New York, NY...Philadelphia, PA...Baltimore, MD...Milwaukee, WI...Boston, MA...
SPC AC 161732
Day 2 Convective Outlook
NWS Storm Prediction Center Norman OK
1232 PM CDT Tue Jul 16 2019
Valid 171200Z - 181200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER A PORTION OF
THE UPPER MISSISSIPPI VALLEY...
Strong/severe thunderstorms are possible across portions of the
upper Mississippi Valley. Isolated strong storms may also be noted
across parts of the Plains and over portions of the northeastern US.
Upper pattern will change little through Wednesday with belt of
stronger westerlies confined to the northern third of the country. A
low amplitude shortwave trough currently moving through the
northwestern U.S. will undergo further deamplification as it moves
through the mean ridge position across the northern Plains and into
the upper MS valley. Farther east, remnants of Barry will become
absorbed within slightly stronger westerlies and weaken further as
it continues through the central Appalachians and Middle Atlantic
region. By 12Z Wednesday a quasi-stationary front should extend from
the upper Great Lakes to a weak surface low over SD. A cold front
will trail southwest from the low through western NE with a
pre-frontal trough from the eastern CO into southwestern NE. Farther
east a cold front will advance southeast into the Northeast States
during the day.
...Upper MS Valley region...
A very moist boundary layer will with 70 F dewpoints will reside
along and south of the quasi-stationary front from eastern SD into
southern MN and WI. It is likely that an MCS will be ongoing north
of this boundary on nose of a modest southerly low-level jet posing
some risk for strong to damaging wind gusts. Future evolution of
this MCS is somewhat uncertain, and model solutions including the
CAMS differ significantly. It is possible that MCS could reorganize
and intensify while continuing east as the boundary layer in
vicinity of the front destabilizes and especially since at least a
modest low-level jet is forecast to persist within the exit region
of a mid-level jet. Another possibility is that the MCS could weaken
or dissipate, and additional storms develop upstream later in the
afternoon or early evening along/north of the front as the low-level
jet strengthens. If this occurs, strong vertical shear and
instability in vicinity of the convectively enhanced but modifying
stationary front would support supercells capable of large hail and
possibly a few tornadoes. This activity would subsequently grow
upscale and move east through southern MN and WI during the evening
and overnight with a continuing threat for mainly damaging wind.
Given these uncertainties regarding the mesoscale and convective
scale evolution, will maintain SLGT risk this outlook, but an
enhanced might be required for a portion of this region in future
day 1 updates.
...Central and northern Plains region...
Within a modest post-frontal upslope regime, dewpoints at least in
the 50s F will persist beneath steep lapse rates contributing to
moderate instability over the central High Plains. This region will
reside beneath belt of stronger winds aloft and vertical shear will
support supercells as storms develop and move off the higher
terrain. Will maintain the MRGL risk category this update given
uncertainty regarding storm coverage, but an upgrade to SLGT risk
may be needed in later updates. Other storms with multicell
characteristics are expected to develop within the more deeply mixed
regime along the pre-frontal trough from western KS into south
central NE with downburst winds the main threat.
A moist, weakly capped warm sector will reside across the
pre-frontal warm sector over the northeast U.S. and the atmosphere
may become moderately unstable as the boundary layer destabilizes
during the afternoon, south of any ongoing convection/clouds.
Mid-level lapse rates will be very weak along with weak vertical
shear. Nevertheless, storms are expected to intensify south of the
cold front in association with remnant boundaries as well as over
the higher terrain and spread east into the destabilizing boundary
layer. A few locally strong wind gusts will be possible as storms
merge into line segments and clusters, but modest winds aloft and
the overall marginal thermodynamic environment may serve as limiting
factors for a more robust threat.
...MAXIMUM RISK BY HAZARD...
Tornado: 5% - Slight
Wind: 15% - Slight
Hail: 15% - Slight
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