Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
1151 AM EDT Tue Jul 09 2019
Valid 12Z Fri Jul 12 2019 - 12Z Tue Jul 16 2019
...Overview and Guidance/Predictability Assessment...
A strong upper high will slowly weaken over the central/southern
Rockies as the jet stream sinks a bit south along the
U.S./Canadian border. With a weaker upper ridge off the Southeast
coast, troughing over the lower Mississippi Valley/northern Gulf
will support a potential tropical system at the surface. This
system will pose a heavy rainfall threat to areas along the
central and portions of the western Gulf Coast and points
northward. Overall the ensembles were in good agreement over the
lower 48 (06Z GEFS mean and 00Z ECMWF ensemble mean) in a fairly
typical summertime pattern. The deterministic models showed the
most disagreement with the track/evolution of the Gulf system but
have continued to slowly show more agreement. The 00Z
GFS/ECMWF/UKMET/Canadian formed a broad consensus late this week
with the Gulf system moving westward then turning northward near
the TX/LA coastline in the weaker flow region. The 00Z ECMWF was
closest to the ensemble consensus/continuity position with a
slight nudge eastward from overnight based on the latest
models/trends. Preferred to limit changes to the forecast since
the ensembles have been relatively steady in the most recent
cycles. By next week, an ensemble consensus/continuity served as a
starting point with increasing uncertainty over the middle
Mississippi Valley.
Elsewhere there is better than average agreement and continuity
with the overall pattern. A fairly strong upper high should
persist over the southern Rockies/Four Corners region while an
eastern Pacific mean trough may drift ever so gradually toward the
West Coast. Shortwaves ejecting from the Pacific trough will
become embedded in progressive northern U.S./southern Canada flow
and likely feed into a broad/shallow mean trough over the
Northeast. These shortwaves will support a progression of
waves/frontal systems which at times will be accompanied by
showers and thunderstorms.
...Weather Highlights/Threats...
Highest rainfall potential certainly lies near the track of the
potential Gulf system, though not necessarily constrained around
its center. Combination of Gulf inflow on its east side and the
stalled front to the north will modulate other precipitation
maxima. Some locally enhanced rainfall amounts will be possible
over the Northeast with one system late this week while the
northern Plains/Upper Mississippi Valley may be another area of
interest due to the arrival of another front and its subsequent
stalling. The shortwaves brushing the Pacific Northwest may bring
one or more periods of light to perhaps isolated moderate rainfall.
Western and northern portions of the lower 48 should see above
average temperatures during most of the period. The northern
Plains to Great Lakes area may see some pockets of plus 10F or
greater anomalies for min and/or max readings by early next week.
Parts of the interior West may see some mins exceed 10F above
normal one or more days. Meanwhile clouds/rainfall associated with
the possible Gulf system may hold daytime highs below normal over
parts of the southern tier.
Fracasso/Rausch
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