Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 04/18/19

National Weather Service Kansas City/Pleasant Hill MO
646 PM CDT Wed Apr 17 2019 .Discussion... Issued at 322 PM CDT WED APR 17 2019 First severe weather threat of the season expected to get underway late this afternoon and and evening as well-advertised cold front moves south over the region. Afternoon 1-min visible satellite imagery finally starting to show some breaks in the overlying status deck, which should help the atmosphere become weak to moderately unstable as MLCAPE values exceed 1500-2000 J/kg later today. Biggest uncertainty with this evening`s event continues to be the strength of the capping inversion, and whether enough frontal convergence and column lifting associated with large-scale ascent from an approaching shortwave to our northwest will be able to provide enough forcing to initiate surface based convection. In fact, latest ACARS soundings from MCI still show a fairly strong cap in place over our region, which may be showing some signs of weakening as latest 7.34 um water vapor imagery is showing the warmest brightness temperatures associated with the cap beginning to move east into eastern Missouri and western Illinois. Given this scenario, along with the fact that various high-res model solution`s suggest the cold front will eventually light up early this evening, we expect expect activity to get underway around the 00z time frame. An additional area of uncertainty continues to be just how much of this activity impacts the greater Kansas City Metro. Latest high- res model runs seem to want to develop convection a little further north than previously expected, which means a sizable portion of the KC metro may be under the gun for developing storms later this evening. That said, best chances still look to occur along and south of the I-35 corridor, with activity decreasing in areal extent the further north one goes. In any event, given sufficient buoyancy for ascent, along with unidirectional shear profiles through the atmospheric column, it currently appears the main threats will be large hail and strong winds owing to steep low and mid-level lapse rates along with decent downdraft CAPE values (500-1000 J/kg) which should allow adequate mixing of thunderstorm generated downdrafts to the surface. Storm mode will likely be messy as deep-layered shear vectors will become increasingly parallel to the incoming boundary as the evening hours progress. While enough shear may exist for a few isolated storms initially, the prevailing idea is that activity will congeal into a MCS fairly quickly this evening. While an isolated tornado or two cannot be ruled out with initial discrete activity, the main threats will undoubtedly be large hail and strong winds, especially as activity becomes more and more linear in nature. In addition to the severe wx threat, the other concern will be the potential for heavy rainfall as models continue to paint 1+" amounts across southern portions of the fcst area, especially south of Route 50. Fortunately, 1- and 3-hr flash flood guidance values largely remain over 2" for a good portion of the area, which combined with the expectation that the heaviest rains will occur over a non-urban landscape, should promote a limited flash flood threat despite PWAT values exceeding the 90th percentile for this time of year. Rain/storms should gradually start working to the south and east during the predawn hours which should be followed by a drying trend on Thursday. Temperatures will be noticeably cooler both Thursday and Friday as cold air advection remains in place both days. From this point forward, the fcst largely looks dry through the first half of the weekend before a southward sagging cold front brings the next chance for organized rainfall to the area on Easter Sunday. And looking even further out, unsettled weather looks to remain across the region through midweek as longwave troughing takes hold over the southern Rockies and Plains, which should allow several migrating disturbances to pass overhead in persistent southwesterly flow aloft. && .Aviation...(For the 00Z TAFS through 00Z Thursday Evening) Issued at 646 PM CDT WED APR 17 2019 Cold front moving slowly southeastward across all TAF sites will arrive between 00z-02z, bringing through a broken line of storms and a sharp wind shift to the northwest. Ceilings should be mostly VFR but may drop briefly below 3 kft in individual storms. Otherwise, no significant aviation hazards are expected. && .EAX WATCHES/WARNINGS/ADVISORIES... KS...NONE. MO...NONE. && $$ Discussion...32 Aviation...Laflin
Area Forecast Discussion
National Weather Service Austin/San Antonio TX
