Current Conditions at Sanborn Field

 

Tuesday Night: Partly cloudy. Low: 29

 

Wednesday: Scattered clouds. High: 49

 

Wednesday Night: Overcast. Low: 30

 

Thursday: Overcast. Rain and snow. High: 41

 

Thursday Night: Overcast and snowy. Low: 24

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Discussion:

Winter is making a boldly comeback with cold winds and temperatures. Starting tonight, the winds will become more northerly and vary from 5 to 15mph. These winds, paired with the cold temperatures, will cause wind chill values to be in the teens to lower-20s. The rest of the week is looking to be cloudy, but we may see sunshine Wednesday before the moisture returns Wednesday night. This return of moisture will be responsible for rain and snow on Thursday through Friday. While there is uncertainty with this system's timing and location, we currently believe rain/freezing rain will begin early-morning Thursday becoming a rain/snow mix mid-day. This will continue until Thursday night where the precipitation will turn into freezing rain, before midnight. We expect less than 2 inches of snow to accumulate and less than .1 inches of rain to fall.

- Alexander

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Forecasters: Alexander, Duff, Orr

Date Issued: 3/8/2022 5:00 PM CST

Technical Discussion:

    After last weeks quiet weather led to an active weekend, the pattern continues for this week. Colder and quieter weather for the beginning of the week will lead to the potential for a late season winter event on Thursday and Friday. The overall problem during this forecast is the timing of the rain and snow event, the type of precipitation and the changeover from rain to freezing precipitation, as well as,  snow accumulations. It is also important to note that temperatures during this period are much colder than in the days previous.   

    In the forecast the NAM was primarily used to forecast atmospheric conditions as it had a better handle on current placements of low pressure in Southern Canada. Both the NAM and the GFS were spotty when forecasting surface temperatures, but the GFS performed slightly better and the members of the GEFS plumes seamed to be more in agreement. NAM forecasted soundings were used for timing of the event and precipitation type. 

    The beginning of the week will start off quieter as very zonal flow dominates the upper atmosphere. A trough develops over the western part of the CONUS early on Thursday. A jet streak seen on a 300-mb chart of heights and wind shows the streak approaching Mid-Missouri later on Thursday. The streak is relatively weak with wind speeds of around 110 knots, but should allow for some divergence in the upper part of the atmosphere. 

    A similar story is told at 500-mb where plots of heights and vorticity show some higher values of circulation associated with a shortwave disturbance early on Wednesday. This indicates the development of some cloud cover on Wednesday, as a lack of abundant moisture will inhibit any chances for precipitation. The second important feature at this level is the increase in circulation associated with the positively tilted trough in the western part of the United States. This occurs after 12Z Thursday and continues throughout the end of the forecast period Thursday night. 

    At 700-mb a pocket of moisture enters Missouri from the south early Wednesday, but values of relative humidity and the dry air that moves in behind it indicates the potential for only development of clouds during this time. The rest of the moisture that will be responsible for rain and snow chances on Thursday arrive ahead of the trough on Thursday around 12Z. There is also an increase in omega values during this time, indicating some upward vertical motion that will aid in the start of precipitation. 

    Winds at 850-mb are out of the south until a mild cold front passes through Mid-Missouri around 09Z Wednesday. Moisture from a southerly wind ahead of the front and limited forcing due to the passage of the front may lead to the development of some cloud cover on early Wednesday. The bulk of the moisture arrives around 12Z Thursday ahead of the low pressure system to southwest. 

    As mentioned earlier the difficulty in this forecast was diagnosing the timing and the type of the precipitation. There is still a lot of uncertainty with total snow accumulations due to the wintry mess that may occur Thursday into Friday. The upper level conditions, arrival of moisture, and use of soundings indicate that precipitation should start early Thursday morning. Temperatures will be in the lower 30s, but a significant dry layer indicates that any precipitation is likely to start as rain or freezing rain. As temperatures increase during the day on Thursday, most of the precipitation will likely fall as rain. A transition to a rain/snow mix is likely later on Thursday, then back to freezing rain before midnight Thursday as the upper levels of the atmosphere dry out. There is still a lot of uncertainty to how the dry layer will effect precipitation type.

 Future forecasters should pay close attention to timing and precipitation type for the upcoming winter event, as well as, potential of colder temperatures and higher wind speeds leading to cold wind chills going into the weekend. 

-Duff