Area Forecast Discussion
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FXUS64 KLUB 171130

Area Forecast Discussion
National Weather Service Lubbock TX
630 AM CDT Wed May 17 2017

Gusty west winds through the day will diminish with sunset. VFR
conditions through the period. TS chances nil.


.PREV DISCUSSION... /issued 329 AM CDT Wed May 17 2017/

Deep layer subsidence was well established early this morning south
of a vigorous trough now lifting across western Kansas. Respectable
cold air advection behind the long-departed Pacific front was still
managing to transport some higher momentum air to the surface
before daybreak mainly in our NW counties. As low level mixing
deepens after sunrise, a belt of 25-30 mph westerlies around 2000
feet should readily mix to the surface over much of the area,
before this stronger gradient flow departs farther east by midday.
Some locales may see wind advisory levels achieved, but this
threat is much less in both time and space than was the case
yesterday. Following transient upper ridging today, cyclonic SW
flow will resume in earnest on Thursday south of another upper
low slowing and becoming vertically stacked over CO. Reservoir of
rich Gulf moisture in south TX will undergo rapid poleward
transport tonight through Thursday, but its westward progress
locally will likely be hindered by deeper SW flow and mean surface
troughing progged to camp out over the CWA for most/all of the day
on Thursday. The result could be another active dryline as we saw
Tue, except displaced farther east this time, possibly even beyond
our Highway 83 counties. We continue to favor rain chances a bit
farther west than raw guidance indicates given their usual easterly
dryline bias.

As a vort lobe pivots out of the base of the upper low Thu night,
a modified Pacific front will be directed across the South Plains,
before stalling in response to another vort lobe approaching from
NM. This frontal behavior is obviously very complex and hinges on
subtle vorticity maxima embedded within the larger gyre, but the
entire operational model spectrum is in good agreement that low
level winds will shift from NW to a S-SW status on Friday with
the dryline once again residing near or just east of the Highway
83 corridor. This pattern is unusual in that some of the same
areas hit hard by severe wx on Tue could again be dealt heavy
blows both Thu and Fri. Again, subtle changes to the vorticity
budget of this low and its impact on Thu night`s front could
significantly augment the severe storm distribution.

As the upper low finally mobilizes northeast out of Colorado by
Fri night, a modified cP front will drop south across the region
and quickly scour out rich Gulf moisture over much of the Lone
Star State. ECMWF appears overly generous with convection Fri
night during this FROPA in our area, especially as it does not
retreat the dryline any further west than other models indicate.
Therefore, we`ll continue to keep PoPs Fri night lower and more
befitting of aggressive drying from N-S which fits this pattern
of an unseasonably cool cold front. What residual moisture is left
spanning the decaying cold front in South TX or the northern
GOMEX by late weekend could certainly curl northward in a return
flow regime by early next week. This would be crucial for additional
rain chances Mon or Tue preceding a broad NW flow trough progged
to occupy the middle of the Nation by midweek.




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