008
FXUS02 KWBC 070708
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
208 AM EST WED DEC 07 2022
VALID 12Z SAT DEC 10 2022 - 12Z WED DEC 14 2022
...HEAVY COASTAL RAINS AND MOUNTAIN/INLAND HEAVY SNOW THREATS
ACROSS THE WEST/ROCKIES...
...HEAVY RAINFALL THREATS OVER THE MISSISSIPPI VALLEY/VICINITY
ALONG WITH HEAVY SNOW/ICE/FREZZING RAINS THREATS OVER THE
NORTH-CENTRAL U.S....
..OVERVIEW
A LEADING WAVY FRONT ACROSS THE SOUTHERN TIER MAY PROMOTE SOME
LOCALLY HEAVY RAINFALL LATE THIS WEEK INTO THE WEEKEND. GUIDANCE
ALSO AGREES UPSTREAM TO SHOW A MEAN TROUGH AXIS WORKING INLAND
FROM THE WEST COAST THROUGH THE WEEKEND INTO EARLY NEXT WEEK, WITH
THE DEEPEST REINFORCING ENERGY ARRIVING SUNDAY INTO MONDAY LEADING
TO CLOSED LOW/TROUGH FORMATION, WITH THE DYNAMIC SYSTEM LIFTING
OVER THE PLAINS TUESDAY/WEDNESDAY. THIS PATTERN WOULD SUPPORT A
PERIOD OF WIDESPREAD AND SIGNIFICANT TERRAIN-ENHANCED RAIN AND
MOUNTAIN SNOW OVER THE WEST FROM LATE THIS WEEK THROUGH THE
WEEKEND. THIS IS INCREASINGLY EXPECTED TO BE FOLLOWED BY
EXPANDING/INTENSIFYING RAINFALL OVER THE MISSISSIPPI
VALLEY/VICINITY EASTWARD ACROSS THE EAST-CENTRAL U.S. ALONG WITH
POSSIBLY SIGNIFICANT WRAPBACK SNOW OVER THE NORTH-CENTRAL U.S.
EARLY NEXT WEEK IN ASSOCIATION WITH DEEPENING LOW PRESSURE AND
CORRESPONDING FRONTS. EXPECT MOSTLY BELOW NORMAL HIGH TEMPERATURES
OVER THE WEST AND NEAR TO ABOVE NORMAL PRE-FRONTAL READINGS OVER
MUCH OF THE EASTERN HALF OF THE COUNTRY.
..GUIDANCE/PREDICTABILITY ASSESSMENT
IT REMAINS THE CASE THAT THE MOST SIGNIFICANT LARGE-SCALE ASPECT
OF THE FORECAST INVOLVES RECENT PRONOUNCED TRENDS IN GUIDANCE OVER
THE PACIFIC INTO BERING SEA/ALASKA REGION LEADING TO A SIMILARLY
DRAMATIC CHANGE FOR UPPER DYNAMICS REACHING THE LOWER 48 MID-LATE
PERIOD. THIS RECENT ADJUSTMENT IN THE MODELS HAS LED TO MORE
PRONOUNCED DIGGING OF TROUGH ENERGY INTO THE WEST COAST BY SUNDAY
AND THEN A SLOWER AND MORE AMPLIFIED DEPICTION OF THE TROUGH AS IT
MOVES EASTWARD. THE ENSEMBLE MEANS ALSO CONTINUE TO SHOW THIS
TREND. SUBSEQUENT EJECTION CONTINUES TO SHOW A GROWING SIGNAL IN
SUPPORT OF A POTENTIALLY SIGNIFICANT CENTRAL U.S. LOW
PRESSURE/FRONTAL SYSTEM, ALBEIT SLOWER SYSTEM/QPF DEVELOPMENT AND
PROGRESSION THAN CONTINUITY.
