SPC AC 172000
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0300 PM CDT Tue Jul 17 2018
Valid 172000Z - 181200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS THE CENTRAL
HIGH PLAINS AND ALSO PORTIONS OF THE NORTHEAST...
Severe thunderstorms capable of damaging winds are possible over the
Northeast States through early evening. Scattered severe storms are
also expected across parts of the central High Plains during the
late afternoon and evening.
The Marginal and Slight Risks have been trimmed in the immediate
wake of the leading line of convection across portions of the
Northeast. Some redevelopment is occurring further west along the
cold front where some pockets of heating have allowed for moderate
destabilization, and a Marginal Risk has been maintained for the
cold frontal convection into early evening.
...Southern Plains into the Ozarks...
Some expansion of the Marginal Risk has been included across
portions of AR, downstream of an intensifying cluster of convection
across far northeast OK/northwest AR. Confidence is decreasing in
redevelopment along an outflow boundary further west across OK, but
a conditional risk remains and no change has been made to the severe
probabilities in this area.
...Central/Northern High Plains...
Minor adjustments to the severe probabilities have been made across
portions of the central/northern High Plains, but the previous
forecast reasoning remains valid. See the previous discussion below
for more information.
.PREV DISCUSSION... /ISSUED 1130 AM CDT Tue Jul 17 2018/
...Northeast States/southern New England...
Bands of east/northeastward-moving storms continue to intensify at
midday from eastern PA/southeast NY into southern New England within
a warm conveyor and zone of differential heating in advance of an
eastward-moving cold front. Weak mid-level lapse rates and modest
strength effective shear of 20-30 kt are still expected to limit the
overall magnitude of today's severe. However, steep low-level lapse
rates and ample moisture content will nonetheless contribute to some
severe risk. Damaging winds including scattered downed trees will be
the most common hazard before storms weaken and/or move offshore by
early evening. Reference Mesoscale Discussions 1064/1065 for
...Central High Plains...
Weak height falls and a moderate strengthening of west-northwesterly
winds aloft will occur across the region in advance of a shortwave
trough progressing from eastern ID/southern MT into WY. 30-40 kt
500-mb westerlies attendant to this feature will overspread much of
WY with mid-to-late afternoon storm initiation expected off the
higher terrain. In the presence of MLCAPE ranging from 1000-2000
J/kg, speed shear through the cloud-bearing layer should be
sufficient for supercells with large hail and isolated severe gusts
being the primary hazards. Some upscale growth may occur this
evening with storms spreading southeastward across the region with a
continued damaging wind/sporadic hail risk.
...KS/OK to the Ozarks/ArkLaTex...
The remnants of an overnight weakening MCS continue to spread
southeastward over southeast KS at midday. The related MCV may help
semi-focus afternoon-intensifying thunderstorms across eastern OK
into parts of the Ozarks and ArkLaTex. Microburts capable of
localized damaging winds are possible through the afternoon.
Farther west/northwest across portions of northern OK/far southern
KS, MCS-related outflow may gradually stall and modify across the
region this afternoon with a hot/well-mixed air mass to its south.
Although overall forcing will be weak, at least some severe risk,
including the possibility of a few transient supercells, may exist
particularly along the corridor of modified outflow presuming storms
redevelop. This region will be reevaluated this afternoon for any
need of a Slight Risk upgrade.
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