862 FXUS63 KTOP 142121 AFDTOP Area Forecast Discussion National Weather Service Topeka KS 321 PM CST Thu Feb 14 2019 .SHORT TERM...(This evening through Friday) Issued at 321 PM CST Thu Feb 14 2019 21Z water vapor imagery shows an upper level shortwave rotating through the Upper Midwest. Another closed upper low was located over the gulf of Alaska as a shortwave rotated through the base of the closed low into the Pacific Northwest and northern CA. A decent plum of subtropical moisture could be seen streaming from the Pacific into the southern half of the CONUS. At the surface, a cold front was progressing through the forecast area and just about to exit Anderson CO. Observations show good pressure rises behind the boundary with temps in the teens and 20s across NEB. For tonight, the weather is expected to remain quiet. Winds should gradually diminish through the night as the pressure gradient relaxes. Mid and high clouds should remain over the area with the subtropical plum of moisture continuing to stream over the Rockies. Lows should fall into the teens as this most recent arctic airmass pushes south. Snow chances will increase through the morning hours Friday as a piece of energy from northern CA approaches the forecast area. The models have trended a little more defined with this wave, while keeping it opened and rather progressive. But the models prog a little better forcing as seen by the Q vector convergence and even some frontogenesis mainly through the morning. There is also a trend to increase QPF amounts. While the GFS solutions maintains relatively light QPF amounts, the concensus is for about a third of an inch to occur over a large part of the forecast area in the morning. Given the pretty cold airmass that is moving into the area now, think that the snow to liquid ratio is likely to increase to between 10:1 and 16:1 from south to north. This is an adjustment to higher ratios than prev forecast have had. The result is for increased snow amounts through the morning, with storm totals expected to be in the 3 to 6 inch range. There is some potential for locally higher amounts as the NAM and GFS both show signs of upright instability. It is not out of the question that snowfall rates could be around an inch per hour. Have considered the need to upgrade the advisory to a warning but given the nature of the wave remaining open without a strong surface response and the short duration of the snow to about a 6 hour window or so, think chances for totals exceeding 6 inches is not high enough for a warning at this point. Later shifts will want to reevaluate this however. The potential for freezing rain or sleet looks to be pretty low. Forecast soundings do show mid level drying with the loss of ice in the cloud during the evening. But this occurs as the lift exits. So I expect as long as there is lift for precip, the dendritic growth zone will remain saturated and snow being the main precip type. Highs Friday will not be very warm with continued low level cold air advection and snow occurring. Have highs ranging from the mid teens to the lower 20s. .LONG TERM...(Friday night through Thursday) Issued at 321 PM CST Thu Feb 14 2019 All of the forcing for precip looks to have pushed off to the east by 00Z Saturday. So think the precip should be over by the evening. Another shortwave is progged to lift out across the forecast area Saturday afternoon and Saturday night. This wave has better dynamics with it and good forcing for precip. But the models struggle with the saturation within the column. This poses a precip type problem as forecast soundings briefly show saturation in the dendritic growth zone, only to dry it out. So confidence in all snow for Saturday afternoon and evening is rather low. For this reason have a mix of freezing drizzle and snow in the forecast. The good news may be that because the models have limited moisture for this wave, they do not generate a whole lot of QPF. There may be a need for another winter weather advisory for Saturday afternoon and evening for minor accumulations of snow and ice, but will wait for the event on Friday to conclude before issuing anything for Saturday. Temps should not rebound much on Saturday with clouds inhibiting insolation and low level easterly winds maintaining a neutral advection pattern. After lows fall into the single digits above zero Saturday morning, highs are forecast to range from the middle 20s to around 30. For Sunday through Monday, models maintain a westerly to southwesterly flow. A reinforcing surface ridge is expected to move through the Upper Midwest keeping afternoon temps in the 20s and lower 30s. There are some signs of weak perturbations within the flow, but predictability of these is somewhat limited. The forecast has some small chances for snow on Monday because of the weak waves. A better shortwave is shown to move through the central plains on Tuesday, and there is reasonable agreement among the models in timing and location. GFS forecast soundings and 1000-500 MB thicknesses would support another snow event for Tuesday and Tuesday night. So POPs have been increased into the likely range for Tuesday night. At this point, the system looks to be somewhat progressive system that doesn't have a strong surface low. So an early expectation would be for a couple inches of snow by Wednesday morning. Wednesday and Thursday are expected to remain dry in the wake of this last shortwave. There are some discrepancies between the ECMWF/GFS/Canadian with an upper trough along the west coast by the end of the period. The ECMWF/Canadian would amplify the upper trough out west and allow heights to rise over the plains and temps to moderate. But the GFS solution would keep things colder with another chance for precip by the end of the week. Will need to watch trends and hopefully models come in line better with one another. For now have been somewhat optimistic with trending highs warmer into the 30s and around 40 for Thursday. && .AVIATION...(For the 18Z TAFS through 18Z Friday afternoon) Issued at 1130 AM CST Thu Feb 14 2019 FROPA has occurred across all terminals at this hour. Winds will continue to back to a more northwesterly component then eventually a northerly to northeasterly component during the overnight period. Sustained winds of 15-20kts should be common beginning by the early to mid afternoon hours then continue into the evening with gusts as high as 30kts possible due to enhanced cold air advection into the region. Weather conditions are expected to take a turn for the worse as snow moves into the area and just after the 12Z time frame. Right now, have only gone as low as MVFR CIGS but because of the snow have reduced VIS restrictions to around 2SM by mid morning. If the most intense band of snow moves through the terminals then the expectation is lower CIG/VIS restrictions will be possible. && .TOP WATCHES/WARNINGS/ADVISORIES... Winter Weather Advisory from 6 AM to 6 PM CST Friday for KSZ008>012-020>024-026-034>040-054>056-058-059. && $$ SHORT TERM...Wolters LONG TERM...Wolters AVIATION...Drake