Thursday, October 23, 2014

Outlook for the fall and winter - 10/23/14

This will be long, because I'm going to explain a lot of things.  If you want to cut to the chase (not recommended because I want to explain some reasoning), then scroll right to the bottom.

If you go to the internet and Google "winter weather 2014-15" you will get dozens and dozens of outlooks for this coming winter.  Are any correct?  Possibly, but there are so many opinions out there, some not even based on science.   I WON'T post the fictitious map that came out about a month ago that was released by a satirical web site and unbelievably was shared millions of times on social networks as if it was a "real" outlook.  There were even decision makers ready to jump on it - which is very scary in my opinion.

By the way, you can click on any image in this post for a larger version.

I chuckle at the Farmer's Almanac outlook on the left.  It's going to be frosty at Brownsville, Texas?  Apparently in this large block of states (NM, TX, OK, AR, LA) the weather will be the same?  I guess if one spot verifies, they all verify.  They claim 90 percent accuracy over the years.


I'm going to go ahead and offer the "official" winter outlook produced and posted by the fine folks at the Climate Prediction Center.  If you want to take the time and read their reasoning, then click here.  I don't necessarily agree with their assessment as they tend to go with persistence and composite analogs, that rarely verify.

CPC's precipitation outlook for the winter
(December, January, February)

CPC's  temperature outlook for the winter
(December, January, February)

NOTE:  On the CPC maps above, the "equal chances" DOES NOT imply normal conditions!  It simply means the forecasters did not have enough confidence to state an outcome.  Probabilities greater than 33% indicates the direction they (forecasters) were leaning.  Example, the >40% in the warmer shaded area is leaning towards above normal temperatures. 

A little background on extended outlooks

For the High Plains of Kansas the climate is characterized by highly variable conditions, both in short and long time periods. The proximity to the Rocky Mountains and the Gulf of Mexico moisture source are just two of the reasons for such variability.  But it is much more complicated than that. There are numerous intra-seasonal, multi-seasonal, multi-year, multi-decade and even multi-century ocean/atmosphere cycles that have influences on our weather.

Interactions with land masses, oceans and the sun are what drives our weather. Understanding these interactions can help (or hurt) long range forecasts.  Because of millions and millions of interactions across the globe and the fluctuation of the suns energy, forecasts beyond just a few days can suffer in accuracy.  So, ANY seasonal outlook can be WAY off!  The following are just a few of the tele-connection cycles and oscillations that impact our weather (and feel free to Google these for an explanation of each):

The Madden Julian Oscillation (MJO)
Global Wind Oscillation (GWO)
El Niño/La Niña - Southern Oscillation (ENSO)
North Atlantic Oscillation (NAO)
Arctic Oscillation (AO)
Pacific Decadal Oscillation (PDO)
Atlantic Multdecadal Oscillation (AMO)
Solar cycles (this could be a HUGE player in the next couple of decades)

A friend of mine from back in my college days at the University of Oklahoma (BOOMER) and I had many, many discussions about the weather and apparent cycling of weather patterns.  He was originally from southern California where it hardly EVER rained and just the sight of a cloud got him excited about weather. Through observations, it became apparent that even though weather systems moving around the globe were mostly transitory and often chaotic, there was a subtle observation that weather patterns would repeat throughout the year.   In other words, the jet stream would show very similar behaviors on a specific time scale.  This cycle length appeared to vary from year to the next. 

The cycling pattern

It is complicated and I'm not going to try and convince anyone that this cycling pattern does exist during the year.  During the northern hemisphere Fall the jet stream (band of westerly winds aloft) will increase in velocity and traverse from a higher to lower latitude or vice versa.  The jet stream winds occasionally amplify into a north/south fashion which is an unstable position for this wind energy to be in.  At some point the jet stream will "snap" back into place (west to east) and starts a sinusoidal rhythm.   Once this first rhythm begins, it will eventually repeat and then continues to do so until the velocity of the wind decreases during the late northern hemispheric summer months. This cycling pattern of the winds aloft and the behavior is similar from one cycle to the next.  The cycle length can vary considerably from one year to the next though (on the order of 25 to 60 days).  Last year (fall of 2013 though the late summer of 2014) the length was about 57 days, give or take (it's not always exact). 

