596
FXUS02 KWBC 140700
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
259 AM EDT SAT OCT 14 2023
VALID 12Z TUE OCT 17 2023 - 12Z SAT OCT 21 2023
..OVERVIEW
THE MODELS AND ENSEMBLE MEANS CONTINUE TO SHOW THE UPPER PATTERN
TRANSITIONING TO AN AMPLIFIED WESTERN RIDGE/EASTERN TROUGH
CONFIGURATION FOR THE LATTER HALF OF THE COMING WEEK, AIDED BY THE
EXTRATROPICAL REFLECTION OF BOLAVEN WHICH SHOULD REACH THE
EAST-CENTRAL PACIFIC BY THE START OF THE FORECAST PERIOD EARLY
TUESDAY. THE AMPLIFYING CENTRAL-EASTERN U.S. TROUGH AND LEADING
FRONT/LOW PRESSURE SHOULD PRODUCE SOME AREAS OF LIGHT TO MODERATE
RAINFALL, WITH SOME AREAS OF HEAVIER ACTIVITY POSSIBLE OVER THE
EAST BY THE END OF THE WEEK DEPENDING ON UNCERTAIN EXACT DETAILS
OF UPPER FLOW AND SURFACE EVOLUTION. MEANWHILE AN UPPER TROUGH
OVER THE EAST COAST ON TUESDAY SHOULD QUICKLY DEPART, AND
SHORTWAVE ENERGY BEHIND THE BUILDING WESTERN U.S. UPPER RIDGE MAY
BRING A FRONT AND ASSOCIATED MOISTURE CLOSE TO THE WEST COAST BY
NEXT SATURDAY. THE FORECAST PATTERN WILL PROMOTE ABOVE NORMAL
TEMPERATURES OVER THE WEST AND AT TIMES INTO THE HIGH PLAINS,
ALONG WITH NEAR TO BELOW NORMAL READINGS OVER THE EAST.
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
THE PRIMARY FORECAST CHALLENGE INVOLVES THE DETAILS OF FLOW WITHIN
THE OVERALL CENTRAL-EASTERN U.S. AMPLIFYING TROUGH. MODELS SHOW
MULTIPLE PIECES OF SHORTWAVE ENERGY, INCLUDING THE INITIAL FEATURE
OVER AND JUST NORTH OF THE NORTHERN ROCKIES AS OF TUESDAY, AND AT
LEAST ONE AND POSSIBLY MORE UPSTREAM IMPULSES THAT MAY FEED INTO
THE TROUGH. THE SCALE OF INDIVIDUAL IMPULSES IS SMALL ENOUGH TO
KEEP PREDICTABILITY FOR SPECIFICS FAIRLY LOW WHEN PROJECTING
SEVERAL DAYS IN ADVANCE. OVER THE PAST COUPLE DAYS SPORADIC GFS
RUNS AND ONE CMC RUN HAVE BEEN TRYING TO PULL OFF UPPER LOW ENERGY
AS FAR SOUTHWEST AS THE SOUTHERN HIGH PLAINS WHILE ECMWF RUNS HAVE
REMAINED MORE OPEN AND PROGRESSIVE WITH THE TROUGH (ASIDE FROM
PERHAPS A TRANSIENT LOW OVER THE NORTHERN TIER) UNTIL CLOSING OFF
A LARGER SCALE LOW OVER/NEAR THE SOUTHEAST BY DAY 7 SATURDAY PER
THE PAST TWO RUNS. WHILE THE ENSEMBLE SPREAD HAS INCLUDED THE
POSSIBILITY OF THE SLOWER/SEPARATED SCENARIO, THE MAJORITY OF
MEMBERS AND THUS THE MEANS HAVE SIDED WITH THE OPEN AND
PROGRESSIVE SCENARIO. LATEST GFS/CMC TRENDS HAVE ALIGNED WITH THIS
IDEA AS WELL, WAITING UNTIL THE TROUGH REACHES THE EAST BEFORE
CLOSING OFF A SIGNIFICANT UPPER LOW IF AT ALL. NEEDLESS TO SAY THE
UPPER FLOW DETAIL UNCERTAINTY TOWARD NEXT SATURDAY KEEPS
CONFIDENCE LOW FOR SURFACE SPECIFICS BY THEN, THOUGH IN A BROAD
SENSE THE GUIDANCE DOES SHOW THE POTENTIAL FOR A MEANINGFUL SYSTEM
TO DEVELOP SOMEWHERE NEAR THE EAST COAST. AN OPERATIONAL MODEL
BLEND EARLY IN THE PERIOD FOLLOWED BY A TRANSITION TO HALF
MODELS/HALF ENSEMBLE MEANS BY DAY 7 SATURDAY PROVIDES A REASONABLE
ACCOUNT FOR DECREASING DETAIL CONFIDENCE WITH TIME AND ADDS A
LITTLE DETAIL TO THE MEANS LATE WHILE NOT COMMITTING TO ANY
SPECIFIC MODEL SOLUTION. ELSEWHERE, RECENT GUIDANCE TRENDS HAVE
HELD ONTO THE IDEA OF FARTHER OFFSHORE ATLANTIC LOW PRESSURE
THROUGH MIDWEEK DUE TO THE DEPARTING EASTERN U.S. UPPER TROUGH
BEING SUFFICIENTLY OPEN, WHILE GUIDANCE SHOWS ONLY MODEST SPREAD
RELATIVE TO DAY 7 FORECASTS FOR THE SHORTWAVE/SURFACE FRONT
NEARING THE WEST COAST LATE IN THE PERIOD. THE AVERAGE OF
GUIDANCE PROVIDES A REASONABLE STARTING POINT FOR THOSE ASPECTS OF
THE FORECAST.
