Area Forecast Discussion
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FXUS64 KLUB 190547

Area Forecast Discussion
National Weather Service Lubbock TX
1147 PM CST Sat Feb 18 2017

IFR to LIFR conditions are expected at KCDS overnight due to the
development of low stratus and fog. Confidence is not as high
that KLBB and KPVW will experience flight category reductions, and
we have trimmed back IFR conditions in the forecast for KPVW to
MVFR. Any reductions at KPVW and KLBB should end by mid-morning
Sunday, but may continue at KCDS until 17 UTC or so. TSRA activity
will be possible in the vicinity of KCDS Sunday afternoon and
evening, but chances are too slim to include in the TAF. Also,
Some afternoon light virga showers are possible in the vicinity of


.PREV DISCUSSION... /issued 552 PM CST Sat Feb 18 2017/

Moisture advection on E-SE winds is expected to yield another
round of low stratus and patchy fog tonight. IFR to LIFR
conditions are expected at KCDS, although the latest guidance
suggests that the onset may be later that previously indicated.
And there is still some uncertainty whether or not KPVW and KLBB
will experience flight category reductions, with higher
confidence of occurrence at KPVW than KLBB. Any reductions at
KPVW and KLBB should end by mid-morning Sunday, but may continue
at KCDS until 17 UTC or later. TSRA will be possible in the KCDS
area Sunday afternoon, but chances are too remote to include in
the TAF at this point.

PREV DISCUSSION... /issued 249 PM CST Sat Feb 18 2017/

Following the decay of a NW-SE oriented surface trough over the
CWA this morning, increasingly moist easterly winds were expanding
west onto the Caprock. This process is tied to pressure falls in NM
preceding a mature upper cyclone near Baja CA complete with
thunderstorms in its cold pocket.

Semi-dirty upper ridge presently atop our area will shift east
tonight ahead of an influx of mid and upper subtropical moisture. At
the low levels, dewpoints in the mid-to-upper 40s should grow to
envelop all but our far western zones tonight within steady E-SE
winds. Fine resolution models performed admirably with stratus and
fog this morning, and their current theme of an aggressive westward
push this evening and overnight looks on track given 50 dewpoints
already creeping west to the Highway 83 corridor.

Toward daybreak Sunday, a north-to-south ribbon of enhanced
isentropic ascent within the LLJ may saturate enough to garner a few
showers or storms mainly off the Caprock. Comparably better ascent
will arrive later in the morning across our western zones as mid-
level height falls ~30 meters precede the decaying upper low. Said
low is still favored to lift too far NW of the local area, so deep
layer ascent remains on the weak side. Nonetheless, abundant mid-
level saturation already in place could begin precipitating as lift
arrives. Forecast soundings indicate tall saturated layers with
bases lowering to 9000 feet AGL at times, all above a deep dry sub-
cloud layer. These profiles usually yield sprinkles/non-measurable
rain at best, so have trended the forecast this way while relegating
thunder to off the Caprock.

What, if any, further precip can develop as weakening height falls
spread east is not looking good, particularly with such abundant
stratus curbing insolation off the Caprock. PoPs were trimmed back
even further to account for this and the continued dismal NWP
trends. By late day, a dryline should still move to near a Pampa-
Abilene line ahead of some breezy SW winds, but gut feeling is that
vertical mixing along the dryline will be hindered by abundant mid
clouds within such deep southerly flow aloft. Still, we did keep a
window open for some dryline convection near the Highway 83 corridor
in case forcing proves more substantial. Strong and severe storm
prospects are rather conditional in our eastern counties given
meager lapse rates and troubling CIN for most/all of the day.

Negatively tilted trough across the Pacific Southwest will break
into two pieces of energy with one to our north and one to our south
on Monday though an elongated trough will exist from MT to SW KS to
Durango (MX).  In it`s wake, we`ll see some ridging extending from a
high SW of Baja.  Then, into Thursday, a nice shortwave will sweep
across the west providing quite a nice height gradient overhead on
Thursday.  Thereafter, zonal flow is expected to return for the rest
of the extended.

On to our sensible weather, thunderstorm activity should be east of
the FA Sunday by evening as a Pacific front/dryline shoves the
moisture back east. A mild cold front should make it in Monday
afternoon. Return flow sets up on Tuesday bringing winds again to
the southwest. Speeds will increase somewhat Wednesday afternoon
(closer to 10-15 mph out west) then increase substantially (25-35
mph) for Thursday with a Pacific front sweeping through Thursday
evening keeping speeds up in the 20-30 range much of the night and
a cold front by Friday morning. A pleasant and cool day is
anticipated on Friday with a warming trend into the weekend.




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