03/21/06 DISC: NE/KS/IA/MO/IL/IN Snow

I've written up my thoughts in a sort of Post Mortem on this storm and posted them to my blog and will cross-post them here. I'm trying to do better at assessing my failed forecasts to learn from them rather than skip right on to the next event. I've focused all along on the impact this storm would have on the Kansas City area and surrounding communties and continue to in this post-analysis.

In most respects*, this was one blown forecast for this area. The much-anticipated spring snowstorm never materialized for the Kansas City region with only a dusting to two inches falling across the area. To the credit of forecasters across the region, this was a particularly difficult forecast from the start, with a strong low and models that were all over the place. The low was slated to undergo several transition periods, which it did in fact do, just not quite as forecast. Most notably, the surge of warm, dry air that intruded in the middle layers of the atmosphere during the daylight hours Monday was stronger and more pronounced than any of the models had anticipated, right up until the RUC picked up on it only about 3-6 hours out. This dry slot was beautifully visible in the 24-hour water vapor loop. By that time, the seeds for a bust had been sewn: the forecast was out there, the snow had shut off, and the damage had (or hadn’t, depending on how you look at it) been done.

Secondly, the movement – the speed and the track – of the upper level low through KS did not come to fruition as anticipated. In both aspects, the models were not far off, but off by just enough to matter. As others have mentioned in previous posts as this event was ongoing, in terms of speed, the upper level low stalled out in SW KS for about 6 hours midday Monday; a seemingly minor detail that was not anticipated by the GFS or NAM (even the RUC didn't grab ahold of this stall until the low started inching NE again!). The GFS was the first to hint at this stall in its morning run, but even then it late in the game. Hindsight shows that this slowdown, while only barely indicated by the GFS, was a detail that should have served as a hint of what was to come. In analyzing model run after model run, as I did with this system, I normally pride myself in having a good grasp on the trend, the run-to-run changes. But in this case, it is clear that this trend was not given its proper recognition. The trend was nothing new either: even going back 5-7 days when the storm system first came into the sights of the models, it was progged to be a Sunday/Monday event – a full 24-36 hours earlier than what would eventually verify. Not only did this slowdown displace a good deal of the moisture westward and northward, it also served to zap the dynamics, using up the lift in a dry atmosphere through the NE KS, NW MO area, thus further decreasing the significant snowfall potential for this area.

By the time the upper level low started moving again late in the afternoon Monday, it tracked slightly farther north than had been anticipated, placing the highest snowfall totals north of the KC area, in a swath from north-central KS through SC and EC Nebraska and even into Central IA. Widespread reports of 25â€+ were common through central NE, forcing the closure of hundreds of miles of I-80, not to mention the closures of schools, businesses, and the rest of the usual impacts a massive snowstorm of this scale will bring.

*: One aspect of this storm that verified relatively well was the QPF: Here in NE KS, a total of 1.13†of liquid equivalent fell between Sunday morning and Tuesday morning. As early as Thursday, significant precipitation was forecast, with a 1-1.5†QPF forecast several days out. While this isn’t the headline making news (in fact, this aspect has gotten virtually no media attention through Tuesday morning), it is certainly a headline with respect to the looming drought for this region. Additionally, as hinted at by the forecasts, some borderline-convective sleet showers did verify yesterday afternoon, dropping a 1-2 tenths of an inch of sleet at a time in a series of short, pronounced bursts each lasting 4-6 minutes. Over 0.4†of liquid equivalent was received in a relatively short window Monday afternoon (~2-5pm) which included several of these bursts.
 
Well, the storm has wound down over the High Plains and out here at my farm we achieved a foot and a half of snow, give or take two inches. Four to six foot drifts were not uncommon, and we were snowed in from Sunday night to around noon today, when the county finally sent out a roadgrader to clear the road we live on. Snow totals in the area were quite dramatic in difference within only a couple dozen miles. At Fort Morgan, 21 miles to the south of our farm, they only received 8 to 10 inches of snow, and 50 miles west in Greeley they only got 5 inches. The snowfall amounts seemed to rapidly increase north and east of I-76 here in northeastern CO, where the changeover to snow ocurred about three to five hours earlier, the heaviest snow trained over and the wraparound bands from the low lingered longer. This was definitely an Eastern Plains storm, as the Metro Area pretty much got screwed out of anything substantial. Oh well, they've had several storms this winter where they've had much better snow totals than us, so I suppose it wa finally our turn.
Our driveway was impassable;my dad had to use his tractor to clear it and the area in front of the house and the garage, it took him almost an hour late last night to do that. The sweetest thing that came as a result of this storm aside from the very much needed beneficial moisture is the fact we got TWO days off of school, because it took them most of the day today to clear the highways and county roads of the massive drifts. :D And our spring break is next week, so we only have three days of school and then a week off. It's pretty sweet. B)
A wonderful storm whose timing could not have been better; hopefully we will get several more significant snow/rainstorms in the coming weeks to further replenish the soil moisture sucked out by the seemingly unendingly windy, mostly snowless winter.
 
