681 FXUS64 KLCH 221149 AFDLCH Area Forecast Discussion National Weather Service Lake Charles LA 549 AM CST Fri Feb 22 2019 .DISCUSSION... 22/12/Z TAF Issuance. && .AVIATION... Widespread LIFR conditions are seen acrs the area this morning, with a frontal boundary located between ARA and LFT, and extending SW off the coast south of Cameron. The front is expected to lift north this morning, with winds at the LFT/LCH/BPT turning southeasterly through 16-17Z. As this happens, expect vsbys improving to VFR and cigs improving to MVFR. At AEX, the front is expected to move through around midday, followed by improving conditions. Southerly winds are then expected to prevail through the remainder of the TAF period, with intermittent -SHRA. Can not totally rule out TSRA, but point probabilities are too low to carry at this time. Cigs are again expected to lower to LIFR this evening, with patchy fog at the southern terminals reducing vsbys to MVFR/IFR. 24 && .PREV DISCUSSION... /issued 517 AM CST Fri Feb 22 2019/ SYNOPSIS... A potent storm system gathering strength over the southern Rockies will move eastward through the weekend and provide a roller- coaster of conditions for the forecast area. First, cooler conditions will be replaced by unseasonably warm and spring like today into the first part of Saturday, then back to more seasonable winter conditions later Saturday into the remainder of the weekend. This system will bring some potential hazards to the forecast area. Dense sea fog will be possible up to the I-10 corridor this morning, with the dense sea fog lingering near the coast into Saturday morning. Also, a Marginal to Slight Risk of Severe Weather will be possible, especially ahead of a cold front that the storm system will bring on Saturday. Rua DISCUSSION... A warm front as of 22/10Z was located from around New Iberia Louisiana (KARA) to about 40 miles south of High Island Texas. This front has been quasi-stationary overnight, however looks to be moving to the northwest again as winds have just become southerly again at KARA and temperatures and dew points are up to the upper 60s. Typical pre-warm frontal conditions are occurring with lowering stratus developing into areas of fog. This fog may be dense at times, especially near the coast. As strong upper level energy moves east across the southern Rockies a storm system and surface low will develop today. This will allow southerly flow to increase and accelerate the warm front to the north this afternoon. Any fog over inland areas is expected to lift as the front moves through and wind speeds increase. Most of the shower activity today will be ahead of the warm frontal system. Some of the shower activity may become on the strong side late this afternoon across northern sections of the forecast area as favorable right entrance region of 50H speed max intersects the leading edge of the warm frontal boundary. Most unstable CAPES will be near 1500 j/kg with daytime heating, and this could lead to elevated convection over the warm frontal boundary combining with the shear aloft to produce some small to marginal severe hail. The Storm Prediction Center has outlined the area north of a line from roughly Woodville to Marksville as having a Marginal Risk (5 percent) of severe storms. If any strong storms develop they will diminish in the evening hours with loss of daytime heating and speed max moving off to the northeast. As the upper level storm system moves east out of the Rockies it will deepen and phase with the strong sub-tropical jet stream and take on a negative tilt. As this system moves further east it will trail a Pacific cold front across the forecast area on Saturday afternoon. Low level jet will increase ahead of this cold front, and southerly winds around 40 knots will be found at 92H. This will help further increase the elevated moisture values across the forecast area with precipitable water values between 1.75 and 1.90 inches during Saturday, with these values well over twice the standard deviation and around the moving mean max for this time of year. Moisture convergence ahead of the front, and favorable divergence aloft from the increasing negative tilt of the upper level trough, will allow widespread shower activity to form, that will eventually form a squall line along the front. Meanwhile, increasing southwest winds aloft will be noted with the upper level system with 50H winds around 70 knots. This will allow for good shear to develop across the forecast area with 0-6km bulk values between 50 and 60 knots. With front timing in the afternoon hours, daytime heating will help increase low level instability. Most unstable CAPES will be between 1000 and 1500 j/kg, with most surface based CAPES around 1000 j/kg, which would tend to mean that some instability will be elevated due to the modified Gulf marine layer, and how much that modifies or mixes out will play a big part in how strong or severe the storms will become. With the respectable wind dynamics and shear values, the Storm Prediction Center has outlined the forecast area north of roughly a Beaumont to Lake Charles to Lafayette line in a Slight Risk (15 percent) for severe storms and a Marginal Risk (5 percent) for the remainder of the forecast area. Damaging straight line winds and hail will be the main hazards. However, a few short lived tornadoes can not be ruled out, especially if storms can become discrete and/or surface based, as 0-1km helicity values are over 200. Cooler and drier air will move in behind the front, ending shower activity, and setting up a nice Sunday with seasonal temperatures and sunny skies. Still some differences in the guidance as to how much return flow moisture will move back into the forecast area early next week before the next significant cold front moves through on Thursday. Will keep close to the superblend numbers which keeps rain chances for Tuesday into Thursday. Rua MARINE... A warm front this morning as of 22/10Z is located across the coastal waters from just inland of south central Louisiana to about 40 miles south of High Island Texas. Typical pre-warm frontal conditions occurring with lowering stratus causing dense fog ahead of the front, then south winds bringing warm and moist air over the cooler shelf waters producing dense sea fog behind the warm front. This warm front is expected to move north and inland during the morning hours, leaving a light to modest southerly flow over the coastal waters. This again will continue the problems of sea fog especially over the near shore waters. The southerly winds will increase later tonight, as a surface low pressure system develops east of the southern Rockies. Wind speeds may get to small craft exercise caution criteria for the outer waters by late tonight into Saturday morning. The winds may help lift the sea fog some, although the potential for dense sea fog will likely linger for the near shore waters into Saturday morning. A cold front will move through the coastal waters on Saturday afternoon. Modest northwest winds will develop behind the front with the possibility of small craft exercise caution conditions late Saturday night into Sunday morning. The northwest flow will bring in drier and cooler air to end sea fog and rain chances for the remainder of the weekend. Rua && .PRELIMINARY POINT TEMPS/POPS... AEX 75 65 75 44 / 60 50 80 0 LCH 78 68 77 48 / 30 30 70 0 LFT 79 69 79 51 / 30 20 70 10 BPT 75 67 75 48 / 50 30 70 0 && .LCH WATCHES/WARNINGS/ADVISORIES... LA...Dense Fog Advisory until 10 AM CST this morning for LAZ041>045- 052>055-073-074. TX...Dense Fog Advisory until 10 AM CST this morning for TXZ215-216. GM...Dense Fog Advisory until noon CST today for GMZ430-432-435-450- 452-455. && $$ AVIATION...24