226
FXUS02 KWBC 200714
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
314 AM EDT TUE OCT 20 2026
VALID 12Z FRI OCT 23 2026 - 12Z TUE OCT 27 2026
..SOUTHERN CALIFORNIA/SOUTHWEST/ROCKIES HEAVY PRECIPITATION
..OVERVIEW
A UPPER-LEVEL TROUGH AND ASSOCIATED MOISTURE PLUME WILL BRING
CHANCES FOR SHOWERS AND THUNDERSTORMS ACROSS THE SOUTHWEST INTO
THE ROCKIES AND PLAINS, WITH POTENTIAL ACCUMULATING SNOW OVER
HIGHER TERRAIN. THE SYSTEM WILL CONTINUE TO MOVE EASTWARD INTO THE
PLAINS BRINGING ADDITIONAL SHOWERS AND THUNDERSTORMS INTO EARLY
NEXT WEEK. ANOTHER PACIFIC SHORTWAVE WILL MOVE INTO THE NORTHWEST
BRINGING PRECIPITATION ACROSS THE REGION. ACROSS THE SOUTHEAST,
ONSHORE FLOW WILL SUPPORT ADDITIONAL RAINFALL ACROSS PORTIONS OF
FLORIDA THROUGH THE MONDAY.
..GUIDANCE/PREDICTABILITY ASSESSMENT
MODEL GUIDANCE REMAINS WELL CLUSTERED FOR THE START OF THE PERIOD
WITH THE TROUGHING OVER WESTERN U.S., RIDGING OVER CENTRAL U.S.,
AND TROUGHING BEGINNING TO EXIT OFFSHORE OVER EASTERN U.S. HOWEVER,
DIFFERENCES ARISE IN REGARD TO THE TIMING, AMPLITUDE, AND EASTWARD
PROGRESSION OF THE WESTERN TROUGH, ESPECIALLY WITH THE GFS/GEFS
SERVING AS OUTLIERS COMPARED TO THE ECMWF AND CMC. THESE
DIFFERENCES WILL INFLUENCE THE LOCATION AND ORGANIZATION OF
PRECIPITATION ACROSS WESTERN U.S. OTHERWISE, MODELS SEEM TO CAPTURE
THE EASTWARD PROGRESSION OF THE RIDGE THROUGH EARLY NEXT WEEK.
THEREFORE, THE FORECAST FAVORED A MULTI-MODEL BLEND WITH THE
ECMWF/CMC, WITH INCREASING EMPHASIS ON THE ENSEMBLE MEANS TOWARD
THE LATTER PORTION OF THE PERIOD.
..WEATHER/HAZARDS HIGHLIGHTS
ACROSS WESTERN U.S., THE UPPER TROUGH EXTENDING INTO THE SOUTHWEST
WILL CONTINUE TO SUPPORT PERIODS OF RAIN AND EMBEDDED
THUNDERSTORMS FROM CALIFORNIA AND THE GREAT BASIN INTO THE FOUR
CORNERS REGION AND CENTRAL ROCKIES BY LATE WEEK. ANOMALOUS MOISTURE
TRANSPORT INTO THE REGION, COMBINED WITH ASCENT ASSOCIATED WITH
THE UPPER LOW AND FORCING, COULD PRODUCE LOCALLY HEAVY RAINFALL. ANY
PERSISTENCE OF DEEP MOISTURE AND SLOW STORM MOTION WOULD INCREASE
THE POTENTIAL FOR EXCESSIVE RUNOFF, ESPECIALLY OVER VULNERABLE
TERRAIN AND BURN SCARS. THEREFORE, A MARGINAL RISK OF EXCESSIVE
RAINFALL FOR PORTIONS OF THE NEW MEXICO INTO WESTERN TEXAS
CONTINUES FOR FRIDAY, WHILE A SLIGHT RISK IS INTRODUCED FOR
SATURDAY ACROSS PORTIONS OF NEW MEXICO AND TEXAS INTO THE CENTRAL
PLAINS.
FURTHERMORE, SNOW LEVELS AND PRECIPITATION TYPE WILL DEPEND ON THE
STRENGTH OF THE COLD ADVECTION ACCOMPANYING THE UPPER LOW. HIGHER
ELEVATION OF THE SIERRA NEVADA AND SOUTH/CENTRAL ROCKIES COULD
RECEIVE ACCUMULATING SNOW, PARTICULARLY AS THE SYSTEM SHIFTS INLAND
AND COLDER AIR BECOMES MORE ESTABLISHED. AS THE SYSTEM CONTINUES
TO PUSH EASTWARD, STRENGTHENING SOUTHERLY FLOW MAY PROMOTE LEE
CYCLOGENESIS OVER THE HIGH PLAINS. THEREFORE, SHOWERS AND
THUNDERSTORMS WILL EXPAND ACROSS PORTIONS OF THE HIGH PLAINS AND
ADJACENT CENTRAL OR SOUTHERN PLAINS THROUGH THE WEEKEND INTO EARLY
NEXT WEEK. GULF MOISTURE AND FRONTAL CONVERGENCE WILL MAY LEAD TO
ORGANIZED CONVECTION. FURTHER NORTH, AN UPPER LOW/TROUGH DIGGING
SOUTHEASTWARD FROM THE GULF OF ALASKA IS EXPECTED TO MOVE INTO THE
NORTHWEST BY THE WEEKEND. INCREASING ASCENT AND PACIFIC MOISTURE
TRANSPORT MAY SUPPORT RENEWED PRECIPITATION ACROSS THE PACIFIC
NORTHWEST/INTERMOUNTAIN WEST. THE HIGHEST TERRAIN COULD EXPERIENCE
ACCUMULATING SNOW AS COLD AIR ACCOMPANIES THE SYSTEM.
A BROAD UPPER TROUGH EXTENDING TOWARDS THE WESTERN ATLANTIC MAY
SUPPORT PERSISTENT EASTERLY FLOW AND MOISTURE TRANSPORT INTO
FLORIDA. PERIODS OF SHOWERS AND THUNDERSTORMS COULD DEVELOP ALONG
THE FLORIDA COAST, WITH RAINFALL POTENTIALLY BECOMING MORE
WIDESPREAD ACROSS THE SOUTHERN PENINSULA IF ONSHORE FLOW PERSISTS.
REPEATED RAINFALL OVER URBANIZED AREAS AND LOCATIONS WITH POOR
DRAINAGE COULD LEAD TO LOCALIZED FLASH FLOODING CONCERNS THROUGH
THE WEEKEND INTO EARLY NEXT WEEK. THIS IS REFLECTED WITH A SLIGHT
RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF SOUTHEAST FLORIDA FOR
SATURDAY.
OUDIT
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, EXCESSIVE RAINFALL OUTLOOK,
WINTER WEATHER OUTLOOK PROBABILITIES, HEAT INDICES AND KEY MESSAGES
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
HTTPS://WWW.WPC.NCEP.NOAA.GOV/#PAGE=OVW
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