Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
232 AM EDT Wed Jun 26 2019
Valid 12Z Sat Jun 29 2019 - 12Z Wed Jul 03 2019
...Overview and Weather Highlights/Threats...
Transition to quasi-zonal flow marks the arrival of a typical
summertime pattern but that will be punctuated by an inverted
trough over Texas. That leaves the northern stream to waver along
the US/Canadian border with bouts of rainfall and mostly afternoon
thunderstorms. No clear signal exists for organized heavy rainfall
though the potential is there on a local level. Temperatures will
be well above average in the northern Plains/Upper Midwest (80s to
upper 90s, warmest on Saturday), but with a daily risk of
showers/storms with locally heavy downpours in the vicinity of a
warm front Saturday and a persistent stationary front Sunday
onward. The Southeast and lower MS Valley/Gulf Coast region will
see a daily chance of showers/storms in typical summertime fashion
that may be enhanced via the upper trough and lower-level moisture
increases from the Gulf.
...Guidance/Predictability Assessment...
The deterministic models mostly clustered together for the first
few days before uncertainty in timing/evolution (mostly off the
West Coast) resulted in decreased confidence in specifics. Trended
to a majority ensemble mean weighting by next Tue/Wed. Largest
question remains west of the WA/OR and how the positively-tilted
(and latitudinally-elongated) trough evolves downstream of a
significant positive height anomaly over southern Alaska. These
scenarios often present mutually exclusive forecasts (e.g.,
vorticity either sliding westward under the upper high or coaxed
eastward into the in-situ trough) and a blend would result in a
less than realistic solution. However, a blended mean starting
point sufficed for now which indicates less amplitude over the
Pacific Northwest that does not favor any singular deterministic
model.
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:
- Flooding possible across portions of the Central Plains and the
Middle Mississippi Valley.
- Flooding occurring or imminent across portions of the
Central/Southern Plains, the Middle/Lower Mississippi Valley, and
the Ohio Valley.
- Flooding likely across portions of the Central Plains and the
Middle Mississippi Valley.
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