431
FXUS02 KWBC 022012
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
411 PM EDT TUE MAY 02 2023
VALID 12Z FRI MAY 05 2023 - 12Z TUE MAY 09 2023
...COOL/WET PATTERN FOR THE PACIFIC NORTHWEST/GREAT BASIN/ROCKIES
INTO THE WEEKEND WITH LOCALIZED FLOODING CONCERNS...
..OVERVIEW
THE UPPER LEVEL PATTERN IS FORECAST TO EVOLVE FROM THE STUBBORN
OMEGA BLOCK CENTERED OVER THE CONUS THIS PAST WEEK/WEEKEND AND
TOWARDS MEAN RIDGING BUILDING OVER THE CENTRAL/EASTERN CONUS AND
MEAN TROUGHING OVER THE CENTRAL/WESTERN CONUS. CONDITIONS WILL BE
COOL AND WET IN THE WEST UNDER THE INFLUENCE OF THE UPPER-LEVEL
TROUGHING, WITH HEAVY RAINFALL ON TOP OF MOUNTAIN SNOW MELT
LEADING TO LOCALIZED FLOODING CONCERNS IN THE GREAT BASIN/NORTHERN
ROCKIES. MOISTURE SOURCED FROM THE GULF AND PACIFIC WILL BRING THE
POTENTIAL FOR MULTIPLE REGIONS OF LOCALLY HEAVY RAIN TO THE
PLAINS/MISSISSIPPI VALLEY THROUGH THE WEEKEND AND INTO NEXT WEEK
DEPENDING ON THE EVOLUTION OF SHORTWAVE ENERGY ALOFT.
..GUIDANCE/PREDICTABILITY ASSESSMENT
THE 00Z/06Z GUIDANCE PACKAGE DID A GOOD JOB OF CAPTURING THE
OVERALL SYNOPTIC EVOLUTION ACROSS THE CONUS EARLY IN THE PERIOD
BEFORE MODEL SPREAD INCREASED TOWARD THE END. A GENERAL MODEL
BLEND CONSISTING OF THE 00Z EC/CMC/UKMET AND 06Z GFS WERE UTILIZED
THROUGH DAY 4 BEFORE INTRODUCING THE ENSEMBLE MEANS INCREMENTALLY
THROUGH DAY 7 AND PHASING OUT THE 06Z GFS. THE 06Z GFS/GEFS WERE
WEIGHTED LESS ON DAYS 6 AND 7 DUE TO RUN TO RUN AND ENSEMBLE
MEMBER INCONSISTENCIES WITH RESPECT TO THE TIMING OF UPPER-LEVEL
ENERGY AND MOVING ACROSS THE WEST AND CENTRAL U.S.. THE 00Z EC/ECE
APPEARED TO HAVE BETTER RUN-RUN CONSISTENCY, ENSEMBLE MEMBER
AGREEMENT AND CLOSER CLUSTERING WITH THE 00Z CMC/CMCE.
..WEATHER/HAZARDS HIGHLIGHTS
PRECIPITATION CHANCES WILL REMAIN HIGH AND WIDESPREAD FOR THE
PACIFIC NORTHWEST/GREAT BASIN/NORTHERN ROCKIES LATE THIS
WEEK/WEEKEND AS AN UPPER-LEVEL WAVE AND MULTIPLE FRONTAL SYSTEMS
IMPACT THE REGION. RAINFALL MAY BE LOCALLY HEAVY AT TIMES, WITH
SOME SCATTERED THUNDERSTORM CHANCES. THE RAINFALL ON TOP OF
ONGOING SNOW MELT MAY LEAD TO SOME FLOODING CONCERNS IN TERRAIN
SENSITIVE AREAS AROUND THE FOOTHILLS OF MOUNTAIN RANGES AS WELL AS
ALONG LOCAL STREAMS/RIVERS FRIDAY, WITH A BROAD "MARGINAL RISK"
EXCESSIVE RAINFALL OUTLOOK IN PLACE. SOME SNOW SHOWERS WILL BE
POSSIBLE AT HIGHER MOUNTAIN ELEVATIONS. TEMPERATURES WILL REMAIN A
BIT COOL MORE BROADLY ACROSS THE WEST, WITH HIGHS RUNNING 5-10
DEGREES BELOW AVERAGE THROUGH THE PERIOD.
