751
FXUS02 KWBC 031855
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
254 PM EDT WED MAY 03 2023
VALID 12Z SAT MAY 06 2023 - 12Z WED MAY 10 2023
..OVERVIEW
THE FLOW PATTERN OVER NORTH AMERICA FROM THE WEEKEND INTO EARLY
NEXT WEEK IS FORECAST TO SLOWLY EVOLVE AWAY FROM STUBBORN BLOCKING
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 VERY BROADLY FROM THE PLAINS TO THE EAST-CENTRAL
U.S..
..GUIDANCE/PREDICTABILITY ASSESSMENT
GUIDANCE SHOWS A GENERALLY SIMILAR AND SLOWLY EVOLVING LARGER
SCALE PATTERN THROUGH THE WEEKEND INTO MONDAY DESPITE TRANSITIONAL
BLOCKY FLOW OVER NORTH AMERICA AND ADJOINING WATERS. EVEN SO,
AMPLE DIFFERENCES AND RUN TO RUN CONSISTENCY ISSUES REMAIN WITH
LOCAL WEATHER FOCUSING SMALLER SCALE SYSTEMS EMBEDDED WITHIN THE
FLOW. A COMPOSITE BLEND OF REASONABLY COMPATIBLE MODEL GUIDANCE
FROM THE 06 UTC GFS AND 00 UTC ECMWF/UKMET/CANADIAN SEEMS TO
PROVIDE A GOOD FORECAST BASIS THAT TENDS TO MITIGATE SMALLER SCALE
VARIANCE CONSISTENT WITH SYSTEM PREDICTABILITY, BUT WPC SYSTEM
CONTINUITY IS NOT STELLAR. THIS SOLUTION THOUGH DOES HAVE GOOD
ENSEMBLE AND NATIONAL BLEND OF MODELS (NBM) SUPPORT. ENSEMBLE
SPAGHETTI AND CLUSTER PLOTS SHOW ENOUGH OF AN INCREASE IN FORECAST
SPREAD/UNCERTAINLY INTO NEXT WEEK TO THEN SWITCH PREFERENCE TO THE
STILL COMPATIBLE 06 UTC GEFS/00 UTC ECMWF ENSEMBLE MEANS AND THE
NBM. RUN TO RUN CONTINUITY WITH NEWER 12 UTC GUIDANCE IS NOT
ENCOURAGING AS EARLY AS THIS WEEKEND HOWEVER, LOWERING FORECAST
CONFIDENCE.
..WEATHER/HAZARDS HIGHLIGHTS
THE OVERALL PATTERN LOOKS WET FOR THE CENTRAL TO SOUTHEASTERN
CONUS THROUGH THE PERIOD AS MEAN SOUTHWESTERLY UPPER 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 UNCERTAIN SURFACE FRONTAL SYSTEMS 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/EAST 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 FOR EARLY NEXT WEEK DOWN TO THE LOWER MS/TN VALLEYS. 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.
PERIODIC MODERATE RAINFALL CHANCES ARE NOW SLATED TO LINGER
THROUGH THE WEEKEND FOR THE PACIFIC NORTHWEST/GREAT BASIN/NORTHERN
ROCKIES AS UPPER-LEVEL TROUGHS/SURFACE SYSTEMS LIFTS OVER THE
REGION. ADDITIONAL SHORTWAVE IMPULSES/SURFACE FRONTAL SYSTEMS
PUSHING THROUGH THE WEST WILL KEEP SOME PRECIPITATION CHANCES INTO
EARLY NEXT WEEK, PARTICULARLY ACROSS THE NORTHERN TIER. SOME SNOW
SHOWERS WILL BE POSSIBLE AT HIGHER MOUNTAIN ELEVATIONS.
TEMPERATURES WILL REMAIN A COOL, ESPECIALLY ACROSS THE WEST COAST
STATES THROUGH THE WEEKEND INTO NEXT WEEK.
PUTNAM/SCHICHTEL
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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