976
FXUS02 KWBC 211826
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
226 PM EDT MON OCT 21 2024
VALID 12Z THU OCT 24 2024 - 12Z MON OCT 28 2024
..GENERAL OVERVIEW
A LEADING COLD FRONT IS FORECAST TO EXIT THE EAST COAST BY
THURSDAY MORNING AND BRING A RETURN TO MORE SEASONABLE TEMPERATURES
AFTER A WARM SPELL, WITH A LARGE SURFACE HIGH SETTLING IN ACROSS
THE EASTERN U.S. BEHIND IT. A SECOND FRONTAL BOUNDARY IS ALSO
EXPECTED TO DROP SOUTH ACROSS THE MIDWEST AND OHIO VALLEY BY THE
WEEKEND, REINFORCING THE AUTUMNAL AIRMASS AND MAINLY DRY WEATHER.
OUT WEST, A PACIFIC COLD FRONT IS LIKELY TO REACH THE PACIFIC
NORTHWEST COAST SATURDAY, BRINGING A RETURN TO RAIN AND MOUNTAIN
SNOW FROM NORTHERN CALIFORNIA TO WASHINGTON STATE. A MORE ROBUST
PATTERN CHANGE IS ON THE DISTANT HORIZON FOR THE WEST AS THE UPPER
LEVEL TROUGH LIKELY AMPLIFIES FURTHER GOING INTO EARLY NEXT WEEK,
AND A STRONG COLD FRONT PASSING THROUGH THE REGION.
..GUIDANCE/PREDICTABILITY ASSESSMENT
THE WPC MEDIUM RANGE PRODUCT SUITE WAS PRIMARILY DERIVED FROM A
COMPOSITE BLEND OF REASONABLY CLUSTERED GUIDANCE FROM THE 06 UTC
GFS AND 00 UTC ECMWF/CANADIAN/UKMET ALONG WITH COMPATIBLE GUIDANCE
OF THE 13 UTC NBM FOR THURSDAY INTO SATURDAY. IN THIS BLEND, THE
06 UTC GFS TRENDED LESS AMPLIFIED OVER THE WEST LATE PERIOD, BUT
FELL WITHIN THE ENVELOPE OF POSSIBILITIES, ALBEIT LESS LIKELY.
OPTED TO BLEND INTO THIS COMPOSITE COMPATIBLE GUIDANCE OF THE
GEFS/ECMWF/CANADIAN ENSEMBLE MEANS AT LONGER TIME FRAMES FOR THE
REST OF NEXT WEEKEND/MONDAY AMID SLOWLY GROWING FORECAST SPREAD AS
FORECAST CONFIDENCE LOWERS FROM JUST ABOVE NORMAL TO NEAR NORMAL
LEVELS. A SIMILAR GUIDANCE PLAN SEEMS EVEN BETTER CLUSTERED WITH
LATEST 12 UTC GUIDANCE. IN PARTICULAR, THE 12 UTC GFS HAS FALLEN
BACK INTO BETTER AGREEMENT WITH MOST OTHER GUIDANCE IN SHOWING A
MORE AMPLIFIED UPPER TROUGH HOLDING OVER THE WEST EARLY NEXT WEEK.
..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 MIDWEST ON THURSDAY AROUND THE BACKSIDE OF THE SURFACE
HIGH SHOULD SUPPORT MAINLY LIGHT TO MODERATE SHOWERS AHEAD OF AN
APPROACHING COLD FRONT FROM THE NORTHERN PLAINS, AND THIS WILL
LIKELY WEAKEN FURTHER AS IT REACH THE NORTHEAST TO CLOSE OUT THE
WORK WEEK. SOME SHOWERS ARE ALSO LIKELY FOR PORTIONS OF THE FLORIDA
PENINSULA WITH NORTHEASTERLY FLOW IN PLACE.
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
(THURSDAY AND FRIDAY) 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.
HAMRICK/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 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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