Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Austin/San Antonio Texas
952 am CDT Friday may 22 2015
seeing some light returns along the i35 corridor this morning. The
del Rio sounding this morning shows a strong capping inversion at
700 mb. So not expecting much growth to these showers at least
this morning. Lowered probability of precipitation for the remainder of the morning for
del Rio. Fog is showing signs of lifting at 15z this morning.
Otherwise...mostly cloudy skies will prevail today.
Previous discussion... /issued 616 am CDT Friday may 22 2015/
Update.../update to add fog/
patchy fog has dropped a few visibilities to 1/4 mile so will add some
fog to the forecast through 15z. The chance of thunderstorms still
exists for this morning...especially south of Highway 90...but most
areas should expect to see patchy light rain or drizzle.
Previous discussion... /issued 615 am CDT Friday may 22 2015/
LIFR/vlifr conditions have developed across the area terminals
this morning. Expect these conditions to continue through middle-late
morning with some slow improvement. Cant completely rule out the
chance of a shower or thunderstorm today but probability was too
low to mention in the tafs and will handle this with
amendments if needed. More widespread showers and storms are
expected after 06z tonight beginning out west and will mention the
activity in tafdrt. Future shifts will likely need to shift this
east. Otherwise...another round of IFR is expected tomorrow
Previous discussion... /issued 406 am CDT Friday may 22 2015/
Short term (today through saturday)...
a Flash Flood Watch will likely be issued within the next 12 hours
or so...given the strong storm system approaching Texas. Scattered
showers and a few thunderstorms will continue to develop over the
area...but the heaviest rainfall potential is not expected to
begin until Saturday afternoon.
A shallow frontal inversion today will keep cooler than normal
temperatures and limit the potential for persistent deep convection. A
few thunderstorms moving inland from the coastal Bend will be in a
precipitable water region of around 1.8 inches...so there could be a few cell
clusters that produce rainfall amounts over an inch over mainly
the coastal prairies. While runoff concerns are not anticipated
for today...the rains today will continue to keep soils near
saturation and enhance concerns for the heavy rain event this
Surface winds should turn more southeasterly late this
afternoon...leading to increased potential for surface based
convection late today. However...most of the model data show
limited deep convection through early Saturday...with the Canadian
being one exception that develops an early Saturday morning
complex over the Edwards Plateau. Late Saturday...more models come
into alignment on ramping up higher precipitation amounts. With
the event only just beginning will discuss this environment in
further detail in the long term section.
Long term (saturday night through thursday)...
afternoon heating is expected to be modest due to the near 2 inch
precipitable water values keeping clouds abundant for much of the day. A few
peeks of sunshine could late Saturday afternoon could present a
minor severe concern through Saturday evening...but the
development of a large heavy rain producing complex late in the
day is expected to present the highest impact over the area
Saturday evening into early Sunday. With recent model trends
developing a slightly broader upper trough just west of Texas during
this period...the quantitative precipitation forecast forecasts among the recent synoptic model
runs continue to be varied on timing and location of the higher
precipitation amounts. Will hold off the Flash Flood Watch
issuance and give the models another shot to come into better
alignment before adding better details on the event timing.
Forecast rainfall totals remain centered around this higher impact
period from Saturday afternoon through early Sunday evening...and
would suggest widespread 1-3 inch rains with isolated 6 inch
A well-developed mesoscale convective system sweeping across Texas would likely help provide
some relative stability for late Sunday...but the quantitative precipitation forecast patterns in
the most of the synoptic model forecasts do not suggest such a
complex. Should there be smaller...progressive storm clusters as
suggested...the atmosphere will reload quickly with strong to
severe storms in addition to the training and heavy rain threats.
Convective available potential energy are suggested to approach 4000 j/kg by the GFS Sunday which
would combine with ample wind shear for an hp supercell threat.
The lifting of the first lobe ejection of the upper trough late
Sunday would suggest relative minima for rain chances late Sunday
evening into early Monday. 00z models are showing better
agreement on a secondary lobe to move into northwest Texas and increase
storm potential for late Monday into early Tuesday. The pattern
aloft is expected to flatten out to offer some potential for
reduced thunderstorm potential for the remainder of the forecast
period...but a general cyclical troughing pattern remains over
the southwestern US through at least Thursday.
Preliminary point temps/pops...
Austin Camp Mabry 78 71 82 70 79 / 40 20 50 70 80
Austin Bergstrom international Airport 79 70 82 70 79 / 40 20 50 70 80
New Braunfels Muni Airport 80 71 82 70 80 / 50 20 50 70 80
Burnet Muni Airport 76 69 80 68 78 / 30 20 60 70 80
del Rio International Airport 84 71 82 69 89 / 40 40 60 60 30
Georgetown Muni Airport 77 70 81 69 78 / 40 20 50 70 80
Hondo Muni Airport 79 71 81 69 83 / 50 20 50 80 70
San Marcos Muni Airport 78 71 81 70 79 / 40 20 50 70 80
La Grange - Fayette regional 80 72 83 72 80 / 40 20 50 50 80
San Antonio International Airport 80 72 82 69 81 / 50 20 50 70 70
Stinson Muni Airport 80 72 83 71 82 / 50 20 50 70 70
public service/data collection...Treadway