U.S. Severe Weather Forecast (Convective Outlook)

Day Three

acus01 kwns 241957 
Storm Prediction Center ac 241955 

Day 1 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
0255 PM CDT Thu may 24 2018 

Valid 242000z - 251200z 

..there is a slight risk of severe thunderstorms across parts of 
the Great Plains and upper Mississippi Valley... 

Isolated to scattered strong to severe thunderstorms are expected 
across the Great Plains and upper Mississippi Valley this afternoon 
and evening. 

Several changes have been made to the outlook for this issuance. The 
first change is to extend the slight risk westward into eastern 
Colorado where thunderstorms are currently developing. This 
convection is expected to have a severe threat as it moves eastward 
into increasing instability later this afternoon. The second change 
to the outlook is to expand the slight risk area westward across 
parts of northern Nebraska and east-central South Dakota. A maximum 
of instability is analyzed by the rap to the southeast of Pierre, South Dakota 
where a severe threat would be possible if storms can develop. The 
third change to the outlook is to adjust the thunder line further 
north across the mid Mississippi Valley where convection is ongoing 
in northeast Arkansas. 

.Broyles.. 05/24/2018 

Previous discussion... /issued 1142 am CDT Thu may 24 2018/ 

Models are rather inconsistent today regarding location/timing and 
intensity of convection later today. This leads to a relatively 
low-confidence outlook. Nevertheless, a few changes have been made 
to the marginal/slight areas based on 12z cam consensus. 

..ND/SD/MN this afternoon/evening... 
Water vapor loop shows a strong upper trough rotating northward 
across Montana/ND into Manitoba. Most of the lift associated with this 
system will move into Canada by this afternoon, but some potential 
for organized severe storms will be present across parts of 
northern/northeastern ND and eastern South Dakota. Those storms that form 
along a weak surface boundary/dryline will be in an environment of 
at least moderate cape and sufficient vertical shear for 
Bow/supercell structures. Large hail and damaging winds will be 
possible in the strongest cells. This activity should spread 
eastward across Minnesota through the evening. 

Strong heating will yield steep lapse rates and minimal cap this 
afternoon over parts of central NE into central Kansas. Forecast 
soundings suggest a very unstable air mass is also likely, with 
sufficient mid/upper level flow for some convective organization. 
The main forecast uncertainty is the extent of convective 
development. About half of the morning cam solutions suggest storms 
will form over north-central NE. If this occurs, damaging winds and 
hail would be possible. A more consistent convective signal is 
apparent over far eastern Colorado into western KS, where parameters 
appear favorable for damaging wind gusts. 

..West Texas/southeast nm... 
Once again today, a few thunderstorms are expected to form in the 
hot/unstable air mass in place across southeast nm and West Texas. 
Shear profiles are a little weaker than yesterday and upper forcing 
is minimal. Nevertheless, a few storms could produce hail and gusty 

A large upper trough is digging into CA, with height falls expected 
to commence along the Sierra later today. A cluster of 
thunderstorms is forecast to develop over northwest NV, spreading 
northward into southern or tonight. Forecast soundings show 
inverted-v profiles and sufficient steering flow for some risk of 
gusty/damaging wind. 

..MN/northern WI/western Upper Michigan... 
A decaying cluster of thunderstorms over northern WI will leave a 
remnant outflow boundary, possibly focusing redevelopment of storms 
later today. If so, the strongest cells could produce hail and 
gusty winds. 


Mesoscale Discussion

acus11 kwns 242048 
sels mesoscale discussion 
Storm Prediction Center mesoscale discussion 242047 

Mesoscale discussion 0512 
National Weather Service Storm Prediction Center Norman OK 
0347 PM CDT Thu may 24 2018 

Areas affected...western Nevada and vicinity 

Concerning...severe potential...watch unlikely 

Valid 242047z - 242245z 

Probability of watch issuance...20 percent 

Summary...a threat for damaging wind gusts exists this afternoon 
into the evening. A ww is not anticipated at this time. 

Discussion...visible satellite imagery has indicated towering 
cumulus developing along the Sierra. Krgz has steadily shown an 
increase in reflectivity values over the past half hour. Given these 
trends and the approach of a mid-level trough, more wide-spread 
initiation is likely in the next hour or so. A modified rev 18z 
sounding shows modest SBCAPE values approaching 1000 j/kg. A 
relatively dry sub-cloud layer indicates that a risk of severe wind 
gusts will be the main threat with any storms. Shear will be 
sufficient for storm organization -- currently at 20-30 kts per rap 
analysis -- and should improve with the approach of the mid-level 
wave. Given the expected limited storm coverage and modest buoyancy, 
a ww is not expected at this time. 

.Wendt/Hart.. 05/24/2018 

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


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