204 FXUS64 KMOB 092336 AFDMOB Area Forecast Discussion National Weather Service Mobile AL 636 PM CDT Sun May 9 2021 .AVIATION... 00Z issuance...VFR conditions prevail through the evening hours. Clouds increase overnight, maintaining at VFR ceilings, while rain showers and thunderstorms begin to move in late tonight into Monday morning. Local reductions in ceilings and visibility are possible in any storms. /13 && .PREV DISCUSSION... /issued 354 PM CDT Sun May 9 2021/ NEAR TERM UPDATE /Now Through Monday/...A complicated and messy pattern will set up across our forecast area late tonight into Monday as a rather noisy looking series of upper shortwaves and impulses over the ArkLaTex region will translate eastward in the zonal flow across the Lower MS Valley into early this evening, then across MS and into AL later this evening into late tonight. The high-resolution Convection Allowing Models (CAMs) are not in agreement at all with the development and subsequent movement of the anticipated convection due to their differences in handling the noisy pattern aloft, so will rely mainly on the short-term and spectral models (NAM, GFS, and ECMWF). With this said, will need to monitor the convection to our west this afternoon for a potential mesoscale convective system (MCS) to develop and eventually determine a speed of motion eastward this evening. For now, we are still forecasting the leading edge of an MCS to move into interior portions of southeast MS and southwest AL sometime around midnight tonight, give or take a couple of hours on either side dependent on the strength of cold pools allowing for propagation of the system toward our area. Low level wind fields should gradually weaken over MS/AL by late this evening as the stronger dynamics associated with the low pressure system quickly lift northeast toward the Appalachians and Eastern Seaboard. This will probably result in a weakening trend with convection approaching our northwest zones late this evening. However, plentiful moisture and instability will be available and there is a high chance that convection will arrive in these northwest zones late this evening or shortly after midnight, so will have POPs increasing to likely coverage over these areas starting at 06Z. Will need to watch for a couple of strong to marginally severe storms embedded within the line as it approaches our NW counties. The main concern would be strong/gusty winds and possibly some small hail. Precipitable water values trend up to near 1.9 to 2 inches over this portion of our forecast area overnight, while MLCAPE values also trend up to around 1000-1500 J/KG late tonight into Monday morning per the latest RAP and NAM. The GFS and ECMWF hold off with the MLCAPE values of 1000-1500 J/KG until early Monday afternoon. The very moist/unstable airmass and available ascent will support the development of numerous showers and thunderstorms northwest of a line from Greenville AL to Mobile AL late tonight, and a few could be strong with gusty winds, small hail, and very heavy rainfall. This line of convection should continue to weaken as it shifts southeast of I-65 through mid morning. There could be a brief lull in convection late Monday morning before yet another additional round of showers and storms develops Monday afternoon in association with another mid level perturbation arriving within the zonal flow. Instability with MLCAPE inching upward to between 1200-2000 J/KG across the western 2/3rds of the forecast mid afternoon along 40 to 50 knots of deep layer shear. This should be more than sufficient for few strong to marginally severe storms capable of producing strong to locally damaging gusts, small hail, and pockets of locally heavy rainfall Monday afternoon. The latest QPF/rainfall forecast in the near term has trended downward about one-half inch area-wide. While we still expect widespread rainfall amounts between 1 to 2.5", localized higher amounts have dropped slightly to between 2.5 to 3.5". We will however still need to watch for localized flooding concerns late tonight through Monday. /22 SHORT TERM /Monday night Through Wednesday night/...The active pattern remains as the shortwave train keeps on trucking. Westerly to slightly southwesterly flow aloft will continue through Wednesday night. Several weak shortwaves will progress through the flow each day bringing the potential for several rounds of showers and thunderstorms. At the surface, rain chances will be focused along a slow moving boundary that will drift south each day. Cape values will range in the 1500 to 2500 J/kg each day and shear will range in the 30 to 40 knot range which would certainly support at least some organization to the convection. This will likely bring at least the chance for a few strong storms with a damaging wind threat. Lapse rates are rather pathetic and mostly moist adiabatic which could inhibit more widespread stronger storms. The bigger threat will likely by the potential for heavy rainfall. PWATS will be in the 1.5 to 1.8 range and even some 2 inch PWATS will be possible along the surface boundary. With westerly flow aloft running parallel to the west to east oriented boundary this could lead to training storms. Additional rainfall amounts could range in the 2 to 4 inches with locally higher amounts where training occurs. All of this on top of the already soggy antecedent conditions leads me to believe that I would not be shocked to see a flash flood warning or two. Temperatures will remain mild through the period with highs ranging in the upper 70s to low 80s. Rain and cloud cover will probably be the main thing keeping temperatures down from getting too warm. Lows will be on the muggy side as low level moisture continues to funnel into the area. Lows will range from the upper 60s to near 70 along the coast and mid to low 60s inland. BB/03 EXTENDED TERM /Thursday Through Sunday/...The active pattern will come to an end on Thursday and into Thursday night as a large upper trough/low centered over the Great lakes will progress eastward into the northeastern US. This will break the zonal flow and bring a more northwesterly component allowing for drier air to move into the area and the surface boundary to push offshore. Rain will linger through Thursday as the remaining dynamics move through but by Friday skies and remain clear through Sunday as high pressure builds over the central US. Once we get through Thursday, conditions will be about as perfect as you can get for a beach weekend as highs will be in the low 80s to begin the period and eventually warming into the mid 80s by Sunday. Lows will also be a little more manageable as the drier air moves in leading to lows in the mid to upper 50s. The best part will be the dewpoints in the 50s leading to much more comfortable conditions. BB/03 MARINE...A light to moderate southerly flow will prevail through Tuesday ahead of a weak cold front approaching from the north. Southerly winds will be elevated enough that small craft will need to exercise caution at times this morning. Light easterly to variable winds are expected midweek as the cold front stalls near the coast, followed by light to moderate northeasterly winds Thursday as the front moves further offshore. Showers and thunderstorms will increase in coverage starting late tonight and will continue into Thursday. /22 && .MOB WATCHES/WARNINGS/ADVISORIES... AL...None. FL...None. MS...None. GM...None. && $$ This product is also available on the web at: http://weather.gov/mob