Area Forecast Discussion
Issued by NWS Austin/San Antonio, TX

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FXUS64 KEWX 271743 AAA
AFDEWX

Area Forecast Discussion...UPDATED
National Weather Service Austin/San Antonio TX
1243 PM CDT Thu Apr 27 2017

.AVIATION...
/18Z TAFS/
Breezy and gusty conditions are in place under a southerly wind flow
through this evening. VFR flight conditions are expected to remain
across area airports through late this evening. Wind speeds are
expected to decrease a bit late this evening into Saturday morning
while low clouds develop during the same period. Cigs are expected
to lower to MVFR along the I-35 sites around midnight tonight as
humidity increases. IFR cigs are expected to develop few hours after
midnight along the I-35 terminals as moisture continues to increase
and push to the north from the Gulf of Mexico. There is a slight
chance for light drizzle across the coastal plains and parts of the
escarpment as the surface airmass nears saturation levels. VFR
conditions are expected to return to the I-35 sites by early Friday
afternoon.

KDRT will remain VFR through late tonight with MVFR conditions
expected for several hours around sunrise times. VFR conditions are
expected to return after by 15Z Saturday.


&&

.PREV DISCUSSION... /ISSUED 616 AM CDT Thu Apr 27 2017/

AVIATION DISCUSSION...FOR 12Z TAF PERIOD...
Only a few clouds seen across the region this morning keeping all
terminals at VFR. Only impacts during the day will be increasing
winds by around noon to around 15 kts with gust potential up to 25
kts. Wind gust potential should drop by around dusk but winds are
expected to stay at around 10 kts through the evening before becoming
light before dawn tomorrow morning.

MVFR CIGs are expected to return around midnight due to a return of
low level moisture at KSAT/KSSF and a couple hours later at
KAUS/KDRT.

PREV DISCUSSION... /ISSUED 349 AM CDT Thu Apr 27 2017/

SHORT TERM (Today through Friday)...

The main weather highlight to close out the week will be the 10-12F
degrees above normal high temperatures expected Friday that will lead
to heat indices in the upper 90s to near 100F during peak afternoon
heating. While record highs appear unlikely to be broken, some will
come close (AUS/DRT). Dry weather is expected through at least
Friday night.

A shortwave trough is shifting east and away of the region across
the mid-Mississippi Valley this morning per water vapor satellite.
This system helped usher in much drier air yesterday and has set the
stage for the cooler than normal temperatures ongoing this morning.
Lows will fall into the mid to upper 40s for the Hill Country with
low to mid 50s elsewhere. With only high passing clouds, the dry
airmass, and warm south winds expected to increase this afternoon,
temperatures will rebound to near normal highs in the mid 80s most
locations with a few low 90s in the Rio Grande Plains.

Overnight into Friday, surface low pressure will strengthen across
north and west Texas. Rapid moisture advection will take place with
PWATs nearly doubling from noon today to early afternoon Friday.
Dewpoints will reach into the low 60s to near 70 in the coastal
plains by Friday afternoon. Luckily, a strong capping inversion will
be in place across the entire region despite the high temperatures
and moisture resulting in unrealized instability. Believe there will
be some storms over the higher Mexican terrain but it should stay
confined west of the Rio Grande. The combination of the high heat and
humidity will result in heat indices reaching into the upper 90s to
near 100F Friday afternoon. Please stay hydrated and take frequent
breaks if planning prolonged outdoor activities.

LONG TERM (Saturday through Wednesday)...

Main hazard focus will be the increasing strong and severe
thunderstorm risk Saturday afternoon through early Sunday morning
generally along and east of a Burnet to San Antonio to Cuero line.
Main concerns will be straight-line damaging winds and large hail as
a cold front moves through the area. Cooler and dry weather is
expected Sunday through the beginning of the week with slight rain
chances returning by mid-week as another front approaches the area.

A strong and deepening shortwave trough is forecast to develop per
many global and regional models and pivot across north-central Texas
Saturday afternoon into Sunday morning. A dryline will shift west to
east through the day and act to sharpen the dewpoint gradient south
of a developing cold front in north Texas. By Saturday afternoon, a
well established warm sector characterized by >3500 J/Kg MLCAPE, near
40 kt 0-6km shear, ~30C vertical totals, and weak convective
inhibition will provide a favorable environment for strong/severe
storms. At this time, there appears to be two windows for strong and
severe storms with greater confidence placed on the second window.
The first window will be mid to late afternoon across the warm
sector but limited synoptic forcing and just enough capping could
preclude storm development during this timeframe. However, if a storm
does develop during this window, it will go severe quickly given
very steep H7-H5 lapse rates near 8C/km - favoring hail and
downburst winds. Greater confidence in deep, moist convection will be
after 7pm Saturday as the dryline merges with the southward
progressing front and storms form along this boundary. With deeper
upward forcing and height falls Saturday evening, feel this is the
most likely time of strong/sever storms to develop into a line along
the front. Favorable thermodynamics will remain in place to support
the hail and wind risk. Low-level 0-1km and 0-3km shear will be low
and does not align well with the most unstable area. Therefore, the
potential for tornadoes associated with this activity appears very
low at this time. However, the tornado threat appears to increase
into Sunday morning as the line shifts into east Texas and the
coastal plains will have to be closely watched for this evolving
risk late Saturday night/early Sunday morning. While pockets of
heavy rain will be likely, the progressive nature of the front will
sweep the entire system through quickly Sunday morning. Overall
rainfall totals will be 0.5 to 1.5 with some localized 2 inch spots
east of I-35 possible if the earlier afternoon round develops.

All storm activity will push east by Sunday morning as a cool and
dry airmass shifts in. Temperatures will be well below normal Sunday
afternoon - only reaching the low 70s north to low 80s south. Fire
weather concerns may increase for western locations where wind and
low humidity combine for elevated fire weather concerns.

Monday and Tuesday will be tranquil with below normal temperatures to
start with a warming trend expected into mid-week. Both EC/GFS agree
on another cool front shifting into the region near mid-week with
low-end rain chances.

&&

.PRELIMINARY POINT TEMPS/POPS...
Austin Camp Mabry              69  93  75  88  58 /  10  10  20  40  70
Austin Bergstrom Intl Airport  69  92  76  87  58 /  10  10  20  40  80
New Braunfels Muni Airport     69  93  75  88  58 /  10  10  20  30  70
Burnet Muni Airport            67  91  72  84  52 /  10  10  20  40  60
Del Rio Intl Airport           68  97  71  93  55 /   0  -   10  10  10
Georgetown Muni Airport        68  91  74  86  56 /  10  10  20  40  70
Hondo Muni Airport             68  95  73  91  57 /  -   -   10  20  40
San Marcos Muni Airport        69  92  76  88  58 /  10  10  20  30  80
La Grange - Fayette Regional   69  93  77  86  60 /  10  10  10  40  80
San Antonio Intl Airport       70  93  75  90  59 /  10  10  20  20  70
Stinson Muni Airport           70  95  75  89  60 /  10  10  10  20  60

&&

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

$$

Mesoscale/Aviation...17
Synoptic/Grids...Runyen
Public Service/Data Collection...33


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