RSS Mesoscale Discussions from Storm Prediction Center
No watches are valid as of Sun Sep 23 13:57:01 UTC 2018.
No Mesoscale Discussions are in effect as of Sun Sep 23 13:57:01 UTC 2018.
SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0740 AM CDT Sun Sep 23 2018
Valid 231300Z - 241200Z
...NO SEVERE THUNDERSTORM AREAS FORECAST...
Severe storms are not anticipated across the U.S. today.
The upper-air pattern this period will feature a progressive
northern stream. A synoptic trough initially was apparent in
moisture-channel imagery from the Canadian Rockies southwestward
across WA/OR and offshore northwestern CA. By 00Z, this trough
should reach southern SK, north-central/southwestern MT,
northwestern NV, and northern CA. By 12Z, the trough should reach
central/eastern MT, western WY, UT and the Sierra Nevada, as a
series of shortwaves pivot through the associated cyclonic-flow
field. In the southern stream, a weak but well-defined perturbation
-- currently located from southeastern OK to south-central TX --
should move slowly northeastward, reaching southeastern MO, AR and
southeast TX by the end of the period.
At the surface, 11Z analysis showed a wavy, quasistationary front
from the Hampton Roads area across western NC, middle TN, and
northwestern LA, to a weak low over east-central TX, to northern
Coahuila. This front should remain near its present position
through most of the period, with some northward drift possible over
the Mid-South and Arklatex regions. Another front was drawn across
northern Upper MI, northern/western MN, central/southwestern SD, and
eastern MT. Little movement is expected until after 00Z, when
frontal-wave low development is forecast over eastern SD, ejecting
northeastward. By 12Z, the low should be located over northwestern
MN, with cold front southwestward across central NE to northeastern
CO, and warm front over western Lake Superior.
General thunderstorm potential will exist mainly near and south of
the frontal zone over the Southeast and Ohio Valley, in patches of
the northern/central Rockies region today beneath the ascent field
preceding the progressive synoptic trough, and late in the period
over parts of MN and the Dakotas, near the northern front/low. In
the latter area, widely scattered to scattered, elevated
thunderstorms are possible after 06Z, rooted near 700 mb. Forecast
soundings suggest steep lapse rates and mucape 1000-1500 J/kg, but
weak effective shear. Small hail may be possible with relatively
discrete/strong cells early in the convective cycle.