438
FXUS02 KWBC 280700
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
159 AM EST MON NOV 28 2022
VALID 12Z THU DEC 01 2022 - 12Z MON DEC 05 2022
...WET/SNOWY CONDITIONS EXPANDING ACROSS THE WEST WITH BELOW
NORMAL TEMPERATURES...
..OVERVIEW
LATEST MODELS AND ENSEMBLE MEANS ARE CONSISTENT IN SHOWING A LATE
WEEK THROUGH WEEKEND UPPER PATTERN FEATURING WEST-SOUTHWESTERLY
MEAN FLOW BETWEEN WEST COAST UPPER TROUGHING AND A GULF OF MEXICO
RIDGE. THE PATTERN SHOULD PERSIST INTO EARLY NEXT WEEK OVER MOST
AREAS BUT WITH THE OVERALL TROUGH AXIS MOVING INLAND OVER THE WEST
WITH THE EJECTION OF THE SECOND OF TWO PRIMARY SHORTWAVES. THIS
LARGE SCALE FLOW WILL FAVOR BELOW NORMAL DAYTIME TEMPERATURES OVER
MOST AREAS TO THE WEST OF THE ROCKIES, AS WELL AS THE NORTHERN
HIGH PLAINS AT TIMES, WHILE THE WEST SEES EPISODES OF LOCALLY
SIGNIFICANT RAIN AND HIGHER ELEVATION SNOW. MOST OF THE EASTERN
HALF OF THE COUNTRY WILL BE DRY LATE THIS WEEK BUT RAINFALL SHOULD
INCREASE IN COVERAGE AND INTENSITY OVER EAST-CENTRAL AREAS DURING
THE WEEKEND AS MOISTURE INTERACTS WITH A FRONT THAT A
FRIDAY-SATURDAY CANADIAN SURFACE LOW BRINGS INTO THE REGION.
..GUIDANCE AND PREDICTABILITY ASSESSMENT
WITH THE DEPARTURE OF A STRONG UPPER SHORTWAVE AND SURFACE LOW
PRESSURE FROM EASTERN NORTH AMERICA EARLY IN THE PERIOD, THE MAIN
FOCUS OF THE FORECAST IS ON THE INDIVIDUAL SHORTWAVES WITHIN THE
WEST COAST MEAN TROUGH. WHILE NOTABLE DIFFERENCES STILL EXIST,
THERE HAS BEEN SOME IMPROVEMENT IN THE DEPICTION OF EACH OF TWO
PRIMARY FEATURES.
THE FIRST SHORTWAVE SHOULD BE JUST OFFSHORE AS OF EARLY THURSDAY
AND THEN PROGRESS INLAND WITH TIME, SUPPORTING A SURFACE SYSTEM
THAT ULTIMATELY TRACKS INTO EASTERN CANADA WHILE PUSHING A
TRAILING COLD FRONT THROUGH THE EAST. CONSENSUS OF MODELS THROUGH
THE 18Z RUN AND WHAT HAS ARRIVED SO FAR FROM THE 00Z CYCLE
SUGGESTS THE GFS COULD BE SOMEWHAT FAST AND THE 12Z ECMWF SOMEWHAT
AMPLIFIED/SLOW. AT THE VERY LEAST, RECENT ECMWF TRENDS HAVE BEEN
GRADUALLY FASTER AND IN TURN LEADING TO A SHORTER DURATION OF
POTENTIAL INTERACTION WITH OFFSHORE SOUTHERN STREAM
MOISTURE/WAVINESS THAT WOULD ENHANCE PRECIPITATION AMOUNTS ALONG
THE CENTRAL WEST COAST AROUND THURSDAY-FRIDAY. THE TIMING
DIFFERENCES PERSIST FOR THE SURFACE SYSTEM EAST OF THE ROCKIES,
WITH THE SLOWER ECMWF DIFFERING THE MOST FROM THE ENSEMBLE MEANS
WHICH IN RECENT DAYS HAVE BEEN THE MOST STABLE GUIDANCE WITH THIS
SYSTEM BY THE WEEKEND. THE NEW 00Z ECMWF HAS INDEED TRENDED FASTER
WITH THIS SHORTWAVE.
