12/9/2016 Short Term

An active weather weekend is expected as a system brings looks to bring precipitation to the area on Sunday. Saturday looks to be a clear day until a chance for precipitation moves in Saturday night. Southerly surface winds will bring moisture from the south to this area. Strong, widespread warm air advection moves into the area. Along with the warm air advection, strong positive pressure advection moves into the area as well. This will lead to rising motion and bring the precipitation that is expected during this time period. The temperature profile Saturday night into Sunday and Sunday night is very important, as being colder even just a couple degrees could change the precipitation we see drastically. Temperatures Saturday night will be in the mid 20s. Some light snow is possible Saturday night, but not much accumulation will be expected due to the majority of the moisture moving in on Sunday. Temperatures will gradually increase Saturday night into Sunday, eventually topping out in the mid 30s on Sunday. The heaviest precipitation will move through the area Sunday night. Warm air advection and positive pressure advection will remain in the area until Monday morning, so enough rising motion is expected to bring precipitation all day Sunday. Snow looks to fall throughout the day Sunday, but with temperatures slowly climbing into Sunday night, the precipitation should turn to a rain/snow mix and eventually to all rain. According to a forecast sounding from the GFS, temperatures will be below 0 in the atmosphere until about 850mb at 3z Monday morning/Sunday night, where the sounding becomes almost isothermal just above 0 degrees Celsius. This system looks to bring almost every type of precipitation to the area. A mix of rain, snow, sleet, and some light freezing rain is possible with this system. Just the slightest temperature variance could lead to this being an all snow event or an all rain event. This system will have to be carefully looked at throughout today and tomorrow to try and pinpoint the majority type of precipitation, but right now it looks like mainly a rain event with snow mixed in at various times, mainly during the day on Sunday. The system should move out Monday morning, and the rest of the day Monday looks dry and cool with highs in the mid 30s.

Figure 1: Widespread warm air advection at the 850mb level over the area attributing to rising motion and the precipitation expected this weekend.

Pressure advection at the 300K isentropic level at 0z Monday. Widespread areas of positive pressure advection will lead to rising motion and precipitation over the area Sunday into Monday.

Forecast sounding from GFS for the area at 3z Monday morning. The sounding is below freezing until about 850mb, where it becomes mainly isothermal just above 0 degrees. This type of profile most likely leads to a cold rain.