THE WPC MEDIUM RANGE PRODUCT SUITE WAS PRIMARILY DERIVED FROM A
BLEND OF BEST CLUSTERED GUIDANCE FROM THE 18 UTC GFS/GEFS AND 12
UTC ECMWF/ECMWF ENSEMBLE MEAN ALONG WITH WPC CONTINUITY AND THE 01
UTC NATIONAL BLEND OF MODELS, APPLYING THE BULK OF BLEND WEIGHTS
TO THE MODELS INTO THE WEEKEND BEFORE TRANSITIONING TO MOSTLY
THESE ENSEMBLE MEANS FOR EARLY-MID NEXT WEEK.
..WEATHER/HAZARD HIGHLIGHTS
LEAD SYSTEM EJECTION OUT FROM THE WEST MAY SUPPORT MODERATE TO
HEAVY RAINFALL WITH SOME POTENTIAL FOR RUNOFF ISSUES CENTERED OVER
THE SOUTHERN PLAINS AND MID-LOWER MISSISSIPPI/TENNESSEE VALLEYS
AND INTO THE SOUTHEAST THIS WEEKEND AS THE UPPER ENERGY INTERACTS
WITH GULF MOISTURE INFLOW INTO A WAVY SOUTHERN TIER FRONTAL
SYSTEM. MEANWHILE EXPECT RENEWED POTENTIAL FOR HEAVY PRECIPITATION
OVER THE WEST THROUGH THE WEEKEND, INCLUDING HEAVY
TERRAIN/MOUNTAIN ENHANCED SNOWS. LATEST CONSENSUS SUGGESTS HIGHEST
PRECIPITATION TOTALS SHOULD BE ALONG THE CENTRAL WEST COAST INTO
THE SIERRA NEVADA. MOISTURE WILL SPREAD INLAND AS WELL AND BRING A
PERIOD OF ENHANCED RAIN/MOUNTAIN SNOW TO THE GREAT BASIN/ROCKIES.
WITH RECENT GUIDANCE TRENDS SUPPORTING A SLOWER UPPER LOW REACHING
THE PLAINS BY NEXT TUESDAY AND ASSOCIATED DEEPENING LOW
PRESSURE/FRONTAL SYSTEM, CONFIDENCE IS GRADUALLY RISING THAT GULF
INFLOW MAY HELP TO ENHANCE THE NORTHWARD FLOW OF GULF MOISTURE TO
PRODUCE SIGNIFICANT RAINFALL OVER THE MISSISSIPPI VALLEY AND
VICINITY. SOME STRONG TO SEVERE CONVECTION IS ALSO POSSIBLE, WITH
THE STORM PREDICTION CENTER ALREADY MONITORING THIS POTENTIAL.
MOISTURE WRAPPING BACK INTO THE NORTHERN TIER MAY PRODUCE
SIGNIFICANT SNOW/ICE/FREEZING RAIN. PROBABILITIES FOR AT LEAST A
QUARTER-INCH OF LIQUID EQUIVALENT IN THE FORM OF SNOW OVER THE
NORTHERN PLAINS CONTINUE TO INCREASE.
THE WEST SHOULD SEE BELOW NORMAL HIGHS THROUGH THE PERIOD, WITH
THE MOST WIDESPREAD READINGS OF AT LEAST 10-15F BELOW NORMAL AS
THE DEEP UPPER TROUGH CROSSES THE REGION EARLY NEXT WEEK. SOME OF
THIS COLDER AIR SHOULD SPILL INTO THE HIGH PLAINS BY NEXT TUESDAY
BEHIND THE EXPECTED PLAINS STORM. ON THE OTHER HAND,
SOUTHERN/EASTERN AREAS WILL BE NEAR TO ABOVE NORMAL FOR
TEMPERATURES. ANOMALIES SHOULD BE GREATEST FOR MORNING LOWS, WITH
SOME PLUS 15-25F ANOMALIES ACROSS THE SOUTHERN TIER AND STRAYING
FARTHER NORTHWARD OVER SOME AREAS THIS FRIDAY AND AGAIN BY NEXT
TUESDAY/WEDNESDAY.
SCHICHTEL
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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