386
FXUS02 KWBC 060658
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
257 AM EDT FRI OCT 06 2023
VALID 12Z MON OCT 09 2023 - 12Z FRI OCT 13 2023
..OVERVIEW
A DEEP UPPER LEVEL LOW IS FORECAST TO PARK ITSELF OVER
SOUTHEASTERN CANADA AND THE GREAT LAKES AND CHURN IN PLACE THROUGH
MOST OF NEXT WEEK. A NEARLY STATIONARY SURFACE LOW WILL CREATE
PRECIPITATION CHANCES NEAR THE GREAT LAKES EARLY IN THE WEEK WITH
SOME LAKE EFFECT ENHANCEMENT POSSIBLE. IN THE WEST, A TROUGH WILL
MOVE ONSHORE EARLY IN THE WEEK AND PROGRESS EAST. THIS FEATURE
WILL DRIVE A SURFACE FRONTAL SYSTEM EAST ACROSS THE COUNTRY
THROUGH THE WEEK. PRECIPITATION CHANCES WILL BE GREATEST ON MONDAY
AND TUESDAY IN THE PACIFIC NORTHWEST WHERE LOCALLY HEAVY RAINFALL
MAY BE POSSIBLE, THEN PRECIPITATION CHANCES WILL SPREAD INTO THE
CENTRAL U.S. MIDWEEK AND TO THE EAST COAST BY FRIDAY.
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
MODEL GUIDANCE IS IN GOOD AGREEMENT ON THE OVERALL PATTERN WITH
SOME SLIGHT DISAGREEMENTS NEAR THE END OF THE PERIOD. THE MAIN
DIFFERENCES ARE WITH HOW THE DEEP UPPER LEVEL LOW OVER
SOUTHEASTERN CANADA AND THE GREAT LAKES WILL INTERACT WITH THE
APPROACHING TROUGH LATER IN THE WEEK. ENERGY FROM THE TROUGH WILL
BE SWEPT UP INTO THE LOW AND SHUNT IT NORTHEAST WHILE CREATING AN
ELONGATED LOW PRESSURE AREA FROM EASTERN QUEBEC TO THE
WESTERN/SOUTHERN GREAT LAKES REGION. SEVERAL SHORTWAVES WILL MOVE
AROUND THE LOW AND THROUGH THE TROUGH DURING THIS PROCESS, WHICH
WILL COMPLICATE TIMING AND POSITIONING OF SURFACE LOWS THAT FORM.
MODELS ALSO DISAGREE ON HOW ENERGY FROM TROPICAL CYCLONE LIDIA
WILL MOVE INTO THE MID-LATITUDES. THE GFS AND CMC PULL THE ENERGY
NORTH OVER WESTERN MEXICO, BUT PREVIOUS RUNS SHOWED THE ENERGY
POTENTIALLY BEING PULLED TOWARDS TEXAS. IF THIS ENERGY DOES GET
PULLED EAST, IT COULD ENHANCE RAINFALL CHANCES IN THE SOUTHERN
U.S. MID/LATE WEEK.
FOR THIS FORECAST CYCLE, A DETERMINISTIC BLEND OF THE GFS, ECMWF,
CMC, AND UKMET WAS USED FOR DAYS 3-5 (MONDAY-WEDNESDAY) WITH
SLIGHTLY STRONGER WEIGHT ON THE ECMWF AND GFS. ENSEMBLE MEANS WERE
ADDED TO THE FORECAST BLEND BEYOND DAY 5 TO CREATE A MIDDLE OF THE
ROAD SOLUTION THAT SMOOTHS OUT SOME OF THE MINOR SMALLER SCALE
DIFFERENCES BETWEEN THE DETERMINISTIC MODEL RUNS.
..WEATHER/HAZARDS HIGHLIGHTS
THE THREAT FOR EXCESSIVE RAINFALL IS FORECAST TO REMAIN LOW MONDAY
AND TUESDAY. THE ONLY AREA OF CONCERN IS THE PACIFIC NORTHWEST
WHERE MOISTURE WILL STREAM ONSHORE AHEAD OF AN APPROACHING FRONTAL
SYSTEM. LOCALLY HEAVY RAINFALL WILL BE POSSIBLE AT TIMES DUE TO
THE COMBINATION OF SURFACE LIFT AND UPPER LEVEL DYNAMIC SUPPORT
FOR ASCENT, AND UPSLOPE AREAS OF THE COASTAL MOUNTAIN RANGES,
OLYMPICS, AND CASCADES WILL LIKELY SEE THE HIGHEST RAINFALL
TOTALS. A MARGINAL RISK OF EXCESSIVE RAINFALL AREA WAS CONSIDERED,
BUT WAS NOT INTRODUCED FOR EITHER DAY AT THIS TIME BECAUSE THE
SYSTEM SEEMS QUITE PROGRESSIVE, A STRETCH OF DRY WEATHER WILL
PRECEDE THIS EVENT, AND IT IS STILL EARLY IN THE WET SEASON. THESE
FACTORS WILL ALL LIMIT THE FLASH FLOOD POTENTIAL. MUCH OF THE
PACIFIC NORTHWEST IS STILL EXPERIENCING DROUGHT CONDITIONS, SO
MUCH OF THIS RAINFALL MAY BE CONSIDERED BENEFICIAL.
PRECIPITATION CHANCES WILL EXPAND EAST THROUGHOUT THE WEEK AS A
FRONTAL SYSTEM MOVES ACROSS THE NATION, REACHING THE CENTRAL U.S.
MIDWEEK AND THE EAST COAST BY FRIDAY. SOUTHERLY WINDS AHEAD OF THE
SYSTEM WILL PUSH MOISTURE FROM THE GULF OF MEXICO INTO THE
SOUTHERN U.S., WHICH MAY RESULT IN LOCALLY HEAVY RAINFALL IN PARTS
OF THE SOUTH AND SOUTHEAST WEDNESDAY THROUGH FRIDAY. MOISTURE WILL
ALSO SPREAD UP THE EAST COAST BY FRIDAY, EXPANDING THE CHANCES OF
HEAVY RAINFALL INTO THE NORTHEAST. DAILY CHANCES FOR SHOWERS AND
THUNDERSTORMS WILL PERSIST OVER THE FLORIDA PENINSULA AND INCREASE
THROUGH THE WEEK AS A FRONTAL BOUNDARY SLOWLY MOVES NORTH ACROSS
THE STATE.
TEMPERATURES WILL BE COOLER THAN NORMAL DURING THE FIRST HALF OF
NEXT WEEK FROM THE MIDWEST TO THE NORTHEAST UNDERNEATH THE UPPER
LOW. HIGH TEMPERATURES ARE FORECAST TO BE 10-15 DEGREES BELOW
AVERAGE, AND OVERNIGHT LOWS WILL BE COLD ENOUGH FOR FROST TO FORM
IN PARTS OF THE UPPER MIDWEST AND GREAT LAKES REGION. ABOVE
AVERAGE TEMPERATURES ARE FORECAST TO START THE WEEK ACROSS MUCH OF
THE CENTRAL U.S. AND THE WEST, BUT TEMPERATURES WILL DROP THROUGH
MIDWEEK AS THE FRONTAL SYSTEM MOVES THROUGH.
DOLAN
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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