909
FXUS02 KWBC 300700
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
159 AM EST WED NOV 30 2022
VALID 12Z SAT DEC 03 2022 - 12Z WED DEC 07 2022
...BELOW NORMAL TEMPERATURES OVER THE WEST WITH RAIN/MOUNTAIN SNOW
GRADUALLY TRENDING LIGHTER...
..HEAVY RAINFALL POTENTIAL OVER THE EAST-CENTRAL U.S.
..OVERVIEW
MOST GUIDANCE SUGGESTS THAT THE INITIAL PATTERN CONSISTING OF
STRONG WEST-SOUTHWESTERLY UPPER FLOW BETWEEN A GULF OF MEXICO
RIDGE AND CENTRAL CANADA UPPER LOW, WITH A MEAN TROUGH NEAR THE
WEST COAST, SHOULD TRANSITION TO BROADLY CYCLONIC FLOW AS THE WEST
COAST TROUGH MOVES INLAND AND AN UPPER RIDGE BUILDS IN ITS PLACE
BY NEXT WEDNESDAY. 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.
THE FIRST OF TWO PRIMARY SYSTEMS OF INTEREST WILL BE TRACKING AWAY
FROM THE UPPER GREAT LAKES ON SATURDAY WHILE THE SECOND WILL
INITIALLY BE NEAR THE WEST COAST AND THEN MOVE INLAND. THERE IS
MORE OF A QUESTION TODAY THAN BEFORE AS TO WHAT PROPORTION OF THE
DYNAMIC SUPPORT FOR A POSSIBLE EASTERN U.S. SYSTEM DURING THE
FIRST HALF OF NEXT WEEK MAY COME FROM THE WEST COAST SYSTEM VERSUS
NORTHERN STREAM CYCLONIC FLOW PUSHING INTO THE LOWER 48 FROM
CANADA. THE SETUP AHEAD OF THIS SYSTEM MAY SUPPORT A PERIOD OF
HEAVY RAINFALL OVER PARTS OF THE EAST-CENTRAL U.S., WHILE THE
SOUTHERN TIER STATES SHOULD SEE ABOVE NORMAL TEMPERATURES.
..GUIDANCE AND PREDICTABILITY ASSESSMENT
BASED ON GUIDANCE AVAILABLE THROUGH THE 12Z/18Z CYCLES, AN
OPERATIONAL MODEL COMPOSITE REPRESENTED FEATURES WELL AT THE START
OF THE PERIOD BUT THEN THE 12Z UKMET/ECMWF/CMC ALL BEGAN TO
DIVERGE FROM EACH OTHER AND THE ENSEMBLE MEANS IN VARYING WAYS.
THIS LED TO TRENDING THE FORECAST MORE TO THE 18Z GEFS/12Z ECMWF
MEANS WITH LINGERING INPUT FROM THE 18Z GFS BY THE END OF THE
PERIOD. THE UKMET AND TO SOME DEGREE ECMWF WERE MORE AGGRESSIVE
THAN OTHER SOLUTIONS WITH ENERGY DROPPING INTO THE NORTHWEST BY
EARLY MONDAY, THE CMC WAS ON THE SLOW SIDE TO BRING THE INITIAL
WEST COAST SYSTEM INLAND, AND BY LATE IN THE PERIOD THE ECMWF
PULLED THE CANADA UPPER LOW WELL WEST OF CONSENSUS PLUS CLOSED AN
UPPER LOW OFF THE CANADIAN MARITIMES TO BLOCK THE PATTERN OVER THE
NORTHEASTERN U.S.--PERHAPS PLAYING A ROLE IN THE SLOWER EVOLUTION
OF ITS EASTERN U.S. SYSTEM. THE NEW 00Z RUNS ADD MORE UNCERTAINTY,
WITH THE GFS JOINING THE CMC FOR SLOWEST INLAND PROGRESSION OF THE
WEST COAST SYSTEM. BOTH MODELS TAKE ONLY A SMALL PORTION OF THAT
ENERGY (SHEARING AHEAD OF NORTHERN STREAM FLOW) TO PRODUCE THE
EARLY WEEK SYSTEM TO THE EAST O THE ROCKIES. THUS IN 24-36 HOURS
THE GFS HAS TRENDED FROM HAVING ONE OF THE STRONGEST SYSTEMS TO A
RATHER WEAK ONE. THE CMC AND MOST ENSEMBLE MEANS HAVE TENDED TO
HAVE A FAIRLY MODEST REFLECTION OF THIS WAVE. THE UKMET CONTINUES
TO BE AMPLIFIED WITH THE NORTHWEST ENERGY ON TUESDAY. NOT
SURPRISINGLY, THERE IS WIDE ENSEMBLE MEMBER SPREAD FOR THE OVERALL
FORECAST OF HOW THE WEST COAST SYSTEM PROGRESSES INLAND AND
CHARACTER OF UPPER TROUGHING TO THE NORTH/NORTHEAST.
