Weekly Outlook: Several strong cold outbreaks


COLD will be the theme of the week across both the eastern and western districts this week and that has already started today with an Arctic front pushing through the area.  Our weather event impact index is “high” for both the confidence in the cold and the impacts it will have.  Remember that a “high” rating in both categories means take action and in this case, that action means preparing for very cold weather.

2015-01-05-0812-THREAT MATRIX_COLD

Here are some reminders for dealing with the cold weather.  We’re not currently expecting lows to rival last January and last winter’s lowest temperatures when lows dropped to -8 in STL and -11 in KC because we don’t have a thick snowpack on the ground, but temperatures within a few degrees either side of zero are expected at least twice this week.  These readings are still 15-20 degrees below the average lows for this part of the winter.


We’re entering the “heart of winter” next week when average lows and highs are at their lowest point of the year.  Those averages start to climb toward Spring on January 26th, although it’s a slow climb at first.

The overall weather highlights for the central U.S. this week are outlined below,  with accumulating snows tied to a clipper passing Mon/Tues to the north with accumulating snows from SD to northeast IL including Chicago.  This will be a light powdery 6″+ snow with blowing and drifting possible.  Lake effect snows will return to the Great Lakes snowbelts, but outside of that, the only story will be the cold from the Front Range to the eastern U.S. There is no threat for any major snow events across either the eastern district or the western district at this time, in fact, we should not see much in the way of anything but a few flurries. The next chance for any precipitation arrives next weekend with a weak system (if it materializes) and that does not look like a major storm at this point.


The first cold wave reaches it’s peak overnight and Monday when a pair of 1043 MB Arctic highs settle in.  The chart below shows the 6AM temperature (close to lows) difference from average, NOT the actual temperature. The worst of the cold (temps nearly 40 degrees below average) will be up over Iowa in deeper snow cover.  Locally temperatures 13 to 18 degrees below average are expected (by the model) and that puts morning lows in the single numbers west and low to mid teens east (where average lows are warmer). The model might be just a bit on the cold side.  Winds will remain noticeable tonight and early Monday morning so wind chill values will be an issue and those WILL be below zero..bundle up and give yourself extra time to defrost/warm the car.


The pattern driving this week’s chill can be found at the mid levels of the atmosphere.  A ridge of high pressure and warm air aloft extends from Alaska south and just off the west coast of the U.S.  An upper low and cold pool aloft is centered near Hudson’s Bay. Between the two we have a cross polar flow allowing Arctic air to be directed south into Canada and the central U.S.



This type of upper air pattern leads to repeated generation of Arctic highs.  The stronger mid-week Arctic high is shown here building down into the Dakotas on Wednesday morning.  The next upstream high is seen already on the north coast of Alaska, but that high is expected to weaken somewhat before arriving next weekend (at least as currently forecast by the models).


The mid/late week peak cold..how cold we get will be determined by 1) Clear skies 2) Light winds 3) Dry air and 4) Snowpack.   We’ll likely have 1 and 3 going for us.  Snowpack (4) is little to none, so we can scratch that one off as a major contributing factor. Winds (2) will depend upon exactly where the center of the high is located on Thursday morning.  Right now, the models are putting the high over SEMO/W KY at 6AM.  That would not time out for the coldest night possible as it would bring winds back around the southwest by late in the night. Any wind would be able to mix warmer air down from above and cause a boost of a few degrees temperature wise.  If this stands…we can expect lows to occur between 9PM-3AM with rising temperatures by sunrise. It still will be VERY cold though and ANY wind would cause wind chill issues.  We’ll have to see how this plays out this week and we’ll have a better idea on how things will time out.

Looking forward, it might be one of those weeks that we don’t see freezing… These GFS high resolution charts show the dip early week, some recovery and then the much colder dip mid week.  Don’t get overly worried about the big dip to well below zero late in the chart a week from Tuesday.  That would depend on the snow which the model forecasts next weekend, which may be a phantom storm (there have been a lot of those these past few weeks) and the other model (not shown here) shows no significant snow and a bit of a thaw developing in that same timeframe.




The overall theme for the week will be the cold!


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