Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 04/17/17


Area Forecast Discussion
National Weather Service Austin/San Antonio TX
934 PM CDT Sun Apr 16 2017 .UPDATE... /FFA ISSUANCE/ Convective initiation was handled relatively well by the HRRR which suggested some heavier rainfall to occur vs some of the coarser models. With this trend, the likelihood of a 5+ inch rain over western parts of the CWA increases, as we are meeting the 2 standard deviation pwat criteria for flood potential. Later tonight, a possible expansion of the watch may need to be considered should the ARW verify with a more progressive solution into northern counties. For now will expect the broad circulation seen in stratiform rain over the Serranias del Burros should delay this eastward expansion, and downdrafts to dictate a more slow eastward progression. Other meso model features suggest additional heavy rains entering the area from the north late Monday, so at some point, parts of Central TX will need to be considered at least for Monday. Low end severe weather remains a concern as well, given moderate values of CAPE and shear. && .PREV DISCUSSION... /ISSUED 749 PM CDT Sun Apr 16 2017/ UPDATE... /HIGHLIGHTING LOCALLY HEAVY RAIN...INCREASED POPS/ Radar echoes are increasing rapidly over western counties to suggest the more bullish storm scenario depicted by the last several HRRR runs. Given the earlier progress and location of convective initiation, felt the need to increase pops farther east for late tonight and boost overall QPF and mention locally heavy rainfall in the zones. These threats are already covered in the HWO. PREV DISCUSSION... /ISSUED 639 PM CDT Sun Apr 16 2017/ AVIATION... SHRA/TSRA are ongoing over the Big Bend to Serranias del Burro with weak SHRA over Central Texas due to an MCV drifting to the east. Will go with VCSH and tempo VCTS at KDRT this evening as a consensus of Hi-res models and radar trends continue show movement to the east with formation into an MCS. Have introduced VCSH at KAUS due radar trends for this evening. The western MCS will slowly weaken overnight encountering a capped environment. Redevelopment is expected Monday and maintain VCSH for the I-35 TAFs for the morning, then introduce VCTS for the afternoon hours as the cap erodes. VFR skies start this TAF cycle. CIGs lower to MVFR later this evening, then IFR as patchy BR and MVFR VSBYs develop overnight into morning. CIGS/VSBYs rise to VFR midday to afternoon. IFR/MVFR CIGs/VSBYs are possible in any SHRA/TSRA. MVFR CIGs return later Monday evening. S to SE winds 5 to 14 KTs will prevail. Gusts to 45 KTs are possible in TSRA downdrafts with gusts to 22 KTs possible elsewhere. PREV DISCUSSION... /ISSUED 337 PM CDT Sun Apr 16 2017/ SHORT TERM (Tonight through Monday Night)... Broken to overcast skies blanket most of South Central Texas this afternoon as a weak midlevel shortwave near Llano County continues to move northeast. Elevated echoes continue to show up on radar over the Hill Country associated with this feature, but these echoes have been evaporating before reaching the surface. Although weaker than this time yesterday afternoon, a relatively strong capping inversion just above 800 mb continues to show up on aircraft soundings at SAT and AUS. Most hi-res model trends continue to show that this cap will hold for the next several hours over the I-35 corridor, but a few notable outlier including the Texas Tech WRF indicate some storms may develop over the Hill Country and move southeast by 5-6 pm. These solutions seem a bit unrealistic given the movement of this shortwave and lack of any convective development aside from a brief cell that went up in Sutton County. Thus, the current forecast follows the broader model consensus and trends that this cap will hold for the I-35 corridor, with the best chances for any isolated thunderstorms confined to the Hill Country and Edwards Plateau this afternoon. Showers and thunderstorms continue to develop along a dryline in Big Bend and off the Serranias del Burros in Mexico as a stronger shortwave evident on WV imagery is providing some additional dynamic forcing via PVA and cooling aloft. There is quite a bit of model uncertainty in how these cells will organize and move to the east- southeast this evening, but it does appear that they will cross the border during the early evening hours and affect at least the Rio Grande Plains where 60 POPs have been added. Shear parameters continue to be rather unimpressive, but CAPE values peaking around 3000 J/kg just before sunrise and steep lapse rates aloft will support a marginal risk of some strong to severe thunderstorms early this evening in the Rio Grande Plains. Damaging winds will probably the main threats with these storms, but quarter to possibly golf ball size hail will be possible with multicellular clusters if this system does not become more linear before crossing the border. Most models are showing that the strength of the capping inversion and weakening dynamics from the shortwave will be enough to suppress convection tonight along and east of the I-35 corridor, but have maintained 20-30 POPs just in case a stronger cold pool develops to help propagate the system further east. Rain amounts should generally remain below one inch, but some locally higher amounts are possible in the Rio Grande Plains and Edwards Plateau that may cause isolated instances of flash flooding or (more likely) flood advisories. There will most likely be a brief lull late in the overnight hours and early tomorrow morning as a closed midlevel low or MCV left behind from tonight`s convection moves over the southern portion of South Central Texas. Cooling aloft with this feature should help weaken the cap at 800 mb