|D4||Friday Aug 23 2019 - Saturday Aug 24 2019
||D7||Monday Aug 26 2019 - Tuesday Aug 27 2019
|D5||Saturday Aug 24 2019 - Sunday Aug 25 2019
||D8||Tuesday Aug 27 2019 - Wednesday Aug 28 2019
|D6||Sunday Aug 25 2019 - Monday Aug 26 2019
||(All days are valid from 12 UTC - 12 UTC)
PREDICTABILITY TOO LOW is used to indicate severe storms may be
possible based on some model scenarios.
However, the location or occurrence of severe storms are in doubt
1) large differences in the deterministic model solutions,
2) large spread in the ensemble guidance, and/or
3) minimal run-to-run continuity.
POTENTIAL TOO LOW means the threat for a regional area of
organized severe storms appears highly unlikely during the entire
period (e.g. less than a 30% probability for a regional severe
storm area across the CONUS through the entire Day 4-8 period).
ACUS48 KWNS 190835
SPC AC 190833
Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0333 AM CDT Mon Aug 19 2019
Valid 221200Z - 271200Z
On Thursday/D4, a vertically stacked low will develop over southern
Quebec with strong southwest winds aloft overspreading the
northeastern states. A cold front will rapidly move across New
England and will trail southward toward the Delmarva, though models
differ in timing. MUCAPE on the order of 1000 J/kg is expected over
northern areas ahead of the front, with greater values approaching
2000 J/kg into NJ and eastern VA where dewpoints will be in the 70s
F. Shear will be less over southern areas, but still sufficient to
support at least a marginal wind and hail threat. Long hodographs
will favor cells or fast-moving line segments over northern areas,
but there is more model discrepancy regarding speed of the cold
front. If the more progressive model solutions are correct, there
may be little opportunity for severe storms north of Long Island. As
such, will defer possible upgrades to later outlooks.
To the west, a lesser shortwave trough will move across the northern
Rockies and Plains during the Thursday/D4 to Friday/D5 period,
though models vary greatly with the strength of this feature.
Regardless, southeast surface winds may result in enough moisture
advection into the northern Plains for at least a marginal severe
risk along an attendant cold front.
For the Saturday/D6 to Monday/D8 period, a relatively strong upper
jet is forecast to nose into the northern Rockies and Plains, then
eventually into the upper MS Valley. Increasing shear and lift will
likely interact with increasing low-level moisture and instability
over the Dakotas, MN, NE and IA. Predictability is low for this time
frame, but probabilities could be added in future outlooks.