Area Forecast Discussion
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056
FXUS64 KLUB 171134
AFDLUB

Area Forecast Discussion
National Weather Service Lubbock TX
534 AM CST Sun Dec 17 2017

.AVIATION...

Conditions have improved to MVFR at LBB and PVW but IFR ceilings
remain at CDS. A cold front moving through the Panhandle should
help to clear out low clouds with winds shifting to the northwest
around 14Z. Guidance is hinting at low clouds and fog again with
light northwest winds overnight.


&&

.PREV DISCUSSION... /issued 244 AM CST Sun Dec 17 2017/

DISCUSSION...
The forecast period is split roughly in two this morning with a
period through Wednesday characterized by split flow aloft
followed by the development of a full-latitude long wave upper
trough over the vast majority of the continental U.S. The devil,
however, is in the details.

Into Wednesday the models, especially the WRF-NAM, is trending
toward a high amount of mostly nocturnal surface and low level
relative humidity. While this is often a bias, the trend this
morning with some fog and stratus developing certainly lends
credence to this idea. This might help explain the wide range in
MOS temperatures, especially daytime highs, with the potential for
stratus to linger well into the daylight hours. Will not bit
completely on this cooler and more moist solution but will trend
the forecast to the mean and lower daytime highs a bit the next
few days. The other item of note in this part of the forecast is a
closed low that has formed over Baja California. Models are
showing good consistency in lifting this low slowly out over
northern Sonora later today to near El Paso by end of day Monday
and finally across the South Plains and Panhandle on Tuesday,
becoming more elongated and sheared as it makes this last step. As
mentioned above low level moisture will be a bit more plentiful
than was seen with a similar low/trough that moved across the
region yesterday. This may allow a little more precipitation make
it to the ground with this system, although still only on the
order of a couple to few hundredths of an inch. Will maintain
20-30 percent PoPs across roughly the southeastern third of the
forecast area.

Moving to Thursday and beyond, the transition to the more
amplified pattern aloft has been consistently handled by the
models for several days now. This will usher in cold air into the
forecast area Thursday and linger through next weekend. However,
the models have been far less consistent in the handling of short
wave energy embedded in this flow. After trending toward a
significant closed low forming to our west then moving eastward on
a track favorable for precipitation across the forecast area, just
about the entire operational model suite as well as an easy
majority of ensemble members favors a more progressive and open
solution to how this energy moves through the main trough. The
impact on the forecast is two-fold: much less (if any)
precipitation and the cold air moving southward in at least two
waves, the latter now being more significant than the former. This
leaves us with low confidence in how things will play out. Have
stuck quite close to the model blend initialization this morning
as a result, both in terms of temperatures and precipitation.
Temperatures, mainly high temperatures, have been increased some
both Friday and Saturday as the coldest air is not progged to be
delayed until Sunday. Have also dried things out until just beyond
the scope of this forecast when a short wave trough is progged to
approach from the northwest. That said, there could very well be
more adjustments by the models, so the evolution of this cold air
and possible wintry precipitation that would affect holiday
travel will remain fluid as we head through the next several days.

&&

.LUB WATCHES/WARNINGS/ADVISORIES...
None.
&&

$$

99/99/08



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