Thursday, February 6, 2020

Thursday Night - Mostly cloudy, clearing. Low: 20-24

Friday - AM clear, PM overcast with light snow. High: 34-38

Friday Night - Cloudy. Low: 22-26

Saturday - Morning fog, becoming clear. High: 34-38

 Sunday - Overcast with rain. High: 44-48

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As moisture clears out tonight into Friday morning, skies will become mostly clear. Clouds will build back in Friday afternoon bringing the possibility of snow showers in the afternoon. It will remain cloudy Friday night becoming clear on Saturday. Due to the snow pack and low winds, freezing fog is possible during the early morning hours Saturday. Overcast skies will return Sunday with rain likely.
Forecasters: Lieberman, Dowell, Ritter
Issued:  5:00pm: February 6, 2020

Technical Discussion (The nerdy stuff we are discussing in class) 
At 200MB, a long wave trough is passing over Columbia and moving East. A jet max is centered over New England oriented from SW to NE putting Columbia in the left entrance region. At 500MB, the trough is significantly deeper south of Columbia in Texas and northern Mexico. In the same area, there is significant rotation indicated by high vorticity values in addition to rotation over central and northern Illinois (downstream of our forecast area). Moving down to 700MB, the trough is less defined and flow is nearly zonal over Columbia. Additionally, all significant moisture is either up or downstream of our location. Finally, at the surface, there are no discernible large scale features in our area. The trough is not identifiable and no cyclones or anticyclones are near us.

For our forecast, we used primarily the 18Z run of the NAM, complemented with SREF plumes. We avoided the GFS as the WPC Model Diagnostics advised a non-GFS model blend. From now until late Saturday night, we expect the long wave trough that has dominated our weather to slowly move east and fill in at the upper levels. This will bring increasingly zonal flow. This is supported by both the 250MB and 500MB height profiles. Also reflected to the 850MB and surface level, we expect primarily zonal flow with negligible short or long wave features.

Friday afternoon into late evening, 850MB solutions show sufficient moisture and UVM for anticipate precipitation. This is supported by skew-T analysis which shows a moist layer from appx 900-700MB and omega values sufficient to anticipate precipitation. With the majority of the air column being well under freezing--with the exception of warmer temperatures at and just above surface--we believe that the precipitation will be snow. Future forecasters should monitor the temperature profile. Around 22Z, UVM will begin to clear and precipitation should halt.

Early Saturday morning, skew-T analysis shows saturation and near zero wind speeds at the surface. This combined with moisture from Friday's precipitation and the current snow pack indicate freezing fog is likely. With moisture clearing out of the lowest levels, we expect clear skies going into the afternoon.

Sunday we expect significant moisture and lift. Starting at appx 13Z, soundings show expected saturation from around 800-700MB and significant UVM. Little if any of the temperature profile is forecasted to be below freezing so we expect that rain to last until around 22Z when UVM slows. Therefore, there is a chance of rain beginning Sunday morning and persisting into Sunday afternoon. Future forecasters should pay close attention to the temperature profile.

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