731
FXUS02 KWBC 050716
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
216 AM EST SUN NOV 05 2023
VALID 12Z WED NOV 08 2023 - 12Z SUN NOV 12 2023
..OVERVIEW
THE UPPER FLOW PATTERN ACROSS THE CONTIGUOUS U.S. DURING THE
LATTER PART OF THIS WEEK INTO NEXT WEEKEND LOOKS TO BE FAIRLY
ZONAL AND PROGRESSIVE FROM THE MULTI-DAY MEAN PERSPECTIVE, BUT
MULTIPLE EMBEDDED SHORTWAVES WILL BE IMPACTFUL IN SPINNING UP LOW
PRESSURE/FRONTAL SYSTEMS. AS THE LEADING SYSTEM IN THE SERIES
PULLS AWAY FROM THE NORTHEAST ON WEDNESDAY, THE NEXT SYSTEM OF
CONCERN IS A POSITIVELY TILTED SHORTWAVE EMERGING FROM THE WEST,
EVENTUALLY REINFORCED BY SOME CANADIAN FLOW, THAT SHOULD PROGRESS
TOWARD THE EASTERN U.S. WITH ASSOCIATED LOW PRESSURE PUSHING A
TRAILING COLD FRONT SOUTHEASTWARD ACROSS MUCH OF THE COUNTRY AS
THE WEEK PROGRESSES. THIS FRONT WILL GRADUALLY SUPPRESS WHAT
STARTS AS A WIDESPREAD AREA OF ABOVE AVERAGE TEMPERATURES.
MEANWHILE, THE WEST LOOKS TO HAVE A LIKELY BREAK IN PRECIPITATION
AROUND MIDWEEK, ASIDE FROM SNOW IN THE CENTRAL ROCKIES. BUT AN
APPROACHING PACIFIC SHORTWAVE AND FRONTAL SYSTEM SHOULD INCREASE
RAIN/SNOW CHANCES LATE NEXT WEEK WITH THE AMPLIFYING UPPER TROUGH
MOVING INLAND BY THE WEEKEND.
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
THE 12/18Z MODEL GUIDANCE SHOWED SOME NOTABLE DIFFERENCES IN THE
DETAILS WITH THE SHORTWAVE OVER THE WEST-CENTRAL U.S. EVEN AS THE
MEDIUM RANGE PERIOD BEGINS WEDNESDAY. THE 18Z GFS IN PARTICULAR
APPEARS TO BE AN OUTLIER IN ITS HANDLING OF THE ENERGY, AND AS THE
SHORTWAVE PROGRESSES EAST, THE SURFACE LOW ASSOCIATED WITH IT DOES
NOT ALIGN WELL WITH OTHER GUIDANCE THAT SHOWS MORE OF A TREND
TOWARD SPLIT LOW PRESSURE (ONE LOW NORTH OF LAKE SUPERIOR THAT IS
TRENDING STRONGER, AND ONE ATOP LAKE HURON OR SO). THE 12Z GFS
SEEMED MORE REASONABLE, SO UTILIZED IT IN COMBINATION WITH THE 12Z
ECMWF/CMC/UKMET FOR WEDNESDAY-THURSDAY RATHER THAN THE 18Z RUN.
SOUTHERN AND NORTHERN STREAM ENERGY LOOK TO COMBINE AROUND FRIDAY
FOR GREAT LAKES TROUGHING, BUT THE 12Z GFS AND NOW THE 00Z GFS DO
SEEM TO BE ON THE SHALLOW SIDE WITH THAT TROUGHING COMPARED TO
OTHER GUIDANCE AND THE ENSEMBLE MEANS. MEANWHILE THE 12Z AND NEW
00Z CMC WERE ON THE DEEP SIDE, WITH SOMEWHERE AROUND THE 12Z ECMWF
AND ITS ENSEMBLE MEAN A GOOD COMPROMISE FOR THAT FEATURE.
