Area Forecast Discussion (AFD)
Issued by Huntsville, AL (HUN)
610 FXUS64 KHUN 181253 AFDHUN Area Forecast Discussion National Weather Service Huntsville AL 753 AM CDT Wed Jul 18 2018 .NEAR TERM...(Rest of Today) Issued at 753 AM CDT Wed Jul 18 2018 Dense fog areas continue mainly east of I-65, tucked in many of our eastern valleys. Have extended this an hour in the weather grids. This should dissipate fairly quickly over the next hour or two. The cold front is still situated over northern TN (i.e. Nashville dew point is 64). This will gradually shift southward today. There is still a very low chance of a thunderstorm this afternoon in our southwest counties given the boundary and some support from the NAM. However, the latest HRRR run does not indicate development at this time for our counties. .SHORT TERM...(Tonight through Friday Night) Issued at 450 AM CDT Wed Jul 18 2018 Tonight will be dry and have the coolest temps of the forecast period with values in the mid to upper 60s. The sfc high across the Great Lakes will start to shift eastward on Thursday and be along the east coast by Friday. This will veer winds to the southeast and start returning moisture to the area. A few storms along the southern tier of counties is possible Thursday afternoon, and in NE AL towards the evening as a wedge front starts to push in. Still stuck in northwesterly flow aloft, attention will also be on the active weather occurring in the Midwest. This activity could slide an MCS into the region on Friday. Models still do not agree on exactly what time the MCS will arrive, however they do agree a round or two of storms will push into the TN Valley on Friday. Kept with an increase in clouds as we head into Friday with POPs also increasing from Thursday night into Friday night. Will not rule out a strong storm or two on Friday with forecast soundings bringing PWATS back towards 2 inches, a plentiful amount of CAPE in place and bulk shear around 30kts combined with diffluent flow aloft. As models come to a better consensus, these factors along with timing could change so be sure to keep an eye on further updates. .LONG TERM...(Saturday through Tuesday) Issued at 450 AM CDT Wed Jul 18 2018 Medium range guidance suggests that the TN Valley will be embedded within an unseasonably strong northwest flow regime at the beginning of the long term period, with the region between an amplified mid- level trough over the Great Lakes and a subtropical high centered across the southern high Plains. The trough is predicted to drift slowly southeastward into the upper OH Valley over the course of the weekend, while digging as far southward as the southern Appalachians by 00Z Monday. Flow at the 500-mb level will likely peak in the 45-55 knot range at some point Saturday afternoon/evening, which will support the threat for perhaps a couple of highly-organized clusters of thunderstorms to drop south-southeastward into the region from adjacent portions of middle TN. Based on the thermodynamic/kinematic environments projected by forecast soundings, conditions during the day on Saturday will be quite favorable for organized severe thunderstorms producing perhaps some significant winds. We have indicated the greatest coverage of storms to occur during the day Saturday, with conditions improving from west-to-east Saturday evening as a southeastward-moving cold front begins to advect drier air into the region. The northwest flow regime is predicted to subside beginning Sunday night/Monday morning, as the trough to our east weakens and the mid- level subtropical high to our west retrogrades further into the southern Rockies. Although a few diurnal showers and thunderstorms will be possible in the higher terrain of southern middle TN and northeast AL on Sunday/Monday, a drier boundary layer will limit coverage compared to previous days. However, a subtle increase in low-level moisture should result in a few more afternoon convective cells by Tuesday. High temperatures in the drier airmass will still range from the m-u 80s east to lower 90s elsewhere, with lows mainly in the u60s-l70s. && .AVIATION...(For the 12Z TAFS through 12Z Thursday morning) Issued at 628 AM CDT Wed Jul 18 2018 Fog could create down to IFR conditions at KHSV and MVFR conditions at KMSL until 14Z. Once the fog dissipates, VFR conditions will prevail with light northerly winds with mid-high clouds in place. A shower or storm may impact KMSL this afternoon, however due to the uncertainty of storms directly impacting the terminal, kept the mention of it out of this TAF issuance. && .HUN WATCHES/WARNINGS/ADVISORIES... AL...NONE. TN...NONE. && $$ NEAR TERM...17 SHORT TERM...JMS LONG TERM...70/DD AVIATION...JMS For more information please visit our website at weather.gov/huntsville.