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Area forecast discussion 
National Weather Service Austin/San Antonio Texas
556 am CDT Wednesday may 6 2015

Aviation...
the bulk of the shower and thunderstorm activity has pushed away
from kaus with only isolated showers lingering across the area.
Ceilings have been holding steady in MVFR categories as the low-
levels remain too mixed for them to drop into IFR. Will keep IFR
out of the tafs this morning but will monitor trends for any
amendments. VFR is expected by the late afternoon hours. Isolated
to scattered showers and storms will be possible this afternoon
and evening and will continue with the mention of vcsh for the
I-35 taf sites. Hi-res models are showing the possibility of
thunderstorms coming near kdrt from the west late this afternoon
and evening and will handle that with thunderstorms in the vicinity. Another round of MVFR
and possibly IFR ceilings are expected once again tonight. Winds
will remain breezy from a south/southeasterly direction.

&&

Previous discussion... /issued 449 am CDT Wednesday may 6 2015/

Short term (today through thursday)...

Impactful heavy rains are ending this morning with a continued
unsettled weather pattern for the short term as humid conditions
persist.

An 500 mb closed low over Colorado and associated negative tilt
trough axis extending into south-central Texas combined with rich
335k h925-700 mb Theta-E moisture flow on southerly nocturnal low-level
jet of 40 knots was supporting the heavy rainfall earlier this
morning. Elevated instability and effective shear near 200 m2/s2
helped a lone discrete supercell produce copious amounts of rain
and some hail along with strong winds. The main branch of forcing
has shifted farther north as the overall parent trough shifts
towards the Central Plains and thus a decrease in activity is
expected through much of the morning hours.

For this afternoon...instability will redevelop but the question
of how strong will the cap be remains key. NAM is more bullish on
steeper lapse rates and more instability with GFS less. Hi-res
ensemble guidance from Storm Prediction Center sseo and ncar tend to reflect the GFS
solution with a stronger cap and more of a scattering of showers
and some thunderstorms. Greater coverage should develop along and
east of the serria del burro mountains with the possibility of
crossing the Rio Grande late afternoon into the evening. Latest 06z
GFS has slowed a 700 mb shortwave trough vs. The 00z run and brings it
across the I-35 area by 06z. While the impulse is noted h7-h5...it
is weaker than todays forcing tied to the parent low. Will need to
watch the Rio Grande plains to the US 281 corridor closely for
more robust development as nocturnal jet occurs again Wednesday
evening. East of I-35...negative h850 Theta-E advection looks to
occur and this may help deplete some support of any complex that
possibly develops in the Rio Grande plains. There is also a
likelihood of a complex developing across north-central Texas
Wednesday night into Thursday morning and these motions will need
to monitored as well.

For Thursday...a near repeat is expected as continued SW flow and
embedded impulses over-top moist low-level flow persist. Near 340k
Theta-E h850 air in place and interacting with yet another impulse
could support another rain/tstorm cluster across the region. With
ample shear and instability a strong to severe tstorm can not be
ruled out. Localized flash flooding also remains a possibility
given this set-up and day to day variations will be need to be
closely watched.

Long term (thursday night through tuesday)...

The continued unsettled weather pattern looks to continue based on
global model agreement through much of the long term and finally
turning drier middle to late next week. Yet...several rounds of
showers and storms through early next week could lead to flash
flooding in localized areas.

A large western Continental U.S. Cyclonic 500 mb gyre will be ongoing by late
week that will maintain the active southern jet stream branch over
the region. Ample moisture with precipitable waters 1.5-1.8" and SW impulse
embedded flow...continued rounds of showers and storms will be
possible each afternoon and evening. Determining convective
evolution this far out on subtle features is difficult as these
features will ultimately determine coverage and intensity. Heavy
rain pockets will be likely with such a pattern. The cyclonic gyre
finally opens up and shifts east by Sunday that may result in
higher chances Sunday into Monday morning for a more organized
precipitation event. A Pacific tropical connection may even
develop by this time and into early next week as the southern jet
branch remains well intact. Both GFS and ec global models agree
that at least 2-4 inches of rain will be quite likely across the
region through middle of next week. Some areas will likely have
higher amounts as the active El Nino pattern presses on. /Allen/

&&

Preliminary point temps/pops...
Austin Camp Mabry 83 70 84 71 83 / 30 20 40 20 40
Austin Bergstrom international Airport 83 71 84 71 84 / 30 20 40 20 40
New Braunfels Muni Airport 83 70 84 72 84 / 30 30 30 20 40
Burnet Muni Airport 81 69 81 69 82 / 30 20 40 20 40
del Rio International Airport 83 70 89 72 88 / 30 40 20 20 30
Georgetown Muni Airport 82 70 82 70 83 / 30 20 40 20 40
Hondo Muni Airport 83 70 84 71 85 / 30 30 30 20 40
San Marcos Muni Airport 83 70 83 71 84 / 30 20 30 20 40
La Grange - Fayette regional 83 72 85 73 85 / 30 20 30 20 30
San Antonio International Airport 83 71 84 72 84 / 30 30 30 20 40
Stinson Muni Airport 84 71 85 72 85 / 30 30 30 20 40

&&

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

$$

Mesoscale/aviation...29
synoptic/grids...15

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