580
FXUS02 KWBC 301853
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
152 PM 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. THE SETUP
AHEAD OF THIS SECOND 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
THE LATEST GUIDANCE THROUGH THE 00Z/06Z CYCLES SHOWS FAIRLY GOOD
AGREEMENT ON THE INITIAL STRONG SYSTEM THROUGH THE NORTHEAST AS
WELL AS AN UPPER LOW DROPPING DOWN THE NORTHWEST COAST. THE 00Z
CMC AND UKMET BOTH BECOME TOO AMPLIFIED OVER THE NORTHEAST AROUND
SUNDAY-MONDAY, WITH THE CMC OUT OF LINE WANTING TO DEVELOP A
CLOSED LOW OVER THE CANADIAN MARITIMES WHICH LINGERS FOR A FEW
DAYS. MEANWHILE THE UKMET IS MUCH TOO AMPLIFIED WITH SOME ENERGY
COMING IN ON THE WESTERN SIDE OF AN UPPER LOW OVER NORTH-CENTRAL
CANADA AT THE SAME TIME.
BY AS EARLY AS DAY 5, THERE ARE SOME IMPORTANT DETAIL DIFFERENCES
WHICH ARISE SURROUNDING ENERGY ROTATING AROUND THE CANADIAN UPPER
LOW ACROSS THE NORTHERN TIER OF THE U.S., AS WELL AS DIFFERENCES
IN ENERGY AS IT EJECTS FROM THE WESTERN U.S. TROUGH. THIS LEADS TO
SOME FAIRLY IMPACTFUL DIFFERENCES IN FRONTAL PLACEMENT AND
HEAVIEST QPF AXIS ACROSS THE EAST-CENTRAL U.S. DAYS 5-7. THE ECMWF
IS MORE AMPLIFIED/SHARPER WITH A NORTHERN STREAM SHORTWAVE LEADING
TO A MORE SOUTHERN SHIFT WITH THE HEAVIER QPF. THE REST OF THE
MODELS, ALONG WITH THE NATIONAL BLEND OF MODELS AND THE ENSEMBLE
MEANS, WOULD SUGGEST A LITTLE FARTHER NORTH FOOTPRINT ACROSS THE
TENNESSEE VALLEY. AT LEAST THE 12Z GFS HOWEVER, AVAILABLE AFTER
FORECAST GENERATION TIME, DID COME IN FARTHER SOUTH, SO ANY
POTENTIAL SOUTHWARD TREND SHOULD CONTINUE TO BE MONITORED. BY DAYS
6-7, THERE CONTINUES TO BE A WIDE ENSEMBLE MEMBER SPREAD FOR HOW
THE WEST COAST SYSTEM EVENTUALLY PROGRESSES INLAND AS WELL AS IN
THE CHARACTER OF UPPER TROUGHING TO THE NORTH/NORTHEAST.
THE GOOD ENOUGH AGREEMENT IN THE EARLY PERIOD ALLOWED FOR A
GENERAL DETERMINISTIC MODEL BLEND, LED BY THE GFS AND ECMWF. AFTER
DAY 4 THOUGH, HAD TO INCORPORATE THE ENSEMBLE MEANS IN PLACE OF
THE CMC AND UKMET DUE TO THE DIFFERENCES DESCRIBED ABOVE WITH A
NEARLY 50/50 DETERMINISTIC/ENSEMBLE MEAN BLEND BY DAY 7. THIS
APPROACH KEPT FAIRLY CLOSE TO THE PREVIOUS SHIFT, WITH MAINLY ONLY
MINOR CHANGES NEEDED FROM CONTINUITY.
..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 OVER THE NORTHERN PLAINS 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.
SANTORELLI/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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