SPC Sep 13, 2019 2000 UTC Day 1 Convective Outlook

SPC 2000Z Day 1 Outlook

Day 1 Outlook Image

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
0239 PM CDT Fri Sep 13 2019

Valid 132000Z - 141200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER SOUTHEAST
LOWER MI AND NORTHERN OH...

...SUMMARY...
Scattered damaging winds, a couple tornadoes, and isolated severe
hail are possible across southeast Lower Michigan into northern Ohio
through about 9 PM EDT.

...20Z Update...

...MI/OH/IN...
Severe Thunderstorm Watch 652 was recently issued across far
northeast IN, northwest OH, and southeast Lower MI to cover the risk
for scattered damaging wind gusts and isolated large hail with the
thunderstorms developing along the pre-frontal trough. A tornado or
two is also possible. 

Isolated thunderstorms are still possible across southeast IN and
southwest OH but weaker deep-layer vertical shear should keep any
severe risk more isolated.

...Western NC...Western/Central SC...
Thunderstorm cluster along the central SC/NC border has recently
shown southwestward forward-propagation into central SC. The
downstream air mass is warm and moist and the discrete propagation
of this thunderstorm cluster is anticipated. Vertical shear is weak,
leading to predominantly disorganized storms. Even so, strong
updrafts support water loading and the potential for wet downbursts
capable of damaging wind gusts.

...North-Central MT...
Isolated thunderstorms are still anticipated later this
afternoon/evening as the shortwave trough currently moving through
southern Alberta/far northwest MT continues eastward. Low-level
moisture will be limited but modest buoyancy will still develop
amidst a deeply mixed boundary layer and increasing mid-level
moisture. A strong wind gust or two is possible, although overall
severe coverage is expected to be too low to introduce any risk
areas.

..Mosier.. 09/13/2019

.PREV DISCUSSION... /ISSUED 1127 AM CDT Fri Sep 13 2019/

...MI/OH/IN...
An upper low over northwest ON will evolve into an open wave while
moving northeastward towards James Bay, as embedded speed maxima
rotate around the southeastern periphery of the low. At the
surface, a cold front arcing into far southwest Lower MI to the
Wabash Valley will progress east across the rest of IN/Lower MI.
Thick overcast and residual stratiform rain have tempered
destabilization ahead of the front across most of Lower MI, except
across the southeast portion with nearly cloud-free insolation
occurring from there southward across much of OH and eastern IN.
Surface temperatures were already warming through the 80s and will
reach the low 90s across most of OH where surface dew points should
mix down into the low 60s. A confined corridor of upper 60s dew
points should remain near the front and where boundary-layer mixing
is not quite as pronounced across southeast Lower MI. 

Scattered storms are expected to develop in the next couple hours
near the front, and then continue eastward across Lake Erie and
parts of northern OH into this evening. Despite being on the
southeast periphery of the Upper Great Lakes mid-level jet, largely
unidirectional/veered wind profiles should hold effective shear to
between 25-40 kts. The greatest potential for supercells will exist
across southeast Lower MI where the low-level hodograph should be
adequately enlarged, yielding a short-duration risk for a couple
tornadoes before surface winds veer. Modest mid-level lapse rates
will probably limit hail magnitudes. Scattered damaging winds should
be the primary hazard with this threat likely diminishing shortly
after dusk. 

...Western NC into SC...
Strong surface heating and lingering low-level moisture along and
southwest of a reinforcing frontal surge could provide some focus
for thunderstorm development this afternoon. Thermodynamic profiles
will favor some risk for damaging downbursts given DCAPE values near
1000 J/kg. Minimal deep-layer shear will temper the potential for
organized clustering.

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