SPC AC 051730
Day 2 Convective Outlook
NWS Storm Prediction Center Norman OK
1130 AM CST Sun Mar 05 2017
Valid 061200Z - 071200Z
...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS
NORTHWESTERN AR AND SOUTHWESTERN MO...
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
THE UPPER/MID MS VALLEY TO THE OZARKS AND VICINITY...
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS MUCH OF
THE UPPER/MID MS VALLEY TO PARTS OF THE SOUTHERN PLAINS AND
MID-SOUTH...
...SUMMARY...
Severe thunderstorms will be possible mainly from Monday evening
through early Tuesday morning across much of the upper and middle
Mississippi Valley southwestward to the Ozarks and Mid-South. The
likelihood for a greater concentration of severe thunderstorms,
including the risk for a few tornadoes, appears to be across parts
of northwestern Arkansas and southwestern Missouri Monday evening.
...Synopsis...
A large-scale upper trough over the western CONUS with multiple
embedded vorticity maxima will move eastward across the
northern/central Plains by Monday evening, eventually reaching the
Upper Midwest/Great Lakes regions by the end of the period. Ascent
attendant to the upper trough will encourage a surface low initially
over the Dakotas Monday morning to develop northeastward to southern
Manitoba/Ontario by Monday night while deepening. An associated cold
front will spread southeastward across parts of the central/southern
Plains into the upper/mid MS Valley and Ozarks region, eventually
overtaking a dryline extending southward from the front across the
central/southern Plains.
...Upper/Mid MS Valley to the Ozarks...
The cold front will be the primary forcing mechanism for convective
initiation across the upper MS Valley and central Plains. Initiation
will likely occur by Monday evening across southern/eastern MN into
IA, northwestern MO, and eastern KS, with convection quickly growing
upscale into a line along the front. Strong to damaging wind gusts
will be the main threat with this activity. Latest guidance suggests
weak instability may develop as far north as southern/eastern MN
into western WI by Monday evening, with the 12Z NAM remaining more
aggressive regarding the degree of low-level moisture return than
the 12Z GFS or 00Z ECMWF. Regardless, enough instability should be
present to support surface-based convection across parts of the
upper to mid MS Valley through early Tuesday morning, as strong
shear associated with the upper trough and long, generally straight
hodographs support an organized convective line with damaging wind
potential. Eventually the southeastward-moving line will encounter a
less unstable airmass across IL into western KY and the Mid-South,
with a slowly decreasing severe threat overnight.
Farther south across far southeastern KS/eastern OK into MO and AR
greater low-level moisture, characterized by at least low 60s
surface dewpoints, should be present. There is increasing concern
for pre-frontal convective initiation along/ahead of the dryline
Monday evening across this region, mainly after 00Z. Forecast
soundings from the NAM/GFS both show enlarged low-level hodographs
and strong effective bulk shear, which will support discrete
supercells if convection can form. Nearly all
convective-parameterizing guidance suggests there will be enough
glancing influence/ascent from the upper trough to the north
combined with strong low-level warm air advection to break the cap
across this area. All severe hazards will be possible with any
supercells that can form, including a few tornadoes. Higher severe
probabilities have been introduced for northwestern AR into
southwestern MO to account for this scenario. The
southeastward-moving cold front will eventually overtake this
pre-frontal convection, with a continued risk of mainly damaging
winds continuing overnight into early Tuesday morning across parts
of the Mid-South.
..Gleason.. 03/05/2017
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