Day 2 Convective Outlook
NWS Storm Prediction Center Norman OK
1124 AM CST Mon Feb 05 2018
Valid 061200Z - 071200Z
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS LATE TUESDAY
AFTERNOON AND EVENING ACROSS PARTS OF NORTHEASTERN TEXAS...SOUTHERN
ARKANSAS...NORTHERN LOUISIANA AND NORTHWESTERN MISSISSIPPI...
...SUMMARY...
Thunderstorms are expected to develop within a corridor from
northeast Texas through the Mississippi Delta region late Tuesday
afternoon and evening, perhaps accompanied by a risk for severe hail
and gusty winds.
...Discussion...
Blocking within the large-scale mid/upper flow will remain present
west of the Pacific coast through this period. The mid-latitude
high/ridging portion of this regime appears likely to remain the
most amplified, with a series of cold intrusions continuing to
develop southeastward to the lee of the Rockies, beneath northwest
flow to the east of the ridge. At the same time, however, low-level
moistening also continues across parts of the southwestern Gulf of
Mexico into the lower Rio Grande Valley. A northeastward surge of
this air across the lower Mississippi Valley into the portions of
the Tennessee/Ohio Valleys appears possible by late Tuesday night.
Models suggest that this will occur downstream of one short wave
trough within the mid-latitude westerlies, forecast to dig through
the southern Rockies, in association with one or two lower amplitude
impulses preceding it, within a belt of westerlies emanating from
the subtropical eastern Pacific.
...Texas through the Mid South/central Gulf States...
It appears possible that destabilization associated with the
moisture influx, in the presence of initially weak mid-level capping
and ascent associated with low-level warm advection, may be
sufficient to support scattered thunderstorm activity with somewhat
increasing probabilities from upper Texas coastal areas through
portions of southern Louisiana and Mississippi during the day
Tuesday. However, guidance is generally suggestive that the more
substantive increase in convective potential will take place late
Tuesday afternoon through Tuesday evening, roughly in a corridor
from parts of north central/northeast Texas toward the Mississippi
Delta region. This is expected to occur coincident with
strengthening of south/southwesterly 850 mb flow to 30-50+ kt, along
a tightening low-level frontal zone, beneath increasingly divergent
upper flow (associated with at least one subtropical perturbation
and the right entrance region of a strengthening upper jet within
the mid-latitude westerlies).
The bulk of the thunderstorm development seems likely to form above
at least a shallow, but substantive near-surface stable layer, to
the cool side of the surface frontal zone. However, by early
Tuesday evening, it appears that elevated moisture return could be
sufficient to support CAPE on the order of 500-1000 J/kg, with
higher CAPE over central through northeast Texas, decreasing in
magnitude to the northeast. Coupled with favorable shear within the
inflow layer, and perhaps through the convective layer, the
environment may become at least marginally conducive to the
generation of severe hail, before convection becomes increasingly
widespread across the Ark-La-Texas and Mid South by late Tuesday
night.
..Kerr.. 02/05/2018