SPC 1200Z Day 1 Outlook

Day 1 Outlook Image

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
1055 PM CST Tue Jan 12 2021

Valid 131200Z - 141200Z


Showers, occasionally accompanied by lightning, are possible in a
corridor across the eastern Gulf Coast states into the Carolinas
today through tonight.

Strong cyclogenesis appears underway across the mid-latitude Pacific
(near/west of 160 W longitude), with substantial further development
forecast.  Through 12Z Thursday, the center of the evolving broad,
deep and occluding cyclone is forecast to slowly migrate across the
northeastern Pacific, toward the Gulf of Alaska.  Coinciding with
this development, considerable amplification of downstream mid/upper
flow appears likely, with pronounced ridging developing along an
axis from the subtropical eastern Pacific northward through Canadian
Pacific coastal areas.  

To the east of the mid-level ridging, models indicate that a
vigorous short wave trough will dig across and to the lee of the
northern Rockies.  It appears that this will be accompanied by
deepening surface troughing across the eastern Great Plains into
upper Mississippi Valley, to the south of a deep surface cyclone
migrating across the Canadian Prairies.  This likely will extend as
far south as the southern Great Plains, but lingering surface
ridging across the northwestern Gulf of Mexico will preclude a
return flow of Gulf moisture.  Seasonably moist boundary-layer air
will remain confined to the south of a quasi-stationary frontal
zone, generally south of the Florida Peninsula and Keys into the
southern Gulf of Mexico.

In response to the upstream developments, a short wave trough and
embedded mid-level low, emerging from the southern Great Plains, are
forecast to accelerate east-northeast of the lower Mississippi
Valley today, across and east of the south Atlantic Seaboard.  It
appears that this will contribute to a developing frontal wave off
the Carolina coast, and potential for vigorous thunderstorm
development along a trailing cold front.  This could initiate close
to southeastern Florida coastal areas, but offshore.

Much of the nation will remain generally stable with negligible risk
for thunderstorms.  However, there does appear at least low
probabilities for convection capable of producing lightning in a
narrow corridor across the eastern Gulf Coast states into the

Although well to the cool side of the surface frontal zone, 13/00Z
soundings do indicate the presence of relatively steep mid-level
lapse rates across much of the region, in advance of the mid-level
low emerging from the southern Great Plains.  With the approach of
the low, forecast soundings indicate elevated moisture return near
the base of this layer (around the 700 mb level) will contribute to
weak CAPE supportive of convective development.  Aided by forcing
for ascent in the exit region of an associated mid-level jet, which
may continue to slowly strengthen as it propagates eastward through
the period, it appears that thermodynamic profiles may become at 
least occasionally supportive of lightning with some of this
activity.  This is expected to remain confined to a narrow corridor
near the 700 mb thermal gradient, across parts of the eastern Gulf
Coast states into the Carolinas by tonight.

..Kerr.. 01/13/2021

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