340
FXUS02 KWBC 080659
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
258 AM EDT MON MAY 8 2023
VALID 12Z THU MAY 11 2023 - 12Z MON MAY 15 2023
***PERIODS OF HEAVY RAIN EXPECTED FOR PORTIONS OF THE SOUTHERN
PLAINS AND ALSO THE NORTHERN HIGH PLAINS AND VICINITY***
..SYNOPTIC SCALE OVERVIEW
AN AMPLIFIED UPPER LEVEL TROUGH WITH AN ACCOMPANYING SURFACE LOW
WILL BE MAKING WEATHER HEADLINES ACROSS THE ROCKIES AND THE
WESTERN HIGH PLAINS FOR THE END OF THIS WEEK AS THE MAIN UPPER LOW
TRACKS FROM THE CENTRAL ROCKIES TO THE DAKOTAS. THERE WILL LIKELY
BE AN ENHANCED SURGE OF GULF MOISTURE NORTHWARD THAT WILL FUEL
SCATTERED TO NUMEROUS SHOWERS AND STORMS WITH HEAVY RAINFALL
POTENTIAL ACROSS MUCH OF THE PLAINS. THIS LOW THEN SLOWLY WEAKENS
ACROSS THE UPPER MIDWEST GOING INTO THE WEEKEND WITH A RATHER
PRONOUNCED UPPER RIDGE DEVELOPING ACROSS THE PACIFIC NORTHWEST
INTO SOUTHWESTERN CANADA BY SUNDAY AND EARLY NEXT WEEK.
MEANWHILE, THE UPPER RIDGE OVER THE EAST-CENTRAL U.S. AHEAD OF THE
PLAINS STORM SYSTEM WILL LIKELY BREAK DOWN GOING INTO SUNDAY AND
BEYOND WITH A TROUGH LIKELY BUILDING SOUTHWARD FROM EASTERN CANADA
ACROSS THE NORTHEASTERN QUADRANT OF THE NATION. MUCH OF THE
SOUTHERN PLAINS WILL LIKELY REMAIN QUITE UNSETTLED WITH NUMEROUS
ROUNDS OF SHOWERS AND STORMS THROUGH THIS FORECAST PERIOD.
..GUIDANCE/PREDICTABILITY ASSESSMENT
THE 00Z MODEL GUIDANCE SUITE HAS A GOOD OVERALL SYNOPTIC SCALE
DEPICTION OF THE TROUGH CROSSING THE CENTRAL ROCKIES EARLY IN THE
PERIOD, WITH THE CORE OF THE UPPER LOW LIKELY SITUATED OVER
SOUTH-CENTRAL COLORADO BY THURSDAY MORNING AND RECENT GFS RUNS
TRENDING CLOSER TO THE ECMWF/CMC SOLUTIONS. THERE ARE SOME
RELATIVELY MINOR MESOSCALE DIFFERENCES WITH LEAD SHORTWAVE ENERGY
AND RESULTING CONVECTIVE EVOLUTION ACROSS THE GULF COAST REGION
AND ALSO ACROSS NEW ENGLAND FOR THE END OF THE WEEK. LOOKING
AHEAD TO NEXT WEEKEND, THE MODELS AGREE WELL ON A STRONG UPPER
RIDGE BUILDING INTO SOUTHWESTERN CANADA, WASHINGTON AND OREGON,
AND THE UPPER LOW OVER THE DAKOTAS EVOLVING INTO AN OPEN WAVE THAT
MERGES WITH THE DEEPENING TROUGH FROM EAST-CENTRAL CANADA BY
SUNDAY. THE GREATEST MODEL DIFFERENCES EXIST ACROSS SOUTHERN
CANADA FOR THE SUNDAY-MONDAY TIME PERIOD AND THIS IS WHERE THE
ENSEMBLE MEANS ARE MOST HELPFUL AS A STARTING POINT. A
MULTI-DETERMINISTIC MODEL BLEND WAS USED THROUGH FRIDAY, FOLLOWED
BY GRADUALLY INCREASING CONTRIBUTIONS FROM THE ENSEMBLE MEANS FOR
THE WEEKEND AND INTO MONDAY.
