704
FXUS02 KWBC 010659
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
159 AM EST THU DEC 01 2022
VALID 12Z SUN DEC 04 2022 - 12Z THU DEC 08 2022
...BELOW NORMAL TEMPERATURES OVER THE WEST WITH RAIN/MOUNTAIN SNOW
GENERALLY TRENDING LIGHTER...
...HEAVY RAINFALL POTENTIAL OVER THE EAST-CENTRAL U.S. EARLY NEXT
WEEK...
..OVERVIEW
EXPECT A MAJORITY OF THE LOWER 48 TO SEE FAST FLOW ALOFT BETWEEN A
MEAN LOW OVER CENTRAL CANADA AND A RIDGE OVER THE GULF OF MEXICO.
SOME ENERGY FROM AN UPPER LOW INITIALLY NEAR THE WEST COAST MAY
GET INCORPORATED INTO THIS FAST FLOW BUT A POSITIVELY TILTED
TROUGH MAY PERSIST OVER THE EASTERN PACIFIC AND WESTERN U.S. WITH
ONLY A GRADUAL EASTWARD DRIFT DURING THE EARLY-MID WEEK TIME
FRAME. AN UPSTREAM RIDGE SHOULD MOVE INTO THE NORTHWEST
U.S./WESTERN CANADA BY MIDWEEK OR SO, FOLLOWED BY A SHORTWAVE
TROUGH APPROACHING THE PACIFIC NORTHWEST NEXT THURSDAY. THIS
PATTERN SHOULD PROMOTE BELOW NORMAL TEMPERATURES OVER MOST OF THE
WEST AND NORTHERN PLAINS ON MOST DAYS, WHILE THE RAIN AND MOUNTAIN
SNOW AFFECTING SOME PARTS OF THE WEST SHOULD STEADILY DECREASE IN
COVERAGE AND INTENSITY WITH TIME. ON THE OTHER HAND IT LOOKS TO
BE A FAVORABLE SETUP FOR HEAVY RAINFALL OVER PORTIONS OF THE
EAST-CENTRAL U.S. EARLY NEXT WEEK AS MULTIPLE MOISTURE SOURCES
INTERACT WITH A COUPLE FRONTS. THE FAR SOUTHERN TIER STATES
SHOULD SEE MOSTLY ABOVE NORMAL TEMPERATURES.
..GUIDANCE AND PREDICTABILITY ASSESSMENT
VARIOUS ASPECTS OF THE FORECAST HAVE BEEN IN FLUX OVER RECENT
RUNS. THESE INCLUDE THE SHORTWAVE DETAILS WITHIN THE
CANADA/NORTHERN TIER U.S. STREAM, SPECIFICS OF THE WEST COAST
UPPER LOW THAT OPENS UP AND RESIDUAL TROUGHING, AND HOW THE
COMBINATION OF ENERGY WILL CONTRIBUTE TO A FRONTAL SYSTEM/LOW
PRESSURE OVER THE EAST BY TUESDAY-WEDNESDAY. OPERATIONAL MODELS
HAVE BEEN FAIRLY CHAOTIC WITH SOME OF THE SPECIFICS ACROSS
SOUTHERN CANADA AND THE NORTHERN TIER DURING THE PERIOD, WITH THE
ENSEMBLE MEANS PROVIDING SOMEWHAT MORE STABILITY. AMONG THE
12Z/18Z GUIDANCE EVALUATED FOR THE UPDATED FORECAST, THE 18Z GFS
STRAYED THE MOST AWAY FROM CONSENSUS FOR THE NORTHERN STREAM
DURING THE LATTER HALF OF THE PERIOD. MEANWHILE THE PAST 24-36
HOURS OF GUIDANCE HAS TRENDED TOWARD A MUCH SLOWER PROGRESSION OF
WHAT TROUGHING REMAINS OVER THE EASTERN PACIFIC/WESTERN U.S. AS A
PORTION OF THE SYSTEM'S ENERGY SHEARS OUT INTO THE PROGRESSIVE
FLOW DOWNSTREAM. THIS TREND HAS GENERALLY LED GUIDANCE TO DEPICT
SOMEWHAT WEAKER WAVINESS ALONG THE FRONT THAT REACHES THE EASTERN
U.S. BY TUESDAY-WEDNESDAY, BUT CONSIDERABLE SPREAD FOR DETAILS DUE
TO THE VARIABILITY IN THE NORTHERN STREAM. THERE IS SOME IMPROVED
CLUSTERING AS AN EMBEDDED WAVE MAY REACH NEW ENGLAND AND THE
CANADIAN MARITIMES. FOR THE SHORTWAVE NEARING THE NORTHWEST NEXT
THURSDAY, 12Z AND NEW 00Z GFS RUNS ARE A BIT ON THE SLOW/AMPLIFIED
SIDE WHILE THE 18Z GFS FIT MORE IN LINE WITH THE MODEL/ENSEMBLE
MEAN MAJORITY. THE STARTING BLEND INCORPORATED THE 12Z/18Z
OPERATIONAL MODELS EARLY IN THE FORECAST AND THEN GRADUALLY PHASED
OUT THE 18Z GFS WHILE INCREASING 18Z GEFS/12Z ECMWF MEANS AND
HANGING ONTO SOME ECMWF/CMC INPUT.
