Area Forecast Discussion
Issued by NWS Mobile, AL

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364 FXUS64 KMOB 202340 AFDMOB Area Forecast Discussion National Weather Service Mobile AL 640 PM CDT Tue Apr 20 2021 .AVIATION... 21/00Z Issuance...VFR conditions through the period with only a few high clouds expected. Winds initially south to southwest 5 to 10 knots this evening, but shifting to the west and northwest overnight as a dry cold front moves south across the area. By Wednesday morning, the northwesterly winds will increase to around 10 to 15 knots with a few higher gusts possible. /12 && .PREV DISCUSSION... /issued 402 PM CDT Tue Apr 20 2021/ NEAR TERM UPDATE /Now Through Wednesday/...Aloft, mainly zonal flow is expected over the northern Gulf coast through the near term period. Surface high pressure will also persist into this evening. A cold front will then approach the Deep South this evening, with passage over the local area expected late tonight through early Wednesday morning. PWATs between 0.6-0.8 inches are shown by model guidance around midnight along and ahead of the cold front, which is expected to extend from Louisiana up through middle Tennessee and Kentucky by this time. However, this moisture will decrease as the front moves southeast through the overnight hours. By early Wednesday morning when the front moves through, PWATs will only be around 0.6 inches over the local area, decreasing even further through the morning as dry air is filtered in behind the front. With cold FROPA late tonight into early Wednesday morning, lows tonight will be a bit cooler. Expecting lows to range from the lower 40s to upper 40s and around 50 degrees along and northwest of I-65. Areas southeast of I-65 will then be in the lower to mid 50s. In fact, these low temperatures are just below the seasonal norms for this time of year, with normal lows being 56 degrees and 58 degrees for Mobile, AL and Pensacola, FL, respectively. A cooler day is also on tap for Wednesday, as highs will struggle to get out of the 60s along and northwest of I-65. Highs will then be in the upper 60s to lower 70s for areas southeast of I-65. Lastly, a LOW RISK of rip currents will continue through Wednesday night. /26 SHORT TERM /Wednesday night Through Friday night/...A dry mainly zonal flow pattern aloft will persist across the forecast area Wednesday night and Thursday, while a cool surface ridge of high pressure continues to build across the Mississippi and Tennessee Valley regions and adjacent north central Gulf Coast region. Mostly clear skies and a dry surface airmass along the building surface ridge will allow for cold temperatures across our forecast area early Thursday morning. Near record low temperatures remain a good possibility over much of our region with lows forecast to range in the upper 30s to lower 40s along and north of the Interstate 10 corridor to the mid 40s to around 50 degrees along the immediate coast. We continued to trend low temperatures toward the warmer guidance numbers given that elevated northerly winds could keep temperatures a little higher than would otherwise occur in a calm wind pattern. Here is the list of record lows for April 22: Mobile: 42 (1993) Pensacola: 46 (1993) Evergreen: 38 (1993) Greenville: 38 (1993) Andalusia: 35 (1993) Crestview: 41 (1993/2000) Niceville: 38 (1993) Waynesboro: 36 (1993) Wiggins: 40 (1993) An upper level trough over the Desert Southwest Thursday night is is forecast to move toward the southern Plains through Friday and then will quickly translate toward the ArkLaTex region by late Friday night. Clouds will gradually increase across our area Thursday night into Friday as layer moisture trends upward within the zonal mid level flow pattern. The lower levels will remain quite dry Thursday night, so will keep a dry forecast going into Thursday night. Deep layer moisture will increase considerably Friday-Friday night along an approaching shortwave trough embedded within the westerly flow aloft. Precipitable water values will increase to 1.4 to 1.7 inches Friday and Friday night across our area. Ascent will increase over northwestern portions of our area Friday afternoon and across southeast MS and adjacent southwest AL during the day Friday and over most of our CWA Friday night. Showers and a few thunderstorms will spread over our region during this time. We will have POPs increasing to 60-80% Friday night over most locations away from the coast. The highest coverage currently looks focused over interior southeast MS after midnight. Deep layer and low level shear increases over the region after midnight. 45-55 kt of southwesterly 850 mb flow is expected to spread into locations west of I-65 after midnight, along with 500-1000 J/KG of MLCAPE, which could bring a low end threat of severe storms over northwestern portions of our area overnight Friday night. Locally heavy rainfall will also be possible. Still some uncertainty on overall timing of any severe and heavy rain threat, but will watch trends closely over the next several days. /21 EXTENDED TERM /Saturday Through Tuesday/...The severe weather threat may increase across much of our CWA during the day Saturday. Surface dewpoints are forecast to rise into the mid to upper 60s across much of the area through Saturday morning, which could contribute to MLCAPE values between 1000-2000 J/KG. The increased instability along with strong deep layer and low level shear continuing to overspread the region will create a favorable environment for damaging winds, large hail, and possibly a couple of tornadoes embedded within the convective complex moving across our region through Saturday afternoon. Locally heavy rainfall and flooding concerns may also be possible on Saturday. We have POPs very high (70-90%) across our forecast area through the day Saturday. Drier conditions return Sunday through Tuesday as northwest flow aloft returns late in the weekend in the wake of the departing shortwave trough and as ridging aloft builds in early next week. Temperatures may warm back into the upper 70s to lower 80s by Monday and Tuesday underneath the building ridge aloft. Increasing southerly flow will bring an increasing risk of rip currents and elevated surf to our local beaches late Friday and Saturday. /21 MARINE...Light to moderate westerly flow this afternoon will become moderate to occasionally strong and northerly late tonight into early Wednesday morning as a cold front moves over area waters. A Small Craft Advisory has been issued for Southern Mobile Bay, Mississippi Sound, and the Alabama Gulf Waters during this time due to increased winds. Another Small Craft Advisory may be needed once again Wednesday night into Thursday morning due to elevated winds, mainly over the Gulf waters. Winds are then expected to decrease and transition to be easterly by Thursday afternoon. Winds will be moderate and from the southeast on Friday, then shift to be southerly and increase to be moderate to strong overnight ahead of another cold front. Seas will also increase during this time. This will be monitored for the potential of needing a Small Craft Advisory. Moderate northerly flow is then anticipated in the wake of the front Saturday night. /26 && .MOB WATCHES/WARNINGS/ADVISORIES... AL...None. FL...None. MS...None. GM...Small Craft Advisory from 5 AM to 1 PM CDT Wednesday for GMZ631- 632-650-670. && $$ This product is also available on the web at: http://weather.gov/mob

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