345
FXUS64 KEWX 271159
AFDEWX

Area Forecast Discussion
National Weather Service Austin/San Antonio TX
659 AM CDT Mon May 27 2024

...New AVIATION...

.SHORT TERM...
(Today through Tuesday)
Issued at 309 AM CDT Mon May 27 2024

Our Excessive Heat/Heat Advisory event continues as the final day of
unusually hot weather for the month of May. Grid populate schemes
were not adjusted much off the previous forecast and NBM as the day-
to-day fluctuations in how much mixing occurs over our western half
of counties has been a bit of a goose-chase with pockets of higher
moisture holding into localized areas to vary high temps by 10
degrees from nearby areas. Yesterday`s high temperatures and heat
indices versus the forecast were again a mixed bag, with DRT living
up to it`s billing for a new monthly high temperature record for
May, while over central counties an outflow or undular bore effect
seemingly held onto a deeper low cloud layer that prevented the I-35
corridor counties from mixing out to see those triple digit temps.
Thus, if we get a similar day of thicker low clouds over I-35,
Austin metro looks to possibly get out of the month of May without
seeing the first 100 degree days of the year. However, the first 100
degree day is still within reach for one more day. Compared to
yesterday, the forecast west or north winds above the morning
boundary layer look weaker, so one would think that the mixing of
low clouds would be extended closer to noon as it was yesterday.
Needless to say, forecasting excessive heat criteria weather early
in the warm season is much more challenging than in the middle of
the summer when the low level moist layer is less established. For
this long-winded explanation of uncertainty, we opted to leave the
Advisory and Warning counties unchanged, as the fluctuation of max
heat index values shouldn`t be much more than a couple degree
adjustment off the values we saw Sunday. This still means some areas
getting up to 115, and ambient temperatures along the Rio Grande
still threatening to reach 110.

As we get close to the end of the day there could be an increased
risk of elevated convection with any areas that mix out the lower
moisture could set up with an inverted-V sounding, and surface
convergence from a dry-line and approaching cold front could pull
together an isolated deep layer convective cell. Either scenario
could provide a severe threat. The transport of mid level moisture
seems to be the more predictable scenario, but a triple point
settling into the Hill Country could improve confidence on a locally
enhanced storm and severe weather threat. Then there is also an
outside chance convection gets firing off the slopes of higher
terrain to the west. With the upper ridging influence holding back
most areas from getting convection, the low-end Marginal (1 of 5)
Risk is the best we can offer as a message for such a broad area of
possibilities.

Some outflows and seepage of north winds from a weak cool front
overnight should bring down some of those evening heat index values,
and reduce the potential record high min temps for all but the areas
near the Rio Grande. Milder weather and higher amounts of mid and
high clouds will help with a more typically hot late May temperature
profile for Tuesday. Late in the day, shortwave activity increases
from the west and brings about a potentially more impactful storm
event. With the majority of the event taking place after 00Z, will
save the severe risk messaging for the long term forecaster.

&&

.LONG TERM...
(Tuesday night through Sunday)
Issued at 309 AM CDT Mon May 27 2024

Scattered convection will likely be ongoing at the beginning of the
long-term portion of the forecast Tuesday night. Should see some
possible scattered clusters of activity moving southeast through the
CWA with the initial activity in the western CWA. Not all areas will
likely see rain Tuesday night, but some locally heavy rainfall and a
strong to severe storm will be possible. Most of the CWA is in a
slight risk (Level 2 of 5) of severe storms in the new Day 2 outlook
from SPC. Large hail and damaging winds will be the main risk of
severe storms with this activity.

The risk for daily isolated to scattered storms continues for much
of the long-term portion of the forecast. The forecast will likely
be highly uncertain through the remainder of the period as much of
what happens each day will depend on what occurred the previous day.
It is good news that we have some chances for rain this week and we
are hopeful that most locations will pick up some rain at some point
this week. Instability and moisture amounts will remain elevated and
locally heavy rainfall and a strong to severe storm will be possible
as well most days. Temperatures during the extended forecast period
will be closer to climatological values for this time of year. Highs
will range from the upper 80s in the northeast CWA to near 100 in
the southwestern CWA. Low temperatures will mainly be in the 70s for
most locations. This is also good news in comparison to the early
season heat wave we have been seeing the past several days.

&&

.AVIATION...
(12Z TAFS)
Issued at 652 AM CDT Mon May 27 2024

12Z cigs are mainly IFR around I-35, and a brief IFR or MVR cig could
drift west again into DRT for an hour or two. Improvent to VFR was
left as similar to persistence and earlier projections, as the late
arrival of low cigs looks fairly thick on satellite nighttime
microphysics. Due to the threat of wind shifts, we went ahead with a
Prob30 for thunder along I-35 for early evening. Late night clouds
projected again after midnight, but simply went with NAM MOS as a
guess on how long the low clouds last into the morning.

&&

.PRELIMINARY POINT TEMPS/POPS...
Austin Camp Mabry              99  75  94  73 /  20  20  30  40
Austin Bergstrom Intl Airport  98  74  94  71 /  20  20  30  40
New Braunfels Muni Airport    100  75  96  73 /  20  20  20  30
Burnet Muni Airport            95  72  91  71 /  20  20  30  50
Del Rio Intl Airport          108  81  99  76 /  20  10  40  30
Georgetown Muni Airport        96  73  92  71 /  20  30  30  40
Hondo Muni Airport            101  75  97  72 /  10  20  20  40
San Marcos Muni Airport        98  74  95  71 /  20  20  30  30
La Grange - Fayette Regional   98  75  94  75 /  20  20  20  20
San Antonio Intl Airport       99  75  96  74 /  20  20  20  30
Stinson Muni Airport          102  77  97  75 /  10  20  20  30

&&

.EWX WATCHES/WARNINGS/ADVISORIES...
Heat Advisory until 8 PM CDT this evening for Kinney-Maverick-
Uvalde-Val Verde-Williamson-Zavala.

Excessive Heat Warning until 8 PM CDT this evening for Atascosa-
Bastrop-Bexar-Caldwell-Comal-De Witt-Dimmit-Fayette-Frio-Gonzales-
Guadalupe-Hays-Karnes-Lavaca-Lee-Medina-Travis-Wilson.

&&

$$

Short-Term...18
Long-Term...29
Aviation...18