272 FXUS64 KMOB 010602 AFDMOB Area Forecast Discussion National Weather Service Mobile AL 1202 AM CST Fri Jan 1 2021 .NEAR TERM UPDATE /Now Through Friday night/...Showers and storms will continue through the overnight hours; however, the severe threat appears to be diminishing. An occluded upper level system is currently centered over the Red River Valley and continues moving north-northeast into southern MO and eventually into the Great Lakes region. A strong low-level jet was noted over central LA and is expected to strengthen as it moves over central MS into the overnights. This feature will diminish as the upper low moves off to the northeast through Friday. At the surface, the approaching cold front continues moving east towards the region through Friday morning. Ahead of the front, showers and storms have developed and will continue into the morning. Current observations would suggest the severe threat continues to diminish as instability lacks over the region. Convection has struggled to organize due to a lack of stronger forcing which displaced to our west. Additionally, dry air has overspread the region in the mid-levels which is inhibiting strong updrafts from forming. Any convection that forms should be relatively shallow. However, the main front line should push through SW AL during the early morning hours and our FL Panhandle and south central AL counties by early afternoon. If timing lines up, there could be some instability present in the early morning hours over the FL panhandle which would allow for a few thunderstorms to develop, a strong storm cannot be ruled out. Precip chances quickly taper off from west to east in the wake of the front as cooler, drier air filters into the region. A strong surface pressure gradient will keep a strong southeasterly flow over the Gulf resulting in high risk current risk and dangerous high surf at all beaches through the period. Along with dangerous surf, minor coastal flooding throughout Mobile Bay is occurring and expected to continue through the high tide cycle through Friday morning. Min temps overnight are expected to be in the low to upper 60s tapering off from west to east as the front moves across the region. High temps Friday follow suit, with upper 60s west of I-65, and low to mid 70s east of I-65. JEH/88 && .AVIATION... 06Z issuance...Mixed LIFR/IFR conditions were present across the region including TAF sites MOB and PNS with MVFR at BFM at time of issuance. Conditions will likely remain through Friday morning before tapering off from west to east as the front moves across the CWA. Southeast winds gradually switch to southwest between 10-20kts are expected with higher gusts possible. LLWS is also a factor with the passage of this cold front. Fourty knots of south-southwesterly wind shear is expected to occur between now and ~14Z. Conditions for flying is expected to improve to MVFR/VFR from west to east Friday morning through afternoon in the wake of a cold front. Conditions will be monitored with the passage of this system and updated if necessary. JEH/88 && .PREV DISCUSSION... /issued 754 PM CST Thu Dec 31 2020/ MESOSCALE UPDATE...Water vapor imagery shows a potent mid level low pressure system centered close to Austin, TX as of 7 PM CST, while surface analysis shows the associated surface low centered a little further northeast over eastern TX. A surface cold front extends south and southeast from the surface low into far southeast TX/far southwest LA and the adjacent western Gulf waters, while another frontal boundary extended to the east of the surface low across central portions of LA, MS, AL, and GA. Much of our forecast area is located to the south of the eastward extending frontal boundary early this evening with a warm and moist southeasterly surface flow in place. Temperatures at 7 PM CST are in the upper 60s to the lower 70s with surface dewpoints in the mid 60s to near 70 degrees south of the U.S. Hwy 84 corridor (around 60 to the lower 60s north of the Hwy 84 corridor in our far interior areas). MLCAPE values are generally averaging between 500-800 J/KG along and southeast of a Richton MS to Destin, FL line, but the stronger low level jet of 40- 45 knots remains oriented to the west of our CWA across southwest LA and into LA at this time. Looking ahead for the next several hours, an increasingly diffluent flow pattern aloft still looks to advance eastward across our forecast area over the next few hours as the deep low pressure system lifts N-NE toward the TX/OK border. Associated increased deep moisture and ascent spreading over our region will continue to result in increasing coverage of rain showers and a few thunderstorms over the next few hours. High resolution model guidance continues to show a strengthening low level jet on the order of 40-50 kt through around midnight, while MLCAPE of 500+ J/KG extends to the south of the surface boundary across our CWA. A narrow corridor of MLCAPE near 1000 J/KG could extend northward into southern portions of southeast MS, Mobile/Baldwin counties, and into the western FL panhandle through late tonight. We still expect convection, potentially with cells embedded within a developing linear complex, to increase in coverage and move east across our forecast area late this evening/overnight within this zone of diffluence, increased low shear, and low level moisture and instability. The shear and instability will still be sufficient to support a threat of damaging wind gusts, while 0-1 km SRH up to around 200 m2/s2 could result in a brief tornado. Factors that could limit the severe potential include: 1) overall weak instability over inland locations through the night, and 2) mid level subsidence that may move over the region late, keeping convection/updrafts relatively shallow. SPC has maintained the Slight Risk of severe weather over most of our CWA, which looks good considering the supporting factors listed above. We will continue to monitor trends closely through the night. /21 In addition, minor coastal flooding is looking more likely late tonight across immediate coastal areas of Mobile and Baldwin Counties, especially the northern end of Mobile Bay. Southeast winds of 20-25 kt with higher gusts will combine with high tide (after midnight) to produce minor coastal flooding in vulnerable, low lying areas. The eastbound lanes of the US 90 Causeway could be impacted near the I-10 intersection, as well as across portions of other low lying coastal roads. Therefore, a Coastal Flood Advisory has been issued until 6am Friday. 34/JFB PREV DISCUSSION... /issued 552 PM CST Thu Dec 31 2020/ AVIATION... 