147 FXUS64 KHUN 291525 AFDHUN Area Forecast Discussion National Weather Service Huntsville AL 1025 AM CDT Sun Aug 29 2021 .NEAR TERM...(Rest of Today) Issued at 1015 AM CDT Sun Aug 29 2021 Regional weather interests are largely focused on Ida, which is nearing the Louisiana coast at this time as a high-end Cat 4 Hurricane. We will begin to experience direct impacts with the remnants of the hurricane here in our area beginning later tomorrow. Those impacts are outlined well below, but we'll have the latest information with the updated forecast package later this afternoon. Otherwise, our region remains situated on the western flank of the broad sub-tropical ridge this morning, which has shifted SWWRD as expected over the last 24 hours. Abundant clouds have streamed into the region, which have been inhibiting temperature rises a little, nevertheless temperatures are still in the low 80s as of 10 AM. Just a few light showers have been noted on radars locally, but some bands of showers can be seen well south, in south-central AL. Some confluent flow appears probable to develop later this afternoon, especially in West/Central portions of the area, in concert with an upr wave passing NWWRD. This may lead to development of showers/storms mainly later this afternoon. Due to the locations for better forcing/instability...POPs are highest in SW portions of the area. Forecast thermodynamic profiles suggest higher low-lvl lapse rates may develop if better sfc heating can be realized among the clouds. Lapse rates could exceed 7 C/km, while modest overall MLCAPEs will be present...which could lead to some strong wind gusts with any intense cells. Otherwise, the threat for svr wx today appears to be very small. Morning forecast updates are out, and look for the afternoon updates by 230-3 PM. .SHORT TERM...(Tonight through Tuesday) Issued at 535 AM CDT Sun Aug 29 2021 Scattered showers and thunderstorms in the regime discussed above will persist into the evening hours, and we have maintained a fairly high POP in the grids through 03Z to account for this. However, with the development of outer rainband convection closely tied to the diurnal warming cycle, we anticipate most of this activity to dissipate by late evening. Overnight lows will be rather mild (l-m 70s), with a gradual increase in high-level cirrostratus clouds and gentle southeast flow at the surface expected to limit the coverage of fog. Outer rainband convection will likely develop across our region fairly quickly after sunrise on Monday morning, as the remnants of Hurricane Ida begin to accelerate northeastward into central MS. However, the overall coverage of thunderstorms is expected to be quite a bit lower compared to today, as moistening aloft will contribute to weaker lapse rates and thick mid/high-level clouds will limit boundary layer destabilization, as max temperatures will only reach the l-m 80s. The latest official forecast from the National Hurricane Center still suggests that the remnants of Ida will advance northeastward into northeastern MS Monday night, before spreading across northwest AL and into Middle TN by early Tuesday evening. Moderate-locally heavy rainfall directly related to the tropical cyclone's circulation will begin to spread northeastward into the region by late Monday afternoon, and should persist through the morning hours on Tuesday before ending from SW-to-NE during the afternoon. This will also be accompanied by several well-defined rainbands that will feature heavier convective-type showers and perhaps a few thunderstorms. With latest rainfall amounts from WPC continuing to advertise 1.5-2 inch totals across northeast AL and widespread 3-4 inch totals across northwest AL, we have issued a Flash Flood Watch for roughly the western half of the CWFA from 18Z Monday-06Z Wednesday. It is important to note that these amounts do not capture higher rainfall rates that will likely occur in deeper convective cells. The risk for brief tornadoes will also increase considerably beginning late Monday night, with this threat continuing through Tuesday afternoon, as both veering and speed shear strengthen in the very moist 0-3 KM AGL layer. Finally, it is worth noting that environmental flow will be rather strong throughout the day on Tuesday, with sustained wind speeds around 15-20 MPH and gusts of 25-30 MPH expected (both values will be greater in elevated terrain). .LONG TERM...(Tuesday night through Saturday) Issued at 535 AM CDT Sun Aug 29 2021 The remnant circulation of Ida will begin to open into a wave and undergo the transition to an extratropical cyclone as it shifts northeastward across the southern Appalachians and into the western Mid-Atlantic states on Tuesday night/Wednesday. As this occurs, deep- layer flow will veer to the northwest across the TN Valley, and this will usher a cooler/drier airmass southward from a Canadian high building southward into the Great Lakes region. Dewpoints could potentially fall into the m-u 50s for portions of the period from Wednesday night through Friday night, which will allow for a couple of pleasantly cool mornings on Thursday/Friday with lows in the u50s- l60s. Highs will still reach the l-m 80s each day. The airmass will begin to modify late next week/early next weekend, but it appears as if significant chances for rain will not return until beyond the end of the extended period. && .AVIATION...(For the 12Z TAFS through 12Z Monday morning) Issued at 703 AM CDT Sun Aug 29 2021 VFR conditions will prevail at the HSV/MSL terminals throughout the forecast period, with few-sct lower-lvl Cu beneath an increasing coverage of high-lvl As/Cs. The coverage of scattered SHRA/TSRA is expected to be slightly greater today invof the terminals as an outer rainband associated with Hurricane Ida lifts northward into the region. However, it appears that this activity will mainly occur late this aftn/early this evening, with PROB30 groups introduced btwn 21-03Z. Although some patchy fog will be possible in portions of the region early Monday morning, a SE flow of 5-10 knots and increasing coverage of mid/high-lvl clouds will reduce this threat sufficiently to avoid inclusion in the TAFs. && .HUN WATCHES/WARNINGS/ADVISORIES... AL...Flash Flood Watch from Monday afternoon through late Tuesday night for ALZ001>007-016. TN...Flash Flood Watch from Monday afternoon through late Tuesday night for TNZ076-096. && $$ NEAR TERM...KDW SHORT TERM...70/DD LONG TERM...70/DD AVIATION...70/DD For more information please visit our website at weather.gov/huntsville.