774 FXUS64 KFWD 022236 AFDFWD Area Forecast Discussion National Weather Service Fort Worth TX 436 PM CST Wed Jan 2 2019 .DISCUSSION... ...Winter Weather Event Rundown... The main concern with the forecast package is the potential for continuing winter weather across the Big Country and parts of North Texas. Light freezing rain and/or freezing drizzle will continue tonight mainly near and west of the US HWY 281 corridor. A gradual transition to a sleet/snow mix is anticipated early Thursday, mainly west of US HWY 81 and north of US HWY 380 towards sunrise Thursday. Some of this snow may be heavy, with snowfall totals in the 3" to 5" range and thus a Winter Storm Warning has been issued for Young, Jack and Montague counties from much of Thursday and into early Friday. For areas northwest of a Comanche to Denton to Sherman/Denison line...snowfall amounts will average between 1" and 3". South of this line, a dusting of snow/sleet will be possible. All winter weather should come to an end by early Friday. ...Impacts... The greatest impacts to travel will be for areas generally north of US HWY 380 and west of US HWY 81. Winter weather may result in snow covered roads resulting in slick and hazardous conditions. Travel will be hampered significantly across this area, if not impossible. For areas north of I-20 and west of the I-35/35W corridor (not including the heart of the D/FW Metroplex), slick road conditions are possible, especially on elevated surfaces. Areas southeast of a Comanche to Denton to Sherman/Denison line should only see very minor impacts with perhaps a few slick bridges and overpasses. In addition to winter weather, pockets of flooding are likely to continue this afternoon and into the evening hours. While rain rates have remained below 1"/hr, the very cold soils and dormant vegetation have proven to result in efficient runoff rates and we've already fielded reports of road closures of mainly secondary and tertiary thoroughfares. It's probable that additional flood issues will occur through the night. ...Forecast Uncertainty... The forecast hinges on the track of the upper low to the west as well as surface temperatures. At this time, confidence in the track of the upper low is moderate given the decent model agreement. Confidence in the temperature forecast is OK, but will be something to monitor. If the tropospheric column is cooler or warmer, some alterations to the snow/ice accumulation forecast will need to be made. There also remains a risk for slightly more convective elements which could help to bolster snow/ice amounts. At this time, feel that there is a decent chance for some of these elements across the Winter Storm Warning. If these elements are more expansive in areal coverage, there could be some heftier snowfall amounts outside of the Winter Storm Warning area. ...Meteorological Reasoning... A very challenging forecast from a meteorological standpoint exists across North Texas. A very potent upper low continues to churn and nose eastward into the Pacific southwest. Slight warming has commenced across much of the area as northerly winds have weakened, shutting down the CAA. With sunset, temperatures will likely hold steady or even fall slightly and it's probable that there won't be much in the way of change temperature-wise tonight. The exception would be for locations that experience heavier bursts of frozen precipitation which may help to cool the column some. For tonight, the strong isentropic ascent that resulted in the large rain shield should subside across East and Central Texas resulting in it shrinking in areal coverage across our area. I've lowered PoPs some after midnight across East and Central Texas. During the overnight hours, the highest PoPs were confined to areas west of I-35 as isentropic ascent ramps up quickly. Steepening 700-500mb lapse rates ahead of the very deep PV anomaly (1.5 PVU surface down to 590mb) should foster some convective elements. The presence of convection would be two-fold for sensible weather...1) quick accumulations of winter precipitation (provided that it is cold enough) and 2) further cooling of the column. At this time, it appears that this potential is greatest west of the US HWY 281 corridor. For now, I'll advertise freezing rain until just after midnight, with a transition to snow/sleet. If the convection is very deep (produces lightning), this transition may occur a little sooner than advertised in the forecast. Farther east of this line, it appears that temperatures will be high enough such that only a cold rain falls, though we will need to watch areas just east of the Sherman/Denison area for any lingering freezing drizzle/light freezing rain. As we near daybreak Thursday, it appears that the rain/freezing rain and snow/sleet