Scientific Forecaster Discussion
000 FXUS64 KFWD 231434 AAA AFDFWD Area Forecast Discussion...UPDATED National Weather Service Fort Worth TX 934 AM CDT Fri Aug 23 2019 .UPDATE... The southern edge of a backbuilding storm cluster crossed the Red River about an hour ago and continues to move slowly east. POPs along the Red River have hence been increased to reflect RADAR trends. Outflow from the ongoing convection should become the focus for additional development as the atmosphere destabilizes this afternoon. Chance to slight chance POPs have been expanded southward as it appears that one or more of these outflow boundaries will push south of the I-20 corridor by late afternoon. The severe threat still appears to be low, but any storm which occurs during peak heating hours will have the potential to produce gusty winds. Seasonably hot and humid conditions can otherwise be expected outside of precipitation areas. 30 && .AVIATION... /Issued 641 AM CDT Fri Aug 23 2019/ /12Z TAFS/ The main concern through this TAF cycle will be the potential for thunderstorms around the Metroplex this afternoon and again on Saturday. A weak frontal boundary is near the Red River this morning and will slowly sag south through the day. Thunderstorms are already ongoing across southern Oklahoma and may continue to impact northbound arrivals/departs for the next few hours. Scattered thunderstorms are expected to develop along the southward moving boundary early this afternoon. We have a VCTS in for the Metroplex TAF sites at 20Z with thunderstorm activity continuing into the early evening hours. Thunderstorm coverage should diminish this evening with the loss of daytime heating. Additional scattered thunderstorms are expected again on Saturday, just beyond the current TAF period. At Waco, most thunderstorm activity should be both to the north and to the south of the airport. We'll have to watch the inland push of sea breeze convection this afternoon, but most activity should remain to the southeast. Outside of thunderstorms, VFR should prevail. Dunn && .SHORT TERM... /Issued 316 AM CDT Fri Aug 23 2019/ /Today and Tonight/ Early morning objective surface analysis shows a broad area of convergence across southern Oklahoma, likely the result of an outflow boundary from earlier convection. This, combined with a respectable 20-25 kt south wind above the surface, has resulted in a reinvigoration of showers and thunderstorms across Oklahoma during the overnight. Given the slightly weakened state of the upper ridging across North Texas, we'll have to watch for a southward shift in the low level convergence through the day today along with additional southward moving outflow boundaries. Summertime convective forecasts in weak flow regimes are especially difficult with respect to location, but we think the most favored area for thunderstorms today will generally be north of I-20 with areas along the Red River and northwest of the Metroplex having the best chance. This is where low level convergence is expected to be maximized as southward moving outflow spreads into the region. Given the absence of any capping, towering cumulus should be able to develop into thunderstorms in a few locations. The atmosphere across North Texas will be modestly unstable later this morning and afternoon featuring a deep warm moist layer to 400 mb (PWs ~2"), paltry deep layer winds (0-6km shear ~15 kt), and boundary layer mixed to around 750 mb. This environment will generally be supportive of non-severe, poorly organized slow moving convection, capable of producing very heavy rainfall over short periods of time. The strongest storms could produce a severe downburst wind gust given the decent precip loading potential and fairly well mixed boundary layer. Widespread severe weather is not expected. We'll have highest PoPs this afternoon (~30-40%) northwest of the Metroplex with additional low PoPs across our far southeast counties to account for an uptick in sea breeze convection spreading inland. Some of this activity in the northwest may linger into the evening hours, so we'll hang on to some low PoPs into early tonight. High temperatures may be tempered some by an increase in clouds, so we should see slightly cooler readings across our northern counties this afternoon, but it'll still be plenty warm. We'll have highs in the low/mid 90s north of the Metroplex with upper 90s elsewhere. Other than the lingering low storm chances across the north tonight, it should be mostly quiet with lows in the mid/upper 70s areawide. Dunn && .LONG TERM... /Issued 316 AM CDT Fri Aug 23 2019/ /This Weekend Through Next Thursday/ The dampened and flat upper ridge present to end of the week will continue to break down in response to an impressive mid level impulse tracking across Kansas/Oklahoma/and North Texas on Saturday. Sans uncertainty regarding any mesoscale storm outflow boundaries left over from today's activity, no significant synoptic surface fronts will be present across the area. Despite weak mid level flow overhead, our environment will be characterized by very warm temperatures in the 90s, rich moisture with PWATs 1.75-2 inches, and high