DFW FORECAST DISCUSSION
000 FXUS64 KFWD 191227 AAA AFDFWD Area Forecast Discussion...UPDATED National Weather Service Fort Worth TX 727 AM CDT Sun Aug 19 2018 .AVIATION... 12 UTC TAF Cycle Concerns---Near term windshift and convective potential this afternoon and tonight. Outflow from RA/TSRA will briefly interrupt southerly winds across the Metroplex TAFs. Accompanying this windshift will be the potential for a few instances of SHRA and I`ve included both of these elements (windshift and SHRA) in a TEMPO group for Metroplex TAFs. The windshift should be light enough such that area terminals remain in a south flow. More continuous southwest to southerly winds will likely resume during the late morning into the early afternoon hours across the Metroplex. Southerly winds will prevail at Waco through the entire 12 UTC TAF cycle. The next challenge will be timing the potential bouts of SHRA and/or TSRA at the Metroplex. This morning`s convection should leave behind a boundary which should act as a focus for renewed convective development this afternoon. I`ll maintain the inherited afternoon VCTS with low confidence, but if the aformentioned boundary is shunted south of D10 airspace and/or vanishes beneath the ambient flow, it`s possible that little to no new TS develops across the Metroplex this afternoon. This evening offers a better opportunity for convective development as low level ascent increases from the west and southwest. I`ve appended a 3 hour window for VCTS between 03-06 UTC Monday with modest confidence. Depending on the location of convection, south flow operations could be briefly disrupted due to numerous convective outflows. Confidence in timing/placement of these chaotic wind shifts is too low to explicitly mention in the TAF. Waco will remain far enough to the south such that shower or storms appear unlikely through the 12 UTC TAF cycle, though the potential is non- zero...especially between the 6 and 12 UTC Monday time frame. Outside of rain/storms, VFR is expected at all terminals. Bain && .SHORT TERM... /Issued 407 AM CDT Sun Aug 19 2018/ /Today and Tonight/ The main challenge in the short term will be convective trends and consequently the high temperature forecast. This morning, a large shield of rain with embedded thunderstorms continues to slowly advance eastward across southwestern Oklahoma and adjacent parts of North Texas. Regional VWP sampled 20-30 knots southerly flow around 1km this morning. Despite this flow, convective outflow continues to race east and southeastward from this rain/storm activity suggesting that its overall progression through the rest of North Texas may be limited. For now, I`ll advertise a 40-50 PoP across the Big Country and western reaches of Texoma during the pre-dawn hours. This complex should dissipate completely as its convective outflow becomes further displaced, limiting the ability for the regeneration of new convective cells. With this in mind, PoPs will decrease through noon with highest chances for rain near and north of I-20. Widespread cloud cover from this complex should slide southward across much of North and Central Texas through the day. Beneath the large cirrus canopy, low level flow late this morning and this afternoon should once again veer some to the southwest. While the clouds may hinder diabatic heating and keep temperatures 1-3 degrees lower than Saturday, it`ll still be another hot day with afternoon highs climbing into the upper 90s to near 101 degrees. The exception will be along the immediate Red River Valley where temperatures may only climb into the low to mid 90s. Heat index values across the area may climb into the 100 to 105 degree range...especially across East Texas. At this time, I don`t see a need for a heat advisory as the areal coverage of heat indices above 105 appears patchy in nature. Regardless, please exercise your heat safety rules! Model derived wind fields indicate that front/convective outflow should slide southward towards the I-20 corridor in the evening. As a result, convection is expected to re-develop late this afternoon and into the evening hours ahead of this feature. There will be a risk for strong to possibly severe downburst winds given steep 0-3km lapse rates (nearly 9 C/km) and DCAPE values in excess of 1100 J/kg. Though the exact coverage of showers/storms is unknown, it seems reasonable to increase PoPs during the 00-03 UTC time frame Monday (or Sunday evening) as the front/convective outflow slides southeastward. I`ll keep a 60 PoP across northeast Texas, but given the decent CAM consensus, I`ve elected to increase PoPs up to around 50% further southwest towards the D/FW Metroplex and into the eastern Big Country. Storm motion should be a little faster today, but there will still be a heavy rain/flood potential with showers and thunderstorms. Bain && .LONG TERM... /Issued 407 AM CDT Sun Aug 19 2018/ /Monday through Saturday/ Although the main forcing associated with a departing upper low will be confined to the Central Plains, the tail end of a final spoke of energy will skirt the Ark-La-Tex on Monday. At daybreak Monday morning, showers and thunderstorms may be ongoing along the associated cold front within North Texas, but as the boundary moves deeper into Central and East Texas, it will become increasingly separated from the upper support. Minimal low-level convergence along the boundary will both reduce compressional warming at peak heating and limit the potential that surface parcels will be able to overcome lingering inhibition, particularly if morning cloudiness is slow to erode. Warming southwesterly winds ahead of the front may help to overcome the reduced insolation, but even with extraordinary MLCAPE values Monday afternoon, limited shear and marginal lapse rates aloft should prevent any updrafts from persisting long enough to become strong. Thus, only low-end PoPs will accompany the front, with a conditional severe threat. Strengthening northwesterly flow above the frontal layer should assure its forward progress and preclude any postfrontal precipitation. However, if the slower NAM/ECMWF solutions pan out, there may be a wider window (both temporally and spatially) for thunderstorms Monday afternoon into Monday evening, with an enhanced severe threat. In any event, any showers and storms should exit to the southeast Monday night. Milder and drier air will filter into the region on Tuesday, but with abundant sunshine, high temperatures may be within a degree or two of normal values. But after the oppressive heat and humidity of preceding days, the middle of the week will feel noticeably more comfortable in comparison. The low-level advection will wane Tuesday night, but with an unseasonably mild start to Wednesday and weak northeasterly surface flow, similar daytime temperatures are expected. Southerly winds will return on Thursday, and Gulf moisture will steadily increase late in the week. The GFS has come into agreement with other extended guidance with late-season ridging reasserting itself over the Lone Star State. As a result, the extended portion of the forecast will remain free of rain chances, and temperatures will climb into the upcoming weekend. 25 && .PRELIMINARY POINT TEMPS/POPS... Dallas-Ft. Worth 97 77 93 74 93 / 20 50 10 5 0 Waco 101 78 99 74 96 / 10 40 20 20 5 Paris 91 74 91 68 89 / 30 60 20 5 5 Denton 96 74 92 69 92 / 30 50 10 5 0 McKinney 96 75 92 69 91 / 20 50 10 5 0 Dallas 99 78 94 74 94 / 20 50 10 5 0 Terrell 98 77 93 71 93 / 20 50 20 10 5 Corsicana 99 78 97 74 94 / 10 40 30 20 5 Temple 98 77 99 74 97 / 5 20 20 20 10 Mineral Wells 94 73 93 70 94 / 30 40 10 5 0 && .FWD WATCHES/WARNINGS/ADVISORIES... None. && $$ 24/25