900
FXUS02 KWBC 160652
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
152 AM EST SAT NOV 16 2024
VALID 12Z TUE NOV 19 2024 - 12Z SAT NOV 23 2024
***HEAVY RAIN FOR BOTH THE PACIFIC NORTHWEST AND THE CENTRAL GULF
COAST THROUGH THE MIDDLE OF THE WEEK***
..OVERVIEW
A RATHER ACTIVE WEATHER PATTERN IS EXPECTED TO BE IN PLACE ACROSS
THE CONTINENTAL U.S. NEXT WEEK. A LARGE CUT-OFF UPPER LOW IS
LIKELY TO DEVELOP OVER THE GREAT LAKES AND OHIO VALLEY REGION BY
THE SECOND HALF OF THE WEEK, WITH COLDER WEATHER MOVING IN ACROSS
THIS REGION, AND A STRONG SURFACE LOW IS LOOKING MORE LIKELY TO
DEVELOP NEAR THE EAST COAST. IN TERMS OF THE TROPICS, ALTHOUGH
TROPICAL STORM SARA WILL LIKELY REMAIN WELL TO THE SOUTH ACROSS
CENTRAL AMERICA AND THE FAR SOUTHERN GULF, A PLUME OF ENHANCED
MOISTURE IS LIKELY TO ADVECT NORTHWARD ACROSS THE GULF AND BRING
THE POTENTIAL FOR HEAVY RAIN AHEAD OF AN APPROACHING COLD FRONT FOR
PORTIONS OF THE CENTRAL GULF COAST AND THE FLORIDA PENINSULA.
MEANWHILE, RAIN AND MOUNTAIN SNOW RETURNS TO THE PACIFIC NORTHWEST
BY MIDWEEK AS MULTIPLE PACIFIC STORM SYSTEMS APPROACH THE REGION.
..GUIDANCE/PREDICTABILITY ASSESSMENT
OVERALL, THE LATEST 00Z MODEL GUIDANCE HAS COME INTO BETTER
AGREEMENT ON THE OVERALL SYNOPTIC SCALE SET-UP ACROSS THE
CONTINENTAL U.S. THROUGH THE MIDDLE OF THE WEEK. A POTENT SOUTHERN
STREAM SHORTWAVE WILL LEAD TO THE DEVELOPMENT OF A DEEP AND CUT-OFF
UPPER LOW OVER THE OHIO VALLEY/GREAT LAKES REGION, AND THE GUIDANCE
HAS ALSO COME INTO BETTER AGREEMENT OVER THE PAST COUPLE OF RUNS,
IN CONTRAST TO THE BIG RUN-TO-RUN DIFFERENCES SEEN YESTERDAY. OUT
WEST, THERE ARE SOME MESOSCALE DIFFERENCES WITH A SERIES OF
PACIFIC STORM SYSTEMS THAT WILL BE IMPACTFUL TO THE PACIFIC
NORTHWEST. THE ENSEMBLE MEANS WERE GRADUALLY INCREASED TO ABOUT 50%
BY NEXT SATURDAY AMID GROWING MODEL DIFFERENCES, MAINLY ACROSS THE
WESTERN U.S. AS THE FLOW PATTERN FROM THE EASTERN PACIFIC BECOMES
MORE UNCERTAIN.
..WEATHER/HAZARDS HIGHLIGHTS
HEAVY RAIN IS EXPECTED TO MAKE WEATHER HEADLINES ACROSS THE CENTRAL
GULF COAST REGION DURING THE DAY 4 PERIOD TUESDAY. A SURGE OF DEEP
TROPICAL MOISTURE, SOME OF WHICH ORIGINATES FROM TROPICAL STORM
SARA WELL TO THE SOUTH, WILL FUEL MULTIPLE ROUNDS OF HEAVY SHOWERS
AND THUNDERSTORMS AHEAD OF A COLD FRONT. GIVEN THE POTENTIAL FOR
SOME 2-4 INCH RAINFALL TOTALS IN A FEW SPOTS, THE EXISTING SLIGHT
RISK AREA HAS BEEN EXPANDED SOME FOR THE DAY 4 ERO TO INCLUDE THE
FLORIDA PANHANDLE, SOUTHERN ALABAMA, AND FAR SOUTHWESTERN GEORGIA.
FOR THE PACIFIC NORTHWEST, MULTIPLE DAYS OF HEAVY PRECIPITATION
ASSOCIATED WITH ATMOSPHERIC RIVERS AHEAD OF SLOW MOVING PACIFIC
FRONTS WILL LIKELY LEAD TO SEVERAL INCHES OF QPF EXTENDING FROM
NORTHWESTERN CALIFORNIA TO THE OLYMPIC PENINSULA, AND THIS INCLUDES
BOTH THE DAY 4 AND 5 PERIODS WHERE A MARGINAL RISK IS IN EFFECT.
THE PATTERN DOES NOT CHANGE MUCH GOING INTO THE END OF THE WEEK
WITH ADDITIONAL HEAVY RAINFALL LIKELY, AND HEAVY SNOW FOR THE
CASCADES.
A DYNAMIC STORM SYSTEM IS FORECAST TO DEVELOP OVER THE OHIO VALLEY
AND THEN ACROSS THE GREAT LAKES AND NORTHEAST U.S. AS A DEEP UPPER
LOW FORMS, AND A POTENTIALLY STRONG SURFACE LOW DEVELOPING NEAR THE
MID-ATLANTIC AND THEN TOWARDS NEW ENGLAND. THE COLD AIR ALOFT FROM
THE UPPER LOW, IN COMBINATION WITH INCREASING MOISTURE, WILL LIKELY
RESULT IN THE FIRST SIGNIFICANT SNOWFALL OF THE SEASON FOR THE
CENTRAL APPALACHIANS, AND PERHAPS A LAKE EFFECT SNOWFALL EVENT BY
NEXT SATURDAY AS COLDER AIR MOVES OVER THE WARMER LAKE WATERS,
ESPECIALLY ACROSS ELEVATED DOWNWIND TERRAIN. DEPENDING ON HOW
STRONG THE SURFACE LOW GETS, WINDY CONDITIONS AND HEAVY RAIN NEAR
THE COAST COULD ALSO BE A PROBLEM.
TEMPERATURES ARE EXPECTED TO BE QUITE CHILLY ACROSS THE ROCKIES AND
ADJACENT PORTIONS OF THE INTERMOUNTAIN WEST AND THEN PLAINS IN THE
WAKE OF COLD FRONTAL PASSAGES, WITH A STRONG SURFACE HIGH BUILDING
IN. SOME OVERNIGHT LOWS COULD BE NEAR OR EVEN BELOW ZERO FOR
PORTIONS OF THE CENTRAL AND NORTHERN ROCKIES TUESDAY AND WEDNESDAY
MORNINGS. MEANWHILE, WARM AND HUMID PRE-FRONTAL CONDITIONS ARE
LIKELY FOR THE GULF COAST AND TO THE SOUTHEAST U.S. WITH DEEP
SOUTHERLY FLOW FROM THE TROPICS THROUGH MIDWEEK. PRE-FRONTAL WARMTH
FARTHER INLAND ACROSS THE EAST-CENTRAL U.S. AND EAST/NORTHEAST
WILL BE FOLLOWED BY A RETURN TO MUCH COOLER FALL-LIKE CONDITIONS TO
CLOSE OUT THE WORK WEEK.
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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