698
FXUS02 KWBC 291849
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
249 PM EDT TUE OCT 29 2024
VALID 12Z FRI NOV 01 2024 - 12Z TUE NOV 05 2024
...HEAVY RAIN THREAT FROM THE SOUTHERN PLAINS TO THE MID-
MISSISSIPPI VALLEY TO DEVELOP THIS WEEKEND...
..GENERAL OVERVIEW
AN UPPER TROUGH AND MODERATE SURFACE LOW WILL EJECT THROUGH THE
NORTHEAST AND EASTERN CANADA FRIDAY OVERTOP A WARM AMBIENT UPPER
RIDGE HELD OVER THE SOUTHEAST. A COLD FRONT WILL SWING THROUGH THE
EASTERN U.S. TO FOCUS LINGERING SHOWERS AND USHER IN MODERATING
POST-FRONTAL HIGH PRESSURE. THE TRAILING PORTION OF THE FRONT IS
FORECAST TO SLOW, BUT OFFER SOME CONVECTIVE FOCUS. AN EMERGING
HEAVY RAINFALL PATTERN THEN EMINATES UP THROUGH THE SOUTH-CENTRAL
U.S. WITH RETURN FLOW IN A DEEPENING MOISTURE CHANNEL BETWEEN THE
SOUTHEAST UPPER RIDGE AND THE APPROACH OF UPPER TROUGH ENERGY AND
FRONT FROM THE WEST. TOWARDS THAT END, AFOREMENTIONED UPSTREAM
UPPER TROUGH ENERGY WILL DIG SHARPLY INTO AN UNSETTLED WEST, WITH
MODERATE RAINS AND ELEVATION SNOWS OVER THE NORTHWEST AND
UNCERTAINLY SOUTHWARD TO CALIFORNIA ALONG WITH LESS ORGANIZED
ACTIVITY TO THE INTERMOUTAIN WEST/ROCKIES. THIS PATTERN MAY LEAD TO
CLOSED LOW DEVELOPMENT AT THE BASE OF A MAIN TROUGH.
..GUIDANCE/PREDICTABILITY ASSESSMENT
MODELS HAVE TRENDED SLOWER AND DEEPER WITH AN ANOMALOUS TROUGH THAT
MAY DIG INTO THE WEST BEGINNING THIS WEEKEND. A GENERAL MODEL
BLEND CONSISTING OF THE DETERMINISTIC 00Z EC/CMC/UKMET AND 06Z GFS
WERE USED ON DAYS 3 AND 4, WITH HEAVY WEIGHTING PLACED ON THE EC
AND GFS SOLUTIONS ON DAY 3, BECAUSE THEY ARE BOTH MORE PROGRESSIVE
AND IN LINE WITH THE ENSEMBLE MEANS WITH THEIR DEPICTION OF A
CLOSED MID- LEVEL LOW DROPPING INTO THE NORTHWEST FROM THE GULF OF
ALASKA.
WEIGHTING SHIFTS TO THE GFS ON DAY 4 BECAUSE IT, MUCH LIKE ALL OF
THE ENSEMBLE MEANS, AVOIDS CLOSING OFF A MID-LEVEL LOW OVER THE
NORTHWEST WHILE MAINTAINING A POSITIVELY TILTED TROUGH AXIS ALONG
THE WEST COAST. THE 00Z ECE/CMCE AND 06Z GEFS ARE INTRODUCED TO THE
BLEND ON DAY 5 IN PLACE OF THE DETERMINISTIC CMC AND UKMET WHICH
ARE COMPARATIVELY MUCH MORE BULLISH WITH THE WESTERN TROUGH THAN
THE DETERMINISTIC EC/GFS AND ENSEMBLE MEANS. THE ENSEMBLE MEANS ARE
FAVORED THROUGH THE REST OF THE PERIOD AS THEY CLUSTER FAIRLY WELL
ON A SLOW MOVING TROUGH OVER THE CENTRAL U.S., DESPITE SOME TIMING
SPREAD, PARTICULARLY FOUND IN THE ECE AND CMCE.
THE 06Z AIFS RESEMBLES MORE OF A 00Z CMC SOLUTION WITH A CLOSED
POSITIVELY TILTED MID-LEVEL LOW OVER THE SOUTHWEST ON DAY 6
(MONDAY). THE GRAPHCAST LOOKS MORE LIKE THE 06Z GEFS MEAN, WHICH IS
MORE PROGRESSIVE THAN THE REST OF THE DETERMINISTIC, ENSEMBLE AND
ML MODELS (FUXI, PANGU, FOURCASTNET).
..WEATHER/HAZARDS HIGHLIGHTS
A HEAVY RAINFALL PATTERN SEEMS LIKELY ON TAP BY THE WEEKEND OVER
THE SOUTHERN PLAINS AND VICINITY. A WPC DAY 4/FRIDAY EXCESSIVE
RAINFALL OUTLOOK (ERO) MARGINAL RISK AREA IS IN PLACE TO ADDRESS
POTENTIAL, WITH THE NEW DAY 5/SATURDAY ERO INTRODUCING MARGINAL
AND SLIGHT RISK AREAS GIVEN CONSISTENT GUIDANCE SIGNALS. 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 FLOW LOOK TO
INCREASE THE CHANCES OF MORE WIDESPREAD, HEAVY RAINFALL WITH
FLOODING CONCERNS DESPITE DRY ANTECEDENT CONDITIONS, ESPECIALLY
FROM THE SOUTH-CENTRAL PLAINS TO THE MIDDLE MISSISSIPPI VALLEY.
PRECIPITATION ASSOCIATED WITH PACIFIC SYSTEM APPROACH AS ENHANCED
BY TERRAIN AND MODERATE LONG-FETCH MOISTURE IS FORECAST TO FOCUS
AND WITH MUCH UNCERTAINTY WORK SOUTHWARD OVER THE WEST COAST LATER
IN THE WEEK AND THROUGH THE WEEKEND, WITH HIGH- ELEVATION SNOW
REACHING INTO 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.
KEBEDE/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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