Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Austin/San Antonio Texas
1111 am CST Friday Jan 30 2015
stratocu deck around 5kft is beginning to develop across the
central portions of the County Warning Area at the present time. This VFR cloud
deck is expected to persist through the afternoon. Strong low-
level flow will continue to moisten the lower levels of the
atmosphere and should see MVFR ceilings develop after midnight. Ceilings
and visibilities could lower even further into IFR around sunrise
and persist through the day as light rain develops. Rain should
begin in del Rio first...as the system moves through the area from
west to east. Initially...the middle-levels of the atmosphere will be
dry which will limit the precipitation intensity. Rain should be
off an on throughout the day after the onset...and will just
prevail -ra for simplicity sake.
Previous discussion... /issued 533 am CST Friday Jan 30 2015/
Discussion...12z aviation below.
Aviation...bkn-ovc VFR deck will prevail through the morning
hours...around 10k feet across the northern and eastern County Warning Area...
including aus. Very patchy -ra is possible across this area
through the morning...before lifting north midday. Across southern
and eastern areas...ceilings running 4-6 feet out near drt and
developing towards Sat/ssf midday. Ceilings gradually lowering to
MVFR at drt around 00z...Sat/ssf roughly 03z...and aus around or
after 06z. As an upper level disturbance approaches from the west
overnight...-ra will develop west to east...impacting drt 06z-12z
and Sat/ssf/aus terminals after 12z. IFR ceilings and MVFR
visibilties developing in the -ra/br at drt after 06z and MVFR
ceilings and visibilities at Sat/ssf/aus after 12z Sat. NE wind
around 15 kts early this morning at aus...7-12 kts at Sat...and
less than 7 kts at drt. Winds turning east this afternoon and evening
aus/Sat and southeast this afternoon at drt.
Previous discussion... /issued 402 am CST Friday Jan 30 2015/
Short term (today through saturday)...
As of 345 am...very light returns were seen on radar over The Hill
Country and spanning into Travis and Williamson counties. With
dewpoint depressions on the order of 20+ degrees...measurable
precipitation reaching the ground will be unlikely. Hi res models move
this activity out by middle morning so just left sprinkle mentions
through 15z for this.
Otherwise...a much cooler day today as the cooler air mass and
increasing clouds inhibit diurnal temperatures from rising much beyond 60
for the County Warning Area...if that. A steady northeast wind of 10-15 miles per hour will
persist through the morning and will shift to the east by tonight.
The onset of rain along the Rio Grande Valley looks to be right
around midnight tonight as the upper low just off the coast of
Southern California brings broad upper level energy into the
western half of Texas. During the overnight hours and through the
morning...a 40+ knots 850 mb low level jet will develop and begin feeding ample
moisture into the broad lift associated with the low. This should
result in widespread shower activity for much of the state
Saturday with Saturday afternoon and evening looking to be the
time frame in which the bulk of the rain would fall.
However...each forecast run is advertising less and less quantitative precipitation forecast with
this system. While the official quantitative precipitation forecast grids only call for a quarter
inch to three quarter inch totals through Sunday...do think there
is a decent shot at locations getting over an inch where the
heavier rains fall. With the very broad nature of the forcing with
this system...pinpointing those locations would be futile. But its
probably a safe bet to say the best shot at that would be the
northern half of the County Warning Area.
Long term (saturday night through thursday)...
The aforementioned system will clear out after a cold front
passage late Sunday. Believe some lingering shower activity will
persist in the moist airmass until the front dries out the area.
There is a slight chance we could see some thunder Sunday ahead of
the frontal passage. Forecast soundings are showing some decent
surface based cape and steep lapse rates 18z Sunday so some thunder
was introduced in the grids for this time period.
It is looking like the front will be a rather strong one once it
comes through...characterized by a return of temperatures in the
middle 30s for the Escarpment Monday morning and gusty winds up to 30
miles per hour overnight Sunday.
More seasonable temperatures will be in store for the rest of the
week. GFS/European model (ecmwf) continues to advertise the aforementioned upper
low to translate through southern Texas and the coastline bringing
probability of precipitation to the east and southeast Tuesday night but should be clear
of the area by Wednesday.
Preliminary point temps/pops...
Austin Camp Mabry 59 45 59 55 63 / 10 20 60 70 60
Austin Bergstrom international Airport 58 44 60 54 64 / 10 20 60 70 60
New Braunfels Muni Airport 58 46 61 56 65 / - 20 70 70 50
Burnet Muni Airport 55 42 56 51 60 / 10 30 80 70 50
del Rio International Airport 59 48 58 52 64 / 10 60 80 30 30
Georgetown Muni Airport 57 43 57 53 60 / 10 20 60 70 60
Hondo Muni Airport 59 46 61 54 67 / 10 50 70 60 50
San Marcos Muni Airport 58 45 61 55 64 / - 20 70 70 60
La Grange - Fayette regional 60 46 63 56 66 / - 10 50 70 60
San Antonio International Airport 58 47 60 56 66 / 10 30 70 60 50
Stinson Muni Airport 59 47 62 56 67 / - 30 70 60 50
public service/data collection...12