Area forecast discussion
National Weather Service Austin/San Antonio Texas
1147 PM CDT Sat may 25 2013
Aviation...
MVFR ceilings prevailing with isolated rain showers...with rain showers/thunderstorms and rain becoming
more numerous between 08z and 12z as an upper level disturbance
approaches from the west and northwest. Ceilings/visibilities occasionally
lower in the rain showers/thunderstorms and rain overnight. Rain showers/thunderstorms and rain decreasing during the
day Sunday...but a isolated rain showers/thunderstorms and rain will redevelop with heating
Sunday afternoon. Ceilings lifting to VFR most areas between 17z and
18z. S-southeasterly prevailing at 5-15 knots for the next 24 hours.
&&
Previous discussion... /issued 902 PM CDT Sat may 25 2013/
Update...
no significant changes made to ongoing forecast. The threat for
additional rainfall...locally heavy...will continue overnight.
Discussion...
a lull in activity will continue this evening...but another round
of showers and thunderstorms is expected overnight as a middle/upper
level short-wave moves across the area. Storm development overnight
will be less widespread than we have had the last 24-36 hours.
However...the combination of rich moisture through the lower
levels (00z area soundings indicate precipitable water values of 1.5 to near 2
inches)...and a weak stalled front suggest the potential for
efficient rain-producing thunderstorms which will also move slowly
and/or train over the same area. Therefore...locally heavy
rainfall remains a concern. New rainfall totals for midnight
through Sunday morning will average one to two inches...with
spotty amounts of two to four inches...and isolated totals as high
as six inches possible. The potential for the highest rainfall
totals will generally be across the eastern Hill Country...greater
Austin metropolitan area...and the plains east of Austin. However...due
to the recent heavy rains over the last 24-36 hours...any additional
rainfall will likely be problematic and will therefore keep the
Flash Flood Watch in effect for the eastern half of the region.
The only changes made to the ongoing forecast package were to
reduce probability of precipitation and quantitative precipitation forecast for 00-06z as well as remove wording of heavy
rainfall before midnight. New zones will be out shortly.
Previous discussion... /issued 630 PM CDT Sat may 25 2013/
Aviation...
slow eastward moving upper air trough over south Texas will keep
a moist southerly low level flow into S Texas over the next 24 hours.
Generally VFR conditions...except for isolated rain showers/thunderstorms and rain 04z will
give way to MVFR ceilings after 04z and MVFR-IFR ceilings 08z-14z.
Ceilings/visibilities lower after 05z more organized rain showers/thunderstorms and rain could develop
along the i35 corridor and continue through about 12z before lifting
northeastward out of the area. Otherwise S-southeasterly winds of 5-15 knots prevailing.
MVFR ceilings after 15z Sunday becoming VFR most areas by 18z...with
isolated rain showers/thunderstorms and rain mainly due to afternoon heating behind the
upper trough.
Previous discussion... /issued 347 PM CDT Sat may 25 2013/
Short term (tonight through Sunday night)...
flood potential has temporarily abated for most areas for late
this afternoon as the majority of the middle to upper level
disturbance has shifted east. However...an additional shortwave
will lift northeast into south central Texas by late this evening. A
few strong thunderstorm cells will possible take advantage of
outflow boundaries...pooled moisture and heating to produce
locally heavy rainfall across areas SW of San Antonio. We
currently think this could be a brief late afternoon round of rain
that should be separate from the shortwave induced activity that
develops later tonight. The effects of this more progressive
shortwave seems poorly handled by most of the models given the
very high precipitable water values close to 2 inches...so will factor in some
slower departure from our counties as the convection taps into a
broader middle-level shear axis. Thus there remains an isolated
potential for another outbreak of warm core rains...but the more
progressive upper level pattern should shift the heavier rainfall
totals slightly east of I-35. Still...with a potential for heavy
slow moving thunderstorms capable of producing a 4 inch rain in
one hour...will continue the existing watch area through 8 am
Sunday to account for the extra sensitive soils and swollen
streams. This forecast may appear to be a bit of an outlier to
what is forecast by most models...but recollections of how models
handled earlier warm season shear axis-based pattern such as the
July 2002 patterns...would suggest the models are too quick to
improve stability.
Long term (monday through saturday)...
the large amount of water stored in soils should also continue to
linger into daytime hours Sunday and possibly have a slight
influence on weather...particularly temperatures...for the next
week or so. Thus have trended on the moist side of probability of precipitation for the
next 5 days...as a possible disturbance that could enhance rain
and storm chances by middle-week should still benefit from locally
higher precipitable water values. Model consensus shows a flat ridging pattern
that should eventually establish hotter and drier days by next
weekend.
&&
Preliminary point temps/pops...
Austin Camp Mabry 69 90 69 91 71 / 70 30 10 10 -
Austin Bergstrom international Airport 69 88 68 90 71 / 70 30 10 10 -
New Braunfels Muni Airport 68 90 67 90 70 / 70 30 10 10 -
Burnet Muni Airport 67 87 66 89 69 / 50 20 10 10 -
del Rio International Airport 73 91 72 95 74 / 20 10 10 10 -
Georgetown Muni Airport 68 87 67 88 70 / 70 30 10 10 -
Hondo Muni Airport 70 90 69 93 71 / 50 20 10 10 -
San Marcos Muni Airport 69 89 69 90 71 / 70 30 10 10 -
La Grange - Fayette regional 73 88 72 89 74 / 60 30 10 10 10
San Antonio International Airport 70 89 70 91 72 / 60 30 10 10 -
Stinson Muni Airport 70 89 69 91 71 / 60 30 10 10 -
&&
Ewx watches/warnings/advisories...
Flash Flood Watch until 8 am CDT Sunday for the following counties:
Atascosa...Bastrop...Bexar...blanco...Burnet...Caldwell...Comal...
Delaware Witt...Fayette...Gillespie...Gonzales...Guadalupe...Hays...
Karnes...Kendall...Lavaca...Lee...Llano...Travis...Williamson...
Wilson.
&&
$$
Mesoscale/aviation...01
synoptic/grids...25
public service/data collection...31
