Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
338 PM EDT Fri Apr 26 2019
Valid 12Z Mon Apr 29 2019 - 12Z Fri May 03 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 fairly persistent pattern will develop in the medium range
period, with a deep upper low in north central Canada gradually
retrograding a bit westward later in the period, and troughing
over the northwestern U.S. extending southward. A subtropical
ridge is 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 some typical
uncertainty in timing and placement of shortwaves moving across
the general troughing pattern in the west and central U.S. WPC
used a multi-model deterministic blend of the 00Z and 06Z GFS, 00Z
UKMET, and 00Z ECMWF early in the period, then leaning toward the
EC and GEFS means later in the week as uncertainty develops in the
deterministic runs regarding the upper low in western Canada and
potentially shearing out its energy, which affects the downstream
features. Run to run inconsistency remains high, so stayed with
the means for now.
...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 Great Basin and central/northern Rockies
early in the period. 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 the 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 in the Ohio Valley and into the
northern Mid-Atlantic to Lower Great Lakes region as well.
Flooding will be 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 snows for portions of the Northern High
Plains with low genesis and approach.
Tate/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
Hazards:
- Heavy precipitation across portions of the Central Rockies, the
Central Plains, and the Central Great Basin, Mon-Wed, Apr 29-May 1.
- Heavy rain across portions of the Central Plains, the
Mid-Atlantic, the Lower Mississippi Valley, the Central
Appalachians, the Tennessee Valley, the Great Lakes, the Middle
Mississippi Valley, the Northeast, the Upper Mississippi Valley,
the Southern Plains, and the Ohio Valley, Mon-Fri, Apr 29-May 3.
- Heavy snow across portions of the Central Rockies, the Central
Plains, the Northern Plains, and the Northern Rockies, Mon-Wed,
Apr 29-May 1.
- Heavy snow across portions of the Northern Plains, Tue-Wed, Apr
30-May 1.
- Severe weather across portions of the Lower Mississippi Valley
and the Southern Plains, Tue, Apr 30.
- Flooding possible across portions of the Northeast, the Great
Lakes, the Upper Mississippi Valley, and the Northern Plains.
- Flooding occurring or imminent across portions of the Lower
Mississippi Valley, the Northern Plains, the Great Lakes, the
Northern Rockies, the Middle Mississippi Valley, the Northeast,
the Northern Great Basin, the Upper Mississippi Valley, the
Southern Plains, and the Ohio Valley.
- Flooding likely across portions of the Northern Great Basin.
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