- 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.
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