Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
339 PM EDT Mon Jul 22 2019
Valid 12Z Thu Jul 25 2019 - 12Z Mon Jul 29 2019
...Weather Highlights/Threats and Guidance/Predictability
Assessment...
A summertime medium range flow pattern will persist over the
nation to include a lingering/weak eastern U.S. upper trough
downstream of an hot West/Southwest upper ridge. Expect some
scattered monsoonal convection will work around the ridge over the
southern Great Basin/Rockies/High Plains in upper diffluent flow.
A far southward sagged front through the South/Southeast and into
the Gulf of Mexico will remain a main focus for heavy
convection/rainfall. Activity will be fueled by deeply pooled
moisture/instability and runoff issues may be compounded by
slow/repeat cell motions. Meanwhile overtop, mid-level impulses
and wavy surface fronts will traverse the northern tier states
from the Pacific Northwest eastward to the Northeast. These will
enhanced local moisture, instability and periods of convection/MCS
activity, especially from the n-central U.S. into the
Midwest/Great Lakes. However, system timing and local focus are
increasingly uncertain over time.
Model forecasts cluster well with ensembles Thursday to Saturday,
with forecast spread then increasing more ernestly into early next
week. Accordingly, WPC medium range surface fronts/pressure and
500mb progs were primarily derived from a composite blend of the
06 UTC GFS and 00 UTC ECMWF/UKMET/Canadian days 3-5, then a blend
of the compatable 06 UTC GEFS mean and 00 UTC ECMWF ensemble mean
into days 6/7. This maintains good WPC continuity.
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
Hazards:
- Heavy rain across portions of the Great Lakes and the Upper
Mississippi Valley, Sat-Mon, Jul 27-Jul 29.
- Flooding possible across portions of the Mid-Atlantic, the
Northeast, the Central Appalachians, the Upper Mississippi Valley,
and the Northern Plains.
- Flooding occurring or imminent across portions of the Middle
Mississippi Valley, the Lower Mississippi Valley, the Upper
Mississippi Valley, and the Northern Plains.
- Flooding likely across portions of the Central Plains, the
Middle Mississippi Valley, and the Upper Mississippi Valley.
- Excessive heat across portions of California and the Southwest,
Fri-Sat, Jul 26-Jul 27.
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