UPSTREAM, EASTERN PACIFIC ENERGY HAS BEEN RATHER TROUBLESOME FOR
RESOLVING DETAILS BY THURSDAY-FRIDAY AS SOME ENERGY/TROUGHING
ENTERS THE WEST. MODELS OVERALL OVER THE PAST DAY HAVE TRENDED
MORE TOWARD A PHASED TROUGH COMING INTO THE WEST ON THE FASTER
SIDE. BUT THE 12Z ECMWF HAD A CLOSED LOW THAT PUSHES INTO THE
NORTHWEST MORE SLOWLY, WITH A RIDGE TO THE EAST FRIDAY-SATURDAY
THAT ENDED UP OUT OF PHASE WITH OTHER GUIDANCE, AS THE OTHER
MODELS HAD A FASTER PROGRESSION OF THE TROUGH BASICALLY WHERE THE
ECMWF RIDGE WAS. THE EC ENSEMBLE MEAN REFLECTED A SLOWER SOLUTION
OF THE TROUGH/RIDGE AS WELL, WHILE THE 18Z GEFS MEAN WAS RATHER
FAST AND THE 12Z GEFS MEAN IN BETWEEN. ENSEMBLE MEMBERS SHOW A
LARGE AMOUNT OF SPREAD. THE OUT OF PHASE SOLUTIONS MADE IT TOUGH
TO BLEND MODELS, AND THIS PROBLEM MAY PERSIST INTO THE INCOMING
00Z MODEL SUITE. CONFIDENCE IS LOW IN THE TIMING OF THESE FEATURES
AND THUS THE PATTERN IN GENERAL.
THE WPC FORECAST WAS BASED ON A BLEND OF THE 12Z DETERMINISTIC
MODELS EARLY ON, BUT QUICKLY TRANSITIONED TO FAVOR THE GEFS AND EC
ENSEMBLE MEANS AS THE PERIOD PROGRESSED TO OVER HALF BY DAY 6 AND
WELL OVER HALF ON DAY 7, CONSIDERING THE INCREASING SPREAD. EXPECT
THE FORECAST TO CHANGE WITH DECREASING LEAD TIME, PERHAPS EVEN
MORE THAN USUAL GIVEN THE HIGH UNCERTAINTY AND LOW CONFIDENCE.
..WEATHER/HAZARDS HIGHLIGHTS
AS A NOTABLE SHORTWAVE AND ITS SURFACE LOW REFLECTION TRACK EAST
THROUGH THE PLAINS WEDNESDAY INTO THE MIDWEST/GREAT LAKES AND
NORTHEAST THROUGH THE LATTER PART OF THE WEEK, PRECIPITATION IS
LIKELY, BUT MODEL DIFFERENCES LEAD TO CONSIDERABLE UNCERTAINTY
WITH THE PRECIPITATION COVERAGE, AMOUNTS, AND TYPE. OVERALL THIS
MAY BE A SOMEWHAT COLDER SYSTEM, WITH PRECIPITATION IN THE FORM OF
SNOW POSSIBLE IN AREAS NEAR THE CANADIAN BORDER AND AT LEAST THE
HIGHER ELEVATIONS OF THE INTERIOR NORTHEAST, PERHAPS EVEN INTO
LOWER ELEVATIONS OF NORTHERN NEW ENGLAND. THERE IS LOW CONFIDENCE
IN SNOW LEVELS AND AMOUNTS AT THIS POINT THOUGH. THIS FORECAST
SHOWS A TREND TOWARD SNOW PROBABILITIES LINGERING LONGER INTO
FRIDAY. LIGHT LAKE EFFECT PRECIPITATION WILL BE POSSIBLE AFTER
THIS SYSTEM PASSES. SOME RAIN IS POSSIBLE FARTHER SOUTHWEST ALONG
THE FRONTAL CORRIDOR, POTENTIALLY PEAKING THURSDAY IN THE
SOUTH-CENTRAL CONUS. EASTERN PACIFIC AND GULF MOISTURE ARE
FORECAST TO COMBINE IN THE VICINITY OF THE FRONT, WITH THE RIGHT
ENTRANCE REGION OF THE JET STREAM OVERHEAD. THIS COULD LEAD TO
HEAVY RAINFALL CAUSING FLASH FLOODING, SO A MARGINAL RISK IS
PLANNED IN THE DAY 5/THURSDAY EXCESSIVE RAINFALL OUTLOOK ACROSS
PORTIONS OF THE SOUTHERN PLAINS AND LOWER MISSISSIPPI VALLEY. THE
SOUTHERN PORTION OF THE RISK AREA SHOULD SEE THE HIGHEST
INSTABILITY, WHILE FARTHER NORTH LOOKS TO HAVE THE HIGHEST RISK OF
TRAINING CONVECTION. PLUS MODEL VARIABILITY IN THE PLACEMENT OF
THE HEAVIEST AMOUNTS LEADS US TO COVER A LARGER AREA AT THIS
POINT, THAT COULD BE NARROWED WITH TIME AS MODELS CONVERGE. BY
LATE WEEK, ANY REMAINING HEAVY RAINFALL SHOULD BE ACROSS SOUTHERN
TEXAS AHEAD OF THE FRONT CLEARING OUT THE HIGHEST MOISTURE.
