Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
1151 AM EDT Sat Jul 27 2019
Valid 12Z Tue July 30 2019 - 12Z Sat Aug 3 2019
16Z Update: Very good deterministic model agreement exists across
the continental U.S. for Tuesday and Wednesday. The upper low
near British Columbia mid-week introduces more uncertainty into
the forecast going forward to the end of the week, especially
across southern Canada. The GFS and ECMWF indicate a shortwave
originating from this low to track near the southern border of the
Northwest Territories, with the GFS the faster solution. However,
teleconnections with the broad upper low expected over northeast
Canada and the upper level ridge over the Four Corners region next
weekend are more supportive of a broad ridge axis extending
northward into Canada, which limits the level of confidence on
this feature being noteworthy. By the end of the forecast period
next Saturday, confidence is greatest with the upper level high
over Colorado and the broad upper trough over the eastern third of
the U.S., and lowest with the eventual breakdown of the trough
near the Pacific Northwest. The deterministic ECMWF, GFS, and
some of the CMC was incorporated early in the forecast period,
followed by some of the ensemble means and previous WPC continuity
for Thursday through Saturday.
D. Hamrick
...Overview and Guidance/Predictability Assessment...
An upper high will meander around the Four Corners region as
troughing digs into the eastern states as well as the Pacific
Northwest. The models/ensembles largely agree for the first few
days of the period (Tue into Thu) and a general model blend
sufficed. For later next week into next Saturday, 18Z GFS and 12Z
ECMWF showed reasonable agreement though displaced a bit from the
ensemble means in the northeast Pacific where the guidance has had
trouble settling on a solution. Trend seems to be for a bit slower
progression which favors the GFS/ECMWF more than the slightly
quicker ensemble means, so shifted the forecast in that direction
but with limited confidence. Downstream result may be for a bit
deeper troughing and a farther southward push of a cold front into
the TN Valley.
...Weather Highlights/Threats...
Temperatures in the Southwest will trend cooler as monsoonal
moisture increases and clouds/showers/storms expand in coverage.
Convective rainfall including some locally heavier
downpours/runoff issues will focus along and ahead of the frontal
boundaries from the Great Lakes to the Northeast and southward to
the southern Plains/lower MS Valley/Southeast. Florida may see an
enhanced period of rainfall with a dissipating surface boundary
over the central peninsula early next week. The Pacific Northwest
will see an increased chance of rain with an approaching system
later in the week.
Fracasso
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