SPC Jul 11, 2018 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 Wed Jul 11 2018

Valid 112000Z - 121200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS THE UPPER
MS VALLEY...

...SUMMARY...
Severe thunderstorms are expected this evening into tonight across
northern Minnesota and vicinity.

...Discussion...

No appreciable changes are warranted to 1630z outlook.

Strong short-wave trough is currently ejecting east across SK/MB
region and the southern influence of this feature should influence
northern MN later this evening. Warm advection convection has now
retreated to areas north of the international border and the primary
concern for severe development is focusing near the ND/MN border.
However, substantially more boundary-layer heating is required for
surface parcels to reach their convective temperatures. For this
reason it appears deep convection should be delayed for a few hours
and likely displaced downstream over MN.

..Darrow.. 07/11/2018

.PREV DISCUSSION... /ISSUED 1128 AM CDT Wed Jul 11 2018/

...MN area this afternoon through tonight...
A midlevel shortwave trough will continue moving east-northeastward
from southern SK across MB through early tonight.  An associated
surface cold front will progress eastward from ND to northwestern MN
this evening, as weak height falls will brush northern MN.  A
remnant MCV over eastern ND and residual cloud cover will tend to
slow surface heating some today.  The timing of the MCV suggests it
will interact with the warm front this afternoon in MN, though
residual clouds may slow surface heating.  Also, mainly weak/shallow
ascent is expected across northern/northwestern MN this afternoon
along the surface warm front and cold front.  These factors cast
some doubt on the timing of storm initiation and subsequent storm
coverage prior to sunset, which could limit the potential for
surface-based supercells and related tornado potential.  The
mesoscale environment will otherwise be conditionally favorable for
tornadic supercells across northern MN in the zone of greatest
overlap of buoyancy with deep-layer and low-level shear.

The more probable scenario may be for later storm initiation (near
or after dark) across northern MN, with storms transitioning to a
cluster mode fairly quickly.  Large hail and damaging winds will be
the main threats, though a couple of tornadoes will be possible if
any discrete storms form by this evening.

...Southern VA/northern NC this afternoon through late evening...
One embedded mid-upper speed max over southern PA/MD will move
southeastward over Chesapeake Bay this afternoon, as an upstream
wave moves from the upper Great Lakes to northern VA and vicinity
overnight.  A weak pre-frontal surface trough will also move slowly
southeastward across VA this afternoon, providing some focus for
thunderstorm development.  Potentially moderate buoyancy (MLCAPE up
to 1500 J/kg), DCAPE near 1000 J/kg, and effective bulk shear around
25 kt will support multicell clusters capable of producing isolated
damaging outflow gusts for a few hours this afternoon/evening as
storms move southeastward into north central and northeastern NC.

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