Area Forecast Discussion
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FXUS64 KLUB 102148

Area Forecast Discussion
National Weather Service Lubbock TX
348 PM CST Tue Jan 10 2017

The mild weather pattern for West Texas continues with the region
under broadly cyclonic flow aloft with deep westerly winds. At the
surface, a weak front has moved through most of the forecast area
this afternoon turning winds to the northwest, but this boundary
will wash out and winds will return to the southwest on Wednesday.
Temperatures tonight will be cooler than last night with lows
ranging from the upper 30s northwest to middle 40s southeast. High
clouds should thin out this evening but partly cloudy skies will
continue tomorrow. Near-record temperatures are expected on
Wednesday with highs mainly in the 70s, with some low 80s out in the
Low Rolling Plains. The record high for January 11 at Lubbock is 76
degrees, which is also our forecast high.

A pattern change to colder and wintry weather at times is still a
good bet beginning late this week and heading into the weekend.
This change is tied to a southward oscillation of a Polar Vortex
trough across the Canadian Prairies tomorrow. This will drive an
Arctic airmass south ahead of a modest surface high, which will
receive a stronger push on Thursday ahead of a 1040+ mb surface
high. Earlier snow cover through the central Great Plains has since
diminished considerably to an inch or less, so we`d expect the
first wave of Arctic air to modify considerably before reaching
our NE zones on Thursday.

With the reinforcing push expected Friday, chilly surface ridging
should dominate the region with highs probably ending up below the
latest MOS numbers which is reflected in our latest forecast. The
upper air pattern overall is just not conducive for a true Arctic
airmass (usually denoted by 850mb temps of -10C or colder)
reaching our forecast area given the Polar Jet will be flattening
along the 49th Parallel on Friday. This will keep the Arctic high
displaced well to our north from the Dakotas into Wisconsin.
However, we`ll still be hard pressed to shake a modified
extension of this cold airmass through Saturday before it
finally overturns ahead of a vigorous upper low on Sunday
complete with unseasonably rich PWATs over 1", mild thicknesses
and low level dewpoints rising to above 32 degrees.

Until the upper low arrives, there is still a critical window for
very light freezing rain to start early on Friday as weak
isentropic ascent saturates the lower layers. Provided our narrow
diurnal temp curve verifies, high temps should rise to above
freezing Fri afternoon, before dipping back below Fri night
through early Saturday. Opted to undercut model temps for both
highs and lows on Saturday, particularly in our NE zones where
this cold airmass will be most persistent. This should favor the
largest window for freezing rain in our climatologically favored
southeast Panhandle counties, especially on Sat and Sat night as
saturated layers deepen and omega improves. With such marginal
freezing temperatures at times, icing could be largely relegated
to trees, power lines and bridges with roads faring just wet.

By Sat night and early Sun, models and GEFS members show very
good clustering regarding the track of an upper low northeast
from Chihuahua, across the El Paso vicinity, and to near Amarillo
by Sun night. Such a track strongly favors a rapid influx of
milder thicknesses which should easily overturn the earlier
modified cold airmass and change any freezing rain over to rain,
perhaps heavy at times complete with some thunder given the degree
of forcing/height falls and deep saturation. Dry slotting should
take control late Sunday with maybe some rain/snow mix in our NW
counties near the low and its distant deformation zone snowfall.




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