- Day Three
acus03 kwns 200727
Storm Prediction Center ac 200726
Day 3 convective outlook
National Weather Service Storm Prediction Center Norman OK
0226 am CDT Fri Jul 20 2018
Valid 221200z - 231200z
..there is a marginal risk of severe thunderstorms Sunday afternoon
and evening across parts of the eastern Gulf and South Atlantic
coast region...as well as portions of the northern plains...
Strong thunderstorms may impact parts of the southeast and northern
plains Sunday afternoon and evening, accompanied by at least some
risk for severe weather.
Models indicate that a subtropical high will remain prominent across
much of the southwestern and south central U.S. During this period,
but the center of highest mid-level heights is forecast to shift
westward/northwestward from the southern High Plains into the
southern rockies. It appears that troughing within the mid-latitude
westerlies to the north of this feature will broaden, with one or
two embedded impulses forecast to progress across the
Saskatchewan/Manitoba/northwest Ontario vicinity. This likely will
be accompanied by the southeastward progression of a weak surface
front through the northern U.S. Plains.
At the same time, near/east of the Mississippi Valley through the
Atlantic Seaboard, upper troughing is forecast to linger between the
aforementioned subtropical high and another over the western
Atlantic. Some southward elongation of the trough through the
eastern Gulf Coast may occur, in response to another significant
embedded digging perturbation. Seasonably high moisture content
characterized by precipitable water of 2+ inches may linger near
southern and mid Atlantic coastal areas, while spreading northward
through coastal New England. At the same time, this moisture may
become increasingly suppressed southward into areas near/south of
the eastern Gulf Coast, though fairly moist air will probably linger
beneath the upper trough across the lower Ohio Valley into western
slopes of the Appalachians.
Stronger surface heating coinciding with higher lingering boundary
layer moisture, supportive of the development of moderate to large
cape, appears likely to become increasingly confined to near the
base of the elongating upper trough, across portions of northern
Florida into the Carolinas. This is where mid-level forcing for
ascent ahead of the digging short wave impulse, coupled with
momentum/shear associated with 30-40+ kt flow in the 850-500 mb
layer, could contribute to an environment conducive to organized
strong to severe storm development. Uncertain sub-synoptic scale
developments through this time period, though, preclude anything
more than 5 percent severe probabilities at the present time.
Stronger mid-level forcing for ascent appears likely to remain
generally north of the international border through this period.
This contributes to uncertainty concerning the extent of potential
convective coverage ahead of the southeastward advancing cold front.
However, instability will probably be sufficient to contribute to at
least some severe weather potential with storms that do form Sunday
afternoon and evening.