Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
201 AM EDT Sat Apr 06 2019
Valid 12Z Tue Apr 09 2019 - 12Z Sat Apr 13 2019
...Overview and Guidance Assessment/Preferences...
On Day 3, the eastern upper trough indicate height falls over the
northeast leading to low pressure development on the front as it
moves off the New England coast, with a trailing trough across the
region. The southern portion of the front slowly progresses
across the southeast on Tue before moving off the coast Wed.
The ECMWF was on the fast edge of the cluster of solutions with
the upper trough progression, with the 12z ECMWF ensemble mean
several hours slower and clustering well with the GEFS Mean, so
the means were given more weighting given better overlap.
Attention turns west with the the first of the western troughs
crossing the Great Basin to the WY/CO Rockies. Low pressure
develops on the high plains by Wed morning and continues moving
northeast towards the mid MS Valley Thu and Great Lakes Fri while
occluding. On Sat a triple point low develops near the New
England coast and eventually depart into the Canadian maritimes.
For this system, the 18z GEFS/12z ECMWF ensemble means hold good
run to run continuity and overlap with one another , as the
operation the 12z ECMWF/18z GFS were bookends on either side of
the means (ECMWF/GFS south).
The next in the series of upper-level waves should amplify along
the West Coast Thu-Fri and continue into the Great Basin and
southwest Fri with a surface frontal system develops in the
southwest. The 12z ECMWF has the highest amplitude/shorter
wavelength upper ridge approaching the Pacific northwest, leading
to higher amplitude/slower moving trough across the southwest.
Most ECMWF ensemble members have a lower amplitude coupled
northeast Pacific ridge and downstream southwest trough, so more
weighting was given towards the mean solution, again with support
from the 18z GEFS Mean.
...Weather Highlights/Hazards...
Showers and thunderstorms with locally heavy rains are possible in
the Southeast to southern mid Atlantic Tue as the first southern
stream shortwave/low pressure system moves slowly across the
region.
The second and most significant southern stream system during the
period should produce widespread rains and mountain snows (some
potentially heavy) across the central/northern Rockies Tue. As the
system reaches the central U.S. by the middle of next week, a band
of precipitation along the l0ow level frontogenesis maxima is
expected to develop from the Central to Northern High Plains to
the Midwest and Great Lakes.
A band of moderate to heavy snow appears probable north and west
of the surface low track, with a transition zone and areas of
moderate to heavy rain as well.
See the Storm Prediction Center outlooks for severe convective
weather potential.
Once the system moves into the lakes, the precip should progresses
across the Great Lakes to the mid Atlantic and northeast next
Fri-Sat 13 Apr.
The next west coast trough brings valley showers and mountain snow
showers across the Great Basin to the central Rockies Fri into Sat
13 Apr.
Warm temperatures are expected across much of the central and
eastern U.S. during the early to middle portion of next week. 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 southern Plains to lower MS Valley Tue-Wed. 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 Wed and into the Central/Northern Plains
Thu-Sat. Very little of the country is forecast to be above
normal Sat 13 Apr, mainly focused on FL and northwest WA.
Petersen
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