904
FXUS02 KWBC 041857
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
257 PM EDT SAT NOV 04 2023
VALID 12Z TUE NOV 07 2023 - 12Z SAT NOV 11 2023
..OVERVIEW
THE UPPER FLOW PATTERN ACROSS THE CONTIGUOUS U.S. DURING THE
TUESDAY-SATURDAY PERIOD 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. THE LEADING SYSTEM IN THE SERIES WILL AFFECT THE
NORTHEAST U.S. AND SOUTHEASTERN CANADA TUESDAY INTO WEDNESDAY WITH
MOSTLY LIGHT PRECIPITATION AND BREEZY CONDITIONS. THEN A
POSITIVELY TILTED SHORTWAVE EMERGING FROM THE WEST, EVENTUALLY
REINFORCED BY SOME CANADIAN FLOW, 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 IN THE
WEST, PRECIPITATION SHOULD LINGER INTO TUESDAY BEFORE A LIKELY
BREAK AROUND MIDWEEK. 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 LATEST MODELS AND ENSEMBLES GENERALLY DEPICT THE THREE PRIMARY
SYSTEMS OF INTEREST IN PRINCIPLE, BUT WITH SOME IMPORTANT DETAIL
DIFFERENCES YET TO BE RESOLVED. FOR THE NORTHEAST U.S. INTO
CANADA SYSTEM TUESDAY-WEDNESDAY, LATEST CMC RUNS AND THE 12Z UKMET
ARE ON THE SLOWER SIDE OF THE SPREAD BUT THE CMC CATCHES UP THE
REMAINING MAJORITY CLUSTER BY EARLY WEDNESDAY. WITH THE NEXT
SYSTEM, GUIDANCE CLUSTERS DECENTLY FOR THE PLAINS TO EASTERN GREAT
LAKES WAVE FROM WEDNESDAY INTO EARLY THURSDAY BUT RAPIDLY DIVERGES
THEREAFTER IN RESPONSE TO DIFFERENCES IN NORTHERN TIER
U.S./SOUTHERN CANADA ENERGY ALOFT. SOLUTIONS FOR THE SURFACE LOW
RANGE FROM A SYSTEM OCCLUDING INTO CANADA SUCH AS SEEN IN THE NEW
12Z GFS TO A VERY SUPPRESSED WAVE ACROSS THE NORTHERN MID-ATLANTIC
PER THE 00Z ECMWF. THE 12Z GFS REPRESENTS A SIGNIFICANT CHANGE
FROM THE 00Z/06Z RUNS THAT TRACKED ACROSS SOUTHERN NEW ENGLAND.
ENSEMBLE MEANS HAVE BEEN SPLIT AS WELL, WITH THE CMCENS BECOMING
NORTHWEST AND OCCLUDED LIKE THE 12Z GFS, THE ECENS SUPPRESSED LIKE
ITS PARENT RUN, AND THE GEFS TRENDING FROM AN IN-BETWEEN 06Z RUN
TO A MORE OCCLUDED 12Z VERSION. GIVEN THE SPREAD AND VARIABILITY
AMONG LATEST GUIDANCE, PREFER AN INTERMEDIATE SOLUTION WITH
ADDITIONAL CONSIDERATION OF CONTINUITY THAT DEPICTED A SUPPRESSED
WAVE BUT NOT TO THE DEGREE OF THE 00Z ECMWF. ALSO OF NOTE, BY LATE
IN THE WEEK THE AVERAGE OF GUIDANCE HAS TRENDED A BIT SLOWER WITH
THE WAVY FRONT CROSSING THE EASTERN U.S. (WITH THE WAVE/S
INFLUENCE BY SHORTWAVE ENERGY TRACKING OUT OF THE WEST) AND THE
UPDATED BLEND REFLECTS THIS IDEA.
