SPC AC 171950
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0250 PM CDT Wed Jul 17 2019
Valid 172000Z - 181200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
THE UPPER MISSISSIPPI VALLEY...NORTHERN HIGH PLAINS...AND FROM
EASTERN PENNSYLVANIA INTO SOUTHERN NEW ENGLAND...
Severe thunderstorms capable of severe wind gusts and large hail are
expected across the northern High Plains and mid-to-upper
Mississippi Valley through tonight. Storms capable of damaging wind
gusts will be possible across portions of the Northeast this
afternoon and evening.
Little change was made to the previous outlook as multiple areas of
potential continue to evolve.
An MCS with near-severe wind gusts recently measured over southeast
IA will continue southeastward across eastern MO and western IL,
with a continued threat of strong to locally severe wind gusts as
the storms propagate into a very unstable air mass. While temporary
stabilization has occurred behind this system, further development
is expected this evening and overnight across the Upper MS Valley in
association with a strengthening low-level jet. For more information
see Mesoscale Discussion 1502.
To the east, numerous small storms persist from PA into southern New
England, where a very moist air mass exists. Good instability along
with pockets of heating will continue to support localized
.PREV DISCUSSION... /ISSUED 1154 AM CDT Wed Jul 17 2019/
...Iowa/northern Missouri to western Illinois...
A quasi-linear cluster of storms will likely persist generally
southeastward across the region as the downstream air mass continues
to destabilize, with persistence aided by warm/moist advection
focused in vicinity of a sharp surface-850 mb moisture/instability
gradient across the region. A focused corridor of damaging winds
could evolve and some severe hail is possible as well.
...Minnesota/eastern Dakotas to western Wisconsin...
Although forecast confidence is not particularly high across the
region, storm redevelopment is expected later today as the air mass
and/or source region trajectories recover in the wake of early day
convection and/or the earlier MCS across far southern Minnesota and
Iowa. Such surface-based redevelopment could initially focus later
this afternoon across eastern North Dakota and nearby northeast
South Dakota/northwest Minnesota, and subsequently develop eastward
through the evening. Other storms may develop farther south across
central Minnesota, with overall intensity/surface-based likelihood
depending on air mass recovery. Where the air mass does
moderately/strongly destabilize, deep-layer shear will be more than
adequate for supercells/organized multicells. Multiple sub-regional
corridors of storms capable of hail/wind are possible across the
region later this afternoon into tonight, and some tornado risk may
exist as well, particularly as the low-level jet strengthens early
...Northern High Plains...
A shortwave trough feature will move into Montana/Wyoming this
afternoon, helping to develop scattered thunderstorms. Isolated
severe thunderstorms including a few supercells capable of large
hail and damaging winds will affect parts of the western Dakotas and
nearby Wyoming/Nebraska later this afternoon and evening.
...NY/PA/NJ into southern New England...
A moist and potentially very unstable air mass is in place across
this region today, with dewpoints in the upper 60s to lower 70s and
early visible satellite imagery is showing the potential for strong
heating. Afternoon SBCAPE values of 2000-3000 J/kg are expected,
with scattered thunderstorms forming by mid-afternoon. Vertical
shear profiles will not be particularly strong, but sufficient
westerly steering flow will help organize outflows and pose a risk
of locally damaging wind gusts in the strongest cells. Coverage and
intensity of storms will decrease farther south across the Delmarva
region, but isolated strong convection is possible.
NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 0100Z