..WEATHER/HAZARD HIGHLIGHTS
LOW PRESSURE NEAR THE WEST COAST DURING THE WEEKEND WILL LIKELY
BRING THE HIGHEST RAINFALL/MOUNTAIN SNOW TOTALS TO AREAS FROM THE
SOUTHWEST CORNER OF OREGON THROUGH NORTHERN CALIFORNIA AND THE
SIERRA NEVADA. LIGHTER TOTALS ARE POSSIBLE OVER THE PACIFIC
NORTHWEST, SOUTHERN CALIFORNIA, AND PORTIONS OF THE ROCKIES. THE
FLOW ALOFT AHEAD OF THIS SYSTEM MAY CARRY IN SOME ADDED MOISTURE
FROM THE EASTERN PACIFIC, LEADING TO AREAS OF RAINFALL ACROSS
ARIZONA AND NEW MEXICO. SOME OF THIS ACTIVITY COULD BE ON THE
LOCALLY MODERATE TO HEAVY SIDE BUT CONFIDENCE IN THE DETAILS IS
STILL FAIRLY LOW. THE SOUTHERN HALF OF THE WEST SHOULD TREND DRIER
BY EARLY NEXT WEEK AS UPPER TROUGHING MOVES FARTHER INLAND BUT
SOME PRECIPITATION MAY PERSIST OVER THE NORTHWEST/ROCKIES. THE
WEST COAST SYSTEM MAY PRODUCE GUSTY WINDS OVER SOME AREAS ON
SATURDAY.
AREAS EAST OF THE ROCKIES SHOULD SEE A FAIRLY ACTIVE PATTERN BUT
WITH SOME UNCERTAINTIES GIVEN THE SPREAD IN THE GUIDANCE FOR
SPECIFICS. BEST CONTINUITY IS WITH A VIGOROUS SYSTEM TRACKING AWAY
FROM THE UPPER GREAT LAKES AFTER EARLY SATURDAY WITH A BRIEF
PERIOD OF BRISK TO STRONG WINDS CROSSING THE NORTHEASTERN QUADRANT
OF THE LOWER 48. THE ASSOCIATED COLD FRONT COULD BRING SOME LIGHT
TO LOCALLY MODERATE RAINFALL OVER THE EAST. THIS FRONT SHOULD
STALL AND THEN RETURN NORTHWARD AS A WARM FRONT AHEAD OF THE NEXT
SYSTEM EMERGING OVER THE PLAINS/MIDWEST, SERVING AS A FOCUS FOR
INCREASING RAINFALL OVER THE MIDDLE LATITUDES OF THE EAST-CENTRAL
U.S. SUNDAY ONWARD. BOTH LOW LEVEL FLOW FROM THE GULF AND THE
WEST-SOUTHWESTERLY FLOW ALOFT SHOULD CONTRIBUTE MOISTURE FOR THIS
EVENT THAT COULD PRODUCE AREAS OF MODERATE TO HEAVY RAINFALL. SOME
RAIN MAY EXTEND BACK INTO THE PLAINS AS WELL. THE SYSTEM'S COLD
FRONT COULD MAINTAIN AN ENHANCED RAINFALL FOCUS INTO TUESDAY. IT
SHOULD BE NOTED THAT WHILE THE GENERAL RAINFALL SIGNAL HAS BEEN
PERSISTENT OVER RECENT DAYS, CONFIDENCE IN THE SPECIFICS IS NOT
GREAT IN LIGHT OF THE GUIDANCE SPREAD FOR HOW THE SURFACE SYSTEM
EVOLVES/TRACKS EARLY NEXT WEEK. SOME SNOW COULD FALL IN THE
NORTHERN/NORTHWESTERN PERIPHERY OF THIS SYSTEM
MUCH OF THE WEST SHOULD SEE BELOW NORMAL HIGH TEMPERATURES FROM
THE WEEKEND INTO THE MIDDLE OF NEXT WEEK, WITH MOST LOCATIONS
5-15F BELOW NORMAL. THE NORTHERN PLAINS WILL GENERALLY BE BELOW
NORMAL, WITH SUNDAY LIKELY BEING THE MOST MODERATE DAY CLOSEST TO
NORMAL. THEN HIGHS SHOULD DROP TO 15-25F BELOW NORMAL OVER SOME
AREAS FOR MONDAY-TUESDAY WITH A SLIGHT WARMING TREND BY WEDNESDAY.
SOUTHERN/EASTERN AREAS WILL TEND TO SEE NEAR TO ABOVE NORMAL
TEMPERATURES, WITH VARIOUS AREAS OF PLUS 10-15F ANOMALIES LIKELY
DURING THE WEEKEND INTO TUESDAY (THEN DROPPING AS A COLD FRONT
REACHES THE EAST BY WEDNESDAY). THE SOUTHERN TIER SHOULD SEE
MULTIPLE DAYS OF PLUS 15-25F ANOMALIES FOR MORNING LOWS AND SOME
DAILY RECORDS FOR WARM LOWS MAY BE POSSIBLE MONDAY-TUESDAY.
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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