Area Forecast Discussion
Issued by NWS

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FXUS64 KLUB 290245

Area Forecast Discussion
National Weather Service Lubbock TX
945 PM CDT SUN AUG 28 2016

Minor update to clean up grids a bit in the wake of the afternoon
and evening convection. Convective outflows have helped knock many
spots back into the 60s and lower 70s making for a pleasantly cool
late August evening. The scattered convection earlier in the day
put down somewhat spotty but very heavy rain distributed fairly
evenly/randomly across the CWA. The heaviest activity through the
early evening hours was concentrated over eastern parts of Lubbock
County into northeast Lynn County where radar estimates of 1-3
inches were common. It now appears the near-term focus will be
across the far southern South Plains into the northern Permian
Basin, though new development along with existing activity edging
eastward out of New Mexico will also pose a heavy rain threat
across the southwest Texas Panhandle into the western South
Plains. The ongoing forecast had a good handle on this and only
minor tweaks to the PoP/wx grids were made ATTM. Given the slow
storm motion, high PWATS and efficient rain rates this late
evening activity will continue to bring a threat of locally
heavy/flooding rain. For that matter, a slow to evolve weather
pattern featuring plenty of moisture along with periodically
enhanced lift by an upper low spinning off to our west will mean
additional chances of strong thunderstorms featuring torrential
rains over the next few days.


.PREV DISCUSSION... /issued 642 PM CDT SUN AUG 28 2016/

A messy, low-confidence forecast for aviation concerns for the
next 6 hours or so, as scattered t-storm activity across the
region will be tied to numerous outflow boundaries due to
relatively weak winds aloft. Heavy rainfall reducing visibility
and strong wind gusts will be possible in and near the t-storms.
Storm activity is expected to gradually weaken tonight, but may
persist. Some guidance is suggesting the possibility of some low
ceilings early Monday morning. We will continue to assess and
amend as necessary.

PREV DISCUSSION... /issued 341 PM CDT SUN AUG 28 2016/

Atmosphere was destabilizing nicely once again this afternoon
complete with scattered storms, although a weak mesohigh and
associated lack of Cu was noted around Plainview in the wake of an
MCV lifting northeast of Amarillo. As increasingly moist easterly
upslope flow expands west onto the Caprock, convection should expand
in kind especially with assistance from outflow boundaries. Crisp
appearance to these storm tops thus far indicate lapse rates and
MLCAPEs are likely more robust than the RUC mesoanalysis indicates.
As such, will insert some severe pulse storm mention in the HWO.

Forcing for ascent should only improve overnight as an upper low
over NE Arizona glides east into NW New Mexico. This process will
position a SW-NE oriented jet streak across far eastern NM complete
with enhanced speed divergence in the RRQ of this jet - likely near
northern Lea County if models are correct. East of this divergence
lies an axis of weak but persistent diffluence over the South
Plains; however, this focus for ascent will be diminished as the
nose of a southeasterly LLJ advances into southeast NM and funnels
rich Theta-E with PWATs at or above 1.5 inches. As such, we continue
to favor the highest PoPs near the NM border overnight. Potential
for training cells in this pattern of improved meridional flow
warrants mention of heavy rain in the grids across our western zones.

Monday will see little change to this pattern as the upper low
stalls in NW New Mexico and keeps a deep meridional fetch of
subtropical moisture over the region. The brunt of lift should once
again favor our western zones near the RRQ of the aforementioned jet
streak, although we have boosted PoPs off the Caprock as adequate
diurnal heating and attainable CCLs will once again foster scattered
storms. Overall, models have not handled this pattern all that well
as forcing has been rather muted, but with improving mesoscale and
synoptic ascent in the next 24-48 hours we may be able to define a
Flood Watch at some point for portions of the Caprock. Reason
against this for now is that tonight`s heavy precip appears too
narrow in space and heavily dependent on cell training - a critical
factor which is not in good agreement among high res CAMs and
operational models.

Upper level low to our west will slowly fill and evolve to a
weakness between high across the SERN CONUS and a ridge from WY to
SRN California and beyond.  This weakness appears to hang around
through mid week before high pressure appears to more or less take
back control of the weather with a ridge extending will into Central
Canada.  Indications are that the ridge will be shunted southwest
into northern Mexico.  As a trough moves eastward off the Pacific
Coast next Saturday, we will probably see a return of southwesterly
flow aloft.

Thunderstorm activity should be ongoing Monday evening with all
indications pointing to favoring the west though, given the airmass,
certainly cannot rule out pop-up storms anywhere in the CWFA.  Rich
theta-e air will continue to be in place with PWATs averaging about
1.5 inches which is about double of the seasonal norms. With the
stagnant pattern and rich moisture, heavy rain potential certainly
exists and the next 24 hours will shed a great deal of light on
how things will evolve and interact. Will keep rain chances going
much of the week.  Deterministic guidance suggests that Friday
could be a bit more dry though, given the lack of significant
changes in the airmass, am reluctant to deviate very far from the
blend as it conveys the uncertainty of the rain threat as best as
can be expected.

Getting back to Monday night and Tuesday, do have some concerns for
flooding potential as there could be training and/or a couple of
days of repeat rainfall.  Flash flooding is awfully hard to get in
our western zones as the playa lake system accumulates and holds the
runoff effectively.  While confidence in accumulations and spatial
extent is lacking, we will continue to monitor the potential threat.
At this point, as was introduced in the HWO earlier today, it bears


.LUB Watches/Warnings/Advisories...


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