149
FXUS02 KWBC 170700
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
200 AM EST FRI NOV 17 2023
VALID 12Z MON NOV 20 2023 - 12Z FRI NOV 24 2023
..PATTERN OVERVIEW
THE DOMINANT FOCUS OF NEXT WEEK'S FORECAST WILL BE A DEEPENING
STORM SYSTEM FORECAST TO TRACK FROM THE SOUTH-CENTRAL PLAINS
THROUGH THE GREAT LAKES AND INTO EAST-CENTRAL CANADA, IN RESPONSE
TO DIGGING WESTERN CANADA ENERGY THAT PHASES WITH AN INITIAL
PLAINS UPPER LOW/TROUGH. THIS INTERACTION SHOULD YIELD A DEEP
UPPER LOW SOMEWHERE BETWEEN THE UPPER MIDWEST/GREAT LAKES AND
SOUTHERN CANADA BY WEDNESDAY. THE UPPER LOW AND TROUGH TO THE
SOUTH SHOULD GRADUALLY LIFT NORTHWARD LATE IN THE WEEK WHILE A
SHORTWAVE TROUGH MOVES INTO THE WEST. THE WINDY STORM SYSTEM WILL
LIKELY PRODUCE SIGNIFICANT PRECIPITATION OVER THE EASTERN HALF OF
THE COUNTRY DURING THE FIRST HALF OF THE WEEK, FOLLOWED BY AN
EXPANDING AREA OF BELOW NORMAL TEMPERATURES OVER MANY AREAS EAST
OF THE ROCKIES WITH SOME SNOW POSSIBLE TO THE LEE OF THE GREAT
LAKES. THE WEST WILL BE FAIRLY DRY BUT NORTHERN AREAS MAY SEE SOME
LIGHT PRECIPITATION AS THE LATE WEEK TROUGH MOVES IN.
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
BASED ON THE 12Z/18Z GUIDANCE, THE PRIMARY CONSIDERATION DURING
THE FIRST HALF OF THE PERIOD WAS TO EXCLUDE THE UKMET AS ITS
NORTHERN STREAM PATTERN FROM THE PACIFIC THROUGH NORTH AMERICA
STRAYED TO THE FAST SIDE. THIS LEFT AN AVERAGE OF THE 18Z GFS, 12Z
ECMWF, AND 12Z CMC TO PROVIDE A REASONABLE DEPICTION OF CONSENSUS
IDEAS FOR THE PLAINS THROUGH GREAT LAKES STORM SYSTEM. THIS
SOLUTION DID YIELD A SLIGHTLY SLOWER TREND FOR THE PORTION OF THE
TRAILING FRONT CROSSING THE SOUTHERN TIER TO THE EAST COAST. AMONG
THE NEW 00Z RUNS, THE UKMET IS STILL RUNNING ON THE PROGRESSIVE
SIDE IN THE NORTHERN STREAM WHILE THE GFS IS A SOUTHWESTERN
EXTREME WITH ITS UPPER LOW AS OF EARLY WEDNESDAY (LEADING TO A
FARTHER SOUTH SURFACE LOW). BOTH THE 18Z AND 00Z GFS RUNS HOLD
ONTO MORE TROUGHING OVER THE CANADIAN MARITIMES VERSUS MOST OTHER
GUIDANCE BY TUESDAY-WEDNESDAY, SLOWING FRONTAL PROGRESSION OVER
THE NORTHEAST AFTER EARLY WEDNESDAY. HOWEVER DIFFERENCES ARE STILL
WITHIN TYPICAL SPREAD FOR FIVE DAYS OUT IN TIME THUS ALLOWING FOR
KEEPING THE GFS AS PART OF A COMPROMISE. LATER IN THE PERIOD, THE
00Z GFS TRACKS ITS EASTERN UPPER LOW FARTHER SOUTHEAST THAN
CONSENSUS WHILE A MODEL/MEAN COMPOSITE OFFERS A GOOD STARTING
POINT FOR THE UPPER TROUGH MOVING INTO THE WEST THURSDAY-FRIDAY. A
MODEL/MEAN BLEND ALSO MITIGATES DETAIL DIFFERENCES THAT DEVELOP IN
SOME SOLUTIONS FOR FLOW NEAR THE WESTERN HALF OF THE CANADIAN
BORDER. THUS THE INITIAL GFS/ECMWF/CMC BLEND TRANSITIONED TO
INCLUDE SOME OF THE 18Z GEFS/12Z ECENS MEANS AFTER MIDWEEK.
