515
FXUS02 KWBC 220659
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
259 AM EDT TUE OCT 22 2024
VALID 12Z FRI OCT 25 2024 - 12Z TUE OCT 29 2024
..GENERAL OVERVIEW
A QUASI-ZONAL UPPER LEVEL FLOW PATTERN SHOULD BE IN PLACE ACROSS
MOST OF THE COUNTRY ON FRIDAY, WITH BROAD CYCLONIC FLOW ACROSS THE
GREAT LAKES AND A DEPARTING TROUGH OFF THE NORTHEAST COAST. THE
PATTERN IS EXPECTED TO TREND MORE AMPLIFIED BY EARLY NEXT WEEK AS A
LARGE SCALE TROUGH BUILDS IN ACROSS THE WESTERN U.S., ACCOMPANIED
BY A STRONG COLD FRONT AND PRECIPITATION FOR THE NORTHWESTERN
QUADRANT OF THE NATION. MEANWHILE, AN UPPER RIDGE AND WIDESPREAD
ABOVE AVERAGE TEMPERATURES ARE LIKELY FROM THE PLAINS TO THE EAST
COAST, WITH THE SURFACE HIGH SLOWLY MOVING OFFSHORE BY TUESDAY AND
ALLOWING FOR SOUTHERLY FLOW AHEAD OF THE WESTERN U.S. TROUGH.
..GUIDANCE/PREDICTABILITY ASSESSMENT
THE 00Z MODEL GUIDANCE HAS COME INTO BETTER AGREEMENT WITH THE
OVERALL SYNOPTIC SCALE PATTERN ACROSS THE CONTINENTAL U.S. AND THE
UPCOMING PATTERN CHANGE WITH A MORE AMPLIFIED UPPER LEVEL FLOW
EVOLVING LATER IN THE FORECAST PERIOD. IT IS WORTH NOTING THAT
THERE ARE STILL SOME DIFFERENCES IN THE LATEST GFS RUNS ACROSS THE
WEST COAST REGION REGARDING THE ARRIVAL OF THE TROUGH AXIS, SHOWING
A SLOWER TREND WITH THE HEIGHT FALLS COMPARED TO THE MORE
PROGRESSIVE CMC/ECMWF/ENSEMBLE MEAN SOLUTIONS, INCLUDING THE GEFS
MEANS. THEREFORE, THE WPC FORECAST WAS HEDGED SLIGHTLY MORE IN THE
CMC/ECMWF DIRECTION FOR EARLY NEXT WEEK. THE ENSEMBLE MEANS WERE
GRADUALLY INCREASED TO ABOUT 40% BY NEXT TUESDAY.
..WEATHER/HAZARDS HIGHLIGHTS
IT OVERALL REMAINS THE CASE THAT MOST OF THE COUNTRY SHOULD BE
VOID OF HEAVY RAINFALL AS MOISTURE WILL BE LIMITED DESPITE A FEW
FRONTAL BOUNDARIES AND TROUGHS PASSING THROUGH. WARM AIR ADVECTION
ACROSS THE OHIO VALLEY AND GREAT LAKES ON FRIDAY AROUND THE
BACKSIDE OF THE SURFACE HIGH AND AHEAD OF THE COLD FRONT SHOULD
SUPPORT MAINLY LIGHT SHOWERS. THERE MAY ALSO BE A FEW SHOWERS
ACROSS PORTIONS OF THE SOUTHEAST STATES, BUT THESE SHOULD BE MORE
SCATTERED AND MANY AREAS SHOULD REMAIN DRY.
THE EXCEPTION WILL BE WESTERN WASHINGTON AND OREGON WHERE ONSHORE
FLOW AND TERRAIN ENHANCEMENT WILL TEND TO INCREASE RAINFALL
PROSPECTS ACROSS THIS REGION, MAINLY NEXT WEEKEND AS THE MOISTURE
PLUME AHEAD OF THE PACIFIC FRONT MOVES INLAND. A FEW INCHES OF
RAINFALL WILL BE POSSIBLE FOR THE COASTAL RANGES AND THE WESTERN
SLOPES OF THE CASCADES. HEAVY SNOW IS POSSIBLE FOR THE HIGHEST
MOUNTAINS INLAND THROUGH THE NORTHWEST. HOWEVER, THE RAINFALL
TOTALS SHOULD BE LIMITED ENOUGH DURING THE DAY 4 AND 5 PERIOD
(FRIDAY AND SATURDAY) TO WARRANT KEEPING THE EXCESSIVE RAINFALL
OUTLOOKS FOR THOSE DAYS BLANK FOR NOW. THERE IS STILL SOME
DISCREPANCY IN THE GUIDANCE FOR THE ARRIVAL OF THIS RAINFALL EVENT.
IN TERMS OF TEMPERATURES, IT WILL REMAIN WARM AND MOSTLY SUNNY
ACROSS THE SOUTHERN TIER OF THE U.S. THROUGH MOST OF THE FORECAST
PERIOD. AN UPPER TROUGH CROSSING THE NORTHEAST BEHIND A COLD FRONT
SHOULD RESULT IN A BRIEF RETURN TO COLDER TEMPERATURES ON SUNDAY
BEFORE A MODERATING TREND COMMENCES NEXT WEEK. WIDESPREAD HIGHS
10-20+ DEGREES ABOVE AVERAGE ARE LOOKING LIKELY ACROSS THE PLAINS
INTO THE GREAT LAKES AND OHIO VALLEY EARLY NEXT WEEK AS THE RIDGE
AXIS BUILDS AND A WARM FRONT LIFTS WELL TO THE NORTH INTO SOUTHERN
CANADA. MEANWHILE, CONSIDERABLY COOLER CONDITIONS ARE EXPECTED
ACROSS MUCH OF THE WESTERN U.S. AS A PATTERN CHANGE EVOLVES AND AN
UPPER TROUGH DEVELOPS OVER THE REGION.
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 FORECAST (QPF), EXCESSIVE RAINFALL
OUTLOOK (ERO), WINTER WEATHER OUTLOOK (WWO) PROBABILITIES, HEAT
INDICES, AND KEY MESSAGES CAN BE ACCESSED FROM:
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
HTTPS://WWW.WPC.NCEP.NOAA.GOV/#PAGE=OVW
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