189
FXUS02 KWBC 231918
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
217 PM EST WED NOV 23 2022
VALID 12Z SAT NOV 26 2022 - 12Z WED NOV 30 2022
...MEANINGFUL PRECIPITATION IS POSSIBLE ACROSS EASTERN PARTS OF
THE U.S. THIS WEEKEND...
...SNOW IS LIKELY ACROSS HIGHER ELEVATIONS OF THE WEST EARLY NEXT
WEEK AND MAY SPREAD INTO THE NORTH-CENTRAL U.S. BY
TUESDAY-WEDNESDAY...
...THE CHANCE FOR WIDESPREAD, POTENTIALLY HEAVY RAINFALL
INCREASING BY THE MIDDLE OF NEXT WEEK...
..OVERVIEW
THE MEDIUM RANGE PERIOD WILL BEGIN SATURDAY WITH A CLOSED UPPER
LOW ATOP THE SOUTH-CENTRAL U.S., WHILE A SURFACE LOW PRESSURE
SYSTEM SHOULD LIFT QUICKLY FROM THE LOWER MISSISSIPPI VALLEY
TOWARD THE GREAT LAKES REGION THIS WEEKEND. THIS PATTERN WILL
PRODUCE WIDESPREAD RAIN CHANCES ACROSS THE SOUTHEAST, WHERE SOME
LOCALIZED FLOODING MAY BE POSSIBLE, AND FARTHER NORTH ACROSS THE
MISSISSIPPI VALLEY INTO THE OHIO/TENNESSEE VALLEYS, SHIFTING INTO
THE MID-ATLANTIC AND NORTHEAST LATER SATURDAY INTO SUNDAY. SOME
PRECIPITATION MAY FALL AS SNOW IN HIGHER ELEVATIONS OF THE
INTERIOR NORTHEAST. BY EARLY NEXT WEEK, THE UPPER PATTERN LOOKS TO
HAVE A BRIEF TRANSITION TOWARD ZONAL FLOW BEFORE TROUGHING DIGS
INTO THE WESTERN U.S. MONDAY-TUESDAY, INCREASING PRECIPITATION
CHANCES THERE. AS THE TROUGH SHIFTS EASTWARD, THE CURRENT FORECAST
SHOWS A CONSOLIDATING SURFACE LOW PRESSURE SYSTEM MAY SHIFT INTO
THE MIDWEST FOR TUESDAY-WEDNESDAY, WITH SOME SNOW POSSIBLE NORTH
AND WEST OF THE LOW FOR THE NORTHERN PLAINS INTO MINNESOTA, AND AN
INCREASING POTENTIAL FOR HEAVY RAINFALL AHEAD OF A TRAILING COLD
FRONT IN THE EAST-CENTRAL CONUS.
..GUIDANCE AND PREDICTABILITY ASSESSMENT
THE FOCUS AT THE START OF THE FORECAST PERIOD IS ON THE PLACEMENT
AND PROGRESSION OF THE UPPER-LEVEL CLOSED LOW OVER THE SOUTHERN
PLAINS FORECAST TO LIFT NORTHEASTWARD ACROSS THE MIDWEST OVER THE
WEEKEND. IN GENERAL, THE DETERMINISTIC GUIDANCE IS RELATIVELY
SIMILAR IN TERMS OF THE CURRENT PLACEMENT AND TREND FOR THE CLOSED
LOW TO MOVE A BIT SLOWER THAN PRIOR FORECASTS, RESULTING IN A
SLOWER PROGRESSION OF THE FRONTAL SYSTEM AT THE SURFACE AND
SUBSEQUENT DOWNSTREAM EFFECTS ON PRECIPITATION COVERAGE. ONE
NOTABLE OUTLIER WAS THE 00 GEFS MEMBERS THAT TENDED TO CLUSTER
AROUND A MORE PROGRESSIVE SOLUTION. THERE WAS MORE UNCERTAINTY
WITH THE PLACEMENT OF AN UPSTREAM SHORTWAVE OVER THE WESTERN U.S.,
THOUGH THE MORE RECENT RUNS OF THE ECMWF HAVE TRENDED TOWARDS A
SOMEWHAT SIMILAR SOLUTION TO THE 06Z GFS AND 00Z UKMET/CMC. THE
PHASING SLIGHTLY DIFFERS BETWEEN THE GUIDANCE BUT THE FORECASTS AT
LEAST TEND TO AGREE ON A LOWER AMPLITUDE, POSITIVELY TILTED WAVE
OVER THE WEST. THUS, THE INITIAL WPC FORECAST CONSISTED OF A
STRAIGHT BLEND OF THE DETERMINISTIC GUIDANCE ALONG WITH THE 00Z
ECENS MEAN TO SMOOTH OUT ANY TIMING DIFFERENCES AND COME TO A
GENERAL CONSENSUS ON THE PLACEMENT OF THE CLOSED LOW. THE
UNCERTAINTY INCREASES WITH THE DOWNSTREAM EVOLUTION OF THE CLOSED
LOW, WITH THE RUN-TO-RUN CONSISTENCY OF THE DETERMINISTIC GUIDANCE
IN DISAGREEMENT WITH THE PROGRESSION AND LINGERING INTENSITY OF
THE LOW AS IT LIFTS INTO THE MIDWEST AS AN OPEN WAVE AS WELL AS
THE SUBSEQUENT UPSTREAM SHORTWAVE PROGRESSING EASTWARD. THE ECMWF
AND GFS HAVE GENERALLY TRENDED TOWARDS A MORE PROGRESSIVE
SOLUTION, WHICH ALSO MATCHES THE 00Z UKMET. THE 00Z ECENS MEAN IS
ALSO CLOSER TO THIS SOLUTION WHILE THE 00Z GEFS MEAN IS EVEN MORE
PROGRESSIVE WITH THE LIFTING WAVE. THE 00Z CMC DIFFERS THE MOST
WITH SPLIT NORTHERN AND SOUTHERN STREAM ENERGY, SO THE FORECAST
BLEND TRENDED THIS DOWN WITH THE OTHER GUIDANCE UP.
