596
FXUS02 KWBC 290700
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
259 AM EDT SAT OCT 29 2022
VALID 12Z TUE NOV 01 2022 - 12Z SAT NOV 05 2022
..GREAT BASIN/ROCKIES HEAVY MOUNTAIN SNOW THREAT NEXT WEEK
..OVERVIEW
THE DOMINANT FOCUS OF THE MEDIUM RANGE PERIOD WILL BE THE
AMPLIFYING LARGE SCALE UPPER PATTERN, WITH A DEEP TROUGH DIGGING
INTO AND MOVING THROUGH THE WEST WHILE A RIDGE BUILDS OVER THE
EAST. THE UPPER TROUGH WILL SPREAD A BROAD AREA OF RAIN/MOUNTAIN
SNOW AS WELL AS BELOW NORMAL TEMPERATURES ACROSS THE WEST.
PRECIPITATION SHOULD INCREASE IN COVERAGE AND INTENSITY OVER PARTS
OF THE CENTRAL U.S. LATE IN THE WEEK ONCE THE WESTERN SYSTEM
REACHES FAR ENOUGH EASTWARD. HOWEVER THERE IS A DECENT AMOUNT OF
UNCERTAINTY REGARDING THE SHAPE AND TIMING OF THE UPPER TROUGH BY
THAT TIME, SO FOR NOW THE CONFIDENCE IN SPECIFICS OF ASSOCIATED
PRECIPITATION IS FAIRLY LOW. AHEAD OF THIS SYSTEM, AN INITIAL
SOUTHERN PLAINS UPPER TROUGH MAY PRODUCE SOME ENHANCED RAINFALL
ALONG THE WESTERN HALF OF THE GULF COAST ON TUESDAY AND THEN COULD
BRING SOME MOISTURE INTO THE EAST AS THE FEATURE FILTERS THROUGH
THE BUILDING MEAN RIDGE. A LEADING WEAK SHORTWAVE WILL DEPART
FROM THE EAST AFTER TUESDAY. THE BROAD AREA OF MOSTLY ABOVE
NORMAL TEMPERATURES EAST OF THE ROCKIES THROUGH MIDWEEK WILL SEE A
WEST-TO-EAST EROSION OVER THE CENTRAL U.S. BY LATE IN THE WEEK.
..GUIDANCE AND PREDICTABILITY ASSESSMENT
THE PAST DAY OF GUIDANCE HAS OFFERED MORE SPREAD THAN WAS
PREVIOUSLY THE CASE FOR THE ULTIMATE EVOLUTION OF THE WESTERN
UPPER TROUGH AFTER MIDWEEK OR SO, WITH BOTH THE GFS AND ECMWF
JUMPING BETWEEN SLOWER CLOSED LOW AND FASTER/PHASED TROUGH
SOLUTIONS. THE MAJORITY OF GFS RUNS HAVE FAVORED THE SLOW CLOSED
LOW, WITH THE GFS FROM 24 HOURS AGO (28/00Z) BEING THE PRIMARY
EXCEPTION. THAT RUN ENDED UP BEING SIMILAR TO WHERE THE 12Z ECMWF
TRENDED. THERE WERE ENOUGH PROGRESSIVE ECMWF ENSEMBLE MEMBERS
THAT THE RESULTING MEAN TRENDED SOMEWHAT FASTER/BROADER WITH THE
TROUGH VERSUS THE PRIOR TWO RUNS, BUT AT LEAST THE SOUTHEASTWARD
AMPLITUDE OF THE OVERALL TROUGH WAS LESS EXTREME THAN IN THE
OPERATIONAL RUN. GEFS MEANS HAVE TENDED TO BE CLOSE TO THE GFS
TIMING FROM LATEST RUNS (BUT WEAKER/NORTHWARD WITH THE IMPLIED
UPPER LOW). MEANWHILE THE CMC HAS TRENDED TO THE CLOSED LOW
SCENARIO AFTER BEING MORE PROGRESSIVE EARLIER AND THE NEW 00Z
UKMET SHOWS BETTER TIMING AGREEMENT AFTER THE 12Z RUN WAS
QUESTIONABLY SLOW.
SOME OF THESE DIFFERENCES RELATE TO THE SHAPE OF FLOW ACROSS THE
GULF OF ALASKA AND THEN SOUTHWESTERN CANADA/NORTHWEST U.S. THE
GFS AND SOME GEFS MEMBERS ARE THE MOST PRONOUNCED WITH HOW MUCH
RIDGING EXTENDS INTO THE NORTHEASTERN PACIFIC AND THEN INTO NORTH
AMERICA AFTER EARLY WEDNESDAY. THE 12Z ECMWF AND SOME OF ITS
ENSEMBLE MEMBERS ARE ON THE FLAT EXTREME. UNTIL THERE IS
COMPELLING EVIDENCE, FAVOR AN INTERMEDIATE SOLUTION FOR THIS
ASPECT OF THE FORECAST. THE NEW 00Z CMC REFLECTS SUCH AN IDEA.
