165
FXUS02 KWBC 261805
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
104 PM EST SAT NOV 26 2022
VALID 12Z TUE NOV 29 2022 - 12Z SAT DEC 3 2022
...WET/SNOWY CONDITIONS EXPANDING ACROSS THE WEST WITH BELOW
NORMAL TEMPERATURES...
...HEAVY RAIN AND SEVERE WEATHER POSSIBLE ACROSS PARTS OF THE
SOUTH AND INTO THE OHIO VALLEY TUESDAY-WEDNESDAY...
18Z UPDATE: AN ANALYSIS OF THE LATEST MODEL GUIDANCE REVEALS GOOD
OVERALL SYNOPTIC SCALE AGREEMENT AT THE BEGINNING OF THE FORECAST
PERIOD ON TUESDAY. HOWEVER, TIMING DIFFERENCES EMERGE WITH THE
TIMING OF THE DEVELOPING STORM SYSTEM OVER THE PLAINS AND ITS
TRAILING COLD FRONT AS EARLY AS TUESDAY NIGHT. THE PAST FEW RUNS
OF THE GFS APPEAR TO BE TOO SLOW IN THE PROGRESSION OF THE COLD
FRONT ACROSS THE SOUTHEAST AND THEN ACROSS THE EAST COAST, WITH
THE PARENT SURFACE LOW POSITIONED TO THE SOUTHWEST OF THE MODEL
CONSENSUS. THE CMC/ECMWF/ECENS ARE RELATIVELY CLOSE AND THIS ALSO
HAS SOME SUPPORT FROM THE ICON AND JMA MODELS, SO THE
FRONT/PRESSURES FORECAST WAS HEDGED IN THIS DIRECTION WITH A
FASTER FRONTAL PROGRESSION. THE 12Z GFS DID TREND A LITTLE FASTER
COMPARED TO ITS 6Z RUN, BUT STILL SLOWER COMPARED TO THE
CONSENSUS. THE UKMET ALSO STRAYED FROM CONSENSUS NEAR THE PACIFIC
NORTHWEST GOING INTO THURSDAY AND BEYOND, SO IT WAS ONLY USED
THROUGH WEDNESDAY.
FOR THE QPF FORECAST, ABOUT HALF OF THE NBM AND 1/6 EACH OF THE
ECMWF, CMC, AND ECENS WAS USED AS A BASELINE THROUGH THURSDAY, AND
THEN GRADUALLY INCREASED NBM PROPORTION GOING INTO FRIDAY AND
SATURDAY. A SLIGHT RISK OF EXCESSIVE RAINFALL WAS INTRODUCED FOR
THE DAY 4 PERIOD FROM SOUTHERN MISSISSIPPI TO SOUTH-CENTRAL
TENNESSEE TO ACCOUNT FOR A BETTER MODEL SIGNAL OF 1-3 INCH
RAINFALL TOTALS WITH LOCALLY HIGHER AMOUNTS. LOCAL INCREASES WERE
MADE DOWNWIND OF THE GREAT LAKES ON THURSDAY TO ACCOUNT FOR LAKE
EFFECT SNOW POTENTIAL. ACROSS THE WESTERN U.S., THERE HAS BEEN AN
UPWARD TREND IN EXPECTED OVERALL QPF FOR THE LATTER HALF OF THE
FORECAST PERIOD, ALTHOUGH PRECIPITATION AMOUNTS WERE TRIMMED BACK
SLIGHTLY FROM THE AFOREMENTIONED MODEL BLEND. THE PREVIOUS
FORECAST DISCUSSION FOLLOWS BELOW FOR REFERENCE. /HAMRICK
---------------------
..OVERVIEW
THE MODELS AND ENSEMBLE MEANS GENERALLY AGREE FROM THE LARGE-SCALE
PERSPECTIVE, SHOWING A MEAN TROUGH SETTING UP NEAR THE WEST COAST
WHILE AN UPPER RIDGE OVER THE BAHAMAS/CUBA AS OF EARLY TUESDAY