Thoughts concerning this particular event:

Sioux City, Iowa was on the northern fringe of this particular storm system. The total storm accumulation in Sioux City area ranged from an official measurement of 8.5" to unofficial measurements around the siouxland area of up to 12" of accumulating snow.

The first wave of this snowstorm moved through Sunday evening with total snow accumulations normally around 2". This wave of accumulating snow then shut down by monday morning, as dry air rotating around strong high pressure once again shut down the snow machine, though significant virga continued to show a threat.

At this time, a forecast discussion from FSD came through, stating thoughts that they were unsure that the moisture would win over the strong dry air that was consistently moving through the area. The snowfall accumulation forecast for Sioux City was for 1 to 2" overnight.

As another post has mentioned, this was prior to the stall out of the upper low. During the day, it was becoming obvious that more and more moisture was feeding farther north than predicted. Virga and moisture returns continued over the area but were still evaporated by continual dry air feed from the east and northeast. However, this was soon not to be.

At approximately 3:30, a significant banding began to set up in a west to east slightly curved pattern. The radar echoes rapidly intensified and the snow won the battle. At around 6:00 PM I believe, in an area in Dixon County, NE, radar echoes hit 40 dbz, and an observer said it was snowing so heavy it was difficult to see practically any difference. Heavy snow, reducing visibilities to 1/4 mile, was observed in Sioux City, Iowa.

The snow continued at moderate to heavy intensities and did not let up until 7:00 the next morning with the heaviest snows between 6:00 PM and midnight as part of the heavy banding. Of note, there was a very sharp cutoff to the heavy snow just north where the dry air won the battle big time.

Some observations.

The National Weather Service WFO in FSD maintained a Winter Weather Advisory for the counties of SE South Dakota and extreme NE Nebraska through the entire event, as did OAX for the northeast three tiers of counties. This is puzzling to me to say the least, since it was becoming obvious that this was winter storm warning criteria. Winds were in excess of 20 MPH in gusts causing noticable blowing and drifting. Snowfall accumulations were widespread between 8 inches and 12 inches over the entire advisory area. Schools were forced to close, and many workforces shut down early.

NWS Winter Weather Advisory definitions state that a winter weather advisory is issued for winter weather situations that may cause significant inconvenience and, if caution is not exercised, could lead to life threatening situations. Issued when events are occurring, imminent or highly likely to occur, and is issued when a combination of 5 inches or less of snow is expected. My questions are:

1. Why was it that when the National Weather Service doppler radar, satellite trends, surface observations, and models indicated a snowfall depth of greater than 5" of snow was imminent was the advisory not upgraded to a warning.

2. When actual observations began to show widespread winter storm warning criteria, that there was no winter storm warning issued for these counties. As a note, winter storm warnings remained for southern counties in that area.

3. Is this not a violation of NWS rules out of curiosity for failure to upgrade an advisory to a warning when the conditions verify?

4. Am I just missing something in the procedure that would cause them to maintain an advisory?

Continuing with storm analysis, the storm quickly lost energy in Siouxland area and skies cleared as much drier air again took over the area. The snow was a heavy and wet consistency, perfect for snowman and snowfort making for the many children who were home from school.

It was the most intense snowstorm for this area of the country this season, on the first day of Spring 2006.

(note: this was NOT an attempt to disregard or disrespect the NWS as they do a tremendous job in warning the public in inclement weather situations, this is an honest call for answers to a puzzling handling of the situation.)
 
The Linconln, IL NWS has a really nice Web page on the impact of this storm on Illinois, including a snowfall map and a really cool satellite pic showing the swath of snow across Illinois. The Web page is located at:

http://www.crh.noaa.gov/crnews/display_sto...d=1946&source=0

On the map, note the sharp gradient in snowfall accumulations, especially along the southern side of the storm as it moved across Illinois - goes, in one spot, from less than an inch to more than 9 inches in less than 50 miles.

Here in Edwardsville, we got about 2 and a half inches, but locations 30 miles north got 6-8 inches.

Here is a picture I took from our driveway:
IMG_2332smc.jpg
 
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