U.S. Severe Weather Forecast (Convective Outlook)

Day Three

acus01 kwns 011943 
Storm Prediction Center ac 011942 

Day 1 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
0242 PM CDT Sat Aug 01 2015 

Valid 012000z - 021200z 

..there is a slight risk of severe thunderstorms from eastern South Dakota into southern Minnesota... 

..There is a marginal risk of severe thunderstorms across the northern plains and upper 
MS valley... 

..there is a marginal risk of severe thunderstorms across eastern Maine... 

severe thunderstorms may develop this afternoon and move 
southeastward this evening across parts of the north-Central Plains 
and upper Midwest...offering damaging wind and severe hail 
potential. A few thunderstorms may produce hail and damaging gusts 
near severe levels in New England. 

..nrn plains... 
Given satellite and surface observations as well as recent model 
output...have expanded the slight risk a bit nwwd across northestern South Dakota/western 
Minnesota where storms are expected to initiate later this afternoon. 
Convergence is currently maximized across southeastern ND/northestern South Dakota...with 
instability levels rapidly increasing via heating. Damaging winds 
and hail are likely in the slight risk corridor as storms travel 
southeastward later today. The greatest risk will be across western portions of 
the slight risk area with more of a conditional threat over southeastern 
Minnesota/WI as cin increases ahead of the developing storms. 

.Jewell.. 08/01/2015 

Previous discussion... /issued 1117 am CDT Sat Aug 01 2015/ 

..Midwest states... 
A broad upper ridge is present today over the western states...with 
cyclonic flow aloft from the northern plains across the northeast 
states. Water vapor loop shows a subtle shortwave trough moving 
across eastern Montana/western ND. This feature will help to initiate 
isolated afternoon thunderstorms over parts of eastern ND/South Dakota and 
central/southern Minnesota. Those storms that form will track 
east-southeastward through the evening...where moderate cape values 
and favorable vertical shear will support supercell/bowing storm 
structures. Hail and damaging winds will be possible in the 
stronger cores. 

Farther south...considerable uncertainty exists regarding the 
coverage and location of strong convection. Overnight convection 
over eastern Nebraska has created widespread clouds that will reduce 
heating/destabilization and lessen the probability of convective 
initiation. 12z model solutions show little consistency across much 
of Nebraska/Iowa and northern Illinois. Therefore...have backed off to marginal 
category for this region and will re-evaluate in later updates. 

..New England... 
Satellite/radar data show scattered thunderstorms developing over 
parts of eastern Quebec and northern New England. This activity 
will affect parts of Vermont/NH/ME through the middle afternoon before 
moving eastward and away from the US. Forecast soundings show 
considerable effective shear for fast-moving storms capable of gusty 
winds. However...thermodynamic profiles are rather benign with middle 
level lapse rates only around 6 c/km and MLCAPE values of 500-800 
j/kg. Isolated severe storms are possible with gusty winds and 
hail...but overall threat appears marginal. 

Mesoscale Discussion

acus11 kwns 012013 
sels mesoscale discussion 
Storm Prediction Center mesoscale discussion 012013 

Mesoscale discussion 1576 
National Weather Service Storm Prediction Center Norman OK 
0313 PM CDT Sat Aug 01 2015 

Areas affected...portions of southeastern ND...eastern South Dakota...southwestern Minnesota 

Concerning...severe potential...watch possible 

Valid 012013z - 012115z 

Probability of watch issuance...40 percent 

Summary...isolated to widely scattered thunderstorms will have the 
potential to produce a few large hail reports/damaging wind gusts 
late this afternoon into this evening. As such...a watch may be 
needed by early evening for parts of this area. 

Discussion...20z surface analysis revealed weak low pressure in far 
S-central ND...with an attendant warm front extending to its southeast...and 
a trough extending to its SW. Enhanced convergence along these 
boundaries...in concert with forcing for ascent from a 
southeastward-progressing impulse aloft...should offer enough focus for 
convective initiation over the next few hours. Visible satellite 
trends exhibit a developing cumulus field near Dickey/LaMoure counties in 
ND...likely in response to the aforementioned forcing. 

Ample insolation /E.G. Surface temperatures rising into the upper 80s to near 
90/ and sufficient low-level moisture have yielded MLCAPE on the 
order of 2500-3000 j/kg along a narrow corridor near/SW of the warm 
front. Within this corridor...effective shear values around 30-35 
kts should favor multicellular/transient supercellular structures 
capable of large hail. Furthermore...inverted-v low-level profiles 
will likely support a strong-wind threat in more organized 
convection. To the SW of this favorable thermodynamic/kinematic 
environment...cloud cover/overturning from morning convection has 
limited destabilization and the resultant spatial extent of the 
potential severe threat previously described. 
Nonetheless...convective trends will be monitored for possible ww 

.Picca/Hart.. 08/01/2015 

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


Latitude...Lon 45090010 46510041 46960015 47129844 46489679 44829445 
44059490 43659564 43509685 45090010