Area Forecast Discussion (AFD)
Issued by Huntsville, AL (HUN)
856 FXUS64 KHUN 202002 AFDHUN Area Forecast Discussion National Weather Service Huntsville AL 202 PM CST Tue Feb 20 2018 .NEAR TERM...(Tonight) Issued at 202 PM CST Tue Feb 20 2018 Another warm day with a mid level ridge and surface high pressure off the southeast coast, continuing to usher in a warm southerly flow and low level moisture. With a little more moisture and also some instability today, clouds are a little more widespread than what we saw yesterday. This will impact the highs today but Muscle Shoals already reached 77 as of 1PM and Huntsville reached 76. Both records for today are 79 so it's going to be tough with the cloud cover out there. Winds are gusty like yesterday, thanks to the sufficient mixing. Gusts of 20-25mph will continue through sunset. Winds remain elevated overnight, around 10mph so fog formation won't be an issue. The southerly flow keeps lows tonight even warmer, in the middle 60s. Clouds will also be on the increase overnight, or stay steady depending on how overcast the clouds become this afternoon. With the increased moisture and weak isentropic lift, a few showers will be possible this evening and have kept the slight chance of showers in the forecast. .SHORT TERM...(Wednesday through Thursday Night) Issued at 202 PM CST Tue Feb 20 2018 The mid level ridge remains strongly in place on Wednesday. A surface low north of Maine will have a cold front dragging south all the way through south TX. This front will be inching east through tonight and into the short term, leaving us firmly placed in the warm sector. Models are in decent agreement on keeping most of the precip confined to NW AL through the day Wednesday with a few showers popping up in the rest of the area. There isn't much lift ahead of the system but with the moisture present and CAPE values in the 500-600 J/kg range, we could get a few showers out of the cumulus clouds that should develop by afternoon. There are still some discrepancies in the high temperatures for Wednesday. The sustained southerly flow and similar 850mb temps to previous days will keep it in the upper 70s, near 80. However, we will see more clouds and rain so will cap the highs in the 76-78 range at this time. Multiple waves of low pressure will ride along the previously mentioned frontal boundary, giving areas to our west plenty of rainfall. The front continues to inch east Wed night into Thursday with it essentially dissipating over the area Thursday afternoon, without even a noticeable wind shift. Overall, Dekalb/Jackson counties may see no precip from this front. The tale of extremes in regards of precip for Thursday with the NAM very dry, GFS very wet and ECMWF somewhere in the middle. The drier solution seems more reasonable due to the ridge but there is going to be plenty of low level moisture so showers still won't be out of the question east of the frontal boundary. In terms of thunderstorms, pulse like thunderstorms Wednesday, maybe a few at most, would be most likely with the higher instability and moisture although little lift. Storms Wed night would be more lift driven, again a few storms at best, nothing strong. Same story for Thursday, if we get anything at all, the storms wouldn't be strong, especially with a more saturated sounding. The biggest impact would be potential flooding issues in NW AL. Thursday night the front will be lifting back north and it may be dry after midnight. Highs on Thursday will be a touch cooler, in the middle 70s with the additional cloud cover. Lows both nights will be in the lower 60s. .LONG TERM...(Friday through Monday) Issued at 202 PM CST Tue Feb 20 2018 The mid level ridge strengths once again and builds west on Friday, keeping the frontal boundary moving off to the northwest. Friday should be dry and with no change in air mass with the front, highs will be in the mid to upper 70s. Dew points drop to the upper 50s/around 60 on Friday and don't get into the lower 60s until Sat afternoon. The bad thing about the strong ridge and warm weather is that a trough has been deepening into the southwestern states through the last few days. Surface cyclogenesis will occur near TX/OK Saturday and the low will track northeast, along the upper ridge, through Sunday. Ahead of the system locally on Saturday, in the warm sector, dew points increase and we do get a few hundred J of CAPE in the afternoon. There is no lift to speak of outside of weak isentropic lift. So it looks like we could have a widespread mid level cloud deck even with a dry mid level. Could be showery and cloudy all day, therefore lessening a severe threat later in the evening. The one change with this forecast package (still looking at 00z ECMWF) is that the GFS is about 6-12 hours faster. A pre-frontal trough/decaying squall line would arrive in NW AL around 6z and be out of NE AL by 18z. ECMWF has the line at NW AL around 12z, making Sunday a little more interesting once it heats up. Shear will be sufficient, even abundant, with this system. Given the fairly significant shortwave with it, only a few hundred J of CAPE would be necessary to sustain damaging winds in a squall line, even overnight. This needs to be monitored and will keep the mention of possibly severe storms in the HWO. The biggest concern would be between 00-06z Sunday, in NW AL. Monday/Tuesday should be dry but will maintain a low pop Monday as the front may hover just south of the area. Highs on Saturday will still be in the lower 70s but drop to the mid to upper 60s behind the front on Sunday. Lower 60s highs return for Mon/Tue. Lows that have been in the upper 50s/lower 60s will drop to the upper 40s for the start of the week. && .AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon) Issued at 1109 CST Tue Feb 20 2018 Scattered to broken ceilings are currently being observed but luckily the broken cigs are VFR. KMSL dropped to BKN015 temporarily but those clouds have moved off to the west. There's a chance both terminals could dip to around BKN030 at times but not expected to go too much lower than that this afternoon. Winds will be gusty again today, slightly more frequent than yesterday. Gusts 20-25mph are possible this afternoon. Another low stratus deck moves in overnight with once again, questions on coverage and how low the cigs get. For now, will bring the 2kft clouds back in around 7z at both terminals but there is a chance it drops lower before sunrise tomorrow. Should see the cigs mix out once again by late morning. There's also a 20% chance of a shower overnight so chances are too low to include in the TAFs at this time. && .HUN WATCHES/WARNINGS/ADVISORIES... AL...NONE. TN...NONE. && $$ NEAR TERM...LN SHORT TERM...LN LONG TERM...LN AVIATION...LN For more information please visit our website at weather.gov/huntsville.