Monday, February 18, 2019

Monday - Cloudy. High 28-32

Monday Night - Cloudy. Low 20-24

Tuesday - Clouds remain. Snow beginning in the evening. High 30-34

Tuesday Night - Clouds persist. Breezy. Snow transitioning to freezing rain overnight. Some sleet may mix in. 2-4" of snow possible. 0.10" of ice accumulation possible. Windy. Low 28-32
Wednesday - Cloudy. Freezing drizzle or drizzle possible before noon. High 36-40

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After a weekend of active winter weather, Columbia is in store for yet another significant winter event this forecast period. We will see a brief period of calm and cold weather Monday into Monday night. Despite the dry air in place over Missouri, low level clouds remain. Precipitation will begin as snow Tuesday evening and persist into the overnight hours until it is expected to transition to freezing rain after midnight. Columbia could see snow accumulations in the range of 2-4", and ice accumulations up to 0.10". Wednesday precipitation will transition to a cold rain. Freezing drizzle is possible into Wednesday morning hours, but no additional accumulations are expected. Conditions Tuesday night into Wednesday morning will make for hazardous travel, so please exercises caution on your morning commute to class or work!

Forecasters: Ritter, Travis, and Hirsch
Issued: 10:00 a.m., February 18, 2019

Technical Discussion (The nerdy stuff we are discussing in class!)
Cold and dreary conditions that were with us during the day Sunday will persist through the early part of this week. At present, satellite imagery shows a low-level cloud deck overhead, and METARs from KCOU confirm this. Conditions at the surface have also been breezy this morning, although recent METARs show sustained NW winds decreasing below 10 kts. Looking ahead through the rest of the day today, GFS soundings show saturation around 900 hPa throughout the entire day, meaning that those low clouds will be overhead all day. By the evening, the low clouds clear out, but about the same time this is occurring, high clouds will start to filter in ahead of our next system. GFS soundings show the layer between 200 and 250 hPa saturating around 03Z, with this saturated layer growing closer to the surface throughout the day Tuesday. This means that, while there may still be high clouds around Tuesday morning, ceilings will gradually drop throughout the day Tuesday. Because weather conditions will be very similar today and Tuesday as they were Sunday, kept afternoon high temperatures for both Monday and Tuesday similar to Sunday's high. Also, I kept Monday's overnight low close to Sunday's overnight low for the same reason.

With the dreary Monday and Tuesday covered, all eyes now turn to yet another winter storm aiming to impact our area Tuesday Night. By 00Z Wednesday, Columbia will be sitting under the right-entrance region of a 110-kt 250 hPa jet with plenty of divergence aloft. At 500 hPa, several small vorticity maxima will move NE out of Arkansas and through mid-Missouri throughout the night. Also, at 850 hPa, a 40-kt LLJ will develop over Arkansas and push N/NE toward our area, leading to plenty of moisture advection. All this, combined with high omega values throughout the column, points to even more winter weather. The main question for this system is precipitation types and resulting amounts. Currently, all model guidance starts this system as snow between 21Z Tuesday and 00Z Wednesday, and continues as all snow through roughly 06Z Wednesday. After that, model guidance diverges, with all precipitation types being shown between the models used. With soundings showing veering winds in the column and a strong LLJ present, there will be WAA advection, likely beginning around 06Z Wednesday. Also, cloud ice will be rapidly lost between 06Z and 12Z Wednesday. With this being said, I have leaned toward a snow to freezing rain transition between 06Z and 12Z Wednesday, with some sleet mixing in. After 12Z Wednesday, the system will be mostly done impacting the area, although cannot rule out some drizzle or freezing drizzle before 18Z Wednesday. As for amounts, I believe 2-4" of snow and up to 0.1" of ice accretion is likely based on current information. Now, as is a caveat with all winter weathe forecasting, this is still roughly 36 hours away; therefore, these details are subject to change, especially with uncertainty in precipitation types, so continue to check back for updated forecasts.

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