Scientific Forecaster Discussion
000 FXUS64 KBMX 191120 AFDBMX Area Forecast Discussion National Weather Service Birmingham AL 620 AM CDT Sat Oct 19 2019 .UPDATE... For 12Z Aviation. && .SHORT TERM... /Updated at 0351 AM CDT Sat Oct 19 2019/ Today and Tonight. Tropical Storm Nestor continues to move northeastward and is expected to make landfall this morning along the Florida Gulf Coast near Mexico Beach. The system is asymmetrical with the stronger winds and most of the rain on the east side of the storm. As Nestor moves through the Florida Panhandle and into Southern Georgia today, it is expected to transition to a post-tropical storm. Overall, the impacts to Central AL from Tropical Storm Nestor look to be minimal. Winds today will be noticeably higher, especially this morning for areas south of I-85 (sustained 10-15 with gusts 20mph+), but the strongest winds should remain to our south. By the afternoon, winds will decrease area-wide. Nestor has a current forward speed of around 20mph, which will help keep any flooding threat to a minimum across Central AL as well. Timing has been fairly consistent the last few forecasts. Light rain is already moving into the southeastern counties this morning. This is expected to spread northward through the morning, with the best chances of rain being generally east of I-65. Rain will decrease west to east in the early afternoon and most of Central AL should be rain-free by 7-10pm tonight. Temperatures today will be moderated by the expansive cloud cover and rainfall. Highs will range from the low 60s in the east, where there will be more rainfall, to the low 70s in the west. Lows tonight will drop into the low 50s. 25/Owen .LONG TERM... /Updated at 0351 AM CDT Sat Oct 19 2019/ Sunday through Saturday. Between weather systems, height rises will take place on Sunday as a significant trough digs toward the Central Plains. A dry and warm afternoon is expected under the influence of southerly flow. Temperatures should reach the upper 70s to the lower 80s. Pressure falls will take place Sunday night into Monday across the span of the Mississippi River Valley as a powerful jet carves out a deep trough centered over the Upper Midwest. A 40-50 kt low-level jet should be located along the MS River at 12Z Monday with upper 60s to near 70 degree dewpoints advecting northward across the ArkLaMiss. Most of our forecast area will remain dry through the early afternoon, but a band of showers and storms will move in from the west during the afternoon and evening. The low-level jet is expected to weaken into the 35-40 kt range as it moves into our northwest counties. However, with SBCAPE of 500-1000 J/kg, there appears to be a marginal threat for isolated damaging winds and perhaps a brief tornado. The entrainment of a subtropical shortwave into the larger-scale trough may complicate the convective evolution for areas farther southeast. This feature may shift the strongest forcing and lift toward our southeastern counties, causing a localized minimum in the low-level jet and a lull in convection across the middle of the area. Additionally, the subtropical shortwave could cause a small-scale enhancement of the low level jet across our southeast counties Monday night. Therefore, the marginal risk for isolated damaging winds and a brief tornado will be expanded to cover all of our forecast area. Forecast confidence is low with this system, but an upgrade to a slight risk may become necessary. Cooler and much drier air will move into the region on Tuesday behind a cold front with high pressure in control through early Thursday. Another large trough is expected to take shape Thursday night and Friday to our northwest, leading to the potential for widespread rain for Thursday night through Saturday. 87/Grantham && .AVIATION... 12Z TAF Discussion. Tropical Storm Nestor will continue to move northeastward and will lead to some messy weather for portions of Eastern and Southeastern AL this morning and into the early afternoon. Expect gradual decrease in CIGs to MVFR as the rain shield moves into Central AL. The strongest winds for our TAF sites will likely be at TOI and MGM in the the later morning hours. VIS could be reduced to MVFR or IFR temporarily during the heaviest rain at ANB, ASN, TOI, and MGM. We've already seen some reduction in VIS at TOI as a band of rain passed over. I've tried to capture this for TOI and MGM in TEMPO groups. Rain should begin to move out in the early afternoon, but guidance hangs on to the low CIGs for the rest of the period. I'm not confident that CIGS will go to IFR/LIFR with the departing tropical system, so I've kept lower MVFR conditions in the forecast. 25/Owen && .FIRE WEATHER... Tropical Storm Nestor will be responsible for bands of light to moderate rain today especially across the eastern half of the area. Dry conditions will return for Sunday, but a cold front will bring showers and storms for Monday afternoon into Monday night. The Alabama Forestry Commission continues to have a fire alert in effect that includes all of Central Alabama. For more information about restrictions, visit their web site at forestry.alabama.gov. && .PRELIMINARY POINT TEMPS/POPS... Gadsden 64 50 78 59 80 / 60 10 0 10 50 Anniston 63 51 79 61 80 / 70 20 0 10 40 Birmingham 68 55 80 64 80 / 50 10 0 20 60 Tuscaloosa 70 54 82 65 81 / 30 10 0 20 70 Calera 68 53 80 63 80 / 50 10 0 10 50 Auburn 64 53 79 61 80 / 80 10 0 10 30 Montgomery 69 54 82 63 82 / 60 10 0 10 50 Troy 68 53 81 61 83 / 80 10 0 10 40 && .BMX WATCHES/WARNINGS/ADVISORIES/... None.