424
FXUS02 KWBC 111927
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
326 PM EDT MON SEP 11 2023
VALID 12Z THU SEP 14 2023 - 12Z MON SEP 18 2023
..HURRICANE LEE LOOMS OVER THE WESTERN ATLANTIC
..HEAVY RAINFALL THREAT FOR THE SOUTH-CENTRAL ROCKIES/PLAINS
..OVERVIEW
IT REMAINS THE CASE THAT THE MODELS AND ENSEMBLES AGREE FAIRLY
WELL ON THE IDEA OF A STRONG UPPER RIDGE BUILDING OVER THE WEST
LATE THIS WEEK INTO THE START OF NEXT WEEK, WHILE DEPARTING
WESTERN U.S. SHORTWAVE ENERGY AND SOUTHERN CANADA ENERGY COMBINE
TO YIELD AN AMPLIFYING UPPER TROUGH OVER THE EASTERN HALF OF THE
COUNTRY. AHEAD OF THIS DEVELOPING TROUGH, A LEADING UPPER
LOW/TROUGH WILL EJECT ACROSS SOUTHEASTERN CANADA AND THE
NORTHEASTERN U.S. LATE THIS WEEK. PRECISE UPPER FLOW DETAILS NEAR
THE EAST COAST AND SPECIFICS OF RIDGING FARTHER EAST OVER THE
ATLANTIC WILL BE IMPORTANT IN DETERMINING THE EXACT TRACK AND
TIMING OF HURRICANE LEE AND CORRESPONDING EFFECTS ON NEW ENGLAND
AND ESPECIALLY THE CANADIAN MARITIMES THAT MAY PROVE SIGNIFICANT.
THE INITIAL SHORTWAVE ENERGY OVER THE WEST INTO THE PLAINS ALONG
WITH EASTERLY LOW LEVEL FLOW OVER PARTS OF THE SOUTHERN PLAINS
WILL HELP TO GENERATE AREAS OF RAIN AND THUNDERSTORMS THAT COULD
BE LOCALLY HEAVY OVER THE SOUTH-CENTRAL ROCKIES PLAINS. COOLER
THAN AVERAGE HIGHS PREVAILING OVER A MAJORITY OF THE
CENTRAL/EASTERN U.S. LATE THIS WEEK SHOULD MODERATE SOME BY THE
WEEKEND WHILE ABOVE NORMAL HIGHS SHOULD BECOME ESTABLISHED OVER
THE PACIFIC NORTHWEST INTO NORTHERN HIGH PLAINS LATE THIS WEEK
INTO THE START OF NEXT WEEK.
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
THE MAIN WEATHER STORY WILL LIKELY TURN TO HURRICANE LEE WHOSE
NORTHWARD LIFTING IN MOST GUIDANCE OVER THE WESTERN ATLANTIC THIS
WEEK COULD LEAD TO A TRACK OFFSHORE NEW ENGLAND TO THE CANADIAN
MARITIMES BY THE WEEKEND. RELATIVE TO THE FULL RANGE OF GUIDANCE,
RECENT GFS RUNS HAVE LEANED SOMEWHAT ON THE WESTERN SIDE OF THIS
FORECAST ENVELOPE, BUT THE 12 UTC GFS HAS SHIFTED SOME EAST.
RECENT ECMWF/ECENS/UKMET/CANADIAN SOLUTIONS SEEMED MORE PREFERABLE
AS THEY WERE BETTER IN LINE WITH THE NHC TRACK FORECAST AND WERE
DECENTLY CLUSTERED FOR MUCH OF THE REST OF THE LOWER 48 INTO THE
WEEKEND, BUT THE CAVEAT IS THAT THE 12 UTC ECMWF IN PARTICULAR HAS
TRENDED FASTER WITH LEE. MODEL AND ENSEMBLE MEMBERS STILL SHOW
INCREASING DETAIL SPREAD WITHIN THE OVERALL TROUGH AMPLIFYING OVER
THE EAST-CENTRAL U.S. LATER WEEKEND/MONDAY. POSSIBILITIES RANGE
BETWEEN AN OPEN TROUGH AND ONE OR MORE EMBEDDED LOWS ANYWHERE
BETWEEN THE MIDWEST/GREAT LAKES AND CANADA. POOR CLUSTERING AND
RUN-TO-RUN VARIABILITY STILL FAVORS A CONSERVATIVE APPROACH MORE
LIKE THE OPEN TROUGH OF THE GEFS/ECENS ENSEMBLE MEANS AT THESE
LONGER TIME FRAMES.
..WEATHER/HAZARDS HIGHLIGHTS
DURING THE DAY 4 EXCESSIVE RAINFALL OUTLOOK PERIOD OF
THURSDAY-THURSDAY NIGHT THERE SHOULD BE A BROAD AREA OF RAIN AND
THUNDERSTORM POTENTIAL FROM THE CENTRAL HALF OF THE ROCKIES INTO
THE SOUTHERN PLAINS, WITH ONE AREA OF SHORTWAVE ENERGY OVER THE
GREAT BASIN AND SOME WEAK IMPULSES FLOWING INTO THE PLAINS.
EASTERLY LOW LEVEL FLOW DIRECTED OVER THE SOUTHERN HIGH PLAINS
INTO A POTENTIAL SURFACE TROUGH MAY ALSO SUPPORT CONVECTION. A
MARGINAL RISK AREA ENCOMPASSES THIS OVERALL REGION THAT COULD SEE
LOCALLY HEAVY RAINFALL. THERE ARE TWO EMBEDDED SLIGHT RISK AREAS
THAT REFLECT THE BEST COMBINATION OF GUIDANCE SIGNALS/PARAMETERS.
