839
FXUS02 KWBC 180659
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
158 AM EST FRI NOV 18 2022
VALID 12Z MON NOV 21 2022 - 12Z FRI NOV 25 2022
..OVERVIEW
BY THE START OF THE MEDIUM RANGE PERIOD MONDAY, THE UPPER PATTERN
IS EXPECTED TO BE DEAMPLIFYING SOMEWHAT COMPARED TO THE BROAD AND
STRONG TROUGH ATOP THE U.S. DURING THE SHORT RANGE PERIOD.
REGARDLESS, LOWER AMPLITUDE TROUGHING COULD PERSIST INTO THE
NORTHEASTERN U.S. WHILE A SHORTWAVE ALSO CROSSES THE SOUTHERN
PLAINS. THIS FLATTER MEAN FLOW TRANSITION REPRESENTS AN IMPORTANT
CHANGE IN THE SOURCE OF FLOW DIGGING INTO THE CENTRAL/EASTERN U.S.
MEAN TROUGH, FROM A COLD CANADIAN ORIGIN SUNDAY-MONDAY TO A MORE
MODERATE PACIFIC ORIGIN MID-LATE WEEK AS THE WEST COAST RIDGE
REBUILDS. THIS PATTERN EVOLUTION WILL FAVOR SOME ROUNDS OF RAIN
AND HIGH ELEVATION SNOW OVER THE NORTHWEST AS WELL AS RAINFALL
OVER PORTIONS OF THE GULF COAST STATES. BY MID-LATE WEEK THIS
SOUTHERN TIER MOISTURE SHOULD EXPAND NORTHWARD AHEAD OF AN
AMPLIFYING TROUGH AND COLD FRONT IN THE CENTRAL U.S., POTENTIALLY
TRACKING INTO THE EAST BY LATE WEEK.
..GUIDANCE AND PREDICTABILITY ASSESSMENT
MODEL GUIDANCE REMAINS IN GOOD AGREEMENT FOR DAY 3/MONDAY
REGARDING THE OVERALL PATTERN AND EVEN WITH THE PLACEMENT OF THE
RELATIVELY SMALLER FEATURES LIKE THE SOUTHERN PLAINS SHORTWAVE.
BUT GUIDANCE CONTINUES TO STRUGGLE BEGINNING DAY 4/TUESDAY AND
BEYOND WITH ENERGY THAT LOOKS TO DIVE SOUTHWARD ACROSS THE EASTERN
PACIFIC AS WELL AS WITH ANOTHER STRONG SHORTWAVE DIGGING INTO THE
NORTHWEST. THE MAIN INITIAL OUTLIER WAS THE 12Z UKMET AS IT
APPEARS TOO PROGRESSIVE WITH THE LATTER SHORTWAVE AND DRIFTS THE
FORMER WESTWARD IN THE PACIFIC, DISCONNECTED FROM THE NORTHERN
STREAM FLOW. BUT THE 12Z CMC/ECMWF AND 12/18Z GFS RUNS ALSO
CONTINUE TO DIVERGE THROUGH THE LATTER HALF OF THE WEEK WITH THESE
FEATURES. THE 12Z ECMWF AND CMC WERE MORE AGGRESSIVE WITH CREATING
A CLOSED LOW IN THE SOUTHWEST U.S. BY WEDNESDAY NIGHT/THURSDAY
THAT MEANDERS THERE THROUGH FRIDAY. MEANWHILE, THE GFS RUNS
THROUGH 18Z KEPT THAT ENERGY MORE PHASED WITH THE NORTHERN STREAM
FOR A STEADIER PROGRESSIVE SHIFT OF THE TROUGH EASTWARD THROUGH
THE CENTRAL CONUS. ENSEMBLE MEMBERS FROM THE GEFS/ECENS/CMCE 12Z
CYCLE SUGGESTED THAT THE WESTERN, SLOWER CLOSED LOW FROM THE CMC
AND ECMWF WAS ON THE WESTERN SIDE OF THE SPREAD AND THAT THE GFS
RUNS MIGHT BE MORE REASONABLE WITH THEIR TROUGH/POSSIBLE CLOSED
LOW PLACEMENT, CLOSER TO THE ENSEMBLE MEANS' POSITION AS WELL.
HOWEVER, THE NEWER 00Z GFS DETERMINISTIC RUN CAME IN WITH A
SLOWER/FARTHER WEST CLOSED LOW--WHILE THE 00Z ECMWF WAS FARTHER
NORTHEAST WITH A CLOSED LOW, A FLIP-FLOP FOR BOTH. THE 00Z CMC WAS
SIMILAR TO ITS 12Z RUN. ALL THIS DEMONSTRATES THE UNCERTAINTY
REMAINING WITH THIS UPPER LEVEL FEATURE, WHICH ALSO HAS
IMPLICATIONS FOR THE SURFACE LOW/FRONTAL PATTERN AND THE
ASSOCIATED QPF.
