SPC 1730Z Day 2 Outlook

Day 2 Outlook Image

Day 2 Convective Outlook  
NWS Storm Prediction Center Norman OK
1107 AM CST Tue Nov 17 2020

Valid 181200Z - 191200Z


Severe thunderstorms are not expected on Wednesday or Wednesday

A progressive, but relatively low amplitude upper pattern is
anticipated across the CONUS on Wednesday. A shortwave trough is
forecast to begin the period just off the Northeast coast, before
quickly progressing northeastward. In the wake of this shortwave,
modest upper ridging is expected to move from the northern/central
Plains through the Upper MS Valley and Upper Great Lakes. Farther
west, a series of shortwave troughs will move across the Pacific
Northwest and northern Intermountain West. The lead wave in this
series will likely move through the northern Plains early Thursday
morning as the most substantial wave in the series moves into the
coastal Pacific Northwest.

At the surface, expansive high pressure over much of the eastern
CONUS early Wednesday is forecast to gradually shift eastward as
troughing associated with lead Pacific Northwest shortwave deepens
and shifts eastward across the northern/central Plains into the
Upper Midwest. 

Short wavelength between shortwave troughs will limit the duration
of southerly return flow, keeping areas across the central and
eastern CONUS too stable for thunderstorms. Cold mid-level
temperatures atop moist onshore flow will result in modest
instability along the Pacific Northwest coast, supporting the
potential for isolated lightning flashes, particularly early
Wednesday morning and late Wednesday night/early Thursday morning as
shortwave troughs move through the area. Given the cold mid-level
temperatures, small, sub-severe hail is possible with some of the
stronger, more persistent cells. Very isolated (i.e. less than 10%
coverage) lightning flashes may also occur across eastern OR/WA into
ID late Wednesday afternoon/evening as the initial shortwave trough
moves through.

..Mosier.. 11/17/2020

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