SPC AC 121939

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0239 PM CDT Sun Jul 12 2020

   Valid 122000Z - 131200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS CENTRAL AND
   SOUTHERN ALABAMA...

   ...SUMMARY...
   Severe thunderstorms are expected across Alabama and far eastern
   Mississippi this afternoon. Isolated to widely scattered severe
   thunderstorms are also expected this afternoon through late evening
   across parts of the central and southern High Plains.

   ...20Z Outlook Update...
   Stabilizing effects from convective overturning associated with the
   central Alabama MCS will likely mitigate any severe risk from
   redeveloping this afternoon/evening across portions of eastern
   Tennessee and northern Alabama this afternoon.  Portions of the
   region have been removed from severe probabilities to address
   ongoing convective trends.

   Additionally, Marginal severe weather probabilities have been
   reconfigured around a cluster of elevated storms located across
   north-central portions of Nebraska.  

   Other remaining areas of the outlook are in tact with minimal
   changes.

   ..Cook.. 07/12/2020

   .PREV DISCUSSION... /ISSUED 1143 AM CDT Sun Jul 12 2020/

   ...Alabama/eastern Mississippi...
   A belt of seasonably strong northwesterly flow aloft will contribute
   to organized severe potential today. Several small-scale bows are
   evident at late morning in association with an increasingly
   organized southeastward-moving linear complex across far northeast
   Mississippi/northern Alabama. Aided by a moist/unstable feed from
   the west, these storms should continue to organize and thrive along
   the instability gradient as they move south-southeastward across
   Alabama/far eastern Mississippi this afternoon. Some hail will be
   possible, but damaging winds should be the most common severe
   hazard. For additional short-term details, see Mesoscale Discussion
   1198. 

   ...Southern/central High Plains this afternoon/evening...
   In the wake of a large overnight MCS across Oklahoma, moist upslope
   flow has established along and north of a surface front from the
   Texas Panhandle into northeast New Mexico. Subtle midlevel
   perturbations moving across Colorado (around the northeast periphery
   of the Four Corners high), daytime heating and the aforementioned
   upslope flow will contribute to thunderstorm development along the
   Front Range by mid afternoon. Moderate buoyancy and steep midlevel
   lapse rates, along with straight hodographs and sufficient
   deep-layer shear, will support splitting supercells capable of
   producing isolated hail near 2 inches in diameter. Steep low-level
   lapse rates and a deep mixed layer will also support the potential
   for isolated severe outflow gusts as clusters of storms spread
   eastward onto the High Plains through late evening.

   ...Ohio Valley...
   Scattered thunderstorms are expected to develop/increase across the
   region this afternoon in advance of a southeast-moving shortwave
   trough. Pockets of moderate destabilization are expected, although
   some areas will be influenced by source region trajectories from the
   late morning MCS near the Tennessee/Alabama/Mississippi border
   region. Regardless, isolated severe thunderstorms can be expected
   across the region this afternoon into evening, with severe hail/wind
   expected.

   ...Eastern Montana/western North Dakota this afternoon/evening...
   Height falls will increase later today into tonight in association
   with a shortwave trough crossing the Canadian/northern Rockies.
   Modest low-level moisture advection (dewpoints in the mid-upper 50s)
   will occur from the south today, while surface heating/mixing
   deepens the boundary layer and reduces convective inhibition along
   the wind shift in eastern Montana this afternoon. There will be a
   narrow window of opportunity for surface-based thunderstorm
   development along the wind shift this evening (highest chances
   across far northeast Montana into northwest North Dakota), in an
   environment conditionally favorable for supercells. A few elevated
   storms with an isolated hail threat may also develop/persist
   overnight as the stronger forcing for ascent spreads eastward from
   Montana into North Dakota.

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