Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
352 PM EDT Tue May 14 2019
Valid 12Z Fri May 17 2019 - 12Z Tue May 21 2019
...Overview and Weather Highlights/Threats...
Overall, amplified mean troughing aloft will bring a wet period to
a large portion of the western U.S. and Plains states during the
weekend to early next week. Much of the western US to the
northern high Plains will turn colder, with much of the mid-lower
MS Valley eastward turning more summerlike.
Guidance is steadily trending toward resolving the leading strong
trough progressing from the West and Rockies Fri/Sat and in ernest
over the central then east-central states from the weekend into
early next week. This neg-tilt system will spawn surface system
genesis and offers rounds of locally heavy convection/severe
weather as per SPC. Underneath, a gradually weakening closed low
is expected to meander from the northern to eastern Gulf of Mexico
and offer some heavy rain potential for southern Florida.
There is some agreement that upstream flow will bring another
round of strong height falls and widespread precipitation/terrain
enhanced snows to the western states Fri into this weekend,
continuing inland early week across the Great Basin to the High
Plains. Upstream, there is a still uncertain guidance signal to
develop a deeper low in the eastern Pacific early next week that
offers potential to reach CA and the Great Basin/Southwest by
Tuesday 21 May along with renewed unsettled weather/precipitation.
Meanwhile, model and ensemble solutions continue to show above
normal forecast spread with respect to downstream northeastern
U.S./Mid-Atlantic flow through the medium range period as a series
of potent Canadian upper systems progress within an energetic
northern stream. These upper systems and surface system
reflections have trended stronger into the weekend.
Teleconnections relative to the negative height anomaly center
associated with the West Coast mean trough then favor modest
cyclonic flow aloft into early next week.
...Guidance Assessemnt and Preference...
The latest deterministic models (06 UTC GFS/FV3 and 00 UTC
ECMWF/UKMET/Canadian) seem to offer better than expected forecast
clustering Fri into Sun morning, but confidence remains somewhat
muted due to less than stellar continuity issues. Even so, the WPC
product suite primarily was derived from a composite model
solution during this period that seems increasingly reasonable
before quickly transitioning to the much more compatable ensemble
means (06 UTC GEFS/00 UTC ECMWF ensemble mean) into early next
week amid growing forecast spread.
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 Great Basin,
California, and the Southwest, Fri, May 17 and Sun-Tue, May 19-May
21.
- Heavy precipitation across portions of the Central Rockies, the
Central Great Basin, the Northern Rockies, the Northern Great
Basin, and the Northern Plains, Fri-Sat, May 17-May 18and Sun-Tue,
May 19-May 21.
- Heavy rain across portions of California and the Pacific
Northwest, Fri-Sat, May 17-May 18and Sun-Mon, May 19-May 20.
- Heavy rain across portions of the Central Plains, the Lower
Mississippi Valley, the Northern Plains, the Great Lakes, the
Middle Mississippi Valley, the Upper Mississippi Valley, and the
Southern Plains, Fri-Sun, May 17-May 19.
- Heavy rain across portions of the Central Plains, the Lower
Mississippi Valley, the Northern Plains, the Middle Mississippi
Valley, the Upper Mississippi Valley, and the Southern Plains,
Mon-Tue, May 20-May 21.
- Severe weather across portions of the Central Plains, the Middle
Mississippi Valley, the Southern Plains, the Upper Mississippi
Valley, and the Northern Plains, Fri, May 17.
- Severe weather across portions of the Central Plains, the Middle
Mississippi Valley, the Lower Mississippi Valley, the Southern
Plains, and the Upper Mississippi Valley, Sat, May 18.
- Severe weather across portions of the Central Plains and the
Southern Plains, Mon, May 20.
- Severe weather across portions of the Central Plains, the Lower
Mississippi Valley, the Northern Plains, the Middle Mississippi
Valley, the Upper Mississippi Valley, and the Southern Plains,
Tue, May 21.
- Severe weather across portions of the Middle Mississippi Valley,
the Lower Mississippi Valley, the Great Lakes, the Ohio Valley,
and the Tennessee Valley, Sun, May 19.
- Flooding possible across portions of the Northern Rockies.
- Flooding occurring or imminent across portions of the Central
Plains, the Lower Mississippi Valley, the Northern Plains, the
Great Lakes, the Middle Mississippi Valley, the Upper Mississippi
Valley, the Southeast, the Southern Plains, and the Ohio Valley.
- Flooding likely across portions of the Northern Rockies and the
Northern Great Basin.
- Much below normal temperatures across portions of California,
the Central Great Basin, the Pacific Northwest, and the Northern
Great Basin, Mon-Tue, May 20-May 21.
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