Area Forecast Discussion
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FXUS64 KLUB 260918

Area Forecast Discussion
National Weather Service Lubbock TX
418 AM CDT FRI AUG 26 2016

Model guidance is fairly mixed today regarding convective chances
although will overall remain lower than yesterday. A very weak short
wave trough will pass overhead later this morning following the one
from yesterday evening. However, subtle subsidence will be filling
in behind the departing upper level jet streak. Furthermore, drying
will be advecting in at mid and upper levels limiting the amount of
moisture available. Mixed layer instability will be notably less
with values on the order of less than 500 J/kg this afternoon.
Overall, less moisture and less lift for the atmosphere to work with
will be more limiting on the convective chances today. Best chances
may ultimately be limited to old surface boundaries from convection
yesterday evening and early this morning.

Thunder and shower chances should be down notably Saturday following
ejection of the weak high level trough to the northeast with
weaker southwest flow aloft and building heights. Deep moisture
also severely depleted by that point. We are retaining slight
chance for late in the day only in our northwest where heights
will be least in advance of the next upper trough system starting
to take shape over the lower Colorado far to the west.
Temperatures should warm another notch or two. Also occurring
Saturday that will have influence on our area is a gradual west
and southwest track taken by a weak mid level low along the Texas
coast. Latest runs seem slightly deeper with this low, though the
deeper yet WRF/NAM is an unfavored outlier.

This Texas coastal low is expected to meander down the coast
Sunday and Monday, then track more or less west-northwest near the
Rio Grande valley eventually losing definition by mid-week or so.
But early on, in the Sunday-Monday time-frame, it may be able to
send out bands of mid level moisture towards our area. This is
what solutions seem to be banking on for improved shower chances
late weekend into early next week. Heights aloft are expected to
fall slightly again by then even though a westward extension of
the Bermuda ridge should remain overhead. This also should mostly
block an eastward path of that previously mentioned Arizona weak
upper trough with some portions perhaps ejecting northward into
the central Rockies and high plains, while other portions may
drop south-southwest towards Baja and yet further out of the
picture. We also are not seeing any notable nearby upper jet
dynamics except for across the Panhandle and our north-northwest
zones late Monday and early Tuesday as a 300 millibar weak trough
ejects into the central Rockies. This may be our real peak period
for best shower/thunder expectations and also favoring our north
to northwest areas.

So, with all of that diagnostics, how to present shower chances in
the days ahead? Superblend seems overblown banking on showers
Sunday spreading into eastern zones directly beneath upper ridge
axis, perhaps over-weighting the WRF/NAM. We have trended down
though like yesterdays day shift, will retain a low chance mention
the entire area until deterministic solutions pick up better on
true signals. We also have retained low chance Sunday night into
Monday night favoring our west-northwest areas where the jet
dynamics may factor-in, and near the eastern edge of the
monsoonal plume at that time. For Tuesday, should a weak upper
trough be ejecting to the north, it may support a low mention all
areas again. Temperatures may taper slightly Sunday into early
next week with less upper heights and improved moisture.

Beyond that, upper heights are expected to rebuild with dry
subsidence dominating. Gradual warming perhaps back into the
lower 90s even on the Caprock may occur by the middle or end of
next week. RMcQueen


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