267
FXUS02 KWBC 141845
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
245 PM EDT THU SEP 14 2023
VALID 12Z SUN SEP 17 2023 - 12Z THU SEP 21 2023
..OVERVIEW
AN UPPER TROUGH AMPLIFYING OVER THE MIDWEST SUNDAY IN THE WAKE OF
LEE WILL REACH THE EASTERN SEABOARD MONDAY BEFORE LIFTING OVER THE
NORTHEAST BY TUESDAY. THE FRONT ASSOCIATED WITH THIS TROUGH SHOULD
PRODUCE AREAS OF RAIN WITH VARYING INTENSITY OVER THE SOUTHEAST
AND MID-ATLANTIC SUNDAY WITH LAKE EFFECT RAIN OFF THE EASTERN
GREAT LAKES SUNDAY INTO MONDAY. A PERSISTENT WAVY FRONT SHOULD
MAINTAIN A WET PATTERN OVER THE FLORIDA PENINSULA THROUGH NEXT
WEEK. OVER THE WEST, GUIDANCE CONTINUES TO ADVERTISE A SIGNIFICANT
PATTERN CHANGE AFTER INITIAL RIDGING WEAKENS AND PROGRESSES
EASTWARD, WITH A TROUGH AND LEADING COLD FRONT BRINGING SOME
MOISTURE INTO THE PACIFIC NORTHWEST AND NORTHERN ROCKIES. ABOVE
NORMAL TEMPERATURES OVER THE INTERIOR NORTHWEST AND NORTHERN HIGH
PLAINS ON SUNDAY WILL SHIFT EASTWARD ACROSS THE NORTHERN TIER
WHILE MOST OF THE WEST SEES A PRONOUNCED COOLING TREND.
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
A FAIRLY QUIET WEATHER PATTERN FOR THE CONUS FOR THIS TIME OF YEAR
DEVELOPS THIS WEEKEND WITH A TROUGH OVER THE EAST IN THE WAKE OF
LEE, A BROAD RIDGE DRIFTING EAST OVER THE WEST-CENTRAL PORTIONS,
THEN RENEWED TROUGHING OVER THE NORTHWEST AROUND MIDWEEK. THERE
WAS DECENT AGREEMENT AMONG 00Z/06Z GUIDANCE ALLOWING THE FORECAST
TO RELY ON DETERMINISTIC INPUTS FROM THE 00Z ECMWF/CMC/UKMET AND
06Z GFS THROUGH DAY 5, THEN MIXING IN SOME 00Z ECENS/06Z GEFS
MEANS FOR DAYS 6/7.
THE MAIN FORECAST DIFFERENCES ARE WITH THE PLACEMENT AND DEPTH OF
THE TROUGH BUILDING OVER THE NORTHWEST TO THE INTERMOUNTAIN WEST
TUESDAY THROUGH THURSDAY. THE GFS IS FARTHER EAST, BRINGING MORE
PRECIP TO THE NORTHERN ROCKIES WHILE THE ECMWF IS A BIT FARTHER
WEST (AND THE CMC EVEN FARTHER WEST AND MORE CLOSED/ OFF).
HOWEVER, THE DIFFERENCES WERE NOT GREAT ENOUGH TO ELIMINATE ANY
FROM THE FORECAST BLEND.
..WEATHER/HAZARDS HIGHLIGHTS
THERE IS A LESS THAN 5% RISK FOR AREAS OF ORGANIZED FLASH FLOOD IN
THE DAYS 4-5 EXCESSIVE RAINFALL OUTLOOKS COVERING SUNDAY THROUGH
MONDAY NIGHT.
A SERIES OF FRONTS STALLING OVER THE FLORIDA PENINSULA WILL
MAINTAIN A FAIRLY WET PATTERN. HOWEVER MOISTURE ANOMALIES ARE ONLY
MODERATELY ABOVE NORMAL, FLASH FLOOD GUIDANCE VALUES ARE HIGH, AND
MODELS DO NOT SHOW MUCH CLUSTERING FOR ANY RELATIVELY HEAVIER RAIN
THAT MAY FALL. SHORTER TERM GUIDANCE MAY ULTIMATELY HELP TO REFINE
ANY AREAS THAT COULD AT LEAST MERIT A MARGINAL RISK. ON SUNDAY,
THERE WILL BE SOME LINGERING MOISTURE AND INSTABILITY NEAR THE RIO
GRANDE FROM TEXAS INTO NEW MEXICO, BUT ORGANIZED HEAVY RAIN IS NOT
EXPECTED. A COLD FRONT PUSHING THROUGH THE APPALACHIANS/SOUTHEAST
SUNDAY INTO MONDAY MAY PRODUCE SOME LOCALLY ENHANCED RAINFALL BUT
AVAILABLE MOISTURE LOOKS NEAR CLIMATOLOGY.
THE FLORIDA PENINSULA SHOULD CONTINUE TO SEE PERIODS OF RAIN
BEYOND MONDAY DUE TO THE WAVY FRONT, WITH HEAVIER AMOUNTS STILL
TENDING TO BE LOCALIZED. THE SOUTHEAST COAST MAY BE NEAR THE EDGE
OF RAINFALL THAT PERSISTS OVER THE WESTERN ATLANTIC. UPPER
TROUGHING EXPECTED TO AMPLIFY OVER THE WEST NEXT WEEK MAY BRING
SOME PRECIPITATION TO AT LEAST THE PACIFIC NORTHWEST AND NORTHERN
ROCKIES WITH TIMING DIFFERENCES AMONG GUIDANCE. HIGH ELEVATIONS IN
THE NORTHERN ROCKIES WOULD SEE SOME SNOW IF THE UPPER TROUGH AND
POSSIBLE EMBEDDED LOW ARE DEEP ENOUGH. AHEAD OF THE WESTERN
TROUGH/LOW, AREAS OF RAIN WILL LIKELY DEVELOP UP THE SOUTHERN
PLAINS TUESDAY-THURSDAY. WITH A PROLONGED FETCH FROM THE WESTERN
GULF DURING THIS TIME, HEAVY RAINFALL MAY BECOME ORGANIZED,
PARTICULARLY AROUND WEDNESDAY.
AN AREA OF HIGH TEMPERATURES UP TO 15F ABOVE NORMAL SHIFTS FROM
THE INTERIOR NORTHWEST/HIGH PLAINS ON SUNDAY WILL DRIFT EAST WITH
THE RIDGE AXIS, REACHING ONLY THE GREAT LAKES BY THURSDAY. THE
UPPER TROUGH FORECAST TO AMPLIFY OVER THE WEST NEXT WEEK SHOULD
PROMOTE A COOLING TREND OVER THE REGION STARTING TUESDAY, WITH
HIGH TEMPS 5-15F BELOW NORMAL STRETCHING FROM MT TO SOUTHERN CA BY
NEXT THURSDAY. OTHERWISE EXPECT MOST TEMPERATURE ANOMALIES TO BE
IN THE SINGLE DIGITS, INCLUDING THE EAST LEANING A LITTLE BELOW
NORMAL SUNDAY-MONDAY BEFORE MODERATING TO NEAR NORMAL.
JACKSON
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
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page