Winter Storm Postmortem: Flooding Rains SE, Snow NW and a look at the week ahead

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.

A wider view of Saturday's precipitation shows the corridor of heavy rains from Arkansas to Ohio.

A wider view of Saturday’s precipitation shows the corridor of heavy rains from Arkansas to 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″.

Heavy rain and flooding the story on the eastern side of the district, with a persistent band of heavy rains setting up SE of St. Louis and concentrating over SE Missouri and S Illinois. Two day totals are listed here.

Heavy rain and flooding the story on the eastern side of the district, with a persistent band of heavy rains setting up SE of St. Louis and concentrating over SE Missouri and S Illinois. Two day totals are listed here.

Here are the wide scan views from each radar:

Wide view: St, Louis radar precip estimate.

Wide view: St. Louis radar precip estimate.

Wide view: Paducah radar precip estimate.

Wide view: Paducah radar precip estimate.

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.

Missouri southeast of I-44 and Illinois south of I-70 have received 110-300% of the average December precipitation, while NW of those interstates it has been a very dry month with 50-90% of average precipitation.

Missouri southeast of I-44 and Illinois south of I-70 have received 110-300% of the average December precipitation, while NW of those interstates it has been a very dry month with 50-90% of average precipitation.

The NWS in St. Louis has prepared this rainfall graphic showing total rains within its service area:

Rainfall reports as prepared by NWS St. Louis MO.

Rainfall reports as prepared by NWS St. Louis MO.

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.

Total snow from the event with 8" or more from far NE Kansas through far NW Missouri and on into Iowa. Kansas City was on the outer edge of the 4-8" band with rapidly decreasing totals southeast toward Lee's Summit and points beyond. Around .1" to .2" of ice underlies the snow in KC with more ice SE and less NW.

Total snow from the event with 8″ or more from far NE Kansas through far NW Missouri and on into Iowa. Kansas City was on the outer edge of the 4-8″ band with rapidly decreasing totals southeast toward Lee’s Summit and points beyond. Around .1″ to .2″ of ice underlies the snow in KC with more ice SE and less NW.

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 track of the mid level low will determine where the heaviest snow will fall. That low will track just SE of the KC area.  Typically heavier snow falls a little ways NW of the low in an area called the "deformation zone" where mid level winds turn around the back of the storm. This creates rising air and aids in snow production.  Southeast of the low, a "dry punch" aloft moves in and strips away mid and upper level moisture.  This mid and upper level moisture consists of mid and high clouds made up of ice crystals.  Ice crystals have to be present to cause the low level moisture to turn to snow.  Otherwise you get freezing drizzle. This process is called "seeder-feeder" as the high clouds "seed" the lower level clouds with ice and "feed" the development of snowflakes. (See the Seeder-feeder graphic for details).  The passage of the upper low so close to the KC area means a very sharp cutoff southward in snow totals. Any wobble north..by as much as 30-50 miles..could reduce snowfall to nearly nothing in parts of the KC Metro.  (Mentally shift the snow totals and the low northwest on the map) By the same token, any southward shift by as much as 30-50 miles could bring the bigger snow totals directly into KC.

The track of the mid level low will determine where the heaviest snow will fall. That low will track just SE of the KC area. Typically heavier snow falls a little ways NW of the low in an area called the “deformation zone” where mid level winds turn around the back of the storm. This creates rising air and aids in snow production. Southeast of the low, a “dry punch” aloft moves in and strips away mid and upper level moisture. This mid and upper level moisture consists of mid and high clouds made up of ice crystals. Ice crystals have to be present to cause the low level moisture to turn to snow. Otherwise you get freezing drizzle. This process is called “seeder-feeder” as the high clouds “seed” the lower level clouds with ice and “feed” the development of snowflakes. (See the Seeder-feeder graphic for details). The passage of the upper low so close to the KC area means a very sharp cutoff southward in snow totals. Any wobble north..by as much as 30-50 miles..could reduce snowfall to nearly nothing in parts of the KC Metro. (Mentally shift the snow totals and the low northwest on the map) By the same token, any southward shift by as much as 30-50 miles could bring the bigger snow totals directly into KC.

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.

