he medium-range models begin the Day 4 to 8 period in good
agreement. Model solutions show southwest mid-level flow from the
south-central U.S. to the Northeast. An upper-level low is forecast
over southern California. At the surface, a cold front is forecast
to advance southeastward across the southern Plains, Ozarks and mid
Mississippi Valley. Thunderstorm development will be possible along
parts of the front during the afternoon and evening. Although
instability is forecast to be weak ahead of the front Thursday
afternoon, strong deep-layer shear should be adequate for at least
isolated severe storms. The severe threat should extend from
northwest Texas northeastward across the Ozarks and into the lower
Ohio Valley. Hail and wind damage will be the primary threats.
On Friday, the models continue to be in good agreement. The
solutions move the upper-level low into the Desert Southwest and
have an upper-level ridge in the south-central states. The cold
front is forecast to move slowly southward and may stall from the
southern Plains eastward into the mid Mississippi Valley during the
day on Friday. Model forecasts suggest that thunderstorm development
will be possible along and near the front during the afternoon and
evening. The greatest potential for severe storms would be from
Oklahoma eastward into Arkansas, where low-level moisture, deep
layer shear and instability are forecast to be maximized.
Although there is some spread among the GEFS members, on Saturday
the deterministic solutions remain in relatively good agreement. The
upper-level low is forecast to move into the Four Corners region as
a mid-level jet moves into the southern Plains. Ahead of the
approaching system, strong moisture advection is forecast in the
southern Plains where a corridor of 60+ surface dewpoints appears
likely by afternoon. Thunderstorms should be ongoing across parts of
the southern Plains and Ozarks throughout the day. An increase in
thunderstorm coverage may take place in the late afternoon and
evening as instability maximizes across the region. Model forecasts
show a potential for moderate instability, widespread large-scale
ascent and strong deep-layer shear from the southern Plains eastward
into the Ozarks. All severe threat hazards will be possible, but the
magnitude and spatial extent of the severe threat will depend upon
moisture return and the eastward timing of the system.
...Sunday/Day 7 and Monday/Day 8...
On Sunday and Monday, the upper-level low is forecast to move
eastward across the Great Plains. At the surface, a cold front is
forecast to move quickly eastward from the Great Plains into the
Ohio and Tennessee Valleys. Severe thunderstorms will be possible
along parts of the front both on Sunday and on Monday. At this time,
models suggest that the greatest severe threat will be located in
eastern parts of the southern Plains and in the Ozarks on Sunday.
The severe threat should shift eastward into the Ohio and Tennessee
Valleys on Monday. However, uncertainty concerning the timing of the
system is substantial at this extended range in the forecast period.