U.S. Severe Weather Forecast (Convective Outlook)

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000 
acus01 kwns 261258 
swody1 
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 
by 12z. 
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 
Plains. 


..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. 


..interior northwest... 
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 
more details. 


..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 
trajectories. 


..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. 


.Edwards/Jewell.. 06/26/2019 


$$ 

Mesoscale Discussion


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acus11 kwns 261134 
sels mesoscale discussion 
Storm Prediction Center mesoscale discussion 261134 
nez000-ksz000-261330- 


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 
continues. 


Summary...a few strong wind gusts or marginal hail remains possible 
across the watch area. Additional watches are not expected at this 
time. 


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 
severe gusts. 


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. 


.Jewell.. 06/26/2019 


..please see www.Spc.NOAA.Gov for graphic product... 


Attention...WFO...oax...top...Gid...lbf... 


Latitude...Lon 40349753 41849875 42249907 42439890 42169804 41579712 
40969629 40509581 40109562 39799599 39609673 39839728 
40349753