Area Forecast Discussion
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FXUS64 KLUB 021123

Area Forecast Discussion
National Weather Service Lubbock TX
523 AM CST Fri Dec 2 2016

Conditions are progged to worsen as the day continues. VFR at LBB
and PVW will give way to MVFR in the next few hours. A more rapid
development of precipitation could lower cigs to IFR faster at LBB
and PVW. CDS looks to hold off on lowering to IFR until sometime
late tonight, and since timing was too uncertain, left mention out
of this TAF issuance.


.PREV DISCUSSION... /issued 430 AM CST Fri Dec 2 2016/

What began as a crystal clear night will be rapidly changing as we
head towards the morning, and the first signs of change are evident
on IR satellite as a few clouds are beginning to develop to the
south and west of the forecast area. The parent storm system is
still deepening over the Desert Southwest early this morning, and
will continue to gather strength today as it churns to the south-
southeast into northwestern Mexico by tomorrow morning. That`s the
elephant in the room, but that`s not the weather maker for today.

Today, we`ll be dealing with winds backing to the southeast at
around 850 to 800mb which will, in turn, lead to excellent
isentropic upglide. By noon today, our southern zones will be well
saturated and this trend will continue to spread northward. Light
drizzle early on should give way to a cold rain throughout the day.
Though the cold front has pushed through the entire forecast area,
our push of moisture from the southeast will help keep everyone on
the warmer side (read: above freezing) and in the liquid phase of
precipitation. Things start to become tricky in the late overnight
and early Saturday morning hours across our northwestern zones as
temperatures at the surface cool but a warm nose aloft remains.
Model soundings are in a bit of disagreement on how quickly this
feature will cool to make the changeover from rain to snow. The NAM
shows a slow turning of winds at H850 to the northeast beginning in
the 0-3Z window for Saturday. This will aid in trimming back the
pesky warm nose but not entirely. Therefore, have elected to go with
a wintry mix across the northwest as the uncertainty for cooling
aloft is too great to go with all snow overnight. The rest of the
South and Rolling Plains should stay above freezing throughout the
column, keeping all with a dreary, cold rain.

With the likelihood for frozen precipitation across the northwestern
zones beginning as early as tonight, a winter weather advisory will
be raised starting 9PM tonight.

An active weather pattern is in store for the extended and the trend
is certainly toward cooler temps.  Saturday should see anticipated
low across western Sonora resulting in a split flow regime.  The low
should dig as far south as Durango before heading northeast into the
Big Bend on Monday.  As is usually the case with systems like this,
there continues to be variability in exactly when and where the low
will eject.  Today, the GFS and ECM are in good agreement now that
the system is starting to be sampled by RAOB and AMDAR.  Today`s
track is a bit further south coming across Sanderson toward the
Metroplex Monday night before filling and moving into the Ohio
Valley.  To our north, we`ll see a passing trough axis to our north
tomorrow evening followed by another on Tuesday as the parent low
drifts out of Saskatchewan into Manitoba. This has the
characteristics of a nice cold air intrusion into the southern
states with a high amplitude ridge along the West Coast. Beyond
Wednesday, the UA pattern evolution becomes quite incoherent. The
ECM typically handles these systems best though we will have to
see how the latest iteration of the GFS20 goes. A batch of cold
air from the north slope of Alaska into Nunavut will become
dislodged starting around Saturday and it is quite easy to see the
propagation along the eastern Rockies arriving on Wednesday. This
corresponds very well with entry into MJO phase 2 about 2 weeks
ago. The surface front looks to make its way all the way into
Central America.

Backing up a bit and looking at local impacts, precipitation should
be ongoing Saturday morning.  We continue to be cautious about the
cooling of the stout warm nose Friday night into Saturday.  That
said, Saturday morning is when winds at H8/H9 become more
northeasterly and thus more likely to induce cooling aloft.
Isentropic ascent looks quite strong during Saturday AM through
noon with period of enhanced lift through midnight Monday morning.
It would appear that precipitation will come across in waves. Very
nice omega fields are indicated well into the dendritic growth
region Saturday morning which will help intensify precipitation.
In regards to p-type: the only place which continues to show a
risk of wintry precip is up in our northwestern snow belt. Even
there, we could see a bit of a mixed bag before noon with a
changeover to rain again with modest diurnal heating. Like is
often the case, a degree or two between the SFC and 5KFT will have
a bit impact on how things evolve. Accumulations of 1-3 seem
reasonably with some risk of locally higher amounts. Snowfall is
expected to remain generally limited to northwest of a Morton to
Tulia line.

Some rain activity will continue into Sunday though we`ve dried
things out a bit faster than the previous forecast.  Precip chances
look fairly low for the remainder of the extended.  We are
anticipating a dry cold front on Tuesday with the arctic front due
in early Wednesday.  In fact, we look to stay in the 30s for highs
on Thursday with lows in the teens here in Lubbock Wed and Thu
night. So, if you have to deal with pipe freezing and
pet/livestock issues, it`s time to start your mitigation routine.


Winter Weather Advisory from 9 PM this evening to noon CST
Saturday for TXZ021-022-027-028.



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