Scientific Forecaster Discussion
000 FXUS64 KSHV 232046 AFDSHV Area Forecast Discussion National Weather Service Shreveport LA 346 PM CDT Tue May 23 2017 .UPDATE... Precipitation continued to develop along and behind the front, as it near deep east TX and northwest LA with a quick movement to the southeast. Increasing instability provided by an upper level jet streak coupled with plentiful low-upper level moisture, may result in some of the storm activity to become strong to severe particularly across deep east Texas. The main threats will be large hail and damaging winds. A Severe Watch is in effect until 11 pm CDT. && .PREV DISCUSSION... /issued 300 PM CDT Tue May 23 2017/ DISCUSSION... A broad UA low across the Northern Plains late this aftn, was progressing south-southeast thus resulting in the sharpening of southwest flow aloft across the Four-State Region. Embedded in this southwest flow aloft is a 90+ kt jet max at 250 mb rounding the base of this trough, and moving across the region which is allowing for increasing UL diffluence. Looking at the sfc, a cold front has impinged upon the FA and located along a kcdh, to a ktxk to a ktyr line, with a movement to the southeast. Increased UL support provided by the aforementioned jet streak, coupled with frontogenetical forcing by the cold front and a rather moist atmospheric profile /PWATS of 1.20-1.60 inches/ has resulted in isolated showers and thunderstorms, mainly along and behind the cold front. The stratus deck has eroded but BKN-OVC VFR CIGS remained, further validating the moist atmosphere. Nonetheless, there have been breaks in the cloud cover which have allowed temps to warm into the 70s. As a result, some daytime destabilization/steepened lapse rates has been realized which could aid in a few of the storms nearing strong levels and producing small hail. The precip is expected to not stick around for long, as model solutions displayed precip exiting from west to east by tonight, as the UL jet streak will be pushing east and hence UL support will be fleeting. Overnight, skies are expected to scatter out and perhaps become clear across most of the region, whilst relatively light west- northwest sfc winds ensue. If this does indeed come into fruition, this could set the stage for decent radiational cooling and promote overnight temps to drop into the upper 40s across portions of southeast OK, extreme northeast TX and southwest AR to lower to upper 50s elsewhere. Tomorrow, as the UA low commence to near the middle/lower Mississippi Valley, the ARKLATEX will be on the backside of the disturbance and mid-upper level atmospheric drying will occur. However, southwest AR and northeast LA will be the last areas for the drier air to take effect, so a few lingering showers nearing/brushing across the said areas can not be ruled out during the day tomorrow. Otherwise, slight pressure rises tomorrow aftn will result in a tightened pressure gradient, which will lead to northwest sfc winds approaching Lake Wind Advisory speeds. Due to this close call, will elect to hold off on a Lake Wind Advisory for this forecast package and let the midnight shift make the call /and see if models continue to show this trend/. Tomorrow night, wind speeds will become light and at times variable a few hours after sunset, whilst clearing skies take place. This will once again result in excellent radiational cooling /and perhaps some patchy fog/ leading to tomorrow night temps plummeting into the lower 40s across the north to lower 50s elsewhere /or some 10-15 degrees below norm/. We continue to undercut model guidance by a few degrees for tomorrow night because guidance tends to trend towards climo and in this case, it is not representative. On Thursday, srly sfc flow will return to the region and the quick passage of UA ridging on Friday will result in temps rebounding into the upper 80s to lower 90s by the end of the week into early weekend /some 5 or so degrees above normal/. Thereafter, long term solutions hint at an UA trough getting carved out across the Southern Rockies by late weekend, resulting in flow aloft veering from near zonal to the west-southwest across the Four- State Region. The best UL dynamics will remain north of the region closest to the center of the disturbance, but a sfc trough and the impingement of another cold front will cause the generation of showers and thunderstorms. Furthermore, the front is progged to become quasi-stationary across the southern zones which will maintain the unsettled wx into early next week. It is too early to say with certainty whether or not a severe weather threat will exist this weekend, but we will continue to monitor this plausibility. && .PRELIMINARY POINT TEMPS/POPS... SHV 54 73 52 85 / 60 10 0 0 MLU 56 73 50 83 / 70 10 10 0 DEQ 49 72 43 83 / 30 10 0 0 TXK 52 72 49 83 / 50 10 0 0 ELD 52 71 46 83 / 70 10 0 0 TYR 53 75 54 86 / 40 0 0 0 GGG 53 73 52 87 / 40 0 0 0 LFK 56 78 54 89 / 60 0 0 0 && .SHV WATCHES/WARNINGS/ADVISORIES... AR...None. LA...None. OK...None. TX...None.