Joe’s Weather Blog: Winter cold is coming (WED-11/29)

Well at least you’re going to know about this cold shot off air…and I’ve been telling you this now for the last few days and as we get closer and closer to what will turn into a roughly 10-20 day shot of colder than average days and nights…you’ll know it’s coming. Last year it waited till mid December to hit hard…as low as -9° at KCI with many outlying areas closer to -15°…but that was the worst of winter last season at least. we also had a couple of fresh inches of snow on the ground as well aiding that tanking. This time through…odds favor little snow at all the transition to cold…but there is no doubt that the Arctic is going to be open for business and dropping frigid air southwards into mid December.



Forecast:

Today: Lots of clouds today with perhaps a few breaks this afternoon. Temperatures are sort of dicey today but let’s shoot for highs around 50° with some upside depending on the sunshine. There may be a few sprinkles south of KC this morning and a few more out there this evening as well.

Tonight: Clearing out later tonight into Thursday AM and chilly with lows dropping into the 30s

Thursday: Sunny and pleasant for the last day of November with highs into the 50s

Friday: Nice as well to kick off the new month…highs well into the 50s



Discussion:

Well the change IS coming…it’ll be here within a week or so. Between now and then…every day will feature highs above average…in some cases well above average (SUN and perhaps MON) but it will start to chanbge MON>TUE as a strong cold front comes through…this will usher in a prolonged change in the jet stream as I’ll illustrate for you in the blog today. Of note are several other things…1) a lack of snow in the US so far late this month and 2) checking on the comparison of the incoming air masses next week…and the nasty cold air mass that we dealt with for a few days LAST DEC.

Before I get to all that though…I had a wild gumption last night when I realized that yesterday marked the 6th straight day with highs 60° or above…for so late in the year…I thought “hmmm has that happened before”?

Well yes it had…but it’s not exactly common. again the key is that this happened so late in the year…so I tried to do some fast research and eye-balled 1000s of high temperatures in late November and December to look for these consectutive streaks. I sent out the information in a series of two tweets…

The stretch in 1998 was 9 days…this one was 6 days…but still it doesn’t happen all that often…only 5 times total of 6+ days this late in November into December.

So on that warm note…let’s talk about more warmth…over the next few days…once we get passsed this system passing to the south of the area today…and we start seeing more of a southerly wind flow…temperatures will be going up…we should be in the 60s on Sunday…and depending on the timing of the front…we may be in the 60s on Monday too…BUT a cold front will change things for quite some time…the timing on that front looks to be sometime on Monday.

Hopefully we’ll get some moisture from the front…because the long term precip chances don’t look too great. It’s getting pretty dry out there and in the last 5 weeks we’ve only had about 1/4″ of moisture…so we’ll need something decent on Monday before the ground starts to freeze up with the (more or less) prolonged cold heading this way through mid-month.

So what is creating this change? Actually it’s multiple triggers…each sort of related to each other and acting in concert to dump out the soon to be building cold air across the Arctic region.

  • 1) A storm in the Gulf Of Alaska…you can sort of see it by looking the latest satellite picture…

That storm will move into the Pacific NW over the weekend…through the northern Rockies on Sunday and into the upper Plains on Monday. Attached to the storm will be a seasonably strong cold front which will sweep through the region sometime on Monday…that front will usher in the step-down process of us getting colder and colder (mostly). Ahead of the front…we’ll really warm up on Sunday (tempered by lots of high clouds)…then when the front comes through…we’ll drop.

  • 2) This storm will set off a dumping of cold air behind the system…as we go up to about 5,000 feet on Tuesday (the 5th) you can see the temperature anomalies (at that level)…

via Pivotal Weather

That will be air that’s colder (and even below average) but in the scheme of things not terribly unusual for December. Highs on Tuesday should be in the 30s to near 40° but with the wind it’ll “feel” colder.

  • 3) From there we start paying attention to what’s happening above the surface…and we’re going to go up to about 18,000 feet…this is halfway up through the atmosphere and we look for a variety of features at that level of the atmosphere…and for the purpose of this discussion we’re looking for “dips” or “troughs” in the jet stream, which signify lower pressure and “ridges” which signify higher pressure. Take a look at this chart for next Monday evening.

There is a lot going on…the main features are what’s happening off the west coast of the US and what’s happening towards Greenland. Those are ridges which are poking farther and farther north with time…as that happens a rather significant chunk of the polar vortex will be splitting into two pieces. One piece will be migrating towards Asia and another will be dropping southwards…and that will be the key to our longer term cold weather.

Then as we finish the next work week…this is what the same map above looks like NEXT Friday…note the changes…

The ridge on the west coast has poked up towards the North Pole…the ridge near Greenland is poking towards the North Pole…and a big chunk of the Polar Vortex is dropping southwards through Hudson Bay in Canada. This is what we refer to as “cross polar flow” and it gets VERY cold around these parts.

Now let’s go farther down in the atmosphere and show you what’s happening at around 5,000 feet and show how the air (at that level) differs from “average” and remember that shows the anomalies in °C…so you have to double that for °F (apprx) and that’s several thousand feet up.

Note, that compared to average it’s really “warm” (relative for Canada) from the western US up through Alaska towards the North Pole…through Greenland and into the northern Atlantic Ocean region. This FORCES the cold from up there southwards into the US. This will be a Plains eastwards cold outbreak and this is also something that has a tendency to hang around for quite some time. With the flow noted above, every time a wave comes southwards or SSEwards, it drags colder air down with it…and that’s how you stay mostly cold for an extended amount of time.

So how cold? Well in a process over the course of several days I see a path where lows are in the single digits and highs are only in the 20s>30° range for a day or two later next week. So basically 15-25° below average. In a weird way for just as warm Sunday or Monday will be…15-25° above average…later next week may be the exact reversal of that.

Clouds are a wild card for the low temperature potential in this…we’ll deal with that later next week.

Our feature photo comes from Bobbi Jones Burkett‎ from NW of Leavenworth of a pretty sunset a few days ago!

I’ll probably take a blog day off or two…so have a great rest of the week.

Joe

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