THE SECOND SYSTEM OF INTEREST WILL LIKELY APPROACH THE NORTHWEST
COAST BY SATURDAY. THE 12Z ECMWF WAS A BIT ON THE SLOWER SIDE
WHILE THE 12Z/18Z GFS RUNS IN PARTICULAR DROPPED THE UPPER LOW
FARTHER SOUTH THAN MOST OTHER GUIDANCE FROM LATE FRIDAY INTO
SUNDAY. THE NEW 00Z GFS HAS FAVORABLY TRENDED CLOSER TO CONSENSUS.
EVEN WITH SOME OF THE DIFFERENCES ALONG THE WAY, BY EARLY MONDAY
THERE IS ACTUALLY BETTER THAN AVERAGE AGREEMENT AS THE UPPER LOW
OPENS UP AND MOVES INTO THE WEST. FARTHER EAST, TYPICAL
VARIABILITY DEVELOPS REGARDING THE ULTIMATE LATITUDE OF THE FRONT
THAT IS LIKELY TO STALL DURING THE WEEKEND AND BECOME A FOCUS FOR
INCREASING RAINFALL. SOME EARLIER GUIDANCE HAD BEEN A LITTLE
PREMATURE TO DEVELOP RAINFALL OVER THE MISSISSIPPI/OHIO/TENNESSEE
VALLEY REGION BUT OVERALL THE MODELS AND ENSEMBLES ARE STARTING TO
SHOW A MORE COHERENT SIGNAL LATE IN THE PERIOD. TELECONNECTIONS
RELATIVE TO THE FORECAST MEAN PATTERN ALSO FAVOR ENHANCED
PRECIPITATION POTENTIAL OVER THIS REGION.
ALSO OF NOTE, AN UPPER LOW DROPPING SOUTH FROM THE CANADIAN
ARCHIPELAGO SHOULD PUSH A COLD FRONT INTO THE NORTHERN TIER STATES
DURING THE WEEKEND. THERE HAS BEEN SOME MODEL SPREAD/VARIABILITY
BUT A CONSENSUS MODEL/MEAN APPROACH HAS MAINTAINED FAIRLY GOOD
CONTINUITY OVER THE PAST DAY.
BASED ON THE ARRAY OF GUIDANCE AVAILABLE THROUGH THE 12Z/18Z
CYCLES, THE UPDATED FORECAST STARTED WITH AN OPERATIONAL MODEL
COMPOSITE TO START AND THEN INCORPORATED MODEST 18Z GEFS/12Z ECMWF
MEAN INPUT INTO MID PERIOD TO BLUNT THE LESS DESIRABLE ATTRIBUTES
OF THE ECMWF (INITIAL WEST COAST SHORTWAVE) AND GFS (SECOND
SYSTEM). THE BLEND TRANSITIONED TOWARD NEARLY EVEN WEIGHT OF
MODELS/MEANS LATE IN THE PERIOD.
..WEATHER/HAZARD HIGHLIGHTS
THE FIRST PRIMARY SYSTEM TO AFFECT THE WEST SHOULD BRING HIGHEST
TOTALS OF RAIN AND MOUNTAIN SNOW TO CALIFORNIA LATE THIS WEEK
(NORTHERN-CENTRAL AREAS THURSDAY AND PUSHING FARTHER SOUTH BY
FRIDAY) WITH SOME MOISTURE ALSO EXTENDING INTO THE
NORTHERN-CENTRAL ROCKIES. THIS SYSTEM MAY INCORPORATE SOME
OFFSHORE LOWER-LATITUDE MOISTURE/WAVINESS TO ENHANCE AMOUNTS BUT A
SOMEWHAT FASTER TREND OF THIS SYSTEM OVER THE PAST DAY OR SO HAS
LOWERED THE POTENTIAL FOR THE HEAVIEST TOTALS THAT SOME GUIDANCE
HAD BEEN ADVERTISING. THE TRAILING SYSTEM SHOULD BRING INCREASING
RAIN AND MOUNTAIN SNOW TO AREAS ALONG THE NORTHERN HALF OF THE
WEST COAST AROUND FRIDAY, WITH BEST FOCUS DRIFTING SOUTH INTO
NORTHWESTERN CALIFORNIA AND THE SIERRA NEVADA DURING THE WEEKEND.
