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

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FXUS64 KEWX 181753 AAA

Area Forecast Discussion...UPDATED
National Weather Service Austin/San Antonio TX
1253 PM CDT Sun Mar 18 2018


MVFR ceilings linger at KAUS/KSAT/KSSF as of 1745Z but rapid
improvement is expected over the next hour to VFR as mixing finally
lifts the lower cloud deck. South to southwest winds of 5-10 knots
are occurring and will persist next few hours. A dryline boundary
will approach TAF sites from the west and help winds become more
southwest through the afternoon. The dryline will pass through KDRT
and aid in stronger west winds this afternoon near 15 knots. TSRA is
expected to develop well east of the terminals and no impacts are
expected. A brief return to MVFR ceilings and 4SM BR conditions for
KAUS/KSAT/KSSF are probable 05-10Z Monday morning. KDRT will remain
VFR being on the west side of the dryline. Ceilings and visibilities
will increase after 10Z post front as it finally shifts east of the


.PREV DISCUSSION... /ISSUED 1202 PM CDT Sun Mar 18 2018/

Low clouds with patchy fog and drizzle has continued across much of
South Central Texas this morning east of the dryline, which is
currently located in eastern Val Verde County. Skies are clear behind
the dryline, but another clearing is occurring ahead of the dryline
along a secondary boundary that stretches from near Leakey to Eagle
Pass along with some clearing in Atascosa, Karnes, and DeWitt
Counties. Thus, it appears that boundary layer mixing is occurring in
these areas, with this clearing expected to spread east-northeast
over the next few hours as the dryline pushes east. A significant cap
that is stronger than this time yesterday is currently present along
the I-35 corridor based on aircraft soundings at AUS and SAT. The
relatively fast movement of the dryline into the I-35 corridor before
significant heating is able to occur also makes convective initiation
along the I-35 corridor unlikely. Thus, most hi-res models are
showing that convective initiation will be east of the I-35 corridor,
with a few showing isolated thunderstorms developing as they cross
the Highway 77 corridor. However, the global models that won out
yesterday have development in the I-35 corridor and the dryline is
expected to slow down due in part to the low clouds, so we kept 20
POPs along and east of I-35/37 through 4 PM, before keeping things
east of I-35 from 4-7 PM once the dryline cross I-35. The evening
hours should be dry, but another convective line may develop with the
front as it pushes through during the overnight hours.

Near critical fire weather conditions are still expected across parts
of the Rio Grande Plains and southern Edwards Plateau due to dry
conditions and southwesterly 10-15 knot winds. Significant warming is
expected this afternoon in these areas as temperatures climb into
the lower to mid 90s. However, winds appear to be a limiting factor
for more critical Red Flag Warning type conditions except possibly
the far west and northwestern edges of Val Verde County where winds
may briefly increase to 15-20 mph winds with 20-foot winds possibly
exceeding 15 mph for an hour or two this afternoon. Thus, these
conditions will probably be too short-lived and over too small an
area to warrant issuing a Red Flag Warning for Val Verde County this
afternoon. Elevated fire weather conditions are expected to spread
into the western Hill Country and eastern portions of the Rio Grande
Plains this afternoon as relative humidity values briefly drop to
20-25 percent before the dryline retreats west early this evening.

Critical fire weather conditions over at least the western half of
South Central Texas is still expected for tomorrow, so we will most
likely upgrade the Fire Weather Watch to a Red Flag Warning for
tomorrow with the afternoon package. Eastward expansion of the Fire
Weather Watch into the I-35 corridor and possibly further east is
also expected as near critical fire weather conditions are becoming
more likely and critical conditions may be possible based some models
that are trending towards increasing wind speeds in the afternoon.

PREV DISCUSSION... /ISSUED 630 AM CDT Sun Mar 18 2018/

For KAUS, KSAT, KSSF, IFR/MVFR CIGs/VSBYs slowly lift and erode as a
dryline shifts east around midday or shortly thereafter, leaving VFR
skies for afternoon into evening. As dryline shifts back west, IFR
CIGs redevelop late evening. A Pacific front moves across the sites
eroding the CIGs again, with VFR returning late tonight through
Monday. S/SE winds less than 10 KTs turn SW late morning to midday,
then back to S/SE in the evening, before finally W/NW late tonight
and increasing to 10 to 20 KTs and gusty Monday. There is a potential
for SHRA/TSRA today and late tonight, however, chances are currently
too low to mention.

For KDRT, VFR skies will prevail. Although there is a potential for
brief IFR CIGs early this morning, chances are low and have only
mentioned FEW clouds. NE winds 5 KTs turn to W and increase to 12 to
25 KTs in the wake of the dryline today, then decrease to less than
10 KTs in the evening, and finally become NW 10 to 20 KTs and gusty
late tonight into Monday.

