- Day Three
acus01 kwns 301300
Storm Prediction Center ac 301258
Day 1 convective outlook
National Weather Service Storm Prediction Center Norman OK
0758 am CDT Tuesday Jun 30 2015
Valid 301300z - 011200z
..there is a slight risk of severe thunderstorms much of eastern Continental U.S....
..there is a slight risk of severe thunderstorms portions northern High Plains and
..there is a slight risk of severe thunderstorms portions central/southern Arizona...
..There is a marginal risk of severe thunderstorms elsewhere from eastern Continental U.S. Across
lower MO valley to northern plains...
..there is a marginal risk of severe thunderstorms elsewhere over central/southern
Scattered severe storms with damaging winds and some hail are most
probable across the Ohio Valley to the deep south and the
Middle-Atlantic States this afternoon into early evening. Afternoon
thunderstorms will offer a damaging-gust threat over parts of
central and southern Arizona. Large hail and severe winds are
expected with a few severe storms over the northern Great Plains and
Black Hills in the late afternoon and evening.
Positive pna pattern persists in middle/upper levels over Continental U.S....as
characterized by mean eastern trough and western ridge. Embedded within
this basic regime...two pairs of shortwave features should be most
pertinent to day-1 severe potential.
1. Closely spaced perturbations are evident in moisture-channel
imagery over Ohio and over lm. Leading feature will eject northeastward across
western/northern New York roughly along Canadian border and weaken...while lm
trough pivots southeastward then eastward to western New York by 12z.
2. Trough now penetrating large-scale ridge position over southeastern
ab/northwestern Montana/southwestern sk area will turn southeastward over northern/eastern Montana through afternoon
then across Dakotas overnight. Smaller/weaker perturbation
immediately preceding this one over southern sk likewise should turn
southeastward...reaching southern Minnesota around 00z and southern Indiana by end of period.
This pair of features is rather messy in structure...and
smaller-scale vorticity lobes may be present between them that would
reach the Lower-Middle MO valley overnight based on extrapolation.
Separate shortwave trough -- likely including convectively
generated/enhanced vorticity lobe -- is supporting convection over
Permian Basin region of West Texas at this time. However...this feature should
pass southwestward over northwestern mex and remain too far S to exert substantial
influence on Arizona area.
At surface...old/frontolytic baroclinic zone from Carolinas to middle south
has been obscured further in many areas by succeeding convective
outflows. Farther north...weak lows over lm and le should consolidate
today ahead of northern-stream shortwave troughs...resulting in somewhat
better-defined low moving northeastward over southern ont middle-late period.
Trailing/weak cold front should reach southern Indiana and southern Illinois by
12z...becoming stationary/warm front westward to another weak low that
should develop in vicinity of southeastern Wyoming/Nebraska Panhandle and move east-southeastward across northern
Kansas. Surface troughing will extend from Central Plains low north-northwestward across
western South Dakota and eastern Montana.
Extensive swath of central-eastern Continental U.S. Will experience at least
isolated to widely scattered thunderstorms and marginal-slight categorical severe
potential today. Though these areas have some spatial overlap...we
will treat causative regimes independently below.
..sern Continental U.S....
several multicellular clusters of thunderstorms are ongoing over southern
Appalachians and portions MS/al/AR. Isolated strong-severe gusts will
remain possible with this activity for another few hours due to
sporadic production of locally intense/water-loaded downdrafts. Reference
Storm Prediction Center mesoscale discussion 1237 for additional/near-term guidance.
These thunderstorms...and/or additional development along their associated
outflow/differential-heating boundaries...along with
subsequent/separate convection over this general region...should
increase in severe potential from midday through afternoon. Ambient boundary
layer diabatically destabilizes amidst surface dew points commonly middle
60s to low 70s f...amidst favorably steep deep-tropospheric lapse
rates. Preconvective air mass by middle-afternoon accordingly should be
characterized by MLCAPE around 3000 j/kg...locally higher...atop
well-mixed subcloud layer.
Multiple clusters of scattered to locally numerous thunderstorms are
expected in aggregate over this region between now and late
evening...contributing to broad area of 15% severe-wind risk...with
localized/denser concentrations of severe reports possible.
However...meso- and smaller-scale processes driving those
concentrations remain too uncertainly placed to assign corridors of
higher unconditional probabilities at this time. Isolated large hail also
may occur. Severe threat should become more dispersed and marginal through
Combination of surface heating and weak large-scale ascent ahead of
northern-stream perturbations will destabilize sufficiently moist air
mass across this region today...ahead of aforementioned surface cold
front. This should support development of scattered thunderstorms from eastern
Indiana to central/southeastern Illinois today...perhaps as early as late morning
but expanding/intensifying eastward across outlook area through much of
this afternoon. Large hail and damaging gusts will be main
concern...from multicellular clusters. Transient supercellular
characteristics also may be noted amidst small areas of 30-35-kt
effective-shear magnitudes...though nearly unidirectional deep-layer
wind profiles in most areas will limit total shear.
