243
FXUS02 KWBC 030701
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
301 AM EDT WED MAY 03 2023
VALID 12Z SAT MAY 06 2023 - 12Z WED MAY 10 2023
..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 THROUGH THE WEEKEND IN THE WEST UNDER THE INFLUENCE
OF THE UPPER-LEVEL TROUGHING. EJECTING SHORTWAVE ENERGY OVER THE
CENTRAL/EASTERN U.S. WILL TRIGGER MULTIPLE AREAS OF SHOWERS AND
THUNDERSTORMS FROM THE PLAINS TO THE MISSISSIPPI VALLEY AND
SOUTHEAST, WITH ABUNDANT GULF MOISTURE AVAILABLE FOR THE POTENTIAL
OF LOCALLY HEAVY RAINFALL.
..GUIDANCE/PREDICTABILITY ASSESSMENT
MOST OF THE GUIDANCE SHOWS SHORTWAVE ENERGY LINGERING WEST OF
DEPARTING UPPER TROUGH OVER THE EAST COAST AS WELL AS A SHORTWAVE
LIFTING NORTH THROUGH THE NORTHERN GREAT BASIN/ROCKIES IN THE MEAN
FLOW TO THE WEST WILL BOTH DEPART INTO CANADA AS A RIDGE OVER THE
EAST BEGINS TO AMPLIFY A BIT. THE 12Z GFS, AND TO A LESSER EXTENT
THE 18Z GFS, SHOW THIS ENERGY ACTUALLY SHIFTING SOUTHWARD AND
DISRUPTING THE AMPLIFICATION OF THE RIDGING OVER THE EAST COAST,
WHICH WOULD HAVE A POTENTIAL IMPACT ON PRECIPITATION CHANCES IN
THE REGION. THE TREND HAS BEEN FOR A CLOSED LOW TO EVENTUALLY
DEVELOP OVER ATLANTIC CANADA, WITH IMPACTS FOR THE WEATHER IN NEW
ENGLAND AND THE INTERIOR NORTHEAST. THE UPDATED 12Z UKMET HAS
FALLEN IN LINE WITH THE OTHER GUIDANCE WITH RESPECT TO THE
HANDLING OF TROUGHING OVER THE WEST AFTER BEING A BIT OUT OF
PHASE.
IN THE MID-FORECAST PERIOD, ALL OF THE DETERMINISTIC GUIDANCE
DEPICTS SHORTWAVE ENERGY TRAVERSING THE LARGER TROUGH EJECTING
OVER THE PLAINS AND DISRUPTING THE RIDGE TO THE EAST. HOWEVER,
RUN-TO-RUN CONSISTENCY ON THE TIMING AND LOCATION OF THIS FEATURE
REMAINS POOR IN BOTH THE MORE RECENT GFS AND ECMWF RUNS. DESPITE
THE SMALLER-SCALE NATURE OF THIS FEATURE, IT HAS REMAINED A
CONSISTENT PRESENCE IN THE FORECAST FOR DAYS, AGAIN PRESENT IN THE
MOST RECENT 00Z GFS. THIS COMPLICATES THE FORECAST AS THERE IS
CONFIDENCE IN THIS OVERALL SCENARIO, WHICH WILL HAVE DOWNSTREAM
IMPACTS ON THE SURFACE FRONTAL EVOLUTION AND SHOWER/STORM CHANCES,
BUT THE SPECIFICS HAVE CHANGED DAY TO DAY.
THE HANDLING OF THE PATTERN EVOLUTION TOWARDS THE END OF THE
PERIOD REMAINS VERY POOR ACROSS THE GUIDANCE. IN GENERAL, THE
GUIDANCE SUGGESTS THE TROUGH OVER THE WEST WILL SHIFT EASTWARD
WITH TIME. HOWEVER, THERE IS LITTLE CONSISTENCY RUN-TO-RUN IN BOTH
THE ECMWF AND GFS IN HANDLING THE OVERALL PHASING OF THE EASTERN
RIDGE/WESTERN TROUGH PROGRESSION, LET ALONE MORE SMALLER-SCALE
IMPULSES TRAVERSING THE FLOW. AT LEAST SOME OF THE UPDATED RUNS
SHOW SOME SIMILARITY. THE 12Z CMC DIVERGED AWAY FROM THE WEAK
CONSENSUS BETWEEN THE OTHER GUIDANCE WITH A CLOSED LOW DEVELOPING
OVER THE SOUTHWEST. ADDING TO LOW CONFIDENCE, THE 12Z ECENS AND
18Z GEFS MEANS SHOW A FLATTER FLOW, BUT AT LEAST KEEP THE FLOW
SOUTHWESTERLY FROM THE SOUTHWEST TO THE MIDWEST WHICH WOULD BE
EXPECTED IN SOME FASHION WITH THE INITIAL PLACEMENT AND EXPECTED
MOVEMENT OF THE TROUGH. A MORE DETAILED REVIEW SHOWS THAT THE
DETERMINISTIC GUIDANCE TENDS TO HAVE WEAK RIDGING OVER THE WEST
COAST/INTERMOUNTAIN WEST, WHILE THE ENSEMBLE GUIDANCE HAS FLAT
FLOW TO SLIGHT TROUGHING OVER THE REGION. THE UPDATED 00Z GFS WAS
MORE PROGRESSIVE WITH THE POTENTIAL FOR RIDGING, SHIFTING IT OVER
THE PLAINS WITH A TROUGH TO THE WEST, SIMILAR TO THE EARLY RUNS OF
THE ENSEMBLE MEANS.
