841
FXUS02 KWBC 172041
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
340 PM EST THU NOV 17 2022
VALID 12Z SUN NOV 20 2022 - 12Z THU NOV 24 2022
..OVERVIEW
THE LARGE SCALE PATTERN WILL BE FAIRLY AMPLIFIED WITH MEAN
TROUGHING NEAR THE WEST COAST AND TROUGHING DOWNSTREAM, WITH A
BRIEF TRANSITION OF FLATTER MEAN FLOW EARLY NEXT WEEK. THIS
TRANSITION REPRESENTS AN IMPORTANT CHANGE IN THE SOURCE OF FLOW
DIGGING INTO THE CENTRAL/EASTERN U.S. MEAN TROUGH, FROM A COLD
CANADIAN ORIGIN SUNDAY-MONDAY TO A MORE MODERATE PACIFIC ORIGIN
MID-LATE WEEK AS THE WEST COAST RIDGE REBUILDS. THIS PATTERN
EVOLUTION WILL FAVOR MULTIPLE EPISODES OF RAIN AND HIGH ELEVATION
SNOW OVER THE NORTHWEST, ALONG WITH RAINFALL OVER PORTIONS OF THE
GULF COAST STATES. BY MID-LATE WEEK THIS SOUTHERN TIER MOISTURE
SHOULD EXPAND NORTHWARD AHEAD OF A SURFACE SYSTEM SUPPORTED BY AN
AMPLIFYING TROUGH REACHING THE CENTRAL U.S.
..GUIDANCE AND PREDICTABILITY ASSESSMENT
MODELS/ENSEMBLES AGREE WELL INTO DAY 4 MONDAY. FEATURES OF NOTE
INCLUDE A LEADING DEEP UPPER TROUGH LIFTING THROUGH THE NORTHEAST
AND A BROADER UPSTREAM TROUGH ACROSS SOUTHERN CANADA AND THE GREAT
LAKES, AS WELL AS A WEAK SHORTWAVE EMERGING FROM THE SOUTHERN
ROCKIES. AFTER MONDAY THE GUIDANCE DIVERGES WITH VARIOUS ASPECTS
OF THE FORECAST, MOST PROMINENTLY REGARDING THE TIMING/AMPLITUDE
OF ENERGY FLOWING INTO THE NORTHWESTERN U.S./SOUTHWESTERN CANADA
(AFFECTING PRECIPITATION AMOUNTS AND SOUTHWARD EXTENT IN THE
NORTHWEST) FOLLOWED BY THE DETAILS OF UPPER RIDGING THAT BUILDS
NEAR THE WEST COAST ALONG WITH CORRESPONDING TROUGH AMPLIFICATION
FARTHER EAST. WITHIN THE AMPLIFYING OVERALL TROUGH, A NUMBER OF
ECMWF/CMC RUNS HAVE BEEN FORMING A CLOSED LOW OVER OR NEAR THE
SOUTHERN ROCKIES BY EARLY THURSDAY WHILE LATEST GFS RUNS HAVE
DEPICTED SUCH A LOW FARTHER NORTHEAST (CENTRAL PLAINS IN THE
00Z/06Z RUNS AND NORTHERN PLAINS IN THE NEW 12Z RUN). NOT
SURPRISINGLY THE FULL ENSEMBLE SPREAD ENCOMPASSES THIS RANGE OF
POSSIBILITIES, INCLUDING A MORE OPEN TROUGH. FAVORING A
BLEND/MEAN SOLUTION LEADS TO AN OPEN TROUGH FOR THE TIME BEING
WHILE GUIDANCE SORTS OUT WHERE AN EMBEDDED UPPER LOW MAY BE MORE
LIKELY TO FORM. ISSUES ALSO DEVELOP WITH THE AMPLITUDE AND
PROGRESSION OF THE UPPER TROUGH OVER EASTERN CANADA AND
NORTHEASTERN U.S., INFLUENCING THE DETAILS OF A SURFACE FRONT
REACHING THE CANADIAN BORDER AROUND TUESDAY AND POSSIBLY SINKING
SOUTHWARD THEREAFTER. GUIDANCE HAS VARIED CONSIDERABLY FOR THE
DETAILS OF THIS FRONT BY LATE IN THE PERIOD.
BASED ON THE ARRAY OF GUIDANCE AVAILABLE THROUGH THE 00Z/06Z
CYCLES, THE UPDATED FORECAST INCORPORATED AN OPERATIONAL COMPOSITE
FOR ABOUT THE FIRST HALF OF THE PERIOD. GFS INPUT INCORPORATED
BOTH THE 00Z/06Z RUNS AS VARIOUS DETAILS IN ONE OR THE OTHER
COMPARED BETTER TO CONSENSUS. THEREAFTER THE BLEND TRANSITIONED
TOWARD GREATER EMPHASIS ON THE ENSEMBLE MEANS AND SOME CONTINUITY
WITH ONLY MODEST OPERATIONAL MODEL INCLUSION BY DAY 7 THURSDAY
GIVEN THE INCREASING DIFFERENCES IN DETAILS AT THE SURFACE AND
ALOFT. THIS APPROACH HELPED TO MAINTAIN AS STABLE OF A FORECAST
AS POSSIBLE OVERALL, WITH THE MOST PROMINENT ADJUSTMENT BEING TO
REFLECT LATEST CONSENSUS THAT BY MIDWEEK SHOWS A MORE PRONOUNCED
SOUTHWARD PUSH OF THE FRONT THAT REACHES NEAR THE CANADIAN BORDER
EARLY TUESDAY.
