SPC 1730Z Day 2 Outlook

Day 2 Outlook Image

Day 2 Convective Outlook  
NWS Storm Prediction Center Norman OK
1212 PM CDT Mon Jun 21 2021

Valid 221200Z - 231200Z


Isolated strong to severe storms may occur Tuesday across parts of
the Mid-Atlantic and Southeast. Strong to damaging wind gusts should
be the main threat. Other isolated severe storms also appear
possible across parts of the Midwest into the central Plains, and
the Pacific Northwest.

...Mid-Atlantic/Coast Southeast...
An upper trough is forecast to cover much of the eastern CONUS early
Tuesday morning. Several embedded shortwave troughs are expected to
progress through this upper troughing, contributing to some
deamplification of the upper trough as well as a general eastward
movement. Southernmost embedded shortwave trough, beginning the
period over the central and southern Appalachians, will likely have
the largest impact on thunderstorm chances. The quick
eastward/northeastward progression of this system will help push a
cold front through the Mid-Atlantic and coastal Southeast States.

Air mass ahead of this cold front will be moist, buoyant, and weakly
sheared. This should result in mostly multicellular storm
structures, with updrafts/downdrafts that could occasionally become
strong enough to produce damaging wind gusts.  

...Central Plains/Mid MO Valley..
Across the central CONUS, a weak frontal zone from the western Gulf
Coast into south TX will further diminish throughout the day as
strong moisture return occurs across the southern/central Plains. A
warm front is expected to develop/sharpen near where the leading
edge of this moisture return meets the more continental air mass in
the wake of upper trough.

Strong heating and low-level convergence in the vicinity of this
boundary (perhaps aided by a subtle shortwave trough) are expected
to result in thunderstorm initiation during the late afternoon. Only
modest buoyancy is anticipated, but southerly low-level flow veering
to relatively strong northwesterly flow aloft will result in enough
vertical shear for organized updrafts capable of large hail. Five
percent hail probabilities will be maintained with this outlook, but
higher probabilities may be needed in later outlook. Uncertainties
at this forecast range, including the extent of moisture return and
diurnal heating as well as the location of the strongest low-level
convergence, preclude the confidence needed for higher probabilities
at this forecast range. 

...Pacific Northwest...
Low-amplitude shortwave trough is expected to eject northeastward
through the far northwestern periphery of the upper ridging Tuesday
afternoon. Favorable timing of this shortwave coupled with
increasing mid-level moisture and strong diurnal heating should
result in afternoon thunderstorm development. Moderate deep-layer
vertical shear (i.e. 30-35 kt) should be enough for a few organized,
high-based storms capable of producing strong/gusty winds
approaching severe limits.  

...Southern High Plains...
Northwesterly flow aloft will promote afternoon thunderstorms off
the high terrain and into the southern High Plains. Environment
across the southern High Plains will be well mixed, resulting in the
potential for damaging downbursts with any more robust storms.
However, overall coverage is too uncertain to introduce any
probabilities with this outlook.

..Mosier.. 06/21/2021

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