Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
324 PM EDT Tue Sep 17 2019
Valid 12Z Fri Sep 20 2019 - 12Z Tue Sep 24 2019
...Overview and Guidance Evaluation/Preferences...
Latest global guidance is similar on the large scale pattern into
Sunday/Day 5 before divergence on the depth of a low over the
southwest CONUS and how cut off it becomes into Day 7. There are
some notable small scale differences, particularly with the Day
3/4 shortwave lifting over the northern Great Plains. The 06Z GFS
is more amplified and farther south than the 00Z ECMWF/UKMET. This
feature is much weaker in the 00Z CMC, so the CMC is excluded from
the blend after Day 3. The 00Z UKMET has a similar approach to
this north-central wave through Day 4 before diverging with a
stronger shortwave crossing the central Plains on Day 5, so the
00Z UKMET is excluded after Day 4. The blend of Days 5-7 are a
combination of the 06Z GFS/GEFS mean and 00Z ECMWF/ECENS mean.
Both deterministic runs close the low over the southwest CONUS on
Day 6 and cut it off on Day 7. There is considerable separation of
the zonal northern stream trough over Canada and the low off the
southern CA coast on Day 7 in the ECMWF while the 06Z GFS has a
ridge over southwestern Canada with the low over the Great Basin.
A climatology of the southwest CONUS does indicate a great
increase in cutoff lows over the southwest CONUS from mid to late
September, so this is a reasonable solution. A preference was
given to the 00Z ECMWF/ECENS for Day 7 given its longer trend of a
Deep tropical moisture will lift north to the east-central Plains
to the middle MS Valley ahead of a trough crossing the northern
Great Plains this weekend. This will focus heavy convection/runoff
issues with cell training from the east-central Plains to the
Mid-MS Valley/Midwest this weekend and into the Midwest early next
week. There is a severe thunderstorm threat ahead of that northern
Great Plains trough Friday into Saturday.
Additional 3-7 Day Hazards information can be found on the WPC
medium range hazards chart at:
- Heavy rain across portions of the Central Plains to the Midwest,
Sat-Sun, Sep 21-Sep 22.
- Heavy rain across portions of the Lower Mississippi Valley and
the Southern Plains, Fri, Sep 20.
- Heavy rain across portions of the Upper Mississippi Valley and
the Northern Plains, Fri-Sat, Sep 20-Sep 21.
- Severe weather across portions of the Northern Plains and Upper
Mississippi Valley, Fri, Sep 20.
- Flooding possible across portions of the Central Plains, the
Lower Mississippi Valley, the Northern Plains, the Middle
Mississippi Valley, the Upper Mississippi Valley, and the Southern
- Flooding occurring or imminent across portions of the Central
Plains, the Middle Mississippi Valley, the Great Lakes, the Upper
Mississippi Valley, and the Northern Plains.
- Flooding likely across portions of the Central Plains, the
Middle Mississippi Valley, the Upper Mississippi Valley, and the
- Much below normal temperatures across portions of the Great
Basin and Northern Rockies, Fri-Sat, Sep 20-Sep 21.
WPC medium range 500mb heights, surface systems, weather grids,
quantitative precipitation, winter weather outlook probabilities
and heat indices are at: