Area Forecast Discussion
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FXUS64 KLUB 230842

Area Forecast Discussion
National Weather Service Lubbock TX
342 AM CDT FRI SEP 23 2016

Amended TAFS for speed shear of 35kts at 500ft out of the south-
southeast for KLBB and KPVW terminals.


.PREV DISCUSSION... /issued 1133 PM CDT THU SEP 22 2016/

VFR is expected through the TAF period. Any thunderstorms are
expected to remain east of the TAF sites through tomorrow

PREV DISCUSSION... /issued 333 PM CDT THU SEP 22 2016/

A healthy cumulus field has developed across the eastern half of the
area this afternoon after a weak surge of moisture in the h850 to
h700 millibar layer and beneath the weakened trailing edge of the
remnant upper level shear axis still overhead. It seems unlikely to
swell further, with a weak cap in place and not impressive dynamics,
though temperatures climbing into the lower 90s could turn one or
two pin-point showers loose over the next couple hours.

Otherwise another dry and seasonably mild night will follow, again
with enough dry air still in place at least on the Caprock for
temperatures to bottom out in the 50s in some locations, below
guidance again.

Friday will see a northward surge of mid and upper level moisture
from an inverted trough over northern Mexico and a re-tightening of
the upper shear axis. Low level moisture will improve further
especially after daybreak with deepening surface low pressure along
the lee-side of the Front Range as the upper low approaches through
the eastern Great Basin into the western Rockies. Solutions are
fairly consistent with an area of thunder developing late in the
afternoon from the Concho Valley into the Big Country, barely east
of our area. But solutions remain more mixed about high-based
activity developing northward from the Trans Pecos towards the
southwestern South Plains late in the day as well. Our forecast will
remain dry through the afternoon, but the surface trough along our
western border very well could become a thunderstorm activation zone
by early evening. RMcQueen

The extended forecast remains focused around rain/storm chances this
weekend along with a decent late September FROPA on Sunday. The
western upper low discussed in the short term section will be
lifting through the northern High Plains on Saturday. The bulk of
the lift with this initial low will just graze the area but it,
combined with the tail end of a Pacific front/surface trough and
increasing tropospheric moisture will support a chance of
thunderstorms expanding from west to east across the South Plains
Friday night. Strong jet energy diving southward behind the lead low
will then carve out a significant trough or closed low somewhere
near/over New Mexico on Sunday. Lift ahead of this sharping wave,
convergence along the surface trough and daytime destabilization
should fuel more widespread thunderstorm development during the
afternoon and evening hours, with spots off the Caprock most
favored. This is where PWAT values will increase in excess of 1.5
inches, and coupled with the potential for training cells from
southwest to northeast, this could support a localized heavy rain
threat. Additionally, improved instability and deep layer shear
could even lead to a few strong to briefly severe cells.

The northern stream portion of the system will then propel another
stronger cold front southward with the FROPA anticipated through the
CWA during the first half of Sunday. Gusty northerly winds may
briefly threaten low-end advisory levels across the northwest zones
as they advect in cooler and drier air. Rain chances may briefly
increase as the frontal forcing moves through, though the low-level
drying may tend to thwart rain efficiency with time. However, the
ECMWF and DGEX in particular develop a strong closed low close
enough (sinking from southern NM into Mexico) to keep mid-upper
level moisture streaming up and over the frontal zone with light QPF
in parts of the CWA Monday and Tuesday. We are not totally sold on
this, but have accepted the minimal rain mention output by the
blended guidance across the southern and eastern zones through early
next week. Regardless, temperatures will tumble from highs mostly in
the 80s on Saturday to only 60s and lower 70s Sunday and Monday. A
slow warming trend is forecast thereafter, though this will depend
on the eventual evolution of whatever upper low remains and where it
tracks (which is very uncertain ATTM).


.LUB Watches/Warnings/Advisories...


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