Scattered thunderstorms in clusters and small bands should develop today
with occasional damaging gusts possible...along with isolated/marginal severe
hail. Gradually tightening height gradient aloft will support 30-40
knots effective-shear magnitudes over much of this region this afternoon in
support of storm organization. Higher low-level moisture content
should remain S of weak/quasistationary front evident over
Delaware-Maryland-Virginia/eastern VA/Carolinas. Relative min in convective coverage has
been inconsistently prognosticated by several operational models and
convection-allowing guidance somewhere between eastern PA and Carolinas.
This may be reasonable considering marginal lapse rates forecast between
northern areas of colder temperatures aloft and southern areas of stronger
heating/cape. However...mesoscale uncertainties remain too great to
carve relative min out of existing probabilities at this time.
..nrn Great Plains/Black Hills...
Widely scattered thunderstorms should for this afternoon across western/northern parts of
this region...and perhaps higher terrain of Black Hills as
well...offering severe hail and sporadic damaging gusts. Increasing
large-scale lift/destabilization aloft is expected from northwest-southeast across
this region today ahead of shortwave trough...along with
strengthening middle-upper winds due to approach of related speed maximum.
High clouds now evident in infrared imagery will delay/restrict surface
diabatic heating west of ongoing precipitation plumes over northestern Mt/Dakotas.
However...sufficient insolation should occur through cloud
breaks/thinness...in conjunction with surface dew points 50s to low 60s
f...to produce narrow swath of 500-1500 j/kg MLCAPE atop weak cinh
and inverted-v thermodynamic profiles.
Although hodograph curvature is not expected to be very large given
geometry of low-level flow...strong speed shear will contribute to
long...rather straight hodographs and at least some supercell
potential with associated enhancement to hail risk. Given
well-mixed subcloud layers...stg-svr gusts may occur as well.
Widely scattered thunderstorms are forecast to develop along/NE of Mogollon Rim
this afternoon and grow in coverage while shifting westward to west-southwestward
toward/over lower deserts. Damaging gusts will be primary concern.
Morning tus sounding was affected by earlier convection but phx radiosonde observation
showed daily record precipitable water above 1.5 inches...with upper 60s/low 70s surface
dew points over some of this area. While mixing is expected
today...this will support robust instability. Concerns about
sufficient coverage still linger...however... presence of rich
low-level moisture beneath 30-40 knots middle-upper-level elys is uncommon
for end of June and heating should be strong over much of this area
based on infrared cloud trends. As such...probabilities are being raised
over portions/central Arizona.
..lower MO valley...
Elevated/low-level warm air advection will strengthen overnight ahead of
sewd-moving/nrn-stream perturbations. With steep midlevel lapse
rates and favorable deep shear prognosticated...isolated large hail is
possible from overnight thunderstorms streaking southeastward across this region.
acus11 kwns 301300
sels mesoscale discussion
Storm Prediction Center mesoscale discussion 301259
Mesoscale discussion 1237
National Weather Service Storm Prediction Center Norman OK
0759 am CDT Tuesday Jun 30 2015
Areas affected...E-cntrl Alabama / north-central and west-central Georgia
Concerning...severe potential...watch possible
Valid 301259z - 301500z
Probability of watch issuance...40 percent
Summary...storms are forecast to intensify during the next 2-4 hours
and a Severe Thunderstorm Watch is possible later this morning.
Discussion...radar mosaic shows a mesoscale convective vortex located 35 Michigan east-northeast cbm moving
east-southeastward and expected to track across north-central Alabama this morning. A belt
of stronger middle-level flow associated with this feature /30 knots at
500 mb/ sampled on the 12z bmx radiosonde observation will support organized multicells.
Moderate buoyancy /1500 j per kg MLCAPE/ with ample precipitable water observed on
the bmx radiosonde observation will increase this morning as surface temperatures warm
through the 70s and into the 80s by the late morning hours.
Upstream of the mesoscale convective vortex...an upper trough over the lower Tennessee/Ohio valleys
will pivot into the Tennessee Valley by early afternoon and lend at least
large-scale support for a continuation of vigorous convective
activity as this storm cluster moves eastward towards the Alabama/Georgia vicinity.
Therefore a gradual uptick in storm intensity is forecast with
primarily a wind damage threat developing later this morning.
Convective trends will be monitored over the next several hours if
storms can develop/strengthen on the leading edge of the evolving
..please see www.Spc.NOAA.Gov for graphic product...
Latitude...Lon 32368628 33928564 34348504 34318381 33758327 32718361
32008422 31878529 32368628