Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
212 AM EDT Sat Jul 03 2021
Valid 12Z Tue Jul 06 2021 - 12Z Sat Jul 10 2021
...Elsa is forecast to impact Florida and the Southeast through
the middle of next week with heavy rainfall and potential for high
winds...
...Repeating heavy rain is likely to persist over southern Texas
through much of next week as low pressure lingers...
...Overview...
A summer pattern persists through next week as the main jet
stream/westerlies meander over the northern U.S. and southern
Canada. An upper ridge over the Desert Southwest is forecast to
strengthen, while a weak upper trough/low merely drifts southwest
over Texas and into northern Mexico, and a fairly low amplitude
trough will be centered around the Great Lakes region.
Additionally, what is currently Hurricane Elsa is forecast to
impact Florida and the Southeast through the middle of next week.
...Guidance/Predictability Evaluation...
Guidance remains reasonably agreeable with the mid-latitude
pressure pattern described above except for continued uncertainty
with the track/timing/strength of Elsa. A deterministic model
blend of the 18Z GFS, and 12Z ECMWF/UKMET sufficed for Days 3-5.
The main differences outside of Elsa are with the timing and
amplitude of shortwave trough ejecting east from the Pacific
Northwest/southwest Canada. The 00Z GFS is now the fastest with
this low ejection, just slightly ahead of the 12Z ECMWF. The 12Z
CMC was the largest outlier of the deterministic guidance with
this feature by re-amplifying it off the Pacific Northwest, making
it the slowest solution by far, so it was limited in the blend.
Regarding Elsa, the deterministic GFS and CMC are the strongest
with the GFS west of the Florida Peninsula and the CMC east (the
CMC has also slowed considerably from being by far the fastest
model). The ECMWF and its ensembles are still weaker with the
system with track generally east of Florida while the GFS/GEFS are
generally west. The UKMET is still similar to GFS, just a bit
weaker, farther east, and slower. The GFS remains steady for
multiple days have been steady with similar track, though it has
shifted farther west into the Gulf. A more westward track is
expected with a stronger Elsa (currently a hurricane), so it
continues to work well to follow NHC's forecasts for Elsa's track
and strength for the QPF.
...Weather Highlights/Hazards...
An upper low/trough drifts southwest over southern Texas into
northern Mexico through next week making for a repeating heavy
rain threat there each day of the next workweek, with multi-inch
totals expected with totals over a foot likely (though the
heaviest looks to be just south of the Rio Grande. Farther west,
late-day monsoonal type showers and thunderstorms are likely to
continue through Wednesday over the Central/Southern Rockies.
Heavy rainfall, flooding, and high winds are potential threats
where Elsa tracks. Timing and strength of Elsa still have
considerable uncertainty, but the heavy rain threat is more for
the western Florida Peninsula Tuesday and across north Florida to
eastern Georgia/South Carolina coast Wednesday. Periods of rain
are forecast along and ahead of a front moving through the week
from the north-central to northeastern CONUS, and tropical
moisture from Elsa may help increase rain totals in the
Mid-Atlantic and Northeast in the latter part of the week
depending on its track.
The heat wave persists over the western CONUS through next week as
ridging restrengthens with max temperature anomalies of generally
10 to 15 degrees above normal for the Northwest/northern Great
Basin, challenging several daily high temperature record, mostly
in the northern Great Basin Tuesday and Wednesday. Temperatures
will generally be a few degrees lower than average in the
south-central U.S./Texas through the week due to cloudiness and
rain from the persistent upper level disturbance there.
Jackson
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