916
FXUS02 KWBC 180701
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
300 AM EDT TUE OCT 18 2022
VALID 12Z FRI OCT 21 2022 - 12Z TUE OCT 25 2022
..OVERVIEW
A SIGNIFICANT PATTERN CHANGE IS IN STORE FOR THE MEDIUM RANGE
PERIOD AS UPPER TROUGHING LIFTS OUT OF THE EAST LATE WEEK WHILE AN
UPPER TROUGH DEVELOPS AND STRENGTHENS OVER THE WEST, PROGRESSING
TOWARD THE CENTRAL U.S. EARLY NEXT WEEK. THIS DEEP TROUGH AND A
COUPLE OF COLD FRONTS WILL LEAD TO AREAS OF LOWER ELEVATION
RAIN/HIGHER ELEVATION SNOW AS WELL AS COOLER TEMPERATURES OVER THE
WEST, AND WILL EVENTUALLY SPREAD INCREASING RAIN CHANCES TO THE
PLAINS/MISSISSIPPI VALLEY. AHEAD OF THE TROUGH, WARMER THAN
AVERAGE TEMPERATURES ARE FORECAST TO SHIFT FROM THE CENTRAL U.S.
INTO THE NORTHEAST, WITH MAINLY DRY CONDITIONS ASIDE FROM SOME
POSSIBLE RAIN ALONG THE EAST COAST DEPENDENT ON THE POSITIONING OF
A WAVY OFFSHORE FRONT AND UPPER-LEVEL ENERGY.
..MODEL AND PREDICTABILITY ASSESSMENT
MODEL GUIDANCE IS QUITE AGREEABLE WITH THE OVERALL PATTERN CHANGE
TRANSITIONING TO A WESTERN TROUGH/EASTERN RIDGE FOR THE MEDIUM
RANGE PERIOD. THE BULK OF GUIDANCE ALL BRINGS NOTABLE MID-UPPER
ENERGY INTO THE NORTHWEST THAT DEEPENS A TROUGH IN THE WEST LATE
WEEK INTO THE WEEKEND, WHILE A SOUTHERN STREAM UPPER LOW MEANDERS
OFFSHORE SOUTHERN CALIFORNIA/MEXICO. BUT FOR EARLY NEXT WEEK,
MODELS ARE CONSIDERABLY MORE VARIABLE REGARDING THE POTENTIAL
PHASING OF THESE NORTHERN/SOUTHERN STREAM FEATURES. THE ECMWF HAS
SHOWN NOT MUCH PHASING AT ALL, LEADING TO A FASTER NORTHERN STREAM
TROUGH AND A SOUTHERN STREAM LOW LINGERING WEST, WHILE THE MORE
PHASED 18Z GFS AND 12Z CMC SOLUTIONS INDICATE ONE SLOWER TROUGH.
ENSEMBLE MEMBERS REMAIN QUITE VARIABLE AND LEAD TO LOW CONFIDENCE
IN CHOOSING EITHER SOLUTION. THEN, MODELS END UP OUT OF PHASE WITH
THE UPSTREAM FLOW COMING INTO THE NORTHWEST BY AROUND TUESDAY,
IMPACTING POTENTIAL FOR ADDITIONAL PRECIPITATION THERE. GFS RUNS
HAVE BEEN PARTICULARLY RIDGY WHILE THE ECMWF HAS SHOWN TROUGHING
AS ADDITIONAL ENERGY ENTERS. THE 00Z ECMWF AND CMC HAVE TRENDED A
BIT MORE RIDGY THOUGH, AND THIS IS AN ASPECT OF THE FORECAST THAT
REMAINS QUITE UNCERTAIN.
IN THE EAST, THERE REMAIN LINGERING ISSUES WITH MODELS HANDLING
ENERGY SPILLING INTO THE SOUTHERN STREAM WHILE THE BULK OF THE
TROUGH IN THE NORTHERN STREAM RETREATS CONSIDERABLY FROM ITS
POSITION IN THE SHORT RANGE. RECENT ECMWF RUNS HAVE NOT BEEN AS
AGGRESSIVE WITH DEVELOPING A CLOSED LOW IN THE SOUTHEAST COMPARED
TO PREVIOUS RUNS FROM STRONGER ENERGY REMAINING SOUTH, BUT MOST
GUIDANCE DOES SHOW SOME ENERGY IN THE SOUTHEAST OR NEARBY, FOR
SOME MODEL CONVERGENCE. BUT THIS RELATIVELY SMALL SCALE FEATURE
REMAINS ON THE LOWER PREDICTABILITY SIDE AND COULD AFFECT SURFACE
FRONTAL POSITION AND POTENTIAL FOR A SURFACE LOW TO SPIN UP (AS IN
ECMWF RUNS AND THE 18Z GFS), AS WELL AS RAIN CHANCES FOR COASTAL
PORTIONS OF THE EAST, SO ADDITIONAL REFINEMENTS TO THE FORECAST
ARE LIKELY.
