Austin / Travis County and South Central Texas Weather Update #5 Prepared by UT University/Incident Meteorologist Troy Kimmel 325pm CT - Sunday / 14 January 2018 .. Confidence Increasing on Potential Winter Weather Event Late Tomorrow Night into Tuesday .. NWS Issued Winter Storm Watch Now In Effect for all of South Central Texas Late Tomorrow Night through Tuesday Evening ... .. Now Monitoring a Secondary Disturbance Wednesday Night into Thursday with Renewed Possible Winter Weather Threat .. .. Ice / Sleet / Snow Accumulations Now Likely Monday Night Through Tuesday .. On this Sunday afternoon, I continue to watch an arctic air mass that is forecast to move southward into our area by late tomorrow night into Tuesday. After a brief warm up tomorrow (highs now forecast into the lower 60s), we'll see northerly winds increase and temperatures fall rapidly following the surface cold frontal passage which I am expecting in the 9pm to 12 midnight time period tomorrow night for the IH35 corridor. In the hours before and around the forecast time of the surface cold frontal passage, an upper air low pressure disturbance is forecast to track eastward over our area with clouds picking up late in the afternoon tomorrow with light rain and drizzle starting sometime around the dinner hour with the precipitation persisting as the front passes and continuing as much as 24 hours after the frontal passage as moisture overruns the much colder surface air moving into the area. Surface temperatures, following the cold frontal passage, will fall into the 30s quickly with freezing temperatures likely by 1am to 3am Tuesday morning then into the mid to upper 20s by daybreak with daytime highs on Tuesday (with the associated cloud cover) staying primarily in the 20s with a strong northerly wind and impressive wind chill in the low to mid teens. As temperatures fall following the frontal passage, any precipitation that is occurring locally would transition over to freezing rain, freezing drizzle and sleet (ice pellets) as we make our way into post midnight hours tomorrow night/Tuesday morning. As the atmospheric column aloft continues to cool, although we will see some freezing drizzle/freezing rain beginning by 3am Tuesday, I still think that precipitation would transition over to a little more sleet (ice pellets) and light snow after 8am Tuesday and that will continue through day Tuesday into Tuesday evening. Ice accumulations will average up to a tenth of an inch with isolated spots up to a quarter of an inch possible with additional sleet (ice pellets) and snow accumulation possible on top of this. As mentioned above, temperatures will likely fall below freezing in the predawn hours Tuesday and remain below freezing Tuesday and Tuesday night before rising back into mid and upper 30s Wednesday. As a result, hazardous/dangerous road conditions will result throughout the IH35 corridor and south central Texas for the late Monday night, Tuesday, Tuesday night into Wednesday time period given this forecast scenario. As it appears now, any precipitation associated with this first passing disturbance will end, with the departure of the disturbance, by late Tuesday night into Wednesday. Clouds may break a bit on Wednesday. However, another secondary upper air low pressure disturbance is now seen in the Wednesday night into Thursday time period with clouds increasing and precipitation chances returning for the period. Current thinking is that we could see some freezing rain, freezing drizzle, sleet (ice pellets) and snow once again but timing and amounts as well as exact temperature profiles are uncertain and forecast confidence is lower particularly with exact surface temperatures and precipitation type. As I mentioned previously, I continue to think that the models may be a little too warm with this incoming air mass - something we tend to see when you get this type of air mass this far south - so we are now seeing temperatures trending a little colder; this will be especially true if we see any ice/sleet/snow accumulations. The exact time of the frontal passage could be a little earlier than we're currently thinking - another possibility when you see these arctic fronts pressing southward through Texas. At this point locally, regarding the initial system tomorrow night into Tuesday, my confidence in the much colder air arriving continues to be very high with very high confidence that precipitation will occur. Being able to forecast exact precipitation type, at any given time in the forecast, is a lower confidence although I have very high confidence that we'll see freezing/frozen precipitation locally. Please understand that timing of the individual ingredients (of colder air arrival, atmospheric column temperatures aloft and the upper air disturbance) is indeed everything when you consider the forecast given this potential winter weather event for south central Texas. In other words, if one of our ingredients or timing changes, the forecast can and will change. I'll continue to keep you advised on both of these potential winter weather events. tk CALL TO ACTION: Please remain "weather aware" and listen for the latest weather statements, advisories, watches and warnings from the National Weather Service. Make sure that your NOAA All Hazards Weather Radio is operational and are set to alarm in case of severe and inclement weather watches and/or warnings. FOLLOWUP STATEMENTS: I will continue to keep you informed regarding this severe/inclement weather event. Any questions or if you have a storm report that I can forward on your behalf to the National Weather Service, please let me know at [email protected] GENERAL WEATHER INFORMATION LINKS: NWS/Austin-San Antonio Current Statements/Advisory/Watches/Warnings NWS/Austin-San Antonio Web Page NWS/Storm Prediction Center (Outlooks) NWS/Storm Prediction Center (Mesoscale Discussions - Severe Weather & Snow) NWS/Storm Prediction Center (Severe Thunderstorm/Tornado Watches) NWS/Weather Prediction Center (Mesoscale Discussions - Heavy Rain & Flooding) NWS/National Hurricane Center --- TXZ171>173-183>194-202>209-221-223-151100- /O.NEW.KEWX.WS.A.0001.180116T0600Z-180117T0000Z/ Llano-Burnet-Williamson-Val Verde-Edwards-Real-Kerr-Bandera- Gillespie-Kendall-Blanco-Hays-Travis-Bastrop-Lee-Kinney-Uvalde- Medina-Bexar-Comal-Guadalupe-Caldwell-Fayette-Wilson-Gonzales- Including the cities of Llano, Burnet, Georgetown, Del Rio, Rocksprings, Leakey, Kerrville, Bandera, Fredericksburg, Boerne, Blanco, San Marcos, Austin, Bastrop, Giddings, Bracketville, Uvalde, Hondo, San Antonio, New Braunfels, Seguin, Lockhart, La Grange, Floresville, and Gonzales 250 PM CST Sun Jan 14 2018 ...WINTER STORM WATCH IN EFFECT FROM LATE MONDAY NIGHT THROUGH TUESDAY AFTERNOON... * WHAT...Significant icing possible. The ice will result in dangerous travel conditions for late Monday tonight through the day on Tuesday. Total ice accumulations of up around one tenth of an inch are expected with isolated totals up to one quarter inch. * WHERE...Most of South Central Texas. * WHEN...From late Monday night through Tuesday evening. * ADDITIONAL DETAILS...In addition to the wintry precipitation and the impacts of accumlating freezing rain, sleet, and snow temperatures will be very cold. Temperatures will drop into the upper 20s by Tuesday afternoon and with strong north winds windchill values could drop into the teens. Overnight Tuesday into Wednesday as temperatures continue to drop some single digit windchill values will be possible in the Hill Country. PRECAUTIONARY/PREPAREDNESS ACTIONS... A Winter Storm Watch means there is potential for significant snow, sleet or ice accumulations that may impact travel. Continue to monitor the latest forecasts. &&