..WEATHER/HAZARD HIGHLIGHTS
LOW PRESSURE NEAR THE WEST COAST THROUGH SUNDAY SHOULD PRODUCE
SOME ENHANCED RAIN AND MOUNTAIN SNOW ALONG FAVORED TERRAIN OF THE
SIERRA NEVADA WITH LIGHTER TOTALS OVER CALIFORNIA AND PARTS OF
OREGON. SOME OF THE MOISTURE FROM THIS SYSTEM WILL ALSO EXTEND
INTO THE GREAT BASIN AND CENTRAL ROCKIES. MOIST SOUTHERN STREAM
PACIFIC FLOW ALOFT AHEAD OF THIS SYSTEM MAY CONTINUE TO PRODUCE
SOME RAINFALL OVER PARTS OF ARIZONA AND NEW MEXICO THROUGH SUNDAY
AS WELL. SOME OF THIS ACTIVITY COULD BE ON THE LOCALLY MODERATE
TO HEAVY SIDE. THE SOUTHERN HALF OF THE WEST SHOULD TREND DRIER
EARLY NEXT WEEK AS THE WEST COAST SYSTEM OPENS UP, THOUGH IT IS
POSSIBLE FOR A LITTLE MOISTURE TO RETURN EVENTUALLY OVER FAR
SOUTHERN AREAS IF RESIDUAL UPPER TROUGHING IS SLOW ENOUGH. A
FRONTAL SYSTEM APPROACHING THE NORTHWEST MAY BRING AN INCREASE OF
PRECIPITATION BY NEXT THURSDAY.
FARTHER EAST, A FRONT SETTLING NEAR THE GULF COAST ON SUNDAY MAY
RETURN NORTHWARD AS A WARM FRONT EARLY NEXT WEEK WHILE A SYSTEM
(CURRENTLY EXPECTED TO BE OF MODERATE STRENGTH) EMERGES FROM THE
PLAINS WITH A TRAILING COLD FRONT. WEST-SOUTHWESTERLY UPPER LEVEL
FLOW OF MOISTURE FROM THE PACIFIC AND A GRADUAL INCREASE OF LOW
LEVEL GULF INFLOW MAY INTERACT WITH THE FRONTS TO PRODUCE AN AREA
OF HEAVY RAINFALL OVER THE EAST-CENTRAL U.S. EARLY NEXT WEEK.
CURRENTLY THE SIGNAL IS FAVORABLE ENOUGH TO DEPICT A SLIGHT RISK
AREA ON THE EXPERIMENTAL DAY 5 EXCESSIVE RAINFALL OUTLOOK (VALID
MONDAY-MONDAY NIGHT) CENTERED PRIMARILY OVER MOST OF TENNESSEE AND
SOUTHERN KENTUCKY. FAIRLY WET GROUND CONDITIONS WILL MAKE THIS
AREA SENSITIVE TO SIGNIFICANT RAINFALL AS WELL. RAINFALL COULD
PERSIST OVER PARTS OF THE SOUTH-CENTRAL U.S. THROUGH AT LEAST
MIDWEEK IF THE WAVY FRONT CROSSING THE REGION IS SLOW ENOUGH. ANY
SNOW SHOULD BE CONFINED TO FAR NORTHERN LATITUDES OF THE EAST.
EXPECT BELOW NORMAL HIGH TEMPERATURES TO PERSIST OVER MUCH OF THE
WEST THROUGH THE SUNDAY-THURSDAY PERIOD, WITH MOST LOCATIONS 5-15F
BELOW NORMAL. THE NORTHERN PLAINS WILL GENERALLY BE BELOW NORMAL
AS WELL, WITH MONDAY-WEDNESDAY HAVING THE COLDEST HIGHS OF AT
LEAST 15-20F BELOW NORMAL AT SOME LOCATIONS. THE SOUTHERN TIER
WILL TEND TO SEE ABOVE NORMAL TEMPERATURES, AND ESPECIALLY FOR
MORNING LOWS THAT COULD BE UP TO 20-25F ABOVE NORMAL EARLY-MID
WEEK. A FEW DAILY RECORDS FOR WARM LOWS MAY BE POSSIBLE. SYSTEM
PROGRESSION SHOULD BRING VARIABLE TEMPERATURES TO THE NORTHERN
HALF OF THE EAST.
RAUSCH
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, 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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