U.S. Severe Weather Forecast (Convective Outlook)

Day Three

acus01 kwns 261250 
Storm Prediction Center ac 261248 

Day 1 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
0748 am CDT Sat Jul 26 2014 

Valid 261300z - 271200z 

..there is a MDT risk of severe thunderstorms this afternoon into tonight for 
central Illinois into central/southern Indiana... 

..there is a slight risk of severe thunderstorms from eastern Nebraska to western WV... 

severe storms...some accompanied by very large hail...damaging gusts 
and a couple of tornadoes are expected later this afternoon into 
tonight from eastern Nebraska to parts of the middle Mississippi and 
lower Ohio valleys. The most concentrated risk area should be this 
evening into tonight from central Illinois into central and southern 
Indiana...where one or more organized thunderstorm clusters could 
produce swaths of damaging winds. The damaging wind risk could 
reach as far as southern Ohio and northern Kentucky overnight. 

..ern Nebraska to Ohio/Kentucky this afternoon through tonight... 
A closed midlevel low over southern sk this morning will begin to move 
southeastward toward the upper MS valley by early Sunday...while 
strengthening flow aloft overspreads the middle MS and lower Ohio valleys 
in the exit region of a 60-90 knots middle-upper jet streak on the southern 
periphery of the closed low. A surface low reflection of the upper 
wave will develop southeastward from southeast mb to northern WI and western Upper Michigan...while 
a remnant Lee cyclone translates eastward from NE Kansas across northern MO in 
advance of an mesoscale convective vortex over north central Kansas. A corridor of low-middle 70s 
boundary layer dewpoints will expand eastward today across the corn belt 
from eastern Nebraska to IL/Indiana...beneath the eastward extension of a warm 
elevated mixed layer. The moisture and steep lapse rates...in 
combination with daytime heating...will support strong buoyancy 
/MLCAPE of 3000-4000 j per kg/ in conjunction with effective bulk 
shear of 45-55 knots. 

Forecast soundings are favorable for supercells given the strong 
buoyancy and long hodographs with strong deep-layer vertical shear. 
It appears that the initial convection may form along the synoptic 
wind shift entering southeast South Dakota and NE Nebraska this afternoon...on the southern 
flank of the morning elevated storms. Storm coverage is a bit 
uncertain in vicinity of eastern Nebraska/western Iowa...but any storms that form will 
likely become southeastward-moving supercells with an attendant risk for 
isolated very large hail and damaging winds into this evening. 

Farther east...separate storms are expected to develop by late 
afternoon/evening across central Illinois...in advance of the remnant mesoscale convective vortex 
that is expected to accelerate eastward from northern Kansas this morning in 
response to strengthening flow aloft. This convection will also be 
in an environment favorable for supercells with very large hail and 
damaging winds...as well as sufficient low-level moisture and srh 
for a couple of tornadoes. Upscale growth into one or more bowing 
segments is expected tonight across Illinois/Indiana with an increasing 
risk for swaths of damaging winds. The clusters will then move 
east-southeastward through early Sunday...reaching southern Ohio and northern Kentucky with a 
damaging wind risk overnight. The evolution of the storms overnight 
and the magnitude of the damaging wind risk is somewhat in 
question...since the synoptic wave is still located far to the 
northwest...and the greatest strengthening of midlevel flow will occur 
within the MDT risk area the last 3-6 hours of the forecast period. 

..srn Arizona this afternoon/evening... 
The modified 12z tus sounding suggests MLCAPE could reach 1000-1500 
j/kg this afternoon as surface temperatures warm into the 90s and 
weaken convective inhibition. Isolated storms should form this 
afternoon over the higher terrain in Southeast Arizona...and then spread west-northwestward 
through this evening. Westerly low-level flow and 20-30 knots east-southeasterly flow 
aloft will result in sufficient vertical shear for organized 
storms/clusters...with the potential to produce isolated 
strong/damaging outflow gusts. 

.Thompson/jirak.. 07/26/2014 

Mesoscale Discussion

acus11 kwns 252026 
sels mesoscale discussion 
Storm Prediction Center mesoscale discussion 252025 

Mesoscale discussion 1466 
National Weather Service Storm Prediction Center Norman OK 
0325 PM CDT Friday Jul 25 2014 

Areas affected...southern and central Arizona 

Concerning...severe potential...watch unlikely 

Valid 252025z - 252130z 

Probability of watch issuance...5 percent 

Summary...thunderstorm coverage is likely to increase through the afternoon 
across southern/central Arizona...with an accompanying localized threat for damaging 
wind gusts possible. A ww is not anticipated. 

Discussion...convective trends are increasing across the higher 
terrain of southern/central Arizona...within the eastern fringe of a subtropical 
moist plume. 18z sounding from tus sampled near 1.3 inch of precipitable water...and 
an increasingly unstable air mass where MLCAPE values are likely 
approaching 1000-2000 j/kg. Water vapor loop shows an enhanced area 
of moistening Colorado-located with stronger convection over southeastern Arizona and 
northern Sonora...which could be aided by an apparent subtle impulse 
progressing westward along the southern periphery of a strong midlevel 
anticyclone centered over nm. Thunderstorm coverage is likely to continue to 
increase through middle-late afternoon...and spread into the lower 
deserts /including the tus and possibly phx metropolitan areas later/. Weak 
low-level flow increasing to around 20 knots in the middle-upper levels 
will be supportive of pulse and brief multicell convective 
modes...capable of producing localized damaging wind gusts given the 
deeply mixed boundary layer. However...due to the isolated nature of 
the threat...a ww appears unnecessary. 

.Rogers/dial.. 07/25/2014 

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


Latitude...Lon 31921294 33191320 34181308 34801250 34801207 34651136 
34051061 33441032 31311030 31331109 31921294