374 FXUS63 KFSD 191124 AFDFSD Area Forecast Discussion National Weather Service Sioux Falls SD 524 AM CST Sun Feb 19 2017 .SHORT TERM...(Today and Tonight) Issued at 429 AM CST Sun Feb 19 2017 Today is likely to be one of the warmest days we've experienced in some time. With daybreak temperatures starting out 5 to 10 degrees above our normal daily highs, it won't take long to really feel the warmth today. Breezy winds should promote mixing up to 900 mb, again pushing highs well into the 60s. 70 degree readings seem possible as well especially along the Missouri River valley region. At the surface, mid-40 dewpoints have already reached southern Nebraska with near 50 dewpoints anticipated by this afternoon. By this evening, low level moisture transport really increases as the LLJ intensifies. Boundary layer dewpoints surge into the lower 50s, which in many winter months would mean widespread dense fog. However, this has been anything other than a typical February, and we'll rather end up with low stratus and a mix of lower end fog. Theta-e advection increases through the night, but the best synoptic forcing won't reach the region until after midnight and closer to daybreak Monday. Soundings again look marginal for any thunder potential, but wouldn't rule out an isolated rumble as a few showers begin to develop into Monday morning. The other story tonight will be extreme warmth over the region. Cloud cover, persistent southerly winds, and high dew points will hold overnight temperatures in the middle to lower 50s. Basic climatology searches looking at peak hourly temperatures during February reveal that we'll likely set new records for the warmest hourly readings on record for the month of February. .LONG TERM...(Monday through Saturday) Issued at 429 AM CST Sun Feb 19 2017 Band of showers will likely start the day fairly close to I-29 and eastward, shearing north and east fairly quickly during the morning with punch of strong meridional jet across the area. Coverage of precipitation should continue to improve as the area lifts northeast. Not more than isolated rumbles of thunder are expected with instability profiles fairly small and thin. Behind the band, wind fields should veer and result in reduction of QG lift forcing back toward the location of approaching lower- to mid-level boundary. Instability component for additional precipitation beyond the early morning band is fairly dismal, as prospect for significant destabilization along the frontal boundary is fairly small at this point, and have only mentioned an isolated thunder threat with the fairly low chance PoP. Should have quite a bit of cloudiness ahead of the boundary, but a window to thin somewhat near and after passage when airmass will still be at its warmest. Therefore, with the very mild start propped up by the high surface dewpoint, should have a chance to mix into the lower to mid 60s many areas, especially with increasing westerly winds behind the front. Weak surface ridge slips across the area during the evening and early overnight, with drier air allowing for temps to drop a bit more toward midnight, and likely keeping temps from remaining high enough to set an all-time monthly high minimum temperature (44 degrees). Ironically, temps could easily begin to rise again later in the night, especially at elevation, as southwesterly low-level jet becomes established. Tuesday still on track to be the warmest day of this exceptionally mild pattern. Very little on the negative side to potential warming considering lack of clouds, flow direction with a westerly component, and warm start to the day. Numerous records will certainly fall, some by potentially large margins. while a frontal boundary will push across the area later Tuesday night or Wednesday as a trough slings along the International Border. Not a great deal of cooling initially, so Wednesday will remain quite mild in the upper 50s to mid 60s. Confluence of northern/southern streams evolves going through Wednesday night and Thursday, with approach of the southern stream wave the most significant element of the forecast package despite being in the day 4-6 period. Operational 00z GFS is an weaker, more open, and more southern outlier within a pretty diverse ensemble set, and support remains for a stronger closed system in EC/Canadian. Would be premature to slide into a GFS fairly null solution at this point, and other than a subtle southward shift, have not made too many sensible weather changes during the Thursday night through Friday night period. Confidence in system existence remains high, details at this point quite a bit lower. Precipitation which breaks out Thursday will likely be battling a drier east to northeast lower level fetch, setting up potential issues with wet bulbing and timing of rain to snow transition on the front side of the system. Period of overnight Thursday night into Friday morning could potentially have most impactful weather in terms of wind and snow accumulation. Best to keep a watchful eye on the progress of the system which is still well off the West Coast this morning as it approaches the region late week. One thing for sure, much more normal February temperatures will follow for the weekend, likely the first below normal period in two weeks. && .AVIATION...(For the 12Z TAFS through 12Z Monday morning) Issued at 522 AM CST Sun Feb 19 2017 VFR conditions persist into Sunday evening. Attention turns to the overnight hours as moisture lifts northward. Indications further south across Kansas and Oklahoma suggest that LIFR stratus will be possible after midnight locally, intermixed with periods of 3 mile or lower fog into daybreak. && .FSD WATCHES/WARNINGS/ADVISORIES... SD...None. MN...None. IA...None. NE...None. && $$ SHORT TERM...Dux LONG TERM...Chapman AVIATION...Dux