875
FXUS02 KWBC 201900
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
200 PM EST WED NOV 20 2024
VALID 12Z SAT NOV 23 2024 - 12Z WED NOV 27 2024
..OVERVIEW
A QUIETER OVERALL WEATHER PATTERN CAN BE EXPECTED TO INCREASINGLY
PREVAIL OVER THE WEEKEND FOR THE CONUS WITH WANE OF THE PROLONGED
ATMOSPHERIC RIVER EVENT IN THE SHORT RANGE PERIOD, AND AS THE LOW
PRESSURE SYSTEM OVER THE NORTHEAST U.S. SLOWLY SHIFTS ALONG WITH
WRAP-BACK SNOWS MORE TO CANADA. THE UPPER LEVEL FLOW PATTERN THEN
BECOMES MORE QUASI-ZONAL FOR THE SUNDAY TO MONDAY TIME PERIOD WITH
THE WESTERN U.S. TROUGH MOVING QUICKLY INLAND AND BECOMING LESS
AMPLIFIED. HOWEVER, THERE WILL STILL BE ENOUGH MOISTURE TO PRODUCE
MODERATE TO LOCALLY HEAVY SNOW FROM THE SIERRA TO THE
CENTRAL/NORTHERN ROCKIES, AND LINGERING LIGHT TO MODERATE RAINS
FOR THE LOWER ELEVATIONS OF THE WEST COAST. A WAVY SURFACE FRONT IS
EXPECTED TO DEVELOP ACROSS THE PLAINS AND THEN SPREAD A COLDER
POST-FRONTAL AIRMASS FROM THE CENTRAL TO EASTERN U.S. EARLY-MID
NEXT WEEK. THIS IS AS AN UPPER LEVEL LOW/TROUGH DIGS UPSTREAM INTO
THE EASTERN PACIFIC/WEST COAST, TRENDING WESTWARD FROM CONTINUITY
TO OFFER A LESS CERTAIN RETURN OF IMPACTFUL ONSHORE PRECIPITATION.
..GUIDANCE/PREDICTABILITY ASSESSMENT
MODEL AND ENSEMBLE FORECAST SPREAD AND PREDICTABILITY SEEM BETTER
THAN NORMAL FOR THE COMING WEEKEND AND A COMPOSITE 06 UTC GFS AND
00 UTC ECMWF/CANADIAN/UKMET SOLUTION OFFER A SOLID FORECAST BASIS
ALONG WITH THE NATIONAL BLEND OF MODELS AND WPC CONTINUITY.
FORECAST SPREAD AND CYCLE TO CYCLE CONTINUITY BECOME LESS THAN
STELLAR NEXT WEEK, MAINLY ATTRIBUTABLE FROM THE EXTENT OF UPPER
TROUGH/LOW ENERGY OVER THE EASTERN PACIFIC VERSUS MORE INLAND INTO
THE WEST IN UNSETTLED/COOLED FLOW. 00/06 UTC GUIDANCE TRENDED WELL
WESTWARD OVER THE EASTERN PACIFIC WITH SYSTEM DIGGING. THE WPC
PRODUCT SUITE PRODUCED EARLIER TODAY ACCEPTED MUCH OF THIS TREND
GIVEN STRONG SUPPORT FROM MACHINE LEARNING MODELS AND GIVEN
ANCHORING AND AMPLIFIED UPPER RIDGING UP TOWARD ALASKA WHOSE
LINGEIRNG POSITION AND SLOWER DEMISE SEEMS TO FAVOR DOWNSTREAM
DIGGING. HOWEVER, 12 UTC MODELS REVERTED SOME AND LIE IN-BETWEEN.
..WEATHER/HAZARDS HIGHLIGHTS
THERE WILL BE SOME ABATEMENT IN THE ATMOSPHERIC RIVER ACROSS
CALIFORNIA GOING INTO SATURDAY AS THE ATTENDANT COLD FRONT MOVES
INLAND AND THE MOISTURE FLUX ANOMALIES DECREASE SOME. THE BEST
MODEL SIGNAL FOR THE HEAVIEST RAIN IS ACROSS THE WESTERN SLOPES OF
THE SIERRA NEVADA, WHERE THE MARGINAL RISK AREA WILL REMAIN FOR THE
NEW DAY 4 EXCESSIVE RAINFALL OUTLOOK WITH 1 TO LOCALLY 2 INCHES OF
RAIN BY EARLY SUNDAY. MODEST RAINFALL IS ALSO EXPECTED FOR THE
COASTAL RANGES OF CENTRAL AND NORTHERN CALIFORNIA, SO NO RISK AREAS
APPEAR WARRANTED AT THIS TIME FOR THOSE AREAS. SNOW LEVELS WILL BE
DROPPING IN THE WAKE OF THE FRONT, AND THIS IS EXPECTED TO RESULT
IN HEAVY SNOW FOR THE HIGHER ELEVATIONS OF THE SIERRA NEVADA, AND
MODERATE SNOW FOR THE INTERMOUNTAIN WEST RANGES AND EVENTUALLY THE
CENTRAL AND NORTHERN ROCKIES FOR THE SUNDAY TO MONDAY TIME PERIOD.
IMPROVING CONDITIONS ARE ALSO FORECAST FOR THE EASTERN U.S. AS THE
STRONG LOW PRESSURE SYSTEM SLOWLY EXITS THE REGION. THERE WILL
LIKELY BE SOME LAKE EFFECT RAIN/SNOW SHOWERS FOR THE EASTERN GREAT
LAKES AND SNOW FOR ESPECIALLY HIGHER TERRAIN OF NEW ENGLAND ON
SATURDAY, WITH BREEZY TO WINDY CONDITIONS IN NORTHWEST FLOW. MOST
AREAS SHOULD BE DRIER BY SUNDAY AS HIGH PRESSURE STARTS BUILDING
BACK IN. GUIDANCE HAS TRENDED PROGRESSIVE WITHA MAIN WAVY FRONTAL
PUSH ACROSS THE SOUTH-CENTRAL TO SOUTHEASTERN/EASTERN U.S. NEXT
WEEK, SO OVERALL BACKED OFF ON PRECIPITATION AMOUNTS.
TEMPERATURES ARE EXPECTED TO SLOWLY MODERATE TO NEAR AVERAGE
ACROSS THE EASTERN U.S. OVER THE WEEKEND COMPARED TO THE RATHER
CHILLY CONDITIONS LATE THIS WEEK. THERE IS STILL THE POTENTIAL FOR
ARCTIC AIR TO REACH PORTIONS OF MONTANA AND INTO NORTH DAKOTA NEXT
WEEK WITH HIGHS IN THE 10S AND LOW 20S, AND OVERNIGHT LOWS IN THE
0S. THERE IS STILL SOME UNCERTAINTY ON HOW FAR SOUTH THIS ARCTIC
AIRMASS GETS, SO THIS WILL BE REFINED IN FUTURE FORECASTS. WARM
CONDITIONS SHOULD CONTINUE FROM SOUTHERN TEXAS TO FLORIDA, WITH
HIGHS IN THE 70S AND 80S.
HAMRICK/SCHICHTEL
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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