instability. Through midday, the main focus for isolated-scattered thunderstorms will be mainly along and north of I-20 in closer vicinity of better large-scale ascent associated with the mid level shortwave tracking eastward across Oklahoma into Arkansas. As diurnal heating cranks up and instability increases, we'll see better chances across our northern and eastern counties with more isolated chances across the majority of Central Texas. Outside of the immediate Red River Valley where highs in the upper 80s- lower 90s are advertised in an area of more expansive cloud cover; the rest of the CWA should see highs still surge into the mid to to upper 90s. We could see a few stronger storms in the afternoon and evening Saturday hot temperatures this time of year resulting in higher values of DCAPE and high cloud bases. Thus gusty downburst winds will likely occur with stronger storms. Mid level lapse rates on the order of 6-6.5 deg C/km and modified pockets of drier air aloft should allow for some deeper updrafts and even the possibility of hail with the strongest of activity. Lastly, slow steering currents and/or storm mergers with the moist environment in place will also present the potential for pockets of heavier rainfall and the possibility of minor flooding...mainly areas north of I-20 and east of I-35. Mid level heights will briefly rise Saturday night in wake of our departing impulse moving through the Ozarks to the northeast of the area. I have lingered slight chances mainly east of I-35 and along the immediate Red River Valley for any lingering ascent Saturday evening. However, another mid level impulse will be right on the heels of the first one Saturday night, but is being advertised to track southeast across Northeast Oklahoma/Southeast Kansas -- before heading into the Ozarks on Sunday. GFS wants to develop an MCS and associated cold pool much further south across Eastern Oklahoma versus it's NAM counterpart which would obviously have drastic differences on convective chances across especially our northeast CWA late Saturday night into Sunday. I have decided to take a mean of these solutions for now and keep the better chances just north through east of the immediate DFW area on Sunday. With our area being grazed by this mid level impulse and warmer 850 temperatures across the west, I will lean toward warmer guidance on high temperatures Sunday pushing the century mark along and west of I-35, with lower-mid 90s more the rule across East Texas. Again with the hot temperatures in place, the possibility of strong to even marginally severe storms with downburst winds, frequent lightning, and heavy rainfall will be a possible during especially the afternoon and evening hours. The heat returns with a vengeance for the early half of the week, as a strong mid level anticyclone to our west re-establishes eastward and over North and Central Texas. In addition, a mid level impulse tracking east across the Oklahoma/Kansas border will help to draw a cold front southward across the Panhandle and Central Oklahoma which will likely result in veering low level flow just above the surface out in advance. Outside of highs in the mid- upper 90s across our East Texas counties, the remainder of the CWA should easily see high temperatures range between 100-103 degrees with heat indices between 105-110 degrees across a vast part of the area on Monday afternoon. It's going to be steamy and models have been consistent on this trend for the past several days...so be ready. Consensus of medium range models bring this cold front across the Red River, but begin to slow it down or even stall it north of I-20/30. This feature will provide a focus for a few showers and thunderstorms and combined with continued hot temperatures Tuesday, there will be an increasing threat for strong storms -- particularly across our far northern tier counties near the surface front and better large-scale ascent with the mid level impulse. Further south and west, hot high temperatures around the century mark will continue on Tuesday. Similar convective chances will continue into mid week with slightly cooler temperatures occurring near the immediate Red River Valley, but increased cloud cover should allow high temperatures to settle well back down into the 90s. Otherwise, a flat mid level ridge will slowly re- establish toward the end of the week, but not be overly intense. Seasonably hot temperatures with diurnal, isolated convective chances each day can be expected. With long-range model blends being notoriously too cool due to trends toward climatology, I did trend toward warmer guidance of the European model during this time frame. 05/ && .PRELIMINARY POINT TEMPS/POPS... Dallas-Ft. Worth 97 78 94 78 98 / 40 20 30 20 20 Waco 100 76 97 78 100 / 20 5 20 10 10 Paris 93 73 88 73 90 / 40 20 40 20 40 Denton 95 76 93 77 96 / 40 20 30 20 20 McKinney 96 75 92 76 95 / 40 20 30 20 30 Dallas 97 79 95 79 98 / 30 20 30 20 20 Terrell 97 75 95 76 97 / 20 10 30 20 30 Corsicana 98 75 94 76 96 / 20 5 30 20 20 Temple 98 76 96 77 99 / 20 5 20 10 10 Mineral Wells 97 74 94 74 98 / 40 20 30 10 10 && .FWD WATCHES/WARNINGS/ADVISORIES... None.