line will inch closer to the HWY 281 corridor. Forecast soundings show a decent isothermal layer just above 0 C around ABI...SEP and SPS. This coupled with decent omega (likely due to strong low-mid level frontogenesis) in the dendritic growth zone should favor some heavy snowfall. It's possible that if NAM FGEN progs are to verify, a band of heavy snow may extend to the south of the current Winter Storm Warning. Some of the HREF members support heavier snowfall south of I-20 with snowfall output showing a potential for 2-5". For now, we are comfortable with letting the Winter Weather Advisory handle areas outside of the Winter Storm Warning, but we will need to monitor this closely for travel along I-20. Towards noon on Thursday, the upper low should scoot eastward, cooling the column sufficiently such that a rain/snow mix is the most likely p-type for a good portion of North Texas. Heavy snow is still expected for areas along northwestern North Texas and northern Big Country, but things should start to wind down here. Closer towards the I-35 corridor, there could be some accumulating snows, mainly north of HWY 380. South of this line, a dusting of snow will be possible, mainly on grassy surfaces and elevated surfaces. Once we get towards Thursday evening and into midnight Friday, lingering wrap around precipitation may persist, especially along the Red River. Additional accumulation will be possible here, but for now I'll keep new snowfall amounts around 1/2". For the remainder of the forecast, generally above normal warmth is anticipated as northwest flow should promote some downsloping. The exception to this will be Friday as lingering snowpack and the dense cold airmass both remain in place. This weekend and into early next week should be nice. The next chance for rain will be next week, though limited moisture should preclude any flood concerns. Temperatures above normal should also preclude any threat for winter weather as it stands right now. Bain && .AVIATION... /Issued 1219 PM CST Wed Jan 2 2019/ /18z TAFs/ Widespread forcing for ascent continues across most of North Texas, well ahead of the primary upper level storm system over the Southwest U.S. A fairly large shield of light to moderate rain will continue to drift eastward across the region this afternoon, affecting all TAFs sites prior to sunset. However, the back edge of this initial precipitation area should begin to clear the Metroplex airports in the 23z-02z timeframe, followed by a brief mostly rain-free window prior to 10z. This timeline will be mirrored at Waco, but delayed by approximately an hour. Surface temps have now climbed above freezing at all TAF sites, and have omitted any FZRA references for today/tonight. As the upper low enters West Texas late tonight, lift will and lapse rates aloft will begin to increase. This will lead to the development of a new batch of showery precipitation which will build into the Metroplex TAF sites and Waco in the 10z-12z time period. For the most part, lower level temperatures will remain sufficiently warm to maintain all rain precipitation types prior to 15z Thursday. However, there is a good chance that the column will cool enough to produce a rain/snow mixture, or perhaps even a total changeover to all snow after 18z Thurs. At this point, have refrained from including any mention of -SN at KDFW after 18z, but later forecasts will need to assess this potential closely and include as necessary. Have generally maintained IFR ceiling trends through the period, though some variability and brief improvement to MVFR is possible this afternoon and this evening. Visibilities should remain in the MVFR range through 02z, owing mainly to the continued light/moderate rain and patchy fog. Should see improvements on this front after 00-02z, but reductions will reoccur after 10z as the next round of precipitation moves into the area tomorrow morning. The easiest dimension of the forecast will is the winds - they'll be continuously from the north at speeds averaging 8-12 knots through tonight and Thursday. Bradshaw && .PRELIMINARY POINT TEMPS/POPS... Dallas-Ft. Worth 35 36 33 53 37 / 90 90 40 0 0 Waco 36 39 32 55 37 / 90 90 5 0 0 Paris 38 38 34 53 34 / 60 90 80 20 0 Denton 33 35 30 52 34 / 90 90 40 0 0 McKinney 34 36 32 52 35 / 90 90 50 5 0 Dallas 35 37 33 54 37 / 90 90 40 0 0 Terrell 38 38 34 54 36 / 80 90 40 0 0 Corsicana 40 40 34 54 37 / 100 90 20 0 0 Temple 35 41 32 56 37 / 90 80 0 0 0 Mineral Wells 30 35 28 54 33 / 90 90 20 0 0 && .FWD WATCHES/WARNINGS/ADVISORIES... Winter Weather Advisory until 6 AM CST Friday for TXZ092-093-102- 103-115>117. Winter Weather Advisory until noon CST Thursday for TXZ129>132- 141>143. Winter Storm Warning from 3 AM Thursday to 6 AM CST Friday for TXZ091-100-101. && $$ 24/66