ATTENTION THEN TURNS TO THE WEST WITH THE NEXT UPSTREAM TROUGH
STARTING TO AMPLIFY OVER THE NORTHWEST. THE 00Z ECMWF AND 06Z GFS
WERE RELATIVELY SIMILAR IN PHASING AND AMPLITUDE WHILE THE 00Z
CMC/UKMET WERE LESS AMPLIFIED. THE TREND IN THE WPC FORECAST BLEND
WAS TO DECREASE THE INFLUENCE OF THE 00Z CMC/UKMET WITH MORE
WEIGHT GIVEN TO THE 00Z ECENS WHILE INTRODUCING 00Z GEFS MEAN AS
IT WAS MORE IN LINE WITH THE OTHER GUIDANCE COMPARED TO THE
HANDLING OF THE CLOSED LOW EARLIER IN THE PERIOD. THE FORECAST
GROWS MORE COMPLEX DURING THE LATTER PORTION OF THE PERIOD WITH A
BIT OF A SPLIT IN THE ENERGY BETWEEN THE NORTHERN AND SOUTHERN
STREAM OVER THE WEST. THE 06Z GFS TRENDED AWAY FROM THIS PATTERN
WHILE THE 00Z ECMWF TRENDED TOWARDS IT, COMPLICATING THE FORECAST.
FURTHERMORE, THERE WAS DISAGREEMENT IN THE GUIDANCE FOR THE TIMING
AND AMPLITUDE OF THE NEXT WAVE UPSTREAM OVER THE PACIFIC AND
MOVING TOWARDS THE PACIFIC NORTHWEST. THERE WAS SIGNIFICANT
RUN-TO-RUN UNCERTAINTY IN BOTH THE 00Z ECMWF AND 06Z GFS IN THE
HANDLING AND PROGRESSION OF THESE FEATURES AS THE FIRST BEGINS TO
EJECT OUT OVER THE PLAINS AND THE SECOND REACHES THE PACIFIC
NORTHWEST. THE INDIVIDUAL ENSEMBLE MEMBERS IN THE 00Z GEFS AND
ECENS SHOWED A GOOD DEAL OF UNCERTAINTY IN THE TIMING AND
AMPLITUDE OF THE WAVES AS WELL. THE 00Z CMC WAS IN EVEN LESS
AGREEMENT WITH THE OVERALL PATTERN, DEVELOPING MULTIPLE SHORTWAVES
ROUNDING BROADER LARGER-SCALE TROUGHING. THEREFORE, THE LATTER
PORTION OF THE FORECAST INCLUDED A BLEND INITIALLY EDGED SLIGHTLY
TOWARDS THE 00Z ECMWF/06Z GFS DETERMINISTIC GUIDANCE WITH AN
INCREASE IN THE MEANS OVER THE DETERMINISTIC GUIDANCE FOR THE END
OF THE PERIOD. THIS HELPED TO BETTER REPRESENT THE FIRST TROUGH IN
THE WEST INITIALLY WITHOUT GETTING TOO DETAILED IN A MORE COMPLEX
SOLUTION GIVEN THE UNCERTAINTY AND FORECAST LEAD TIME, WITH THE
GOAL OF CAPTURING THE GENERAL PHASING PATTERN OF THE WAVES
OVERALL.
