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Extended Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1815Z Sep 19, 2020)
 
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Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
215 PM EDT Sat Sep 19 2020

Valid 12Z Tue Sep 22 2020 - 12Z Sat Sep 26 2020

...Heavy rainfall threat from Beta continues for the northwest
Gulf Coast and lower Mississippi Valley into the later half of
next week...

...Hurricane Teddy is forecast to move through eastern Atlantic
Canada late Tuesday through Wednesday...


...Overview...
A deep lows persisting in the Gulf of Alaska into Friday and
another east of New England Tuesday/Wednesday allow ridging to
increase over the Rockies and onto the Great Plains Wednesday to
Friday. In the Gulf, Beta is forecast to be a tropical storm as it
slowly moves northeast along/near the middle/upper Texas coast
Tuesday through Wednesday night before it weakens as it moves
inland over southwest Louisiana Thursday. This track would bring
heavy rain along the upper TX and western LA coasts into Thursday
with a noted degree of uncertainty. South of Nova Scotia,
hurricane Teddy will merge with a non-tropical low before skirting
eastern Nova Scotia keeping most wrap-around rain and wind east of
Maine. In addition, Teddy will continue to churn up waves along
the East Coast which could cause life-threatening surf and rip
current conditions.


...Guidance/Predictability Assessment...
00Z/06Z deterministic guidance was reasonable through Wednesday
night across the CONUS including the Gulf of Mexico. Starting
Thursday preference goes to the 00Z ECMWF/ECENS due to timing of
troughs off the Northwest and crossing the Great Lakes. The the
00Z CMC and UKMET were faster with the Great Lakes trough while
the 06Z (and now 12Z) GFS were weaker with the Great Lakes. This
general blend generally worked well for the 15Z NHC track of Beta.
The 06Z/12Z GFS/GEFS are much slower than the 00Z ECMWF/ECENS,
which the preference is again for the ECMWF/ECENS.


...Weather/Hazard Highlights...
Tropical storm Beta is forecast to take a slow path northeast
along the upper TX coast and into southwest LA to the southern MS
Valley and spread heavy rain along its track. Given the official
track, leaned toward the higher end which includes the 00Z
UKMET/ECMWF. Teddy is now expected to be far enough east of Maine
to not bring much rain to that state. A cold front and trough from
the Gulf of Alaska will bring several days of rainfall to western
WA/OR Wednesday through Friday. Showers will continue behind the
front eastward over the northern Rockies. Temperatures will remain
above to much above normal throughout the period across the
north-central U.S. and back into the interior West (through
Thu/Fri). Highest anomalies will lie over the Dakotas/Upper
Midwest where 80s will be common. The approaching cold front next
weekend will start to cool temperatures over the Rockies, but only
back down to near normal. Overall, minimum temperatures through
the medium range remain above freezing (after recent days of
frost/freeze).


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