644
FXUS02 KWBC 131902
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
302 PM EDT FRI SEP 13 2024
VALID 12Z MON SEP 16 2024 - 12Z FRI SEP 20 2024
..OVERVIEW
UPPER LOW SWINGS FROM CA TO MT MONDAY THROUGH TUESDAY NIGHT WITH A
REINFORCING TROUGH SHIFTING DOWN THE PACNW COAST TUESDAY TO AT
LEAST THE CENTRAL CA COAST THURSDAY, WHICH WILL PROMOTE COOLER
WEATHER WITH RAIN AND HIGHER ELEVATION SNOW. MEANWHILE IN THE
EAST, RIDGING IN THE NORTHEAST LOOKS TO DIRECT ANY SUBTROPICAL LOWS
OFF THE SOUTHEAST COAST INTO THE CAROLINAS MONDAY/TUESDAY. THE
EVOLUTION OF THE PATTERN IN THE EAST RETAINS UNCERTAINTY WITH THE
POSITIONING OF THE UPPER LOW AND PROGRESS TOWARD/INTO THE EASTERN
STATES.
..GUIDANCE/PREDICTABILITY ASSESSMENT
GREAT AGREEMENT OF BOTH INITIAL AND SECOND LOW OVER THE WEST
THROUGH NEXT WEEK. THE TIMING OF THE FIRST LOW IS EVEN IN BETTER
AGREEMENT WITH THE 12Z CYCLE AS THE CMC IS A BIT SLOWER AND THE
ECMWF IS A BIT QUICKER. AND THE 12Z UKMET SLOWED A BIT WITH THE
SECOND LOW PROGRESSING DOWN THE WEST COAST TUESDAY
NIGHT/WEDNESDAY.---
THERE WAS CONSIDERABLE UNCERTAINTY IN THE 00Z/06Z GUIDANCE WITH
LOW PRESSURE INTO THE CAROLINAS MONDAY/TUESDAY AS THE ECMWF HAD
SUPPRESSED TROUGHING WHILE THE GFS MAINTAINED A LOW INTO NC. THE
12Z GFS HELD SERVE, THE CMC CAME IN STRONGER WITH TROUGHING, AND
THE 12Z ECMWF NOW HAS A LOW SIMILAR TO THE GFS. FOR NOW THIS
INCREASES CONFIDENCE IN THE FORECAST.
THE WPC FORECAST WAS BASED ON A GENERAL MODEL BLEND FOR THE HIGHER
CONFIDENCE WEST AND A NON-GFS SOLUTION FOR THE EAST GIVEN THE 06Z
GFS WAS AN OUTLIER. ENCOURAGEMENT WOULD BE TO NOW GO MORE TOWARD
THE 12Z GFS/ECMWF.
..WEATHER/HAZARDS HIGHLIGHTS
DRASTIC SHIFT IN THE 12Z ECMWF TOWARD RECENT GFS SOLUTIONS WARRANTS
A SLIGHT RISK ERO UPGRADE ON DAY 4 GIVEN THE PRESENCE OF LOW
PRESSURE (LIKELY SUBTROPICAL IN NATURE - PLEASE STAY TUNED TO NHC
FORECASTS FOR FURTHER UPDATES) MOVING INTO NC. FOR NOW THE SLIGHT
RISK IS FOR SOUTHERN NC.
THIS LOW TRACKS INLAND PER THE 12Z GFS/ECMWF WITH A MARGINAL RISK
INTRODUCED FOR MUCH OF VA AND NORTHERN NC. THE PRESENCE OF TERRAIN
IN THE EASTERN APPALACHIANS MAY WARRANT FURTHER EXPANSION OF
EXCESSIVE RAINFALL RISKS AS THIS FORECAST CONTINUES TO EVOLVE.
ALSO ON DAY 5 IS A LINGERING FRONTAL ZONE OVER THE CENTRAL GULF
COAST/FL PANHANDLE WHERE HEAVY RAIN SHOULD DEVELOP AND A MARGINAL
RISK WAS INTRODUCED.
LINGERING MOISTURE FROM THE PACIFIC TROPICAL STORM ILEANA WILL BE
DRAWN NORTH AHEAD OF THE LOW OVER NV, SO THE DAY 4 MARGINAL RISK
IS MAINTAINED/EXPANDED A BIT FOR THE FOUR CORNERS STATES.
THE DAY 5/TUESDAY MARGINAL RISK IS MAINTAINED FOR THE WESTERN HALF
OF MT AS HEAVY RAIN RATES AHEAD OF THE INITIAL LOW TRACK LOOK TO
PERSIST OVER THE SAME AREAS FOR MULTIPLE HOURS WITH SOME
INSTABILITY IN PLACE. THE HIGHER ELEVATIONS CAN EXPECT SNOW WITH
THIS SYSTEM GIVEN THE DEPTH OF THE UPPER LOW. ANOTHER ROUND OF
ENERGY WILL CAUSE THE PACIFIC NORTHWEST TO SEE PRECIPITATION ON
TUESDAY, SHIFTING INTO MUCH OF THE GREAT BASIN MIDWEEK AND THEN
INTO THE NORTHERN ROCKIES. FARTHER EAST, SCATTERED RAIN AND
THUNDERSTORMS ARE LIKELY IN THE PLAINS FOR MULTIPLE DAYS NEXT WEEK
NEAR AND AHEAD OF FRONTAL SYSTEMS.
THE WEST CAN EXPECT MUCH COOLER THAN NORMAL TEMPERATURES NEXT WEEK
UNDER THE UPPER TROUGH. HIGH TEMPERATURES WILL BE 15-25F BELOW
NORMAL ACROSS MUCH OF THE WEST, GRADUALLY MODERATING CLOSER TO
NORMAL ACROSS THE WEST COAST STATES BUT PERSISTING IN THE INTERIOR
WEST. SOME AREAS MAY REACH THE FREEZING MARK IN THE HIGHER
ELEVATIONS OF THE GREAT BASIN/ROCKIES. MEANWHILE, THE CENTRAL U.S.
SHOULD SEE WARMER THAN NORMAL HIGHS BY 10-15F AND LOWS BY 15-20F,
INCLUDING HIGHS IN THE 90S IN THE SOUTHERN HALF OF THE PLAINS.
WARMER THAN AVERAGE TEMPERATURES WILL STRETCH INTO THE GREAT LAKES
AND NORTHEAST, WITH MORE TYPICAL TEMPERATURES SOUTH OF THERE.
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 (QPF), EXCESSIVE RAINFALL
OUTLOOK (ERO), WINTER WEATHER OUTLOOK (WWO) PROBABILITIES, HEAT
INDICES, AND KEY MESSAGES CAN BE ACCESSED FROM:
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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