SPC Jul 17, 2019 0600 UTC Day 1 Convective Outlook

SPC 1200Z Day 1 Outlook

Day 1 Outlook Image

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
0100 AM CDT Wed Jul 17 2019

Valid 171200Z - 181200Z


Severe thunderstorms capable of severe wind gusts and large hail are
possible across portions of the northern High Plains and
mid-to-upper Mississippi Valley through tonight. Storms capable of
damaging wind gusts will be possible across portions of the
Northeast this afternoon and evening.

...Minnesota/Iowa into the mid MS Valley...
A great deal of uncertainty remains regarding convective evolution
leading into the Day 1 period across portions of MN/IA and vicinity,
but a substantial severe threat may evolve later today somewhere in
the vicinity of IA and southern MN, and potentially further south
into the mid MS Valley. Substantial midlevel flow will move into MN
and northern IA in conjunction with a shortwave trough, while a
seasonally strong low-level jet will impinge on this region from the
SSW. Strong to extreme buoyancy will develop south of any convective
outflow this afternoon, as steep midlevel lapse rates over spread a
very warm and moist boundary layer. The timing, intensity, and
location of any early morning thunderstorm clusters and subsequent
redevelopment remain highly uncertain, however. Possible scenarios
include one or more progressive MCSs capable of damaging wind
swaths, and also supercell development along outflow boundaries,
capable of large hail and possibly a couple of tornadoes. An upgrade
to severe probabilities in subsequent outlooks is possible if the
potential scenarios become clearer. 

Further north across northern MN, shear profiles will be quite
favorable for organized convection, but the amount of available
instability will largely depend on convective development (or lack
thereof) further south. If a substantial MCS impacts southern MN
during the day, that will likely limit destabilization further
north, but if the environment across northern MN remains mostly
undisturbed, then there is some potential for organized clusters and
perhaps a couple of supercells capable of large hail, damaging wind,
and perhaps a tornado. 

...Northern High Plains...
While the northern High Plains will generally be between shortwave
troughs for most of the day, a belt of stronger midlevel westerly
flow will persist across this region, with some potential for winds
to veer to southeasterly during the afternoon, maintaining
sufficient low-level moisture for moderate buoyancy by late
afternoon into the Black Hills and eastern WY. Some uncertainty
remains regarding storm coverage remains in this region, but there
is some potential for a couple of supercells with an attendant risk
of large hail and severe wind gusts. 

...Central High Plains...
Widely scattered thunderstorm development is possible late this
afternoon across in the hot and well-mixed regime from southwest NE
into western KS. Shear will be weaker compared to areas further
north, but sufficient to support some modest storm organization.
Steep low-level lapse rates will support a threat of isolated severe
wind gusts. 

...Ohio Valley into the Mid Atlantic and Northeast...
As the remnants of T.C. Barry get caught up in the westerlies, some
enhancement to the low/mid-level flow is expected later today.
Midlevel lapse rates will be weak throughout the region, but
substantial heating of a moist airmass (PW values generally between
1.5 - 2 inches) will result in the development of moderate buoyancy
from the OH Valley into the Mid Atlantic and portions of the
Northeast. Widespread convection will move across this region this
afternoon into this evening, with thunderstorm clusters capable of
locally damaging wind possible. The best overlap of shear and
buoyancy is forecast to occur from PA into southern New England,
where the greatest relative threat of damaging wind is currently
forecast. Flow/shear will be weaker into the Mid Atlantic, but still
sufficient for wet microburst potential given strong heating and
steep low-level lapse rates.

..Dean/Squitieri.. 07/17/2019

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