U.S. Severe Weather Forecast (Convective Outlook)

Day Three

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Storm Prediction Center ac 040600 

Day 1 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
0100 am CDT Tuesday Aug 04 2015 

Valid 041200z - 051200z 

..there is a slight risk of severe thunderstorms eastern New England southwestward to the 
middle-Atlantic region... 

..there is a slight risk of severe thunderstorms across the southwestern Nebraska/northwestern Kansas 

..there is a marginal risk of severe thunderstorms from New England southwestward into 
central Virginia... 

..there is a marginal risk of severe thunderstorms from eastern Montana southeastward to Kansas/MO/nrn 

Isolated strong to severe thunderstorms will be possible Tuesday 
from eastern portions of New England southwestward to portions of 
the Middle-Atlantic States. Strong to severe storms will also be 
possible from the northern High Plains southeastward into the 
Central Plains. 

A large middle- and upper-level trough centered in vicinity of James Bay at the 
start of the period will drift very gradually eastward with time...while 
broader cyclonic flow regime surrounding the low continues to affect 
the northeast U.S./Great Lakes region. Farther west...a weaker cyclone 
aloft should linger over British Columbia...while shorter-wavelength 
troughing rotating around this feature shifts into the Pacific northwest and 
phases with a vorticity maximum shifting out of the Pacific into northern California 
through the second half of the period. In between the two main 
upper lows...weak ridging will prevail across The Rockies/High 
Plains -- though interrupted by negative-tilt shorter-wavelength 
troughing shifting east-northeastward out of The Rockies and into the plains. 

At the surface...the primary feature with respect to severe 
potential will be a weak cold front extending from eastern Canada south-southwestward 
across New England to the middle-Atlantic region...westward across the 
central Appalachians and Tennessee Valley area to the middle MS valley...and 
then nwwd across the Central Plains into the northern High Plains. This 
front will make gradual eastward progress across New England...while 
returning slowly northward as a warm front across the plains through the 

..ern New England southwestward to the middle-Atlantic region... 
Weak height falls shifting gradually across New England and focused 
low-level ascent in vicinity of a weak cold front shifting eastward through the 
day should support isolated storm development -- fueled by afternoon 
heating/destabilization likely pushing mixed-layer cape into the 
1000 to 2000 j/kg range. With the convection evolving within a 
kinematic environment featuring moderately strong southwesterly flow through 
a deep tropospheric layer... fast-moving...semi-organized 
storms/storm clusters are expected through the afternoon -- with 
isolated damaging wind/hail risk evident. Thus -- will expand 
slight risk northward from the middle-Atlantic region across all of eastern New 
England through early evening. 

..nrn High Plains into the Kansas/Nebraska vicinity... 
While a remnant mesoscale convective system shifts across portions of S central Kansas/OK early 
in the period...destabilization is forecast to commence farther north/northwest 
-- I.E. Across northwestern Kansas and into the northern High Plains. As a middle-level 
trough shifts northeastward across the area through the day and remnants of 
the southeast-to-NW-oriented cold front retreating northward across this region 
focuses low-level ascent...afternoon storm development will likely 
occur in the southwestern Nebraska/northwestern Kansas vicinity. With 35 to 45 knots middle-level 
wnwlys prognosticated to spread across this area atop low-level slys...the 
veering/increasing flow with height should yield shear supportive of 
organized/rotating storms. Thus...have introduced 15%/slight risk 
area across the southwestern Nebraska/northwestern Kansas vicinity given large hail/locally 
damaging wind potential with a few stronger/supercell storms. 
Convection should spread southeastward with time...before weakening by middle to 
late evening. 

.Goss/Gleason.. 08/04/2015 

Mesoscale Discussion

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sels mesoscale discussion 
Storm Prediction Center mesoscale discussion 040405 

Mesoscale discussion 1602 
National Weather Service Storm Prediction Center Norman OK 
1105 PM CDT Monday Aug 03 2015 

Areas affected...Texas Panhandle into western Oklahoma 

Concerning...Severe Thunderstorm Watch 468... 

Valid 040405z - 040600z 

The severe weather threat for Severe Thunderstorm Watch 468 

Summary...an evolving cluster of storms may remain fairly vigorous 
into the 06-09z time frame...with a continuing risk for strong 
surface gusts...in addition to locally heavy rain. The need for a 
new watch is not currently anticipated...but trends will continue to 
be monitored. 

Discussion...lower/mid tropospheric warm advection...accompanying a 
weak middle-level impulse migrating across the south Central High 
plains...likely will maintain the substantive cluster of storms 
which has evolved across the Texas Panhandle to the north of 
Amarillo. Convective outflow has surged southeastward ahead of the 
bulk of the ongoing convection...and there has been some recent 
weakening trend to convection evident in radar and lightning 
data...in the presence of increasingly modest boundary layer 
instability. However...a mesoscale circulation is becoming better 
defined along the northern flank of the convective outflow ... 
could become the focus for increasing storm development through the 
05-07z time frame...as it tracks across the northeast Texas 
Panhandle into areas south of gage OK. 

Although lapse rates are not particularly steep...seasonably high 
moisture content /characterized by precipitable water up to 1.9 
inches/ may contribute to heavy precipitation loading that could 
contribute to another downburst or two...on the nose of a 20-30 knots 
south to southwesterly low-level jet. It is possible that this may 
be accompanied by strong surface gusts...but peak gusts approaching 
or exceeding severe limits probably will be rather localized in 

.Kerr.. 08/04/2015 

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


Latitude...Lon 35480071 35900068 36460032 35999864 35059838 34809967 
35190081 35480071