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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