962
FXUS02 KWBC 190700
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
200 AM EST SUN NOV 19 2023
VALID 12Z WED NOV 22 2023 - 12Z SUN NOV 26 2023
..PATTERN OVERVIEW
BEHIND A SYSTEM FORECAST TO TRACK OVER/NEAR NEW ENGLAND ON
WEDNESDAY, AN UPPER RIDGE OVER THE WEST WILL QUICKLY GIVE WAY TO A
SHORTWAVE TROUGH WHILE AN UPPER RIDGE SETTING UP OVER THE EASTERN
PACIFIC/NORTHWESTERN NORTH AMERICA WILL ULTIMATELY TEND TO FAVOR
INCREASINGLY LARGE SCALE TROUGHING THAT SHOULD BE ALIGNED FROM
NEAR HUDSON BAY SOUTHWEST INTO THE WESTERN U.S. BY THE END OF NEXT
WEEKEND. EXPECT THIS EVOLUTION TO BRING COLDER TEMPERATURES TO
THE CENTRAL U.S. IN PARTICULAR BY FRIDAY-SUNDAY, WITH MANY OTHER
AREAS TRENDING COOLER AS WELL. THE NEW ENGLAND SYSTEM WILL BRING
SOME PRECIPITATION TO THE EAST COAST WHILE THE TROUGH REACHING THE
WEST BY THANKSGIVING WILL SPREAD AN AREA OF SNOW ACROSS THE
NORTH-CENTRAL ROCKIES. SOME OF THIS MOISTURE MAY CONTINUE
EASTWARD BY NEXT WEEKEND WITH A WAVE/FRONTAL SYSTEM WHILE A
POTENTIAL LEADING WAVE COULD ALSO SPREAD SOME PRECIPITATION CLOSER
TO THE EAST COAST. THERE IS ALSO A VERY UNCERTAIN POTENTIAL OF
SOME SOUTHERN EASTERN U.S. RAINFALL FROM A WAVE BEHIND THE LEADING
EAST COAST SYSTEM.
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
THE MODELS AND ENSEMBLES CONTINUE TO HAVE DIFFICULTY IN RESOLVING
IMPORTANT DETAILS OF THE FORECAST. THIS INCLUDES THE FORECAST OF
INITIAL TROUGH ENERGY REACHING THE EASTERN U.S. BY MIDWEEK AND HOW
CORRESPONDING EAST COAST LOW PRESSURE EVOLVES, TRAILING NORTHERN
MEXICO TROUGH ENERGY AND ITS ROLE IN THE SURFACE/QPF PATTERN, AS
WELL AS THE COMBINATION OF THE MEAN UPPER LOW OVER
CANADA/SURROUNDING FLOW PLUS TROUGHING THAT MOVES INTO THE WEST.
GIVEN THE DIVERGENT MODEL SOLUTIONS, THE UPDATED FORECAST USING
12Z/18Z DATA AGAIN RELIED MORE THAN USUAL ON THE 18Z GEFS/12Z
ECENS MEANS, ADDING IN SOME 12Z ECMWF EARLY IN THE PERIOD AND SOME
18Z GFS MID-LATE PERIOD AFTER ITS QUESTIONABLE TRAITS OVER THE
NORTHEAST (BRINGING ACROSS MUCH LOWER HEIGHTS THAN CONSENSUS) EXIT
THE FORECAST DOMAIN.
GUIDANCE STILL HAS NO COHERENT IDEAS FOR EXACTLY HOW TROUGH ENERGY
MOVING INTO THE EAST WILL LOOK AT THE START OF THE PERIOD
WEDNESDAY. THE GFS/UKMET STILL DIG MORE NORTHERN STREAM ENERGY
INTO THE SOUTHERN TIER U.S. BY THE START OF THE PERIOD, LEADING TO
A FARTHER SOUTH TRACK OF LOW PRESSURE NEAR NEW ENGLAND (EAST OF
CAPE COD) BY EARLY THURSDAY. IN CONTRAST, THE 00Z CMC IS A FAST
EXTREME, WELL INTO THE CANADIAN MARITIMES. THE ENSEMBLE MEANS
PROVIDE A REASONABLE INTERMEDIATE AND MORE CONSISTENT SOLUTION FOR
THE TIME BEING.
OVER THE PAST DAY OR SO THERE HAS BEEN A GRADUALLY INCREASING
SIGNAL FOR NORTHERN MEXICO ENERGY TO EJECT NORTHEASTWARD BY THE
LATTER HALF OF THE WEEK, BUT WITH VERY DIFFERENT IMPACTS IN TERMS
OF THE SURFACE REFLECTION AND RESULTING QPF. IN GENERAL THE
LATEST CMC RUNS HAVE BEEN MOST PRONOUNCED WITH ASSOCIATED SURFACE
WAVINESS AND RAINFALL AMOUNTS/COVERAGE. INTERESTINGLY, THE 12Z
CYCLE OF ECMWF-INITIALIZED MACHINE LEARNING MODELS SHOW A
WELL-DEFINED SOUTHERN STREAM UPPER LOW/TROUGH PROGRESSING ALONG
FASTER THAN THE CURRENT CLUSTER OF DYNAMICAL GUIDANCE, BUT WITH NO
HINT OF A GFS/UKMET TYPE EVOLUTION EITHER.