The  tele-connection cycles and oscillations (MJO, GWO, ENSO, NAO, AO, PDO, AMO) that I mentioned above can enhance or even work against this cycling pattern.  In my opinion, some of these may also help to get the pattern started.  Again, it's complicated.

So, the trick is trying to figure out the cycle length and how these other  tele-connection cycles and oscillations will impact the flow above us.  Unfortunately, this cycle length cannot be computed until the first cycle is completed and starts to repeat.   If it's a long cycle, it may not be until late November before I know.  Ugh.

At this point in time, I can only offer a look into some of the indices or background forcing that may be a contributor in the pattern.

The Arctic Oscillation changes quite a bit during the year.  The chart below is just a forecast from long range computer models and is not the gospel truth.  However, the outlook has been consistent in that the index is forecast to be negative through much of January.  A negative phase of the AO (indices below zero) would support Arctic air intrusions into the U.S.

The North Atlantic Oscillation is forecast (again by long range models that may not be entirely accurate) to be near normal to slightly below.  A negative phase of the NAO (indices below zero) indicates a "blocking" Atlantic pattern which would favor systems slowing down and maybe hanging around a bit longer than normal.

The upshot of the two above (AO and NAO) is that IF the guidance is close to being correct, there could be the potential for several Arctic intrusions that would last more than a few days.

The Madden Julian Oscillation (MJO) has not been robust yet, but could be a player in the weather later this winter.  Again, you can Google any of these indices to get a better understanding.  The MJO is a 30 to 45 day pattern oscillation that originates in the western Pacific near the Indian Ocean or Maritime Continents.

There has been much talk about an El Nino developing this fall and winter and some talk of it being exceedingly strong.  A strong El Nino would definitely impact southern California and east across the southern tier states.  I think this is a basis for the CPC forecast.  However, an El Nino has NOT formed yet and is struggling to get going.  Everyone should root for one as this would help alleviate the extremely bad drought that is on-going across California.  The chart below shows the Southern Oscillation Index (SOI) which is a measure of the pressure differences between Tahiti and Darwin, Australia.  A significantly negative value for an extended period indicates El Nino conditions.  

Looking at the Sea Surface Temperature anomalies, the waters across the equatorial Pacific Ocean are slowly warming.

Perhaps more importantly is the above normal temperatures across the north Pacific, tied to the Pacific Decadal Oscillation.   That might be a big player this year if it helps pump up the jet stream into the Arctic or higher latitudes. It will be something to watch.  Also, the temperature profile across the Pacific basis is favorable for the sub-tropical jet stream (winds across the lower latitudes) to become a play maker this winter.  That would provide tropical moisture into the U.S. and help lower surface pressures across the southern plains.  Upshot of this would be an increased chance for above normal precipitation there.  We've already seen a significant occurrence of systems moving into the southwest U.S. since late summer and it'll be interesting to see if that trend continues.

Finally, the Outlook

First I want to show you some solutions from one of the long range forecast models.  Agreed, it is not terribly accurate but when a trend is established there is some useful information that can be gleaned from the models output.  This computer outlook is run 4 times a day, every 6 hours.  From one run to the next there can be big differences, so don't get caught up on the details.  But, what it does show is a significant cooling trend going through November and into early December.  The program that generates this output uses slightly different initial conditions to generate various solutions every time it runs.  This is called an ensemble.   Two runs below that were generated 1 day apart....

The most notable thing is the HUGE range of possibilities!    Even the red line (ensemble mean filtered for intraseasonal conditions) changes from one  run to the next.  But I've been watching this for a while and the trend has definitely been for a colder solution.

I think the big players early on will be an unusually strong extension of the East Asian Jet, a developing sub-tropical jet and the position of semi-permanent low pressure areas over the north Pacific and near Hudson Bay.  I'll be watching carefully to see how these features shift during the next 30 to 60 days.

