791
FXUS02 KWBC 181849
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
249 PM 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 AMPLIFIES 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 NEXT WEEK. 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
THE LATEST MODEL GUIDANCE REMAINS 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. BY EARLY NEXT WEEK
HOWEVER, 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 BEFORE
SLOWLY DRIFTING INTO THE SOUTHWEST. THE CMC, GFS, AND UKMET ON THE
OTHER HAND, INDICATE SOME DEGREE OF PHASING BETWEEN THE TWO
STREAMS EVENTUALLY SHOWING ONE TROUGH THAT STEADILY PROGRESSES
EAST. THE CMC AND UKMET, AT THIS POINT, MAY BE TOO QUICK TO PHASE
THESE SYSTEMS AND DEVELOPES A CLOSED AND VERY DEEP UPPER LOW OVER
THE SOUTHWEST. THE ENSEMBLE MEMBERS REMAIN QUITE VARIABLE AND LEAD
TO LOW CONFIDENCE IN ANY PARTICULAR SOLUTION, BUT THE GFS DOES
SEEM TO BE THE BETTER COMPARISON FOR THE ENSEMBLE MEANS. MODELS
HAVE ALSO COME INTO BETTER AGREEMENT WITH THE NEXT SHORTWAVE INTO
THE WEST AROUND MONDAY-TUESDAY, THOUGH WITH SOME DIFFERENCES IN
THE DETAILS WHICH SHOULD SHAKE OUT AS THE FEATURE MENTIONED ABOVE
COMES INTO BETTER FOCUS. THE WPC FORECAST TODAY LEANED MORE ON THE
GFS OVER THE ECMWF, ALONG WITH THE ENSEMBLE MEANS, ESPECIALLY
LATER IN THE PERIOD. THE CMC/UKMET WERE NOT INCLUDED AFTER DAY 4
DUE TO THE MORE EXTREME/DEEPER SOLUTION (NOT THAT ITS NOT A VIABLE
SOLUTION, JUST NOT PREFERRED TO GO THAT DEEP YET). THIS MAINTAINED
GOOD CONSISTENCY WITH THE PREVIOUS WPC FORECAST.
..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 TO POSSIBLY HEAVY RAINFALL ARE LIKELY 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.
SANTORELLI/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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