..WEATHER/HAZARD HIGHLIGHTS
GULF MOISTURE IS FORECAST TO STREAM INTO PARTS OF THE CENTRAL AND
EASTERN U.S. AHEAD OF THE UPPER AND SURFACE LOWS AND PRODUCE
WIDESPREAD RAIN CHANCES THIS WEEKEND. SOME LOCALLY HEAVY RAINFALL
MAY BE POSSIBLE IN THE SOUTHEAST AND INTO THE SOUTHERN
APPALACHIANS AND PIEDMONT ON SATURDAY, WHICH COULD CAUSE ISOLATED
FLASH FLOODING IF RAIN RATES ARE HIGH ENOUGH. PRECIPITATION IS
LIKELY TO SPREAD ACROSS THE MIDDLE MISSISSIPPI VALLEY AND
OHIO/TENNESSEE VALLEYS ON SATURDAY AND INTO THE MID-ATLANTIC AND
NORTHEAST BY SUNDAY. THE TREND HAS BEEN FOR RAINFALL TO PROGRESS
SLOWER AND BE A BIT HEAVIER, LINGERING INTO SUNDAY FOR THE
OHIO/TENNESSEE VALLEYS AND SOUTHEAST. WITH THIS LOW TRACK, MOST
AREAS ARE LIKELY TO SEE RAIN RATHER THAN WINTRY PRECIPITATION, BUT
HIGHER ELEVATIONS OF THE INTERIOR NORTHEAST COULD BE AN EXCEPTION
WHERE SNOW COULD FALL.
THE PACIFIC NORTHWEST INTO THE NORTHERN ROCKIES CAN EXPECT SOME
LIGHT TO MODERATE PRECIPITATION ON SATURDAY IN CONJUNCTION WITH A
COUPLE OF FRONTAL SYSTEMS. PRECIPITATION IS THEN FORECAST TO
SPREAD SOUTHWARD ACROSS CALIFORNIA AND EASTWARD INTO THE GREAT
BASIN AND ROCKIES FOR EARLY NEXT WEEK AS THE NOTED UPPER TROUGH
BEGINS TO DIG INTO THE REGION. LOWER ELEVATION RAIN AND HIGHER
ELEVATION SNOW WILL BE LIKELY. WHILE THE DETAILS ARE UNCERTAIN,
THE CHANCE FOR HEAVY SNOW HAS BEEN INCREASING ACROSS THE CASCADES
AND INTO THE WASATCH AND ROCKIES. HEAVY SNOW IS ALSO POSSIBLE IN
THE SIERRAS, ALTHOUGH THIS HAS TRENDED DOWNWARD COMPARED TO
PREVIOUS FORECASTS.
THE POTENTIAL FOR LOW PRESSURE SYSTEM DEVELOPMENT IN THE CENTRAL
U.S. BY MID-WEEK NEXT WEEK IS INCREASING WHICH WOULD BRING
PRECIPITATION CHANCES TO PORTIONS OF THE CENTRAL AND EASTERN U.S.
WIDESPREAD, POTENTIALLY HEAVY RAINFALL LOOKS POSSIBLE ACROSS THE
MIDWEST, OHIO/TENNESSEE VALLEYS, AND INTO THE LOWER MISSISSIPPI
VALLEY. THE POTENTIAL FOR SNOWFALL IS ALSO INCREASING ON THE
BACKSIDE OF THE LOW AS IT TRACKS NORTHEASTWARD INTO THE MIDWEST
TUESDAY-WEDNESDAY FROM EASTERN MONTANA INTO THE DAKOTAS AND
MINNESOTA. THIS IS AT THE END OF THE MEDIUM RANGE PERIOD THOUGH SO
THE DETAILS OF THE FORECAST MAY NEED TO CHANGE WITH TIME, SO STAY
TUNED TO FUTURE FORECASTS.
SLIGHTLY COOLER THAN NORMAL HIGHS COULD LINGER IN THE
SOUTH-CENTRAL U.S. THIS WEEKEND BEHIND THE INITIAL UPPER LOW,
WHILE MILDER THAN NORMAL TEMPERATURES PARTICULARLY IN TERMS OF
LOWS ARE POSSIBLE IN THE EAST. BUT MORE WIDESPREAD COOLER THAN
NORMAL TEMPERATURES ARE LIKELY TO EXPAND ACROSS THE WESTERN HALF
OF THE U.S. MONDAY-WEDNESDAY AS DEEPENING TROUGHING TAKES HOLD
THERE. ANOMALIES OF 10-20F BELOW AVERAGE MAY FOCUS ACROSS THE
NORTHERN HIGH PLAINS. MEANWHILE, THE SOUTH-CENTRAL AND
EAST-CENTRAL U.S. COULD SEE ABOVE NORMAL TEMPERATURES AHEAD OF THE
WESTERN TROUGH.
PUTNAM/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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