..WEATHER/HAZARDS HIGHLIGHTS
SOME LOCATIONS OVER AND NEAR THE NORTHERN ROCKIES MAY SEE MOSTLY
LIGHT PRECIPITATION ON TUESDAY AS A SHORTWAVE AND SURFACE SYSTEM
CROSS THE REGION. AFTER THAT TIME, UPPER TROUGH AMPLIFICATION
SHOULD SUPPORT SOMEWHAT GREATER COVERAGE OF RAINFALL SPREADING
ACROSS THE CENTRAL AND EASTERN U.S. ALONG AND AHEAD OF THE
CORRESPONDING SURFACE SYSTEM(S). CONFIDENCE IN SPECIFICS IS STILL
NOT GREAT THOUGH, GIVEN THE UNCERTAINTY IN UPPER TROUGH/SURFACE
DETAILS DURING THE LATTER HALF OF THE WEEK. CURRENTLY EXPECT
PROGRESSION TO BE SUFFICIENT FOR MOST CENTRAL U.S. RAINFALL TO BE
IN THE LIGHT TO MODERATE RANGE, WITH SOMEWHAT HEAVIER ACTIVITY
POSSIBLE OVER THE SOUTHEASTERN PLAINS/LOWER MISSISSIPPI VALLEY.
MOIST EASTERLY LOW LEVEL FLOW ACROSS FLORIDA SHOULD INCREASE
RAINFALL OVER THE STATE LATE IN THE WEEK, AND SOME OF THIS
MOISTURE COULD ULTIMATELY GET PULLED FARTHER NORTH OVER THE
EASTERN U.S. BY FRIDAY-SATURDAY. COVERAGE AND INTENSITY OF
RAINFALL OVER THE EAST WILL DEPEND ON HOW MUCH THE UPPER TROUGH
MAY DECELERATE/CLOSE OFF AT THAT TIME. ELSEWHERE, NORTHERN
PORTIONS OF THE PACIFIC NORTHWEST COULD SEE A LITTLE RAINFALL
DURING THE PERIOD WITH A SLIGHT INCREASE POSSIBLE BY THE END OF
THE WEEK AS A FRONT APPROACHES. SOME SCATTERED LIGHT RAIN MAY
LINGER INTO TUESDAY OVER THE EASTERN GREAT LAKES/APPALACHIANS INTO
NORTHEAST BEFORE A DRIER TREND.
EXPECT ABOVE NORMAL TEMPERATURES OVER THE WEST INTO HIGH PLAINS
AND NEAR TO BELOW NORMAL READINGS OVER THE EAST. WARMEST ANOMALIES
WILL LIKELY BE OVER THE HIGH PLAINS ON TUESDAY AND THEN WITH
INCREASING COVERAGE OVER THE NORTHERN ROCKIES INTO
NORTHERN-CENTRAL HIGH PLAINS LATE IN THE WEEK, WITH HIGHS 10-20F
ABOVE NORMAL. COOLEST ANOMALIES OVER THE EAST, INCLUDING FLORIDA,
SHOULD BE ON TUESDAY WITH SOME HIGHS AT LEAST 10F BELOW NORMAL.
AFTER SOME MODERATION WITH THE DEPARTURE OF THE TUESDAY TROUGH,
THE SOUTHERN HALF OF THE EAST SHOULD COOL DOWN ONCE AGAIN WITH THE
ARRIVAL OF THE UPSTREAM AMPLIFIED TROUGH BY 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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