Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
1200 PM EDT Sun Apr 07 2019
Valid 12Z Wed Apr 10 2019 - 12Z Sun Apr 14 2019
...Major winter storm likely from the Northern High Plains to the
Upper Midwest by mid to late this week...
...Overview and Guidance Assessment/Preferences...
A vigorous upper-level trough moving from the Rockies to the
central U.S. on Wed is expected to quickly deepen and spin up a
significant low pressure system. The surface low is expected to
move from the Central High Plains Wed morning to the Midwest on
Thu and the Great Lakes by Fri, before quickly moving northeast
into Quebec by Fri night/Sat. Confidence in the forecast for this
system has improved significantly over the past 24-48 hours.
Deterministic model solutions and ensemble members are now very
well-clustered with respect to the surface low track Wed-Fri, with
the ECMWF and UKMET the two solutions most well-centered within
the broad consensus. The UKMET has performed particularly well
with this system over the past few days, showing a highly
consistent structure and track for the system for at least the
past 4-5 runs. Farther west, additional shortwave energy is
expected to dive south across the western U.S. before amplifying
and perhaps closing off across the Great Basin Thu-Fri. Models
consensus has improved significantly on this system as well, with
a large reduction in spread noted over the past 12-24 hours. Given
these considerations, the WPC forecast during days 3-5 (Wed-Fri)
was based on a multi-model blend of deterministic solutions
including the 00Z ECMWF/UKMET/CMC and 06Z FV3 (which was closer to
consensus than the GFS with the central U.S. system). Particular
weight was placed toward the highly consistent ECMWF/UKMET
solutions.
By next weekend, the primary forecast concern becomes how quickly
the energy across the Southwest Thu-Fri ejects eastward into the
central U.S. Models seem to be demonstrating their usual biases
with this system, with the 06Z GFS racing the shortwave eastward
faster than most other solutions, and the ECMWF on the slow side
of the spread. The GFS has shown run-to-run inconsistency,
flipping between a fast solution (06Z run) and a slower more
ECMWF-like idea (00Z run). In most cases such as this, the actual
verification often ends up in between the two camps, perhaps a bit
more toward the slower solutions. Ensembles provide strong support
for the slower solutions (including even the GEFS mean), despite a
very slight faster trend over the past couple runs. Thus, leaned
heavily toward the ECENS/NAEFS ensemble means and the 00Z ECMWF
during days 6-7 (Sat-Sun). Most solutions, regardless of their
timing, spin up a low pressure system across the central Gulf
Coast/lower Mississippi Valley by next Sun ahead of the upper
trough.
...Weather Highlights/Hazards...
The low pressure system crossing the central U.S. Wed-Fri is
expected to bring significant winter weather impacts from portions
of the central/northern Rockies and adjacent High Plains to the
Upper Midwest/Great Lakes. Models show strong signal for a band of
dynamically forced moderate to heavy snow north of the surface low
track. Strong and gusty winds due to the deep nature of the low
pressure system will likely result in blowing snow and perhaps
blizzard conditions for some areas. Farther south, a strong
capping inversion will initially prevent much in the way of
convection in the warm sector across the Southern Plains on Wed.
By Thu-Fri, increasing moisture return as the system enters the
Mississippi Valley should lead to scattered to numerous showers
and thunderstorms, some of which could be strong to severe. The
system across the western U.S. Wed-Fri should produce scattered
areas of rain and mountain snow from the West Coast to the Great
Basin and Rockies. As the system enters the central U.S. by next
weekend, a developing frontal wave along the Gulf Coast/lower
Mississippi Valley should promote strong moisture return and
widespread rain and thunderstorms from the lower Mississippi
Valley to the Tennessee/Ohio Valleys and the Southeast, with areas
of heavy rainfall possible.
Above average temperatures are expected in the warm sector ahead
of the deep low pressure system. High temperatures are forecast to
be 10 to 20 deg F above average across Southern/Central Plains and
lower/mid Mississippi Valley on Wed, and 10-15 deg above average
across portions of the Southeast and Tennessee/Ohio Valleys on
Thu. In the wake of the low pressure system, much colder air is
expected to spread into the Rockies and the central U.S., with
high temperatures 15-25 deg below average possible through late in
the week.
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