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Extended Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1754Z Sep 16, 2020)
 
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Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
154 PM EDT Wed Sep 16 2020

Valid 12Z Sat Sep 19 2020 - 12Z Wed Sep 23 2020

...Heavy rainfall possible along parts of the western to
west-central Gulf Coast associated with possible tropical
development in the Southwest Gulf...

...Guidance/Predictability Assessment...

For the first couple of days of the medium range period, the
deterministic guidance is pretty well clustered across the CONUS.
Thus, a blend of the latest GFS/ECMWF/CMC/UKMET sufficed for days
3 and 4. After this, there is some question on how much a
shortwave moving through the Great Lakes amplifies across the
Northeast, which has implications for the eventual track of
Hurricane Teddy during the day 6-7 frame. The ECMWF has been
consistent the past few runs with a slower Northeast U.S. trough
which could help to steer Teddy (likely beginning extra tropical
transition by that point) more towards the Canadian Maritimes
during the middle of next week. The latest 12z GFS/CMC are faster
to progress the shortwave across the Northeast which kicks Teddy
out to sea. As expected, there is considerable spread in the
guidance with this so leaning more towards the better compatible
GEFS/ECENS means days 5-7 is the best approach at this point. This
also allows good WPC continuity with last nights forecast.


...Overview and Weather/Hazard Highlights...

In the wake of Sally, strong high pressure settling into the East
will bring well below normal temperatures including a few record
values this weekend into early next week, with gradual moderation
from west to east. The high pressure surge will also act to
confine deeper moisture mainly to Florida and the Gulf of Mexico
near a slow moving trailing front to linger over the next week.
NHC is monitoring a slow moving tropical disturbance over the
southwest Gulf of Mexico and broad deep moisture seems set to fuel
widespread moderate to heavy rainfall that may feed into the
western to west-central Gulf Coast.

Elsewhere, amplified upper trough/embedded low ejection will
spread some welcome rainfall and cooler temperatures out from the
fire stricken Northwest and northern California to the northern
Intermountain West/Rockies this weekend. Ahead of this system, the
warmest temperature anomalies in the 10-15F range will focus into
the northern-central states.

Santorelli/Schichtel

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