SPC 1300Z Day 1 Outlook

Day 1 Outlook Image

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
0635 AM CST Mon Nov 16 2020

Valid 161300Z - 171200Z


Severe thunderstorms are not expected across the contiguous United
States through tonight.

The mid/upper-level pattern will amplify somewhat over the CONUS,
while remaining progressive.  Ridging now over the West Coast States
will shift eastward to the Rockies and build through the period,
while a large cyclone over the Gulf of AK shifts/redevelops
southeastward toward the high-seas areas west of the BC coastline. 
As this occurs, a strong, basal shortwave trough -- now apparent in
moisture-channel imagery near 145W between 30N-40N -- will pivot
east-northeastward toward the northern CA and OR coasts while
gradually losing amplitude.  This perturbation should move ashore
early day-2, but its low-level frontal zone and associated band of
convection may reach parts of the coastline by 12Z.  Conditions
favorable for isolated thunderstorms are expected to remain
offshore, behind this band.  However, some thunder may occur within
a precursory warm-advection plume today over the Olympic Peninsula
and adjoining waters, where forecast soundings show sufficiently
steep midlevel lapse rates above a moist layer near 850 mb to yield
around 100-300 J/kg elevated MUCAPE.

The eastern trough's broadly cyclonic flow regime will be maintained
by a series of shortwave perturbations, following the departure of
the strong shortwave trough now over central/southern QC and New
England.  The associated surface cold front was analyzed at 11Z from
the western parts of the Canadian Maritimes southwestward over
Atlantic waters offshore from the Carolinas, to north-central FL,
and the north-central/northwestern Gulf.  This front will move
southward down the FL Peninsula through the period, decelerating
overnight in southern portions.  Associated convergence generally
will weaken with time.  However, diurnal boundary-layer moisture/
destabilization along and ahead of the front will weaken MLCINH
enough for lift near the front to support isolated thunderstorms,
mainly this afternoon into early evening.

..Edwards/Leitman.. 11/16/2020

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