..WEATHER/HAZARDS HIGHLIGHTS
SCATTERED TO NUMEROUS SHOWERS AND THUNDERSTORMS WILL LIKELY
DEVELOP ACROSS MUCH OF THE PLAINS STATES GOING INTO THE LATTER
HALF OF THE WORK WEEK, AS MOISTURE ADVECTION FROM THE GULF OF
MEXICO INCREASES AHEAD OF A SLOWING FRONTAL SYSTEM OVER THE
CENTRAL/SOUTHERN HIGH PLAINS AND THE UPPER TROUGH/LOW APPROACHES
FROM THE WEST. THE DAY 4 (12Z THURSDAY-12Z FRIDAY) EXCESSIVE
RAINFALL OUTLOOK WILL MAINTAIN A SLIGHT RISK AREA OVER PARTS OF
EASTERN MONTANA INTO NORTHEASTERN WYOMING AND WESTERN PORTIONS OF
THE DAKOTAS. THIS IS BASED ON THE BEST OVERLAP OF ENSEMBLE
GUIDANCE FOR HIGHEST EXPECTED RAINFALL ALONG WITH WET GROUND
CONDITIONS LIKELY TO EXIST DUE TO MODERATE/HEAVY RAINFALL THE
PRIOR DAY. IT WILL TAKE ADDITIONAL TIME TO RESOLVE SPECIFICS THAT
WILL DEPEND ON THE EXACT TRACK OF THE UPPER LOW AND IF/HOW LONG IT
POTENTIALLY STALLS BEFORE EVOLVING INTO AN OPEN WAVE. THE DAY 5
(12Z FRIDAY-12Z SATURDAY) OUTLOOK WILL INTRODUCE A SLIGHT RISK OF
EXCESSIVE RAINFALL ACROSS PORTIONS OF SOUTH-CENTRAL TEXAS WITH A
STRONG MODEL SIGNAL FOR POTENTIALLY 2-4 INCH TOTALS WITH LOCALLY
HIGHER AMOUNTS POSSIBLE. BY NEXT WEEKEND, PORTIONS OF THE
SOUTHERN PLAINS MAY GET ADDITIONAL ROUNDS OF HEAVIER RAINFALL,
WITH SEVERAL INCHES OF RAIN POSSIBLE IN SOME AREAS OF THE SOUTHERN
PLAINS AS MULTIPLE MESOSCALE CONVECTIVE SYSTEMS DEVELOP. THE
COMBINATION OF PERSISTENT LOW LEVEL INFLOW FROM THE WESTERN GULF,
A STALLED SURFACE FRONT, AND ONE OR MORE SOUTHERN STREAM IMPULSES
ALOFT SHOULD CONTRIBUTE TO THIS POTENTIALLY HEAVY RAINFALL THAT
COULD RESULT IN SOME INSTANCES OF FLOODING, SO THIS WILL BE THE
REGION TO CLOSELY MONITOR IN REGARDS TO THAT. AS THE UPPER LOW
CROSSES THE GREAT BASIN AND NORTHERN ROCKIES, THERE SHOULD BE
SUFFICIENT COLD AIR ALOFT TO SUPPORT SOME LATE SEASON HIGHER
ELEVATION SNOW, ESPECIALLY OVER THE HIGHER MOUNTAIN RANGES OF
NORTHERN WYOMING AND WESTERN MONTANA. SOME OF THE CENTRAL U.S.
MOISTURE MAY EXTEND INTO THE OHIO VALLEY AND THE CENTRAL
APPALACHIANS BY THE LATTER HALF OF THE PERIOD AS THE PLAINS SYSTEM
AND LEADING FRONT GRADUALLY MOVE EASTWARD.
IN TERMS OF TEMPERATURES, HIGHS WILL LIKELY BE RUNNING 5 TO 15
DEGREES ABOVE EARLY MAY AVERAGES FROM THE UPPER MIDWEST TO THE
NORTHEAST STATES TO CLOSE OUT THE WORK WEEK, AND THEN TRENDING
COOLER GOING INTO THE WEEKEND AFTER A COLD FRONT GOES THROUGH THE
REGION. WARMTH WILL BUILD ACROSS THE PACIFIC NORTHWEST BY FRIDAY
AND ESPECIALLY INTO THE WEEKEND WITH HIGHS POTENTIALLY UP TO 15-25
DEGREES ABOVE MID-MAY AVERAGES ACROSS MUCH OF WASHINGTON AND
OREGON. LOWS MAY BE A LITTLE LESS EXTREME BUT COULD STILL
CHALLENGE A FEW DAILY RECORDS FOR WARM LOWS BY THE WEEKEND
(ESPECIALLY SUNDAY). HIGHS WILL LIKELY BE SLIGHTLY BELOW AVERAGE
ACROSS PORTIONS OF THE WEST COAST STATES AND THE INTERMOUNTAIN
WEST IN ASSOCIATION WITH THE UPPER TROUGH THROUGH THURSDAY BEFORE
A MODERATING TREND COMMENCES. OVERNIGHT LOWS OVER THOSE AREAS
EARLY IN THE PERIOD SHOULD BE CLOSER TO AVERAGE WHILE AREAS EAST
OF THE ROCKIES SHOULD SEE MOSTLY ABOVE AVERAGE LOWS WITH INCREASED
CLOUD COVER AND HUMIDITY.
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, 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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