U.S. Severe Weather Forecast (Convective Outlook)

Day Three

acus01 kwns 200603 
Storm Prediction Center ac 200602 

Day 1 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
0102 am CDT Tue Aug 20 2019 

Valid 201200z - 211200z 

..there is an enhanced risk of severe thunderstorms across portions 
of the middle MS valley... 

..there is a slight risk of severe thunderstorms across northern 

An organized cluster of thunderstorms capable of severe wind gusts 
and hail will overspread portions of the middle Mississippi and 
lower Ohio valleys today. Hail and isolated strong winds are also 
possible across portions of Minnesota this morning. 

..mid MS valley eastward across the Ohio Valley... 
An organized mesoscale convective system will likely be moving through 
south-central/southeast Iowa early this morning. Expectation is for 
this mesoscale convective system to be near its mature phase at this point with a 
well-developed rear-inflow jet and strong cold pool resulting in 
strong wind gusts. A few of these gusts could be greater than 75 
mph. As the mesoscale convective system continues southeastward through northwest MO and 
central Illinois later this morning and into the early afternoon, it is 
expected to gradually lose intensity as its cold pool accelerates 
and loses depth. By the time the mesoscale convective system reaches in and western KY, it 
is expected to be characterized by weakly organized multicells along 
the cold pool. Even with this anticipated weakening, strong wind 
gusts are still possible. 

..Central High plains/Central Plains... 
A cold front is expected to push into the upper Midwest and Central 
Plains, likely extending from western WI southwestward into 
northeastern Colorado during the late afternoon. Moist upslope flow is 
anticipated into eastern Wyoming/northeast Colorado behind this front, with the 
resulting convergence along the Lee trough expected to result in 
thunderstorm initiation. Downstream environment characterized by 
strong buoyancy and at least moderate vertical shear will support 
supercell storm structures capable of very large hail and strong 
wind gusts. These storms are expected to continue eastward into NE 
during the evening. A strengthening low-level jet will lead to a 
reinvigoration of any ongoing storms and/or development of new 
storms, primarily across central and eastern NE. Given the presence 
of ample low-level moisture and steep mid-level lapse rates, large 
hail is probable with these storms. Isolated very large hail (i.E. 
Greater than 2" in diameter) is possible. Dry mid-levels could also 
contribute to strong wind gusts. 

..upper Midwest... 
Ample low-level moisture and steep mid-level lapse rates will result 
in strong buoyancy ahead of the approaching cold front this morning 
across northern/central Minnesota. Stable low-levels (below 850 mb) will 
likely limit storm strength but large hail and occasional strong 
gusts through the stable layer are possible. 

..northern mid-Atlantic... 
Showers and thunderstorms will likely develop during the afternoon 
within the moist and diurnally destabilized air mass across the 
region. Vertical shear will be weak, leading to predominately 
disorganized, outflow-dominant multicells. Even so, the very moist 
air mass and steep low-level lapse rates support water-loaded 
downbursts capable of damaging wind gusts. 

.Mosier/nauslar.. 08/20/2019 


Mesoscale Discussion

acus11 kwns 201044 
sels mesoscale discussion 
Storm Prediction Center mesoscale discussion 201043 

Mesoscale discussion 1808 
National Weather Service Storm Prediction Center Norman OK 
0543 am CDT Tue Aug 20 2019 

Areas affected...eastern Iowa...north-central and northeast Missouri 
and much of central and northern Illinois 

Concerning...Severe Thunderstorm Watch 601... 

Valid 201043z - 201215z 

The severe weather threat for Severe Thunderstorm Watch 601 

Summary...thunderstorms continue to organize across central Iowa 
this morning. Over the next couple of hours these storms will move 
out of Severe Thunderstorm Watch #601. Hail and damaging wind 
potential will require the issuance of a new watch across portions 
of eastern Iowa, north-central and northeast Missouri and much of 
northern/central Illinois. 

Discussion...thunderstorms continue to organize this morning across 
central Iowa and accelerate southeastward this morning. The airmass 
feeding this complex of storms remains very supportive of severe 
thunderstorms, with most-unstable cape values in excess of 4000 j/kg 
and deep-layer shear between 40-50 knots. 

The leading edge of these thunderstorms currently extends from 
northeast Ringgold County, Iowa, north-northeast toward Polk County, 
Iowa. Additionally, to the northeast of this line, thunderstorms are 
developing in a more northwest-to-southeast orientation, including 
across portions of southeast Iowa that are currently not in Severe 
Thunderstorm Watch #601. 

Given continued development to the east of Severe Thunderstorm Watch 
#601 and the accelerating southeast motion of thunderstorms across 
south-central Iowa, coupled with the extreme instability and 
sufficient deep-layer shear values (in excess of 40 knots), a new 
watch downstream of #601 will be required in the next hour. 

.Marsh.. 08/20/2019 

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


Latitude...Lon 40569423 42529210 42118857 39498937 39199203 40569423