364
FXUS02 KWBC 161923
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
223 PM EST SAT NOV 16 2024
VALID 12Z TUE NOV 19 2024 - 12Z SAT NOV 23 2024
..HEAVY RAIN LIKELY FOR THE CENTRAL GULF COAST TUESDAY
...HEAVY PRECIPITATION WITH LONG DURATION ATMOSPHERIC RIVER(S) IN
THE PACIFIC NORTHWEST AND NORTHERN CALIFORNIA...
..OVERVIEW
A RATHER ACTIVE WEATHER PATTERN IS EXPECTED TO BE IN PLACE ACROSS
THE LOWER 48 NEXT WEEK. A LARGE CUTOFF UPPER LOW IS LIKELY TO
DEVELOP OVER THE GREAT LAKES AND OHIO VALLEY REGION BY THE SECOND
HALF OF THE WEEK, WHICH WILL BRING IN COOLER TEMPERATURES ALONG
WITH WINDIER CONDITIONS AS A SURFACE LOW TRACKS ACROSS THAT REGION
TOWARD THE NORTHEAST. AHEAD OF THIS CONSOLIDATING UPPER LOW,
ENHANCED TROPICAL MOISTURE WILL 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 ON TUESDAY. MEANWHILE, NORTHEASTERN PACIFIC SURFACE LOWS
ARE FORECAST TO BRING IN HEAVY PRECIPITATION TO THE PACIFIC
NORTHWEST AND NORTHERN CALIFORNIA AS ONE OR MORE STRONG ATMOSPHERIC
RIVERS TAKE AIM AT THE COASTAL AREAS.
..GUIDANCE/PREDICTABILITY ASSESSMENT
MODEL AGREEMENT IS PRETTY GOOD WITH THE LARGER SCALE FEATURES OF
THE PATTERN THROUGH MUCH OF NEXT WEEK. CONSOLIDATING ENERGIES FROM
THE FOUR CORNERS REGION, SOUTH-CENTRAL CANADA, AND PERHAPS
RETROGRADING FROM THE GREAT LAKES WILL PRODUCE A DEEPENING UPPER
LOW MOVING ACROSS THE GREAT LAKES/OHIO VALLEY AROUND THURSDAY,
AROUND 2 STANDARD DEVIATIONS BELOW NORMAL FOR 500MB HEIGHTS. THE
UPPER LOW SHOULD BE SLOW TO MOVE EASTWARD INTO LATE WEEK, AND
MODELS VARY SOMEWHAT WITH THE LOW'S EVENTUAL PLACEMENT SOMEWHERE
OVER THE NORTHEASTERN U.S. OR NEARBY SOUTHEASTERN CANADA OR WESTERN
ATLANTIC. ASSOCIATED SURFACE LOWS HAVE SIMILAR SPREAD BUT OVERALL
A MODEL/MEAN BLEND SEEMED TO BE A GOOD MIDDLE GROUND FOR THESE
FEATURES.
MEAN UPPER RIDGING IS FORECAST TO SET UP OVER THE INTERIOR WEST
BEHIND THE EASTERN UPPER LOW. BY LATER WEEK THE NORTHEASTWARD
EXTENT OF THE RIDGE IS IN QUESTION DEPENDING ON WHERE THE EASTERN
UPPER LOW ENDS UP. THEN INTO THE EASTERN PACIFIC, THE FIRST COMPACT
UPPER LOW AND DEEP SURFACE LOW AROUND MIDWEEK ARE IN REASONABLY
GOOD AGREEMENT AMONG MODELS, YIELDING HIGHER CONFIDENCE IN THE
STRONG AR, THOUGH THE NEWER 12Z GFS DOES HAVE THE AR TAKING AIM
FARTHER NORTH OF THE NON-NCEP MODELS BY WEDNESDAY. SECONDARY LOWS
SHOW MORE SPREAD IN THE MODELS. THE ECMWF HAS AN UPPER LOW AND
SURFACE LOW RATHER CLOSE TO THE COAST BY FRIDAY, WHICH WPC LEANED
AGAINST AS IT WAS AGAINST CONSENSUS OF OTHER MODELS AND AI/ML
MODELS. THE NEWER 12Z GFS AND ECMWF FORTUNATELY SEEM TO BE IN
BETTER AGREEMENT WITH THIS SYSTEM.
THE WPC FORECAST WAS BASED ON A BLEND OF THE DETERMINISTIC MODELS
EARLY IN THE PERIOD, WITH A GRADUAL INCREASE OF THE ENSEMBLE MEANS
TO HALF BY DAY 6 AND 60 PERCENT DAY 7 AMID INCREASING MODEL SPREAD.
