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Area forecast discussion...updated 
National Weather Service Austin/San Antonio Texas
640 PM CDT Monday Apr 20 2015

Update...
please see the 00z aviation discussion below.

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Aviation...
thick middle and high level cloud cover continues to stream in from
the west this evening. This cloud cover will remain intact through
the overnight hours into tomorrow morning as winds transition to a
more east and southeasterly direction. Models suggest MVFR low
clouds will develop by late tomorrow morning or early afternoon
and we/ll continue this trend in the latest forecast. We did opt
to include a tempo group for the I-35 corridor during the
afternoon hours for VFR skies as cloud bases temporarily lift. Low
clouds likely to fill in after 22/00z across the region as low-
level moisture increases.

&&

Previous discussion... /issued 252 PM CDT Monday Apr 20 2015/

Short term (tonight through Tuesday night)...
cool surface ridge will give way later tonight into Tuesday as a
surface low develops in the plains. Dewpoints remain low tonight
allowing for one more cool night. Southerly winds return Tuesday
to all areas allowing moisture to increase across south central
Texas. This may lead to isolated showers Tuesday afternoon into
Tuesday night as weak upward motion develops from a strengthening
low level jet. However...warm middle level temperatures due to weak
upper level ridging will inhibit deeper convection. The exception
may be that upward motion is enhanced by orographic lift to
develop isolated thunderstorms on the serranias del burro. Convective available potential energy
around 1000 j/kg suggest some strong storms. However...steering
vectors indicate they should stay near the higher terrain of the
burros keeping them west of the Rio Grande with no impact to south
central Texas. Significantly higher dewpoints bring a warmer more
humid airmass Tuesday night.

Long term (wednesday through monday)...
an upper level trough along or just off the California coast is
forecast to be in the process of undergoing development by
Wednesday morning due to the interaction of several shortwaves.
This trough remains along the coast on Wednesday and moves into
the Desert Southwest on Thursday. Meanwhile...southerly lower
level flow will maintain a humid airmass across south central
Texas. The dryline is forecast to drift east into parts of the
Edwards Plateau and Rio Grande Valley during the late afternoons
on Wednesday and Thursday. Upward forcing and convergence along
the dryline and orographic lift on the serranias del burro should
weaken the convective inhibition to allow for thunderstorm
development. Convective available potential energy in the 2000 to 4000 j/kg range and shear up to
50 kts indicate isolated strong to severe storms are possible.
Further to the east...weak upper level ridging and warm middle level
temperatures should maintain at least some convective inhibition.
However...there remains a potential for storms to form into
clusters and move east across south central Texas. Although will
mention severe potential in the severe weather potential statement...will not mention severe in
the grids yet due to the uncertainty on convective inhibition
remaining. The best chances for showers and thunderstorms occur
later on Friday when the upper level trough moves out across the
plains. This forces the dryline further to the east across south
central Texas. Moisture convergence and upward forcing along the
dryline should weaken the inhibition allowing showers and
thunderstorms to develop. Forecast convective available potential energy similar to middle week
indicate potential for strong to severe storms. As the upper
trough moves into the Mississippi Valley early Saturday a Pacific
cold front moves across our area. However...the dryline will have
scoured most of the moisture with slight chances of showers and
thunderstorms only in the east Friday night. Some uncertainty for
Sunday into next Monday with the GFS showing another upper trough
and cold front early Monday for a slight chance of showers while
the European model (ecmwf) shows zonal flow and no trough/front. Will keep probability of precipitation out
of forecast for now to await some consistency and consensus in the
models.



&&

Preliminary point temps/pops...
Austin Camp Mabry 55 78 66 82 69 / - 10 10 30 20
Austin Bergstrom international Airport 52 77 66 81 68 / - 10 10 30 20
New Braunfels Muni Airport 54 78 66 82 69 / - 10 20 30 20
Burnet Muni Airport 52 76 66 81 67 / - 10 10 30 20
del Rio International Airport 58 79 67 88 69 / - 10 20 20 10
Georgetown Muni Airport 52 77 67 82 69 / - 10 10 30 20
Hondo Muni Airport 54 77 67 82 69 / - 10 20 30 20
San Marcos Muni Airport 53 77 66 82 68 / - 10 10 30 20
La Grange - Fayette regional 54 77 66 82 70 / - 10 10 30 20
San Antonio International Airport 56 77 68 82 70 / - 10 20 30 20
Stinson Muni Airport 56 78 68 82 70 / - 10 20 30 20

&&

Ewx watches/warnings/advisories...
none.
&&

$$

Mesoscale/aviation...24
synoptic/grids...15
public service/data collection...33

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