Area Forecast Discussion
Issued by NWS San Angelo, TX

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000
FXUS64 KSJT 200000
AFDSJT

Area Forecast Discussion
National Weather Service San Angelo TX
600 PM CST Mon Feb 19 2018

.AVIATION...
/00Z TAFS/

Main aviation issue for this TAF period will be the increasing
chance of showers and/or isolated thunderstorms into the overnight
hours. As an upper level disturbance approaches the region from
the west, showers and/or thunderstorm coverage will increase from
the southwest/west later this evening and gradually move to the
east through the overnight hours. Although thunder will be
possible across all of west central Texas, the best chances will
be across eastern portions of the area. Therefore, have included
thunder in the TAFS at KJCT, KSOA, and KBBD. However, this does
not mean thunder cannot happen at KSJT AND KABI, it is just less
likely. This convective activity is expected to be east of all TAF
sites by 10-12Z. There could be some convective redevelopment
tomorrow afternoon across eastern portions of the region, but
will not put any mention in the TAFs for now. Sub-VFR cigs/vsbys
will be possible in any convection that moves over a TAF site. In
addition, there is a chance for some low clouds to develop during
the early morning hours, mainly across the southern portion of
the forecast area. However, have left any mention of this out of
the TAFs for now given the uncertainty. Otherwise, winds will
remain elevated overnight due to a strong low level jet.

&&

.PREV DISCUSSION... /issued 245 PM CST Mon Feb 19 2018/

SHORT TERM...
(Tonight and Tuesday)

A spring-like airmass is over our area this afternoon with
temperatures well above normal in the 70s and dewpoints in the mid
50s to lower 60s, with breezy south winds.

A large upper trough over the western third of the CONUS will shift
east across the northern Rockies and into the central and southern
Rockies tonight into Tuesday. In the southwest flow aloft ahead of
this trough, an embedded shortwave will move northeast into our area
tonight.  By late this afternoon and early evening, a few
thunderstorms may develop along a dryline which is mixing east
across parts of West Texas. Have a low possibility for a few of
these storms to move northeast, off the dryline and into our far
western counties. The main focus for convection in our area,
however, will be with the approach and arrival of the aforementioned
shortwave. Showers and thunderstorms are expected to develop,
increase in coverage and move northeast across our area during the
night. A few strong to severe storms will be possible, with large
hail and damaging winds the main threats. Some of the storms may
also contain frequent lightning and locally heavy rain. PoPs
tonight across our area range from 40-50 percent in the far
western and northwestern parts of our area, to 80-85 percent
across the area east of a Brownwood to Junction line. Temperatures
will be rather mild tonight with lows mostly in the upper 50s to
lower 60s across our area.

Showers and thunderstorms will move east of our counties on Tuesday
morning, with low-level flow veering to the southwest and drier air
advecting into our area. Some redevelopment of convection will be
possible by mid-to-late afternoon across our far eastern and
southeastern counties, as a dryline mixes east into that area. A
decrease in cloud cover is expected from the west during the day.
Temperatures are expected to be warm again Tuesday with highs
in the mid to upper 70s.

LONG TERM...
(Tuesday Night through Sunday)

Main thoughts in the long term have not changed, with a long wave
trough sitting across the western US creating southwest flow aloft
across Texas. A series of shortwaves will rotate around the
trough and bring showers and storms to West Central Texas, but
timing these shortwaves continues to be a problem. After
tonight`s/Tuesdays shortwave, another arrives on Wednesday,
another Thursday, and the last one on Friday. Have kept good rain
chances across much of the area through the end of the week, with
perhaps some drying for the weekend.

Rain totals will be significantly better across the southeast
portions of the area, perhaps more than 2 inches across Mason and
San Saba Counties. Lesser amounts, but still better than what we
have seen so far this year, across the rest of the area.

Strong cold front arrives Tuesday Night as well, bringing much
colder conditions for mid week. Low temperatures may flirt with
freezing Wednesday Night in a few locations across the western and
northwestern Big Country, perhaps allowing for a brief switchover
to freezing drizzle or light freezing rain. At this point, expect
ground temperatures are warm enough to prevent any type of travel
difficulties if it does occur.

&&

.PRELIMINARY POINT TEMPS/POPS...
Abilene  61  77  35  41 /  50  30  30  40
San Angelo  59  78  39  47 /  60  10  40  50
Junction  62  76  51  57 /  80  40  60  80
Brownwood  62  75  39  43 /  80  60  50  70
Sweetwater  57  75  32  40 /  40   5  20  40
Ozona       58  78  46  57 /  60   5  50  60

&&

.SJT WATCHES/WARNINGS/ADVISORIES...
None.
&&

$$



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