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

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FXUS64 KEWX 211451 AAA

Area Forecast Discussion...UPDATED
National Weather Service Austin/San Antonio TX
951 AM CDT Sun Apr 21 2019

Low clouds will continue to scattered out late this morning with
mostly sunny skies anticipated across most areas this afternoon.
Highs will range from the lower 80s across the Hill Country to lower
90s along the Rio Grande. Southerly flow is forecast to pick this
afternoon mainly affecting areas along and east of Highway 281 with
sustained wind speeds of 15 to 20 MPH and gusts up to 30 MPH. Breezy
conditions continue through the evening hours.


.PREV DISCUSSION... /ISSUED 643 AM CDT Sun Apr 21 2019/

Stratus has developed more widespread near and west of a Kerrville
to San Antonio to Pleasanton line than previously anticipated. In
addition, some patchy fog has developed near and east of I-35 along
with patchy stratus. An update was sent to increase cloud cover and
add patchy fog in through the early morning hours. Mixing by mid to
late morning should scour out cloud cover and fog, given the shallow
nature of the moisture.

PREV DISCUSSION... /ISSUED 610 AM CDT Sun Apr 21 2019/

IFR ceilings beginning to spread through terminals along I-35
starting with San Antonio sites before spreading up to KAUS. Ceilings
should mix out by late morning. Winds out of the southeast with
gusts up to 25kts this afternoon before weakening after sunset.

PREV DISCUSSION... /ISSUED 344 AM CDT Sun Apr 21 2019/

SHORT TERM (Today through Monday)...
Southerly low level flow will strengthen today, becoming windy and
gusty by afternoon across central and eastern areas of the CWA. Gusts
up to 30 mph are forecast. A mostly sunny and warm afternoon today,
with high temperatures in the mid 80s across eastern and northern
areas and upper 80s to low 90s across southwestern areas. Stratus
will develop after midnight as a shallow moisture return continues
beneath a strengthening cap. Breezy southerly flow continues on
Monday, with highs temperatures a few degrees cooler than today
given increased cloud cover and dew points.

LONG TERM (Monday Night through Saturday)...
An upper level low is forecast to dig into the Southwest U.S. and
northern Mexico Monday night and Tuesday. Low level moisture will
deepen during this time beneath the cap, leading to patchy drizzle
developing across portions of the Hill Country and I-35 corridor area
late Monday night into Tuesday morning. In addition, a lead
shortwave in the southwest flow aloft is forecast to come out of
Mexico Monday afternoon and night, and could generate a few elevated
showers across western areas of the CWA late Monday afternoon and
night. For most of the day on Tuesday coverage of showers should
remain isolated to scattered as the cap remains in place. However
height falls should help to erode the cap across western areas of the
CWA by late Tuesday afternoon and Tuesday evening, which could lead
to the development of better chances of thunderstorms near the Rio
Grande and across the southern Edwards Plateau and western Hill
Country. Some of these storms could possibly be strong to severe
across this region given steep mid level lapse rates and adequate
deep layer shear. SPC Day 3 currently has a Marginal Risk for severe
storms for these areas Tuesday afternoon and night.

The upper level low is forecast to move through Far West Texas and
the Big Bend Tuesday night. Models are in better agreement with the
track of the core of the upper level low through portions of the
northern Hill Country and Edwards Plateau on Wednesday and into North
Central Texas Wednesday night. Strong forcing in the base of the
trough and height falls ahead of it will assist in the erosion of
the remainder of the cap in place across South Central Texas
overnight Tuesday into Wednesday morning. This should lead to rapidly
expanding coverage of showers and storms from west to east Wednesday
morning. There is disagreement with how far south the associated
surface front makes it overnight Tuesday into Wednesday morning, with
the NAM12 indicating the front by 12Z Wednesday well into the Hill
Country and the 850mb front just north of the CWA. Global model
solutions are delayed with the SFC-850mb fronts until during the day
on Wednesday. The GFS, and to slightly lesser extents the ECMWF and
Canadian, also indicate the front sharpening through the western CWA
during the day on Wednesday as a frontal wave develops through
Central Texas, which also lifts a warm front through the area. These
low level details, that are still unclear at this time, will be key
to where the heavier rainfall occurs Wednesday, especially given the
anomalously high precipitable water values indicated by the models.
At this time we have included a mention of locally heavy rainfall in
the forecast for portions of the Hill Country and Central Texas,
closer to where the forcing along the SFC-850mb fronts strengthens
with the developing frontal wave.

Also, a severe threat may develop on Wednesday, as steep mid level
lapse rates of 7-8 degC/km are indicated on forecast soundings along
with 50kts of 0-6km shear. This could support a few storms producing
large hail and damaging wind gusts. In addition, if the warm front
lifting north through the CWA materializes there could be a small
window through the first half of the day of an isolated tornado
across northeast areas of the CWA as convection becoming surface
based. SPC has highlighted much of the CWA in a risk for severe
storms on Day 4/Wednesday.

The cold front should move east of the I-35 corridor Wednesday
evening and clear east of the CWA by 12Z Thursday. Precipitation
chances end west to east during this time. Dry northwest flow aloft
Thursday and Friday on the back side of the trough departing east,
along with dry northerly surface flow behind the cold front, will
lead to clearing and dry conditions along with seasonal temperatures.
A weak return flow is forecast to develop Saturday into Sunday.


Austin Camp Mabry              83  63  81  66  78 /   0  -   -   10  30
Austin Bergstrom Intl Airport  83  62  81  66  78 /   0  -   -   10  30
New Braunfels Muni Airport     84  62  81  67  78 /   0  -   -   10  30
Burnet Muni Airport            82  61  79  65  75 /   0   0  -   10  40
Del Rio Intl Airport           89  65  84  67  84 /   0   0  -   -   30
Georgetown Muni Airport        83  62  81  66  77 /   0  -   -   10  30
Hondo Muni Airport             88  63  85  67  81 /   0  -   -   10  30
San Marcos Muni Airport        84  62  81  66  79 /   0  -   -   10  30
La Grange - Fayette Regional   83  63  82  67  79 /   0   0   0  -   20
San Antonio Intl Airport       85  63  82  67  79 /   0  -   -   10  30
Stinson Muni Airport           85  63  82  68  79 /   0  -   -   10  30




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