, WITH
MODERATE RAINS AND HIGH ELEVATION SNOWS FROM THE NORTHWEST
SOUTHWARD TO CALIFORNIA. ACTIVITY SHOULD SPREAD MORE MODESTLY TO
THE SOUTHWEST AND THE INTERMOUNTAIN WEST/ROCKIES BY EARLY NEXT
WEEK WITH SLOW AND AMPLIFIED FLOW TRANSLATION AND ENERGY
REINFORCEMENT AND CLOSED LOW DEVELOPMENT AT THE BASE OF THE UPPER
TROUGH/FRONTS.
..GUIDANCE/PREDICTABILITY ASSESSMENT
MODELS AND ENSEMBLES HAVE TRENDED TOWARD A BETTER CLUSTERED OVERALL
SOLUTION OVER THE COMING WEEKEND IN A PATTERN SEEMINGLY NOW WITH
CLOSER TO AVERAGE PREDICTABILITY. A COMPOSITE MODEL BLEND TENDS TO
MITIGATE STILL LINGERING INDIVIDUAL SYSTEM TIMING ISSUES TO OFFER A
SEEMINGLY REASONABLE FORECAST STARTING POINT, GENERALLY IN LINE
WITH THE NATIONAL BLEND OF MODELS AND THREAT MESSAGING CONTINUITY.
FORECAST SPREAD INCREASES INTO LONGER TIME FRAMES, SO PIVOTED TO A
COMPOSITE BLEND OF BEST CLUSTERED AND CYCLE TO CYCLE CONSISTENT
GUIDANCE FROM THE 12 UTC ECMWF/CANADIAN AND THEIR ENSEMBLE MEANS.
..WEATHER/HAZARDS HIGHLIGHTS
A HEAVY RAINFALL PATTERN SEEMS LIKELY ON TAP BY THE WEEKEND WITH
MAIN FOCUS FROM THE SOUTHERN PLAINS THROUGH THE MID-MISSISSIPPI
VALLEY AND VICINITY. THE WPC DAY 4/SATURDAY AND DAY 5/SUNDAY
EXCESSIVE RAINFALL OUTLOOKS (EROS) CONTINUE TO OFFER MARGINAL AND
SLIGHT RISK THREAT AREAS GIVEN CONSISTENT GUIDANCE SIGNALS, WITH A
MODEST EXPANSION OF THE MARGINAL RISK AREAS TO ACCOUNT FOR THE
LATEST MODEL GUIDANCE. EXPECT ACTIVITY TO EXPAND AND FOCUS ALONG A
SOUTHWEST TO NORTHEAST AXIS AHEAD OF ADDITIONAL FRONTAL BOUNDARIES
THIS WEEKEND AND INTO EARLY NEXT WEEK AS ROBUST UPPER
TROUGH/CLOSED LOW ENERGY DIGS UPSTREAM INTO THE WEST COAST TO RE-
AMPLIFY THE FLOW OVER THE LOWER 48 AND VICINITY. MULTIPLE DAYS OF
SOUTHERLY, MOIST GULF INFLOW LOOK TO INCREASE THE CHANCES OF MORE
WIDESPREAD, HEAVY RAINFALL WITH FLOODING CONCERNS DESPITE DRY
ANTECEDENT CONDITIONS, WITH A RISK OF REPEAT/TRAINING CONVECTION IN
A SLOW TO DISLODGE AND DEEPENED MOISTURE CHANNEL BETWEEN THE
WEST/SOUTHWEST U.S. UPPER TROUGH AND EAST/SOUTHEAST U.S. WARMING
UPPER RIDGE. IF THE HEAVY RAINS ON DAY 5 TREND HEAVIER, OR APPEARS
LIKELY TO FALL ON THE SAME AREAS THAT GET IMPACTFUL RAIN IN THE
PRECEDING DAYS, AN EVENTUAL MODERATE RISK COULD BE NEEDED AS THE
EVENT GETS CLOSER IN TIME. THE MULTI- DAY THREAT WILL LIKELY
CONTINUE INTO EARLY NEXT WEEK WHILE SPREADING NORTHEASTWARD OVER
THE MIDWEST IN THIS PATTERN WITH THE DEEP MOISTURE LEADING TO SOME
WARM SECTOR RECORD HIGH OVERNIGHT TEMPERATURES.
PRECIPITATION WITH PACIFIC SYSTEM DIGGING WILL BE LOCALLY ENHANCED
BY TERRAIN AS MODERATE LONG-FETCH MOISTURE IS FORECAST TO WORK
SOUTHWARD OVER THE WEST COAST THIS WEEKEND, WITH HIGH-ELEVATION
SNOW ALSO REACHING FAVORED TERRAIN OF THE NORTHERN INTERMOUNTAIN
WEST/ROCKIES AND ENHANCED RAINS REACHING DOWN INTO CALIFORNIA.
REGARDLESS, THE COLD FRONTAL SURGE AND POSSIBLE CLOSED LOW
DEVELOPMENT AT THE SOUTHERN BASE OF THE MAIN UPPER TROUGH WILL
BRING IN COOLER TEMPERATURES TO MUCH OF THE WEST. THIS AND SLOW AND
AMPLIFIED FLOW TRANSLATION WILL ALSO ACT TO SPREAD MORE MODEST
RAINS OVER THE SOUTHWEST AND INTO THE SOUTH-CENTRAL GREAT BASIN AND
ROCKIES INTO EARLY NEXT WEEK. MEANWHILE, ADDITIONAL PACIFIC SYSTEM
ENERGY UPSTREAM MAY ALSO BRING ANOTHER ROUND OF MODERATE
PRECIPITATION BACK INTO THE NORTHWEST.
SCHICHTEL/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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