PREV DISCUSSION... /ISSUED 506 AM CDT Sun Mar 18 2018/

SHORT TERM (Today through Monday)...
Current observations show the dryline has retreated westward into the
Rio Grande plains and southern Edwards Plateau early this morning.
The dryline is expected to advance eastward to the I-35 corridor by
late afternoon. Most of the hi-res models show some potential for
convection to develop along and east of the dryline today and we will
mention a fairly low chance (20-30%) for showers and storms today.
While we can`t completely rule out the possibility of a strong storm
or two, it looks like most of the stronger storms will remain to the
north of our region. Otherwise, expect another warm day with highs
ranging from the mid 80s in the Hill Country to lower 90s Rio Grande.
For this evening, the dryline will briefly retreat westward to near
the Balcones Escarpment before a Pacific cold front overtakes the
dryline early Monday morning. Several of the hi-res models show a
brief window of opportunity for convection to develop along the cold
front during the very early morning hours Monday. Confidence is
fairly low in this scenario, but given agreement among several of the
hi-res models, we will keep a low chance in the forecast for the
early morning hours Monday. The bigger concern will be the very dry
conditions expected behind the front on Monday. Please see the fire
weather section below for more information. We will see some cooling
behind the front on Monday, but northwesterly downslope will likely
offset any significant cooling. We still expect highs to be above
normal, with mid 70s in the Hill Country to mid 80s in the coastal

LONG TERM (Monday Night through Saturday)...
A fairly uneventful weather pattern is in store for south central
Texas during the early and middle portion of this week. A northern
stream cold front will move through Monday night into early Tuesday
morning, resulting in temperatures near normal on Tuesday. On
Wednesday, southerly flow in the low-levels will return as a
subtropical ridge axis builds in the mid and upper levels. This will
result in dry weather along with a warming trend through Friday. We
could see an increasingly active flow aloft develop late in the
forecast period on Saturday. Fro now, we will only mention a 20%
chance for showers and thunderstorms generally along and east of

Fire weather concerns for today will be centered across portions of
the Rio Grande plains and southern Edwards Plateau. With the onset of
daytime heating and mixing, the dryline will move eastward today,
with dry and breezy conditions in store following the passage of the
dryline. Afternoon humidities are expected to drop below 20% across
the Rio Grande plains into portions of the southern Edwards Plateau.
While we do expect an increase in winds behind the dryline, it
appears winds may remain just below critical levels. Current thinking
is we could see enough mid and high level clouds through mid-
afternoon to help limit the mixing of higher momentum air to the
surface. With this in mind, we will hold off on a Red Flag Warning
for Val Verde county and continue to highlight our concerns in a
Special Weather Statement. Should mixing be better than expected, a
Red Flag Warning may be needed for Val Verde county today.

The greater period of concern for fire weather will be on Monday,
following the passage of a Pacific cold front. Minimum humidities for
Monday afternoon will drop into the teens and single digits for most
of south central Texas. In addition, we expect an increase in
northwesterly winds from mid-morning through late afternoon. The
current Fire Weather Watch across portions of the Hill Country,
Edwards Plateau, Rio Grande Plains, and Winter Garden regions will
remain intact. We will hold off on pushing the Fire Weather Watch any
farther east at this time as winds may be the limiting factor in
reaching critical levels.

Dry weather is expected again on Tuesday, with minimum humidities
from near 20% along the Rio Grande to near 30% in the coastal plains.
Northwesterly winds of 10-15 mph are also expected generally along
and east of Highway 281.


Austin Camp Mabry              58  83  49  72  47 /  10   0   0   0   0
Austin Bergstrom Intl Airport  57  80  47  72  43 /  20   0   0   0   0
New Braunfels Muni Airport     57  81  46  73  45 /  20   0   0   0   0
Burnet Muni Airport            50  76  45  69  44 /  -    0   0   0   0
Del Rio Intl Airport           55  82  49  77  51 /   0   0   0   0   0
Georgetown Muni Airport        54  81  47  69  43 /  10   0   0   0   0
Hondo Muni Airport             55  85  46  78  46 /  10   0   0   0   0
San Marcos Muni Airport        56  83  46  73  44 /  20   0   0   0   0
La Grange - Fayette Regional   59  83  49  71  45 /  20  -    0   0   0
San Antonio Intl Airport       59  84  49  75  47 /  20   0   0   0   0
Stinson Muni Airport           59  85  50  76  48 /  20   0   0   0   0




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