Area Forecast Discussion
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FXUS64 KLUB 241725
AFDLUB

Area Forecast Discussion
National Weather Service Lubbock TX
1225 PM CDT Sun Sep 24 2017

.AVIATION...
It`s going to stay moist with a modest deep southerly flow, and
through the afternoon expect the RADAR to remain dotted with
mostly very light showers. Have opted for now to play this short
term with mostly MVFR ceilings - though clouds still need to rise
a little both at KLBB and KPVW to get out of IFR range - and
indicate showers vicinity rather than outright showers. We may
have to adjust to more persistent showers if coverage increases,
but that is unclear at the moment. Later tonight, solutions seem
in pretty good agreement that rain chances will improve and
ceilings lower. When and how much remain less clear, so taking a
stab at around midnight on the Caprock and a few hours later for
the Rolling Plains, and also predominant MVFR conditions. Also, we
probably will end up seeing at least some periods of thunder,
more likely earlier in the event, but difficult to nail down this
far out. Opted here for TS vicinity. RMcQueen

&&

.PREV DISCUSSION... /issued 649 AM CDT Sun Sep 24 2017/

AVIATION...
Rain showers were now shifting east of KLBB and KPVW, but will
soon affect KCDS. IFR cigs have recently developed behind the rain
at KLBB and MVFR to IFR conditions will likely develop at KPVW
soon too. These sub-VFR ceilings should gradually give way to VFR
by early to mid-afternoon. KCDS should remain primarily VFR,
though it could dip briefly to MVFR as the rain moves through in
the next few hours. Outside of the low clouds, isolated to
scattered convection will be possible again this afternoon and
evening, though pinpointing the terminal impacts will be left to
future forecasts. More widespread precipitation along with sub-VFR
conditions will be possible toward Monday morning, though this
has not been addressed in the current iteration of the TAFs.

PREV DISCUSSION... /issued 609 AM CDT Sun Sep 24 2017/

UPDATE...
Quick update to account for trends with the north-south line of
showers (and some embedded thunder in the south) marching
eastward across the forecast area. Increased PoPs east and reduced
west. Latest CAM runs still suggest that any additional
development will be on the isolated side through the day.

PREV DISCUSSION... /issued 400 AM CDT Sun Sep 24 2017/

UPDATE...
Updated for the cancellation of the Flash Flood Watch.

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

DISCUSSION...
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 chances...at 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
surface.

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.

&&

.LUB WATCHES/WARNINGS/ADVISORIES...
None.
&&

$$

99/99/05



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