954
FXUS02 KWBC 282049
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
348 PM 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 SHIFTS TO THE WEST WITH A COUPLE OF
INDIVIDUAL SHORTWAVES WITHIN THE WEST COAST MEAN TROUGH. WHILE
NOTABLE DIFFERENCES STILL EXIST, THERE HAS BEEN SOME IMPROVEMENT
OVER THE PAST COUPLE OF MODEL CYCLES. THE FIRST SHORTWAVE SHOULD
BE JUST OFF THE WEST COAST 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 ALL
THE WAY THROUGH TO THE EAST. THE 06Z (AND 12Z) RUNS OF THE GFS
CONTINUE TO BE TOO FAST WITH THE SHORTWAVE WITH A BETTER CONSENSUS
FOR POSTIONING FROM THE ECMWF, CMC, AND UKMET WHICH FORMED THE
BASIS OF THE WPC FORECAST THE FIRST HALF OF THE PERIOD. THE SECOND
SYSTEM WILL LIKELY APPROACH THE NORTHWEST COAST (POSSIBLY AS A
CLOSED LOW) BY SATURDAY. THERE ARE SOME NOTABLE DIFFERENCES STILL
ON TIMING, POSITIONING, AND DEPTH OF THIS SYSTEM WITH THE GFS
STILL WANTING TO PULL THE LOW FARTHER SOUTH DOWN THE CA COAST
BEFORE IT BEGINS TO MOVE INLAND EARLY NEXT WEEK. THE CMC ALSO
SEEMS TOO FAST, SO IT WAS NOT INCLUDED IN THE BLEND PAST DAY 5.
THE WPC FORECAST FAVORED THE ENSEMBLE MEANS WITH THE ECMWF DAYS 6
AND 7.
..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 HEAVIER 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.
GUSTY WINDS MAY ALSO ACCOMPANY THIS SYSTEM AS IT EXITS THE ROCKIES
INTO THE NORTHERN PLAINS LATE THIS WEEK.
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 RAIN OR SNOW 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 HAS BEEN AN 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 COULD 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.
SANTORELLI/RAUSCH
HAZARDS:
- HEAVY RAIN ACROSS PORTIONS OF CALIFORNIA, THU, DEC 1.
- HEAVY RAIN ACROSS PORTIONS OF CALIFORNIA, FRI, DEC 2.
- HEAVY RAIN ACROSS PORTIONS OF THE MID-SOUTH AND THE OHIO AND
TENNESSEE VALLEYS, SUN-MON, DEC 4-DEC 5.
- HEAVY SNOW ACROSS PORTIONS OF CALIFORNIA, THU-SUN, DEC 1-DEC 4.
- HEAVY SNOW ACROSS PORTIONS OF THE NORTHERN ROCKIES, THU, DEC 1.
- FLOODING OCCURRING OR IMMINENT ACROSS PORTIONS OF THE SOUTHEAST.
- HIGH WINDS ACROSS PORTIONS OF THE CENTRAL AND SOUTHERN ROCKIES
AND ADJACENT HIGH PLAINS, THU-FRI, DEC 1-DEC 2.
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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