Area Forecast Discussion
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FXUS64 KLUB 230747
AFDLUB

Area Forecast Discussion
National Weather Service Lubbock TX
247 AM CDT Tue Oct 23 2018

.DISCUSSION...
Advection stratus with an abundance of dense fog was making
steady progress north from the Permian Basin at 230 AM, and
should grow to occupy much of the South Plains before daybreak.
Based on area webcams and high res models, a dense fog advisory
is valid until 11 AM. Once fog and eventually stratus thin out, much
of the region will remain mostly cloudy from a myriad of mid and
high clouds sourced within the southern branch of split upper flow.
While saturation aloft will deepen through the day in advance of
a healthy trough (currently near Baja California), stronger
easterlies in the low levels will actually serve to advect dry air
westward, most prominently from 750-850mb. This process still
looks to delay the onset of measurable rain for most of the CWA
until later tonight, but our western zones will likely see some
light precip around sunset as moist isentropic ascent ramps up
combined with top-down saturation overwhelming the dry wedge of
air. For this reason, the rain/no-rain terminus was shoved farther
west on the Caprock today in sync with most operational models
and CAMs.

After midnight and through Wednesday morning, a broad region of
upper divergence and height falls will occupy the CWA immediately
downstream of the approaching trough axis. This will prolong deep
isentropic ascent and serve to maintain a shield of steady rain.
Soundings show little/no elevated instability, so shower mention
was nixed in favor of just rain. High temps may actually occur
after midnight with a gradual decline in temps through the day
with extensive precip. PWATs around 1 inch are certainly
impressive, but a lack of convective instability and a rather
progressive nature to the upper trough should keep aerial flooding
concerns to a minimum. On average, a solid 1/2 inch of rain
appears a good bet for much of the forecast area before precip
rapidly dwindles from west to east later in the day with the
passage of the trough axis. Even though deep subsidence aloft will
erode the brunt of thick clouds, shallow stratus is progged to
remain locked in tomorrow night and early Thursday until daytime
mixing dries this layer out.

Dry northwesterly flow aloft by Thursday night still looks to
dominate through the weekend, complete with one or two weak cold
fronts. The signature of these fronts is becoming more muted on
both the GFS and ECMWF, so high temps Sat and Sun continue to be
warmer than the Superblend indicates since this blend still has
older iterations of these models and hence a cooler output.
Increasingly anticylonic flow aloft by early next week is our
preference given this output by the GEFS mean and ECMWF, but
height rises appear negligible and as a result thicknesses should
not change too much from the seasonably mild values this weekend.

&&

.LUB WATCHES/WARNINGS/ADVISORIES...
Dense Fog Advisory until 11 AM CDT this morning for TXZ027>030-
033>036-039>042.

&&

$$

93



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