Area Forecast Discussion (AFD)
Issued by Huntsville, AL (HUN)
000 FXUS64 KHUN 161108 AFDHUN Area Forecast Discussion National Weather Service Huntsville AL 508 AM CST Fri Nov 16 2018 .NEAR TERM...(Today) Issued at 508 AM CST Fri Nov 16 2018 Seasonably strong west-northwest flow aloft continues across the TN Valley this morning, in the wake of a departing shortwave trough across the mid-Atlantic region. However, near term guidance suggests that this flow will back to the west and diminish throughout the afternoon as a weaker mid-level disturbance over southeastern TX shifts east-northeastward into the central Gulf coast, weakening the height gradient aloft. Scattered-broken cirroform cloud cover ahead of the wave to our southwest has already begun to overspread the region, likely reducing the efficiency of radiational cooling this morning. Furthermore, a gradual increase in low-level southwesterly winds is expected over the next couple hours, as a cold front sweeps eastward into the lower Great Lakes region, and these factors should ensure no significant change in temperatures between now and sunrise. Although environmental conditions are not ideal, patchy freezing fog has recently been reported in a few locations and will remain a possibility across portions of the region through 13-14Z. After sunrise, winds should veer to the west-southwest as the region will become more influenced by a broad ridge of high pressure centered along the Gulf coast. Stronger insolation and light west- southwest flow will result in afternoon highs roughly 20-25 degrees warmer than yesterday, although based on the expected coverage of high clouds we have kept maxes in the l-m 50s. .SHORT TERM...(Tonight through Sunday night) Issued at 508 AM CST Fri Nov 16 2018 Mid and high level flow will back further to the west-southwest and begin to increase overnight, downstream from a well-defined vort max progged to drop southeastward into the northern Rockies. This feature is expected to shift steadily southeastward into the central Plains by 00Z Monday, becoming increasingly sheared as it enters a region of confluent flow to the north of the subtropical jet. Periods of high clouds will be possible in this regime at any time, but should gradually become thicker and more widespread from Saturday night into Sunday as very weak synoptic scale forcing for ascent begins to overspread the region from the west. Based on expectations that high cloud cover will briefly dissipate after Midnight tonight, we feel that conditions will be favorable for radiational cooling once again, with an attendant threat for fog (and freezing fog across portions of the CWFA). Thicker high clouds should limit both temperature falls and the threat for fog on Saturday night/Sunday morning, with lows expected to only reach the u30s-l40s. Highs on Saturday and Sunday will be pleasantly warm compared to the past few days, reaching the l-m 60s for most of the area. By Sunday night/Monday morning, models suggest that the mid-level shear axis over the central Plains will be approaching our region from the northwest. Although lift associated with this disturbance will be quite weak, it may be sufficient for the development of a few showers along or immediately in the wake of a weak cold progged to enter the region during this period. Due to the weak nature of the lift and evidence of dry air in the subcloud layer, we have only included a slight-low chance POP at this point. Due to an increase in lower cloud cover late Sunday afternoon, min temps should only reach u30s-l40s once again Monday morning. .LONG TERM...(Monday through Thursday) Issued at 508 AM CST Fri Nov 16 2018 Models have changed little concerning details of the forecast on Monday. It looks as though a weak pre-frontal boundary ahead of a very weak cold front will move east into northern Alabama and southern middle Tennessee on Monday. Forcing along this convergence feature ahead of the front remains weak in most models. A fairly moisture starved atmosphere is in place along and ahead of it. However, they continue to show just enough moisture for isolated shower development as this boundary continues to move into locations west of I-65 into southern middle Tennessee Monday morning. Most models continue to further dry out the airmass ahead of the front and along this pre-frontal boundary as they push the boundaries further east during the afternoon hours, only allowing some virga to develop. Thus kept less than 20 pop in the forecast during that period. Mostly cloudy conditions are expected to occur with these features Monday morning through the evening hours, before starting to clear out towards daybreak on Tuesday. The dissipating cloud cover and persistent winds around 5 mph should keep low temperatures from really bottoming out. It does look cool though with lows dropping into the upper 30s. Despite more abundant sunshine on Tuesday, some cold air advection behind the front should keep the high temperatures in the lower to mid 50s. Winds remaining around 5 mph or a little higher should keep similar temperature trends in the forecast, despite clear skies overnight. Lows in the lower to mid 30s with highs in the mid 50s look reasonable on Wednesday. With a more zonal to slightly southwesterly flow developing ahead of some upper level energy moving across eastern Texas, it should be warmer late Wednesday night into Thursday (lows in the mid/upper 30s and highs in the upper 50s/around 60 degrees). This trend continues into the weekend, as weather conditions change little through Friday afternoon. Some isolated to scattered showers may push east into the area ahead the afore-mentioned upper level energy as it approaches the area. && .AVIATION...(For the 06Z TAFS through 06Z Friday night) Issued at 1138 PM CST Thu Nov 15 2018 VFR conditions will prevail at each terminal through the period, with a mostly clear sky and light winds. && .HUN WATCHES/WARNINGS/ADVISORIES... AL...NONE. TN...NONE. && $$ NEAR TERM...70/DD SHORT TERM...70/DD LONG TERM...KTW AVIATION...AMP.24 For more information please visit our website at weather.gov/huntsville.