U.S. Severe Weather Forecast (Convective Outlook)

Day Three

acus03 kwns 200654 
Storm Prediction Center ac 200653 

Day 3 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
0153 am CDT sun Apr 20 2014 

Valid 221200z - 231200z 

..no severe thunderstorm areas forecast... 

a few strong storms may form across the High Plains from northwest 
Kansas into southeast Montana during the afternoon and early evening 

..nrn/Central High plains... 

A notable change within the large-scale pattern should lead to 
strengthening Lee trough across the northern and Central High plains 
Tuesday. Latest short-range model guidance is in fairly good 
agreement regarding the evolution of upper trough as it moves inland 
across the interior northwestern U.S. By the end of the period a 
substantial speed maximum will round the base of the progressive trough 
and begin to eject northeastward across co/WY. While this feature will not 
time particularly well for High Plains convection during the 
afternoon hours...it appears sufficient low-level convergence will 
develop along the Lee trough for at least isolated thunderstorms during peak 
heating on day3. 

Moisture will initially be somewhat marginal across the High Plains 
but strengthening low level jet should aid modified boundary layer moisture to 
advect north-northwestward across western Kansas into southeastern Montana where surface dew points are 
expected to rise into the 40s. Strong heating along this corridor 
should prove instrumental in convective initiation where surface 
temperatures rise into the 70s...yielding SBCAPE values of 500-1000 
j/kg. While absolute moisture content is expected to remain 
marginal...strengthening wind fields will become increasingly 
favorable for sustained rotating updrafts. For this reason...along 
with steep lapse rates...have opted to introduce 5 percent severe 
probs to account for hail/gusty winds with high-based convection. 

..ern u... 

Weak positive-tilt long-wave trough should migrate across the eastern 
U.S. During the day3 period. Modest moisture and sufficient 
instability should exist ahead of weak surface front for isolated-scattered 
thunderstorms within a broad corridor from the lower Sabine River valley of 
the Upper Texas coast...northeastward into the northern middle Atlantic. 
Environmental shear/instability appear inadequate for organized 
severe thunderstorms. 

.Darrow.. 04/20/2014