Area Forecast Discussion
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931
FXUS64 KLUB 012318
AFDLUB

Area Forecast Discussion
National Weather Service Lubbock TX
518 PM CST Thu Dec 1 2016

.AVIATION...
VFR conditions will continue for at least another 12 hours before
an extended period of deterioration takes place. Moisture will
stream into the region ahead of a developing storm system which
will bring CIGS down into MVFR on Friday morning with patchy rain
showers. By late in the afternoon or early evening, CIGS could
reach IFR but confidence is low at this time.

&&

.PREV DISCUSSION... /issued 400 PM CST Thu Dec 1 2016/

SHORT TERM...
Our weather will trend downhill this evening with a modest cold
frontal boundary moving south from the Panhandle. It may not seem
important, initially. And also won`t even be cooler, initially;
minimum temperatures early Friday are expected to be a notch or two
more mild than the past couple mornings. But winds will trend
northeasterly later tonight and early Friday, while a little off the
deck a moist warm advection nose with southeast winds centered
around 800 millibars will start to take shape on Friday.

This will result in fairly significant isentropic upglide developing
Friday, especially across central and eastern counties. And combined
with increasing Precipitable Water values to 0.75 to 1.00 inches
across the eastern half of our area will support moderate to high
rain chances as the day goes on. The clouds and rain, and surface
high pressure ridge nosing southward, will result in a significant
temperature drop from today, with most highs not making it out of
the 40s on Friday.

There also are still indications of a thin positive energy area on
forecast soundings between 500 and 700 millibars late Friday,
spreading mainly across the southeast half of the area. We are
leaving thunder mention out, however, because of a sharp inversion
at the bottom of the unstable layer. But this inversion weakens
heading southeast. Something to keep in mind. RMcQueen

LONG TERM...
The upper low will continue to dig across northern Mexico on
Saturday and begin to lift northeast into west central Texas,
well south of the region Monday morning. This southward track and
the lack of a strong reinforcing cold air surge will make the
precipitation type forecast tricky through the weekend. We
continue to expect some changeover from rain to snow Saturday
morning across the far northwest South Plains and southwest
Panhandle but a persistent warm nose a few thousand feet above
the surface will limit the overall snowfall potential through the
event, keeping rain the predominant p-type across the majority of
the forecast area.

Deep ascent will continue across the area Friday evening into
Saturday morning as low level warm advection occurs beneath strong
jet energy lifting across north Texas. This should put the
heaviest precipitation initially across the Rolling Plains Friday
evening before the precipitation shield broadens closer to the
upper low and within expanding diffluence aloft across eastern New
Mexico into far West Texas and the western South Plains. Model QPF
amounts with this second batch of rain are consistently above 1/4"
and with significant melting in the column the precipitation could
change to snow sooner or be locally heavy across the favored
higher locations of Parmer county mid to late Saturday morning.
Sufficient warm air both aloft associated with the warm conveyor
and near the surface should keep the precipitation all rain
further east and south across the remainder of the South Plains
early Saturday. As the upper low bottoms out and the next piece of
jet energy heads into west Texas Saturday afternoon, expect
another batch of precipitation to form and work slowly east across
the area through early Sunday. Model forecast soundings indicate
the column could cool sufficiently for the rain to change to snow
further east across the central South Plains and south central
Panhandle Saturday evening. Expect this to be brief and within the
heavier bands of precipitation so do not anticipate any meaningful
snow accumulations other than across the higher terrain to the
northwest where more northerly flow helps the column remain closer
to freezing. Precipitation will continue but likely be on the
lighter side overnight Saturday into Sunday morning. With more
easterly component in the low levels and continued warm advection
have kept precipitation type mixed on the Caprock with a
transition to rain/freezing rain by daybreak across the
northwestern third of the CWA. The upper low is forecast to
maintain intensity or deepen a bit as it moves east into central
Texas on Monday. This along with a continued fetch of moisture
should keep rain chances across at least the southern half of the
area through the day Sunday. Any precip that remains Sunday night
will likely be in the mixed form, favoring light freezing rain
and light rain across the northwest third of the area once again
as lows drop back to or below the freezing mark.

After this low exits, attention quickly turns to much colder air
of the arctic variety poised to arrive in the South Plains late
Tuesday. Origins for this airmass have hints of Siberia and the
arctic circle as a high amplitude ridge develops west of Alaska
sending an extremely cold airmass southward. With sufficient
modification by the time it enters the High Plains the chill in
the air will be far from record breaking but still cold enough to
take note of with highs averaging 15-20 degrees below normal
across a good chunk of the region on Wednesday. Medium range
models continue to show sufficient lift for some light snow late
Tuesday into Wednesday behind the front so haven`t argued with the
blend and kept mention in the forecast with rain/snow off the
Caprock. Single digit wind chills with lows in the teens across
the northwest half of the area will be another aspect to keep an
eye on as we get closer to the event.

&&

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

$$

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