- Day Three
acus01 kwns 281959
Storm Prediction Center ac 281958
Day 1 convective outlook
National Weather Service Storm Prediction Center Norman OK
0258 PM CDT Wed Jun 28 2017
Valid 282000z - 291200z
..there is an enhanced risk of severe thunderstorms from far
southeast NE into northern Illinois/southern WI...
..there is a slight risk of severe thunderstorms from the Central
High plains to the middle/upper MS valley...
..there is a marginal risk of severe thunderstorms from the
northern rockies to the Great Lakes...
Severe thunderstorms with large hail, wind damage and a few
tornadoes are expected across the middle Missouri Valley
northeastward into the middle and upper Mississippi Valley. Other
more isolated severe storms may occur in the Central Plains and
..severe-weather threat areas...
No changes were needed with the severe-probabilities/categorical
severe risk areas, as previous forecast reasoning remains valid with
this outlook issuance.
..general thunderstorm areas in the Dakotas and eastern New York...
Based on convective/lightning trends in eastern Mt, the general
thunderstorm line in western ND was shifted a little to the east to
indicate some potential for thunderstorms to reach far western ND
late this afternoon to early evening. A little more of central South Dakota
was added to general thunderstorm potential for later tonight.
Meanwhile, much of eastern South Dakota/ND into far northern Minnesota was removed
from the general thunderstorm area, given the decrease in
thunderstorm potential within an area of midlevel subsidence and/or
Farther east, convective trends suggest thunderstorm potential
should continue to shift east/northeast away from portions of
eastern New York.
Previous discussion... /issued 1136 am CDT Wed Jun 28 2017/
..middle MO River Valley to middle/upper MS River Valley...
Related to last night's MCS, scattered showers/thunderstorms and
related prevalent cloud cover continue to progress eastward across
eastern portions of Minnesota/Iowa into WI/northern Illinois late this morning.
This is just ahead of an eastward-moving shortwave trough over Minnesota,
with a few other convectively related disturbances/mcvs noted
farther south, embedded within a belt of moderately strong mid-level
westerlies. A surface low analyzed at 15z near the Minnesota/SD/ND border
vicinity will continue to spread eastward across central Minnesota toward
northern WI and the Western Upper Peninsula of Michigan through this
evening, while a cold front spreads southeastward across MN/IA/WI.
Near and ahead of this cold front, low-level moistening and general
air mass recovery will steadily occur this afternoon in the wake of
the lingering early-day precipitation and cloud cover, particularly
given relatively steep mid-level lapse rates and ample low-level
moisture sampled in source-region 12z observed soundings from Omaha
NE and Topeka Kansas. Increasingly prevalent mid/upper 60s f surface
dewpoints will support upwards of 2000-3000 j/kg MLCAPE particularly
from southeast NE/northern Kansas into IA, with somewhat more modest
(and uncertain) degree of pre-frontal destabilization farther north
into WI/eastern Minnesota owing to early-day cloud cover and some
regenerative precipitation this morning across northern Iowa.
While the aforementioned cloud cover/precipitation lingering into
midday still casts some uncertainty, it seems most likely that
surface-based storms will redevelop just ahead of the front
semi-focused along outflow and zones of differential heating across
southern/eastern Iowa and nearby far northern MO and northern Illinois.
Pending adequate destabilization, other potentially severe
development may occur by late afternoon in closer proximity to the
surface low/front from far eastern Minnesota into western/central WI.
Around 40-45 kt of effective shear will support some initial
supercells capable of large hail, with a few tornadoes possible as
well given the strength of 2-3 km above ground level southwesterly winds and
related 150-250 m2/s2 0-1 km srh (with prospective surface-based
convection). Eastward-moving clusters should evolve by evening with
a related increase in damaging wind potential particularly across
southern Iowa/northern MO into northern Illinois.
..co/Wyoming Front Range to northern Kansas/southern NE...
Within a modestly moist environment, widely scattered thunderstorms
should develop and spread eastward across the region by late
afternoon into evening, including some potential for at least
small-scale mesoscale convective system development this evening. Modest buoyancy and ample
vertical shear will support the possibility of sporadic large hail
and locally damaging winds into this evening.
Ahead of an amplifying shortwave trough over the northern
intermountain region, modest moisture and a strengthening belt of
west-southwesterly mid-level winds should contribute to the
possibility of isolated strong to severe storms spanning parts of
Wyoming/southern Montana and eastern Idaho/northern Utah.
acus11 kwns 282230
sels mesoscale discussion
Storm Prediction Center mesoscale discussion 282229
Mesoscale discussion 1174
National Weather Service Storm Prediction Center Norman OK
0529 PM CDT Wed Jun 28 2017
Areas affected...southeast NE...IA...northern MO
Concerning...Tornado Watch 375...
Valid 282229z - 290000z
The severe weather threat for Tornado Watch 375 continues.
Summary...severe threat continues across ww375.
Discussion...an elongated corridor of severe thunderstorms has
evolved within the base of a strong short-wave trough over the upper
MS valley. Numerous supercells are noted from extreme southeast NE,
through central Iowa into southwest WI, though storm mergers are
beginning to take place which may lead to an mesoscale convective system-like cluster if
trends continue. Shear profiles remain favorable for storm rotation
and potential tornadoes along with very large hail. With time
convection should spread across the remainder of ww375 focusing
along the Iowa/MO border and Iowa/Illinois border later this evening.
..please see www.Spc.NOAA.Gov for graphic product...
Latitude...Lon 40169646 42949391 42948977 40179248 40169646