SPC 2000Z Day 1 Outlook

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
0137 PM CST Thu Nov 19 2020

Valid 192000Z - 201200Z

...NO THUNDERSTORM AREAS FORECAST...

...SUMMARY...
The risk of general thunder is negligible through tonight.

...20Z Outlook Update...
Lightning detection has indicated occasional lightning flashes in a 
localized area near the northern Oregon coast within the  past hour.
However, the window of opportunity for additional brief/weak
thunderstorm development west of the Cascades may be at its maximum
now through about 22-00Z, as the destabilizing influence of further
boundary-layer warming is increasingly countered by warming aloft,
associated with the continuing eastward progression of the mid-level
cold pool. Any additional development may tend to become more
focused along the western slopes of the Washington Cascades, aided
by modest upslope flow, but coverage probably will remain
sparse/isolated.

..Kerr.. 11/19/2020

.PREV DISCUSSION... /ISSUED 0930 AM CST Thu Nov 19 2020/

...Northwest...
While the probability of thunder appears to be less than 10 percent,
three areas of nonzero probability appear to exist. The first is
near the ND/SD border area with a corridor of elevated convection in
association with a shortwave impulse moving across the northern
Great Plains. While a couple flashes occurred in southeast MT
earlier this morning, effective inflow layers should become
increasingly elevated with eastern extent, thereby decreasing
potential for charge separation. 

A lightning flash or two is also possible across parts of western to
southern MT during the late afternoon but predominately 20s surface
dew points will limit appreciable surface-based buoyancy. Finally,
low-topped showers will likely persist across coastal portions of WA
and northwest OR. Mid-level warm advection is underway in the wake
of shortwave trough passage earlier this morning, although this
process should be temporarily curtailed as a weak mid-level impulse
over the northeast Pacific approaches this evening. The weak forcing
for ascent coupled with generally increasingly marginal
thermodynamic profiles should limit thunder potential.

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