THE UPDATED WPC FORECAST PACKAGE BEGINS WITH A GENERAL BLEND OF
THE DETERMINISTIC GUIDANCE. AN EMPHASIS WAS GIVEN TO THE ECMWF
OVER THE 12Z/18Z GFS GIVEN THE DIFFERENCES BETWEEN THE GFS AND THE
OTHER GUIDANCE OVER THE EAST COAST. RELIANCE ON THE DETERMINISTIC
GUIDANCE CONTINUES INTO THE MID-FORECAST PERIOD TO KEEP MORE
DETAIL IN THE EVOLUTION OF THE SHORTWAVE OVER THE PLAINS. THE
CONTRIBUTION FROM THE 12Z CMC IS REMOVED MID- TO LATE FORECAST
PERIOD GIVEN THE DIVERGING SOLUTION OVER THE WEST. A CONTRIBUTION
FROM THE 12Z ECENS AND 18Z GEFS MEANS WAS ADDED FOR THE LATE
FORECAST PERIOD GIVEN INCREASING FORECAST DIVERGENCE IN THE
DETERMINISTIC SOLUTIONS. A FLATTER FLOW IS A RESULTANT COMPROMISE
OVER THE WEST WHERE THERE IS DISAGREEMENT BETWEEN THE
DETERMINISTIC AND ENSEMBLE GUIDANCE, AS WELL AS THE DETERMINISTIC
GUIDANCE RUN-TO-RUN, AND CONFIDENCE IN ANY OTHER SOLUTION WOULD BE
VERY LOW AT THIS POINT.
..WEATHER/HAZARDS HIGHLIGHTS
THE OVERALL PATTERN LOOKS WET FOR THE CENTRAL TO SOUTHEASTERN
CONUS THROUGH THE PERIOD AS SOUTHWESTERLY FLOW SETS IN, WITH TWO
AREAS OF POTENTIALLY GREATER FOCUS OF SHOWERS/STORMS. MOIST,
UPSLOPE FLOW 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 THIS WEEKEND INTO EARLY NEXT WEEK. FURTHER SOUTH,
GULF MOISTURE WILL SPREAD NORTHWARD ACROSS THE CENTRAL/SOUTHERN
PLAINS AND MIDDLE/LOWER MISSISSIPPI VALLEY INTO THE SOUTHEAST
LEADING TO A BROAD REGION OF SHOWERS AND THUNDERSTORMS. IN BOTH
CASES, THE EVOLUTION OF THE PATTERN HAS REMAINED RATHER NEBULOUS
THE LAST FEW DAYS AS THE GUIDANCE HAS VARIED ON THE PRESENCE AND
TIMING OF EMBEDDED SHORTWAVE ENERGY ALOFT, LESSENING CONFIDENCE ON
THE SPECIFICS OF REGIONS OF HEAVIER RAINFALL AND POTENTIAL FLASH
FLOODING CONCERNS. CURRENTLY, THE GREATEST CHANCE OF LOCALLY HEAVY
RAINFALL IS ON SUNDAY OVER PORTIONS OF THE UPPER MISSOURI VALLEY
AND SUNDAY/TUESDAY FOR THE LOWER MISSISSIPPI VALLEY. HIGH
TEMPERATURES WILL BE SEASONABLY WARM FOR EARLY MAY FROM THE PLAINS
TO THE SOUTHEAST/MID-ATLANTIC UNDER THE INFLUENCE OF MEAN RIDGING
ALOFT, WITH SOME HIGHS RUNNING 15+ DEGREES ABOVE AVERAGE IN THE
CENTRAL PLAINS THIS WEEKEND.
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. TEMPERATURES MAY EVENTUALLY TREND COOLER DEPENDING ON THE
EVOLUTION OF A POTENTIAL UPPER-LEVEL CLOSED LOW TO THE NORTHEAST.
PRECIPITATION CHANCES WILL REMAIN LOW THROUGH THE WEEKEND 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 DUE TO A LINGERING FRONTAL BOUNDARY AND
POTENTIAL DOWNSTREAM MCS ACTIVITY.
MODERATE TO LOCALLY HEAVY RAINFALL WILL TAPER OFF THROUGH THE
WEEKEND FOR THE PACIFIC NORTHWEST/GREAT BASIN/NORTHERN ROCKIES AS
AN UPPER-LEVEL WAVE LIFTS NORTH INTO CANADA. ADDITIONAL SHORTWAVE
IMPULSES/SURFACE FRONTAL SYSTEMS PUSHING THROUGH THE WEST WILL
KEEP SOME PRECIPITATION CHANCES, PARTICULARLY ACROSS THE NORTHERN
TIER. SOME SNOW SHOWERS WILL BE POSSIBLE AT HIGHER MOUNTAIN
ELEVATIONS. TEMPERATURES WILL REMAIN A BIT COOL MORE BROADLY
ACROSS THE WEST THROUGH THE WEEKEND, WITH HIGHS RUNNING 5-10
DEGREES BELOW AVERAGE THROUGH THE PERIOD, BEFORE CONDITIONS LOOK
TO MODERATE A BIT LATER IN THE PERIOD AS THE UPPER-LEVEL PATTERN
ALOFT TRENDS MORE NEUTRAL.
PUTNAM
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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