OVER THE WEST, A DEFAULT MODEL BLEND RESOLVES MINOR DETAIL
DIFFERENCES FOR THE LEADING SHORTWAVE THAT CROSSES THE REGION
TUESDAY-THURSDAY. THE NEXT SHORTWAVE THAT ARRIVES BY AROUND FRIDAY
HAS BEEN MORE TROUBLESOME FOR RESOLVING DETAILS, WITH A FAIRLY
WIDE SPREAD FOR HOW EMBEDDED ENERGY MAY BE DISTRIBUTED AS THE
AMPLIFYING TROUGH MOVES INLAND. SOME GFS/ECMWF RUNS OVER THE PAST
COUPLE DAYS OR SO HAVE BEEN SUGGESTING THAT SOME ENERGY IN THE
SOUTHERN PART OF THE UPPER TROUGH COULD PULL OFF TO FORM A CLOSED
LOW, WITH 00Z/12Z GFS RUNS THAT DID THIS TENDING TO BE MORE
PRONOUNCED IN DEPTH/SLOWNESS RELATIVE TO THE ECMWF RUNS. HOWEVER
THIS IDEA HAS TENDED TO BE A LITTLE LESS COMMON AMONG THE
ENSEMBLES, LEADING TO MOST MEANS MAINTAINING A PHASED TROUGH, AND
CMC RUNS HAVE KEPT THE SHORTWAVE OPEN. AMONG THE MEANS, THE 12Z/03
ECENS MEAN SHOWED THE MOST HINT AT SOUTHERN FLOW SEPARATION. WITH
THE 00Z/06Z GUIDANCE AS A WHOLE TILTING A LITTLE MORE AWAY FROM
THE SOUTHERN PART OF THE TROUGH SEPARATING, INCLUDING THE 06Z GFS
ADJUSTING FARTHER NORTHEAST WITH ITS UPPER LOW, FORECAST
PREFERENCE NUDGED A LITTLE IN THE PHASED DIRECTION. THE 12Z GFS
MAKES A DRAMATIC CHANGE IN FAVOR OF THIS IDEA AS IT CARRIES THE
CORE OF ITS DEEPEST ENERGY ACROSS THE NORTHWEST, AND THE 12Z ECMWF
NOW CARRIES A CLOSED OR NEARLY CLOSED LOW A LITTLE MORE SLOWLY
ACROSS THE SAME REGION.
FORECAST PREFERENCES LED TO STARTING WITH A 00Z/06Z OPERATIONAL
MODEL BLEND FOR THE FIRST HALF OF THE PERIOD AND THEN RAPIDLY
TRANSITIONING TOWARD 40-50 PERCENT TOTAL INPUT FROM THE 06Z
GEFS/00Z ECENS MEANS WITH THE REMAINDER COMING FROM MINORITY
COMPONENTS OF THE 06Z GFS AND 00Z ECMWF/CMC.
..WEATHER/HAZARDS HIGHLIGHTS
THE WESTERN U.S. CAN EXPECT PRECIPITATION TO CONTINUE INTO
TUESDAY, BUT WITH LESSENING AMOUNTS COMPARED TO THE SHORT RANGE
PERIOD. HIGHER ELEVATIONS LIKE THE CASCADES AND NORTHERN ROCKIES
ARE LIKELY TO SEE SNOW. PRECIPITATION SHOULD TREND MUCH LIGHTER
FOR THE WEST ON WEDNESDAY AS UPPER-LEVEL RIDGING BRIEFLY BUILDS
BACK IN, THOUGH THE CENTRAL ROCKIES COULD HAVE A PERIOD OF SNOW.
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.
FARTHER EAST, A COUPLE LOW PRESSURE AND FRONTAL SYSTEMS TRACKING
THROUGH THE MIDWEST/GREAT LAKES REGION TO NORTHEAST SHOULD BRING
ROUNDS OF PRECIPITATION NEXT WEEK. A LEADING SYSTEM EXITING NEW
ENGLAND AFTER TUESDAY WILL BRING MOSTLY LIGHT TOTALS AND A BRIEF
PERIOD OF BREEZY CONDITIONS. AMOUNTS AND NORTH-SOUTH EXTENT OF
PRECIPITATION REMAIN UNCERTAIN WITH THE NEXT WAVE FORECAST TO
PROGRESS NORTHEASTWARD FROM THE CENTRAL PLAINS MID-LATE WEEK, WITH
SOME CONNECTING SURFACE REFLECTION POTENTIALLY EXTENDING NORTH
INTO CANADA. AFTER EARLY THURSDAY GUIDANCE DIVERGES ON THE
STRUCTURE OF THIS SYSTEM, INCREASING THE UNCERTAINTY IN
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. LIGHT LAKE EFFECT
PRECIPITATION WILL BE POSSIBLE AFTER THIS SYSTEM PASSES. SOME RAIN
IS POSSIBLE FARTHER SOUTHWEST ALONG THE FRONTAL CORRIDOR, WITH THE
BEST CHANCE FOR HIGHER RAINFALL TOTALS LATE IN THE WEEK OVER
SOUTHERN TEXAS WHERE THE AVAILABLE MOISTURE WILL BE THE HIGHEST.
MUCH OF THE EASTERN TWO-THIRDS OF THE COUNTRY WILL SEE ABOVE
AVERAGE TEMPERATURES AS THE PERIOD BEGINS TUESDAY, WITH THE
GREATEST ANOMALIES OF 15-25F FOR HIGHS ACROSS THE SOUTHERN HIGH
PLAINS AS TEMPERATURES RISE WELL INTO THE 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
TUESDAY-THURSDAY, WITH WARMER THAN AVERAGE TEMPERATURES ACROSS THE
GULF COAST STATES AS WELL. DAILY RECORD HIGH TEMPERATURES COULD BE
SET FROM THE SOUTH-CENTRAL TO SOUTHEASTERN U.S. ESPECIALLY ON
TUESDAY AND 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.
RAUSCH/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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