Area Forecast Discussion
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FXUS64 KLUB 240900

Area Forecast Discussion
National Weather Service Lubbock TX
400 AM CDT Sun Sep 24 2017

Updated for the cancellation of the Flash Flood Watch.


.PREV DISCUSSION... /issued 353 AM CDT Sun Sep 24 2017/

..Heavy rain and flooding concerns highlight the forecast for the
coming week...

Water vapor imagery and upper-air data this morning show a large
upper low centered over the Great Basin with a jetstreak moving
northward through NM and the southern Rockies. Right entrance
region of the jet and a strong LLJ were forcing a line of
convection moving across the western South Plains early this
morning. This activity should slowly weaken as it moves east -
farther away from the upper jet dynamics and with a weakening LLJ.
Some locally moderate rain is occurring within this line but so
far rainfall rates have generally remained under a 1/2 inch or so
per hour and have not caused any flooding issues. A Flood Watch
in effect for our western counties will be discontinued by around
4 am.

Most of the short-range guidance suggests that there will be a
lull in organized precipitation through the afternoon into the
evening due to neutral upper forcing and limited instability.
However, depending on how much clearing and heating we garner
across the forecast area, there is the possibility of isolated to
widely scattered shower and t-storm development, particulary in
the south and west. By tonight, the next upper shortwave and jet
streak will be approaching from the southwest and we should see
another round of precipitation develop, and possibly a MCS which
could bring the potential for heavy rain. The highest chance for
heavy rain will likely be found across the Caprock, in closer
proximity to the large-scale ascent.

A cold front enters the picture late Monday. Convergence and lift
along the frontal zone may temporarily enhance rain chances Monday
night into early Tuesday, before drier and much cooler air work in
behind the front, and with the frontal lift shifting to the south,
this should lower rain least temporarily.

Through all this, the initial upper low to our west opens up and
moves northeast, but the western trough reloads with another low
closing off over the desert southwest. This will maintain
perturbed southwest flow aloft over the cool ridging at the

The forecast gets more complicated Wed through Fri as the breadth
of rain chances and the potential for heavy rain will depend on
whether or not we get a significant contribution of moisture from
Tropical Storm Pilar, currently hugging the west coast of Mexico.
The ECMWF in particular directs moisture caught up with this
system across northwest Mexico into southwest and then west-
central Texas, producing very heavy rain concentrated in the
Rolling Plains. The GFS and GEFS show some different possibilities
that would result in lower moisture and precip for our area - or
could shift the heavier precip swath farther to the west or east
- so there is still quite a bit to hash out in this period. We do
have high confidence though in very cool temperatures (highs in
the 60s and 70s) and a general increase in rain chances. Finally,
the latest model runs linger upper troughing across the region
through next weekend. Deep moisture and lift may be lacking by
that time, but temperatures are likely to remain on the cool side.




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