Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
1107 AM EDT Mon Jul 29 2019
Valid 12Z Thu Aug 01 2019 - 12Z Mon Aug 05 2019
...Overview and Guidance/Predictability Assessment...
The North American medium range upper flow pattern will feature a
closed high over the southern Rockies, with an amplified ridge up
over the west-central U.S. The ridge is sandwiched by persistent
mean troughing from the northeastern Pacific into WA/OR and also
downstream over the east-central U.S. underneath more dynamic
eastern Canadian troughing. Models/ensembles continue to show
forecast spread with respect to incoming/evolving Pacific flow
inland, but most variance occurs from the weekend into early next
week. Confidence remains low there, but is about average
elsewhere. A composite blend of the latest and reasonably well
clustered GFS/ECMWF and GEFS/ECMWF ensemble means seems reasonable
Thu-Sat. Used GEFS/ECMWF ensemble mean guidance that seem more
compatable later Sat into Monday amid growing forecast spread and
embedded feature uncertainty.
...Weather Highlights/Threats...
Below average temperatures in AZ/UT due to monsoonal moisture (and
an abundance of clouds/showers/storms) will moderate with time as
the upper high drifts just enough eastward to focus rainfall over
CO/NM this coming weekend into Monday. Coastal Washington may
flirt with some mainly offshore rain as a cold front moves inland
but most of the dynamics lift into Canada. Downstream, a wavy
frontal boundary draped over the east-central states will be a
focus for convective rainfall including some locally heavier
downpours/runoff issues through the period. Abundant moisture and
modest instability under the mean trough aloft will support less
organized precipitation away from the boundary in the Southeast.
East of Florida, an emerging tropical wave may bring increased
rainfall to parts of the Sunshine State, the Bahamas, and perhaps
into the coastal Carolinas. Finally, the High Plains/Upper Midwest
will see the Canadian system pull its front eastward along with
higher chances of rain/convection Sat-Mon.
Fracasso/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