Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
1201 PM EDT Thu Sep 12 2019
Valid 12Z Sun Sep 15 2019 - 12Z Thu Sep 19 2019
...Heavy rain is possible over portions of the Southeast...
...Overview and Guidance Evaluation/Preferences...
Two key weather features were focused on for the medium range. An
amplified/slow-moving trough digging south from off the Pacific
Northwest across The West and a tropical disturbance tracking from
Florida. The deepening western trough will spread a cold front
east across the Great Basin and Rockies Mon-Tue and possibly into
the central U.S. by Wed-Thu, depending on its eastward progression
which has uncertainty at this time. The tropical disturbance is
now forecast to stay farther east as it moves north from Florida
either into Georgia or toward the Gulf Stream Sunday into Tuesday.
As a note, a northern stream shortwave over the northeastern U.S.
to eastern Canada Sunday night pushes a cold front off the Eastern
Seaboard that lingers over the Carolinas and may influence the
track of the tropical disturbance.
Recent GFS/GEFS runs have been much more anchored to the West
Coast with the positively tilted trough starting on the 17th and
continues to take tropical wave into the Gulf of Mexico. Meanwhile
the 00Z ECMWF/UKMET/CMC are all more progressive with ejecting the
trough in The West east and keep the tropical disturbance over or
east of Florida. The 00Z UKMET continues its trend of having the
tropical farther north. Due to uncertainty with the trough out
west and the tropical, a limited model blend was chosen based on
the 00Z ECMWF/00Z CMC and an increasing weight toward the 00Z
ECENS and 00Z NAEFS from Days 3-7. The tropical track from FL into
GA through Day 5 was coordinated with NHC.
...Weather Highlights/Threats...
The tropical disturbance will bring numerous showers and
thunderstorms along its track which is uncertain at this time.
Non-GFS guidance keeps the system east of FL/GA/SC, so the heavy
rain threat may end up being near the coast (or off the coast),
but for now an inland track would create a large heavy rain threat
over FL into GA and the eastern Carolinas.
Widespread rains (and mountain snows) are expected across the
Pacific Northwest Sunday night through Monday night as the upper
trough begins to amplify. Precipitation will spread south into CA
and inland across the Great Basin and northern Rockies early next
week. Southerly flow east of the upper trough looks to revive
monsoonal showers and storms across the Four Corners region
through Days 3-7.
A broad upper ridge across the central and eastern U.S. will
result in above average temperatures across a wide area. Highs are
forecast to be 5 to 15 F above average for many areas from the
Plains to the Eastern Seaboard into next week. The upper trough
reaching the western U.S. Sun-Mon will bring much cooler
temperatures, with highs 10 to nearly 20 deg below average
expected to overspread the Northwest, Great Basin, and eventually
the northern Rockies. As mentioned above, with increasing
precipitation across the Northwest, temperatures should be cold
enough to support snow at the higher peaks.
Jackson
Additional 3-7 Day Hazards information can be found on the WPC
medium range hazards chart at:
https://www.wpc.ncep.noaa.gov/threats/threats.php
WPC medium range 500mb heights, surface systems, weather grids,
quantitative precipitation, winter weather outlook probabilities
and heat indices 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/wwd/pwpf_d47/pwpf_medr.php?day=4
https://www.wpc.ncep.noaa.gov/heat_index.shtml