- Day Three
acus02 kwns 230541
Storm Prediction Center ac 230540
Day 2 convective outlook
National Weather Service Storm Prediction Center Norman OK
1240 am CDT Fri Aug 23 2019
Valid 241200z - 251200z
..there is a marginal risk of severe thunderstorms across portions
of the plains....
Isolated severe storms are possible over parts of the central and
northern Southern Plains on Saturday. A severe storm or two is also
possible across the northern plains.
A shortwave trough is expected to move southeastward from the
Central High plains across the Central Plains and into the Ozark
Plateau on Saturday. Interaction between this shortwave and the
moist air mass across the Central Plains is expected to result in
Farther northwest, mean cyclonic flow aloft will progress eastward
across western Canada and the northwestern/north-central Continental U.S..
consequently, enhanced mid-level westerly flow will extend from the
Pacific northwest into the central rockies by the end of the period
(12z sunday). A shortwave trough will move quickly eastward within
this enhanced flow aloft along the US/Canada border. An associated
surface low is expected to move eastward across Saskatchewan and
Manitoba, with an attendant cold front moving across eastern Montana and
into the western Dakotas.
Expansive surface high centered over eastern Ontario/western Quebec
will keep much of the northeast Continental U.S. Free of thunderstorms while
warm and moist conditions will persist across the southeast.
Thunderstorms will likely be ongoing from central NE southward into
the eastern Texas Panhandle/western OK early Saturday morning. Strength
and coverage of these storms will have an impact on air mass
recovery and destabilization later during the afternoon.
Additionally, outflow from these storms could provide a boundary for
potential convective initiation. These mesoscale features introduce
uncertainty into the forecast. Current expectation is for the air
mass to destabilize by the late afternoon with isolated storms
developing along the Lee trough extending from northeast nm into
eastern Montana. Higher storm coverage is possible during the evening as
a strengthening low-level jet promotes additional thunderstorm
development across Kansas.
The environment is characterized by favorable low-level moisture,
steep mid-level lapse rates, and strengthening northwesterly flow
aloft with enough vertical shear and buoyancy to support severe
storms. Uncertainty regarding antecedent storms precludes higher
probabilities with this outlook, but an upgrade may be needed in a
subsequent outlook if mesoscale details become more clear.
Elevated storms will likely be ongoing at the beginning of the
period. Modest instability and shear support a marginal hail threat.
Recent model guidance has trended towards less low-level moisture
during the afternoon and evening across the northern plains. As a
result, convective inhibition remains in place across much of the
area, limiting surface-based storm initiation. Best location for
surface-based initiation currently appears to be across
north-Central/Northeast ND. Isolated storms are also possible late
Saturday night/early Sunday morning along the approaching cold
..maximum risk by hazard...
Tornado: 2% - marginal
wind: 5% - marginal
hail: 5% - marginal