955 FXUS64 KMOB 131144 AFDMOB Area Forecast Discussion National Weather Service Mobile AL 644 AM CDT Wed Apr 13 2022 .AVIATION... 12Z issuance...Mainly VFR cigs should prevail at all TAF sites through the day. Some MVFR cigs/vsbys are possible later this afternoon across southeast Mississippi into interior southwest Alabama as a round of showers and thunderstorms move across the area. Cigs/vsbys lower to MVFR this evening as strong low level moisture advection continues in advance of an approaching front. Further deterioration to IFR is expected at the TAF sites after approximately 5-8z, as widespread showers and thunderstorms ahead of the front move through the region. The front should move across the coast with a switch to northerly winds just beyond this forecast period. Brisk southeast to south winds are expected prefrontal sustained between 12 and 15 knots, with occasional gusts in excess of 25 knots through the period. /JLH && .PREV DISCUSSION... /issued 442 AM CDT Wed Apr 13 2022/ .NEAR TERM UPDATE /Now Through Thursday/...Broad upper level ridging remains in place this morning across the central Gulf Coast and extends eastward across the Florida Peninsula. An amplifying upper level trough continues to dig across the Central and Southern Plains this morning and will be the next weather maker across our area later today and tonight. A lead shortwave embedded within southwest flow aloft is currently lifting northeast across the Mid South. This shortwave was responsible for initiating and maintaining a QLCS as it moved across Arkansas into northern Louisiana and western Mississippi. This shortwave is beginning to lift out to the north with the residual squall-line moving into a more stable airmass across eastern Mississippi. This has resulted in a notable weakening and this should continue to weaken and eventually dissipate by sunrise. There may be a few lingering showers across interior portions of southeast Mississippi and southwest Alabama prior to the line completely falling apart. Have maintained a small pop across these locations for early this morning. Another concern early this morning is an area of enhanced winds across locations along and west of I-65. These winds are in association with a weakening wake low that developed behind a dying convective line from Tuesday evening. Winds gusting between 25 and 35 mph have been common across southeast Mississippi and southwest Alabama this morning. This should continue for the next few hours before gradually diminishing around sunrise. Dry conditions will briefly return to the entire area later this morning as mid level ridging briefly builds back in over the forecast area this morning behind the departing early morning shortwave to our northwest. This should allow for appreciable heating by later this morning through the afternoon. In addition, southeasterly low level flow will continue to advect low level moisture northward across our area with dewpoints remaining in the mid to upper 60s across the western half of the forecast area. The amplified upper trough to our west will lift northeast from the Southern Plains through the Lower and Middle Mississippi Valley by this evening as it takes on an increasingly negative tilt. As this occurs, a strengthening upper level subtropical jet streak on the order of 130kts is progged to spread in from the west along the western Gulf Coast. At the same time, a phased polar jet streak to the north in the upper levels will lift north through the Mid South and Middle Mississippi Valley. An area of enhanced differential divergence is noted with the left exit region of the subtropical jet by this afternoon. This should help to enhance large scale ascent across portions of southeast Mississippi by late this afternoon. In addition, the wind fields aloft become quite diffluent across southeast Louisiana into southeast Mississippi by late afternoon also helping to enhance ascent. The atmosphere is likely to remain capped to convection by a warm nose around 850mb through much of the day. Sufficient diurnal heating, low level moistening, and the noted large scale ascent should work to erode and lift out the capping inversion by late afternoon (21-23z). This is supported by much of the latest global model and CAM guidance. As the capping erodes, the atmosphere should become more supportive of deep convective development during this time period. The latest global spectral and CAM model guidance is supportive of storm development across southeast Mississippi by late afternoon, spreading into southwest Alabama by evening. Atmospheric conditions should become increasingly favorable for some severe weather threat, although shear especially in the lowest 1-2km will be somewhat marginal. Thermodynamic instability by late afternoon should increase with MLCAPES between 1000-1500j/kg. This instability combined with 30-40 kts of deep layer shear should support multicell clusters of storms capable of marginally severe wind gusts and potential for large hail. There will be good veering in the lowest few kilometers of the atmosphere, but weaker winds on the order of 25-35kts in the 0-1km layer could limit the overall tornado threat. A Slight Risk for Severe Thunderstorms exists for areas along and west of I-65 beginning late this afternoon and persisting through the overnight hours. A QLCS should form to the west of any late afternoon/early evening convection by later this evening in response to the greater mid level height falls associated