Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
226 AM EDT Sat Apr 27 2019
Valid 12Z Tue Apr 30 2019 - 12Z Sat May 04 2019
...Heavy rain and the potential for flooding and flash flooding
are expected for parts of the Southern Plains and Lower/Middle
Mississippi Valley to Ohio Valley...
...Overview and Assessment of Model/Ensemble Guidance and
Predictability...
A reasonably persistent flow pattern develops next week over the
U.S.as a deep north-central Canadian upper low gradually
retrogrades to western Canada. Northern stream troughing digs
underneath into a wintry northwestern U.S. as an initially closed
southern stream E-Pacific low ejects with various timings inland
into the Southwest. Prefer a southern stream progression on the
slower side of the full envelope of solutions considering the
initially closed nature of the low, with the GFS more progressive
than the ECMWF/UKMET/Canadian. A series of troughs subsequently
eject northeastward from the Plains through the MS/OH Valleys to
the Northeast to support wet low development on a slow moving
front. This occurs overtop a subtropical ridge forecast to build
over the Southeast through midweek before pushing out by Friday.
The overall pattern seems to be generally well handled by the
models, with typical uncertainty in the timing and placement of
shortwaves from a general troughing pattern in the west and
central U.S. WPC used a multi-model deterministic composite blend
Tue-Thu, with transition to the GEFS/ECMWF ensemble means later
week consistent with growing uncertainty and run to run
inconsistency.
...Weather Highlights/Threats...
Passage of multiple shortwaves/height falls in both northern and
southern streams will generate some enhanced rains and mountain
snows for portions of the central/northern Rockies early next
week. These systems will progress downstream and a main weather
focus will develop over the central U.S. Moisture inflow/pooling
into a persistent/slow moving/wavy front will focus multiple
rounds of showers and thunderstorms, with some potential for
severe weather and areas of heavy rainfall. The strongest signal
for heavy rainfall of multiple inches will be from the
Southern/Central Plains to the Lower/Mid-Mississippi Valley, with
some potential for heavy rain to spread over the Ohio Valley and
northern Mid-Atlantic/Lower Great Lakes region. Flooding remains
possible as particularly the Mississippi Valley has had flooding
concerns for weeks, and with the convective element of the
precipitation, flash flooding is possible as well. On the northern
fringe the precipitation, sufficient cold air may be in place to
support some snows for portions of the Northern High Plains with
low genesis and approach.
Schichtel
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