Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
1156 AM EDT Fri Apr 05 2019
Valid 12Z Mon Apr 08 2019 - 12Z Fri Apr 12 2019
...Overview and Guidance Assessment/Preferences...
A moderately progressive pattern is expected across the CONUS
during the medium range with splitting of flow across the West
resulting a series of southern stream systems traversing the
nation. The first of these should cross the lower Mississippi
Valley/Southeast Mon-Tue. The second and more significant of these
features should move into the West Coast Mon-Tue before amplifying
across the Rockies on Wed and perhaps developing a closed upper
low across the central U.S. Wed night-Thu. Finally, a third
upper-level wave should amplify along the West Coast Thu-Fri as
the strong central U.S. system moves into the lower Great Lakes.
Meanwhile, a number of lower amplitude northern stream shortwaves
will traverse areas from the Northern Plains/Midwest to the
Northeast.
In general a blend of the 00Z ECMWF/UKMET/CMC was preferred as a
forecast starting point during days 3-5 (Mon-Wed). These solutions
handled significant features similarly during this time period.
The shortwave reaching the West Coast during this time frame
showed the most substantial differences among the guidance, with
the GFS continuing to show a slower progression/later arrival to
the coast relative to the preferred solutions. The GFS continued
to lag the preferred consensus solution even as the western system
reaches the central Rockies Tue night-Wed and significant
cyclogenesis commences across the Central High Plains. As a strong
low pressure system likely crosses from the Central Plains to the
Midwest Wed into Thu, there was relatively good clustering among
ECENS and CMCE members in the vicinity of the deterministic 00Z
ECMWF. The GFS begins to suffer from the opposite issue to earlier
in the period, showing a much weaker system aloft and racing the
surface low quickly eastward into the Ohio Valley, with the CMC
somewhere between the ECMWF and GFS. Given the good clustering
around the ECMWF, the forecast during days 6-7 (Thu-Fri) was
comprised of a three-part blend including the ECMWF and the
ECENS/NAEFS ensemble means. This approach also worked well for the
next round of energy dropping southward/amplifying across the
western U.S. late next week. Model solutions have shown a high
degree of run-to-run variability with that feature, varying
between a more open wave or one that quickly deepens into a closed
upper low over southern California. With ensemble means similar
here, a majority ensemble-based approach was favored.
...Weather Highlights/Hazards...
Showers and thunderstorms with locally heavy rains are possible
from the Southeast/Tennessee Valley to the Mid-Atlantic Mon-Tue as
the first southern stream shortwave/low pressure system traverse
those areas. A northern stream system may also bring a round of
snow to portions of northern New England Mon/Mon night. The second
and most significant southern stream system during the period
should produce widespread rains and mountain snows (some
potentially heavy) from California to the Pacific Northwest and
then inland across the central/northern Rockies Mon-Tue. As the
system reaches the central U.S. by the middle of next week, a band
of dynamically forced precipitation is expected to develop from
the Northern High Plains to the Midwest and Great Lakes. While the
delineation of precipitation types is unclear at this time, a band
of potentially heavy snow appears probable north and west of the
surface low track, with a transition zone and areas of potentially
heavy rain as well. Relatively weak moisture return and a strong
capping inversion in the warm sector of the system should keep
showers and thunderstorms less extensive in coverage than would
otherwise be expected, but any convective activity that is able to
develop could be potentially strong given the dynamic nature of
the low pressure system.
Warm temperatures are expected across much of the central and
eastern U.S. during the early to middle portion of next week ahead
of the significant low pressure system. High temperatures ranging
from 10 to 20 deg F above average are possible Mon-Wed over a
large area, with the greater anomalies across the Plains. Colder
air and further amplification of upper troughing across the West
in the wake of the mid-week system will support below average
temperatures, with highs 5 to 15 deg below average across much of
the interior West by Wed and into the Central/Northern Plains by
Thu-Fri.
Ryan
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