GUIDANCE STILL SHOWS SOME SPREAD FOR THE UPPER TROUGH ARRIVING
INTO THE WEST AND THEN HOW NORTHERN STREAM FLOW (PLUS THE
CANADIAN/NORTHERN TIER TROUGH) MAY INTERACT. THERE WAS SOME
IMPROVED CLUSTERING AS NEW 00Z RUNS WERE COMING IN BUT THE ECMWF
HAS TRENDED TO A MORE PRONOUNCED CLOSED LOW AND GREATER STREAM
SEPARATION THAN MOST OTHER GUIDANCE BY LATE FRIDAY. WITH A FAIR
AMOUNT OF VARIABILITY, THERE HAS BEEN A GENERAL SIGNAL IN
MODELS/MEANS TOWARD A WAVY FRONTAL SYSTEM REACHING THE
EAST-CENTRAL U.S. BY SATURDAY AND MORE RECENTLY A LEADING WAVE
NEAR THE EAST COAST. THESE FEATURES SHOULD CONTINUE ONWARD INTO
SUNDAY.
..WEATHER/HAZARDS HIGHLIGHTS
WHILE THERE IS STILL LOWER THAN AVERAGE CONFIDENCE FOR HOW THE
SYSTEM AFFECTING NEW ENGLAND ON WEDNESDAY (AND WITH LOWER
PROBABILITY INTO THANKSGIVING) MAY EVOLVE/TRACK, POTENTIAL STILL
EXISTS FOR A PERIOD OF STRONG ONSHORE FLOW OVER PARTS OF EASTERN
NEW ENGLAND. THE NEW DAY 4 EXCESSIVE RAINFALL OUTLOOK THAT COVERS
THE WEDNESDAY-WEDNESDAY NIGHT PERIOD MAINTAINS A MARGINAL RISK
AREA OVER EASTERN NEW ENGLAND TO REFLECT THE POSSIBILITY THAT ANY
ENHANCED BANDS OF RAINFALL COULD LEAD TO LOCALIZED RUNOFF ISSUES
WHERE DRAINAGE IS IMPAIRED DUE TO URBANIZATION/LEAVES/ETC.
HOWEVER INITIALLY DRY SOIL CONDITIONS SHOULD OTHERWISE TEMPER WHAT
THREATS MAY EXIST.
ELSEWHERE, SNOW WILL BE POSSIBLE OVER PARTS OF INTERIOR NEW
ENGLAND WITH THE WEDNESDAY SYSTEM AND A BRIEF PERIOD OF LAKE
EFFECT SNOW WILL BE POSSIBLE AFTER SYSTEM PASSAGE. WITH VERY
UNCERTAIN DETAILS, A TRAILING WAVE MAY PRODUCE SOME RAINFALL OVER
PARTS OF THE SOUTH/EAST DURING THE LATTER HALF OF THE WEEK. OVER
THE WEST, A SYSTEM MOVING INTO THE REGION LATE IN THE WEEK SHOULD
BRING AN AREA OF SNOW ACROSS THE NORTH-CENTRAL ROCKIES ESPECIALLY
AROUND THANKSGIVING, WITH SOME LOCALIZED ENHANCEMENT POSSIBLE.
SOME RAIN/SNOW MAY EXTEND EAST OF THE ROCKIES THEREAFTER WITH A
WAVY FRONTAL SYSTEM EVENTUALLY REACHING THE EAST AND A SEPARATE
COASTAL WAVE COULD ALSO SPREAD MOISTURE OVER PARTS OF THE EAST.
COLDER AIR DROPPING SOUTH OVER THE PLAINS/EASTERN SLOPES OF THE
ROCKIES FROM FRIDAY INTO THE WEEKEND SHOULD SHOULD BRING HIGHS
DOWN TO 10-20F BELOW NORMAL OVER THAT REGION. BELOW NORMAL
ANOMALIES WILL SPREAD ELSEWHERE AS WELL, WITH THE INTERIOR WEST
HIGHS TRENDING TO 5-10F BELOW NORMAL LATE WEEK INTO THE WEEKEND
AND THE MISSISSIPPI VALLEY PLUS PARTS OF THE OHIO VALLEY AT LEAST
10F BELOW NORMAL BY SUNDAY. THIS WILL BE A SIGNIFICANT CHANGE
FROM ABOVE NORMAL TEMPERATURES OVER THE HIGH PLAINS INTO THE WEST
ON WEDNESDAY. THE SOUTH AND EAST WILL SEE A BRIEF PERIOD OF BELOW
NORMAL TEMPERATURES AND FOLLOWED BY A REBOUND TOWARD NORMAL VALUES.
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 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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