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

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830
FXUS64 KEWX 250250
AFDEWX

Area Forecast Discussion
National Weather Service Austin/San Antonio TX
950 PM CDT Fri Mar 24 2017

.UPDATE...
Dry air aloft continues to filter into most of South Central Texas on
the southwest side of a strong upper level low over Central Oklahoma.
Although surface dew points in the 60s are gradually retreating west
towards the I-35 corridor, this will be short lived as the synoptic
cold front currently located just north of Sonora to DFW moves into
the region. The front moving through the I-35 corridor around 1 am
and clears the Coastal Plains by 5 am should quickly halt surface
moisture recovery. Although isentropic descent will quickly fill in
behind the front, there may be a very brief window for showers and
possibly a thunderstorm in the Coastal Plains as SW-NE isentropic
descent moves in just ahead of the front. However, hi-res models are
trending towards a faster progression of the front and holding off
on triggering showers and thunderstorms until after it clears our
CWA. Considering surface convergence will be very weak, we only have
20 POPs over parts of Fayette and Lavaca Counties tonight. Patchy
fog may occur in the Coastal Plains after Midnight before quickly
lifting behind the front. Aside from that, only minor grid edits
were made based on model and observational trends.


&&

.PREV DISCUSSION... /ISSUED 743 PM CDT Fri Mar 24 2017/

UPDATE...Corrected to change sunset to sunrise below...
Winds continue to remain above 15 mph out in parts of Val Verde and
Edwards Counties with relative humidity values remaining around 10-15
percent. Therefore, we have extended the Red Flag Warning for those
three counties for one hour to 8 PM for Val Verde, Edwards, and
Kinney Counties in coordination with FWD and SJT. Winds should fall
below 15 mph and relative humidity values should recover back above
20 percent within the next hour or so.

The showers and thunderstorms that developed along a confluence
boundary just west of the Highway 77 corridor have all moved out of
the county warning area except for one cell in Lavaca County that
moved just to the south-southeast of Hallettsville. We continue to
monitor that cell as storm-relative helicity values remain in the
200-300 m^2/s^2 range and we did have a cell briefly pulse to
possibly produce severe hail in NE Fayette County. However, mid-level
lapse rates remain very modest at 6-6.5 deg C/km, so the potential
for that storm to become severe remains low at this time. Once that
cell exits the CWA within the hour, all storm activity should end
until possibly late in the overnight hours around sunrise in the
Coastal Plains once the synoptic cold front moves through. We will
do one more grid update in the next few hours to address this, but
20 POPs seem reasonable for now.

PREV DISCUSSION... /ISSUED 643 PM CDT Fri Mar 24 2017/

AVIATION.../00Z TAF CYCLE/

VFR conditions prevail across all terminals late this afternoon and
are expected to continue through the TAF period. Isolated TSRA is
ongoing across the Texas Coastal Plains towards Houston. This
activity will shift northeast through the early evening hours into
East Texas. Surface winds remain gusty from the south and west for
KDRT/KAUS at 15-20 knots. These winds will subside next few hours to
sustained winds near or less than 10 knots from the west. Winds will
then shift more northerly through early to mid morning Saturday as a
dry front moves through the region. Low ceilings are likely to return
by Sunday morning however as moisture returns to the region.

PREV DISCUSSION... /ISSUED 320 PM CDT Fri Mar 24 2017/

SHORT TERM (Tonight through Saturday Night)...
Pacific front/dry line was near the I-35 corridor mid afternoon.
Dry slotting has occurred across the southern I-35 corridor. Farther
northeast aircraft soundings near AUS indicate the mid level cap
weakening. There is still a window through late afternoon and early
evening where a strong to marginally severe storm or two could form
across the EWX CWA near and east of U.S. 77. However the better
threat this afternoon and into tonight will be northeast of the area.
A secondary push/front will move into the area after midnight.
The latest few HRRR runs were showing the possibility of convection
developing along this boundary overnight across the far eastern CWA.
In addition, with the initial front/dry line slowing down there will
be a window for fog late tonight across the far southeast counties
before the secondary push of drier air arrives. Sunny and dry on
Saturday.

LONG TERM (Sunday through Friday)...
A progressive pattern will occur through the upcoming week. On
Sunday a weak shortwave will pass through the Southern Plains. A warm
front looks to come back into the CWA Sunday morning and then a dryline
gets dragged east into the western CWA Sunday afternoon. This will
lead to a warm day, especially across the southwest CWA where highs
could climb into the mid 90s. Upper 80s to low 90s are expected
elsewhere. A weak cold front looks to enter the area Monday and
results in highs a degree or two cooler.

Models are then consistent with an upper level low digging into the
Four Corners Tuesday and a rapid moisture return taking place across
South Central Texas ahead of it on Tuesday. Isolated to scattered
showers and storms are possible during the day on Tuesday, favoring
central and western areas of the CWA. This upper level low is
forecast to dig slightly farther south into Texas than the current
system, coming out into West Central Texas Wednesday morning.

South Central Texas becomes placed in a favorable location Tuesday
night into Wednesday morning, with a diffluent flow aloft between
the upper level low to the northwest and sub-tropical jet streak
just to the south. As large scale ascent spreads into the area late
Tuesday night through Wednesday morning both the GFS and ECMWF are
indicating showers and storms increasing in coverage, especially
across the Hill Country and I-35 corridor Tuesday night and along and
east of I-35 Wednesday morning. There are hints that a heavier band
of rainfall could occur near and east of I-35. Ingredients may come
into play for locally heavy rainfall but too soon to determine exact
amounts and locations. There could also be a threat for severe storms
as an organized convective complex may try and develop.

The area looks to eventually get dry slotted Wednesday afternoon from
west to east. GFS is a little more robust with mid level moisture
wrapping around the upper level low Wednesday night and Thursday and
is generating some QPF. Have retained some low pops across the
northeast half of the CWA during this time.

Dry conditions on Friday and then both the GFS and ECMWF indicate
another upper level system possibly impacting the CWA just beyond
Day 7.

FIRE WEATHER...
Winds have been a little slow to respond but in the past hour have
begun to see winds increasing across the western Hill Country and
Edwards Plateau. There will be a window now though sunset where
occasional wind gusts to around 25 mph could occur across Edwards and
Val Verde Counties and possible as far south as Kinney County. RH
values are currently bottoming out around 8-15 percent and should the
winds become gusty this will result in a critical fire danger. Will
allow the Red Flag Warning to remain in place until 7 PM.

&&

.PRELIMINARY POINT TEMPS/POPS...
Austin Camp Mabry              55  81  58  87  63 /  -    0   0  10  20
Austin Bergstrom Intl Airport  52  81  55  87  62 /  -    0   0  10  20
New Braunfels Muni Airport     52  82  56  87  62 /  -    0   0  10  10
Burnet Muni Airport            50  78  56  85  58 /   0   0   0  10  20
Del Rio Intl Airport           53  84  57  91  57 /   0   0   0   0   0
Georgetown Muni Airport        52  79  55  86  61 /  -    0   0  10  20
Hondo Muni Airport             49  86  56  90  59 /   0   0   0  -   10
San Marcos Muni Airport        53  82  56  87  63 /  -    0   0  10  10
La Grange - Fayette Regional   58  80  57  86  66 /  20  -    0  10  20
San Antonio Intl Airport       53  84  58  88  62 /   0   0   0  10  10
Stinson Muni Airport           53  83  58  88  62 /   0   0   0  10  10

&&

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

$$

Mesoscale/Aviation...Allen
Synoptic/Grids...LH
Public Service/Data Collection...Williams



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