Tuesday, February 3, 2015

Aftermath From Snow Storm: Freezing Temps

Public weather briefing

After the current snow storm made its way through Madison, cold air moves in. Below zero temperatures are in store for Wednesday night, which will lead into a very cold Thursday with highs expected around 10 degrees.  It will be mostly clear for the next two days before the next system moves through bringing possible precipitation and warming temperatures.  Highs for the weekend are expected to be in the middle to upper 20s and possibly hit 30.  Along with this likely comes mixed precipitation,  however, on Saturday and Sunday.


Tonight. Slight chance of snow showers after the initial snow storm, before clearing out in the night.  Low around 7 degrees with light winds.

Wednesday. Some clouds and sunny with light northwest winds.  High around 18 degrees.

Wednesday night. Clear and frigid.  Low around -10 degrees with light winds.

Thursday. Sunny and cold. Light winds with negative wind chills. High around 10. Low around 5.

Friday. Clear very early then mostly cloudy and warmer.  High near 30 with a light south wind.  Low just under 20.

Outlook for Saturday through Monday. Mostly cloudy with a chance of precipitation on Saturday and Sunday before clearing out to a partly sunny Monday.  Highs consistently in the middle to upper 20's with a low around 20 on Saturday cooling to a low around 10 Sunday and Monday [CONFIDENCE: MEDIUM]

Forecast Discussion

Currently, a snow storm is in area producing moderate accumulation totals.  This band is moving quickly, but producing snow at a heavy rate and some areas could be seeing 3 inches or more. 
This sounding from Davenport, Iowa this morning is a view of the atmosphere.  It is showing high moisture levels in the lower atmosphere from the surface to 850 mb.  The high levels of precipitation associated with this storm is likely due to a upward vertical velocity maximum centered in the area of the sounding as well as frontogenetical forcing.

Trailing behind the low pressure system, an anticyclone from southern Canada moves down into the northern midwest bringing clear conditions and very cold temperatures.  These conditions will last from Wednesday afternoon to early Friday, before the system moves through and a secondary trough moves into the area from Canada bringing up the next possibility for precipitation.  

Associated with this trough, is warm air advection rising the temperatures from the 10's to the middle to upper 20's.  With this rise in temperature, the type of precipitation is still unsure, so we expect the possibility of mixed precipitation on Saturday and more likely snowy conditions on Sunday if precipitation occurs due to the cooling temperatures.

Will Hahn and Andrew Goenner


  1. Will and Andrew - Nice first discussion! Your snow forecast for Tuesday was a bit off, but on Monday the NWS expected lower snowfall totals as well. Your forecast for cold temperatures Wednesday into Thursday validated, however, and I agree it was frigid last night! I appreciate your effort bringing in vertical profile analyses via soundings. Be careful, though, that the sounding you are analyzing is relevant to the forecast time you are discussing. In this case, your sounding was from early morning and the relatively high surface RH near the surface is likely due to overnight radiative cooling of the boundary layer (notice the dry air aloft and sharp change in wind speed/direction directly above the surface). Also, make sure to use model fields to validate your sounding analysis arguments...you have a lot of information at your disposal to make educated conclusions about what you're seeing in the sounding, don't be afraid to use them! If you do make a conclusion about a characteristic of the vertical profile (for instance upward vertical motion due to frontogenetic forcing), be sure to show that with a quick figure. Overall, keep up the good work. Incorporating more appropriate data into your discussion and making sure to explain your conclusions with data will set you up for a great round two of blog posts.

    Question: You indicate at the end of your discussion that temperatures toward the end of the week will rise upward into the 20s, can you elaborate on your decision to expect mixed precipitation?

  2. Our decision was based on the models showing precipitation over the weekend, but as of Tuesday, when we posted, temperature predictions were still up in the air as far as whether there would be freezing temperatures or not. Our best guess at the time was that it would likely be rain if precipitation occurred during the day, but if there was any precipitation later in the day/night when the temperatures cooled, we may have seen freezing rain or sleet in the later night to early morning.

    Also, regarding the snow totals on Tuesday, you are right, NWS was very conservative and low with their prediction and we followed that. The precip models also showed lower amounts as well. The snow accumulation was a bit of a surprise and certain dynamics (upward vertical motion) intensified greatly from Monday to Tuesday for the time of snow.


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