662
FXUS02 KWBC 050654
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
254 AM EDT FRI MAY 5 2023
VALID 12Z MON MAY 8 2023 - 12Z FRI MAY 12 2023
..SYNOPTIC OVERVIEW
A QUASI-ZONAL UPPER LEVEL FLOW PATTERN WITH A BROAD UPPER RIDGE
OVER THE OHIO VALLEY AND AN ARRIVING UPPER TROUGH NEAR THE WEST
COAST IS EXPECTED FOR MONDAY. THIS TROUGH IS FORECAST TO AMPLIFY
FURTHER GOING INTO THE MIDDLE OF THE WEEK ACROSS THE INTERMOUNTAIN
WEST, AND THIS WILL TEND TO BUILD THE RIDGE THAT WILL BE
DOWNSTREAM ACROSS THE PLAINS, AND A TROUGH AXIS ACROSS THE
NORTHEAST STATES. THE WESTERN U.S. TROUGH SHOULD THEN REACH THE
WESTERN HIGH PLAINS TO CLOSE OUT THE WORK WEEK WITH AN INCREASE IN
SHOWER AND THUNDERSTORM CHANCES ACROSS 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 AGREES WELL ON THE OVERALL SYNOPTIC
SCALE PATTERN ACROSS THE CONTINENTAL U.S. FOR THE BEGINNING OF
NEXT WEEK, AND A GENERAL MODEL BLEND SUFFICES AS A STARTING POINT
IN THE FORECAST PROCESS FOR MONDAY. THE UKMET STRAYS FROM THE
CONSENSUS BY TUESDAY ACROSS THE NORTHERN ROCKIES WITH A STRONGER
SHORTWAVE TROUGH AND FASTER WITH THE LOW OFF THE WEST COAST. THE
GUIDANCE HAS CONTINUED TO TREND MORE AMPLIFIED WITH THE TROUGH
REACHING THE DESERT SOUTHWEST BY WEDNESDAY, WITH THE CMC AND ECMWF
TRENDING TOWARDS THE GFS COMPARED TO EARLIER MODEL RUNS, EVEN
THOUGH THE 00Z ECMWF IS STILL SLIGHTLY NORTH OF THE CMC/GFS BY
WEDNESDAY MORNING. THE MODELS ARE ALSO TRENDING A LITTLE FASTER
BRINGING THE TROUGH ACROSS THE ROCKIES, WITH THE 12Z ECENS NOW
SLOWER THAN THE 00Z CONSENSUS. MODEL UNCERTAINTY INCREASES GOING
INTO FRIDAY, BUT STILL REASONABLE ON DEPICTION OF THE MAIN
FEATURES. THE ENSEMBLE MEANS ACCOUNTED FOR ABOUT HALF OF THE
FORECAST BLEND BY THE SECOND HALF OF THE WEEK.
..WEATHER/HAZARDS HIGHLIGHTS
GRADUALLY INCREASING MOISTURE ACROSS THE EASTERN HALF OF THE
NATION, ALONG WITH SOME WEAK SHORTWAVE DISTURBANCES ALOFT, WILL
TEND TO RESULT IN SCATTERED TO NUMEROUS SHOWERS AND THUNDERSTORMS
DEVELOPING FROM THE DEEP SOUTH TO THE SOUTHERN GREAT LAKES. A
MARGINAL RISK FOR THE DAY 4 ERO IS PLANNED FROM CENTRAL MISSOURI
TO SOUTHERN MICHIGAN WHERE THE MODEL SIGNAL IS BEST FOR HIGHEST
QPF, AND THE POTENTIAL EXISTS FOR EVENTUAL SLIGHT RISK IN FUTURE
UPDATES ONCE THE MAIN QPF AXIS BECOMES MORE APPARENT. THE
HEAVIEST CONVECTION FOR DAY 5 IS CURRENTLY FAVORED ACROSS PORTIONS
OF THE CENTRAL PLAINS, AND A MARGINAL RISK AREA IS PLANNED HERE
FROM CENTRAL NE/KS TO FAR WESTERN KY/TN. LOOKING AHEAD TO
WEDNESDAY AND THURSDAY, A BROADER EXPANSE OF MODERATE TO LOCALLY
HEAVY RAINFALL IS BECOMING MORE LIKELY FROM TEXAS TO THE DAKOTAS
IN ASSOCIATION WITH THE EJECTING WESTERN U.S. STORM SYSTEM. THERE
WILL LIKELY BE ENOUGH COLD AIR ALOFT TO SUPPORT LOWERING SNOW
LEVELS ACROSS PORTIONS OF THE NORTHERN ROCKIES, AND LATE SEASON
SNOW IS PROBABLE FOR THE HIGHER ELEVATIONS OF WYOMING AND MONTANA
DURING THIS TIME.
IN TERMS OF TEMPERATURES, HIGHS WILL LIKELY BE RUNNING 5 TO 15
DEGREES ABOVE EARLY MAY AVERAGES FROM THE CENTRAL/SOUTHERN PLAINS
TO THE OHIO VALLEY TO START THE WEEK, AND THEN REACHING INTO THE
MIDWEST STATES GOING INTO THE MIDDLE OF THE WEEK. IT SHOULD
INITIALLY BE ABOVE AVERAGE ACROSS THE EASTERN U.S. BEFORE A COLD
FRONT USHERS IN A COOLER AND MORE REFRESHING AIRMASS FOR THE
WEDNESDAY-FRIDAY TIME PERIOD. IT WILL LIKELY BE SLIGHTLY BELOW
AVERAGE ACROSS PORTIONS OF THE WEST COAST STATES AND THE
INTERMOUNTAIN WEST IN ASSOCIATION WITH THE UPPER TROUGH, BUT
OVERNIGHT LOWS SHOULD BE CLOSER TO AVERAGE HERE AND GENERALLY
ABOVE AVERAGE EAST OF THE ROCKIES.
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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