638
ACUS48 KWNS 090900
SWOD48
SPC AC 090859

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0359 AM CDT Fri Sep 09 2016

Valid 121200Z - 171200Z

...DISCUSSION...
A bifurcation of the day 3 northwest states trough is expected by
the early part of day 4 (Monday).  The westernmost portion of the
trough should evolve into a closed low Monday night, extending
from the northern intermountain west to northern/central CA.
Meanwhile, the other portion of the trough will shift east across
the central Canadian prairie provinces and ND/northern MN toward
Ontario during day 4.  This trough will remain progressive during
day 5 (Tuesday) and day 6(Wednesday), reaching the Great
Lakes/Quebec and the northeast/mid-Atlantic states, respectively.
Medium range models are in agreement through day 5, generally
cutting off the western states closed low from zonal flow located
over western and central Canada.  However, beyond day 5, the ECMWF
and GFS diverge with the evolution of the closed low, as the ECMWF
shifts this system east and the GFS keeps it cutoff in the west.  

MONDAY (DAY 4)...A cold front attendant to the shortwave trough
moving east across central Canada should advance east from MN into
WI and the upper Great Lakes region, while the trailing portion
moves southeast and south toward the mid MS Valley and through the
central Plains.  Although moderate instability may develop across
the warm sector, stronger forcing aloft and deep-layer shear
should remain north of the front.  This will preclude the
inclusion for 15-percent severe-weather probabilities.

TUESDAY (DAY 5)...The cold front will continue east and southeast
through the Great Lakes toward the Northeast states, OH Valley and
Midwest.  Although strong shear will be expected across these
areas, very weak instability should preclude the severe-weather
threat. 

..Peters.. 09/09/2016

$$