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Displaying AFOS PIL: AFDFWD Received: 2018-08-10 00:53 UTC
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597 FXUS64 KFWD 100053 AAA AFDFWD Area Forecast Discussion...UPDATED National Weather Service Fort Worth TX 753 PM CDT Thu Aug 9 2018 .AVIATION... /00Z TAFs/ After the initial Denton County storm this afternoon, the bulk of the convective activity was south of the Metroplex TAF sites (Arlington the primary exception). However, the dancing outflow boundaries throughout the TRACON are finding particularly unstable air, and a few thunderstorms rooted in the mT boundary layer will occur through nightfall. Despite the chaotic wind field, for ease of operations, DFW/DAL are in south flow, inbound traffic avoiding the thunderstorm clusters south of the Metroplex. While storm impacts at any metro TAF site would be quite brief, some in-flight slaloming will be required early this evening. A low-level trough will remain draped across the Metroplex overnight. This will promote some upglide, but the main corridor of warm/moist advection will be oriented through Central Texas into East Texas. Despite being worked over late this afternoon, this buoyant inflow beneath steep lapse rates aloft will promote the redevelopment of thunderstorms across Central Texas later this evening. This will maintain impacts to south departures and incoming traffic through both Glen Rose and Cedar Creek. Eventually, showers may develop closer to the Metroplex, but probably not until the predawn hours, at which point boundary layer parcels are unlikely to be involved. In addition, with more widespread convection to the south literally stealing its thunder, these shallower updrafts across North Central Texas will have less favorable lapse rates, and the Metroplex TAFs will carry only VCSH Friday morning. In the short term, the wind field will continue to be governed by outflow. With the proximity of surface troughing, light easterly winds will likely take hold this evening within the Metroplex. Veering southerly flow will then overwhelm this late tonight and prevail through Friday. With a moisture-rich boundary layer still in place on Friday beneath weak troughing aloft, some redevelopment of thunderstorms should occur at peak heating. The weak surface wind field will allow residual boundaries to linger. With much of the forcing on the mesoscale, initiation will be largely dictated by the location of these boundaries, which may be determined by the nocturnal activity that has yet to occur. While the timing of this convection would be focused during the typical late afternoon peak heating period, uncertainties about location will preclude any introduction of Friday afternoon thunder in the TAFs at this time. 25 && .SHORT TERM... /Issued 347 PM CDT Thu Aug 9 2018/ /This Afternoon and Tonight/ The main challenge in the short term forecast period will be the location and coverage of precipitation. For the rest of this afternoon, it appears that locations south of I-20 will stand the best opportunity for showers and thunderstorms. A few storms will be possible near the Highway 380 corridor this afternoon as well. Overnight tonight, storm chances will increase quite noticeably across the Concho Valley and into Central Texas. This afternoon, there has been a relative lull in convective activity from about noon through the 3 PM time frame. A broad surface trough continues to slide southward through the forecast area with an mesoscale convective vortex or MCV noted across the Concho Valley. Agitated CU was noted from near a Gatesville to Athens line and I've nudged PoPs into the 50 percent category here. There will be a risk for strong to near severe downbursts given large amounts of DCAPE and a very hot and well-mixed boundary layer. A small thunderstorm cluster was noted just north of the Highway 380 corridor in response to just daytime heating. The cessation of this convection will be interesting, but in general, it should decrease after sunset. Overnight tonight, showers and thunderstorms should blossom across Central Texas and the Concho Valley. RAP and NAM guidance continue to support strong isentropic ascent along the 305K theta surface. As noted yesterday, the NAM has done a pretty good job of handling the overnight LLJ and I see no reason to disregard its output tonight. 