Day 1 Severe Weather Outlook

Valid 181200Z – 191200Z


The risk for severe thunderstorms appears negligible across the
U.S., today through tonight.

Within the main branch of westerlies emanating from the mid-latitude
Pacific, large-scale troughing appears likely to linger east of the
Mississippi Valley into the western Atlantic through this period.

At the same time, models indicate significant upstream amplification
to the flow, including a building ridge across the eastern Pacific
into the Gulf of Alaska. To the east of the ridge, a significant
short wave trough (currently progressing toward the Pacific
Northwest) is forecast to gradually split as it begins to migrate
inland. As one emerging perturbation continues eastward, across and
east of the Cascades, another trailing impulse is expected to dig
into southern Oregon/northern California coastal areas by the end of
the period. In response to the approach of the latter feature, an
initially cut-off mid-level closed low to the west of Baja might
begin to accelerate eastward or northeastward toward 12Z Tuesday.

In advance of the cut-off low, lower/mid-tropospheric moisture
return, northward through the Gulf of California, may contribute to
at least weak destabilization across the Southwestern international
border area late this evening through tonight. However, forcing for
ascent to support thunderstorm development is still unclear, and
appears likely to remain weak, resulting in the maintenance of less
than 10 percent thunderstorm probabilities.

Farther north, the leading edge of a plume of moisture emanating
from the subtropical Pacific, may reach Oregon coastal areas by late
this afternoon. However, cooling aloft to contribute to
thermodynamic profiles supportive of thunderstorm activity is not
expected to spread inland of the Pacific Northwest coast until after
dark. This will tend to minimize destabilization, but a few widely
scattered weak thunderstorms might not be out of the question,
particularly across southern Washington/northern Oregon after

..Kerr/Cook.. 11/18/2019


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