Forecast Discussions mentioning any of
"ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 07/26/20
Area Forecast Discussion
National Weather Service Austin/San Antonio TX
636 PM CDT Sat Jul 25 2020
Hurricane Hanna will move across Deep South Texas tonight into Mexico
on Sunday. Bands of SHRA/ISOLD TSRA will rotate around the center
with occasional passages near or over the TAF sites. Have maintained
VCSH mention through the period. PROBs are too low to mention TSRA
at this time. VFR CIGs/VSBYs prevail, except late tonight into Sunday
morning and in bands of SHRA/TSRA when MVFR/brief IFR CIGS and/or
VSBYs are possible. Easterly winds of 5 to 15 KTs prevail with gusts
to 30 KTs possible.
.PREV DISCUSSION... /ISSUED 254 PM CDT Sat Jul 25 2020/
SHORT TERM (Tonight through Sunday Night)...
Afternoon radar imagery and Hurricane Hunter aircraft data show the
center of `Hanna` is located roughly 55 miles east-northeast of Port
Mansfield. `Hanna` has strengthened recently with maximum sustained
winds near 85 mph. A general westward track is expected through the
afternoon and evening hours. More information on Hanna can be found
from the National Hurricane Center.
A little closer to home, outer rain bands continue to move in from
the east. We should see this trend continue through the afternoon
hours as satellite imagery shows bands of convection developing off
the upper Texas coast. Greater coverage of showers and storms will
likely remain near the coastal plains through this evening. However,
we have seen some convection develop as far west as Del Rio, so all
of south central Texas can expect a chance for rain through at least
early this evening. We have seen some concerns for tropical
tornadoes across the coastal plains and will continue to monitor
this carefully through the afternoon hours. Breaks in the cloud
cover should allow the low-levels to destabilize, supporting
a few stronger updrafts.
A general decrease in activity is likely across most of the region
tonight as daytime heating ends. However, some occasional rounds of
convection will still move into areas generally along and south of
Highway 90. On Sunday, most of the region should again see an uptick
in shower and thunderstorm activity as daytime heating helps
destabilize the atmosphere. As mentioned above, the higher rainfall
amounts will be confined to areas where bands of heavier
precipitation develops. These bands will be difficult to forecast,
but it appears areas along and south of a Del Rio to Austin to La
Grange line will be favored.
Rainfall amounts continue to trend downward slightly as the main
circulation remains well south of the region. In the short term
period, we could see average amounts of 1-1.5 inches through Sunday
night for areas generally along and south of an Eagle Pass to San
Antonio to Austin line. As previously mentioned, there will be some
areas that get a little more than this and some minor, localized
flooding is possible, especially south of Highway 90/east of I-35
LONG TERM (Monday through Saturday)...
With Hanna dissipating in the higher terrains of Mexico, residual
moisture will continue rain chances in the afternoon for the
beginning of the week. With little to hold down convection, isolated
pop up showers and storms will be the main weather challenge. The
upper ridge begins to take back the reigns on the area by Thursday,
and rain chances reduce again as we head into the weekend. With the
ridge back in place, temperatures also begin to increase. Anticipate
temperatures back above normal by Thursday.
.PRELIMINARY POINT TEMPS/POPS...
Austin Camp Mabry 76 91 75 90 75 / 40 60 30 40 20
Austin Bergstrom Intl Airport 76 90 74 89 74 / 40 60 30 40 20
New Braunfels Muni Airport 75 90 74 88 74 / 60 60 30 50 20
Burnet Muni Airport 74 90 72 90 73 / 30 50 20 30 10
Del Rio Intl Airport 77 90 75 93 75 / 40 50 50 50 20
Georgetown Muni Airport 75 91 74 91 75 / 30 50 20 30 20
Hondo Muni Airport 76 89 75 92 74 / 60 70 40 50 20
San Marcos Muni Airport 75 90 74 90 74 / 50 60 30 40 20
La Grange - Fayette Regional 77 91 75 90 76 / 50 60 30 50 20
San Antonio Intl Airport 76 90 75 90 76 / 60 70 40 50 20
Stinson Muni Airport 76 89 75 89 76 / 60 70 40 50 20
Area Forecast Discussion
National Weather Service Phoenix AZ
450 PM MST Sat Jul 25 2020
Chances for showers and thunderstorms will generally favor the
higher terrain north and east of Phoenix this weekend. Southwestern
Arizona and southeastern California will remain dry as the moisture
remains farther east. High pressure will build across Arizona next
week, resulting in a return to above normal temperatures and below
normal precipitation chances.