ONE IS OVER THE SOUTHWESTERN OKLAHOMA/NORTHERN TEXAS, REFLECTING
SOME INDICATION THAT ENHANCED CONVECTION COULD EXTEND
NORTHWESTWARD VERSUS PRIOR ERO ISSUANCE. ESPECIALLY THE WESTERN
PART OF THIS SLIGHT RISK AREA IS EXPECTED TO HAVE MEANINGFUL
RAINFALL BEFORE DAY 4. MEANWHILE A SEPARATE SLIGHT RISK AREA
CENTERED MOSTLY OVER WYOMING WAS INTRODUCED, WITH GUIDANCE
STARTING TO SHOW A MORE PRONOUNCED SIGNAL FOR A SLOW MOVING GREAT
BASIN SHORTWAVE AND ANOMALOUS MOISTURE COMBINING TO SUPPORT
LOCALIZED HEAVY RAINFALL POTENTIAL. THE DAY 5 EXCESSIVE RAINFALL
OUTLOOK THAT COVERS FRIDAY-FRIDAY NIGHT DEPICTS A MARGINAL RISK
AREA FROM THE CENTRAL HIGH PLAINS INTO PARTS OF TEXAS. CONVECTION
SHOULD CONTINUE INTO THIS TIME FRAME BUT MOST GUIDANCE SHOWS SOME
DECREASE IN MOISTURE ANOMALIES AND THE BEST FOCUS FOR RAINFALL
BECOMES LESS DEFINED.
SOME RAIN/THUNDERSTORMS SHOULD CONTINUE OVER PARTS OF THE SOUTHERN
ROCKIES/PLAINS AND PERHAPS THE SOUTH BEYOND EARLY SATURDAY BUT
LIKELY WITH LESS COVERAGE AND LIGHTER TOTALS. MEANWHILE A FRONT
SETTLING OVER THE FLORIDA PENINSULA MAY PRODUCE ONE OR MORE DAYS
OF RAIN OVER THAT REGION. OVER NEW ENGLAND, EXPECT ANY LINGERING
RAIN FROM THE MIDWEEK SYSTEM TO DEPART ON THURSDAY. CONTINUE TO
MONITOR NATIONAL HURRICANE CENTER PRODUCTS REGARDING THE TRACK OF
HURRICANE LEE AND POTENTIAL EFFECTS ON NEW ENGLAND AND THE
CANADIAN MARITIMES BY LATE WEEK AND THE WEEKEND. UNCERTAINTY WITH
DETAILS FOR THE UPPER TROUGH EVOLVING OVER THE EASTERN HALF OF THE
COUNTRY DURING THE WEEKEND AND EARLY NEXT WEEK KEEPS CONFIDENCE
LOW FOR WHAT THE SURFACE PATTERN MAY LOOK LIKE ALONG WITH ANY
AREAS OF RAINFALL, THOUGH INTO FRIDAY OR SO A FRONT REACHING THE
UPPER MIDWEST COULD PRODUCE SOME AREAS OF MOSTLY LIGHT RAIN.
BELOW NORMAL HIGH TEMPERATURES WILL PREVAIL OVER MOST OF THE
ROCKIES, CENTRAL/SOUTH-CENTRAL PLAINS, AND MUCH OF THE EAST LATE
THIS WEEK. EXPECT COOLEST READINGS UP TO 10-15F BELOW NORMAL OVER
PARTS OF THE ROCKIES AND SOUTH-CENTRAL PLAINS WHERE
CLOUDS/RAINFALL SHOULD BE MOST PERSISTENT. THE GREAT LAKES/OHIO
VALLEY/APPALACHIANS SHOULD SEE HIGHS 5-10F OR SO BELOW NORMAL
BEHIND THE COLD FRONT PUSHING OFF THE EAST COAST ON THURSDAY.
TEMPERATURES SHOULD MODERATE SATURDAY-MONDAY, REACHING NEAR NORMAL
BY EARLY NEXT WEEK. CONTINUED HOT WEATHER WITH HIGHS UP TO 5-10F
ABOVE NORMAL WILL BE POSSIBLE OVER SOUTHERN TEXAS THROUGH LATE
WEEK BEFORE A COOLER TREND. THE UPPER RIDGE BUILDING INTO THE
WEST WILL SUPPORT HIGHS 10F OR MORE ABOVE NORMAL OVER THE PACIFIC
NORTHWEST FROM LATE WEEK THROUGH THE WEEKEND, WITH A BROADER AREA
OF MORNING LOWS 5-15F ABOVE NORMAL ACROSS THE WEST. SOME OF THIS
WARMTH MAY EXTEND INTO THE NORTHERN HIGH PLAINS WHILE THE PACIFIC
NORTHWEST MAY START TO SEE A COOLER TREND BY NEXT MONDAY AS A
PACIFIC FRONT APPROACHES.
SCHICHTEL/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
HAZARDS:
- HEAVY RAIN ACROSS PORTIONS OF THE CENTRAL ROCKIES, THE CENTRAL
PLAINS, THE SOUTHERN PLAINS, AND
THE NORTHERN PLAINS, THU, SEP 14.
- HEAVY RAIN ACROSS PORTIONS OF THE NORTHEAST, SAT-SUN, SEP 16-SEP
17.
- FLOODING LIKELY ACROSS PORTIONS OF THE SOUTHEAST.
- HIGH WINDS ACROSS PORTIONS OF THE NORTHEAST, SAT-SUN, SEP 16-SEP
17.
- HIGH SIGNIFICANT WAVE HEIGHTS FOR COASTAL PORTIONS OF THE
NORTHEAST, SAT, SEP 16.
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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