- Day Three
acus01 kwns 261258
Storm Prediction Center ac 261257
Day 1 convective outlook
National Weather Service Storm Prediction Center Norman OK
0757 am CDT Wed Jun 26 2019
Valid 261300z - 271200z
..there is a slight risk of severe thunderstorms in three areas
generally from eastern Oregon across the northern rockies/plains to
parts of Illinois and southeastern Missouri...
Severe thunderstorm winds and hail are most probable today into
tonight from eastern Oregon across the northern rockies/plains to
parts of Illinois and southeastern Missouri.
The synoptic-scale upper-air pattern over the Continental U.S. Will be
influenced by three primary features:
1. A cyclone now centered offshore from the Pacific northwest,
whose center should pivot eastward to near the Columbia River mouth
2. Mean ridging over the Great Plains, forecast to amplify
throughout the period. Several small shortwaves and convectively
generated vorticity maxima/mcvs will move through and downstream
from the mean ridge.
3. An elongated, binary cyclone with centers initially evident in
moisture-channel imagery over northeastern sk an far northern on
near northwestern James Bay. Associated cyclonic flow in its
southern sector contains a shortwave trough -- now located over
southeastern lower Michigan and Lake Huron northward. The shortwave
trough should move eastward to southern qc and northern New York by 00z,
then across much of New England through the rest of the period.
At the surface, 11z analysis showed a wavy frontal zone from western
NE across south-central/southeastern NE, becoming diffuse amidst a
large area of precip and outflow, then evident again across
northeastern MO, south-central IL, central Kentucky and eastern middle Tennessee.
This boundary should move northward as a warm front through the
period, reaching northern portions of Illinois/IA/NE by 00z, low-level
trough deepening and possible cyclogenesis is expected over the
eastern Wyoming/northwestern NE/southeastern South Dakota area. A dryline will mix
eastward through mid/late afternoon over the central/southern High
..northern rockies to Central High plains...
Widely scattered to scattered thunderstorms in clusters are expected
to develop this afternoon in a broad arc from the northern rockies
across Montana to the Lee trough/dryline regime of the central/northern
High Plains. Activity should move generally northeastward from its
genesis zones in higher terrain and along surface boundaries,
offering sporadic severe hail and gusts.
A relative maximum in significant-hail probabilities still appears
possible across portions of the north-Central High plains/Black
Hills/badlands region. Expect supercell-favorable vertical wind
profiles and deep shear, with maximized low-level convergence and
related easterly flow component north of the frontal zone. This area
also will reside near the northwestern rim of the most favorable
inflow-layer moisture content and buoyancy. Peak afternoon MLCAPE
should increase from around 1000-2000 j/kg over northeastern Wyoming/
southeastern Montana to the 3000-4000 j/kg over southern South Dakota and the NE
sandhills. Easterly to southeasterly low-level winds also will
enhance vertical shear northwestward across Mt, albeit in lesser
buoyancy. Initial multicellular to supercellular modes may
transition to one or more clusters moving across the outlook area in
the evening to overnight hours, with the severe threat transitioning
from hail and wind to mainly wind. The most probable area for a
sustained mesoscale convective system appears to be across parts of South Dakota near and St north of
the warm front.
Widely scattered thunderstorms are expected to develop this
afternoon over and east of the Cascades, as strong diurnal heating
substantially destabilizes an air mass with marginal low-level
moisture. The main concerns will be damaging gusts and sporadic
hail, from both supercellular and outflow-dominant multicellular
modes. This activity should move rapidly northeastward across the
outlook area, encountering a deep and well-mixed boundary layer with
very steep low/middle-level lapse rates. Large-scale ascent will
increase in association with low-level warm advection and
frontogenetic forcing, as well as the left-exit region of the
upper-level jet streak, and shots of DCVA from perturbations
embedded in the strengthening cyclonic mid/upper flow. Lower-
elevation surface dew points in the 30s and 40s f will support
pockets of 300-800 j/kg MLCAPE, amidst greater vertical shear
related to the approaching Pacific cyclone. Dry lightning and
strong-severe outflow gusts also will present a fire hazard around
some of this activity; see the Storm Prediction Center day-1 fire-weather outlook for
..north-Central Plains to mid/upper Mississippi Valley...
The threat for isolated severe gusts/hail may persist another couple
hours amidst a general weakening trend noted with the thunderstorm
complex over southeastern NE. See Storm Prediction Center mesoscale discussion 1252 for
additional details. An mesoscale convective vortex from this activity, as well as a
separate one now over eastern South Dakota and produced by a different/earlier
convective complex -- should pivot southeastward across the mid/
upper Mississippi Valley region through the day and contribute to
potential for thunderstorm development this afternoon into evening
south of the warm front.
Though deep shear should be weak, mesoscale enhancements to the
low-level mass response and large-scale lift, related to the mcvs,
may concentrate convective/severe potential in the form of damaging
gusts and sporadic hail. Rich low-level moisture, underlying steep
eml-generated lapse rates, will contribute to strong instability
with peak preconvective MLCAPE in the 3000-4000 j/kg range. One or
two thunderstorm complexes evolving from afternoon/early evening
High Plains convection also may last through much of tonight into
the north-Central Plains or upper Mississippi Valley regions,
offering a threat of severe gusts and hail. Severe threat is
nonuniform across this area, and a relative minimum in severe
potential may exist across parts of the east-Central Plains and Iowa
region, especially following the demise of this morning's complex.
Cold pools from ongoing and prior overnight activity across
southeastern NE and Kansas also should contribute to the relative
minimum in convective potential in the low-level downstream
..lower Great Lakes vicinity...
Widely scattered thunderstorms should develop this afternoon near a
low-level trough/convergence zone preceding the mid/upper-level
shortwave trough, and perhaps on lake-breeze boundaries. Isolated
severe gusts and/or hail are possible. Diurnal heating of a weakly
capped and at least marginally moist boundary layer -- with surface
dew points generally the mid 50s to low 60s f -- will offset modest
mid/upper-level lapse rates enough to support 1000-1500 j/kg MLCAPE.
Steep low-level lapse rates and a well-mixed preconvective boundary
layer will help to maintain strong-severe hail/downdrafts to the
surface. The threat should be almost entirely diurnal in nature,
diminishing rapidly into the evening hours.
acus11 kwns 261134
sels mesoscale discussion
Storm Prediction Center mesoscale discussion 261134
Mesoscale discussion 1252
National Weather Service Storm Prediction Center Norman OK
0634 am CDT Wed Jun 26 2019
Areas affected...eastern Nebraska...far northeast Kansas
Concerning...Severe Thunderstorm Watch 447...
Valid 261134z - 261330z
The severe weather threat for Severe Thunderstorm Watch 447
Summary...a few strong wind gusts or marginal hail remains possible
across the watch area. Additional watches are not expected at this
Discussion...the primary outflow surge continues to turn more
southward, now approaching the Kansas border. Local radar shows outflow
well ahead of this line which has a history of strong to marginally
Behind the outflow, an extensive area of elevated storms persists
northwestward toward onl. These storms have shown hail potential at
times, but in general have been decreasing in intensity as of late.
While winds off the surface remain southwesterly, and the air mass
unstable, the strongest lift from warm advection appears to be over.
In addition, height rises will continue into the day. As a result,
the weakening trend is expected to continue, and additional watches
are not anticipated for this regime.
..please see www.Spc.NOAA.Gov for graphic product...
Latitude...Lon 40349753 41849875 42249907 42439890 42169804 41579712
40969629 40509581 40109562 39799599 39609673 39839728