708
FXUS02 KWBC 070659
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
258 AM EDT SUN MAY 7 2023
VALID 12Z WED MAY 10 2023 - 12Z SUN MAY 14 2023
***PERIODS OF HEAVY RAIN EXPECTED FOR PORTIONS OF THE SOUTHERN
PLAINS AND ALSO MONTANA AND NORTH DAKOTA***
..OVERVIEW
A WELL DEFINED TROUGH EXPECTED OVER THE INTERMOUNTAIN WEST
MID-WEEK IS EXPECTED TO SLOWLY LIFT NORTHEASTWARD ACROSS THE
ROCKIES AND THEN THE NORTHERN PLAINS BY FRIDAY. THIS WILL TEND TO
BUILD THE RIDGE THAT WILL BE DOWNSTREAM FROM THE GULF COAST TO THE
MIDWEST, AND A TROUGH AXIS ACROSS THE NORTHEAST STATES THAT EXITS
ON THURSDAY WITH A SECOND TROUGH BUILDING IN OVER SOUTHEAST CANADA
NEXT WEEKEND. THERE WILL BE AN INCREASE IN SHOWER AND
THUNDERSTORM ACTIVITY ACROSS MUCH OF THE CENTRAL U.S., AND
GENERALLY ABOVE NORMAL TEMPERATURES EAST OF THE ROCKIES IN
RESPONSE TO THE UPPER RIDGE ALOFT.
..GUIDANCE/PREDICTABILITY ASSESSMENT
THE 00Z MODEL GUIDANCE SUITE HAS A GOOD OVERALL SYNOPTIC SCALE
DEPICTION OF THE TROUGH CROSSING THE INTERMOUNTAIN WEST EARLY IN
THE PERIOD, BUT SOME MESOSCALE DIFFERENCES ARE APPARENT WITH
SHORTWAVE ENERGY AND CONVECTIVE EVOLUTION ACROSS THE GULF COAST
REGION. BY THURSDAY THE GFS AND THE ENSEMBLE MEANS ARE FARTHER
NORTH WITH THE CLOSED UPPER LOW OVER THE WESTERN HIGH PLAINS
COMPARED TO THE ECMWF/CMC SOLUTIONS, AND THIS REMAINS THE CASE
GOING INTO FRIDAY. LOOKING AHEAD TO NEXT WEEKEND, THE MODELS
AGREE ON A STRONG UPPER RIDGE BUILDING INTO SOUTHWESTERN CANADA,
AND THE LATEST CMC HAS TRENDED CLOSER TO THE MODEL CONSENSUS
COMPARED TO ITS 12Z RUN. THE GFS IS A LITTLE SLOWER WITH BRINGING
THE NORTHERN PLAINS LOW EASTWARD BY SUNDAY, BUT FOR A DAY 7
FORECAST IT IS CLOSE ENOUGH TO THE CONSENSUS TO INCLUDE IT IN THE
FORECAST BLEND. A MULTI-DETERMINISTIC MODEL BLEND WAS USED
THROUGH THURSDAY, FOLLOWED BY GRADUALLY INCREASING CONTRIBUTIONS
FROM THE ENSEMBLE MEANS BY THE WEEKEND AND DROPPING USE OF THE 12Z
CMC AFTER FRIDAY OWING TO THE GREATER WESTERN U.S. DIFFERENCES IN
THAT MODEL RUN.
..WEATHER/HAZARDS HIGHLIGHTS
SCATTERED TO NUMEROUS SHOWERS AND THUNDERSTORMS ARE EXPECTED TO
DEVELOP ACROSS MUCH OF THE PLAINS STATES GOING INTO THE SECOND
HALF OF THE WORK WEEK, AS MOISTURE ADVECTION FROM THE GULF OF
MEXICO INCREASES AHEAD OF A SLOWING FRONTAL SYSTEM OVER THE
WESTERN HIGH PLAINS AND THE UPPER TROUGH APPROACHING FROM THE
WEST. THE NEW DAY 4 (12Z WEDNESDAY-12Z THURSDAY) EXCESSIVE
RAINFALL OUTLOOK PLANS TO INTRODUCE A SLIGHT RISK AREA OVER PARTS
OF THE ARKLATEX REGION AS MULTIPLE MODELS ARE NOW INDICATING A
BROKEN AXIS OF 2 TO LOCALLY 4 INCH RAINFALL TOTALS AS MULTIPLE
MCSS DEVELOP IN THE WARM SECTOR OF THE LOW. THE HEAVIEST RAINFALL
DURING THE DAY 5 (12Z THURSDAY-12Z FRIDAY) PERIOD IS CURRENTLY
FAVORED ACROSS MUCH OF CENTRAL/EASTERN MONTANA AND EXTENDING INTO
WESTERN NORTH DAKOTA, AND A SLIGHT RISK IS PLANNED FOR PORTIONS OF
THOSE AREAS OWING TO WIDESPREAD 1-2 INCH RAINFALL ON TOP OF
EXPECTED MODERATE TO HEAVY RAINFALL THE DAY BEFORE. SPECIFICS
OVER THE NORTHERN HIGH PLAINS WILL DEPEND ON THE EXACT TRACK OF
THE UPPER LOW EXPECTED TO CROSS THE REGION AND HOW LONG IT
POTENTIALLY STALLS. GOING INTO NEXT WEEKEND, PORTIONS OF THE
SOUTHERN PLAINS MAY GET ADDITIONAL ROUNDS OF HEAVIER RAINFALL,
WITH SEVERAL INCHES OF RAIN POSSIBLE IN SOME AREAS OF TEXAS. AS
THE UPPER LOW CROSSES THE GREAT BASIN AND NORTHERN ROCKIES, THERE
SHOULD BE SUFFICIENT COLD AIR ALOFT TO SUPPORT LATE SEASON HIGHER
ELEVATION SNOW, ESPECIALLY OVER THE HIGHER MOUNTAIN RANGES OF
NORTHERN WYOMING AND WESTERN MONTANA.
IN TERMS OF TEMPERATURES, HIGHS WILL LIKELY BE RUNNING 5 TO 15
DEGREES ABOVE EARLY MAY AVERAGES FROM THE CENTRAL/NORTHERN PLAINS
TO THE DEEP SOUTH FOR THE MIDDLE OF THE WEEK, AND THEN REACHING
INTO THE MIDWEST STATES AND THE GREAT LAKES/NORTHEAST REGION GOING
INTO THE END OF THE WEEK. WARMTH BUILDS ACROSS THE PACIFIC
NORTHWEST BY FRIDAY INTO THE WEEKEND WITH HIGHS POTENTIALLY UP TO
20 DEGREES ABOVE MID-MAY AVERAGES ACROSS WESTERN WASHINGTON AND
OREGON. IT 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, BUT OVERNIGHT LOWS SHOULD BE CLOSER TO AVERAGE HERE AND
GENERALLY ABOVE AVERAGE EAST OF THE ROCKIES 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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