..WEATHER/HAZARDS HIGHLIGHTS
HEAVY RAINFALL POTENTIAL WILL INCREASE ACROSS THE SOUTH-CENTRAL TO
EASTERN U.S. FOR THE UPCOMING HOLIDAY WEEK AS A DEEPENING LOW
PRESSURE SYSTEM TRACKS FROM THE SOUTH-CENTRAL PLAINS THROUGH THE
GREAT LAKES. ALSO THE TIGHTENING PRESSURE GRADIENT BEHIND THE LOW
SHOULD PRODUCE A PERIOD OF HIGH WINDS ACROSS THE HIGH PLAINS EARLY
NEXT WEEK, WITH LESS EXTREME BUT STILL BRISK TO STRONG WINDS
ACROSS THE PLAINS AND INTO THE GREAT LAKES. INSTABILITY AHEAD OF
THE SYSTEM COULD BRING SEVERE WEATHER POTENTIAL TO THE CENTRAL
GULF COAST AROUND MONDAY, AS HIGHLIGHTED BY STORM PREDICTION
CENTER OUTLOOKS. WITH THE SOUTHERN TIER CONVECTIVE POTENTIAL, THE
DAY 4 EXCESSIVE RAINFALL OUTLOOK COVERING MONDAY-MONDAY NIGHT
MAINTAINS A MARGINAL RISK AREA FROM THE PRIOR DAY 5 OUTLOOK TO
REFLECT THE ONGOING SIGNAL FOR ORGANIZED AND POSSIBLY HEAVY
RAINFALL. THE MAIN ADJUSTMENT IN THIS CYCLE IS TO ACCOUNT FOR A
SLIGHTLY SLOWER FRONTAL PROGRESSION. FOR THE NEW DAY 5 ERO
(TUESDAY-TUESDAY NIGHT), A MARGINAL RISK AREA HAS BEEN DEPICTED
FROM THE MID-ATLANTIC SOUTHWEST INTO ALABAMA AS ABUNDANT MOISTURE
SHOULD STREAM INTO THE SOUTHERN AND EASTERN U.S. AHEAD OF THE
MISSISSIPPI VALLEY-GREAT LAKES STORM/FRONTAL SYSTEM. WHILE
ACTIVITY WILL BE FAIRLY PROGRESSIVE AND GROUND CONDITIONS WILL
START OUT ON THE DRY SIDE, LOCALIZED RUNOFF ISSUES WILL BE
POSSIBLE. WITHIN THIS OVERALL AREA, THE MID-ATLANTIC MAY BE A
LITTLE MORE SENSITIVE GIVEN THE COMBINATION OF HIGHEST QPF SIGNALS
IN MODEL/ENSEMBLE GUIDANCE AND POTENTIAL FOR IMPAIRED DRAINAGE DUE
TO LEAVES/ETC. PRECIPITATION WILL CONTINUE THROUGH NEW ENGLAND BY
MIDWEEK. SNOW WILL BE POSSIBLE ON THE FAR NORTHWEST PERIPHERY OF
THE MOISTURE SHIELD, AND POTENTIALLY IN NEW ENGLAND AT THE START
OF THE EVENT. A PERIOD OF LAKE EFFECT SNOW WILL BE POSSIBLE AFTER
SYSTEM PASSAGE, WITH DURATION AND TOTALS DEPENDENT ON HOW QUICKLY
THE SYSTEMS LIFTS AWAY. THE ROCKIES MAY SEE LINGERING
PRECIPITATION EARLY IN THE WEEK. OTHERWISE THE WEST SHOULD BE DRY
EARLY-MID WEEK. A SYSTEM MOVING INTO THE REGION LATE IN THE WEEK
MAY BRING MOSTLY LIGHT TOTALS ACROSS NORTHERN AREAS, POSSIBLY
EXTENDING INTO THE PLAINS FRIDAY.
THE MAIN STORY FOR TEMPERATURES WILL BE THE INCREASING COVERAGE OF
BELOW NORMAL READINGS FROM THE NORTHERN-CENTRAL HIGH PLAINS
EASTWARD MID-LATE WEEK. BY THAT TIME EXPECT LOCATIONS FROM THE
HIGH PLAINS INTO GREAT LAKES TO SEE ONE OR MORE DAYS WITH HIGHS
10-20F BELOW NORMAL. THE WEST WILL TREND FROM NEAR OR SLIGHTLY
BELOW NORMAL EARLY IN THE WEEK TO MODERATELY ABOVE NORMAL
WEDNESDAY, AND THEN DRIFT BACK TO NEAR OR SLIGHTLY BELOW NORMAL
TOWARD THE END OF THE WEEK.
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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