AGAIN THE NORTHERN TWO-THIRDS OF THE ROCKIES WILL SEE MEANINGFUL
SNOW FROM THIS EVENT, ALBEIT WITH SOMEWHAT LOWER LIQUID
EQUIVALENTS THAN EXPECTED NEAR THE WEST COAST. SNOW LEVELS IN THE
NORTHWEST COULD DECLINE TO FAIRLY LOW ELEVATIONS OVER SOME AREAS.
THE NORTHEAST SHOULD SEE BREEZY TO WINDY CONDITIONS ON THURSDAY AS
STRONG LOW PRESSURE DEPARTS OVER EASTERN CANADA, WITH LAKE EFFECT
SNOW GRADUALLY TRENDING LIGHTER WITH TIME. A WAVY FRONT REACHING
THE NORTH-CENTRAL PLAINS/UPPER MIDWEST BY FRIDAY MAY BRING SOME
LIGHT PRECIPITATION TO THE FAR NORTHERN TIER AND POSSIBLY OTHER
AREAS OF LIGHT RAIN AS IT CONTINUES EASTWARD. MORE ORGANIZED
RAINFALL COULD THEN DEVELOP OVER THE EAST-CENTRAL U.S. DURING THE
WEEKEND AS THE FRONT STALLS AND INTERACTS WITH MOISTURE IN THE
WEST-SOUTHWESTERLY FLOW ALOFT AND POSSIBLY LOW LEVEL GULF INFLOW.
A FAIR DEGREE OF UNCERTAINTY STILL EXISTS FOR SPECIFICS, BUT THERE
IS A GRADUALLY INCREASING SIGNAL FOR THE BEST RAINFALL FOCUS TO BE
CENTERED OVER THE OHIO/TENNESSEE/MISSISSIPPI VALLEY REGION. THE
MOISTURE WITHIN THE WEST-SOUTHWESTERLY FLOW ALOFT ALSO PRODUCE
SOME RAINFALL OVER OR NEAR THE FAR SOUTHERN ROCKIES BUT WITH LOW
CONFIDENCE AT THIS TIME.
MUCH OF THE WEST SHOULD SEE BELOW NORMAL HIGH TEMPERATURES FROM
LATE THIS WEEK INTO THE START OF NEXT WEEK, WITH MOST LOCATIONS
5-15F BELOW NORMAL. THERE MAY BE A FEW ISOLATED DAILY RECORDS FOR
COLD MORNING LOWS/DAYTIME HIGHS NEAR THE WEST COAST LATE THIS
WEEK. THE NORTHERN HIGH PLAINS (ESPECIALLY MONTANA) MAY SEE A
COUPLE SEPARATE EPISODES OF COLDER READINGS, WITH HIGHS UP TO
20-30F BELOW NORMAL ON FRIDAY AND MONDAY. THE EASTERN U.S. WILL
SEE A BRIEF PERIOD OF MODERATELY BELOW NORMAL TEMPERATURES
THURSDAY INTO FRIDAY AND THEN A REBOUND TO ABOVE NORMAL READINGS
AHEAD OF THE NEXT FRONT. ABOVE NORMAL TEMPERATURES SHOULD BECOME
MORE PRONOUNCED ACROSS THE SOUTHERN TIER DURING THE WEEKEND AND
EARLY NEXT WEEK. MORNING LOWS MAY BECOME PARTICULARLY ANOMALOUS
WITH SOME PLUS 20-25F READINGS POSSIBLE OVER AND NEAR THE SOUTHERN
PLAINS BY SUNDAY-MONDAY.
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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