Area Forecast Discussion
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FXUS64 KLUB 120539

Area Forecast Discussion
National Weather Service Lubbock TX
1239 AM CDT Sat Aug 12 2017

Isolated to scattered thunderstorms continued to affect KPVW ahead
of a larger batch of storms in eastern New Mexico. These initial
thunderstorms may affect KCDS early this morning as well. Better
chances will exist as the more widespread activity moves into the
terminals by mid morning. However, confidence in timing is low but
this activity will likely bring MVFR CIGS which has been placed in
the TAF.


.PREV DISCUSSION... /issued 1016 PM CDT Fri Aug 11 2017/

A batch of scattered showers and t-storms have developed along a
confluent zone across the central and eastern South Plains in
conjunction with a larger-scale outflow boundary moving southwest
from the Rolling Plains onto the Caprock. This activity will
continue to move northeast over the next few hours, although we
can`t rule out some additional isolated development along the
outflow boundary.

Of greater concern is the t-storm activity in New Mexico
associated with a mid-level vortmax. The latest satellite and
radar imagery shows one MCS taking shape across northeast NM
leaning into the western Panhandles, with indications of another
developing in the vicinity of the Sacramento Mtns in south-
central NM. The latest high-res guidance including the HRRR and
TTU-WRF along with the 00 UTC NAM suggest that this activity will
progress across much of our forecast area in the early morning
hours Saturday - although there is quite a bit of difference in
the details. We have the highest confidence of storms affecting
our western and northern counties, but the picture becomes more
murky to the south and east as the LLJ will be weakening by the
time storms approach that area - likely leading to their weakening
as well. Some pockets of heavy rainfall are certainly possible
across the southwest Texas Panhandle and western South Plains.
PoPs have this scenario well represented and we`ve made only a few
minor adjustments.

PREV DISCUSSION... /issued 649 PM CDT Fri Aug 11 2017/

Isolated convection has recently been attempting to develop
between KPVW and KCDS along a residual boundary, but this activity
will likely fade out later this evening without impacting either
terminal. Of greater concern is more widespread convection
currently over central New Mexico. There is a good signal that a
large batch of showers and thunderstorms will move eastward out of
New Mexico late tonight and across parts or much of the South
Plains region Saturday morning as it gradually decays. Given this
we have decided to include PROB30 remarks at all three terminals
valid Saturday morning at KLBB and KPVW (for thunder) and at KCDS
(for showers) from late morning into the early afternoon.
Increasing moisture may also support the development of sub-VFR
ceilings at times Saturday morning, while light winds prevail
outside of any thunderstorm influences.

PREV DISCUSSION... /issued 402 PM CDT Fri Aug 11 2017/

The biggest change with this forecast iteration was to boost PoPs
considerably late tonight through Sat morning over much of the
Caprock. Rationale for this is tied to a well defined mid-level
vorticity maximum exiting southeast AZ. Water vapor imagery shows an
axis of deeper ascent ahead of this impulse - the leading edge of
which should reach our western zones after midnight. Until then, the
main focus for rain chances appears to favor the southern Panhandle
near a stationary front partially reinforced from overnight storms.
Visible satellite shows agitated Cu near Tulia just after 3 PM which
could easily manifest into some storms with max heating/convective
temps just around the corner. Continued light upslope winds should
also aid in low level ascent for at least spotty storms despite
prevalent upper ridging.

As the aforementioned impulse exits NM on Saturday, the upper ridge
will completely erode as 20-40 meters worth of mid-level height
falls unfold. Such forcing this time of year is sizable enough to
sustain the early A.M. precip through most/all of the morning.
Pending the behavior of the lingering frontal boundary, models favor
the brunt of precip to affect our N-NW zones. PWATs of 1.5 inches on
the Caprock would easily breed some heavy rainfall at times, but
sufficient W-SW flow aloft should keep precip progressive enough to
stave off a larger flooding threat. This more definitive round of
morning precip and thicker clouds could deal a blow to PoP chances
later in the day, particularly behind the departing impulse. Opted
to trim PoPs a bit lower in the afternoon compared to the morning to
reflect the departing wave and generally more stable conditions.
High temps were also scaled a bit lower for Saturday`s thicker
clouds and rain chances.

On Sunday, steady height rises initially are progged to be replaced
by another respectable trough in westerly flow. Favorable SE low
level flow ahead of this wave will maintain good PWATs of 1.5 to 2
inches from W-E across the CWA, so once forcing arrives later in
the day (along with a stalling cold front) we should see our next
good opportunity for rain and perhaps even some flooding.
Thereafter, westerly winds aloft will back more SW as mean
troughing occupies the western CONUS. Such a pattern looks
favorable for directing a monsoonal plume over West Texas, but
subtle day-to-day variations could easily hinder the otherwise
generous Superblend PoPs through late week. Opted to lower these
Superblend values a bit for obvious uncertainty, but max and min
temps look to fall close to climo most days.




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