925mb winds will climb into the 30 to 35 knot range and glide atop the surface trough. There may be some additional assistance from the aformentioned MCV and this should help fuel widespread to numerous convection across Central Texas. HREF members concur with this assessment and mean QPF values are quite aggressive across this area with rain totals in excess of 4". I'm not completely sold on this potential, but given the very moist regime (characterized by 2" PWATs) and the unseasonably strong LLJ, it's not out of the realm of possibility. I've inserted "heavy rain" wording into the western portions of Central Texas tonight and there could be a low end flood threat, especially across some of the more flood prone areas in Central Texas. Elsewhere, there will be a chance for a lower coverage of showers and thunderstorms. Overnight low temperatures will fall into the 70s areawide. There may be a low potential for some patchy fog along the Red River where skies. Bain && .LONG TERM... /Issued 347 PM CDT Thu Aug 9 2018/ /Friday through next Thursday/ Showers and thunderstorms may be ongoing at the start of the long term period Friday morning, forced by robust isentropic ascent/warm advection over-topping a diffuse remnant outflow boundary/wind shift across Central Texas. Recent hi-res guidance is in decent agreement in depicting fairly high precipitation coverage across Central Texas and up to about the I-20 corridor through the morning hours, and this seems reasonable given the anticipated magnitude of lift and copious amounts of moisture. We've increased PoPs to 70% across a good chunk of our Central Texas counties Friday morning. PWATs are forecast to push 2" in spots here, so heavy rainfall will be possible. In addition, upwind corfidi vectors of less than 5-10 kts or so, becoming increasingly boundary-parallel portend some risk for training/backbuilding cells. Relatively high 1 and 3-hour flash flood guidance across Central Texas reduce our concern for widespread flash flooding at this juncture, but some localized hydrological concerns may arise generally south of I-20 through the morning hours. This initial round of convection should diminish into the early- afternoon as the initiating ascent peters out as the low-level wind field relaxes. Given the anticipated convective coverage across Central Texas, re-development of showers and storms during the afternoon is in question, so we've reduced PoPs a bit across the last few rows of counties. Additionally, if this complex exhausts a robust enough outflow, it could even hamper convective chances north of I-20 later in the day. High temperatures will also obviously hinge on the placement of left over cloud cover and mesoscale boundaries. The warmest conditions should occur near the Red River, while locales south of I-20 may have a hard time getting into the 90s. A similar scenario may unfold Friday night into Saturday morning as moist upglide gets cranking once again, and so high-end chance PoPs will be advertised across much of North and Central Texas. These may need to be increased as confidence in the placement of pertinent mesoscale features increases. Over the weekend, upper level troughing will become more established across parts of West Texas. This will keep a persistent fetch of deep southerly flow and associated moisture transport going across the western half of Texas. The brunt of large scale ascent looks like it will remain just west of our forecast area by the end of the weekend and into early next week, and a fairly tight PoP gradient has been introduced from west-to- east starting on Sunday. Both the GFS and ECMWF show some pretty dry air punching into our southeastern and eastern counties during this time frame, and today's mid-range ensemble guidance is similarly advertising the lowest precipitation chances east of the I-35 corridor. Assuming this upper low doesn't pivot any farther west than currently advertised, some of our far western counties may benefit from decent wetting rains Sunday-Tuesday. By the middle of next week, the persistent upper troughing and associated broad cyclonic flow overhead may begin to break down as the southwestern US subtropical ridge attempts to build back eastward. Temperatures should rebound into the mid and upper 90s Wednesday and Thursday, and PoPs will quickly trend downward through this period. Carlaw && .PRELIMINARY POINT TEMPS/POPS... Dallas-Ft. Worth 77 92 73 89 74 / 50 50 50 30 60 Waco 73 93 72 90 74 / 70 70 50 50 60 Paris 73 93 72 89 71 / 20 30 30 30 30 Denton 74 93 70 88 72 / 40 40 50 30 50 McKinney 74 93 72 89 73 / 40 40 40 30 50 Dallas 78 93 75 91 75 / 50 50 50 30 60 Terrell 75 93 73 90 73 / 40 50 50 30 40 Corsicana 75 91 73 90 73 / 50 70 50 50 50 Temple 73 93 74 91 72 / 70 70 50 50 60 Mineral Wells 74 91 70 86 71 / 50 50 50 40 60 && .FWD WATCHES/WARNINGS/ADVISORIES... None. && $$ 25/05