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

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477
FXUS64 KEWX 231144
AFDEWX

Area Forecast Discussion
National Weather Service Austin/San Antonio TX
644 AM CDT Sun Jul 23 2017

.AVIATION... /12Z TAFS/
Isolated convection appears more likely to influence parts of Central
TX and the Hill Country as 850-500 mb flows bring increased moisture
sourced from North TX. A few mid level clouds and isolated elevated
showers are already forming from near San Saba to Fort Worth. For now
will only expect to see activity to impact the AUS TAF, and will
defer to a general vcnty SHRA for now. It should be known, that with
the strong heating and mid level instability, a few strong downdrafts
will be possible. Will defer to later updates to clarify best timing
as the window of chances could be as wide as 21Z to 03Z. Expect an
increase in cloud debris from today`s convection and continued
difficulty in maintaining an early morning low cloud deck. Another
good mixing day today should allow the mostly 5-10 knot winds to
occasionally gust to 20 knots.

&&

.PREV DISCUSSION... /ISSUED 309 AM CDT Sun Jul 23 2017/

SHORT TERM (Today through Monday)...

Main weather impact highlight remains on the 104-108F heat index
values expected today and Monday. In addition, a few isolated to
scattered showers are expected today across the Hill Country and
portions of the Southern Edwards Plateau.

A wind shear axis associated with a mid- and upper-level trough
across the northern Texas Coast is evident on water vapor imagery.
Northeasterly to easterly flow is occurring over the region due to
the trough`s relative position with slight divergence implied due to
weak cyclonic vorticity advection this afternoon. Coupled with peak
heating and left-over boundaries from convection over the Edwards
Plateau this morning, this should support isolated to scattered
thundershowers over the Hill Country and southern Edwards Plateau.
While isolated, there could be a few showers near the I-35 corridor
north of Comal County.

Many areas will not receive rain and thus have ample sun and high
temperatures. Combined with the humidity levels, expect another day
of 104-108F heat index values across much of the region, minus the
Hill Country. This remains on the cusp to just below heat advisory
criteria but will continue the special weather statement
highlighting the danger. The hazardous weather outlook also reflects
the high heat indices.

By Monday, the upper-level low washes out across the northern Gulf
along with its influence of promoting greater lift across the
region. Expect there to be little to no rain Monday with another day
of above normal hot temperatures. Will need to monitor closely if a
surgically placed heat advisory is warranted for select areas.

LONG TERM (Monday Night through Saturday)...

Mid- to long-range will be persistently hot through at least Friday.
Heat Advisories may become necessary late in the week as
temperatures look to reach the low to perhaps the mid 100s across a
good portion of the region. Heat index values could reach upwards of
110F in a few Coastal Plain locations.

Both the ECMWF, GFS and long-range ensemble models indicate both the
subtropical low-level ridge over the lower Mississippi Valley
strengthen in conjunction with a 595DM H5 ridge over the four corner
region. This will help suppress most shower activity minus the
lucky few that see a sea-breeze induced shower across the Coastal
Plains. Temperatures will rise into the upper 90s and low to even mid
100s from mid- to late-week.

Models indicate a back-door front approaching the area on Saturday
that could provide a slightly better chance for rain as it is
suggested to move through the area. While both the ECMWF and GFS
indicate this boundary near the region, little to no "cooler" air is
associated with the new airmass and hot temperatures appear to remain
a high likelihood through at least the weekend with limited chances
of any effective rainfall.

&&

.PRELIMINARY POINT TEMPS/POPS...
Austin Camp Mabry             102  78 101  77 100 /  30  10  10  -   10
Austin Bergstrom Intl Airport 101  77 100  76 100 /  30  10  10  -   10
New Braunfels Muni Airport    101  76 100  76  99 /  20  10  10  -   10
Burnet Muni Airport            99  74  99  74  97 /  30  10  10  -   10
Del Rio Intl Airport          102  77 100  77  99 /  20  10  10  -   10
Georgetown Muni Airport       100  76 100  76  99 /  30  10  10  -   10
Hondo Muni Airport            103  75 102  76 100 /  10  -   -   -   10
San Marcos Muni Airport       100  76 100  76  99 /  20  10  10  -   10
La Grange - Fayette Regional   99  77 100  76  99 /  20  10  10  -   10
San Antonio Intl Airport      100  77 100  78  99 /  10  -   10  -   10
Stinson Muni Airport          101  76 101  77  99 /  10  -   -   -   10

&&

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

$$

Mesoscale/Aviation...Oaks
Synoptic/Grids...Allen



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