Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Austin/San Antonio Texas
808 PM CDT Thursday may 28 2015
Severe Thunderstorm Watch has been issued for the northern Hill
Country and Edwards Plateau. A strong to severe line of showers
and storms is just northwest of our County Warning Area but will continue to be
fed by a rich and unstable airmass and the line should have no
problem surviving for the next few hours. Should see some gradual
weakening later this evening as the atmosphere stabilizes a
bit...but showers and storms should continue to move southeast.
Rainfall amounts still should be in the 1-2 inch rain on average
with isolated higher amounts. It wont take much to aggravate
already saturated soils. Given the expected forecast for
tonight...increased probability of precipitation areawide by 10 to 20 percent.
Previous discussion... /issued 703 PM CDT Thursday may 28 2015/
Aviation... /00z taf update/
Hi-res models suggest that the convective line will likely impact
drt after 02z with isolated cells over Mexico possibly forming and
joining into the line from Mexico by 03z. Impacts of the line
should be after 06z along I-35 with improvements to follow the
convection at roughly 3 hours after the onset. Some bowing
segments of the line could result in spotty wind gusts to near 40
knots...with the chance of strong gusts decreasing gradually
after midnight. Downdraft air should result in some improvements
to skies...but with the complex expected to weaken overnight...
will show more pessimistic skies around daybreak.
Previous discussion... /issued 307 PM CDT Thursday may 28 2015/
Short term (tonight through Friday night)...
Locally heavy rainfall possible across much of area tonight and
potentially Saturday and Saturday night...
severe storms possible across Hill Country and Rio Grande
Scattered thunderstorms have developed this afternoon across the
eastern half of the County Warning Area in an unstable airmass and rich moisture
plume. A few strong storms have developed...including tropical
funnels reported in the Austin/Round Rock area. Overall this
activity should diminish towards sunset.
However...main concern will be developing convective complex
coming out of West Texas and storms coming out of Mexico. Storms
have already developed across West Texas and are beginning to form
in the higher terrain of Mexico...all in advance of approaching
shortwave coming out of nm. Storms developing in the Burroughs of
Mexico could cross into Val Verde County early this evening.
MUCAPE exceeding 4000 j/kg and effective bulk shear of 35 kts will
support storms capable of producing large hail and damaging
straight line winds across Val Verde County. An isolated tornado
can not be ruled.
Several hi resolution models develop the West Texas convection
into an mesoscale convective system this evening with propagation southeast into a
strengthening 35 knots low level Theta-E advection axis up the Rio
Grande plains. The potential mesoscale convective system should make it into the Rio
Grande and northern Hill Country 02z-06z. Severe potential is
possible in this area...for mainly straight-line winds.
Farther eastward into the I-35 corridor...the convective complex
will be encounter increasing cin and weaker low level jet. Much
will depend on how strong of a cold pool develops behind the
complex. The hrrr and nam12 do bring the complex through the I-35
corridor...while Texas tech 4km WRF and global models weaken the
system. There is enough uncertainty...and out of an abudance of
caution given the saturated conditions across the area...to expand
the Flash Flood Watch east through the I-35 corridor.
Fridays forecast will depend highly on what happens tonight. A
organized complex that makes it through the County Warning Area may stabilize
conditions for much of the day. A weakening complex...leaving
potential outflow boundary in an unstable environment...may
result in higher probability of precipitation across the central and eastern County Warning Area Friday.
Long term (saturday through thursday)...models are coming into
better agreement with middle and upper level trough axis sliding
across the Southern Plains Saturday and sharpening across
East Texas/AR/la Sunday into Monday. This will send a cold front
into the area late Saturday...and good chances for rainfall across
the central and eastern County Warning Area Saturday and Saturday night. Higher
precipitable waters will remain pooled ahead of the front and slow movement of
the front could potentially lead to some local pockets of heavier
rainfall. GFS and European model (ecmwf) generally in agreement better chances of
rainfall shift south and east with the front Sunday...but will
have to watch this closely if the front ends up stalling with a
weaker upper trough axis to the east.
Looks like drier conditions do develop Monday through
Wednesday...although not totally removing probability of precipitation across the
southeast zones/coastal prairies where better moisture is pooled
and closer to the lower heights with trough axis just to the
Preliminary point temps/pops...
Austin Camp Mabry 72 85 70 85 67 / 70 40 30 60 50
Austin Bergstrom international Airport 72 84 68 84 65 / 70 50 30 60 50
New Braunfels Muni Airport 73 85 70 85 67 / 60 40 30 60 50
Burnet Muni Airport 70 83 68 82 65 / 70 40 30 60 50
del Rio International Airport 69 88 73 86 68 / 80 20 20 50 60
Georgetown Muni Airport 72 84 69 83 65 / 70 40 30 60 50
Hondo Muni Airport 71 87 71 85 67 / 70 30 30 50 50
San Marcos Muni Airport 72 84 70 84 67 / 60 50 30 60 50
La Grange - Fayette regional 74 85 71 85 68 / 60 50 30 60 60
San Antonio International Airport 73 86 71 85 68 / 70 40 30 60 50
Stinson Muni Airport 73 86 71 85 68 / 60 40 30 50 50
Flash Flood Watch until 7 am CDT Friday for the following counties:
public service/data collection...LH