I feel pretty confident that the balance of October will have normal to above normal temperatures. No widespread freeze is expected!  However, once  we get into November I expect there to be changes.  I would surmise that the first widespread growing season ending freeze will occur that first week of November.  The balance of November will likely be much colder with below normal temperatures on the average.  There should be several opportunities for precipitation (snow too) so that the month should see normal to above normal precipitation.

Getting into December there should be wild swings with Arctic air outbreaks but evened out by dry and "mild" periods.   By the first of December I should have a pretty good feel for the cycle that should be established so I will likely be updating this outlook periodically.

Beyond December and into the spring the only thing I can offer is that I would highly suspect that there will be several high impact winter storms across the high plains, maybe a few more than usual.  A March blizzard seems to be a real possibility this year (greater than climatological chance).

Even though precipitation may be near to above normal across are area, that does not mean snowfall will be above normal.  The reasoning is that some of the storms this year will likely produce freezing rain (or even rain) without producing much snow.   Also keep in mind that EVEN if this map below was close to being correct, not every location in the shaded areas will have the predicted outcome due the variability with individual storms/systems.

Monday, October 20, 2014

Update - 10/20/14

In the previous post (click here) I mentioned the quiet period that was expected.  Other than a few showers this past Saturday moving out of eastern New Mexico, it has been uneventful since the middle part of last week.

 I also had mentioned about a small chance for precipitation early this week.  That system is there (over southwest New Mexico Monday afternoon) and it will provide a chance for rain by late Wednesday through Thursday across the plains.

The satellite image below shows several features.  One such feature is the weakening tropical storm moving by Hawaii.   Former Hurricane Ana was moving northwest and poised to get caught up in the westerly flow which will take the remnants into the Pacific Northwest.  The green line you can see from left to right is an anomalously strong East Asian Jet stream that was transporting several storms towards the Pacific Northwest.  Those features will deposit copious amounts of precipitation from northern California to Washington.  Good news for them, but for the high plains there won't be much impact.

The chance for rain that I mentioned above will come from the weak system (denoted by the red X on the image above) that was over southwest New Mexico.  It will move slowly towards the central plains and will bring a chance for scattered showers and thunderstorms, centered on late Wednesday/early Thursday.  The Weather Predication Center offers the map below, which shows the potential rainfall for our area.  Not expecting heavy rains, but at least some rain.  (BTW, look at the amounts for the Pacific Northwest)!

Back to the satellite map above.  Do you see the blue line with arrows?  That is an extension of the polar jet stream.  That is really the first signs of winter and this jet stream is helping to deliver some near blizzard conditions to the north slopes of Alaska with temperatures expected to drop into the single digits.  We won't see any of that in the states for a while, but it is a start for that a general area (albeit a little late).

Speaking of cold weather, there is no sign of a widespread killing freeze across the high plains anytime soon, at least through the end of this month.  However I'm a little cautious in saying that as the aforementioned East Asian Jet is well extended and strong.  A little buckling could deliver Arctic air into the states within a week to 10 days (IF THERE WAS BUCKLING).  Something to keep an eye on.

Finally, my outlook for the remainder of the fall, winter and spring will be posted sometime Wednesday or Thursday.

As always, remember these are my thoughts only and not an official discussion.

Wednesday, October 15, 2014

A quiet period? Update 10/15/14

In the last two posts I discussed a widespread precipitation event that was about to impact the high plains region.  There were two rains, one late on the 9th (Thursday night) and the other  late Sunday into Monday.  Also, if you go back to the post I did on the 30th of September I was discussing an active period from October 11-17 and that did come to pass but just a little sooner.  The second system that occurred late this past weekend brought very active weather to the eastern half of Kansas and then subsequently across most of the eastern half of the United States this week.  There were killer tornadoes, big hail, high winds and flooding rains in parts of the country, including Arkansas and Missouri.  Across the high plains the precipitation was much lighter as the system did not get organized until after it was passing through (but was in the process of rapidly developing).  The only element that did not occur was a widespread killing freeze.  It did get chilly with some freezes across the plains, but nothing widespread.  I will blog later next week on my thoughts for the late fall/winter/spring outlook and when we can expect the widespread "growing season" ending freeze. These two systems that just impacted the central U.S. "may" be a clue that I'm looking in to for later this year.  More on this later...

