Area Forecast Discussion
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FXUS64 KLUB 042041

Area Forecast Discussion
National Weather Service Lubbock TX
241 PM CST Sun Dec 4 2016

After a couple of raw and damp days it took a northerly wind shift
and weak surface ridging to provide a warm up. This was thanks to
relatively drier air that was carried in and allowed skies to clear
from north to south through the day. The final shreds of low clouds
were finally clearing southeastern Stonewall County as of 20Z.
Broadening our view, the upper low that has been traversing
northwest Mexico the past couple of days is finally moving eastward.
The low is forecast to accelerate northeastward over the next 24
hours, passing south of the Big Bend late tonight and then up into
Central Texas by 00Z Tuesday. As the low glancing the region to the
south we will see an increase in high and perhaps mid-level clouds
overnight and early Monday. However, the best lift within the
diffluent and deformation zones of the low, and thus the better rain
chances, will remain south and east of the area. Even so, it does
appear enough moisture and weak lift may pass just close enough to
bring a risk of showers to the southern Rolling Plains during the
day Monday. Thus, we have maintained a low rain mention roughly
south and east of a Clairemont to Guthrie line.

Otherwise, the passing surface ridge will provide light winds
overnight. There may be enough residual low-level moisture to raise
the risk of patchy fog development, but the expected mid-high clouds
and weak downslope component to the winds after midnight will tend
to mitigate this risk. Hence, any fog mention was excluded from the
grids for now. Lows tonight will range from the mid and upper 20s
northwest to near 40 degrees southeast.

The light overnight winds will transition to increasingly gusty
southwesterly winds Monday afternoon. The stronger winds will be in
response to a tightening pressure gradient associated with a surface
low dropping from northeast New Mexico into the western Texas
Panhandle during the afternoon. Sustained winds of 15-25 mph will
become common over much of the Caprock, with the strongest winds
favoring the northwest zones. The downsloping winds and plenty of
insolation (aside from the Rolling Plains) will yield a mild
afternoon, with highs of 60 to 65 degrees common. The exception will
be in the Rolling Plains where more persistent and thicker cloud
cover may keep them in the middle 50s.

In general, pretty good continuity persists with the 12z model
runs. This will lead to no significant changes to the forecast. A
broad trough will remain over much of the continental U.S. through
the week. More amplified flow Tuesday and Wednesday will allow for
cold air that has been building in Alaska to be unlocked. The
modified version of that air mass will arrive in the forecast area
in two chunks, the first early Tuesday then the second, colder
version arriving sometime Wednesday. It is that latter issue that
is probably the biggest sticking point of the forecast. The GFS,
in particular, has waffled the most with the timing of this second
front; but for now, at least, there seems to be a consensus
developing. A pre-frontal trough will veer winds to the west and
northwest early Wednesday followed by the arctic front during the
afternoon and evening. How much warming can occur behind the
initial trough is a question, as is the timing of this dense air
mass. Will nudge Wednesday`s highs up a bit but will remain below
MOS values for now. Precipitation chances through this period
continue to look very limited.

The cold will not last long. Deamplification of the upper flow
will lead to zonal flow across the southern tier of the CONUS with
increased heights and more southwesterly low level flow and warm
advection. Current expectation is for temperatures to return much
closer to seasonal norms next weekend.




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