141
FXUS02 KWBC 170658
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
158 AM EST SUN NOV 17 2024
VALID 12Z WED NOV 20 2024 - 12Z SUN NOV 24 2024
***STRONG UPPER LOW ACROSS THE GREAT LAKES AND NORTHEAST TO RESULT
IN COLD RAIN AND HIGHER ELEVATION SNOW, AND PROLONGED ATMOSPHERIC
RIVER EVENT EXPECTED FOR THE PACIFIC NORTHWEST***
..OVERVIEW
A DEEP UPPER LEVEL LOW DEVELOPING ACROSS THE GREAT LAKES AND
NORTHEAST U.S WILL MAKE WEATHER HEADLINES TO CLOSE OUT THE WORK
WEEK. THIS WILL LIKELY MEANDER SLOWLY IN PLACE FOR A FEW DAYS WITH
A BLOCKING HIGH TO ITS NORTH ACROSS CENTRAL CANADA. THIS WILL
RESULT IN A COLD RAIN FROM THE OHIO VALLEY TO THE EAST COAST, AND
EARLY SEASON ACCUMULATING SNOW FOR THE CENTRAL APPALACHIANS AND THE
HIGHER TERRAIN OF NEW ENGLAND. OUT WEST, AN UNSETTLED WEATHER
PATTERN ACROSS THE EASTERN PACIFIC IS EXPECTED TO RESULTED IN A
PROLONGED ATMOSPHERIC RIVER EVENT FROM NORTHERN CALIFORNIA TO
WESTERN WASHINGTON FOR THE SECOND HALF OF THE WORK WEEK, WITH
SEVERAL INCHES OF RAINFALL LIKELY FOR THE LOWER ELEVATIONS. BETWEEN
THESE TWO REGIONS, AN UPPER LEVEL RIDGE IS LIKELY TO BUILD ACROSS
THE ROCKIES AND EVENTUALLY ACROSS THE PLAINS BY NEXT WEEKEND.
..GUIDANCE/PREDICTABILITY ASSESSMENT
THERE ARE STILL SOME MODEL DIFFERENCES IN THE EXPECTED EVOLUTION OF
THE LARGE SCALE UPPER TROUGH AND CLOSED LOW ACROSS THE EASTERN
U.S. BY THURSDAY, WITH THE ECMWF/CMC/UKMET SUPPORTING A CLOSED LOW
FARTHER SOUTH ACROSS THE OHIO VALLEY AND INTO PA, WHEREAS THE GFS
AND GEFS MEAN FARTHER NORTH AND CLOSER TO THE GREAT LAKES. HOWEVER,
THE GUIDANCE AGREES WELL THAT A SURFACE LOW IS LIKELY TO DEVELOP
NEAR SOUTHERN NEW ENGLAND AND THEN SLOWLY MOVE OUT TOWARDS NOVA
SCOTIA. MODEL SPREAD HAS ALSO IMPROVED WITH THE TWO SEPARATE LOWS
OVER THE EASTERN PACIFIC THAT WILL BE IMPACTFUL TO THE PACIFIC
NORTHWEST, ALTHOUGH MESOSCALE DIFFERENCES REMAIN THAT ARE TYPICAL
DURING THE DAY 4-6 TIME PERIOD.
THE ENSEMBLE MEANS WERE GRADUALLY INCREASED TO ABOUT 50% BY NEXT
SUNDAY AMID GROWING MODEL DIFFERENCES, WHILE STILL MAINTAINING
SOME OF THE DETERMINISTIC GFS AND ECMWF SOLUTIONS.
..WEATHER/HAZARDS HIGHLIGHTS
CONFIDENCE IS INCREASING FOR A POTENTIALLY MAJOR AND PROLONGED
ATMOSPHERIC RIVER EVENT SETTING UP ACROSS PORTIONS OF NORTHWESTERN
CALIFORNIA AND INTO SOUTHWESTERN OREGON DURING THE WEDNESDAY
THROUGH THURSDAY TIME PERIOD. ENHANCED MOISTURE FLUX AHEAD OF A
MEANDERING COLD FRONT AND TWO SEPARATE LOW PRESSURE AREAS WILL
RESULT IN ENHANCED OROGRAPHIC LIFT AND LIKELY PRODUCE SOME 4 TO
LOCALLY 8 INCH RAINFALL TOTALS DURING THIS TIME. GIVEN THE DURATION
OF THE EVENT, A SLIGHT RISK AREA IS IN PLACE FOR BOTH DAYS 4 AND 5
ACROSS THESE AREAS, INCLUDING THE COASTAL RANGES AND EXTENDING TO
THE COAST. THIS WILL LIKELY HAVE ADDITIONAL STAYING POWER GOING
INTO FRIDAY AS WELL WITH THE FRONT SLOWLY MAKING ITS WAY INLAND
ACROSS THE REGION. SNOW LEVELS WILL INITIALLY BE HIGH, BUT SHOULD
FALL GOING INTO THE WEEKEND, INCLUDING MUCH OF THE SIERRA RANGE.
IMPACTFUL WEATHER IS ALSO EXPECTED FOR A LARGE PORTION OF THE
EASTERN U.S. AS WELL FOR THE LATTER HALF OF THE WORK WEEK. THIS
WILL BE THE RESULT OF A LARGE UPPER LOW CLOSING OFF AND INDUCING
SURFACE CYCLOGENESIS NEAR THE MID-ATLANTIC AND SOUTHERN NEW
ENGLAND. COLD AIR ALOFT WILL BE SUFFICIENT TO SUPPORT ACCUMULATING
EARLY SEASON SNOW FOR THE HIGHER TERRAIN NEAR THE GREAT LAKES AND
INTERIOR NORTHEAST, AND ESPECIALLY FOR THE CENTRAL APPALACHIANS
WHERE SOME TOTALS IN EXCESS OF SIX INCHES ARE A GOOD POSSIBILITY.
THERE MAY ALSO BE SOME LAKE EFFECT SNOW IN THE WAKE OF THIS STORM
SYSTEM, ALTHOUGH TEMPERATURES WILL LIKELY BE MARGINAL AND THIS
COULD MIX WITH RAIN AT TIMES. RAINY AND BREEZY ARE EXPECTED FOR THE
MAJOR CITIES ALONG THE INTERSTATE 95 CORRIDOR THROUGH THURSDAY
NIGHT.
IN TERMS OF TEMPERATURES, WARM AND SLIGHTLY HUMID CONDITIONS CAN
BE EXPECTED FROM THE MID-ATLANTIC SOUTHWARD TO FLORIDA ON WEDNESDAY
AHEAD OF THE APPROACHING COLD FRONT, WHICH WILL BRING A RETURN TO
MUCH COOLER CONDITIONS TO CLOSE OUT THE WORK WEEK. HIGHS SHOULD
GENERALLY BE ABOUT 5-10 DEGREES BELOW AVERAGE ACROSS THE INTERIOR
EASTERN U.S. BY FRIDAY, MAINLY BECAUSE OF THE COLD UPPER LOW
OVERHEAD KEEPING WIDESPREAD CLOUD COVER IN PLACE, AND OVERNIGHT
LOWS CLOSER TO AVERAGE. A GRADUAL WARMING TREND IS LIKELY FOR THE
INTERMOUNTAIN WEST AND THE ROCKIES AFTER THE COLD CONDITIONS
EXPECTED IN THE FIRST HALF OF THE 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
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page