MOIST, UPSLOPE FLOW SETTLING IN ALONG PORTIONS OF THE
NORTHERN/CENTRAL HIGH PLAINS AHEAD OF A POTENTIAL BETTER ORGANIZED
SURFACE FRONTAL SYSTEM PASSING THROUGH THE PLAINS/UPPER MIDWEST
LOOK TO BRING MULTIPLE DAYS OF RAINFALL FRIDAY-SUNDAY. A "MARGINAL
RISK" HAS BEEN MAINTAINED FOR PORTIONS OF THE NORTHERN/CENTRAL
PLAINS FRIDAY WHERE MORE ORGANIZED CONVECTION MAY PRODUCE SOME
LOCALLY HEAVY RAINFALL TOTALS. FURTHER SOUTH, GULF MOISTURE
FLOWING NORTHWARD AS WELL AS ADDITIONAL MOISTURE SOURCED FROM THE
PACIFIC WILL SPREAD NORTHEASTWARD ACROSS THE CENTRAL/SOUTHERN
PLAINS AND MIDDLE/LOWER MISSISSIPPI VALLEY INTO THE SOUTHEAST LATE
WEEK LEADING TO A BROAD REGION OF SHOWERS AND THUNDERSTORMS. THE
EVOLUTION OF THE PATTERN HAS REMAINED RATHER NEBULOUS THE LAST FEW
DAYS AS THE GUIDANCE HAS VARIED ON THE TIMING AND EVOLUTION OF
EMBEDDED SHORTWAVE ENERGY ALOFT, LESSENING CONFIDENCE ON THE
SPECIFICS OF REGIONS OF HEAVIER RAINFALL AND POTENTIAL FLASH
FLOODING CONCERNS. HOWEVER, THE GUIDANCE HAS SHOWN THE HIGHEST
CONFIDENCE IN WIDESPREAD CONVECTION AND HIGH QPF AMOUNTS FROM THE
MIDDLE MISSISSIPPI TO TENNESSEE VALLEY FRIDAY, WITH THE POTENTIAL
FOR TRAINING APPEARING SUFFICIENT TO SUPPORT AN UPGRADE TO A
"SLIGHT RISK" AREA. ADDITIONAL HEAVY RAINFALL CHANCES LOOK
POSSIBLE OVER THE WEEKEND MORE BROADLY ACROSS THE
CENTRAL/SOUTHEASTERN U.S., PARTICULARLY THE LOWER MISSISSIPPI
VALLEY, BUT CONFIDENCE REMAINS LOW GIVEN THE GUIDANCE SPREAD IN
HOW THE SURFACE PATTERN AND SUPPORTING SHORTWAVE DYNAMICS WILL
EVOLVE. HIGH TEMPERATURES WILL BE SEASONABLY WARM FOR EARLY MAY
FROM THE PLAINS TO THE SOUTHEAST UNDER THE INFLUENCE OF MEAN
RIDGING ALOFT, WITH SOME HIGHS RUNNING 10-15 DEGREES ABOVE AVERAGE
IN THE CENTRAL PLAINS.
THE PERSISTENT COOL/WET PATTERN OVER THE GREAT LAKES AND NORTHEAST
DUE TO A STUBBORN UPPER-LEVEL LOW THIS PAST WEEK/WEEKEND WILL
FINALLY MODERATE THIS UPCOMING WEEKEND, WITH HIGH TEMPERATURES
RETURNING TO NEAR TO SLIGHTLY ABOVE AVERAGE LEVELS INTO EARLY NEXT
WEEK. PRECIPITATION CHANCES WILL REMAIN LOW UNDER THE INFLUENCE OF
A BROAD AREA OF HIGH PRESSURE IN PLACE. SHOWER AND THUNDERSTORM
CHANCES WILL INCREASE FOR THE CAROLINAS SOUTH INTO FLORIDA THIS
WEEKEND, WITH AMOUNTS AND COVERAGE LIKELY DICTATED BY A WEAK WAVE
ALOFT AND SURFACE FRONTAL BOUNDARY INFLUENCE THAT REMAIN HARD TO
PIN DOWN AT THIS TIMEFRAME.
KEBEDE/PUTNAM
HAZARDS:
- HEAVY RAIN ACROSS PORTIONS OF THE NORTHERN ROCKIES, FRI, MAY 5.
- HEAVY RAIN ACROSS PORTIONS OF THE LOWER OHIO VALLEY AND INTO
WESTERN KENTUCKY, FRI, MAY 5.
- FLOODING POSSIBLE ACROSS PORTIONS OF MAINE, THE NORTHERN PLAINS,
THE NORTHERN ROCKIES, THE MID-MISSISSIPPI VALLEY, THE NORTHERN
GREAT BASIN, AND THE PACIFIC NORTHWEST.
- FLOODING OCCURRING OR IMMINENT ACROSS PORTIONS OF THE NORTHEAST,
THE NORTHERN PLAINS, THE NORTHERN ROCKIES, MISSOURI, NEW JERSEY,
THE UPPER MIDWEST, AND THE SOUTH CAROLINA.
- FLOODING LIKELY ACROSS PORTIONS OF THE MID-MISSISSIPPI VALLEY,
SOUTH DAKOTA, AND THE NORTHERN ROCKIES.
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, EXPERIMENTAL EXCESSIVE RAINFALL
OUTLOOK, WINTER WEATHER OUTLOOK PROBABILITIES AND HEAT INDICES ARE
AT:
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
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