DFW FORECAST DISCUSSION
000 FXUS64 KFWD 180451 AFDFWD Area Forecast Discussion National Weather Service Fort Worth TX 1151 PM CDT Wed Oct 17 2018 .AVIATION... /06Z TAFs/ Low VFR cigs will continue to prevail overnight and into the morning hours across DFW area airports, while MVFR cigs will prevail at Waco. Waco could see some sporadic low VFR cigs as dry low level air tries to entrain from the north-northeast through mid morning Thursday. This will be due to a south to north sloping frontal inversion which is deeper across DFW and closer to 850mb, whereas Waco`s inversion is more shallow. During this time period, the area will be in between mid level shortwave disturbances. The next mid level shortwave disturbance currently over the Texas Coast will slowly migrate northward through the day Thursday. By afternoon, cigs everywhere will be in the MVFR category as showers increase from the south. Waco will likely see these showers by late morning/midday, while DFW may be delayed more during the mid-late afternoon hours. Rain coverage should increase across the entire area by 00z Friday and beyond with both vsbys and cigs falling. Low MVFR cigs with occasional heavier showers causing vsbys to fall to IFR are expected across the DFW Metro airports Thursday evening, while RUC soundings show Waco going down into IFR even on cigs. Otherwise, light northerly winds around 5 knots overnight will veer northeast or even east-northeast 6-9 knots by Friday afternoon as a secondary shallow surge of cool air arrives from the north. By Thursday evening, northeast winds 4-6 knots will prevail. 05/ && .DISCUSSION... /Issued 328 PM CDT Wed Oct 17 2018/ I`ll just skip ahead to the part of the forecast that everyone wants to know about - the sun will be back this weekend. We know it still exists because our visible satellite shows the bright white cloud cover blanketing the entire region. The water vapor satellite continues to show the cut off upper level low responsible for the prolonged rain event spinning across the southwestern US. Isentropic upglide continues over much of the northern half of the CWA, but the best lift and heaviest rain is primarily the western zones this afternoon. Hi-res and synoptic models are all in good agreement in showing the best lift and rainfall chances tonight will be across the northwestern zones through about midnight before tapering off and shifting northwest. While rainfall rates should remain below 0.35" per hour due to limited instability (which should limit flash flooding) there still is the potential for 1-2 inches of rain across the NW CWA through tonight. Fortunately this region is not quite as saturated as other parts of the CWA, but still flooding of low-lying areas, creeks, and rivers is a concern. Elsewhere across the CWA, rain will be lighter with little or no rain expected across the eastern zones into Central Texas tonight. Temperatures will hold nearly steady near their current readings all night. Models are coming into good agreement in ejecting the bulk of the PV anomaly in the Desert SW out into the Plains this weekend. This will be both good news and bad news. The bad news is that it will cause our low level winds above the frontal inversion to increase out of the southeast resulting in a renewed vigor of the isentropic lift, and perhaps more concerning, greater moisture flux with precipitable water values increasing from the current values of 1.5 inches to near 2 inches during the day Friday. While traditional upright instability continues to look low (limiting the thunderstorm threat), models do show slantwise instability is available with some high res models forecasting frontogenesis to increase. The result is that some of the models are now outputting higher QPF Thursday night into Friday with the upper end amounts of 3 to 5 inches across parts of the northern and western CWA. Since there is still a lot of spread among the QPF guidance, we will hold off on issuing a flood watch at this time, and we will keep average QPF in the 1-2 inch range through Friday night. However we will continue to monitor these trends in the data overnight and will have to consider the resurrection of a flood watch for part of the area. The primary region we`re concerned about is along and west of the I-35 corridor, and the time frame is Thursday afternoon through Friday. The good news is that the ejection of the energy associated with the upper low will help to send another cold front into the region with much drier air in the lower levels. This will result in the chance of rain ending from north to south on Saturday with some sunshine possible in the afternoon too. We`ll still keep some high clouds in the region, but Sunday should be a partly sunny and dry day for the entire area. High temperatures Saturday will be in the upper 60s to near 70, but as the cooler air filters into the region, Sunday`s highs will only be in the low to mid 60s. Lows will also be seasonably cool and in the 40s. Unfortunately another upper level trough will develop off of the coast of California early next week. This will bring the return of southwesterly flow aloft and southerly flow just above the frontal inversion to the region again. Isentropic lift and moisture advection will bring the chances of rain back to the area starting late Monday, but especially into Tuesday and Wednesday. The ECMWF has sped up its timing of the upper level features to match the GFS forecast, so we have increased PoPs Tuesday and Wednesday. Rainfall at this time looks to average 1-2 inches, however both the GFS and ECMWF do show a landfalling eastern Pacific hurricane in Mexico during this time period. This system (should it exist) would likely enhance the upper level dynamics over the state and increase the risk for heavy rainfall. Obviously because it`s a tropical system that hasn`t formed yet, it`s too early to say for sure whether this will occur, but it bears watching. Otherwise temperatures look to cool Tuesday and Wednesday due to the rain over the area. TR.92 && .PRELIMINARY POINT TEMPS/POPS... Dallas-Ft. Worth 52 61 54 59 55 / 60 60 60 80 50 Waco 52 60 56 60 56 / 20 70 50 70 50 Paris 53 63 52 57 53 / 40 20 40 70 60 Denton 52 61 53 58 54 / 70 70 70 80 40 McKinney 53 62 53 57 54 / 60 60 60 80 50 Dallas 53 62 55 59 56 / 50 60 60 80 50 Terrell 53 64 55 59 55 / 30 50 50 70 60 Corsicana 52 63 54 60 55 / 20 50 40 70 60 Temple 51 58 56 60 56 / 20 70 50 70 50 Mineral Wells 50 58 53 58 54 / 80 70 80 80 40 && .FWD WATCHES/WARNINGS/ADVISORIES... None. && $$ 05/25