with the upper trough. As the QLCS pushes southeast ahead of a surface cold front later tonight, it should gradually weaken with southeastward extent as the better large scale forcing lifts out to the north and deep layer shear weakens further. There may be an initial severe threat across interior southeast Mississippi into southwest Alabama during the late evening with the squall-line, but this threat should diminish further south and east later in the night. The line should gradually slow and stretch out from southwest to northeast with time late tonight. This may allow for localized flooding to occur in areas where storms train across the same locations. The front will slowly push out over our coastal waters by later on Thursday with shower and thunderstorm chances diminishing from northwest to southeast through the day. Convection should linger longest across coastal counties of Alabama into the western Florida Panhandle where a flood threat may continue through much of the day. The front should eventually stall out just offshore by Thursday evening as the mid and upper flow becomes zonal along the extent of the surface front. Moderate onshore flow will keep the threat for rip currents high along our area beaches through the near term forecast period. In addition, waves will range between 3 and 5 feet at the coast and result in hazardous swimming conditions for inexperienced swimmers. /JLH && .SHORT TERM /Thursday Night Through Friday Night/...Aloft, mainly zonal flow is expected through the short term, but several subtle shortwaves will move along the flow during that time. At the surface, a stalled cold front will be draped along or just east of the I-65 corridor by Thursday evening. This front will likely push offshore overnight and into early Friday morning; however, guidance indicates that this front will advance back north over our marine zones and coastal counties as a warm front Friday night into early Saturday morning. In terms of sensible weather, some isolated showers and a few storms will be possible east of I-65 as the main storm system discussed in the near term moves east of the local area; however, for the most part, a lull in shower and storm activity is expected for many areas Thursday night. As PWATs increase once again through Friday afternoon (1.5-1.8 inches over southeast Mississippi and far southwest Alabama), anticipating rain chances to return. Although, coverage will remain isolated. As for any thunderstorms that may develop, not expecting these to be severe; however, they will be possible as model MUCAPE values range between 500-1000 J/kg and bulk shear ranges between 30-40 knots. With the increase in moisture on Friday, an increasing trend in low temperatures will take place through late week. Lows Thursday night will drop into the 50s over inland areas and into the lower 60s at the coast. By Friday night, lows will merely drop into the 60s for most areas. Meanwhile, highs Friday afternoon will warm into the lower 80s inland and be in the mid to upper 70s at the coast. Lastly, the HIGH RISK of rip currents will persist through Friday night. /26 && .EXTENDED TERM /Saturday Through Tuesday/...Another upper level shortwave will progress over the Southeast Saturday afternoon, followed by a stronger shortwave that will mover over the region Monday morning (although slight timing differences still exist in the global models). This, along with PWATs between 1.4-1.7 inches, the aforementioned warm front (anticipated to move north over the Gulf coast on Saturday), and another cold front that will move over the region from Sunday into Monday, will lead to a continued unsettled pattern through Easter weekend and into the first part of the work week. With elevated deep moisture combined with already saturated soils from previous rainfall, we will need to monitor for potential flooding concerns - especially where showers and storms move repeatably over the same locations. Although, we do have good news! The second upper shortwave and surface high pressure building in behind the fronts on Monday will push the rainy and stormy weather east, leaving dry weather for the local area by Tuesday and into midweek next week. High temperatures on Saturday will reach the upper 70s to lower 80s, with a slight downward trend by Tuesday as temperatures will likely only top out in the 70s. Low temperatures through the period will follow a similar pattern, beginning in the 60s Saturday night and then dropping into the 50s by Monday night. /26 && .MARINE...Strong onshore flow in excess of 20 kts and seas between 5 and 7 feet will persist over our open Gulf coastal waters today, with 1-3 feet in the bays and sounds. A Small Craft Advisory remains in effect through this afternoon for all offshore waters and including Mobile Bay and Mississippi Sound. Winds and seas should gradually subside later tonight as the pressure gradient relaxes. The flow should turn briefly offshore behind a stalling cold front Thursday night before returning back to onshore flow as the front lifts back to the north on Friday. Light to moderate onshore flow will continue through the weekend. /JLH && .MOB WATCHES/WARNINGS/ADVISORIES... AL...High Rip Current Risk through late Friday night for ALZ265-266. FL...High Rip Current Risk through late Friday night for FLZ202-204- 206. MS...None. GM...Small Craft Advisory until 4 PM CDT this afternoon for GMZ630>632-650-655-670-675. && $$ This product is also available on the web at: www.weather.gov/mob