FARTHER WEST, THE CENTRAL ROCKIES AND VICINITY COULD SEE SOME
NOTABLE SNOW AROUND WEDNESDAY-THURSDAY, BUT THE REST OF THE WEST
SHOULD BE DRY ON AVERAGE AS UPPER-LEVEL RIDGING BRIEFLY BUILDS
BACK IN. CHANCES FOR AT LEAST LIGHT PRECIPITATION MAY INCREASE
AGAIN LATE WEEK FOR THE PACIFIC NORTHWEST, BUT WITH UNCERTAINTY IN
TIMING AND AMOUNTS. ISSUES WITH THE CHARACTER OF THE SUPPORTING
UPPER TROUGH MOVING INTO THE WEST ALSO LOWER CONFIDENCE IN
DETERMINING THE SOUTHEASTWARD EXTENT OF PRECIPITATION.
MUCH OF THE EASTERN TWO-THIRDS OF THE COUNTRY WILL SEE ABOVE
AVERAGE TEMPERATURES AS THE PERIOD BEGINS WEDNESDAY, WITH THE
GREATEST ANOMALIES OF 15-25F FOR HIGHS STRETCHING FROM THE
SOUTHERN PLAINS INTO THE MIDDLE MISSISSIPPI VALLEY AS TEMPERATURES
RISE WELL INTO THE 70S AND 80S. EXPECT A CORRIDOR OF LOWS THAT ARE
20-25F ABOVE NORMAL TO EXTEND ACROSS PARTS OF THE MISSISSIPPI
VALLEY INTO THE OHIO/TENNESSEE VALLEYS ON WEDNESDAY-THURSDAY, WITH
WARMER THAN AVERAGE TEMPERATURES ACROSS THE GULF COAST STATES AS
WELL. DAILY RECORD HIGH MAXIMUM AND MINIMUM TEMPERATURES COULD BE
SET FROM THE SOUTH-CENTRAL U.S. INTO THE TENNESSEE AND OHIO
VALLEYS ESPECIALLY WEDNESDAY. COLD FRONTS TRACKING SOUTH AND EAST
SHOULD GRADUALLY REDUCE THE AREA OF ABOVE NORMAL TEMPERATURES
ACROSS THE CONUS WITH TIME, COOLING TEMPERATURES ACROSS THE
NORTHERN TIER, THEN THE CENTRAL U.S. TO OHIO VALLEY, AND FINALLY
ACROSS THE SOUTHEAST BY FRIDAY-SATURDAY. BEHIND THESE FRONTS,
BELOW NORMAL TEMPERATURES SHOULD BE MOST PREVALENT OVER THE
WESTERN U.S. (WHERE COOL READINGS SHOULD PERSIST MOST OF THE
PERIOD), SPREADING INTO THE SOUTH-CENTRAL U.S. AND TOWARD THE OHIO
VALLEY, GREAT LAKES, AND THE NORTHEAST LATE WEEK.
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 FORECAST, EXCESSIVE RAINFALL OUTLOOK,
WINTER WEATHER OUTLOOK PROBABILITIES, HEAT INDICES AND KEY
MESSAGES 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
HTTPS://WWW.WPC.NCEP.NOAA.GOV/#PAGE=OVW
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