The following map shows the amounts of rain that fell this past 7 days, centered on Kansas.  There were very excessive rains in southeast Kansas with almost 10 inches observed!  Most of the region south of Interstate 70 received generous amounts.

On the following satellite image, there really isn't much going on across the central part of the country.  The big L southeast of Chicago is the remants of the system that moved through Kansas/Oklahoma late Sunday and Monday.  It hasn't made much progress.  Then there is Hurricane Gonzalo which is projected to come very close to Bermuda.  By the time it reaches that island the storm may be very intense and if the Bermuda takes a direct hit there will be catastrophic results.

Otherwise, there is not much to discuss on this map.

Our next opportunity for any moisture across the high plains will be perhaps as early as early next week.  But, the prospect looks slim at this time.  Also, it does not appear to be a major precipitation event, even IF it does occur.   I'll take a closer look at that chance in the next couple of days.  As I mentioned early in this post, I'll get out an extended outlook next week which will discuss what is in store into the spring.

Thursday, October 9, 2014

Quick update - 10/09/14

See the previous post here.

The atmosphere is coming together to produce widespread measurable precipitation!  The only change to the earlier thinking is that just about all locations will receive rain from this several rounds that will move across the area tonight and Friday (and some areas into Friday night).  A lot of the area will receive very generous rain of  3/4 to 1 1/2 inches!  A few locations will receive less, and a few locations will receive more but on average this should be a pretty wet system.

One of the high resolution forecast models has a quite a bit of rain through early Friday morning with additional rain/thunder expected during the day Friday.  Don't take the numbers literally, but in general there should be some decent amounts!

Tuesday, October 7, 2014

Update 10/7/14

The past week has seen a continued transition into a typical fall pattern across North America, including tropical activity across the Pacific Ocean basin.  As of this afternoon there are two areas that will help impact the western High Plains.  The first area is along the Gulf of California coast where Tropical Storm Simon resides.  The second area includes a super typhoon and other typhoons that will ultimately bring a change in a week to 10 days.  I might add that there are two other deep troughs (denoted by the L's on the map below) that will contribute to forecaster uncertainty during the next 7 to 10 days as the pattern gets "messy" and active.

First Simon....although not as strong as former Odile was, this system has the potential to bring widespread precipitation to much of the central U.S.   As of Tuesday afternoon the weakening system was headed north towards the northern reaches of the Gulf of California.

Now, you might remember that Odile did not deliver much to our local area.  Instead, it brought extremely large amounts of rainfall to southern New Mexico and west Texas (and parts of central Texas).  The remnants of Simon appear to be headed in a path that was initially similar to Odile.  See the earlier posts here and here.

Will Simon progress the same as Odile?  There are subtle differences in the flow regime and chances are a little better, at least as it currently appears, that the remnants of Simon might be a little more kind to our area in terms of producing rain.  This is NOT to say that there will be extremely heavy rains, but at least there should be some rain.  How much?  The Weather Prediction Center (WPC) branch of the National Weather Service offers the following solution:

If this solution comes to pass there will be heavy rainfall across Oklahoma, eastern Kansas and into the mid Mississippi valley.  Across much of the western high plains amounts could be generous too but not excessive.  I think that there will be rain, especially Thursday night and Friday, but unfortunately there may still be a few locations that "miss out".  I hope those that miss out have already had some of the rain that fell during the past 1 to 2 weeks. 

During the past 7 days most of the rain fell across the Missouri valley. There was at least some rain locally with the heaviest down near the Oklahoma border south of Ashland where one observer had over 3 inches.

Beyond the system this week, it could get interesting (if not confusing for forecasters) sometime next week.  The aforementioned typhoons across the western Pacific will likely cause a significant amplification in the jet stream coming into the U.S.  It's impossible to say what the impacts might be especially since it is unknown exactly where that amplification will occur.  Later in the fall and winter it will become more obvious but since the cold season pattern is just setting up, I just don't have much faith in where.  Point here is to stay tuned.  I'll try and update again towards the end of the week.  On the table is more precipitation and perhaps the first widespread freeze of the fall (there have been localized areas that have froze already).