Joe’s Weather Blog: Arctic Air Oozing Southwards

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It’s coming, slowly but surely. Yesterday Great Falls, MT dropped about 40°+ in 2 hours…from the 50s to the teens…pretty darn impressive ans since the Canadian snowcover has been increasing in coverage in a big kind of way these airmasses are getting colder and colder. Take a look at yesterday in Great Falls!

ScreenHunter_37 Nov. 20 08.18

That’s a pretty impressive drop.

I alluded to the increased snowcover up there especially. This snowcover is typical and this is one reason why these airmasses get colder and colder as the late fall goes on. The map below shows the extent of the snowcover.

As a matter of fact if you want to see a neat animation on the expanding snowcover…click here

So where is the arctic airmass now? It’s still up across the N Plains region…and really it’s just the beginning of the cold air.

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Now let’s go further to the NW into Canada where AM temperatures are sub-zero. That air will rush into the N Plains states tonight and then modify somewhat as it moves towards us tomorrow.

The temperatures are in RED…pretty cold air up there!

The latest NAM map is out and shows this forecast for tomorrow at Noon….the front will be moving through, but the initial push of the colder air is through the western Plains more so than towards the SE into KC…so the cold air will sort of ooze through here and result in slowly falling temperatures in the afternoon/evening tomorrow. Whereas out west the drop will be much more abrupt.

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By Friday @ 6AM the cold front will have plunged all the way down into Texas. Here is the forecast map off the NAM model. The temperatures are in the dashed RED lines.

We should drop down to about 20-25° by FRI AM. As this transition occurs tomorrow rain should redevelop and become a nuisance through the day and into tomorrow evening. You can see that by looking at the forecast maps for the next few days.

The blue shading shows the precipitation and for those not used to looking at these maps, for time-frame reference 00Z is 6PM/06Z is Midnight/12Z is 6AM and 18Z is Noon.

You can see the cold, dense air building in because our pressures go way up because of High pressure building southwards out of the Canadian Prairies over the weekend.

Now the question is what form the precipitation will take. For the daytime hours tomorrow we should have no issues with any wintry stuff. It will be all liquid rain, steadier during the morning and early afternoon hours I think. We should still be in the upper 30s later THU afternoon.

By 9PM temperatures will be getting closer to 32° at the surface. aloft however since this airmass coming in is shallow and NOT very thick, it will still be “relatively” mild. For example at 9PM THU it will still be around 45° at 5000-6000 feet. That warm air is important because IF there were any snowflakes further up they would melt. When I look at the profile of the atmosphere at that time (9PM) that won’t even be the case. We should still have some rain out there, and as temperatures approach freezing the chances of some ice pellets or some freezing rain starts to increase after 9PM THU moving from the northside into the southside.

The good news is that as this occurs the precip will be shutting down…so any freezing rain/drizzle/sleet would be light an brief. With the residual warm in the pavement at this point I think we’ll be OK in the KC area overnight Thursday. We’ll need to watch areas across NW MO and NE KS since they will be colder faster and depending on how this plays out, some bridges and overpasses will bear watching as well just in case.

By Friday morning a still saturated lower part of the atmosphere will still be present. Temperatures will be down into the 20s. There is the potential of addition very light freezing mist/sleet. This will need to be watched as well because as we know a little of this stuff can go a long ways to creating some issues. Whatever we get wouldn’t be a lot…but it MAY create some issues for AM rush on Friday. We’ll start drying out on FRI afternoon with highs around 32°

Here is the forecast for the “precip type” off the NAM model…it gives you a better idea what I was talking about…

Saturday and Sunday should be sunny and cold. Highs on SAT will be in the 30s and on Sunday we should be somewhere between 35-38°. Lows Sunday AM may drop to near 15° as the race of the coldest air is on as SW winds will start to develop sometime early SUN AM slowing the temperature drop. As I mentioned last weekend, it will be very chilly for the tailgaters on Sunday AM. As a matter of fact I’m very pleased with the forecast from last weekend for this week’s/weekend’s weather.

By the way, this is the beginning of what may well be a pretty long stretch of below average temperatures for the region. Take a look at the forecast for KC off the EURO for the next 10 days. Click on that image to make it larger and more readable.

ScreenHunter_38 Nov. 20 09.04

So it does look cold for awhile before we moderate later in the month (towards next weekend).

Finally a word of thanks to the great folks at Jowler Creek Winery in Platte City, MO. Last night we had our AMS/NWA (@KansasCityAMS on twitter) meeting there and it was a blast. Jason was wonderful and answered a ton of questions from weather enthusiasts and various other weather related professionals. He gave us the history of the winery and in particular he spoke on the weather aspects of what he does. IF you’re interested in joining the KC chapter send me an email and I’ll get you hooked up. Membership dues are $20/year and we have about 6-8 meetings/year at various places in the KC area.

2013-11-19 19.15.09

That’s it for today.

Joe

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