enough to promote at least scattered if not widespread showers and thunderstorms by late morning and the afternoon. The best chances will be over the eastern two-thirds of the region as the western third should have NVA aloft on the backside of the low. Shear parameters still appear to be pretty weak, but moderate instability may support some strong to marginally severe storms, particularly across our southeastern-most counties. Rain chances will decrease by the evening hours, but have maintained 203- POPS over the entire region into Monday evening to account for a few model solution that suggest a complex north of our area will move to the south-southwest on the backside of the closed midlevel low later tomorrow afternoon and evening. LONG TERM (Tuesday through Sunday)... Rain chances will begin to decrease from west to east on Tuesday as the midlevel low or shear axis continues to weaken and slide to the east. However, this shear axis should be enough to support the development of isolated to scattered showers and thunderstorms along and east of Interstate 35 with the best chances in the Coastal Plains. A mid-to-upper level ridge will build in from the southwest on Wednesday and intensify further on Thursday to reestablish the capping inversion aloft and help increase temperatures into the mid 80 to lower 90s for the rest of the work week. Winds on Friday will strengthen ahead of a relatively strong front that both the GFS and ECMWF progress through our area Saturday morning or early afternoon. This should provide a good chance of showers and thunderstorms for at least the eastern half of our region, but models are beginning to suggest more dry slotting for the western half. The GFS suggests that below normal temperatures with dry conditions for at least a few days behind the front into early next week are looking more likely with continued northwest flow aloft, but the ECMWF has a weaker front with temperatures moderating more quickly. && .PRELIMINARY POINT TEMPS/POPS... Austin Camp Mabry 68 81 64 83 66 / 40 50 20 20 - Austin Bergstrom Intl Airport 68 80 64 82 65 / 30 40 20 20 - New Braunfels Muni Airport 68 80 64 82 66 / 40 50 20 20 10 Burnet Muni Airport 65 79 62 80 64 / 50 50 20 20 - Del Rio Intl Airport 65 82 65 85 67 / 70 20 30 10 - Georgetown Muni Airport 66 80 63 82 66 / 50 40 20 20 - Hondo Muni Airport 66 82 67 83 65 / 60 40 30 10 - San Marcos Muni Airport 68 81 64 82 66 / 40 50 20 20 10 La Grange - Fayette Regional 69 81 66 82 66 / 20 40 20 50 10 San Antonio Intl Airport 67 80 66 82 67 / 60 50 20 20 10 Stinson Muni Airport 68 80 67 82 67 / 50 50 20 20 10 && .EWX WATCHES/WARNINGS/ADVISORIES... Flash Flood Watch through Monday morning for the following counties: Bandera...Dimmit...Edwards...Frio...Kerr...Kinney... Maverick...Medina...Real...Uvalde...Val Verde...Zavala. && $$ Mesoscale/Aviation...04 Synoptic/Grids...Oaks Public Service/Data Collection...YB
Area Forecast Discussion
National Weather Service Houston/Galveston TX
914 PM CDT Sun Apr 16 2017 .UPDATE... Tweaked the rain chances for the overnight period. Latest short range and high resolution models are fairly dry overnight. The ARW and NMM both show isolated potential after 4 AM over the western counties. However, the NAMBufr model sounding forecasts develop a capping inversion overnight. The models does show that the cap erodes during the afternoon on Monday. 40 && .PREV DISCUSSION... /ISSUED 635 PM CDT Sun Apr 16 2017/ AVIATION.../00Z TAF/ Radar shows convection coming to an end except for one storm in Houston County. GOES 16 non-op data showing some overshooting tops poking up in Houston county so that activity may go a bit longer. Otherwise expect VFR ceilings through about 06-08Z. After that SREF and other guidance show possibility of MVFR/IFR ceilings for the usual locations including but not limited to CLL/UTS/CXO/LBX/SGR and perhaps IAH. HOU and GLS may have some brief MVFR ceilings in the morning. Convection will be another concern for tomorrow afternoon. Conditions tomorrow look similar to today so will go with some VCTS/VCSH in TAFS 19-23Z. PWAT look to be around 1.3-1.5 again with general troughing aloft as a couple of short waves move across Texas. Overall large scale ascent is not great but enough to support convection with day time heating. Overpeck PREV DISCUSSION... /ISSUED 251 PM CDT Sun Apr 16 2017/ SHORT TERM (Tonight through Monday Night)... Isolated to scattered showers continue to develop and move north this afternoon as temperatures have risen into the low to mid 80s. While strongest updrafts (and coincidentally thunderstorm activity) have remained well to the east of the region so far this afternoon, the New Mexico Tech Houston Lightning Mapping Array has shown some intracloud activity within the past hour in northern Harris County with several cloud to ground strikes observed in southern Montgomery County as daytime heating has contributed to additional destabilization. Showers and isolated thunderstorms will remain possible through the early evening hours, but is expected to quickly dissipate with loss of daytime heating. Water vapor imagery shows two separate shortwave troughs either approaching or moving across the state this afternoon. The first is located over Central Texas, moving northeast, and the second is located over Coahuila, Mexico, moving towards the Rio Grande. Regional radar mosaic also shows some light showers associated with the first shortwave trough, but observations have shown little, if any, of this activity is reaching the ground across Central Texas this afternoon owing to a relatively dry subcloud layer evident on aircraft soundings out of both Houston and Austin. Cannot rule out the possibility of a stray sprinkle across parts of the Brazos