SPC AC 171719
Day 2 Convective Outlook
NWS Storm Prediction Center Norman OK
1219 PM CDT Sun Jun 17 2018
Valid 181200Z - 191200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FOR PORTIONS OF
Several strong to locally severe thunderstorms will be possible
Monday over the Northeast with damaging gusts the primary hazard.
Upper-level low pressure over the Great Basin will move northeast
while slowly weakening on Monday while a mid-level high remains over
the Southeast. A surface cold front will move through a large part
of the Northeast after dark while the westward portion of this
boundary extends through the central High Plains. A surface trough
over the western Gulf of Mexico will move northwest in the vicinity
of the TX coast on Monday.
A very moist troposphere is forecast by model guidance before a cold
front sweeps through the area overnight. Almost saturated
tropospheric profiles and poor mid level lapse rates will limit
updraft intensity. However, ample boundary layer heating with
temperatures rising into the 80s and lower 90s will steepen
low-level lapse rates. U.S.-based suite of operational guidance
(global, convection allowing, and ensemble data) and the Canadian
show prefrontal storm development during the afternoon. In
contrast, the ECMWF, and the UKMET to a lesser extent, are largely
showing only convection near the front yielding uncertainty. MLCAPE
is generally only forecast to range from 250 J/kg north to 1250 J/kg
south. However, increasing 700-500 mb flow overspreading the region
during the afternoon/early evening will result in moderate storm
motions with strong multicells and transient supercell structures.
Damaging gusts capable of tree damage are seemingly the greatest
hazard. Isolated strong gusts 40-55 mph are possible with the
scattered thunderstorms and a couple of localized pockets of gusts
55-60 mph are possible with the most intense downdrafts. This
activity will likely weaken during the evening as surface
temperatures gradually cool.
...Central Plains and Midwest...
Moderate/strong instability will develop Monday afternoon in the
vicinity of the front, as widespread dew points in the upper
60s/lower 70s will be in place. Guidance is consistent in depicting
a weak mid-level impulse lifting northeast across the central
Plains, which may contribute to afternoon thunderstorm development.
Deep-layer shear will not be particularly strong (ranging from 20-35
kts), but supportive of some degree of storm organization. Damaging
winds will be the primary severe risk.
...Northeast CO/southeast WY...
Isolated/widely scattered thunderstorms are expected to develop over
the higher terrain Monday afternoon, aided by low-level upslope
flow. Stronger mid-level flow east of the Great Basin upper low
will result in vertical shear averaging 35-45 kt, and steep
mid-level lapse rates above lower-mid 50s boundary layer dew points
should result in surface-based instability of around 1000 J/kg.
Isolated supercells will be capable of large hail through early
...MAXIMUM RISK BY HAZARD...
Tornado: 2% - Marginal
Wind: 15% - Slight
Hail: 5% - Marginal
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