705 PM CDT Wed Apr 17 2019 .AVIATION... /00Z TAFS/ New cell forming south of Dryden would suggest a slight delay in convective activity around DRT, despite explosive storm growth expected in the next 1-2 hours. It`s position is well lined up the the dryline which would take about 2 hours to move that far ESE. Other cells forming over the Burro mountaintops could spread NE slightly earlier. Meanwhile CI Probabilities over the capped shower activity east of I-35 have occasionally spiked over 60 percent, but the view on satellite and out the window with ragged cloud tops does not suggest that the cap will break ahead of the organized storm clusters to the west. Meso model trends and slow onset of destabilization would suggest that the beginning of the squall lines rolling into the I-35 terminals will be at or after midnight. Severe threats will be addressed about an hour or two in advance of the cells moving into the I-35 Terminals. but only about 30-45 minutes lead time can be expected at DRT where the storms are more isolated. Rapid improvements can be expected after 08Z at SAT/SSF and 09Z at AUS. Gusty winds and fair skies should round out the end of the TAF periods with models showing the winds not picking up significantly until around 15Z or later. && .PREV DISCUSSION... /ISSUED 305 PM CDT Wed Apr 17 2019/ SHORT TERM (Tonight through Thursday Night)... Current surface observations across Texas show the dryline extending across West Texas (roughly from a Childress to Snyder to Ozona line), and the cold front pushing south across the Texas Panhandle, having just made it through Amarillo. It is this cold front that will spur on the thunderstorms expected tonight into Thursday morning. Current short-term forecast soundings and the aircraft soundings from AUS and SAT show the atmosphere still mostly capped across South Central Texas. With the capped atmosphere currently storms should hold off through the rest of the afternoon and into the early evening hours. With the dryline moving east and the front pushing rapidly south the front will overtake the dryline and be the lift that South Central Texas needs for storms. There is plenty of moisture in place with dewpoints in the upper 60s and 70s. The HRRR and other high resolution forecast models show storm initiation between 7pm and 9pm across the Edwards Plateau. When storms do initially form the discrete storms will have a very good chance of producing large hail to do the environment with 2500 to 3000 j/kg of instability/CAPE. All of the models show these discrete storms forming into a line of storms as they approach the hill country between 10pm and 1am. With 50 knots or more of bulk shear in place the severe weather threat will continue as the line approach the I-35 corridor. With the transition into a linear MCS the threat will also transition from a large hail threat to a damaging straight-line wind threat within bowing sections of the line. The line should approach the I-35 corridor between about 11pm and 2am. Based on all of this a good portion of the Hill Country and I-35 corridor have been included in the Enhanced Risk from the Storm Prediction Center, with most of the area in a significant hail hashed area as well. Basically our entire area is in the slight risk, again mainly for the large hail and the damaging wind threat. There is a low risk of tornadoes, but the main risk will be more to the NE towards the ArkLaTex region. As the storms push east of I-35 a new threat will be introduced. While rainfall totals across the area will generally be 1/4 of an inch to 1 inch, there has been increasing signals that parts of the area east of I-35 could see isolated totals as high as 2-3 inches. This could cause some localized minor flooding issues, especially in areas that have seen decent rains of late. The line of storms will continues its eastward progression and be east of the area by morning rush hour on Thursday. In the wake of the line of storms and cold front a drier airmass filters in for Thursday. As skies clear strong north and northwest winds increase. Some portions of the Rio Grande Plains could be close to wind advisory criteria. In addition, with the lower relative humidity values dropping down to 20-30 percent elevated to near critical fire weather conditions are expected across the Rio Grande Plains and Edwards Plateau. For the rest of the area afternoon highs will be a few degrees below normal from the mid 70s to low 80s. Overnight lows Thursday into Friday will also run a few degrees below normal in the low to mid 50s. LONG TERM (Friday through Wednesday)... In the wake of the upper trough that will bring storms tonight into Thursday morning northwest flow will build in aloft on Friday with sunny skies continuing. With northerly flow aloft and at the surface highs Friday will continue to run a few degrees below normal along the I-35 corridor, with near normal temps along the Rio Grande in the mid 70s to mid 80s. Southerly flow returns Saturday morning as an upper level