STEADILY RETROGRADES INTO THE GULF OF MEXICO. A LEADING STRONG
UPPER TROUGH EMERGING FROM THE WEST SHOULD SUPPORT DEEPENING
SURFACE LOW PRESSURE THAT TRACKS FROM THE CENTRAL PLAINS INTO THE
GREAT LAKES TUESDAY-WEDNESDAY. THE TRAILING COLD FRONT MAY FOCUS
HEAVY RAINFALL FROM THE SOUTH INTO THE OHIO VALLEY, WITH SEVERE
WEATHER ALSO POSSIBLE OVER SOUTHERN AREAS, WITH SOME HEAVY
RAINFALL ALSO POTENTIALLY REACHING THE NORTHEAST. SOME SNOW WILL
BE POSSIBLE NORTH/WEST OF THE LOW TRACK. THE FIRST SYSTEM
DROPPING INTO THE DEVELOPING WEST COAST TROUGH SHOULD AFFECT THE
NORTHWEST WEDNESDAY-THURSDAY WITH ANOTHER SYSTEM POSSIBLY
APPROACHING BY NEXT SATURDAY. EXPECT PRECIPITATION TO PUSH
SOUTHEASTWARD ACROSS THE WEST WITH TIME AS THE OVERALL UPPER
TROUGH AMPLIFIES. BY LATE IN THE WEEK THE DETAILS OF INDIVIDUAL
FEATURES AFFECTING THE WEST AND EJECTING DOWNSTREAM TO AFFECT
AREAS EAST OF THE ROCKIES BECOME INCREASINGLY UNCERTAIN. THE
OVERALL PATTERN WILL FAVOR BELOW NORMAL TEMPERATURES OVER MUCH OF
THE WEST AND PARTS OF THE HIGH PLAINS, WITH MONTANA AND NEARBY
AREAS LIKELY TO SEE THE MOST PERSISTENT AND COLDEST ANOMALIES.
..GUIDANCE AND PREDICTABILITY ASSESSMENT
GUIDANCE IS STILL IN THE PROCESS OF REFINING THE FORECAST FOR THE
DEVELOPING STORM SYSTEM EXPECTED TO TRACK FROM THE CENTRAL PLAINS
THROUGH THE GREAT LAKES AND INTO CANADA TUESDAY-WEDNESDAY. TRACK
SPREAD HAS NARROWED NOTICEABLY BUT MEANINGFUL STRENGTH DIFFERENCES
REMAIN. 12Z/18Z GFS RUNS WERE ON THE FAST AND WEAK SIDE OF THE
SPREAD (THE WEAK CHARACTER BEING A PERSISTENT TRAIT FOR MULTIPLE
RUNS). THE NEW 00Z GFS HAS SLOWED DOWN SOME BUT IS STILL AMONG
THE WEAKER SOLUTIONS, ALBEIT NOW JOINED BY THE 00Z CMC. THE 00Z
GFS PARALLEL IS DEEPER AND IN LINE WITH THE OPERATIONAL MODEL
AVERAGE. ON THE OTHER HAND THE 00Z UKMET EXTENDS A RECENT TREND
AWAY FROM ITS DEEP SOLUTIONS. AN INTERMEDIATE SOLUTION CLOSE TO
CONTINUITY CONTINUES TO LOOK REASONABLE FOR THE SURFACE LOW GIVEN
THE BEHAVIOR OF LATEST GUIDANCE. BY EARLY THURSDAY THERE IS AN
INCREASING SIGNAL IN THE MODELS FOR A FAIRLY STRONG FRONTAL WAVE
TO REACH A POSITION CLOSE TO NORTHERN NEW ENGLAND.
WHILE LOOSELY FITTING WITHIN THE EXPECTED MEAN PATTERN, THE
12Z/18Z GFS AND GEFS MEANS IN THEIR OWN DIFFERENT WAYS DIFFERED
SOMEWHAT FROM MOST OTHER GUIDANCE FOR THE WEST COAST UPPER TROUGH.