AMONG THE 12Z/18Z GUIDANCE AVAILABLE FOR THE LATEST FORECAST
UPDATE, PREFERENCE FOR THE 18Z GFS/12Z ECMWF/12Z CMC CLUSTER EARLY
IN THE PERIOD TRANSITIONED TO A BLEND CONSISTING OF THE 18Z
GFS/12Z CMC FOR OPERATIONAL INPUT AND SOMEWHAT MORE 18Z GEFS
RELATIVE TO THE 12Z ECMWF MEAN. THE RESULT HELPED TO KEEP THE
FORECAST FAIRLY CLOSE TO CONTINUITY, WITH JUST A MODEST FASTER
NUDGE. THE NEW 00Z GFS/GEFS MEAN/CMC ALIGN WITH THIS TIMING
FAIRLY WELL. THE NEW 00Z ECMWF HAS REVERTED BACK TO THE SLOW
CLOSED LOW SCENARIO, GREATLY IMPROVING CLUSTERING FOR THE TIME
BEING.
THIS PREFERRED BLEND WORKED WELL FOR LEADING FEATURES AS WELL,
WITH THE 12Z UKMET STILL OUT OF SYNC FOR THE INITIAL SOUTHERN
PLAINS AND EASTERN U.S. SHORTWAVES. AMONG THE NON-UKMET
SOLUTIONS, THE BLEND HELPED TO RESOLVE ONGOING DETAIL DIFFERENCES
FOR THE SHORTWAVE EMERGING FROM THE PLAINS, WITH AN EXPECTED PATH
THROUGH THE BUILDING MEAN RIDGE LEADING TO AN EXTRA DEGREE OF
DIFFICULTY.
..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.
THE BEST FOCUS FOR RAIN/MOUNTAIN SNOW SHOULD BE FROM THE PACIFIC
NORTHWEST/CALIFORNIA INTO THE NORTHERN ROCKIES ON TUESDAY, THEN
REACHING THE GREAT BASIN/SOUTHWEST AND CENTRAL ROCKIES MID-LATE
WEEK. AN EPISODE OF HEAVY MOUNTAIN SNOW WILL BE POSSIBLE OVER
NORTHERN-CENTRAL CALIFORNIA AND ACROSS PARTS OF THE GREAT BASIN
AND NORTHERN-CENTRAL ROCKIES AS DEPICTED IN THE WPC WINTER WEATHER
OUTLOOK PROBABILITIES. UNCERTAINTY OVER THE PRECISE UPPER TROUGH
DETAILS TEMPERS CONFIDENCE IN SPECIFICS OF PRECIPITATION AMOUNTS
AND DURATION THOUGH. THE DEPTH OF THE UPPER TROUGH/LOW IS ALSO A
QUESTION MARK, AFFECTING SNOW LEVELS AND HOW FAR SOUTH THE HIGHER
ELEVATION SNOW MAY EXTEND. STRONG PACIFIC FLOW MAY DROP INTO THE
PACIFIC NORTHWEST TOWARD THE END OF THE WEEK/NEXT WEEKEND,
INCREASING PRECIPITATION OVER THE REGION. AT THIS TIME THE
SOUTHWARD EXTENT OF THIS MOISTURE IS QUITE UNCERTAIN THOUGH.
TEMPERATURES ACROSS THE WEST WILL TREND MUCH COLDER AS THE UPPER
TROUGH ARRIVES AND DRIFTS OVER THE REGION. MUCH OF THE SOUTHERN
TWO-THIRDS OF THE WEST WILL LIKELY SEE DAYTIME HIGHS 10-20F OR SO
BELOW NORMAL BY NEXT WEDNESDAY-FRIDAY, WITH SOME NEARLY AS EXTREME
ANOMALIES EXTENDING INTO THE NORTHERN ROCKIES. EXPECT SOME
MODERATION BY SATURDAY BUT WITH MANY AREAS STILL BELOW NORMAL.
RAINFALL SHOULD INCREASE IN COVERAGE AND INTENSITY OVER THE
CENTRAL U.S. LATE NEXT WEEK AS THE WESTERN UPPER TROUGH
APPROACHES, WITH EXACT TIMING AND LOCATION OF HIGHEST TOTALS BEING
SENSITIVE TO THE PROGRESSION AND SHAPE OF THE TROUGH. AHEAD OF
THIS SYSTEM, SOUTHERN PLAINS SHORTWAVE ENERGY MAY PRODUCE SOME
HEAVY RAINFALL OVER OR NEAR THE GULF COAST REGION AROUND TUESDAY.
THERE IS STILL MEANINGFUL UNCERTAINTY WITH HOW MUCH RAIN FALLS
ALONG/INLAND FROM THE GULF COAST VERSUS OFFSHORE, AS GUIDANCE HAS
BEEN OSCILLATING IN THAT REGARD. THIS FEATURE COULD PRODUCE SOME
AREAS OF RAINFALL OVER PARTS OF THE EAST BUT WITH LOW CONFIDENCE
IN THE DETAILS. LOCATIONS TO THE EAST OF THE ROCKIES WILL BE ON
THE WARM SIDE OF THE AMPLIFYING PATTERN THROUGH AT LEAST THURSDAY,
WITH TEMPERATURES OF 10-20F ABOVE NORMAL MOST COMMON OVER THE
NORTHERN-CENTRAL PLAINS/UPPER MIDWEST. SOME OF THESE WARM
ANOMALIES WILL EXTEND INTO THE GREAT LAKES/OHIO VALLEY/NORTHEAST.
CENTRAL U.S. TEMPERATURES SHOULD TREND COOLER BY FRIDAY-SATURDAY
WHILE THE EAST REMAINS WARM.
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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