THE WPC FORECAST WAS BASED ON A BLEND OF THE 12/18Z GFS RUNS AND
12Z ECMWF AND CMC EARLY IN THE PERIOD, BUT WITH THE INCLUSION OF
THE GEFS/EC ENSEMBLE MEANS WITH INCREASING PROPORTIONS TO OVER
HALF BY DAY 7 GIVEN THE INCREASING DETERMINISTIC MODEL SPREAD.
THIS BLEND ALSO WORKED FOR THE NORTHEAST WHERE THERE REMAIN SOME
FRONTAL PLACEMENT DIFFERENCES DEPENDING ON THE EXTENT OF TROUGHING
ALOFT. CHANGES TO THE QPF FROM THE 01Z NATIONAL BLEND OF MODELS
INCLUDED INCREASING COVERAGE OF LIGHT AMOUNTS ACROSS THE NORTHERN
TIER AS WELL AS IN THE EAST-CENTRAL U.S. BY WEDNESDAY-THURSDAY
WHERE THERE ARE REASONABLE CHANCES FOR QPF TO INCREASE IN COVERAGE
AHEAD OF A CENTRAL U.S. TROUGH, DESPITE DIFFERENCES IN THE DETAILS.
..WEATHER/HAZARD HIGHLIGHTS
CHILLY TEMPERATURES THIS WEEKEND ARE EXPECTED TO CONTINUE INTO THE
FIRST PART OF NEXT WEEK, BUT SHOULD BE GRADUALLY MODERATING. LOW
TEMPERATURES ON MONDAY ARE FORECAST TO BE 10-15F BELOW NORMAL FROM
THE LOWER MISSISSIPPI VALLEY THROUGH THE EAST, BUT ONLY A FEW
DEGREES BELOW AVERAGE TUESDAY AND NEAR TO ABOVE (ESPECIALLY ACROSS
THE SOUTHEAST) NORMAL AS THE WEEK PROGRESSES, THOUGH THE INTERIOR
NORTHEAST MAY SEE ANOTHER BOUT OF COLD AIR THURSDAY-FRIDAY. HIGH
TEMPERATURES COULD REMAIN COOL FOR SOUTHERN TEXAS ON MONDAY, WITH
HIGHS IN THE 50S BELOW NORMAL BY 15-25F, WHICH SHOULD GRADUALLY
WARM THROUGH MIDWEEK AS WELL. THE EAST MAY SEE SOME BELOW NORMAL
HIGHS ONCE AGAIN BY THE LATTER PART OF NEXT WEEK. MEANWHILE THE
WEST COULD SEE INCREASING COVERAGE OF ABOVE AVERAGE TEMPERATURES
BY THURSDAY-FRIDAY GIVEN THE RIDGE ALOFT.
SOME LINGERING LAKE EFFECT SNOW IS POSSIBLE INTO MONDAY DOWNWIND
OF ESPECIALLY THE LOWER GREAT LAKES, BUT THE BULK OF THE
SIGNIFICANT SNOW FOR PLACES LIKE BUFFALO, NEW YORK IS FORECAST TO
FALL DURING THE SHORT RANGE PERIOD. MEANWHILE, MULTIPLE FRONTAL
SYSTEMS MOVING INTO THE NORTHWESTERN U.S. COULD CAUSE ROUNDS OF
PRECIPITATION THERE NEXT WEEK, WITH HIGHER ELEVATION SNOW. HOWEVER
THERE IS STILL A FAIR DEGREE OF UNCERTAINTY OVER THE SOUTHWARD
EXTENT AND INTENSITY OF RAIN/MOUNTAIN SNOW ON A DAY-TO-DAY BASIS.
SURFACE HIGH PRESSURE DOMINATING INTERIOR PARTS OF THE WEST IS
LIKELY TO KEEP THAT REGION FAIRLY DRY. MEANWHILE, A SHORTWAVE AND
MOISTURE ADVECTING FROM THE GULF OF MEXICO COULD LEAD TO SHOWERS
AND SOME THUNDERSTORMS ACROSS TEXAS AND POTENTIALLY FARTHER EAST
ACROSS THE SOUTHEAST EARLY IN THE WEEK. EASTERLY FLOW AND A
FRONTAL SYSTEM MEANDERING NEAR THE FLORIDA PENINSULA WILL ENHANCE
SHOWER/THUNDERSTORM COVERAGE THERE, AND ISOLATED FLASH FLOODING
CANNOT BE RULED OUT ESPECIALLY OVER URBAN AREAS. THEN BY THE
LATTER HALF OF THE WEEK, MOISTURE COULD STREAM NORTH AHEAD OF THE
POTENTIAL CENTRAL U.S. TROUGH AND INCREASE CHANCES FOR
PRECIPITATION ACROSS THE EASTERN HALF OF THE U.S., THOUGH THE
DETAILS REMAIN UNCERTAIN AND WILL DEPEND ON EVOLUTION OF THE UPPER
AND SURFACE SYSTEMS.
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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