Area Forecast Discussion
Issued by NWS

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FXUS64 KLUB 211019
AFDLUB

Area Forecast Discussion
National Weather Service Lubbock TX
419 AM CST Wed Feb 21 2018

.DISCUSSION...
Have issued a Winter Weather Advisory for all but the western
South Plains and SW Panhandle until 6 PM this evening. Satellite
trends show a classic isentropic precip regime underway early
this morning behind a sharp cold front plunging into the Big Bend.
Stratus has been making slow strides northward from the Permian
Basin and into our southern counties, and should envelop the whole
of the CWA by mid-morning. Although regional observations show
2-meter dewpoints have plummeted into the single digits in many
locations, vertical profiles reveal this is very shallow and should
not be a detriment to precip once saturation aloft deepens. This
process is underway just north of the I-20 corridor where the main
axis of 290-295K saturated ascent is directed. By daybreak this
moist ascent should shift north into our domain likely accompanied
by some thunder at times given around 300 J/kg of elevated CAPE.

Expectation is for scattered to numerous sleet showers to expand
northward this morning, while aligning themselves generally along
and east of Brownfield Highway. Model soundings are largely
conducive for sleet given sub-freezing layers of 2000 to 3500 feet
thick beneath a stout warm nose, so have removed earlier freezing
rain wording (even in our SE zones) as this scenario is looking
too conditional. One concern is for warning grade sleet in some
spots given the available convective instability. As a whole, we
feel this should be too localized to justify a Winter Storm Warning
for sleet (1/2" or more), but training of sleet showers could
easily yield some swaths of moderate to heavy sleet at times.

As a whole, the HRRR has exhibited good run-to-run continuity
despite some poor radar initialization at times. We do expect
precipitation to wane from west to east by midday as isentropic
lift trends more neutral, but off the Caprock there should be a
second round or perhaps enhancement of echoes this afternoon as a
mid-level impulse (evident on water vapor just north of the Big
Bend at 4 AM) accelerates northward. A reprieve from wintry precip
is likely tonight behind this impulse, but on its heels will be a
higher altitude and weaker trough arriving in SW flow by Thursday
morning. With stronger SW flow aloft by this time and a deepening
warm nose, recent models are shunting deeper moisture even
farther east, possibly resulting in a null event for even our
Rolling Plains` counties. Opted to lower PoPs considerably given
this trend and WPC`s lower QPF values, but have retained mention
of freezing rain and light icing potential generally off the Caprock
Thursday morning before temperatures recover to above freezing
in the afternoon.

Following another round of SW flow on Friday and some conditional
PoPs hugging our E-SE zones near a residual moist axis, a more
robust upper trough and Pacific FROPA late Fri night should afford
considerable drying of the column with breezy west winds by Sat.
Another trough by early next week embedded in cyclonic westerly
flow doesn`t show much potential for any moisture return locally,
although this theme could improve by mid/late next week as
longwave troughing looks to redevelop across the western CONUS
complete with an active subtropical jet close to home.

&&

.LUB WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until 6 PM CST this evening for
TXZ024>026-030>032-035>038-040>044.

&&

$$

93



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