..WEATHER/HAZARD HIGHLIGHTS
WIDESPREAD WELL BELOW AVERAGE TEMPERATURES FOR THIS TIME OF YEAR
ARE LIKELY ACROSS THE EASTERN HALF OF THE COUNTRY AND SOUTHERN
TEXAS ON SUNDAY, WITH HIGHS UP TO 15-25F BELOW AVERAGE. EXPECT
THE EASTERN U.S. COLD WEATHER TO MODERATE GOING INTO THE BEGINNING
OF THE WORK WEEK WITH READINGS RETURNING CLOSER TO SEASONAL
AVERAGES. HOWEVER, THE DAKOTAS AND MINNESOTA WILL LIKELY REMAIN
SLIGHTLY BELOW AVERAGE FOR MUCH OF NEXT WEEK, BUT NOT AS COLD AS
WHAT IS EXPECTED DURING THE SHORT RANGE PERIOD. THE NORTHEAST MAY
SEE A RETURN TO SOMEWHAT BELOW NORMAL TEMPERATURES BY NEXT
THURSDAY, WHILE CENTRAL U.S. TEMPERATURES WILL DEPEND ON THE EXACT
EVOLUTION OF THE SYSTEM THAT MAY TRACK OVER/EAST OF THE REGION
LATE IN THE PERIOD. THE WEST COAST STATES SHOULD TREND TOWARD
ABOVE NORMAL TEMPERATURES MID-LATE WEEK AS UPPER RIDGING BUILDS
OVER THE REGION.
IN TERMS OF PRECIPITATION, LAKE EFFECT SNOW IS LIKELY TO PERSIST
DOWNWIND OF THE EASTERN GREAT LAKES THROUGH SUNDAY NIGHT OWING TO
STRONG COLD AIR ADVECTION OVER THE WARMER WATERS, AND THEN
TAPERING OFF GOING INTO MONDAY. MEANINGFUL PRECIPITATION IS
LIKELY TO MAKE A RETURN TO WESTERN WASHINGTON AND OREGON WITH
MOIST ONSHORE FLOW EXPECTED AND ONE OR MORE FRONTAL SYSTEMS
APPROACHING. HOWEVER THERE IS STILL A FAIR DEGREE OF UNCERTAINTY
OVER THE SOUTHWARD EXTENT AND INTENSITY OF RAIN/MOUNTAIN SNOW ON A
DAY-TO-DAY BASIS. SHOWERS AND SOME THUNDERSTORMS SHOULD GRADUALLY
INCREASE IN COVERAGE ACROSS MUCH OF THE SOUTHERN TIER OF THE U.S.
AND EVENTUALLY NORTHWARD NEXT WEEK AS RETURN FLOW FROM THE GULF OF
MEXICO INTERACTS WITH A FRONT AND A SHORTWAVE ALOFT. DETAILS OF
SYSTEM EVOLUTION WILL DETERMINE IF/HOW MUCH SNOW MAY FALL OVER
NORTHERN TIER LOCATIONS AROUND MIDWEEK OR SO. A PERIOD OF
EASTERLY FLOW MAY HELP TO ENHANCE RAINFALL EARLY NEXT WEEK OVER
THE FLORIDA PENINSULA.
RAUSCH/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
HAZARDS:
- HEAVY RAIN ACROSS PORTIONS OF THE CENTRAL GULF COAST REGION,
THU, NOV 24.
- HEAVY RAIN ALONG PORTIONS OF THE EAST COAST OF FLORIDA, MON-TUE,
NOV 21-NOV 22.
- HEAVY SNOW ACROSS PORTIONS OF THE NORTHEAST AND THE LOWER GREAT
LAKES, SUN, NOV 20.
- FLOODING POSSIBLE ACROSS PORTIONS OF EAST-CENTRAL FLORIDA.
- FLOODING OCCURRING OR IMMINENT ACROSS PORTIONS OF EAST-CENTRAL
FLORIDA.
- MUCH BELOW NORMAL TEMPERATURES ACROSS THE EASTERN PORTION OF THE
GREAT PLAINS, INTO THE MIDWEST AND MID-MISSISSIPPI VALLEY, AS WELL
AS THE OHIO VALLEY AND MUCH OF THE TENNESSEE VALLEY, SUN, NOV 20.
WPC MEDIUM RANGE 500MB HEIGHTS, SURFACE SYSTEMS, WEATHER GRIDS,
QUANTITATIVE PRECIPITATION, EXPERIMENTAL EXCESSIVE RAINFALL
OUTLOOK, WINTER WEATHER OUTLOOK PROBABILITIES AND HEAT INDICES 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
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