328 FXUS64 KBMX 061752 AFDBMX Area Forecast Discussion National Weather Service Birmingham AL 1252 PM CDT Thu Sep 6 2018 .UPDATE... For 18Z Aviation. && .SHORT TERM... Today and Tonight. Tropical Depression Gordon continues to slowly slide west- northwestward through the ArkLaMiss today. This has set up an area of confluence and weak banding across eastern portions of Central AL overnight, which should shift westward this morning. So far, this band has only produced very light rainfall. This afternoon, locations west of I-65 should expect a few bands of moderate rainfall, and isolated thunderstorms. Areas in the northeast with higher terrain could see a little better coverage of showers and storms this afternoon as well due to some localized orographic effects combining with the convergent bands. As we go into the evening, Gordon will continue to weaken and push westward, which will allow the best chances for rain/storms to slide west of our area, decreasing rain chances during the late evening and overnight hours. I wouldn't rule out some patchy fog development before sunrise in the morning in locations that see a decent amount of rainfall this afternoon. 25/Owen .LONG TERM... Friday through Sunday. Tropical moisture from Gordon will have mostly exited the forecast area by Friday afternoon as PWs decrease from ~2.2" to ~1.6" with drier air working its way in via easterly flow. Ridging across the East Coast will continue to weaken between a large trough working its way across eastern Canada, with a robust Polar Jet streak over Newfoundland, and a broad upper-level low currently northeast of the Bahamas moving westward towards the Florida peninsula. As a result, easterly flow won't last long with a trough axis begins to move eastward across the Great Plains and pick up what's left of Gordon across the southern Missouri Valley. Ahead of this trough we'll experience a transition to southerly/southwesterly flow by Saturday afternoon/evening which will advect higher values of boundary layer moisture into our region. Friday and Saturday look relatively quiet weather wise with mostly sunny skies and 20-30% PoPs respectively for afternoon isolated to scattered thunderstorms with best chances in areas west of I-65. By Sunday, our more humid airmass will begin to interact with dynamics from the approaching trough. An area of low pressure will develop, enhanced by Gordon's remnant circulation, in the Arkansas area and head northeast into the Ohio Valley. Height falls and the associated surface frontal boundary will move into proximity of our northwestern CWA by Sunday, overall increasing chances for thunderstorms in the afternoon/evening and have accounted for this in forecast grids with an increased PoPs to 50%. This will need to be adjusted/fine-tuned in the future as overall trends in the past 24-48 hours have the forward progress of the system farther eastward. High temperatures for Friday and throughout the weekend will be in the upper 80s to lower 90s overall, with a couple degrees cooler on Sunday from increased sky cover/precip chances. Monday through Thursday. The frontal boundary moving into our area will likely stall out across our region and remain a focus for thunderstorm development heading into the next work week. By now split flow in the upper- level jet stream pattern has overtaken a good portion of the US with the stronger branch of the Polar Jet disconnecting from this trough. With this in mind, Gulf moisture will replenish rain/thunderstorm activity with diurnally forced convection each day. Best rain chances look to be Mon-Tue with a decrease in probabilities from there as support for thunderstorms becomes more diffuse, and forecast confidence does as well. Pattern changes indicate upper- level longwave ridging to develop across the eastern portion of North America, with negative height anomalies building over the western CONUS. This supports a push towards a negative Pacific/North America pattern (PNA) that typically leads to above average temperatures in the eastern parts of the country. Thus, warm and moist conditions look to be the best trend for our area through next week. 40/Sizemore && .AVIATION... 18Z TAF Discussion. Scattered showers are developing across the area, moving south to north is disorganized bands (due to convergence on the east side of the remnants of Gordon). Shower coverage should expand through the afternoon, maintaining a south to north motion. Coverage at any terminal will depend on where bands become better established. Thunder will also be possible. Outside of heavy rain causing brief reductions in vis and cigs, do not expect any aviation concerns. Winds will be from the southeast at 6-8kts through this afternoon. Activity will diminish this evening, with skies clearing and winds becoming calm. Depending on where the rain actually falls today, patchy fog may redevelop but opted not to include as confidence remains too low at each individual site. 14 && .FIRE WEATHER... A tropical airmass remains across the forecast area for Thursday, though decreasing deep layer moisture via easterly flow will begin to take place helping to lower rain chances/dewpoints through the end of the week. However, recent rainfall and minimum RH values remain high enough to not be an issue. No fire weather concerns at this time. && .PRELIMINARY POINT TEMPS/POPS... Gadsden 89 69 91 70 91 / 40 10 20 10 30 Anniston 89 69 91 70 92 / 40 10 20 10 20 Birmingham 89 71 91 72 92 / 40 10 20 10 30 Tuscaloosa 90 72 92 72 92 / 50 20 20 10 30 Calera 87 70 89 70 90 / 40 10 20 10 20 Auburn 88 70 88 70 88 / 40 10 20 10 20 Montgomery 90 71 91 71 91 / 40 10 20 10 20 Troy 90 70 90 70 90 / 40 10 20 10 20 && .BMX WATCHES/WARNINGS/ADVISORIES/... None. && $$