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Extended Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1847Z Sep 18, 2019)
 
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Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
247 PM EDT Wed Sep 18 2019

Valid 12Z Sat Sep 21 2019 - 12Z Wed Sep 25 2019

...Imelda moisture brings an East-Central Plains to Midwest Heavy
Rainfall Threat...

...Overview and Guidance Evaluation/Preferences...
The main flow pattern features are an exiting trough over the
northern Plains Saturday that drags a cold front across the
eastern CONUS through Tuesday and a trough digging south off the
Pacific Northwest Coast Saturday into Sunday before closing a
cutting off over California Monday. The 06Z GFS is much farther
east with this low with the center over the Great Basin while the
00Z GFS/ECMWF/CMC/UKMET all have the center over California.
Therefore the 06Z GFS was not included in the model blend beyond
Day 3. The more consistent ECMWF was preferred and by Day 5 a
blend of the 00Z ECENS mean and the 00Z GEFS mean took heavier
weight through Day 7.


...Weather Highlights/Threats...
Deep tropical moisture with the remains of Imelda will offer a
significant threat of locally excessive rainfall into the weekend
over the central CONUS. Expected inland lifting/entrainment into
the flow with approaching mid-latitude upper trough crossing to
the north and a cold front that pivots over the east-central 
plains will focus moisture/heavy convective storm potential with
cell training from the east-central Plains to the Mid-MS
Valley/Midwest, in particular eastern Kansas, northern Missouri
into Illinois.

Meanwhile, an aforementioned upper trough will lift northeastward
over the northern Plains. This will support an organized
convective focus with locally heavy downpours and a severe
thunderstorm risk over the Dakotas into Saturday as per SPC.
Deepened lead moisture may also support some record high minimum
temperatures ahead of the front Saturday morning.

Upstream, upper low/trough energies will reload back into an again
unsettled West/Southwest Sunday into next week with a
precipitation swath over the Northwest then Great Basin for Days
4/5. The risk then shifts to the southwest where moisture from
Lorena is drawn into AZ/NM as the low cuts off over CA. The
combination of monsoonal/tropical moisture and maybe some Lorena
remnants leads to a prolonged heavy rain threat Monday through
Wednesday.
 
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

Hazards:
- Heavy rain from portions of the Central Plains to the Midwest,
Sat-Sun, Sep 21-Sep 22.
- Heavy rain across portions of the Central Plains and the Middle
Mississippi Valley, Mon-Tue, Sep 23-Sep 24.
- Heavy rain across portions of the Southwest, Sun-Tue, Sep 22-Sep
24.
- Flooding possible across portions of the Southern Plains, the
Upper Mississippi Valley, and the Northern Plains.
- Flooding occurring or imminent across portions of the Northern
Plains and the Great Lakes.
- Flooding likely across portions of the Central Plains and the
Middle Mississippi Valley.

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