Latest water vapor imagery reveals a well-defined PVD across Sonora,
with deeper moisture displaced north and east of the vort max across
eastern Arizona. Further west, another closed low is evident across
California. Ahead of this system, relatively dry Pacific air is
being transported into southern California and western Arizona.
Latest ACARS soundings confirm the drying around 850 mb, which is
beginning to make its way to the surface across the lower deserts.
Meanwhile, further aloft at 700 mb, the latest RAP streamline
analysis depicts a weak anticyclonic flow, resulting in
light north and northwesterly winds from Maricopa County eastward.
General consensus amongst the HREF CAMs is that the best chance for
showers and thunderstorms this afternoon will remain confined to the
higher terrain of southern Gila County in the vicinity of the
deeper moisture, and along the moisture gradient across northeastern
Maricopa County. Main concern for today will be slow-moving cells
that have the potential to produce heavy rain and perhaps even
isolated flash flooding near the burn scars.
With the aforementioned northerly component to the flow, storm
motion will generally be southward towards the foothills and lower
deserts. CAPE may be high enough for isolated storms to survive
into the foothills, however the environment remains unfavorable for
convection in the lower deserts with the warm layer near 450 mb
yielding weak mid-level lapse rates. Even the most aggressive CAMs
indicate little potential for outflows to reach the Valley and
consequently PoPs remain below 5 percent for the Phoenix area.
The forecast for tomorrow looks conceptually similar to today but
with slightly lower PoPs over the higher terrain and just
minuscule chances for the lower desert as drier air continues to
overtake more of the region. Guidance trends consistently support
this evolution, but as always the case with convection, the
outcomes from the previous day`s events can change the forecast
from day-to-day. Drier conditions will eventually solidify by
early next week confining most thunderstorm activity over the
higher terrain well east of Phoenix, and over southeastern
The GEFS and EPS are both in pretty good agreement with the
subtropical ridge re-centering over Arizona, which is not the most
ideal location for monsoon rains. Given this, most ensemble members
from both sets of guidance are very bearish regarding rain chances
in Phoenix and most everywhere else in the forecast area beyond this
weekend. If the guidance is off, and the ridge positions closer to
the Four Corners area instead, we might be able to realize a more
favorable monsoonal pattern. Another wrinkle to consider is the
potential implications from Tropical Storm Hanna but confidence in
any particular development is very low at this time.
Otherwise, drier conditions combined with increasing atmospheric
thickness underneath the ridge will support a warming trend.
Forecast highs will approach 110 degrees Sunday/Monday, and remain
in the 108-113 degree range for much of next week. As of now, no
heat watches or warnings are planned but the increased heat risk
will require monitoring.
.AVIATION...Updated at 2350Z.
South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:
With SHRA/TS remaining well east of Phoenix through Sunday evening,
identifying wind shifts will be the primary forecasting challenge.
Storm outflows should be far less defined this evening versus
previous days, and chances of distinct wind shifts are only remote.
A wind shift to the traditional overnight easterly may be more
delayed than usual, and a switch at KPHX may not occur until after
sunrise Sunday, if at all. Otherwise, light westerly winds will
settle over the region by early afternoon with a somewhat better
chance of a more organized easterly outflow boundary later Sunday
Southeast California/Southwest Arizona including KIPL and KBLH:
No substantial aviation issues will exist through Sunday night under
clear skies. Trends in wind shifts will be similar to the past
several days with directions oscillating between SE and SW, and in
many cases variable for extended periods.
Tuesday through Saturday:
High pressure will build across Arizona, resulting in a return to
above normal temperatures and below normal precipitation chances.
Nevertheless, moisture will be sufficient for at least isolated
storms each day, particularly across the higher terrain north and
east of Phoenix. Min RHs will generally fall into the teens each
afternoon. Meanwhile, winds will be light and diurnal each day,
except in the vicinity of with thunderstorms.
.SPOTTER INFORMATION STATEMENT...
Spotters should follow standard reporting procedures.