Tornado and Damaging Wind in Texas, July 4, 2018

Area Forecast Discussion
National Weather Service Austin/San Antonio TX
1232 PM CDT Wed Jul 4 2018

.AVIATION...
Showers and storms have formed north of the morning convection over
Houston and this is the activity we will watch closely this
afternoon for impacts for the TAF sites. Think these should be
nearing KAUS around 19-20z and will mention VCTS with a TEMPO group
for -TSRA. The activity should arrive to the San Antonio sites about
1-2 hours later than AUS. Some of these storms may produce gusty
winds and will mention VRB15G25KT in the TEMPO groups for now but
these could be increased slightly if conditions warrant. Activity
should wane 3-4 hours after the onset with just a VCSH needed for the
rest of the evening for any lingering activity. For DRT, will just
mention VCSH this evening as activity there is not expected to be as
widespread.

Another round of MVFR ceilings is expected overnight with VFR
returning around 17z. Left over moisture tomorrow will allow for some
scattered activity in the afternoon. Will mention VCSH for now but
some isolated thunderstorms will be possible as well.

&&

.PREV DISCUSSION... /ISSUED 1029 AM CDT Wed Jul 4 2018/

UPDATE...
Widespread showers ongoing across Southeast Texas closer to the well
advertised compact mid and upper level low. A weak surface low may
have also formed over Southeast Texas with surface trough extending
to the northwest. The whole system will continue west Today into the
CWA.

CAMs are in relatively good agreement with the rain shield across
Southeast Texas moving into the far eastern zones of Fayette and
Lavaca counties by early afternoon. CAM members are also in good
agreement in showing new convective development between 18Z-21Z
farther northwest through portions of Central Texas and the eastern
Hill Country, including the Austin metro area. This is likely near
where the aforementioned surface trough moves west with the system,
and could also be aided by differential heading on the edge of the
expanding cloud shield into the region. Between 21Z-03Z the storms
propagate southwest into the remainder of the Hill Country, San
Antonio metro, Brush Country, and Winter Garden regions. Mesoscale
outflow boundaries will also assist with convective development and
propagation, but very difficult to pinpoint locations on where these
boundaries develop.

Should the coverage become widespread, like a few CAM members are
showing, then we could see some stabilization take place back across
the eastern CWA and Central Texas/Austin and a reduction in
precipitation after dark for fireworks activities. Lower confidence
in the precipitation ending into the mid evening hours after dark
the farther southwest you go.

Overall the CWA can manage the rainfall without widespread and higher
impact flooding. However, precipitable water values look to increase
to 2.3-2.5" through the afternoon and evening hours from east to
west and combined with mesoscale influence there could be pockets of
heavier rainfall rates that result in localized and brief flooding
issues. This could be realized in urban areas should the pockets of
higher rainfall rates setup there. Also, there could be a threat for
some stronger wind gusts, especially on western and southwestern edge
of deeper and expanding convective development, along and west of
I-35, where warm temperatures produce inverted-V soundings before
becoming more saturated. Finally, with many people outdoors today
lightning safety messaging is urged. While currently there is not
much lightning in the activity across Southeast Texas, we do expect
the activity to increase over South Central Texas this afternoon and
evening.

PREV DISCUSSION... /ISSUED 703 AM CDT Wed Jul 4 2018/

UPDATE...
Please see the 12Z aviation forecast discussion below.

AVIATION...
Low clouds and MVFR cigs continue to fill in along the I-35 corridor.
We expect MVFR conditions to continue through the mid-morning hours.
The focus will then shift to convection chances for the afternoon
hours where we will continue to mention TEMPO groups for TSRA along
I-35 in the 18-23Z time period. Depending on where the strongest
mid-level circulation winds up, we can't rule out continued
thunderstorm activity during the evening and overnight hours. As of
now, this looks to occur to the south of our TAF sites, but this
will need to be monitored. Farther west at DRT, we will continue VFR
conditions through the period. We did opt to mention VCSH after 00Z
as some weakening showers could approach the terminal from the east.

PREV DISCUSSION... /ISSUED 426 AM CDT Wed Jul 4 2018/

SHORT TERM (Today through Thursday)...
A welcome break from the oppressive hot and dry pattern begins today.
A small Tutt low has crossed the Sabine into East TX and will send
a surge of clouds and increased rain chances into our far eastern
counties by around 13Z and the I-35 Corridor by midday. Unlike the
previous late June low pressure system which had more mesoscale
surface influences on convection, this system is set for a better
track for more evenly distributed precipitation and offers more
promise for much needed convective rains to develop farther inland. A
solid core of pwat values approaching 2.4 inches moves with the low
center which tracks loosely along Highway 90 but more in a WSW
direction. Generous afternoon qpf amounts are forecast to produce 1+
inch rains generally east of a Kerrville to Jourdanton line although
we're concerned this might be a bit too optimistic for a heavily
populated area that really needs some rain.

