Surface low pressure shifting across the Rockies Day 5, in
conjunction with the upper trough, is progged to deepen in lee of
the Front Range by the start of the Day 6 period (Saturday 3-9). At
this point, the models begin to diverge substantially in terms of
solutions. The GFS is much deeper with the upper system as it
emerges into the Plains, with evolution into a deep closed low as it
crosses the central U.S. Day 6. Meanwhile, the ECMWF advances this
feature as a much weaker open wave, and as a result,
similar/significant differences exist between the two models with
respect to strength/development of the associated surface low. By
late afternoon Day 6, the GFS depicts a surface cyclone in the
vicinity of the mid-Missouri Valley that is 10 to 12 mb deeper than
the ECMWF's low. Though severe risk would appear to be on the
increase by the upcoming weekend as this western troughing reaches
the central U.S., no risk areas will be highlighted at this time,
given the substantial differences in model solutions.
Prior to the emergence of this system into the Plains, thunder will
likely accompany the advance of this system across the Intermountain
West, but weak instability should preclude appreciable severe risk
Day 4. Some risk for hail may evolve late Day 5, across the
Oklahoma vicinity, with potential for elevated/nocturnal storms
developing north of a Texas warm front in a zone of increasing warm
advection/isentropic lift ahead of the advancing trough. However,
risk remains uncertain enough to preclude issuance of a 15%
probability area this forecast.