THUS THE WPC FORECAST WAS BASED ON A BLEND OF THE DETERMINISTIC
GUIDANCE, PARTICULARLY THE 12/18Z GFS AND 12Z ECMWF, FOR THE EARLY
PART OF THE PERIOD, BUT INCORPORATED COMPONENTS OF THE GEFS AND EC
ENSEMBLE MEANS BY DAY 5 AND QUICKLY INCREASED THEM TO ABOUT HALF
BY DAYS 6/7 GIVEN THE DIFFERENCES IN OPERATIONAL MODELS DESCRIBED
ABOVE. THIS APPROACH MAINTAINED GOOD CONTINUITY WITH THE PREVIOUS
FORECAST ASIDE FROM TYPICAL NUDGES REFLECTING LATEST TRENDS.
..SENSIBLE WEATHER AND POTENTIAL HAZARDS
PRECIPITATION IS FORECAST TO SPREAD INTO THE NORTHWEST LATE WEEK
AS THE UPPER TROUGH ARRIVES AND AMPLIFIES AND THE FIRST SURFACE
COLD FRONT MOVES THROUGH, SPREADING A WEAK-MODERATE ATMOSPHERIC
RIVER QUICKLY ACROSS THE WEST IN ONE OF THE FIRST MAJOR COOL
SEASON-TYPE PRECIPITATION EVENTS. THE BEST FOCUS WILL BE OVER
FAVORED WINDWARD TERRAIN OVER THE PACIFIC NORTHWEST ON FRIDAY AND
THEN EXTENDING SOUTHEASTWARD INTO THE NORTHERN/CENTRAL ROCKIES AND
WASATCH OVER THE WEEKEND, WITH HIGHER ELEVATION SNOW AND LOWER
ELEVATION RAIN. CONFIDENCE IN A MEANINGFUL PRECIPITATION EVENT
REMAINS FAIRLY GOOD, BUT EXACT AMOUNTS OF RAIN/SNOW AND TIMING
WILL STILL NEED TO BE REFINED WITH TIME. PRECIPITATION COULD
CONTINUE/REFORM EARLY NEXT WEEK IN THE NORTHWEST BUT WITH EVEN
MORE UNCERTAINTY. PRECIPITATION MAY ALSO BE POSSIBLE ACROSS THE
SOUTHWEST FRIDAY AND ESPECIALLY SATURDAY DEPENDING ON THE TIMING
AND TRACK OF THE SOUTHERN STREAM LOW AND ITS EVENTUAL POSSIBLE
PHASING. BY EARLY NEXT WEEK, RAIN CHANCES SHOULD GENERALLY
INCREASE ACROSS THE PLAINS AND INTO THE MISSISSIPPI VALLEY AHEAD
OF THE UPPER TROUGH AND A DEVELOPING LOW PRESSURE SYSTEM. AREAS OF
ENHANCED RAINFALL ARE POSSIBLE BUT THE SPECIFICS ARE NOT YET CLEAR
AT THIS TIME. MEANWHILE, SOME RAIN MAY BE POSSIBLE ALONG OR NEAR
THE EAST COAST THIS WEEKEND INTO MONDAY ASSOCIATED WITH A FRONTAL
BOUNDARY AND POSSIBLE LOW PRESSURE SYSTEM, BUT WITH LOW CONFIDENCE
ON HOW MUCH RAIN COULD FALL ONSHORE VERSUS REMAINING OFFSHORE.
TEMPERATURES ARE LIKELY TO BE WARMER THAN AVERAGE ACROSS THE
CENTRAL U.S. LATE WEEK INTO THE WEEKEND AHEAD OF THE DEVELOPING
WESTERN UPPER TROUGH. HIGHS AND LOWS OF 10-20F ABOVE NORMAL WILL
BE WIDESPREAD ACROSS THE PLAINS TO UPPER MIDWEST. AS THE UPPER
TROUGH AND COLD FRONT APPROACH, TEMPERATURES ARE FORECAST TO
MODERATE IN THE CENTRAL U.S. AS THEY PUSH THE RELATIVELY WARM
TEMPERATURES INTO THE GREAT LAKES REGION AND NORTHEAST BY
MONDAY-TUESDAY. MEANWHILE, TEMPERATURES IN THE WEST WILL COOL
CONSIDERABLY FROM SLIGHTLY ABOVE NORMAL ON FRIDAY TO BELOW NORMAL
FOR THE WEEKEND AND BEYOND. LOWS AROUND 5-15F BELOW AVERAGE AND
HIGHS 10-20F BELOW AVERAGE AT TIMES ARE EXPECTED TO BE COMMON
INITIALLY FOR THE WEST COAST AND SPREADING ACROSS THE
INTERMOUNTAIN WEST AND ROCKIES AS THE UPPER TROUGH SLOWLY SHIFTS.
TATE
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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