Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
247 AM EDT Tue Jul 24 2018

Valid 12Z Fri Jul 27 2018 - 12Z Tue Jul 31 2018

...Heat wave lingers over the West...
...Heavy rainfall threat to spread from Central Rockies/Plains to
Mid-South then again over the East...

...Guidance/Uncertainty Assessment and Weather Threats...

Amplified mid-upper level troughing/height falls work over the
Great Lakes/OH Valley Fri through the Northeast this weekend. Some
lingering heavy rains fueled by deepened moisture along and ahead
of surface fronts can be expected early, with some local runoff
issues possible given wet antecedent conditions. Additional
activity will trail southward along or off the east coast and
across Florida. Meanwhile, a hot mid-upper level ridge over the
Southwest/West offers a continuing pattern with above normal
summer heat. A series of active impulses will linger within
monsoonal flow over the Southwest/srn Rockies and also overtop the
upper ridge. These will dig into the central U.S. in a region of
favorable upper diffluence and interact with surface boundaries,
instability, and favorable low level moisture inflow/convergence.
Weekend mid-upper level trough amplification over the n-central
U.S. will dig through the MS Valley early next week and induce an
organized low and gradual frontal system progression downstream
across the East-Central U.S. This pattern supports multiple
episodes of heavy convection from the central Rockies/Plains
through the mid-lower MS/Mid-South into the weekend whose threat
spreads/expands over much of the East-Central U.S. to ern U.S.
early-mid next week. Heavy rainfall and repeat cells offer a
widespread excessive rainfall threat fueled by an increasingly
deep layered moisture inflow pattern to align roughly parallel to
the main front/activity wedged between the upstream trough aloft
and downstream western Atlantic ridge.

The WPC medium range product suite was mainly derived from a
composite blend of reasonably well clustered guidance from the
GFS/ECMWF/UKMET and GEFS/ECMWF ensembles in a pattern with above
normal predictability.

Schichtel

WPC medium range 500 mb heights, surface systems, weather grids,
quantitative precipitation, winter weather outlook probabilities
and heat indexes are found 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