033 FXUS64 KBMX 211741 AFDBMX Area Forecast Discussion National Weather Service Birmingham AL 1241 PM CDT Sun Apr 21 2019 .UPDATE... For 18Z Aviation. && .SHORT TERM... Today and Tonight. High pressure is building into the region as the upper low moves out. With calmer winds and clear skies, radiation cooling is in full effect. The cooling in combination with waters beginning to warm up across the area has resulted in patchy fog development. The thickest fog is in the northeast where the cooler temperatures are. Will monitor to see if this will become more of a widespread issue issue versus patchy. After 9 am, any fog will be gone and sunny skies will prevail. Highs will be in the 70s areawide with just some light winds. As we move into the next period of darkness, winds will die and skies will be clear. A little bit more moisture will be in place so there is a potential for a little bit more in the way of patchy fog but do not see it being a widespread issue at this time. 16 .LONG TERM... Monday through Wednesday. Not looking at a lot of wholesale changes to the forecast for the long-term tonight. Monday will start a transition period with regards to upper-level considerations. Northwesterly flow aloft will have already overtaken much of the Deep South with a ~1022 mb surface high pressure across the Southeast. Stable weather conditions will persist into mid-week with a general eastward progression of the surface high. As such, southerly flow is expected to return by Tuesday/Wednesday with high pressure positioned off the Carolina Coast. Temperatures will respond with further warming into Tuesday as a shortwave ridge develops along the Appalachians in response to upstream & downstream trough axes. Meanwhile, a complex jet stream/split-flow configuration sets up across the CONUS with a mid- level disturbance, having previously separated from the Polar Jet, digging southward into the Southern Rockies. By Wednesday evening this is progged to eject into the Southern Plains & begin merging with the sub-tropical jet. Nonetheless, there are no mentionable rain chances through Wednesday night with forcing/moisture lacking across the region. 70s & 80s will prevail for afternoon highs Mon- Wed with Tuesday likely the warmest day of the upcoming week. Thursday through Saturday. The advertised disturbance is still on track to impact Central Alabama Thursday/Friday. Downstream of the trough/upper-level low (ULL), which should be near the ArkLaTex Thursday morning, broad theta-e advection will signal increasing PoPs for areas across the Gulf Coast & Lower Mississippi River Valley. Best chances for the onset of rain across Alabama should take place Thursday morning & was handled with ~50% in our western counties, generally decreasing eastward. Better quality moisture return & insolation during the afternoon will favor thunderstorm potential in an environment with weak/marginal shear profiles (20-30 kts 0-6 km bulk shear). However, thunderstorms should reside where best synoptic forcing & instability line up which appears to be across the west/south currently. Have left thunder out of forecast elsewhere until it appears that better moisture & instability may spread farther north/eastward in future updates. As the vertically-stacked low progresses eastward overnight, better area-wide coverage of showers & thunderstorms is expected & have increased PoPs to 60-70% with 'slight chance' of thunder mentioned across the entire area. It continues to appear the system will generally remain steady state or slightly weakening with eastward progression into the Southeast CONUS. This notion, combined with positioning favoring better convection along the Gulf Coast where a better low-level jet, wind shear, and instability are likely, suggests any thunderstorm activity across Central Alabama should remain sub-severe. Friday afternoon a better thermodynamic environment is possible given remnant boundary layer moisture & any decent afternoon heating, though NVA & height rises (weakening ULL moving to our east by now) suggest any short-lived, shallow convection should behave. All things considered at this time, there are no indications of severe weather or flooding with this system as rain totals are currently forecast ~0.5-1.25", though locally higher amounts are possible with thunderstorms in the forecast. Would generally expect improving conditions to follow heading into the weekend. 40/Sizemore && .AVIATION... 18Z TAF Discussion. Winds will generally be from the west northwest this afternoon, at 7- 8kts. Winds become calm after sunset, with patchy river/valley fog expected. Maintained a persistence forecast, with MVFR vis at ASN/ANB. Winds will be light and variable Monday morning as surface high pressure moves over the area. 14 && .FIRE WEATHER... A much drier airmass works into the region today and will remain across the area through mid-week. Clear skies and calm winds will allow patchy river and valley fog to develop this morning and again Monday morning. RH values will be in the 30 percent range area-wide this afternoon, and for most of the area Monday afternoon. The next chance of rain arrives early Thursday. && .PRELIMINARY POINT TEMPS/POPS... Gadsden 73 46 80 51 81 / 0 0 0 0 0 Anniston 73 48 81 51 83 / 0 0 0 0 0 Birmingham 75 53 82 55 83 / 0 0 0 0 0 Tuscaloosa 78 51 83 54 84 / 0 0 0 0 0 Calera 75 50 80 53 82 / 0 0 0 0 0 Auburn 72 52 80 54 82 / 0 0 0 0 0 Montgomery 76 49 82 53 84 / 0 0 0 0 0 Troy 75 50 82 53 84 / 0 0 0 0 0 && .BMX WATCHES/WARNINGS/ADVISORIES/... None. && $$