SPC 1300Z Day 1 Outlook

Day 1 Outlook Image

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
0742 AM CDT Sun Oct 04 2020

Valid 041300Z - 051200Z


Severe thunderstorms are not expected across the U.S. through

In mid/upper levels, a substantial mean trough over the eastern
CONUS is forecast to deamplify through the period.  This will occur 
as a series of nearly phased shortwaves -- now apparent in
moisture-channel imagery from the upper Great Lakes across the
middle Mississippi Valley to northeast TX -- eject eastward to the
Atlantic Seaboard and southern Appalachians region.  One of those
shortwave perturbations -- now over IL -- will reach OH by 00Z, then
reach the northern Mid-Atlantic overnight.

At the surface, 11Z analysis showed a warm-frontal zone across he
southern FL Peninsula near Lake Okeechobee, forecast to drift
northward through the period.  Isolated to scattered, episodic
thunderstorms are expected again this period across the FL Peninsula
and adjacent waters, as a rich moisture plume and weak but broad
low-level lift occur within and south of the frontal zone.  Further
north, a low was drawn over IN between IND-HUF, with cold front
southwestward over central AR, north-central TX, the TX Permian
Basin, and southeastern NM.  The low should remain weak and migrate
eastward toward the northern Panhandle of WV around 00Z, with the
front reaching eastern KY, middle TN, and southeast/south-central

...Ohio Valley region...
Isolated to widely scattered thunderstorms are possible from late
morning to afternoon, shifting eastward to northeastward across the
outlook area.  Gusty winds are possible with the strongest activity,
but instability and shear should be insufficient for an organized
severe threat. 

A field of large-scale lift (warm advection and DCVA) related to the
aforementioned IL shortwave trough is contributing to showers across
parts of eastern IL and IN.  From late morning into afternoon, as
the leading edge of this ascent field combined with frontal lift and
impinges on a modestly diurnally destabilizing warm sector, some of
the convection may deepen enough for lightning production.  Forecast
soundings suggest 100-300 J/kg MLCAPE extending past the -20 deg C
isotherm, with buoyancy extending (and supporting some thunder
potential) behind the front. Though winds around 500 mb and higher
levels will be strong, only the very upper reaches of the convective
layer will extend into that regime, and only 20-30 kt effective-
shear magnitudes are forecast.

..Edwards.. 10/04/2020

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