305
FXUS02 KWBC 072002
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
402 PM EDT WED OCT 7 2026
VALID 12Z SAT OCT 10 2026 - 12Z WED OCT 14 2026
...ISAIAS WILL BRING HEAVY RAINFALL AND POTENTIAL FLASH FLOODING
ACROSS PARTS OF THE SOUTHEAST INTO THE MID-ATLANTIC THROUGH THE
WEEKEND...
...REMNANTS OF RACHEL TO INCREASE HEAVY RAINFALL POTENTIAL ACROSS
THE SOUTHWEST AND INTERMOUNTAIN WEST THIS WEEKEND INTO EARLY NEXT
WEEK...
..PATTERN OVERVIEW
ISAIAS AND ITS REMNANTS WILL PRODUCE HEAVY RAIN AND THE POTENTIAL
FOR FLASH FLOODING AS IT TRACKS INTO THE TENNESSEE AND OHIO VALLEYS
THIS WEEKEND BEFORE BEING SWEPT EASTWARD ACROSS THE MID-ATLANTIC
BY MONDAY. AN AMPLIFIED WESTERN TROUGH WILL INTERACT WITH RACHEL
AND ITS REMNANTS, BRINGING WIDESPREAD RAIN ACROSS THE SOUTHWEST AND
INTERMOUNTAIN WEST/ROCKIES SUNDAY INTO MONDAY. MEANWHILE, THE
FIRST WIDESPREAD SNOW OF THE SEASON ARRIVES FOR THE HIGH ELEVATIONS
OF THE NORTHERN ROCKIES THIS WEEKEND AND CONTINUES INTO EARLY NEXT
WEEK.
..GUIDANCE/PREDICTABILITY ASSESSMENT
THE LATEST AVAILABLE GUIDANCE CONTINUES TO HAVE A FAIRLY DECENT
HANDLE ON THE LARGE SCALE PATTERN THROUGH THE MEDIUM RANGE PERIOD,
THOUGH UNCERTAINTIES REMAIN WITH THE SMALLER SCALE DETAILS.
OVERALL, THE MACHINE LEARNING GUIDANCE (AI-GFS/EC-AIFS) ALONG WITH
(TO A LESSER DEGREE) THE DETERMINISTIC RUNS OF THE GFS AND UKMET
SEEM TO HAVE THE BEST DEPICTION OF BOTH THE UPPER AND SURFACE
PATTERNS, ESPECIALLY WITH RESPECT TO THE TEMPORAL AND SPATIAL
DISTRIBUTIONS OF BOTH TROPICAL SYSTEMS (ISAIAS AND RACHEL). THESE
GUIDANCE SOURCES WERE HEAVILY UTILIZED FOR QPF AND OTHER GRIDDED
ELEMENTS, ALONG WITH FRONTS AND PRESSURE. TOWARDS THE END OF THE
PERIOD, MORE WEIGHTING WAS PLACED ON THE ENSEMBLE MEANS OF THE EC
AND GEFS, WHICH HELPED TO SMOOTH LARGER DIFFERENCES.
..WEATHER/HAZARDS HIGHLIGHTS
THE PRIMARY CONCERN FOR THE UPCOMING WEEKEND WILL BE THE ONGOING
HEAVY RAIN AND POTENTIAL FLASH FLOODING AS ISAIAS TRACKS NORTHWARD
INTO THE TENNESSEE AND OHIO VALLEYS. EVEN AFTER ISAIAS BECOMES
EXTRATROPICAL AND WEAKENS NOT LONG AFTER PUSHING INLAND, A DEEP
PLUME OF GULF MOISTURE AND A BROAD CIRCULATION WILL SUPPORT PERIODS
OF MODERATE TO HEAVY RAINFALL ACROSS PORTIONS OF SOUTHEAST. FLASH
FLOODING WILL BE THE MOST LIKELY WHERE TRAINING OCCURS AND/OR WHERE
THE REMNANT CIRCULATION INTERACTS WITH FRONTAL BOUNDARIES.
ANTECEDENT WET SOILS FROM PREVIOUS RAINFALL WILL ALSO INCREASE THE
POTENTIAL FOR RENEWED FLOODING CONCERNS. THE SYSTEM WILL QUICKLY
TRACK NORTH AND THEN SHARPLY EASTWARD SUNDAY INTO MONDAY, BRINGING
PERIODS OF STEADY MODERATE TO LOCALLY HEAVY RAINFALL TO PORTIONS OF
THE OHIO VALLEY, MID-ATLANTIC, AND NORTHEAST. ANY LEFTOVER RAIN
LIKELY ENDS BY TUESDAY WITH DRIER AIR FILTERING INTO THE REGION IN
THE SYSTEM'S WAKE.
OVER THE WESTERN U.S., AN AMPLIFYING UPPER TROUGH WILL BRING
PERIODS OF RAIN TO PORTIONS OF THE PACIFIC NORTHWEST AND
INTERMOUNTAIN WEST THIS WEEKEND, WITH RAIN SPREADING INTO THE
NORTHERN/CENTRAL ROCKIES AS THE TROUGH DIGS SOUTHEASTWARD. COLDER
AIR SURGING IN BEHIND A COLD FRONT WILL QUICKLY LOWER SNOW LEVELS
AND CHANGE ANY RAIN TO SNOW ACROSS THE HIGHER ELEVATIONS OF THE
NORTHERN ROCKIES. ACCUMULATING SNOW WILL CONTINUE IN THE HIGH
COUNTRY THROUGH THE WEEKEND INTO EARLY NEXT WEEK, WITH SOME SNOW
POSSIBLE IN THE LOWER ELEVATIONS AS WELL. THE SNOW WILL LIKELY BE
WET AND HEAVY AT TIMES, WHICH COULD WEIGH DOWN TREES AND POWER
LINES. THE LATEST WSSI-P CONTINUES TO HIGHLIGHT >50 PERCENT
PROBABILITIES FOR AT LEAST MINOR WINTER WEATHER IMPACTS ACROSS THE
HIGHER TERRAIN OF MONTANA AND NORTHWEST WYOMING, WITH 10-20 PERCENT
PROBABILITIES FOR MODERATE IMPACTS.
AS THE WESTERN TROUGH CONTINUES TO DEEPEN, IT WILL LIKELY DRAW
RACHEL AND ITS POST-TROPICAL REMNANTS IN THE EASTERN PACIFIC
NORTHWARD BEFORE SWEEPING IT SHARPLY EASTWARD TOWARDS THE SOUTHWEST
U.S. INCREASING DYNAMIC FORCING FROM THE TROUGH COMBINED WITH THE
TROPICAL MOISTURE FROM THE REMNANTS OF RACHEL WILL LIKELY LEAD TO
WIDESPREAD HEAVY RAINFALL AND LOCALIZED FLOODING OVER PARTS OF THE
SOUTHWEST AND INTERMOUNTAIN WEST/ROCKIES SUNDAY INTO MONDAY. BURN
SCARS, SLOT CANYONS, URBAN AREAS, AND POOR DRAINAGE/LOW-LYING AREAS
ARE LIKELY TO BE MOST AT RISK.
TEMPERATURES SHOULD TREND DOWNWARD BEHIND THE ADVANCING WESTERN
TROUGH OVER THE NORTHWEST INTO THE NORTH/CENTRAL PLAINS THROUGH
WEDNESDAY. PERIODS OF RAIN WILL SPREAD INTO THE PLAINS AND UPPER
MIDWEST ALONG A FRONTAL BOUNDARY MONDAY THROUGH TUESDAY.
MILLER/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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