919 FXUS63 KTOP 262100 AFDTOP Area Forecast Discussion National Weather Service Topeka KS 300 PM CST Thu Dec 26 2019 .SYNOPSIS... Issued at 300 PM CST Thu Dec 26 2019 20Z water vapor imagery shows a closed low just of the southern CA coast with another upper low propagating across Canada. The pattern caused southwest flow to set up over the central plains with some fetch of subtropical moisture streaming over eastern KS. At the surface, high pressure has steadily been building into the forecast area, and an expansive deck of low clouds have been stubborn to mix out. && .SHORT TERM...(This evening through Friday) Issued at 300 PM CST Thu Dec 26 2019 For tonight, the question is what will the stratus do and is there a chance for fog to develop overnight. The NAM has generally been the only model solution to hold onto the stratus this long, and the RAP has started to catch onto this as well. Forecast soundings from both models suggest the stratus will dissipate during the evening and the the boundary layer could saturated as radiational cooling occurs. Although I'm not sure what would cause the inversion and stratus to dissipate after sunset. So there is a large amount of uncertainty with the low level humidity. Have inserted some patchy fog across the north where skies are more likely to be clear for a period of time this evening. Also have held onto the stratus across eastern KS well into the evening. Lows are expected to range from the lower 20s along the NEB state line to the lower 30s over east central KS. If the clouds hold on all night, lows could easily be a few degrees warmer. Friday should start to see moisture return as the upper low over the southwest moves into the souther Rockies. Forcing for vertical motion will be on the increase through the day, but it appears to be at its strongest after Friday. So think Friday will be a mostly cloudy or overcast day with highs slowly climbing into the mid 40s to near 50. Precip chances should increase across central KS and spread east as the day progresses. .LONG TERM...(Friday night through Thursday) Issued at 300 PM CST Thu Dec 26 2019 Have categorical POPs for Friday night through Saturday. This is when models show a consensus for the best forcing and moisture to come together before a dry slot works its way into the state by Saturday evening. With good warm air advection and the forecast area remaining on the warm side of the system through Saturday, precip should be in the form of rain for all of the area. Models show some weak surface based instability developing across eastern KS Saturday afternoon. Lapse rates remain pretty marginal and near the moist adiabat, but low level and deep layer shear are progged to be good enough for possibly some organized convection. We may have to keep an eye out for a strong thunderstorm Saturday afternoon. The dry slot eventually works in Saturday evening bringing a break from precipitation. Then there may be enough wrap around moisture for some precip within the deformation band on the back side. Forecast soundings suggest a wintry mix could be the most likely precip type since saturation within the dendritic growth zone is hard to come by. However any precip looks to be very light so the forecast doesn't anticipate a lot of impacts from this just yet. Highs Saturday over eastern KS are forecast to be near 60 thanks to persistent low level warm air advection. Further west across north central KS, highs may only make it into the lower 50s since the temp advection shouldn't be as strong. Colder temperatures are likely Sunday as gusty northwest winds advect cold air into the region. The forecast remains dry for Sunday night through Tuesday night. Dry air is forecast to be over the area with no well organized disturbance progged by the models. There are some slight chance POPs in the forecast for Wednesday and Thursday as models show energy over the southwest trying to phase in with a northern stream trough moving through the plains. Moisture availability looks to be a limiting factor for POPs at this point. Temps are forecast to see a gradual warming trend, but remain generally seasonable with lows in the 20s and highs in the 40s. && .AVIATION...(For the 18Z TAFS through 18Z Friday afternoon) Issued at 213 PM CST Thu Dec 26 2019 The MVFR stratus has been slower to erode away that the forecast anticipated. Have amended it now the the 19Z RAP and catching on and more in line with the NAM. There is a fair amount of uncertainty in how the low clouds will evolve overnight. Am concerned fog could become more widespread with the center of the surface ridge moving over. But given the uncertainty in the models and anticipating high clouds increasing will hold off on reintroducing fog at this time. && .TOP WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...Wolters SHORT TERM...Wolters LONG TERM...Wolters AVIATION...Wolters