THIS SHOWED REASONABLE CONTINUITY FROM THE PREVIOUS FORECAST.
..WEATHER/HAZARDS HIGHLIGHTS
AS THE MEDIUM RANGE PERIOD BEGINS TUESDAY, DEEP TROPICAL MOISTURE
(PWS LIKELY OVER THE 95TH IF NOT 99TH PERCENTILE) IN PART FROM WHAT
IS CURRENTLY TROPICAL STORM SARA WELL TO THE SOUTH WILL SURGE INTO
THE SOUTHEASTERN U.S. AHEAD OF A COLD FRONT. INSTABILITY SHOULD
HELP CREATE HEAVY RAIN RATES OF MULTIPLE INCHES PER HOUR ACROSS THE
CENTRAL GULF COAST AND THERE IS SOME POTENTIAL FOR BACKBUILDING
STORMS. A SLIGHT RISK REMAINS IN PLACE FOR PORTIONS OF THE CENTRAL
GULF COAST INTO THE SOUTHEAST. EXPECT THE SOUTHERN SIDE TO BE A
HIGH-END SLIGHT RISK, THOUGH STORM MOTION POTENTIALLY BEING ON THE
FASTER SIDE COULD LIMIT WIDESPREAD OR SIGNIFICANT FLOODING CONCERNS
THAT WOULD BE MORE TO MODERATE RISK LEVELS.
FOR THE PACIFIC NORTHWEST, MULTIPLE DAYS OF HEAVY PRECIPITATION
ASSOCIATED WITH ATMOSPHERIC RIVERS AHEAD OF SLOW MOVING PACIFIC
FRONTS SHOULD LEAD TO SEVERAL INCHES OF QPF ACCUMULATING FROM
NORTHWESTERN CALIFORNIA TO THE OLYMPIC PENINSULA. THE PEAK OF THE
AR IS LIKELY TO COME ONSHORE AROUND TUESDAY NIGHT, AND LOOKS TO
STALL ON WEDNESDAY AS A MESOSCALE FRONTAL WAVE PROPAGATING ALONG
THE FRONT CAUSES IT TO MEANDER. ADDED A SLIGHT RISK TO THE DAY
5/WEDNESDAY ERO FOR THIS FORECAST CYCLE, AS MANY HOURS OF RAIN THAT
MAY HAVE 1" PER HOUR RAIN RATES COULD FALL IN THE SAME AREAS. BURN
SCARS WILL BE PARTICULARLY SENSITIVE TO HEAVY RAIN THAT OCCURS.
DESPITE SOME CONTINUED MODEL SPREAD IN EXACTLY WHERE THE MOISTURE
PLUME WILL STALL, DREW IN THE SLIGHT RISK FROM NORTHWESTERN
CALIFORNIA TO SOUTHWESTERN OREGON WHERE THE BEST MODEL CONSENSUS
IS. ONSHORE FLOW IS FORECAST TO CONTINUE INTO LATER WEEK FOR
ADDITIONAL COASTAL HEAVY RAIN AND HIGHER ELEVATION (CASCADES) HEAVY
SNOW.
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, ALONG WITH A REASONABLY DEEP SURFACE LOW. THE COLD AIR
ALOFT FROM THE UPPER LOW, IN COMBINATION WITH INCREASING MOISTURE,
WILL FIRST CAUSE SOME ACCUMULATING SNOW IN THE NORTH-CENTRAL U.S.
ON TUESDAY. THEN THE FIRST SIGNIFICANT SNOWFALL OF THE SEASON IS
LIKELY FOR THE CENTRAL APPALACHIANS, AND PERHAPS SOME LAKE-
ENHANCED AND HIGHER ELEVATION SNOW IN THE NORTHEAST FRIDAY-
SATURDAY. WINDY CONDITIONS ARE EXPECTED IN THE NORTHERN PLAINS
TUESDAY-WEDNESDAY BEHIND THE SURFACE LOW, WITH SOME BREEZY
CONDITIONS INTO THE EAST-CENTRAL U.S. AND POSSIBLY THE NORTHEAST. HEAVY
RAIN MAY IMPACT THE NORTHEAST COASTAL AREAS AS WELL, WITH AMOUNTS
PARTIALLY DEPENDENT ON THE DEPTH AND POSITION OF THE SURFACE LOW AS
IT MAY REDEVELOP OFFSHORE.
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. WESTERN AREAS ARE FORECAST TO WARM TO ABOVE
NORMAL INTO LATER WEEK AS UPPER RIDGING DEVELOPS. 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 WORKWEEK.
TATE/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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