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What's Driving the Brief, But Substantial Cold Wave Late Weekend to Early Next Week?

Interesting data behind the cold....

Posted: Feb 3, 2021 12:36 PM
Updated: Feb 3, 2021 2:03 PM

Hello all, I am able to relax & get a nice blog post on, so I wanted to do so today. 

So what is driving this cold wave coming?  We have never had a winter that has failed to drop below 10, so it is inevitable that we will get colder.  Even the warmest winter on record in 1931-32 saw us drop below 0 & the incredibly mild 1997-98 winter saw 5 (but in March!).

However, why the sudden shift when everything looked warm & wet for a week in early February?

It looked like a cold wave with potential ice event to ice storm & even snow in mid-February with coldest of the year after warmth in the February 3-10 time frame.  Why now cold wave February 7-10?

It looks like the coldest weather since last February with single digit to low teens highs & lows below 0.

It is a bit of an oddity as we are looking at players on the court & not all of them add to cold.  Not all the players are driving cold.

All the players work in tandem to fight around the world & determine our pattern. A cold driver can drown out all the warm drivers if strong enough.  A warm driver can drive out all of the cold drivers.  Case in point, 2011 saw the most negative NAO & AO since the horrendous 1977 winter.  However, although 2010-11 was very snowy & pretty rough, it did not compare to the extreme, historic 1977 winter.  This showed me other drivers were at play.

As for early February......other drivers are at play. 

NOT DRIVING THE COLD:

1.  PNA looks slightly negative to neutral.  Postive PNA corresponds to cold outbreak in eastern U.S. with deep trough & clipper pattern.  So, this isn't a cold driver.

2.  NAO is not overly negative.  On the negative spectrum from 0 to -4 it my dip to near -1.  The more negative, typically the bigger the cold outbreak in the eastern U.S.  This isn't a big cold driver.

3.  AO has been negative since the end of November, so this is not a good measure right.  Typically that would mean cold pattern & it has been a mild winter.

4.  Neutral EPO.  There really isn't a huge Alaska ridge developing per sey that would equal a negative EPO.  Positive EPO means fast-moving Pacific jet with central & eastern U.S. bathed in warmer weather.  Negative means cold.  Not a huge cold driver.

5.  Positive QBO.  We've had a positive QBO since September.  It is +10 right now. Negative tends to correlate with more -NAO & -AO & more frequent cold outbreaks.  We should continue in positive QBO.  So, this does not equate to the cold burst either.

6. Neutral PDO.  It is around -0.65, which is nothing when we have been as low as -4 & as high as +3.5.  + corresponds to cold, snowy winter here & - corresponds to warm & dry winter pattern here.  Not a big cold driver.

7.  Strongly Phase 6 & 7.  This is a warmer, wetter pattern here in February.  This is a warm, wet driver.

8.  Sunspots are way up.  We are entering a more active solar cycle after the sun was asleep for several years (these times tend to correspond with colder weather & cold waves).

9.  La Nina.  Our traditional La Nina promotes dry ridging in southern half of the U.S. with colder weather in northern Plains, so it supports active storm track here, but given its strength it would tend to put us on the warmer side of systems.

SO I'M SCRATCHING MY HEAD...........IT DOESN'T MAKE SENSE. I'D STILL FORECAST WARMTH & WET BASED ON ALL THIS.......

AHHHHHHHH...........BUT..................there are two drivers out-doing all 7 of these.  If more of these drivers would just align strongly to cold side, we'd be in what we had in January 2019 with to -23 & up to -54 wind chill.

In fact, I found in doing research that has EXTREME as cold as in January 2019, if we would have had more snow pack (remember we had little to no snow pack over a large area), it would have equaled the great 1880s outbreaks of all-time record-breaking cold & the 1977, 1994 & 1985 greats.

Modeling it with a deep, deep snow pack would have made it some of the worst cold on record.

THE TWO DRIVERS OF THE COLD:

1.  Stratospheric Warming Episode.  We saw one big episode to equate to big late January cold wave (remember the chaos on social media about -25 here in January for an actual air temperature & the worst blizzard since 1978?............never dropped below 31 degrees in these winter weather events!), but it didn't happen because the other drivers out-weighed it........especially the EPO.  It strengthened the Polar Jet to such a degree to cut off the loose piece of Polar Vortex.

When it gets really warm in the Arctic (as the warmth in the stratosphere is tied to ozone concentration & UV interactions of the sun & the layer above the troposphere warms & that warmth is translating to the surface), the cold that is normally in that zone is displaced south.

It is a complex interaction in which the Polar Vortex has a piece weaken & break off, sending the cold south.  If it is a huge segment, then the cold will be worse & cover a much bigger area in the U.S.

This second warming has occurred without the other indices being strong enough to overcome it.  So, a piece will head south, but it is just a chunk & not the massive whole thing to bring historic cold here.

2.  Snow Cover.  This has been very important.  It has been just cold enough for snow & ice (temperatures near 32 for events), but not warm enough to melt it all (40). So, we have widespread deep snow pack that has developed from a series over storms from Kentucky to Minnesota.  The snow pack then extends to the Arctic.

This is a huge driver for cold.  It will not have a chance to moderate much. The dominoes fall when you lay down such a snow pack & the cold can race over that snow pack with a lack of sunshine or insolation effects.

SO WHAT IS NEXT?

Well, usually these Stratospheric Warmings of this degree support a period of 30-60 days of more dominant cold weather.  HOWEVER, there are too many other drivers at play to outweigh its effects.

So, thoughts are that we get the cold wave with new snow late weekend early next week, then it moderates. There are continued hints of BIG WARM-UP with rain & t'storms following this

(sort of what happened in February 2014 when we had sudden ice jams & a 61-degree day with EF0 tornado in Montgomery County that damaged a gas station & some farm outbuildings with still patches of snow left on the ground!)

This is all do to the significant warm & wet phase MJO out-doing the Polar Vortex pieces.

Then it still appears a cold wave may impact the area for several days at some point in mid-February.  It is unclear whether it will be a potent as the one coming late weekend to early next week, however.

HOWEVER............If the loosening lasts longer & the other indices go weaker, then the cold may last for the ENTIRE first half of February.

On a side note, I modeled & analogged our current snow cover with a vortex event like 2017, 2014, 1996, 1985, 1978, 1977 & they all had record cold.  So, we still have other players bufferring the event to make it more tame & brief.

With likelihood of most indices aligning warm at the end of February to early March, I went much warmer then.

We will continue to monitor closely.  All eyes will be on the Polar Vortex & the other indices to see who is out-done.

SUMMARY

So, ozone concentrations in the stratosphere & snow pack appear to be the overwhelming cold drivers to bring us the coldest weather of 2021 ahead.

Today:  Sunshine   37/27

Thu.  Light mix to rain to snow   40/20

Fri.  Pt. cloudy, windy   26/10

Sat.  Inc. clouds, late snow   25/7

Sun.  Sct'd snow, windy   10/-1

Mon.  Snow possible  18/11

Tue. Snow possible AM  25/6

Wed.  Spotty snow  18/-2

Thu.  Pt. cldy  15/-5

Fri.  Pt. cldy & windy  34/25

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Warmest weather since December is ahead with good timing with the weekend rainfall...
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