735 FXUS63 KTOP 061352 AFDTOP Area Forecast Discussion National Weather Service Topeka KS 752 AM CST Wed Feb 6 2019 ...Update to aviation forecast discussion... .SHORT TERM...(Today and tonight) Issued at 404 AM CST Wed Feb 6 2019 A surface ridge axis and associated shallow dome of cold air remains in place over the CWA this morning. 09Z water vapor imagery shows a broad upper level trough digging across the Great Basin with a plume of moisture surging ahead of the system into eastern KS and MO. Surface cyclogenesis will increase today just east of the Colorado Rockies and begin to advect eastward into the High Plains. Precipitation chances will continue today and tonight. Atmospheric soundings continue to show a shallow layer of saturated air in the lower levels of the column, most of which is below freezing. Drier and warmer air exists just above this layer. Bufkit forecast sounding profiles indicate that freezing drizzle continues to be the most likely form of precipitation today, into tonight. However, the challenges for this forecast period are the timing and amount of freezing drizzle expected. Current thinking is that a round of drizzle is possible through the morning hours today in response to a slight increase in vertical velocities. POPs decrease slightly for the afternoon and while precip is not expected to be continuous through the day, periods of drizzle cannot be completely ruled during the afternoon. The main forcing associated with the upper trough will arrive tonight, bringing our best chance for winter weather. A wintry mix of precipitation is possible overnight until a deeper layer of cold air arrives as a surface low moves across OK, into the Ozarks. With the arrival of the colder airmass, we could see a brief transition to snow overnight and early Thursday morning before precip exits to the east. Snow accumulations are expected to remain less than half of an inch. Total ice accumulations today and tonight are generally expected to remain below or around a tenth of an inch. .LONG TERM...(Thursday through Tuesday) Issued at 404 AM CST Wed Feb 6 2019 Models prog the arctic cold front to have exited the forecast area by 12Z Thursday with much dryer and colder sir advecting in on strong northwest winds. There is some indication from the GFS for some possible flurry activity across northeast KS and the far eastern portions of the forecast area for a few hours into the morning. So will keep some slight chance POPs with little or no accumulations anticipated. Eventually the dry air will win out and bring an end to precip chances with clouds decreasing through the day. The cold air advection looks to persist through much of the day implying there will be little in the way of a diurnal trend in temps. So have highs steady or only warming a handful of degrees with readings expected to range from the mid teens to the lower 20s. The cold air should hang around through Friday night. Then the arctic high pressure is expected to slide east with a modest return flow developing for Saturday. Lows Friday morning look to be very cold with reading from around zero to around 5 above. Factoring in the winds, wind chill reading across northeast KS could be as low as -15. However models are bringing the ridge axis into the forecast area by 12Z, and winds have trended lighter through the early morning hours. As a result, expected wind chill values have trended slightly warmer. There could still be parts of northeast KS to see wind chills below -15 which is the threshold for an advisory. At this point, the more dangerous wind chills may be limited to the northeast couple counties where winds may remain slightly stronger. The next chance for precip looks to be late Saturday night and Sunday morning as a subtle wave moves across the central plains. Right now the models seem to favor the better saturation and forcing along the KS/NEB state line and to the north. Temps and moisture profiles look more favorable for any precip to be snow. And precip amounts look to be fairly light given the limited moisture return ahead of the wave. A better defined wave is expected to move out across the central plains early next week. There continues to be some timing and surface low track differences between the GFS and ECMWF. But the overall consensus suggests a chance for precip Monday afternoon through Tuesday morning. Moisture profiles again look more favorable for mainly snow. And with the GFS showing better dynamics impacted the forecast area, it suggests precip amounts could be a little more robust than over the weekend. There is some uncertainty in the forecast given the stated differences, but think POPs in the 30 to 50 percent range are warranted. Temps are forecast to be fairly close to climatological normals for mid February. And this seems to make since with the synoptic pattern favoring continued waves diving into the southwestern US and allowing periodic cold fronts to move through. Highs for the weekend are forecast to be in the upper 30s and lower 40s. A slight cool down is forecast for Monday and Tuesday as another front pushes south. Lows for Sunday through Tuesday are expected to remain in the 20s. && .AVIATION...(For the 12Z TAFS through 12Z Thursday morning) Issued at 747 AM CST Wed Feb 6 2019 Updated the TAFS to include mention of freezing drizzle due to ground reports of ongoing precip this morning. A mix of wintry precip will continue to be possible through the day with freezing drizzle the most likely type today. Another round of wintry weather is expected overnight. Otherwise, CIGS will be high end IFR/low end MVFR throughout the period. Winds will increase out of the north-northwest after 06Z Thurs as a low passes south of the area and colder air moves in. Gusts could reach around 20 kts by end of period. && .TOP WATCHES/WARNINGS/ADVISORIES... Winter Weather Advisory until 6 AM CST Thursday for KSZ008>012- 020>024-026-034>040-054>056-058-059. && $$ SHORT TERM...Teefey LONG TERM...Wolters AVIATION...Teefey