THEY ALL WERE FLATTER WITH ENERGY NEARING THE NORTHWEST BY
MIDWEEK AND THUS MUCH WEAKER WITH THE SURFACE REFLECTION. THEN
THE GEFS MEAN BECAME LESS AMPLIFIED WITH THE UPPER TROUGH VERSUS
OTHER SOLUTIONS, AS WELL AS WHAT WOULD BE SUGGESTED BY
TELECONNECTIONS RELATIVE TO THE CORE OF POSITIVE HEIGHT ANOMALIES
ASSOCIATED WITH THE UPSTREAM RIDGE. MEANWHILE THOSE TWO GFS RUNS
USED SOME OF THE TROUGH ENERGY TO PULL OF AN UPPER LOW THAT
ULTIMATELY ENDED UP OFFSHORE SOUTHERN CALIFORNIA BY DAY 7
SATURDAY. THE 00Z GFS/GEFS MEAN HAVE ADJUSTED MUCH CLOSER TO THE
MAJORITY SCENARIO BUT WITH THE GFS FARTHER OFFSHORE THAN THE GEFS
OR OTHER GUIDANCE FOR THE SYSTEM AFFECTING THE NORTHWEST BY
WEDNESDAY-THURSDAY. THERE IS MODERATE CLUSTERING FOR THE NEXT
SYSTEM THAT MAY REACH NEAR THE PACIFIC NORTHWEST BY NEXT SATURDAY.
ALSO LATE IN THE PERIOD THE FORECAST BECOMES INCREASINGLY
UNCERTAIN OVER HOW EJECTING WEST COAST ENERGY MAY INFLUENCE THE
SURFACE PATTERN TO THE EAST OF THE ROCKIES. THERE HAS BEEN SOME
SEMBLANCE OF CLUSTERING AND CONTINUITY FOR A WAVY FRONT TO REACH
THE NORTH-CENTRAL PLAINS/UPPER MIDWEST BY FRIDAY BUT THEN MODELS
AND EVEN TO SOME DEGREE THE MEANS RAPIDLY DIVERGE FOR SURFACE
DETAILS FROM THE PLAINS EASTWARD.
THE UPDATED FORECAST MAINTAINED A SOLUTION FAIRLY CLOSE TO
CONTINUITY BY WAY OF AN OPERATIONAL MODEL BLEND FOR ABOUT THE
FIRST HALF OF THE PERIOD, WITH ECMWF INPUT SPLIT BETWEEN THE PAST
TWO RUNS THROUGH 12Z AND A LITTLE LESS 18Z GFS WEIGHT THAN WOULD
TYPICALLY BE THE CASE, AND THEN A MODEL/MEAN MIX THAT TILTED
SOMEWHAT MORE TOWARD THE ECMWF/ECENS/CMC THAN THE 18Z GFS/GEFS
MEAN.
..WEATHER/HAZARD HIGHLIGHTS
OVER THE WEST, A DEPARTING SYSTEM MAY PRODUCE LINGERING LIGHT SNOW
OVER THE NORTH-CENTRAL/CENTRAL ROCKIES ON TUESDAY. A TRAILING
SYSTEM NEARING THE NORTHWEST SHOULD SPREAD MOISTURE INTO THE
REGION TUESDAY-WEDNESDAY WITH SOME LOCALLY MODERATE TO HEAVY RAIN
AND HIGHER ELEVATION SNOW POSSIBLE. GRADUAL AMPLIFICATION OF
UPPER TROUGHING SHOULD EXPAND THE PRECIPITATION SHIELD
SOUTHEASTWARD THROUGH THE REST OF THE WEEK, POSSIBLY REACHING INTO
CENTRAL OR SOUTHERN CALIFORNIA. ALSO WORTH MONITORING DURING THE
LATTER HALF OF THE WEEK IS THE POTENTIAL FOR THE UPPER TROUGH TO
DRAW IN SOME LOWER LATITUDE MOISTURE/SURFACE WAVINESS, WHICH WOULD
ENHANCE RAIN/SNOW TOTALS OVER SOME AREAS. HOWEVER UNCERTAINTY IN
IMPORTANT UPPER TROUGH DETAILS KEEPS CONFIDENCE FAIRLY LOW FOR
PRECISE SOUTHEASTWARD EXTENT AND RAIN/SNOW INTENSITY. SNOW LEVELS
IN THE NORTHWEST COULD DECLINE TO FAIRLY LOW ELEVATIONS TOWARD THE
END OF THE WEEK.