00Z issuance....IFR conditions were present at TAF sites MOB and PNS at time of issuance with MVFR at BFM. Conditions will begin deteriorating as thunderstorms develop over the Gulf and move across the region this evening with CIGs and VISs dropping at times dropping to IFR conditions at times. Some thunderstorms could produce strong to severe wind gusts. Southeast winds gradually switch to southwest between 10-20kts are expected across all TAF sites with higher gusts possible. LLWS is also a factor with the passage of this cold front. This feature has been included at all TAF sites and is expected to occur between 03Z-12Z up to 2kft, with a south- southwest direction, and up to 50kts at TAF sites BFM and MOB. LLWS at PNS is expected to between 05Z-12Z up to 2kft with a south-southwest direction, and up to 50kts. Conditions for flying is expected to improve to MVFR/VFR from west to east Friday morning through afternoon in the wake of a cold front. Conditions will be monitored with the passage of this system and updated if necessary. JEH/88 PREV DISCUSSION... /issued 340 PM CST Thu Dec 31 2020/ NEAR TERM UPDATE /Now Through Friday/...The approaching cold front has now moved eastward off the Texas coast and over the western Gulf waters. A line of convection has developed along and east of the boundary, moving eastward. Satellite imagery also shows an area of deep convection has developed offshore over the north central Gulf, moving northward. A lingering subsidence inversion over the area this morning capped convection preventing thunderstorm development. Model soundings depict this feature weakening and disappearing by late this afternoon allowing for showers and thunderstorms aided by upper level forcing and instability to increase and become widespread into the evening and overnight hours. As the main upper level low is driven northward driving the surface low and associated occlusion with it, the models are suggesting the main squall line will develop around southwest AL and then push eastward into the FL panhandle and south central AL after midnight. Main severe weather concern along this boundary will be the potential for damaging straight line winds of 60 mph or more due to the 50 knot plus low level jet overlying the area. However, still can't rule out a brief tornado or two as low-level shear vectors ahead of the line remain sufficient for possible mesocyclone generation. The actual front will follow the squall line pushing through SW AL during the early morning hours and our FL Panhandle and south central AL counties by early afternoon. Precipitation chances quickly taper off in the wake of the front and drier, cooler air follow into the weekend. Other impacts, a tightening pressure gradient will keep a strong southeasterly flow over the Gulf resulting in building seas producing a high risk current risk and dangerous high surf. /08 SHORT TERM /Friday night Through Sunday night/...The short term period starts off with strong southwest upper level flow of 100 to 120kts over the CWA at 250mb on the east side of a deep ejecting upper level trough over north Texas. This trough shifts northeast into the Great Lakes region through Saturday night as the upper level jet streak pivots over our area. Another upper level shortwave begins to move across the Tennessee Valley with a weak broad trough evident through the gulf coast states Sunday night. At the surface, an area of low pressure will be located over IL/IN with a cold front draped to its south down across AL/MS. This front will progress through the CWA Friday night, becoming rather weak to the east of our CWA Saturday morning. A weak low pressure system begins to develop over the northeastern Gulf of Mexico Saturday afternoon, bringing with it another chance for isolated showers. Best chance for showers Saturday afternoon/evening will be along and east of I-65, moving out of the area Saturday night. Dry air returns for Sunday with clearing skies as a surface high pressure begins to build in. Temperatures Friday night generally stay in the middle to upper 40's west of I-65, with lower 50's east of I-65. Highs Saturday don't recover much, increasing into the upper 50's to lower 60's. Saturday night and Sunday night will be similar with lows in the middle to upper 30's. Sundays high will be in the middle to upper 50's for most locations. MM/25 EXTENDED TERM /Monday Through Thursday/...Calm weather takes precedence Monday and Tuesday as our surface high stays centered over the southeastern U.S. before beginning to shift east into the Carolinas Tuesday night into Wednesday. Likewise, upper level ridging follows suit, followed by an approaching upper level trough Wednesday. Low level warm air advection (WAA) begins ahead of this approaching system as an area of low pressure begins developing over eastern Texas. This low quickly translates east across the interior portions of the gulf coast states, increasing our rain chances as we head into Wednesday and Thursday. By Thursday evening, the low will be moving east of the area with a weak cold frontal passage allowing for rain chances to diminish from west to east. Forecast highs generally remain in the upper 50's to lower 60's each day, with the warmest day being Wednesday where highs may manage the lower to middle 60's for most locations. Lows follow a gradual warming trend, starting in the upper 30's and lower 40's Tuesday morning increasing into the upper 40's to lower 50's by Wednesday night into Thursday morning. MM/25 MARINE...A strong onshore flow continues and strengthens overnight as a cold front approaches from the west. Showers and thunderstorms develop over marine waters tonight and some may become strong to severe. A light to moderate southwest to westerly flow will follow in the wake of the cold front tonight and Friday. A re-enforcing cold front then crosses area waters late Friday night into Saturday, bringing a moderate to strong offshore flow and building seas into early next week. /08 && .MOB WATCHES/WARNINGS/ADVISORIES... AL...High Rip Current Risk through late Friday night for ALZ265-266. High Surf Advisory until 6 PM CST Friday for ALZ265-266. Coastal Flood Advisory until 6 AM CST Friday for ALZ263>266. FL...High Rip Current Risk through late Friday night for FLZ202-204- 206. High Surf Warning until 6 PM CST Friday for FLZ202-204-206. MS...None. GM...Small Craft Advisory until 6 AM CST Friday for GMZ630>636. Small Craft Advisory until 6 PM CST Friday for GMZ650-655-670- 675. && $$ This product is also available on the web at: http://weather.gov/mob