Valley lingering through the evening hours should some top down moistening occur, but expect the remainder of the evening to be dry for most areas. Rain chances heading into the overnight hours become a bit more tricky, however, with several higher resolution models showing one (possibly two) mesoscale convective systems (MCS) making a run towards the region. Model guidance shows the first MCS developing and propagating across Central Texas this evening (affecting the northern counties overnight), aided by the first shortwave trough, and the second developing near the lower Rio Grande Valley as the second shortwave trough crosses out of Mexico (affecting the southwestern counties by Monday morning). Have low confidence in the development of an MCS over Central Texas tonight as convection across this area has been largely limited today by persistent cloud cover and a capping inversion between 800-750 MB. It appears that at least for the Central Texas MCS, model guidance has not done a good job initializing activity that would be able to grow upscale this afternoon as current radar trends show nowhere near the convective enhancement that models like the Texas Tech WRF are currently advertising. Regarding the second MCS, its parent shortwave appears to only have been partially sampled by the upper air observation network over Mexico this morning and have concerns that this shortwave may be stronger than presently indicated by guidance... resulting in potentially better chances for MCS development. Divergent 1000-500 MB thickness contours both west and northwest of the region (indicating rising motion) and Corfidi vectors showing a general west to east propagation indicate that the models may not be too far off in seeing either (or both) of these systems develop. However, increasing southwesterly flow above the surface overnight as the second shortwave trough approaches will actually serve to strengthen the capping inversion across the region tonight. This, combined with a relatively dry atmosphere in place across the region (1000-500 MB relative humidity values below 70 percent), raise concerns that even if the models are right and these systems develop... they would encounter an increasingly unfavorable environment and likely weaken or dissipate before reaching the region. The Storm Prediction Center does have a marginal risk for severe thunderstorms in place for the southwestern counties tomorrow morning in response to this second MCS (for possible hail/wind concerns) and should this system maintain intensity, cannot rule out at least a brief hail or wind threat for these areas. Due to low confidence and the aforementioned environmental conditions, have highlighted northern and western counties with only 20 PoPs for tonight but the evening update or Monday morning forecast package may need to see increased rain chances should either one of these systems materialize or persist beyond what current data supports. Otherwise, expect overnight lows to fall into the mid 60s to mid 70s overnight with patchy fog development again possible outside of the Houston metro early to mid morning Monday. As the second shortwave reaches the region during the day Monday, it should help to enhance convective coverage across the region with isolated to scattered thunderstorms again possible during the late morning through early evening hours. With precipitable water values climbing into the 1.3-1.4 range on Monday and storm motions 10 knots or less across most of the region, cannot rule out some (very localized) heavy rain in stronger showers or thunderstorms. Otherwise, similar to today, expect coverage to diminish with loss of heating with highs in the low to mid 80s. Low (20 PoPs) rain chances will continue into the overnight hours Monday, however, as the shortwave hangs up over the northwest Gulf and keeps a relative weakness in the upper flow aloft into the long term portion of the forecast. Huffman LONG TERM (Tuesday through Saturday)... Not much has changed with the long term forecast. Scattered showers and thunderstorms are expected once again on Tuesday, with a little better coverage than Monday due to added lift from an upper-level weakness passing overhead. Beginning on Wednesday, upper-level ridging builds in from the southwest helping to limit afternoon precip chances and allowing high temperatures to climb well into the mid 80s Wed-Fri. The next system is still expected to approach SE Texas and usher in the next round of showers and thunderstorms sometime around Saturday, with both the GFS and ECMWF back on the same page (for now) with a daytime Saturday frontal passage. After the front passes, clear skies and pleasant temperatures in the 70s are on tap to finish out the weekend. 11 MARINE... The light to moderate onshore flow currently in place will continue for a majority of the upcoming week as high pressure remains off to our east. Winds (south to southeast around 10 to 15 knots) and seas (around 2 to 4 feet) can be expected. Caution flags might be needed Friday night through Saturday morning under a slightly tighter pressure gradient that develops ahead of a strong cold front that is currently expected to move off the coast and through the coastal waters late Saturday afternoon through Saturday evening. Caution and/ or advisory flags will probably be needed Saturday night and Sunday for moderate to strong north winds and rough seas that will be developing behind the front. 42 && .PRELIMINARY POINT TEMPS/POPS... College Station (CLL) 68 83 65 81 66 / 20 30 20 50 10 Houston (IAH) 68 82 67 81 67 / 10 40 20 50 10 Galveston (GLS) 73 80 73 79 71 / 10 10 20 30 10 && .HGX WATCHES/WARNINGS/ADVISORIES... TX...NONE. GM...NONE. && $$ Discussion...40 Aviation/Marine...39