DFW FORECAST DISCUSSION
811 FXUS64 KFWD 201112 AFDFWD Area Forecast Discussion National Weather Service Fort Worth TX 512 AM CST Mon Jan 20 2020 .SHORT TERM... /NEW/ Update: No major changes were made with this morning`s short term forecast issuance, with the previous forecast still on track. Minor adjustments were made to sky/temperature trends to account for the band of cirrus draped across the I-20 corridor. These clouds have allowed temperatures beneath it to stay about 5 degrees warmer than surrounding sites as they inhibit outgoing radiation. Otherwise, the rest of today/tonight`s forecast trends are in good shape as outlined in the previous discussion below. Previous Discussion: /Through Tuesday/ A progressive shortwave trough is ushering some fast-moving cirrus through the forecast area, which is temporarily hampering radiational cooling. However, overcast skies should only last for a few hours at any given location, and most of the area should still have ample time for temperatures to fall to near or just below freezing prior to sunrise. Despite its intensity, passing cirrus will be all that this shortwave can muster due to an absence of any meaningful moisture. Following this morning`s cloud cover, mostly clear skies will resume today with light winds. Another day of near-normal highs will be the result for the MLK JR Day holiday. With dry air remaining in place, overnight lows will be capable of dropping to within a few degrees of the freezing mark once again despite the return of light southerly winds. By daybreak Tuesday, a weak backdoor frontal boundary will nudge into parts of northeastern Texas, briefly resulting in some weak CAA and light NE winds. This may allow temperatures to fall into the upper 20s for lows across our far northeast zones. Later Tuesday morning, the aforementioned boundary will quickly wash out as all winds return to the southeast. Modest warm advection during the day should allow highs to reach the mid 40s to mid 50s despite a gradual increase in mid-level cloud cover from the west. Mid and upper level moisture will spread eastward over the entire CWA within a strong belt of westerlies associated with an approaching upper trough. As a result, most of the area should be overcast by the afternoon. As some top-down saturation occurs, virga may begin falling across some of our western zones, with some light precipitation possibly beginning to reach the ground late in the afternoon. The more widespread rainfall will begin later on, and this potential is addressed in the long term portion of the forecast. -Stalley && .LONG TERM... /Issued 216 AM CST Mon Jan 20 2020/ /Tuesday through Next Weekend/ A wet/cool weather pattern is shaping up mid-week and beyond across North and Central Texas. Rain chances will start to ramp up late Tuesday into Wednesday, with a potential for a wintry mix for parts of Northeast Texas. Instability builds some late Wednesday into Thursday and while a few thunderstorms are forecast, severe weather looks unlikely at this time. Drier conditions can be expected Friday and into the last weekend of January. The temperature forecast on Tuesday remains difficult as a backdoor front is expected to slide through at least parts of the area late Monday into Tuesday. I`ll side with some of the cooler guidance as current upstream observations across the Ozarks indicate some pretty shallow/cold air. While some modification of this airmass is likely, it still appears like that it`ll remain pretty chilly as this shallow airmass invades from the northeast. As is *usually* the case with these shallow cold air intrusions, global guidance struggles with the speed of its forward progress. I`ve trended toward cooler conditions north of US HWY 380 in line closer to NAM/WRF guidance for Tuesday and Wednesday`s high temperatures. If the cold air upstream really modifies, the current forecast will need to be altered to reflect much warmer conditions north of US HWY 380. This would also have ramifications for the p-type on Wednesday morning. For now, highs in the low to mid 40s north of this boundary are expected, with low 50s elsewhere. Ascent atop this cooler airmass is expected to commence late Tuesday night into Wednesday. Initial precipitation will be light as there will be a substantial amount of dry air to overcome. Top down moistening will be first to occur west of US HWY 281 where low level thermal profiles should support largely a very cold rain. Farther east across North Texas (toward the I-35 corridor), there will be a brief window in which moistening thermal profiles may support a rain/light snow/light sleet mix. This potential looks very low and for now, I`ll leave out of the forecast. The best chance for a wintry mix will be for locations near and northeast of a Sherman/Denison to Sulphur Springs line. Given the run-to-run consistency of the colder model guidance and most probable area of coldest air/most favorable thermal profiles, I will continue to mention a wintry mix (light rain, light snow and light sleet) across Northeast Texas. Regarding any snow/sleet accumulation, some SREF members (though largely based off of the colder NAM) indicate that up to 1/2 inch of snow/sleet may fall. While not out of the realm of possibility, this likely represents the worse case scenario. I do believe that the potential exits for minor accumulation of snow/sleet (mainly a light dusting) on mainly grassy surface, however, I don`t expect major travel impacts at this time. Moreover, the increasing WAA regime should foster an eventual transition to just a cold rain by Wednesday afternoon. PoPs on Wednesday will range between 60 and 80 percent range, with the best rain/precipitation chances north of I-20 where large scale ascent will be maximized ahead of the first shortwave trough that will graze the area. Wednesday will be a pretty raw day with temperatures mainly in the 40s. A few low 50s are possible across the Big Country. If NAM guidance is to verify, however, temperatures may remain in the low 40s area-wide. There may be a slight lull in precipitation late Wednesday into Thursday, but this should be short lived as the next upper trough (a little deeper than its predecessor) will arrive from West Texas. This should induce surface cyclogenesis upstream and result in a stronger WAA regime (thus why temperatures on Thursday are greater than Wednesday). The stronger southerly flow will help to boost surface moisture and contribute to building instability. As such, a mention of isolated thunderstorms remains in the worded forecast, though little in the way of severe weather is anticipated. Rain amounts will be a little heftier on Thursday, especially across East Texas thanks to the added convective element of precipitation. Any convective rainfall may exacerbate any remnant creek, stream or river flooding. Rain should taper off through the day on Thursday and by Friday morning, I expect that most areas will be rain/storm-free as a front will sweep through the area. The last weekend of January appears largely dry as a less humid airmass invades from the north. This will mean that we`ll have to contend with cold mornings (lows in the 30s) with pretty pleasant afternoons (highs in the 60s and possibly 70s). Bain && .AVIATION... /NEW/ /12z TAFs/ VFR will prevail through the next 24-30 hours. Winds will generally be light and variable through mid or late afternoon with a diffuse surface pattern in place. However, by this evening, a light prevailing southeasterly breeze should begin which will continue into Tuesday. Otherwise, sky conditions will consist of some passing cirrus through this morning before clearer skies prevail this afternoon. On Tuesday, widespread mid and high cloud cover will begin spilling in from the west, and VFR cigs around 10-15 kft will arrive towards the very end of the TAF period. -Stalley && .PRELIMINARY POINT TEMPS/POPS... Dallas-Ft. Worth 54 33 49 36 45 / 0 0 5 80 80 Waco 55 31 55 35 48 / 0 0 5 70 70 Paris 50 30 42 33 39 / 0 0 0 50 80 Denton 53 32 48 38 45 / 0 0 5 80 80 McKinney 52 31 46 37 43 / 0 0 0 80 80 Dallas 54 33 50 38 45 / 0 0 0 80 80 Terrell 53 31 49 37 44 / 0 0 0 70 80 Corsicana 54 33 54 38 46 / 0 0 0 60 80 Temple 55 36 57 39 49 / 0 0 5 70 70 Mineral Wells 55 33 51 38 48 / 0 0 10 80 60 && .FWD WATCHES/WARNINGS/ADVISORIES... None. && $$ 26/24