What was likely the last big weather and precipitation event for 2013 impacted the district on Saturday with torrential rains east, ice and snow central and west. Rainfall totals on the order of up to nearly 10″ were recorded in deep southern Illinois with widespread totals of 3-6″ over SE Missouri and S Illinois to the immediate southeast of St. Louis. St. Louis itself was in between the zone of persistent heavy rains to the southeast and wintry weather just to the west, so totals in the city itself were around and inch, but dropped of sharply to the west. Kansas City meanwhile revived a glaze of ice up to .2″ thick followed by 2-5″ of snowfall Saturday night. Even with the ice and snow, the rain in this storm system was the major weather story.
The graphic below shows Saturday’s rains only and does not include Friday’s total. A corridor of heavy rain is apparent tracing along and just NW of the Mississippi River in Arkansas to SE Missouri, where it joins the Ohio and traces along and NW of the Ohio from Illinois to west central Ohio.
The graphic below contains screen grabs from the Doppler Radar at St. Louis and Paducah which shows the radar estimated rains for the SE Missouri/S Illinois area (top) and the St. Louis area (lower) along with observation reports of the two day rains. Doppler radar can overestimate rains further from the radar site (example Chester IL) because at that distance, the radar is scanning well up into the cloud layer, sensing large raindrops, or even sleet well above the ground and not actual rainfall reaching the ground. Doppler radar estimates have Chester receiving 3.5″ while the observer reported 2.66″.
Here are the wide scan views from each radar:
These rains have substantially increased the rain surplus for December, but in a classic case of have and have-not, NW Missouri will likely end the month (and year) on a dry note with drought ongoing.
The NWS in St. Louis has prepared this rainfall graphic showing total rains within its service area:
For Kansas City and NW Missouri, snow and ice were the main features. Light freezing drizzle and very light freezing rain began late morning Saturday and continued into evening, the heavier band of snow did not arrive until the dinner hour, when the freezing precipitation changed over to snow. The greatest ice totals were along and either side of I-44 to the south of the region, with much lighter totals in the KC area, still enough to cause major headaches for anyone who had to be out as darkness fell. The graphic below shows where the snow was heaviest, in the far NE corner of KS and NW corner of MO up into Iowa. General 4-8″ amounts fell on the KS side of the state line and north of the river on the Missouri side.
This pretty well matched the forecast issued Saturday morning. This was not an ideal heavy snow setup for the KC area due to several reasons. The track of the upper level storm was far too close to KC for heavy snow, as the heaviest snow band will usually occur some distance 50-100 miles NW of the track of the upper level storm.
The nearby track of the upper storm also brought the snowfall-killing dry slot right up to the SE side of the metro. On the graphic below, the dry slot is on the left side of the image. The dry slot is actually only “dry” at mid and upper levels of the atmosphere, not at the surface. The dry slot strips away that mid and upper level moisture in the form of ice-crystal containing clouds. These ice crystals “seed” the lower level clouds containing super cooled (sub-freezing but still liquid) water droplets. Those ice crystals “feed” the formation of snowflakes, which is called the “seeder-feeder” process. No matter how cold and how moist it is at the ground, without those ice-crystal containing clouds above, you’re not going to get much more than freezing drizzle or a few flurries.
Another limiting factor for big snows was the fact that the snowfall producing “deformation zone” (which is an area where the winds bend back around the north side of the upper low, often looking like a deformed area in the cloud band on satellite hence the name) was in the process of having its moisture feed cut-off from the deep tropical moisture which fed the flooding rains in the eastern district. The dry slot was severing the connection and without that pump of moist air flowing into the cold side of the storm, the snowfall rates gradually wind down as the moisture decreases.
Finally, here are a series of maps prepared by the regional NWS offices detailing the snow, sleet and freezing rain accumulations in each of their service areas:
Caution will be needed everywhere tonight and for the Monday morning commute – either due to snow on the ground or where heavy rains have left standing water which will refreeze. This might be an ongoing issue for several nights to come.
Looking forward to Christmas week, the weather appears non-eventful in terms of any storm system in this part of the country, but a renewed push of Arctic air heads beginning tonight. A Wind Chill Advisory is up well NW of Kansas City and even in the city itself, lows near 5 tonight and highs in the teens Monday will produce wind chills as low as -10.
Lows tonight will fall into the singles below zero far NW to the mid 20s SE.
Much colder Christmas Eve morning with lows well below zero NW to the lower teens SE.
By Christmas Day itself we should be back to near average temperatures, meaning lows in the teens and 20s and highs 35 to 42.
Nationally, rains shown here in the east move off shore by Christmas Eve, with rains in the PACNW diminishing by Monday.
Quiet weather with no major storm systems is anticipated for Christmas Eve and Christmas Day.
With a busy weekend, that will wrap up the blog for a few days, we’ll post any needed updates on the Facebook page (https://www.facebook.com/KCWeatherCenter). After Christmas it will be time to start compiling the December and end of year stats and look forward to what kind of weather January might bring. Until then, happy holidays!