Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
323 PM EDT Thu Aug 01 2019
Valid 12Z Sun Aug 04 2019 - 12Z Thu Aug 08 2019
16Z Update: The deterministic model guidance appeared to be in
above average agreement through Monday across the continental
U.S., with the main exceptions being the CMC with its upper low
off the Pacific Northwest farther east than the model consensus,
and the GFS/GEFS indicating a greater degree of upper level
troughing over the Western Gulf of Mexico. By Tuesday, there is
strong model support for a well-defined upper low west of Oregon,
with normal levels of placement differences. However, the CMC is
weaker with the downstream ridge over the Intermountain West
compared to the ensemble means. By the end of the forecast period
next Thursday, the magnitude of the upper ridge over the Four
Corners region is forecast to weaken some, with the ECMWF having
the most amplified pattern by that time. There has also been a
more amplified trend with the upper low off the West Coast. The
forecast remains similar to the previous version, with mainly
deterministic guidance (ECMWF/GFS/UKMET) for the first half of the
forecast period, and then increasing percentages of the EC and
GEFS mean by Wednesday and Thursday. The previous discussion is
appended below for reference.
Hamrick/Taylor
...Overview and Guidance/Predictability Assessment...
Strong upper ridging over the Gulf of Alaska and the northeast
Pacific favors troughing along the Pacific Northwest and
downstream through the Great Lakes with weakening ridging over the
Four Corners region. The model/ensembles mostly agree on the long
wave pattern and a blend of the deterministic models sufficed for
the first couple of days of the period Sun-Mon. The ECMWF was
still quicker/east of the consensus over Washington to move the
upper low (or part of it) eastward while the GFS and most
ensembles were slower (the preferred position). Thereafter,
models/ensembles showed typical spread for a day 5-7 forecast and
a blend of the GFS/ECMWF and increasingly their ensemble means
served well to minimize change to the forecast given the
relatively stable ensemble means.
...Weather Highlights/Threats...
Monsoonal moisture will focus rainfall over the Four Corners next
week as the upper high weakens. Coverage is expected to slowly
decrease Sun-Tue but the ensembles hint at a resurgence from
western Mexico by next Wed-Thu which may creep into Arizona.
Elsewhere, rainfall will follow the front in the north but be more
scattered and diurnally-favored in the afternoon in the
Southeast.
Temperatures will be a bit cooler than average over the central
states and later over parts of the West as troughing pushes
inland. Milder than average temperatures are expected over the
Great Lakes and Northeast ahead of the northern tier system.
Elsewhere, temperatures will be within a few degrees of typical
early August values during the day and near/above average for
overnight mins in much of the West Sun-Tue then into the Rockies
Wed-Thu.
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
Hazards:
- Heavy rain across portions of the Middle/Lower Mississippi
Valley and the Southern Plains,
Sat-Sun, Aug 3-Aug 4.
- Flooding possible across portions of the Upper Mississippi
Valley and the Northern Plains.
- Flooding occurring or imminent across portions of the Lower
Mississippi Valley and the Northern
Plains.
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