The "seeder-feeder" process: For snow to occur, not only cold temperatures and moisture need to be present, but also a layer of higher clouds aloft composed of ice crystals.  These ice crystals fall into the lower clouds, assisting the transition of the super-cooled (droplets of liquid water below 32F) cloud droplets into snow and ice crystals.  Without this layer of high clouds "seeding" the lower clouds, the super cooled droplets remain in liquid form and will fall as freezing drizzle at the surface - no matter the temperature.  This is a very common occurrence as a winter storm ends, dry air aloft pushes the high clouds east of the area leaving the low overcast.  At the surface, snow diminishes and those outside will notice tiny drops of liquid water falling from the sky.  This can cause a "crust" of ice to form on the newly fallen snow adding to travel difficulties.

The “seeder-feeder” process: For snow to occur, not only cold temperatures and moisture need to be present, but also a layer of higher clouds aloft composed of ice crystals. These ice crystals fall into the lower clouds, assisting the transition of the super-cooled (droplets of liquid water below 32F) cloud droplets into snow and ice crystals. Without this layer of high clouds “seeding” the lower clouds, the super cooled droplets remain in liquid form and will fall as freezing drizzle at the surface – no matter the temperature. This is a very common occurrence as a winter storm ends, dry air aloft pushes the high clouds east of the area leaving the low overcast. At the surface, snow diminishes and those outside will notice tiny drops of liquid water falling from the sky. This can cause a “crust” of ice to form on the newly fallen snow adding to travel difficulties.

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.

As predicted, the track of the upper level storm was not an ideal one for big snows in the KC Metro with the low passing too close and the dry sinking air wrapping into the system (the "dry slot") cutting off snows sharply to the city's southeast.  Snow was also limited in the favorable "deformation zone" by the dry air cutting off the flow of moisture wrapping backward into this zone.  For a very heavy snow event, you need a deep moist channel back into the cold air, and the deformation zone to replenish moisture falling as snow, otherwise, the snows fade with time.

As predicted, the track of the upper level storm was not an ideal one for big snows in the KC Metro with the low passing too close and the dry sinking air wrapping into the system (the “dry slot”) cutting off snows sharply to the city’s southeast. Snow was also limited in the favorable “deformation zone” by the dry air cutting off the flow of moisture wrapping backward into this zone. For a very heavy snow event, you need a deep moist channel back into the cold air, and the deformation zone to replenish moisture falling as snow, otherwise, the snows fade with time.

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:

Snowfall accumulation Kansas City area as prepared by NWS Kansas City MO.

Snowfall accumulation Kansas City area as prepared by NWS Kansas City MO.

Freezing Rain (Ice) accretion in SW Missouri as prepared by NWS Springfield MO.

Freezing Rain (Ice) accretion in SW Missouri as prepared by NWS Springfield MO.

Snowfall in central and SE Kansas as prepared by NWS Wichita KS.

Snowfall in central and SE Kansas as prepared by NWS Wichita KS.

Snowfall in north central and NE Kansas as prepared by NWS Topeka KS.

Snowfall in north central and NE Kansas as prepared by NWS Topeka KS.

Freezing rain (ice) in north central and NE Kansas as prepared by NWS Topeka KS.

Freezing rain (ice) in north central and NE Kansas as prepared by NWS Topeka KS.

Sleet in north central and NE Kansas as prepared by NWS Topeka KS.

Sleet in north central and NE Kansas as prepared by NWS Topeka KS.

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.

An Arctic front will bring dangerously low wind chills to areas well NW of Kansas City overnight as winds increase with the front's passage.  Wind chills to -10 can be expected in Kansas City Monday morning.

An Arctic front will bring dangerously low wind chills to areas well NW of Kansas City overnight as winds increase with the front’s passage. Wind chills to -10 can be expected in Kansas City Monday morning.

Lows tonight will fall into the singles below zero far NW to the mid 20s SE.

Monday morning lows.

Monday morning lows.

Much colder Christmas Eve morning with lows well below zero NW to the lower teens SE.

Tuesday morning lows.

Tuesday morning lows.

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.

A dry 7-day stretch is expected in the center of the country leading up to New Year's Eve with rains depicted here on the eastern seaboard and southeast over with by Christmas Eve.

A dry 7-day stretch is expected in the center of the country leading up to New Year’s Eve with rains depicted here on the eastern seaboard and southeast over with by Christmas Eve.

Quiet weather with no major storm systems is anticipated for Christmas Eve and Christmas Day.

Christmas Eve weather will feature some light snows in the Northern Plains & Northern Rockies and snow belts of the Northeast.  A few showers possible in south Florida.

Christmas Eve weather will feature some light snows in the Northern Plains & Northern Rockies and snow belts of the Northeast. A few showers possible in south Florida.

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!

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