498 FXUS64 KHUN 221711 AFDHUN Area Forecast Discussion National Weather Service Huntsville AL 1111 AM CST Tue Jan 22 2019 .UPDATE... For 18Z TAFS. && .NEAR TERM...(Rest of Today) Issued at 830 AM CST Tue Jan 22 2019 Visible imagery shows clouds in the 040-050agl layer over MS through western AL spreading north-northeast. We may have to speed up the timing of those if this trend holds, although very dry air over north AL and southern TN may tend to scatter the clouds initially. The other lower clouds at 020-030agl in western GA and southeast AL are also progressing northward, but also may tend to scatter out as well. Will continue to monitor cloud trends through this morning and make necessary adjustments. Will also leave the low PoP late this afternoon in our southwest counties. .SHORT TERM...(Tonight through Thursday night) Issued at 335 AM CST Tue Jan 22 2019 Gulf moisture continues to surge northward along a warm conveyor belt tonight. The moistening atmospheric column will see PW values climb above 1" tonight and up to 1.25" tomorrow. Showers move in late this evening from the southwest and spreading over the Mid South tonight. Moderating cloud cover tonight combined with moderate to strong surface winds will keep lows tonight in the mid 40s. A passing low level jet with 850mb winds 55-65 kts will progress over the Tennessee Valley tomorrow morning ahead of the approaching trough. Model soundings show a brief window of elevated CAPE tomorrow morning ahead of the cold front, aligning with the LLJ. However, the atmosphere does not get enough time before the cold front to moisten the cloud layer high enough to include ice particles, a necessary ingredient for thunderstorms. Therefore, have left mention of thunder out with this forecast package. Increasing low level flow will enhance warm air advection, resulting in high temperatures tomorrow into the mid 50s east of I-65, and the upper 50s in Northwest Alabama. Should the cold front pass sooner than forecast, then high temperatures will be a few degrees lower. Moderate rainfall, heavy at times, will continue periodically throughout the day Wednesday. The second forcing for rain will arrive behind the cold front Wednesday afternoon. With higher wind shear in place, this may be more of a QLCS overtaking the morning's WAA showers. Lingering anafrontal precipitation will continue throughout tomorrow night. Top-down methodology on soundings indicate a changeover to mixed wintry precipitation late Wednesday night into early Thursday morning, just as the cold and dry air moves in. A brief window for sleet and light snow will exist on the tail end of the showers overnight Wednesday. Little to no accumulations are expected, and with wet surfaces and soils from earlier rain, no travel impacts are expected. Overall rainfall totals will be 1-2" with locally higher amounts possible in the event of any precip banding. This may result in further rises on area rivers and streams, which will slow any recessions from ongoing flooding. Behind the front, skies gradually clear early Thursday morning with lows bottoming out in the upper 20s. High pressure builds in from the southwest on Thursday with mostly clear skies and calming winds, as high temperatures reach the low to mid 40s. A reinforcing shot of cold air arrives Thursday night, causing lows to fall into the low 20s. Minimum apparent temperatures early Friday morning will sink once again down to the teens. .LONG TERM...(Friday through Monday) Issued at 335 AM CST Tue Jan 22 2019 A cold trend temperature wise will continue across the eastern Lower-48 for the longer term, as an amplified upper pattern remains in place. Some mean features of note: a powerful zonal 250mb jet situated along 35-40N roaring in the 160 to +210kt range was running into an high altitude block NE of Hawaii, producing a split flow west of the North American domain. The more predominate upper flow was moving NE across Alaska/Yukon region, then heading SE, producing large scale troughing over the CONUS. Aiding in the trough's staying power is an upper low north of the Hudson Bay moving southward. A further southward position of this strong low will result in an abnormally deep trough, position approximately from the southern Hudson Bay to the Rio Grande. The disturbance laden jet and its splitting over the west coast ridge will produce many timing issues. As time goes on, there is a lot of inter-model disagreements on exact positions of the Canadian low, as well as other systems forming south of the Gulf of Alaska while the western block starts breaking down early next week. At the surface, a surface high ~1032mb magnitude should be situated over the Mid South, resulting in a cold start in the longer term. Have dry conditions, with colder than normal conditions for the Fri/Sat timeframe. Another cold front, in part pushed southward by another surface high of Arctic origin is forecast to move across the area late Sat and on Sun. The deterministic GFS/ECMWF were generally "dry" for this but the Canadian and GFS-ensemble did see some light QPF. So joined the crowd with a slight chance of a rain/snow mix for that time frame. Becoming dry with still cooler than seasonable norms on Monday. && .AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon) Issued at 1111 AM CST Tue Jan 22 2019 VFR ceilings of 035-050agl will overspread the area this afternoon, arriving in KMSL by 18Z and KHSV by 21Z. These ceilings will lower to 020-030agl (MVFR) by 00-02Z with isolated sprinkles or showers possible. Southeast flow will continue at 14-18kt with gusts of 22-27kt through the period. At times, gusts may exceed 30kt, mainly late tonight into early Wednesday morning. LLWS is expected to develop by 04-06Z this evening and last through the period. A more solid area of showers will arrive by the end of the period when ceilings should drop below 010agl (IFR). && .HUN WATCHES/WARNINGS/ADVISORIES... AL...NONE. TN...NONE. && $$ NEAR TERM...17 SHORT TERM...30 LONG TERM...RSB AVIATION...17 For more information please visit our website at weather.gov/huntsville.