DURING TUESDAY-WEDNESDAY, STRENGTHENING CENTRAL PLAINS INTO GREAT
LAKES LOW PRESSURE AS WELL AS ITS TRAILING COLD FRONT PLUS A
SEPARATE WARM FRONT LIFTING THROUGH GULF OF MEXICO WILL LIKELY
BRING PRECIPITATION TO MUCH OF THE EASTERN HALF OF THE LOWER 48.
WIDESPREAD AND POTENTIALLY HEAVY RAINFALL IS POSSIBLE FROM THE
LOWER MISSISSIPPI VALLEY INTO THE SOUTHERN APPALACHIANS, AND THEN
THE NORTHEAST COULD ALSO SEE A PERIOD OF INTENSE RAINFALL GIVEN
THE STRONG DYNAMICS AND POTENTIAL WAVE WITH THE APPROACHING COLD
FRONT. SUFFICIENT MOISTURE AND INSTABILITY IN THE WARM SECTOR
COULD ALSO LEAD TO SEVERE WEATHER, WITH THE STORM PREDICTION
CENTER HIGHLIGHTING THE CHANCE IN THEIR OUTLOOK FOR NEXT TUESDAY
ACROSS PARTS OF EASTERN TEXAS INTO THE LOWER MISSISSIPPI VALLEY.
MEANWHILE THERE MAY BE A BAND OF MEANINGFUL SNOW TO THE NORTHWEST
OF THE SURFACE LOW TRACK WITH A POSSIBLE FOCUS OVER THE UPPER
MIDWEST. FINALLY, THIS STORM MAY PRODUCE STRONG WINDS OVER SOME
AREAS OF THE NORTHEAST QUADRANT OF THE LOWER 48.
SOME RAINFALL MAY DEVELOP OVER THE EAST-CENTRAL/SOUTH-CENTRAL U.S.
LATE IN THE WEEK, DEPENDING ON HOW THE EXACT PATTERN AT THE
SURFACE AND ALOFT ALLOWS FOR ANY INCORPORATION OF GULF MOISTURE.
AT THIS TIME CONFIDENCE IS VERY LOW WITH RESPECT TO POTENTIAL
COVERAGE AND AMOUNTS.
MUCH OF THE WEST AND NORTHERN HIGH PLAINS SHOULD SEE BELOW NORMAL
TEMPERATURES FOR MOST OF NEXT WEEK. EXPECT THE COLDEST ANOMALIES
TO BE OVER AND NEAR THE NORTHERN HALF OF THE HIGH PLAINS ON
TUESDAY WITH HIGHS 20-30F BELOW NORMAL. HIGHS OF 10-20F BELOW
NORMAL WILL BE COMMON OVER THE INTERIOR WEST ON TUESDAY AND THE
NORTHWEST LATE IN THE WEEK. SOME DAILY RECORDS FOR COLD
LOWS/DAYTIME HIGHS MAY BE POSSIBLE AROUND FRIDAY. MEANWHILE, THE
SOUTH-CENTRAL AND EAST-CENTRAL U.S. WILL LIKELY SEE A BRIEF PERIOD
OF ABOVE NORMAL TEMPERATURES (UP TO PLUS 10-15F ANOMALIES FOR
HIGHS AND SLIGHTLY WARMER FOR MORNING LOWS) ON TUESDAY-WEDNESDAY
AHEAD OF THE SYSTEM EMERGING FROM THE PLAINS. THEN THE COLD AIR
BEHIND THE FRONT WILL DROP READINGS OVER MOST OF THESE AREAS TO
MODERATELY BELOW NORMAL BY NEXT THURSDAY.
RAUSCH
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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