Area Forecast Discussion (AFD)
Issued by Huntsville, AL (HUN)
675 FXUS64 KHUN 181523 AFDHUN Area Forecast Discussion National Weather Service Huntsville AL 1023 AM CDT Tue Sep 18 2018 .NEAR TERM...(Rest of Today) Issued at 1023 AM CDT Tue Sep 18 2018 Earlier, patchy to areas of fog that mainly affected parts of northeast Alabama (especially along the Tennessee River from Pittsburg to Lake Guntersville // and U.S. Hwy 72) has finally dissipated, thanks to daytime heating and mixing. Earlier regional soundings indicated a relatively moist profile with ~1.5" of precipitable water and convective temperatures in the mid 80s. The latter looks true, given "fair weather" cumulus were beginning to form across parts of the greater Tennessee Valley. Further daytime heating, with high temperatures rising again into the lower 90s will lead to further destabilization and isolated shower and thunderstorms forming this afternoon. Except for minor temperature trend adjustments and adding precip amounts from updated WPC QPF, did not make any big changes to the on-going forecast. .SHORT TERM...(Tonight through Thursday night) Issued at 330 AM CDT Tue Sep 18 2018 Will add patchy fog again late tonight into early Wednesday morning given light flow and radiation potential beneath the ridge. More summer weather is ahead through mid week as the upper ridge now over southern Plains shifts eastward into the lower MS and TN valleys Wednesday, and into the Carolinas on Thursday. Northwest flow aloft on the northern and northeast side of the upper anticyclone may bring convective clusters/MCSs into the OH Valley on Wednesday. The models even show some small areas of precipitation developing in KY and into eastern TN Wednesday afternoon, but am expecting our area to remain hot and dry. Will stay above by a few degrees of suggested blended guidance for high temps both Wednesday and Thursday. As the ridge positions at all levels shift to the Carolinas/Georgia area, deep southerly flow will develop across AL into middle TN. A convergence line and showers/thunderstorms is indicated Thursday night across the central FL panhandle north into southeast AL. Will hold off from adding this into our forecast for now. .LONG TERM...(Friday through Monday) Issued at 330 AM CDT Tue Sep 18 2018 Overall, temperatures will tend to remain above normal in the TN Valley for the extended portion of the forecast (through next Monday). However, gradual SE movement and repositioning of the main hemispheric vortex over central and then eastern Canada, will result in an intensification of the polar jet and tracks of mid-latitude cyclones, finally, over portions of the Great Plains and then the northern tier of the CONUS during the period. An initial front on the weekend will likely cross the area, but without much temperature or moisture advection, while another front around the middle of next week appears more promising. More details follow. An initial cyclone will likely be tracking across the Great Lakes region at the start of Friday with an attendant, but weakening surface front moving into the Midwest and OH Valley regions. Our area will still reside under the western flank of an upper level ridge centered near the Carolina coast. However, increasing influence from the upper trough to our NW combined with moisture convergence/pooling ahead of the surface front should give rise to scattered convection in the region on Friday. The better chances generally favor northern and western portions of the area closer to the better dynamic forcing associated with the front. Chances for showers and thunderstorms will increase further for Saturday as the front crosses the region. Thermodynamic profiles suggest just modest ML or SB CAPE likely present, with values generally around 1000-1500 J/Kg, so mainly general thunderstorm activity is expected. Fairly weak deep layer flow an a tendency for some back-building cells could result in a few locally heavy rainfall amounts where deeper convective cells do occur. The bulk of the drier air mass will certainly remain well to our north with the frontal passage across the area. However, some of the drier boundary layer air will gradually filter into the region on Sunday and Monday, but do not look for significant decreases in moisture/humidity with dew point temperatures likely remaining in the mid/upper 60s. A look farther out indicates another frontal passage is possible across the region by about Wednesday or Thursday, bringing somewhat cooler/drier air to the region. The 00z operational GFS and ECMWF show better agreement in this solution with regards to timing and positioning of the air mass, but this is still outside the forecast window. Nevertheless, wanted to mention this for those looking for more autumn-like weather. && .AVIATION...(For the 12Z TAFS through 12Z Wednesday morning) Issued at 605 AM CDT Tue Sep 18 2018 VFR flight weather conditions are expected for most of the next 24 hours. Patchy river valley fog early this morning will dissipate by 14-15Z. An isolated shower or thunderstorm is possible this afternoon, but the probability is too low to include in the TAFs at this time. However, br/fg is expected to develop by 09z along area rivers with visibility of 1-2sm or less after 09z. && .HUN WATCHES/WARNINGS/ADVISORIES... AL...NONE. TN...NONE. && $$ NEAR TERM...RSB SHORT TERM...17 LONG TERM...KDW AVIATION...17 For more information please visit our website at weather.gov/huntsville.