845
FXUS02 KWBC 280659
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
259 AM EDT FRI OCT 28 2022
VALID 12Z MON OCT 31 2022 - 12Z FRI NOV 04 2022
...PACIFIC NORTHWEST HEAVY RAIN LINGERING INTO MONDAY FOLLOWED BY
GREAT BASIN/ROCKIES HEAVY MOUNTAIN SNOW THREAT...
..OVERVIEW
EXPECT AN INCREASINGLY AMPLIFIED UPPER PATTERN OVER THE LOWER 48,
WITH A DEEP TROUGH REACHING THE WEST BY NEXT WEDNESDAY-FRIDAY
WHILE MEAN RIDGING BUILDS OVER THE EAST. THE UPPER TROUGH WILL
SPREAD A BROAD AREA OF RAIN AND MOUNTAIN SNOW, ALONG WITH WELL
BELOW NORMAL TEMPERATURES, ACROSS THE WEST. RAIN MAY DEVELOP OVER
THE PARTS OF THE PLAINS BY LATE WEEK. MEANWHILE A WEAK SHORTWAVE
CROSSING THE EAST EARLY IN THE WEEK WILL SUPPORT SOME RAINFALL
WHILE A TRAILING SOUTHERN STREAM FEATURE COULD PRODUCE AREAS OF
RAIN NEAR THE GULF COAST AND OVER PARTS OF THE EAST BUT WITH LOW
CONFIDENCE IN THE DETAILS. WITHIN A BROAD AREA OF MOSTLY ABOVE
NORMAL TEMPERATURES EAST OF THE ROCKIES, THE WARMEST ANOMALIES
SHOULD GENERALLY BE CENTERED OVER THE NORTHERN-CENTRAL PLAINS AND
UPPER MIDWEST.
..GUIDANCE AND PREDICTABILITY ASSESSMENT
THERE IS DECENT AGREEMENT AND CONTINUITY WITH THE AMPLIFYING
WESTERN UPPER TROUGH IN PRINCIPLE, BUT STILL SOME IMPORTANT
DIFFERENCES IN DETAILS. THE MOST AGREEABLE CLUSTER AMONG THE
12Z/18Z RUNS CONSISTED OF THE 18Z GFS/12Z ECMWF AND THEIR ENSEMBLE
MEANS. THESE SOLUTIONS WERE IN THE MIDDLE OF THE SPREAD (WITH
RECENT ECMWF RUNS TRENDING TOWARD THE SLOWER GFS) WHILE THE MEANS
HAVE AT LEAST HINTED AT SOME POTENTIAL FOR FLOW SEPARATION AS THE
OPERATIONAL RUNS DEPICTED A CLOSED LOW. GFS RUNS ARE STARTING TO
EXHIBIT SOME WAFFLING THOUGH, WITH THE 12Z RUN ON THE SLOW SIDE
AND THE NEW 00Z VERSION STRAYING FASTER BY LATE IN THE WEEK. THE
UKMET/CMC ARE MORE OPEN/PROGRESSIVE WITH THE UPPER TROUGH, DUE IN
PART TO BEING FASTER THAN OTHER GUIDANCE WITH UPSTREAM FLOW FROM
THE BERING SEA/GULF OF ALASKA.
FARTHER EAST, THE MODELS HAVE BEEN VARIED WITH THE DETAILS OF AN
AXIS OF SHORTWAVE ENERGY EXTENDING FROM THE MIDWEST INTO
NORTHWESTERN MEXICO AS OF EARLY MONDAY. TRENDS OF MOST
MODELS/ENSEMBLES OVER THE PAST COUPLE DAYS HAVE BEEN TOWARD
GREATER SEPARATION, WITH THE NORTHERN PART CROSSING THE EAST
MONDAY-TUESDAY WHILE THE SOUTHERN PART TRACKS ACROSS THE SOUTHERN
TIER AT A SLOWER PACE, ULTIMATELY FILTERING THROUGH THE BUILDING
EASTERN U.S. MEAN RIDGE AROUND WEDNESDAY-THURSDAY. THE NEW 00Z
UKMET HAS A QUESTIONABLY SLOW/DEEP DEPICTION OF THE NORTHERN
SHORTWAVE AND IS A SLOW EXTREME WITH THE SOUTHERN ONE. THE WEAK
NATURE OF THE ENERGY, AND POTENTIAL FOR THE SOUTHERN FEATURE TO
TRACK THROUGH A DEVELOPING MEAN RIDGE, WOULD TYPICALLY LEAD TO
MODERATELY LOW PREDICTABILITY.
