Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Austin/San Antonio Texas
954 PM CDT sun may 3 2015
no major changes to the forecast other than re-trending the hourly
variables through 12z. We still expect some light showers toward
daybreak across the Rio Grande plains and Edwards Plateau...but
isolated and very light.
Previous discussion... /issued 635 PM CDT sun may 3 2015/
Update...00z aviation discussion below.
Aviation...low level moisture will continue to increase across
south-central Texas through the taf period...especially across
western areas of the County Warning Area. MVFR ceilings in stratus developing
05z-08z...and lowering into IFR range 10z-12z. A few streamer
showers possible overnight through Monday morning between Sat-
drt...though coverage too low to include mention in tafs. VFR
conditions eventually developing around 18z at aus/Sat/ssf...but
MVFR ceilings likely holding into the early afternoon at
drt...where cap is slightly stronger and better low level
Previous discussion... /issued 337 PM CDT sun may 3 2015/
Short term (tonight through Monday night)...
No weather highlights in the short term except for increasing
clouds and some light shower possibilities overnight and into
Monday along and west of US 281.
Dewpoint values are running 10f degrees higher this afternoon vs.
Yesterday and this is likely being perceived in the relative
humidity values. Nwp depicts h925-850 Theta-E advection this
afternoon up the Rio Grande Valley that is resulting in more Stout
cloud coverage. As a result...have lowered maximum highs there with
rest of region warming up nicely into the upper 70s to low 80s.
Precipitable waters near 1" currently will increase to near 1.3-1.4" through
Monday morning and with increasing low-level wind flow...expect
stratus to develop overnight. This southerly wind flow combined
increasing flow aloft and weak impulses migrating off a parent low
in Mexico will support light isentropic showers generally west of
Highway 83. By Monday afternoon...clouds will slowly break up and
allow for increased surface heating underneath a weak capping
inversion. With weak forcing and no low-level focusing boundary...
feel the cap should hold and only isolated to scattered low-topped
showers should result. While overall coverage will be limited...
best chances for this shower activity will along and west of US
281 through the afternoon.
Long term (tuesday through sunday)...
An unsettled pattern with continued SW flow and embedded impulses
will aid in multiple chances for showers and thunderstorms Tuesday
through the rest of the week. Confidence is low in hazardous
weather during this time frame given lack of deeper forcing and
lift which will be farther north and west. Overall rainfall
amounts will average 0.5-1" north of Highway 90 with lesser
A closed 500 mb low over The Four Corners region will open and pivot
northeast towards Colorado and the Great Plains. Residual negative
tilt troughing and height falls combined with in situ moisture
with a weak cap should allow for a more consolidated signal of
showers and thunderstorms across The Hill Country Tuesday evening into
Wednesday morning. Surface based cape values Tuesday afternoon near
1500-2000 j/kg and vertical totals near 26c in western zones
could possibly support an isolated strong storm.
By Wednesday afternoon...the parent low will continue to track
north with slightly weakening wind fields and a strengthening
capping inversion. Still...some low-topped instability induced
showers could occur Wednesday afternoon. There could be an uptick in
activity by Thursday morning with a prognosticated impulse shifting over
the region as it continues to interact with steadily climbing
moisture values /pwats 1.6-1.8"/. It is not inconceivable Thursday
afternoon for the cap to erode enough to allow for surface based
storms to fire in vicinity of the dryline that will be just west of the
region. Favorable thermodynamics of 2500 j/kg and negative
showalters could support a tstorm cluster near The Hill Country
vicinity and northward.
For Friday into the weekend...another large cut-off low will
develop over the western Continental U.S. And continue to reinforce the
active southern jet stream branch over Texas. Multiple rounds of
showers and thunderstorms will be possible with bulk of activity likely
to remain just north and west of region. This trend will need to
be closely monitored in case of an impulse interacting just right
with a possibly surging dry line for enhanced convective potential
closer to south-central Texas. This unsettled pattern looks to
continue into early next week. /Allen/
Preliminary point temps/pops...
Austin Camp Mabry 65 81 65 81 69 / 10 10 10 40 60
Austin Bergstrom international Airport 63 80 64 81 68 / 10 10 10 40 60
New Braunfels Muni Airport 64 80 64 82 69 / 10 20 10 40 50
Burnet Muni Airport 63 79 63 78 66 / 10 10 10 50 60
del Rio International Airport 69 81 68 82 69 / 20 30 30 30 40
Georgetown Muni Airport 64 79 63 79 67 / 10 10 10 50 60
Hondo Muni Airport 67 80 67 81 69 / 10 20 20 30 40
San Marcos Muni Airport 65 80 64 81 69 / 10 10 10 40 50
La Grange - Fayette regional 63 81 63 81 69 / 10 10 10 40 40
San Antonio International Airport 66 80 66 81 69 / 10 20 10 40 40
Stinson Muni Airport 67 81 67 82 70 / 10 20 10 30 40
public service/data collection...30