Day 4-8 Outlook

Day 4-8 Outlook Image

Day 4-8 Convective Outlook  
NWS Storm Prediction Center Norman OK
0337 AM CST Thu Nov 19 2020

Valid 221200Z - 271200Z

...DISCUSSION...
A progressive upper level pattern is expected during the Day 4-8
period. An upper trough over the Plains on Day 4/Sun will shift
eastward to the Atlantic coast through Day 5/Mon. At the same time,
a surface cold front will sweep east/southeast from the southern
Plains through the Midwest and eastern U.S., moving well offshore
the Atlantic coast by Day 6/Tue. Showers, and perhaps isolated
thunderstorms, are expected to accompany the frontal passage, but
mostly stable boundary-layer conditions will preclude severe
thunderstorm concerns through Day 5/Mon.

As this initial upper trough shifts east of the MS River on Day
5/Mon, an upper ridge will briefly amplify over the Plains.
Meanwhile, a western upper trough will deepen and shift eastward
toward the southern Rockies on Monday, and the central/southern
Plains on Day 6/Tue. Strong deep layer southwesterly flow will
overspread the southern Plains vicinity, and height falls will
result in strengthening lee cyclogenesis developing eastward across
the central/southern Plains Monday night through Tuesday. Increasing
southerly low level flow will transport somewhat modest Gulf
moisture northward. However, medium range guidance is in fairly good
agreement that surface dewpoints as high as the low to mid 60s F are
possible as far north as southern OK. How much destabilization will
ultimately occur remains somewhat uncertain, as the cold frontal
passage on Sunday/Monday could cut-off Gulf return flow more than
guidance currently indicates. Additionally, cloudiness and showers
in a strong warm advection regime could limit destabilization ahead
of the surface low/front. Nevertheless, overall pattern favors at
least some concern for isolated strong/severe thunderstorm potential
across the southern Plains vicinity on Day 6/Tue, but uncertainty
remains too high at this time to introduce probabilities.  

Beyond Tuesday, spread among various guidance increases
dramatically, and predictability is low.

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