Am also concerned the mesoscale model influences on blended
guidances are too generous with rainfall amounts after 00Z Thursday,
and have a feeling that excellent coverage of rain in the late
afternoon will lead to a slightly more stable evening forecast and
provide minimal interruption to after dark fireworks activities over
most areas. QPF forecasts in period 2 are noticeably lower than the
1st, and thus the likely category PoP is perhaps a misleading to
those planning their holiday activities. Ultimately remnant showers
and isolated storms in the early evening and some resurgent shower
activity in the early morning hours precludes the need to lower
tonight's PoPs to chance category for now. As mesoscale interactions
take better shape, perhaps the afternoon forecast can better utilize
the finer-res model output to bring more clarity to timing and
amounts.

By 12Z Thursday, the still fairly well defined mid level circulation
will have moved to near Eagle Pass with still a scattered round of
convection expected over the I-35 corridor and more widespread
activity along the Rio Grande. Below normal max temps will then expand
into western counties.

LONG TERM (Thursday Night through Tuesday)...
Expect mostly isolated activity Thursday night as the progressively
westward shift of the Tutt low impacts shifts into Mexico and pwat
values lower back to below 2 inches for the most part. Enough
residual moisture over the Coastal Prairies will offer the better
chances for rain and this continues into Friday when another surge of
enhanced pwat values arrives from East TX from a prevailing NEly mid
level flow pattern. A few pockets of 1+ inch rainfall amounts are
expected with daytime convection with a most amounts being much
lower. Again blended guidances look a little too robust on nighttime
chances, as the periods Thursday night through Saturday should be
dominated by diurnal convection. Sunday looks similar as well
although there are hints of an inverted trough over S TX that is most
emphasized by the Canadian model. Poor model agreement on the ridge
influence over the Srn US develops by Monday and will trend PoPs
closer to climatology which favors low chances for rain even in the
presence of a fair amount of available moisture.

What does seem probable in the extended is that the low level airmass
and vegetation should be effectively modified by multiple rain
opportunities and about 5 days or possibly more where most afternoon
temperatures fail to climb higher than early July normals.

&&

.PRELIMINARY POINT TEMPS/POPS...
Austin Camp Mabry              93  73  93  75  94 /  80  60  30  20  40
Austin Bergstrom Intl Airport  92  72  92  74  93 /  80  60  30  20  50
New Braunfels Muni Airport     94  73  92  73  92 /  80  60  30  20  50
Burnet Muni Airport            94  70  91  73  92 /  70  50  20  20  40
Del Rio Intl Airport          103  77  91  75  96 /  -   50  60  20  30
Georgetown Muni Airport        92  71  93  73  93 /  80  50  20  20  40
Hondo Muni Airport             99  73  91  73  94 /  50  80  40  20  50
San Marcos Muni Airport        93  71  92  73  92 /  80  60  30  20  50
La Grange - Fayette Regional   86  72  91  75  91 /  80  40  40  30  60
San Antonio Intl Airport       95  73  90  75  93 /  80  80  40  20  50
Stinson Muni Airport           96  74  92  75  93 /  80  80  40  20  50

&&

.EWX WATCHES/WARNINGS/ADVISORIES...
None.
&&

Mesoscale/Aviation...Hampshire
Synoptic/Grids...Runyen
Public Service/Data Collection...BMW

Hazardous Weather Outlook...UPDATED
National Weather Service Austin/San Antonio TX
1056 AM CDT Wed Jul 4 2018

TXZ171>173-183>194-202>209-217>225-228-051600-
Llano-Burnet-Williamson-Val Verde-Edwards-Real-Kerr-Bandera-
Gillespie-Kendall-Blanco-Hays-Travis-Bastrop-Lee-Kinney-Uvalde-
Medina-Bexar-Comal-Guadalupe-Caldwell-Fayette-Maverick-Zavala-
Frio-Atascosa-Wilson-Karnes-Gonzales-De Witt-Lavaca-Dimmit-
1056 AM CDT Wed Jul 4 2018

This Hazardous Weather Outlook is for South-Central Texas..

.DAY ONE...Today And Tonight.

Scattered showers and thunderstorms are expected today and
tonight across south central Texas. Severe thunderstorms are not
expected at this time. However, occasional lightning strikes,
gusty winds and brief heavy rain will be possible with the
thunderstorms.

Those with outdoor activities today and tonight are urged to
closely monitor radar. Postpone activities and move indoors if
lightning is in the area or you can hear thunder. Lightning can
strike as far as 10 miles away from where it is raining.

.DAYS TWO THROUGH SEVEN...Thursday through Tuesday.

No hazardous weather is expected at this time.

.SPOTTER INFORMATION STATEMENT...

Spotter activation is not anticipated.