Day 1 Severe Weather Outlook

Valid 151200Z – 161200Z


Marginally severe hail and strong/gusty winds may occur this
afternoon and evening across parts of the lower Mississippi Valley,
Tennessee Valley, and southern Appalachians.

…Lower Mississippi Valley into the Tennessee Valley and Southern
Strong mid/upper-level westerlies will overlie much of the
central/eastern CONUS today. Embedded within this enhanced flow
aloft, a shortwave trough will advance eastward from the northern
Plains/Upper Midwest to the Great Lakes region by this evening. At
the surface, a weak surface low is forecast to develop northeastward
from eastern KS to New England through the period. A cold front
attendant to this low will move southeastward across parts of the
southern Plains, lower MS Valley into the TN Valley, and southern
Appalachians by late tonight.

Although the primary large-scale ascent associated with the
shortwave trough should remain displaced to the north of the warm
sector, a southern-stream mid-level jet may provide enough lift to
encourage convective initiation along/ahead of the front by this
afternoon from southern AR to eastern TN. Greater low-level
moisture, characterized by mid to upper 60s surface dewpoints,
should be present across southern AR/northern MS and southwestern TN
by peak diurnal heating. Somewhat steepened low-level lapse rates
along with this low-level moisture should support around 1000-1500
J/kg of MLCAPE this afternoon ahead of the front across this region.
Less instability (MLCAPE generally 500-1000 J/kg) should be present
across northern AL/GA, middle/eastern TN, and into far western NC,
as low-level moisture should remain more limited with northeastward
extent across the warm sector.

Any storms that can form and mature while moving eastward across
this region could become organized owing to strong mid-level
west-southwesterly flow supporting 40-50 kt of effective bulk shear.
Isolated instances of marginally severe hail and strong/gusty winds
producing occasional damage should be the main threats with these
storms this afternoon and early evening. Overall coverage of
convection still appears to remain rather isolated, and storms
should gradually weaken by late this evening with the loss of
daytime heating.

Although a favorable environment for severe storms will exist this
afternoon across parts of TX, negligible large-scale ascent aloft
and a low-level inversion should prevent storms from forming along
the front. Elevated storms behind the cold front may form across
parts of the southern Plains late tonight into early Thursday
morning, but instability should remain weak.

…Coastal Pacific Northwest…
Strong shear will develop during the afternoon and evening as a
deepening low develops northeastward toward the WA/BC Coast.
Pronounced lift from low-level warm advection will likely support
widespread precipitation and gusty gradient winds. However, forecast
soundings show only meager surface-based instability along the WA/OR
Coast. Low-topped showers, with occasional embedded thunderstorms,
may affect this area during the afternoon and evening with locally
strong/gusty winds. But, the probability of organized severe storms
still appears low.

..Gleason/Nauslar.. 01/15/2020


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