Day 1 Severe Weather Outlook

Valid 301300Z – 011200Z


Scattered severe thunderstorms will be possible through this evening
across the Arklatex, Lower Mississippi Valley, and Mid-South
regions. A few tornadoes, large hail, and damaging winds are

…Arklatex to Lower MS Valley and Mid-South…
Level 1 (Marginal) categorical risk has been expanded west to
account for ongoing convection across the Lower Red River Valley.
This activity may persist through midday but should largely pose an
isolated severe risk amid weak low-level lapse rates and veered
low-level winds per 12Z FWD sounding.

A plume of upper 60s surface dew points across east TX should be
shunted east across LA and far southern AR this afternoon.
Substantial low-level moistening of a relatively dry air mass in MS
should result in stratus overspreading areas east of the MS River,
limiting prospects for robust boundary-layer heating. But cloud
breaks within the Gulf moisture plume across LA and east TX should
support moderate buoyancy here amid moderately steep mid-level lapse
rates. With north-northeast extent ahead of the front across the
Mid-South, surface-based buoyancy will be increasingly meager.

Deep-layer shear will strengthen as a powerful 500-mb jet amplifies
across the TX Panhandle and OK. This should aid in increasing
convective intensity this afternoon as effective shear averages
around 60 kts. Early morning HRRR-NCEP and HRRR-ESRL runs are more
aggressive than other individual 00Z HREF members with simulations
of several supercells from northern LA to western TN. The parent RAP
appears to be aggressive compared to other guidance with both
boundary-layer moistening and heating east of the MS River. The lack
of nearby cyclogenesis suggests this scenario is uncertain. But
should this scenario appear more likely to occur in later updates,
an upgrade to level 3 (Enhanced Slight) tornado risk would be
warranted. At this time, the more probable forecast is for a few
tornadoes centered on northern LA into western/northern MS.

Overall severe threat should wane with eastern extent across the TN
Valley tonight given a dearth of surface-based instability. However,
with continued amplification to the tropospheric flow and lingering
elevated buoyancy, the severe risks have been extended farther east
than previously forecast.

..Grams/Gleason.. 11/30/2019


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