Area Forecast Discussion
Issued by NWS Austin/San Antonio, TX
Issued by NWS Austin/San Antonio, TX
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278 FXUS64 KEWX 270810 AFDEWX Area Forecast Discussion National Weather Service Austin/San Antonio TX 310 AM CDT Mon May 27 2024 ...New SHORT TERM, LONG TERM, CLIMATE... .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... (06Z TAFS) Issued at 1240 AM CDT Mon May 27 2024 Light E/S winds tonight will probably enable some of the low clouds to dip briefly into IFR. Some of the NAM MOS guidance was depicting VLIFR vsbys around the San Antonio area, so a drop to LIFR vsbys may need to be considered briefly. Typically when the overnight is this warm, the air remains too well mixed for dense fog, especially considering the very low soil moisture levels around SAT/SSF. Late morning MVFR cigs may mix out faster today than Sunday. In the 12Z update, we may consider a faster return to VFR well before 18Z, based on the limited amount of low cloud signals we see on satellite at the current time. Isolated storms are not accounted for in the late afternoon period in regards to wind shifts, but that may need to be adjusted later as storm outflows could expand out significant distances should storms develop at the right time. For now, we just have a subtle suggestion of 2 mid/high cloud layers to signal some instability moving into the region. && .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