SPC AC 081212
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0612 AM CST Thu Mar 08 2018
Valid 081300Z - 091200Z
...NO THUNDERSTORM AREAS FORECAST...
No thunderstorm areas are forecast today.
The large-scale upper-air pattern will remain characterized by mean
eastern troughing and western ridging, dominated by a large cyclone
now located over the Great Lakes. That cyclone will undergo a net
eastward shift as:
1. The main 500-mb low and associated vorticity max -- initially
over eastern lower MI -- pivot east-southeastward to the CT/RI area
by 12Z, and
2. The leading, smaller cyclone -- now centered just east of Cape
Cod -- is forecast to pivot northward in the cyclonic-flow field of
the approaching Great Lakes low today. This perturbation will
deamplify to an open wave and retrograde into the northern
semicircle of the larger cyclone impinging on New England.
Related cyclonic flow will cover a large swath of eastern North
America and southward across the Gulf and Cuba, to the Yucatan
Peninsula and northwestern Caribbean. The associated surface cold
front has passed offshore from FL, leaving behind a large
continental/polar anticyclone that will shift southeastward from the
Plains states to the Southeast. Associated dry/stable conditions
will preclude thunder east of the Rockies, while ridging aloft
suppresses convective potential over the Southwest.
A mid/upper-level shortwave trough -- now evident in moisture-
channel imagery offshore from the Pacific Northwest -- will weaken
considerably as it penetrates the mean ridge inland. Still,
divergence aloft and weak shots of DCVA will spread over the
northern Rockies, destabilizing the midlevels. A rogue lightning
strike cannot be ruled out with shallow elevated convection
occupying small pockets of roughly 50-75 J/kg MUCAPE. Meager
moisture and the weakening character of the perturbation aloft
indicate any related thunder potential will be very isolated and
brief, at best -- too much so to justify a 10% unconditional thunder
area in this outlook.
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NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 1630Z