ridge works across Texas. Highs for the weekend will warm into the 80s area wide, and should flirt with 90 degrees along the Rio Grande Plains. Clouds return on Monday ahead of the next trough, with continued seasonal temperatures. All of the long range models (GFS, Canadian, and ECMWF) show the trough approaching Tuesday, and moving across the OK/TX Red River Valley Wednesday into Thursday. With the approaching trough and the moist atmosphere rain chances begin Monday night and increase through the day Tuesday. Similar to the system moving through today a cold front will approach Tuesday night and Wednesday further enhancing rainfall. && .PRELIMINARY POINT TEMPS/POPS... Austin Camp Mabry 61 75 54 76 53 / 80 10 0 0 0 Austin Bergstrom Intl Airport 60 75 53 76 51 / 80 10 0 0 0 New Braunfels Muni Airport 59 76 52 78 52 / 80 10 0 0 0 Burnet Muni Airport 59 72 52 75 51 / 80 10 0 0 0 Del Rio Intl Airport 63 82 55 85 58 / 40 0 0 0 0 Georgetown Muni Airport 59 73 52 75 51 / 80 10 0 0 0 Hondo Muni Airport 58 79 52 82 53 / 80 0 0 0 0 San Marcos Muni Airport 59 76 52 77 51 / 80 10 0 0 0 La Grange - Fayette Regional 63 77 53 75 51 / 90 20 0 0 0 San Antonio Intl Airport 60 77 54 80 54 / 80 - 0 0 0 Stinson Muni Airport 60 77 55 80 54 / 70 - 0 0 0 && .EWX WATCHES/WARNINGS/ADVISORIES... None. && $$ Aviation...Oaks Short-Term/Long-Term...04 Public Service/Data Collection...BMW
Area Forecast Discussion
National Weather Service Houston/Galveston TX
954 PM CDT Wed Apr 17 2019 .DISCUSSION... At 9 PM, high pressure was located over the SE US and low pressure was located over SW OK with a dry line extending south from the low across the western TX. Some light showers continue to stream into area from the Gulf but precip has remain widely scattered and generally light. All that is about to change as a line of storms approaches the region from the west. Betweem 06-09z, 300 mb winds split as an upper low over West Texas shifts east and SE TX will lie in a well defined jet couplet. The PW values surge to 1.90 inches over the western half of SE TX and there is some weak surface convergence along what looks like a weak outflow. On water vapor imagery there appears to be two short waves lined up and the first of these will approach the region around midnight and help maintain the convection over Central Texas as it approaches SE TX. Instability parameters are impressive with LI values near -10, CAPE values 2800 J/Kg and Helicity around 220. SPC has expanded the Enhanced Risk a bit east and this seems like the right call based on the instability and the approaching the short wave. SPC has also expanded the Slight Risk further east and this now includes the Houston area. AMDAR soundings still show a strong capping inversion in place at 700 mb and the million dollar question is, will the cap hold or will it break. Short term guidance has been trnding a bit more aggressively with the HRRR and TT WRF all showing convection approaching Houston around sunrise as the second short wave approaches the region from the southwest. Feel the combination of the short wave and strong upper level diffluence will help to erode the cap and allow a second area of storms to redevelop over the SW zones and move NE toward Houston and points northeastward. Instability isn`t quite as impressive as points to our west but there could still be some strong storms with gusty winds. Speaking of winds, the actual front will mot reach the coast until about 18z. The winds will become N-NW in the wake of the front and will become strong. A Wind Advisory will likely be required for a large part of SE TX Thursday afternoon. 43 && .PREV DISCUSSION... /ISSUED 704 PM CDT Wed Apr 17 2019/ AVIATION... A mix of MVFR/IFR ceilings across SE TX this evening, should continue to lower in height to IFR through the overnight hours and into tomorrow morning. Scattered light showers are continuing to develop out ahead of tonight`s cold front. E/SE winds remain gusty but should slacken ahead of the frontal passage tonight, and increase in speed out of the W/NW once again tomorrow morning. Strong to severe storms with gusty winds (primary hazard) and hail will be possible as the front passes through the region. The front should arrive at CLL shortly after midnight and reach the coastal terminals before sunrise. Ceilings will be slow to improve tomorrow morning, but anticipating VFR criteria by early afternoon area wide. Hathaway PREV DISCUSSION... /ISSUED 340 PM CDT Wed Apr 17 2019/ NEAR TERM [Through Tonight]... It has been a pretty soupy day today with overcast stratocu and continued moisture advection over SE Texas. Cloud cover has limited heating today which means there is not quite as much instability over the area as there could be and the capping inversion remains strong. AMDAR sounding from 20Z still shows a strong cap near 700mb at 12C with very steep