- 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.
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.
..please see www.Spc.NOAA.Gov for graphic product...
Latitude...Lon 31921294 33191320 34181308 34801250 34801207 34651136
34051061 33441032 31311030 31331109 31921294