Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
1210 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
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