lapse rates above that EML inversion. Surface Theta-E axis continues to run through central Texas and seeing some showers form on the eastern edge of this axis near the Brazos Valley. Right now there does not appear to be enough large scale lift to help erode the cap or a jet streak for divergence. If anything, water vapor imagery shows a jet streak departing the area so look for neutral/subsident vertical motion to continue the next few hours. The upper level low has moved into New Mexico with one part of the polar jet coming across the Big Bend and West Texas. Southern part of this jet should spread over south Texas overnight and into parts of SE Texas by 12Z Thursday. LLJ will be strong but veer around to the SW or WSW ahead of the front and strong jet forcing. There is still a very good chance of showers and thunderstorms mainly 06Z to 12Z Thursday. The WRF/HRRR continue to show a squall line moving into the area around 06-09Z with it becoming weaker 09-12Z Thursday. This is just in time for Houston morning commute from 4AM to 8AM Thursday. We still think SPC outlook is on track especially concerning the capping limiting the severe threat closer to Houston and the coast. There could be some locally heavy rainfall as well but that may depend upon available instability and lift with the higher moisture. Again capping will be the main limiting factor. Upper level lift may just be enough out of phase to keep the cap in place. These are finer details that need to be monitored overnight as convection develops and adjust based on further analysis/guidance. Overpeck SHORT TERM [Thursday Through Friday Night]... Deep upper level trough should develop east of the area over the Mississippi River Valley by Friday morning. Line of storms should be exiting the region Thursday morning as the initial trough axis moves past the area into Louisiana. A cold front at the surface should usher in cooler/drier air into the region for the holiday weekend. We will need to keep an eye on fire weather conditions as winds will be pretty gusty from the north with after RH values getting down around 30-35 percent. Overpeck LONG TERM [Saturday Through Wednesday]... Upper level ridging should continue over the area for the weekend with one short wave trough moving across the southern Plains Sunday as another trough develops over the Rockies Sunday night. GFS/ECMWF/Canadian all have fairly different solutions for the upper level pattern for early next week from Monday into Wednesday. GFS has the trough splitting with still some troughing back to the west while the ECMWF/Canadian have a slower evolution of the trough. At this point lean more on a slower moving trough which the models in some shape/form somewhat agree with on Wednesday next week. However the surface details are all very different and rather not focus on those details since we are looking at the day 6-8 part of the forecast. Forecast will show rain chances slowly ramping up Monday through Wednesday. Overpeck MARINE... Moderate to strong onshore winds and building seas are expected to develop this afternoon and tonight as the gradient tightens ahead of the incoming storm system. Showers and thunderstorms will be pushing west to east across the waters tomorrow morning with a westerly wind shift. The storm system`s cold front is still expected to push through the area in the afternoon with northwest winds increasing in its wake. There could be a period of lower winds and seas (below caution/advisory levels) just ahead of the storms and again just behind the storms, but winds and seas should come back up to those levels after the front moves through the area. Could see some minor overwash at Highway 87/124 on the Bolivar Peninsula tonight around high tide time (~4am), and then we`ll need to keep an eye on possible low water conditions late Thursday night and on into Friday morning at low tide time across northern bay locations. Winds will weaken late Friday an on into Friday night as high pressure builds into the area. Onshore winds come back to the area on Saturday and persist for the remainder of the weekend and on into at least the first half of next week. 42 && .PRELIMINARY POINT TEMPS/POPS... College Station (CLL) 80 63 76 52 74 / 40 100 40 0 0 Houston (IAH) 78 66 80 54 75 / 40 90 80 0 0 Galveston (GLS) 76 70 78 60 74 / 40 60 80 0 0 && .HGX WATCHES/WARNINGS/ADVISORIES... TX...NONE. GM...SMALL CRAFT SHOULD EXERCISE CAUTION until 6 AM CDT Thursday for the following zones: Galveston Bay...Matagorda Bay. Small Craft Advisory until 6 AM CDT Thursday for the following zones: Coastal waters from Freeport to Matagorda Ship Channel TX out 20 NM...Coastal waters from High Island to Freeport TX out 20 NM...Waters from Freeport to Matagorda Ship Channel TX from 20 to 60 NM...Waters from High Island to Freeport TX from 20 to 60 NM. && $$ Discussion...43