U.S. Severe Weather Forecast (Convective Outlook)

Day Three

acus01 kwns 290601 
Storm Prediction Center ac 290559 

Day 1 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
1259 am CDT Thu Jun 29 2017 

Valid 291200z - 301200z 

..there is an enhanced risk of severe thunderstorms for northeast 
Kansas...northern Missouri...and far southeast Nebraska... 

..there is a slight risk of severe thunderstorms from the Central 
Plains into the middle Mississippi Valley... 

..there is a marginal risk of severe thunderstorms across the 
Central High plains through the Midwest and into the lower Great 

Scattered significant severe thunderstorms are possible late this 
afternoon into this evening across the Central Plains with hail and 
wind the primary threats. Isolated strong to severe storms are also 
possible across the Midwest eastward into the lower Great Lakes, and 
across the Central High plains into Wyoming. 

A series of central U.S. Shortwave troughs will move through the 
base of a larger-scale mid-level trough located over the 
north-central states on Thursday. A lead disturbance, perhaps 
modulated by convective processes overnight Wednesday into this 
morning, will move from the Central Plains to eastern Iowa by late 
afternoon. An upstream disturbance will move east across the 
Dakotas during the daylight hours and into the upper Midwest late 
Thursday night. Another mid-level impulse will move southeast from 
the upper Columbia Basin into western Wyoming by early evening. A belt 
of strong 500-mb flow will encompass much of the area from the 
north-central rockies/intermountain regions eastward through the 
plains and into the Great Lakes. In the low levels, a surface low 
will occlude over the upper Great Lakes with frontal segments, 
influenced by convective outflow, extending southwestward into the 
Central Plains. Farther west, a Lee low will meander over the 
south-Central High plains as a front accelerates south over the 
Central High plains. An inverted trough will probably serve as a 
focus for isolated thunderstorm development during the late 
afternoon from Kansas south into the Texas Panhandle. 

..Central Plains east into the middle MS valley... 
It is a complicated forecast for today with a considerable amount of 
uncertainty due in part to perceived consequential influences of 
overnight storms and boundary placement for late afternoon 
development. Several convective complexes will likely move east 
across the Central Plains/middle MS valley during the early morning 
on the nose of a low level jet situated over the Central Plains. Southerly 
low-level flow will maintain A Reservoir of 14-16 g/kg lowest 100-mb 
mean mixing ratios (translating to upper 60s-lower 70s degrees f 
dewpoints) from eastern Kansas into northern MO/southern Iowa to the south 
of early-day outflow. A moderately to very unstable boundary layer 
with 2500-3500 j/kg MLCAPE is forecast by late afternoon with mlcinh 
eroding and storm development focused along boundaries over 
northeast Kansas eastward into northern MO. Strong westerly mid-level 
flow will favor storm organization and supercells capable of large 
to very large hail early in the convective lifecycle. It appears 
the tornado risk is highest over northeast Kansas into parts of west and 
northern MO where low-level shear and buoyancy may maximize. The 
transition to a wind threat and subsequent increase in damaging 
gusts will probably occur during the evening over eastern Kansas east 
towards the MS river. Models vary farther west in central Kansas into 
the Central High plains. Several possible scenarios lend an 
isolated risk for large hail/severe gusts beginning during the late 
afternoon and persisting through the evening and possibly overnight 
as they move east. 

..southern Great Lakes into the New York Adirondacks... 
An upper disturbance over the Great Lakes is forecast to move into 
southeast Canada and an associated strong belt of low- to mid-level 
flow will overspread the lower Great Lakes during the morning. 
Models show surface dewpoints on southwesterly flow increasing into 
the upper 50s (western ny) to upper 60s (southern great lakes) 
during the day. Destabilization of the boundary layer remains in 
question across the lower Great Lakes. Storm intensity and a 
resulting threat for wind damage appear too isolated for a 15% wind 
area at this time. Farther southwest, storm coverage concerns due 
in part to prior convective activity renders confidence low 
regarding the overall severe risk. Isolated hail/wind appear to be 
the primary threats before storms weaken during the evening. 

.Smith/jirak.. 06/29/2017 


Mesoscale Discussion

acus11 kwns 290547 
sels mesoscale discussion 
Storm Prediction Center mesoscale discussion 290547 

Mesoscale discussion 1181 
National Weather Service Storm Prediction Center Norman OK 
1247 am CDT Thu Jun 29 2017 

Areas affected...portions of far southern Nebraska and 
northern/central Kansas 

Concerning...severe potential...watch possible 

Valid 290547z - 290645z 

Probability of watch issuance...40 percent 

Summary...a few severe thunderstorms will pose a risk of large hail 
and perhaps isolated damaging gusts tonight, and a Severe 
Thunderstorm Watch may be needed. 

Discussion...vwp data from Kansas and southern Nebraska tonight 
indicate the terminus of a southwesterly low-level jet is focused 
near the Kansas/Nebraska border. As such, related warm-air advection 
and speed convergence are likely fueling thunderstorms rooted above 
a low-level stable layer. Ddc and top 00z soundings sampled steep 
700-500mb lapse rates, adequate for vigorous updraft accelerations. 
Additionally, westerly mid-level flow of 30-40 kt is offering 
sufficient deep-layer shear for updraft organization/rotation. 
Therefore, a continued threat of occasional large hail is expected. 
Through the night, storms will likely further form along and north 
of an outflow boundary stretching across northern Kansas, and 
upscale growth may yield a downwind-propagating component to the 
southeast. Such an evolution may offer some potential for downdraft 
momentum to penetrate a low-level stable layer, resulting in 
isolated damaging gusts as well. Considering these threats, a Severe 
Thunderstorm Watch may be needed. 

.Picca/Edwards.. 06/29/2017 

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


Latitude...Lon 38689959 38920005 39410016 40040016 40309997 40349937 
40339885 40139752 39839655 38899589 38189630 38129778