FOR THE LATEST MANUAL FORECAST, GUIDANCE COMPARISONS LED TO USING
A 12Z/18Z MODEL COMPOSITE (WITH MORE EMPHASIS ON THE GFS/ECMWF
RELATIVE TO THE UKMET/CMC) EARLY IN THE PERIOD FOLLOWED BY A
TRANSITION TOWARD A MODEL/MEAN BLEND OF THE 18Z GFS/12Z ECMWF AND
THEIR ENSEMBLE MEANS. THE BLEND SPLIT THE MODELS/MEANS EVENLY BY
DAY 7 FRIDAY.
..WEATHER/HAZARD HIGHLIGHTS
THE UPPER TROUGH AMPLIFYING INTO THE WEST AND LEADING SURFACE
FRONTAL SYSTEM WILL BRING A PERIOD OF WETTER AND COLDER WEATHER TO
THE REGION. THE COMBINATION OF DYNAMICS AND MOISTURE SHOULD
SPREAD LOCALLY ENHANCED PRECIPITATION SOUTHEASTWARD WITH TIME,
FROM THE PACIFIC NORTHWEST/FAR NORTHERN ROCKIES INTO
CALIFORNIA/GREAT BASIN AND THEN THE SOUTHWEST U.S. AND CENTRAL
ROCKIES. PACIFIC NORTHWEST ACTIVITY ON MONDAY WILL BE A SOMEWHAT
TEMPERED CONTINUATION OF HEAVY WEEKEND PRECIPITATION OVER THE
COASTAL RANGES/OLYMPICS AND CASCADES. SOUTHEASTWARD PROGRESSION
OF THE MOISTURE SHIELD WILL BRING A THREAT FOR HEAVY MOUNTAIN SNOW
INTO NORTHERN-CENTRAL CALIFORNIA AND ACROSS THE NORTH-CENTRAL
GREAT BASIN/ROCKIES AS DEPICTED IN THE WPC WINTER WEATHER OUTLOOK
PROBABILITIES. TEMPERATURES ACROSS THE WEST WILL TREND MUCH COLDER
AS THE UPPER TROUGH ARRIVES AND DRIFTS OVER THE REGION. MUCH OF
THE SOUTHERN HALF TO TWO-THIRDS OF THE WEST WILL LIKELY SEE
DAYTIME HIGHS 10-20F BELOW NORMAL BY NEXT WEDNESDAY-FRIDAY, WHICH
SUCH ANOMALIES MAY BE MORE SCATTERED OVER NORTHERN AREAS.
RAINFALL MAY INCREASE IN COVERAGE AND INTENSITY OVER THE CENTRAL
U.S. LATE NEXT WEEK AS THE WESTERN UPPER TROUGH APPROACHES, WITH
EXACT TIMING SENSITIVE TO PROGRESSION OF THE TROUGH. THERE SHOULD
BE TWO PRIMARY AREAS OF RAIN AHEAD OF THIS SYSTEM. ONE WILL BE
WITH THE SHORTWAVE/SURFACE SYSTEM EMERGING FROM THE MIDWEST EARLY
IN THE WEEK, WITH MOSTLY LIGHT TO MODERATE TOTALS. THE TRAILING
FEATURE TO THE SOUTH MAY PRODUCE ONE OR MORE AREAS OF HEAVY
RAINFALL OVER THE GULF COAST REGION BUT LOW-PREDICTABILITY DETAILS
WILL BE IMPORTANT FOR DETERMINING HOW MUCH RAIN FALLS ALONG/INLAND
FROM THE GULF COAST VERSUS OFFSHORE. AREAS TO THE EAST OF THE
ROCKIES WILL BE ON THE WARM SIDE OF THE AMPLIFYING PATTERN FOR
MOST OF NEXT WEEK, WITH TEMPERATURES OF 10-20F ABOVE NORMAL MOST
COMMON OVER THE NORTHERN-CENTRAL PLAINS/UPPER MIDWEST. SOME OF
THESE WARM ANOMALIES WILL EXTEND FARTHER EAST AT TIMES, WHILE
COOLER AIR SHOULD START TO REACH THE PLAINS BY FRIDAY.
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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