Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
141 AM EDT Mon Apr 08 2019
Valid 12Z Thu Apr 11 2019 - 12Z Mon Apr 15 2019
...Major winter storm likely from the Northern High Plains to the
Upper Midwest mid to late this week...
...Major spring cyclone to produce heavy snow and high winds in
portions of the north central Plains to upper MS Valley and Upper
Great Lakes...
...Overview and Guidance Assessment/Preferences...
The models are in excellent agreement now on the developing
cyclone in the central Plains that moves in to the upper midwest
on day 3 Thu and across the upper Lakes Fri before exiting up into
Canada Friday. 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 trailing cold front moves off the northeast/mid Atlantic
coasts early Sat.
In the western US, shortwave energy is expected to dive south
across the Pacific Northwest Thu to the southwest US Fri, perhaps
closing off as it crosses south through the Great Basin. The 12z
ECMWF and 18z GEFS Means remain in better than average agreement,
which serve to center in between the 12z ECMWF with its further
west track of the 500 mb wave, the GFS/GFS parallel with its
further east track. The WPC forecast blended the 2 ensembles with
less weight to the operational ECMWF.
Next weekend, the primary forecast concern becomes how quickly the
energy across the Southwest Thu-Fri ejects eastward into the
central U.S. The 18z GFS continues to move the upper trough and
associated sfc low eastward faster than most other solutions,
so was not used, given the GEFS Mean was slower like the 12z ECMWF
and 12z ECMWF Ensemble Mean. The Canadian/Canadian ensemble mean
was a few hours slower in moving the upper trough and sfc low
northeast with a similar track to the GEFS/ECMWF.
Most solutions spin up a low pressure system across the lower
Mississippi Valley next Sun and move the low into the Ohio Valley
and Great Lakes Mon, when the system occludes. The triple point
crosses the mid Atlantic, with a new low developing and moving
northeast towards coastal New York/New England or the adjacent
coastal waters.
The models also show the next upper trough over the northeast
Pacific set to move onshore and inland late Sun into Mon 15 Apr.
Timing and phasing differences persist with the ECMWF/GFS/Canadian
all offering differing solutions, as more weighting was given to
the ensemble means until better agreement develops.
...Weather Highlights/Hazards...
The low pressure system crossing the central U.S. Thu-Fri is
expected to bring major winter weather impacts from portions of
the north central Plains to the Upper Midwest/upper Great Lakes.
Models show strong signal for a band of heavy snow north of the
surface low track. Peak probabilities for heavy snow cover SD,
northern NE, southern to central MN, northern WI, and the UP of
MI. Strong and gusty winds will likely result in blowing snow and
perhaps blizzard conditions for some areas. On Thu-Thu night,
increasing moisture return should lead to scattered to numerous
showers and thunderstorms in the mid MS Valley to the OH Valley,
some of which could be strong to severe. See the Storm Prediction
Center outlooks for severe convective weather probabilities.
The system across the western U.S. Thu-Fri should produce
scattered areas of valley rain and mountain snow from the West
Coast to the Great Basin and Rockies. As the system enters the
central U.S. 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
Appalachians and mid Atlantic, with areas of heavy rainfall
possible.
High temperatures are forecast to be 10-15 deg above average
across portions of the Mid MS Valley to Southeast and
Tennessee/Ohio Valleys on Thu. The anomalous warmth spreads east
into the Appalachians to the southeast on Fri, and then along the
east coast Sat, then the southeast and FL Sun.
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 late in the
week. The anomalies taper on Sun, with the primary area of below
normal temps next Mon 15 Apr under the upper trough in the Plains
to the MS Valley.
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