226
FXUS02 KWBC 221816
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
216 PM 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
UPDATED 00/06Z MODEL GUIDANCE REMAINS IN GOOD AGREEMENT ON THE
SYNOPTIC PATTERN LATE THIS WEEK AND INTO THIS WEEKEND, DEPICTING
QUASI-ZONAL FLOW WITH PERHAPS A COUPLE EMBEDDED NORTHERN AND
SOUTHERN STREAM SHORTWAVES PASSING OVER THE CENTRAL AND EASTERN
U.S. HOWEVER, DESPITE AN ACCOMPANYING FRONTAL SYSTEM AT THE SURFACE
PASSING FORM THE MIDWEST TO THE EAST COAST, THIS LOOKS TO BE A
RELATIVELY DRY SYSTEM WITH MOSTLY SCATTERED LIGHT TO MODERATE
SHOWERS ANTICIPATED. BROAD SCALE RIDGING FOLLOWS UPSTREAM OVER THE
CENTRAL U.S. LIKELY LEADING TO PERIODS OF WARMER TEMPERATURES FOR
THE WEEKEND. SIMILAR TO THE PRIOR FORECAST, THE MAIN AREA OF
UNCERTAINTY LIES IN THE LATTER HALF OF THE FORECAST EARLY NEXT WEEK
WITH RESPECT TO AN UPSTREAM UPPER-TROUGH DROPPING SOUTH FROM THE
NORTHEASTERN PACIFIC OVER THE WESTERN U.S. THE OVERALL TREND FOR
THE DETERMINISTIC MODELS HAS BEEN FOR THE ECMWF/CMC TO BE ON THE
FASTER SIDE OF THE GUIDANCE WITH A NORTHERN STREAM TROUGH DIGGING
SOUTHWARD OVER THE WEST MONDAY AND REACHING THE THE PLAINS BY
TUESDAY, WITH THE ECMWF THE MOST AGGRESSIVE IN DEEPENING A SURFACE
LOW OVER THE MIDWEST AS THE HEIGHT FALLS EXPAND OVER THE REGION. ON
THE OTHER HAND, THE GFS HAS BEEN SLOWER, WITH THE TROUGH REMAINING
POSITIVELY TILTED OVER THE WEST, AND EVEN SUGGESTING A SPLIT
STREAM SOLUTION WITH ENERGY HANGING BACK OVER THE SOUTHWESTERN U.S.
THIS TREND CONTINUED WITH THE UPDATED 12Z GFS. THE ENSEMBLE MEANS
FALL IN THE MIDDLE OF THE GUIDANCE, WITH SMALLER DIFFERENCES BUT
THE ECENS FURTHEST EAST AND THE GEFS FURTHEST WEST. THE SUITE OF AI
MODELS FROM THE EC ARE VERY SIMILAR TO THE CMC/ECMWF SOLUTION
THROUGH MONDAY, BUT BEGIN TO SHOW A SLOWER PROGRESSION INTO
TUESDAY, ADDING FURTHER UNCERTAINTY DURING THIS TIME FRAME AND
SUGGESTING THE GFS SOLUTION MAY NOT BE QUITE THE OUTLIER AT THIS
POINT. FOR NOW, THESE DIFFERENCES DON'T APPEAR TO SIGNIFICANTLY
IMPACT THE EXPECTATION THAT THERE WILL BE PRECIPITATION SPREADING
INLAND OVER THE INTERIOR WEST LATE WEEKEND INTO EARLY NEXT WEEK,
BUT MORE ON THE POTENTIAL FOR COOLER TEMPERATURES AND PRECIPITATION
CHANCES ACROSS THE NORTHERN/CENTRAL PLAINS BY TUESDAY WITH THE
MORE AGGRESSIVE ECMWF SOLUTION.
THE UPDATED WPC FORECAST BLEND REMAINS SIMILAR TO THE PRIOR
FORECAST GIVEN GOOD RUN-TO-RUN CONSISTENCY. A COMPOSITE
ECMWF/CMC/GFS/UKMET BLEND IS USED THROUGH THE WEEKEND GIVEN THE
NOTED SIMILARITIES, WITH A SHIFT TOWARDS THE ECMWF/CMC AND THE
ECENS/CMC ENSEMBLE MEANS FOR THE LATTER HALF OF THE PERIOD. THE
CONTRIBUTION FROM THE MEANS IS INCREASED TO 50% BY THE FINAL DAY OF
THE PERIOD AS TO NOT TREND QUITE AS FAR TOWARDS THE ECMWF SOLUTION
WHICH IS MORE AGGRESSIVE IN DEEPENING THE SURFACE LOW OVER THE
MIDWEST.
..WEATHER/HAZARDS HIGHLIGHTS
IT OVERALL REMAINS THE CASE THAT MOST OF THE COUNTRY SHOULD BE
VOID OF HEAVY RAINFALL, ESPECIALLY EARLY IN THE PERIOD, 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 SCATTERED LIGHT TO MODERATE
SHOWERS, REACHING INTO THE INTERIOR NORTHEAST BY EARLY SATURDAY.
THERE MAY ALSO BE A FEW SHOWERS ACROSS PORTIONS OF THE SOUTHEAST
STATES FRIDAY/SATURDAY, BUT THESE SHOULD BE MORE SCATTERED AND MANY
AREAS SHOULD REMAIN DRY.
THE EXCEPTION WILL BE WEST. THE PACIFIC NORTHWEST/NORTHERN
CALIFORNIA WILL SEE 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. 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
AND POSSIBLE TOTALS. PRECIPITATION SHOULD SPREAD INLAND WITH THE
SYSTEM THROUGH THE GREAT BASIN AND INTO THE NORTHERN/CENTRAL
ROCKIES MONDAY-TUESDAY. SOME HEAVY SNOW WILL ALSO BE POSSIBLE FOR
THE HIGHER ELEVATIONS OF THE PACIFIC NORTHWEST AS WELL AS INTO THE
NORTHERN ROCKIES. PRECIPITATION CHANCES MAY INCREASE OVER THE
NORTHERN/CENTRAL PLAINS BY TUESDAY AS MOISTURE RETURNS AHEAD OF A
DEEPENING SURFACE CYCLONE OVER THE MIDWEST.
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. SOME AREAS OF THE
CENTRAL/NORTHERN APPALACHIANS COULD SEE A FROST OR FREEZE SUNDAY
MORNING. 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. SOME GUSTY CHINOOK WINDS WILL BE POSSIBLE IN THE LEE OF THE
MONTANA AND WYOMING ROCKIES SATURDAY INTO SUNDAY WITH DOWNSLOPING
WINDS, AS WELL AS ACROSS PORTIONS OF THE NORTHERN/CENTRAL PLAINS AS
LEE TROUGHING SETS UP AHEAD OF AN APPROACHING UPPER-LEVEL TROUGH.
ADDITIONAL AREAS OF GUSTY WINDS ARE POSSIBLE MONDAY-TUESDAY WITH
THE EASTWARD PROGRESSION OF THE UPPER-TROUGH AS CYCLOGENESIS
INCREASES FLOW OVER THE CENTRAL PLAINS AND MIDDLE MISSISSIPPI
VALLEY, AS WELL AS WITH A COLD FRONT PASSAGE THROUGH THE
CENTRAL/SOUTHERN ROCKIES AND INTO THE SOUTHWEST.
PUTNAM/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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