401
FXUS02 KWBC 080710
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
310 AM EDT THU OCT 8 2026
VALID 12Z SUN OCT 11 2026 - 12Z THU OCT 15 2026
...ISAIAS WILL BRING HEAVY RAINFALL AND POTENTIAL FLASH FLOODING
ACROSS PARTS OF THE MID-ATLANTIC AND NORTHEAST THROUGH SUNDAY...
...REMNANTS OF RACHEL TO INCREASE HEAVY RAINFALL POTENTIAL ACROSS
THE SOUTHWEST AND INTERMOUNTAIN WEST THIS WEEKEND INTO EARLY NEXT
WEEK...
..PATTERN OVERVIEW
THE REMNANTS OF ISAIAS AND ASSOCIATED DEEP TROPICAL MOISTURE WILL
LIFT NORTHEASTWARDS BRINGING HEAVY RAINFALL AND FLASH FLOODING
POTENTIAL ACROSS PORTIONS OF THE MID-ATLANTIC AND NORTHEAST THROUGH
SUNDAY. MEANWHILE, THE AMPLIFIED WESTERN TROUGH WILL INTERACT WITH
REMNANTS OF RACHEL, BRINGING WIDESPREAD RAINFALL A CROSS THE
SOUTHWEST INTO THE GREAT BASIN AND ROCKIES/PLAINS. ADDITIONALLY,
CHANCES FOR WIDESPREAD SNOW ARRIVES FOR THE HIGH ELEVATIONS OF THE
NORTHERN ROCKIES THIS WEEKEND INTO EARLY NEXT WEEK.
..GUIDANCE/PREDICTABILITY ASSESSMENT
THE MODELS CONTINUE TO SHOW RELATIVELY GOOD AGREEMENT WITH THE
LARGE-SCALE PATTERN OF A TROUGH MOVING SOUTHEASTWARD AND
INTERACTING WITH MOISTURE FROM THE TROPICAL SYSTEM RACHEL. THE
MODELS SEEM TO ALSO CAPTURE THE PROGRESSION OF THE NORTHERN-STREAM
WAVE. THE PRIMARY FORECAST UNCERTAINTY IS RESOLVING HOW QUICKLY
THE WESTERN TROUGH EJECTS INTO THE PLAINS AND HOW STRONGLY IT
AMPLIFIES AS IT INTERACTS WITH THE DEVELOPING RIDGE DOWNSTREAM.
ADDITIONALLY, CONFIDENCE IS LOWER CONCERNING THE TIMING AND
AMPLITUDE OF SHORTWAVES BY MID-PERIOD. THE ENSEMBLE MEANS AND THE
AI GUIDANCE SEEMS TO HAVE A BETTER HANDLE ON SOME OF THE SMALLER-
SCALE DIFFERENCES. THE FORECAST FAVORED A MULTI-MODEL BLEND
APPROACH THROUGH THE EARLY NEXT WEEK, WITH INCREASING RELIANCE ON
ENSEMBLE MEANS AND AI GUIDANCE WHERE DETERMINISTIC SOLUTIONS
DIVERGE.
..WEATHER/HAZARDS HIGHLIGHTS
THE HEAVY RAINFALL CONCERNS FROM SUNDAY INTO MONDAY WILL BE
ASSOCIATED WITH THE LINGERING TROPICAL MOISTURE FROM ISAIAS. THE
REMNANTS OF ISAIAS WILL CONTINUE TO MOVE NORTHEASTWARD FROM THE
MID- ATLANTIC, WITH RAINFALL GRADUALLY BECOMING MORE STRATIFORM AND
SHIFTING OFFSHORE. SOME LOCALLY MODERATE TO HEAVY RAINFALL COULD
PERSIST ACROSS PORTIONS OF THE NORTHEAST AND MID- ATLANTIC ON
SUNDAY INTO MONDAY, LEADING TO ISOLATED FLASH FLOODING RISK. THE
HIGHER LIKELIHOOD FOR FLASH FLOODING WILL OCCUR PARTICULARLY WHERE
THE CIRCULATION INTERACTS WITH FRONTAL BOUNDARIES AND WHERE
REPEATED CONVECTION DEVELOPS.
FARTHER WEST, THE REMNANTS OF RACHEL AND THE ASSOCIATED WESTERN
TROUGH WILL CONTINUE INTERACT, LEADING TO WIDESPREAD HEAVY RAINFALL
AND LOCALIZED FLASH FLOODING FROM THE SOUTHWEST INTO THE GREAT
BASIN, ROCKIES, AND EVENTUALLY THE NORTHERN PLAINS ON SUNDAY INTO
MONDAY. FURTHERMORE, COLD AIR SURGING BEHIND THE COLD FRONT WILL
LOWER SNOW LEVELS, LEADING TO ACCUMULATING SNOW OVER HIGH
ELEVATIONS ACROSS THE NORTHERN ROCKIES THROUGH MONDAY CAUSING
POSSIBLE MINOR TO MODERATE IMPACTS. MOMENTS OF WET AND HEAVY SNOW
MAY CAUSE IMPACTS TO POWER LINES AND TREES.
ANOTHER SHORTWAVE PROGRESSES EASTWARD ACROSS THE NORTHERN-
TIER, BRINGING ANOTHER CHANCE FOR SHOWERS ALONG A FRONTAL BOUNDARY
ACROSS THE NORTH/CENTRAL ROCKIES AND PLAINS AND UPPER MIDWEST ON
MONDAY INTO TUESDAY. FARTHER SOUTH ACROSS THE SOUTHWEST INTO THE
ROCKIES AND CENTRAL/SOUTHERN PLAIN, RENEWED CHANCES FOR HEAVY
RAINFALL DEVELOPS AS TROPICAL MOISTURE FROM SIMON MOVES NORTHWARD
INTO THE AREA. THE MOISTURE WILL MOVE NORTHEASTWARD ALONG THE
FRONTAL BOUNDARY, SPREADING WIDESPREAD SHOWERS ACROSS THE ROCKIES,
PLAINS, AND MIDWEST.
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
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page