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day 4-8 convective outlook
nws storm prediction center norman ok
0328 am cst tue dec 07 2021

valid 101200z - 151200z

...discussion...
large-scale upper troughing should continue to amplify as it moves
eastward over the plains on day 4/friday. an embedded shortwave
trough is forecast to advance northeastward across the lower/mid ms
valley during the day. latest guidance suggests that this feature
may aid convective initiation across this region by friday
afternoon. rich low-level moisture will likely have advanced
northward as well in tandem with a northeastward-developing surface
low over the mid ms valley and midwest. a fairly broad warm sector,
with sufficient instability for surface-based thunderstorms, should
be present from the tx/la/ms gulf coast northward into parts of the
midwest and oh valley. strong low-level and deep-layer shear should
also prove favorable for updraft rotation/organization.

at this point, the best potential for organized severe thunderstorms
may exist over the lower/mid ms valley during the day friday, as
ascent associated with the previously mentioned embedded shortwave
trough overspreads this region. regardless, there remain too many
potentially limiting factors to include 15% severe probabilities for
day 4/friday at this time. namely, the overall positive tilt to the
upper trough and considerable amount of front-parallel flow which
may tend to undercut thunderstorms, uncertainty over early-day
convection contaminating the warm sector, and continued differences
in guidance regarding the strength/placement of the low-level jet,
particularly with southward extent. even with these uncertainties, a
broad area of at least marginal/isolated severe potential is evident
for day 4/friday from parts of the southeast to the oh valley, and
inclusion of some severe probabilities will likely be needed in the
next outlook update.

this marginal/isolated severe risk may persist into day 5/saturday
as the upper trough moves from the central to eastern conus. there
is even more uncertainty with eastward extent regarding sufficient
low-level moisture return to support robust convection, as
thunderstorms along the eastward-advancing cold front will probably
outpace the already weak instability. even so, some severe threat
may continue on day 5/saturday from portions of the southeast into
the oh/tn valleys and perhaps the adjacent southern/central
appalachians. once the surface cold front clears the east coast by
day 6/sunday, severe potential appears very low across the conus
through the rest of the forecast period.

..gleason.. 12/07/2021

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