Scientific Forecaster Discussion
000 FXUS64 KFWD 090945 AFDFWD Area Forecast Discussion National Weather Service Fort Worth TX 345 AM CST Fri Dec 9 2016 .DISCUSSION... It's definitely a cold morning out there now as a strong 1040 mb arctic anticyclone is settling in just to our northeast, although perhaps not quite as bone chilling as we were anticipating a few days ago. Temperatures this hour are generally running in the lower 20s to near 30 degrees with a light northerly breeze resulting in wind chills in the teens for many. Expansive low- level cloudiness is spreading eastward this hour, and will likely envelop most of our region today as residual moisture in the 850-750 mb layer is resupplied by increasing southwesterly flow aloft. Given the potential for this cloud cover today, sided with the cooler temperature guidance and even knocked a degree or two off of that. Thankfully, wind speeds will be greatly diminished from what we experienced yesterday. High pressure slides east of the region on Saturday, which will result in the return of southerly/southwesterly low-level flow and swiftly increasing moisture. By Saturday evening, forecast soundings reveal a saturated, or a near-saturated airmass in the lowest 5000 feet or so, with very dry air above. This should set the stage for the development of drizzle/light rain showers across a good chunk of the CWA Saturday night. That said, the likelihood of measurable precip looks pretty low at this time, and will cap PoPs at 30 percent during this time frame. As a shortwave and associated cold front approach the region on Sunday, shower chances should steadily push east of the I-35 corridor before chances come to an end Sunday evening. As all of the saturated air seems to be relegated below 850 mb and well above 0C, the potential for thunder appears very low at this time, and have left it out of the worded forecast on Sunday afternoon. Cooler and drier air will filter into the region on Monday behind this aformentioned front resulting in a nice, seasonable start to the work week. The moderating temperatures will be short-lived, however, as yet another arctic airmass will be intruding into the northern CONUS on Tuesday. The leading edge of this rejuvenated cold airmass should move through North and Central Texas somewhere during the Tuesday night into Wednesday morning time frame, but substantial model spread and run-to-run consistency issues are plaguing this portion of the forecast. The GFS, which has struggled mightily over the past few days with the timing of this arctic front has largely been ignored in this forecast package given its very tardy frontal timing on Wednesday afternoon. Instead, a blend of the notably faster 09/00Z ECMWF and GFS Ensemble mean seems more reasonable, and matches up a bit better with the 09/00Z Canadian as well. Moisture profiles look very meager during the frontal passage, and as a result, we've maintained the dry forecast during the middle of the week. Temperatures behind the front on Wednesday and Thursday should not be quite as cold as what we experienced this week, but will nonetheless be about 10 to 15 degrees below average. As the cold high pressure center migrates east of the region on Friday, return flow and an approaching disturbance may bring about renewed chances of showers towards the end of the week. Carlaw && .AVIATION... /ISSUED 1151 PM CST Thu Dec 8 2016/ 06 UTC TAF Cycle Concerns---None major. VFR with northerly winds becoming southeasterly by Friday afternoon. VFR is expected to prevail through the entire 06 UTC TAF cycle across all North and Central TX terminals. The previous cloud cover has completely scattered with the departure of a weak low level trough. The 00 UTC FWD RAOB did indicate some residual moisture around FL070-FL080. With any weak perturbation in the westerly flow, additional saturation and additional VFR stratus could develop. This appears to be the case along an ABI to MKN to ACT line. Additional cloud cover is attempting to creep southward from Oklahoma as well. With regards to the forecast, will start Metroplex TAF sites out with SKC before VFR stratus develops around FL080 during the mid- morning hours and into the afternoon. For the Waco TAF site, will continue with a ceiling around FL070 through a majority of the 06 UTC TAF cycle. Northerly winds will eventually become easterly and southeasterly through Friday afternoon at Metroplex TAF sites and southeasterly winds are expected around sunset Friday at Waco. In the extended portion of the forecast, some VFR ceilings may redevelop just after 06 UTC Saturday, but to keep the TAFs simple, I'll abstain from mentioning this at this time. 24-Bain && .PRELIMINARY POINT TEMPS/POPS... Dallas-Ft. Worth 42 31 51 47 70 / 0 0 5 20 10 Waco 41 31 50 48 70 / 0 0 10 20 10 Paris 41 27 48 44 65 / 0 0 5 30 40 Denton 40 28 50 46 70 / 0 0 5 20 10 McKinney 42 28 49 45 68 / 0 0 5 30 20 Dallas 42 32 50 48 70 / 0 0 5 30 20 Terrell 42 29 49 47 68 / 0 0 10 30 30 Corsicana 43 32 50 48 68 / 0 0 10 30 20 Temple 42 31 50 48 69 / 0 0 10 30 10 Mineral Wells 39 28 53 47 71 / 0 0 5 10 5 && .FWD WATCHES/WARNINGS/ADVISORIES... None.