Current Version Previous Versions: 1 2 3 4 5 6 7 8 9
Area Forecast Discussion
126 FXUS64 KHUN 262328 AAA AFDHUN Area Forecast Discussion...UPDATED National Weather Service Huntsville AL 628 PM CDT FRI AUG 26 2016 .UPDATE... For 00Z TAFs. && .SYNOPSIS... (Issued 307 PM CDT FRI AUG 26 2016) The prevailing ridge across the Southeast/Appalachian states will keep the region hot and humid with various rounds of mainly afternoon thunderstorms through the weekend. Further to the northwest, a longwave trough moving across western/central Canada/Intermountain West will actually act to dampen the ridge over the next 3 days. The upper flow pattern then looks to transition to an omega block pattern across north America later next week with the TN valley in NW flow. Meanwhile, scattered storms have developed along a convergence boundary over central AL to northern MS. This convergence boundary will likely remain the focus for storms until this evening. SL.77 && .DISCUSSION... (Issued 307 PM CDT FRI AUG 26 2016) The scattered storms are expected to prevail into the early evening hours with gusty winds of 30-40 MPH possible with any of the stronger storms. After storms diminish/dissipate, patchy fog will be possible overnight with patchy dense fog possible near rivers, lakes, and valleys. Then, on Saturday, expecting this convergence boundary to dissipate/move off to the north due to shift in the upper ridge position towards the central Appalachians. As this shift in the ridge position continues, the TN valley will be positioned on the SW flank of the ridge. An inverted trough/weak vorticity max rotating around the southern flank will approach on Saturday afternoon over the central/northern GA/NE AL. As a result, anticipate isolated thunderstorms to develop again, especially over NE AL. Greater areal coverage in storms may be possible depending on the timing of the trough as instability will be maximized during the afternoon. With wind shear values quite low, any storms that develop will be pulse- like with potential for microbursts. Primary impacts will be gusty winds up to 40 MPH with very heavy rainfall. In addition, temperatures will still be quite hot and humid with temperatures rising into the low 90s, which with dewpoints in the 70s, will translate to heat index value rising close to 105. Similar conditions are anticipated on Sunday as the upper flow pattern begins to transition to a more dampened ridge as the polar jet trough moves up and over the ridge. With the dampening ridge, kept the isolated thunderstorm chances in place for the afternoon especially over NE AL where greater speed convergence within the flow is noted in the mid levels. Though the ridge will be weaker during the early part of the week, weak northeasterly flow is expected which may advect drier air aloft acting to limit deep convective updrafts. Nevertheless, will keep isolated thunderstorms in the forecast through Monday and Tuesday with similar daytime highs in the 90s. The main difference may be somewhat `cooler` dewpoint temperatures which may keep heat index values below 100. The upper flow pattern then begins to transition to an omega flow pattern by day 7/8. In the meantime, on Wednesday and Thursday have kept isolated thunderstorms in the forecast with highs in the 90s and lows in the 70s. This does not take into effect any of the possible impacts from Invest 99L. At this point, too much uncertainty on the track, storm integrity, and intensity still exist with this tropical wave to even incorporate any impacts for the end of next week. SL.77 && .AVIATION... For 00Z TAFs: Next wave of TSRA will affect KHSV through 01Z, then could affect KMSL 01-02Z. Even some weaker storms have been producing gusts around 40 kt so the TAFs will reflect this for now. After this, short term models suggest storms weakening and dissipating. With all the rain occurring today, fog is likely if we are able to get any clearing; will stick with MVFR visibility though IFR/LIFR is possible. Storms should be more isolated tomorrow. BCC && .HUN Watches/Warnings/Advisories... AL...NONE. TN...NONE. && $$ For more information please visit our website at weather.gov/huntsville.