U.S. Severe Weather Forecast (Convective Outlook)

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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 
Black Hills... 


..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 
Arizona... 


... 
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 
tonight. 


..OH valley... 
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. 


..mid-Atlantic states... 
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. 


..cntrl/southern Arizona... 
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. 


.Edwards/Rogers.. 06/30/2015 

Mesoscale Discussion


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sels mesoscale discussion 
Storm Prediction Center mesoscale discussion 301259 
gaz000-alz000-301500- 


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 
cluster. 


.Smith/Edwards.. 06/30/2015 


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


Attention...WFO...ffc...tae...bmx... 


Latitude...Lon 32368628 33928564 34348504 34318381 33758327 32718361 
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