Area Forecast Discussion (AFD)
Issued by Huntsville, AL (HUN)
000 FXUS64 KHUN 171538 AFDHUN Area Forecast Discussion National Weather Service Huntsville AL 1038 AM CDT Mon Sep 17 2018 .NEAR TERM...(Rest of Today) Issued at 1038 AM CDT Mon Sep 17 2018 The big weather maker from late last week to the present had come from now Tropical Depression Florence. It was located approximately 30 miles northwest of Huntington WV moving to the NE around 15 mph. Moisture wrapping around the system extended SW to across much of the central Tennessee Valley. The lower clouds (< 5000' AGL) were mainly affecting parts of far northern Alabama east of I-65 and points northward. Along with the clouds, our Doppler radars indicated a few showers moving in a NNW-SSE manner across parts of the forecast area. As of this writing, those showers were mainly across Middle Tennessee and points northward, but a few showers were noted just west of the Hytop AL radar. Those showers were moving into a drier environment further to the south across northern Alabama, resulting in little to no precip in much of this region at this time. The satellite view confirmed a sharp gradient between the southern extent of the clouds, and generally clear skies to the south. That line as of this writing was roughly from the Quad Cities of NW AL, to Moulton and Cullman. Some sun was making it through breaks in the clouds north of this line. Strong late summer heating today (with high temperatures ranging from the lower 80s southern middle TN to lower 90s in NW AL, will result in destabilization this afternoon. Given higher instabilities forecast by the shorter range models, left isolated thunder in for this afternoon in NE Alabama and our southern middle Tennessee group. Except for minor temperature adjustments, the rest of the forecast looked fine for the rest of today. .SHORT TERM...(Tonight through Wednesday night) Issued at 218 AM CDT Mon Sep 17 2018 Showers or storms that do form during the afternoon hours should quickly dissipate after sunset and as the remnants of Florence continue to shift E/NE away from the area. With calm winds overnight and a clearer sky it's possible we may see fog develop in the valleys in NE AL and in TN. Lows will dip into the mid to upper 60s by Tuesday morning. An upper level ridge centered over the southern Plains will begin to shift east towards the area Tuesday and then will be centered over the TN Valley on Wednesday. Northerly winds continue as this ridge builds east and will reinforce the dry air aloft already in place across the area. The combination of this dry air and increasing subsidence will keep the area rain free both Tuesday and Wednesday. Guidance has been consistently underdoing the high temps by 2-4 degrees the past few days and have nudged temps above guidance. This would put highs both Tuesday and Wednesday in the low to mid 90s but with the strong subsidence wouldn't be surprised if some of the warmer locations made it into the upper 90s. Thankfully, we mix down some of this drier air both days and this will help to keep Heat Index values just below 100 degrees. Lows both Tuesday and Wednesday nights will be in the mid 60s to near 70 degrees. .LONG TERM...(Thursday through Sunday) Issued at 218 AM CDT Mon Sep 17 2018 By Thursday the ridge mentioned above starts to shift east of the area and as a result winds become more southerly. This should allow Gulf moisture to gradually be advected into the area as we head into weekend. While subsidence is in ongoing Thursday think that just enough moisture will have streamed north into the western half of the area for a few isolated storms. With dewpoints back in the 70s and slightly steeper lapse rates, expecting an increase in shower/storm coverage for Friday afternoon. In terms of highs for Thursday and Friday, with weakening subsidence models are going with temps more in the upper 80s to lower 90s. Think those are too low for Thursday and have kept highs in the mid 90s for much of the area. The slightly better rain chances for Friday should allow for temps closer to the 90 degree mark. A shortwave ejecting out of the desert SW on Thursday night/Friday morning will spawn a low pressure system that is forecast to more into the upper Midwest/Great Lakes region over the weekend. This system will push a frontal boundary towards the area. However, models continue to waver on just how strong the frontal feature will be and the influence the ridge to our east will have on the front. We've gone from the front will be completely south of the area to stalling to the north over TN, to now showing it stalling over the TN Valley. With all of this uncertainty have kept lower end PoPs in the forecast for the weekend as even it remains north of the area we should still be able to see isolated to scattered afternoon storms. Based on the dry pattern we've had the past few weeks and the weak forcing associated with the front, think the drier solution might be the better bet at this point. In any case the convergence associated with the front should result in a bit more cloud cover and highs over the weekend will be in the mid 80s to around 90 degrees. && .AVIATION...(For the 12Z TAFS through 12Z Tuesday morning) Issued at 620 AM CDT Mon Sep 17 2018 VFR conditions are forecast through the period. Winds will be N/NW with speeds at or below 10kts. A mid-level cloud deck between 110-160 associated with the remnants of Florence have overspread the area. These are forecast to linger through much of the morning before scattering out this afternoon. Additional low level moisture could result in a 4,000ft deck of clouds developing by 15z. Showers and storms are expected to stay east of both terminals today. && .HUN WATCHES/WARNINGS/ADVISORIES... AL...NONE. TN...NONE. && $$ NEAR TERM...RSB SHORT TERM...Stumpf LONG TERM...Stumpf AVIATION...Stumpf For more information please visit our website at weather.gov/huntsville.