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Category: NAO
Permanent link to this article: https://indywx.com/2018/03/07/video-snowy-for-some-late-march-talk/
Nov 27
Warmth Dominates Now, But A Cold & Wintry Pattern Is Lurking For The Holidays…
The short-term weather pattern will continue to be dominated by rather “boring” conditions for this time of year, along with much milder than normal air. A weak frontal system will swing through here Thursday and while a light shower is possible, that’s really the only significant (if you want to call it that) weather feature through the upcoming 7-10 days.
In addition to the rather quiet weather, relative warmth will dominate as we open December. When “normals” feature lows in the upper 20s and highs in the lower 40s, actual overnight lows will only fall into the low-mid 30s and highs will reach the middle to upper 50s.
When we look ahead, the shelf life of this warmth is certainly limited. The GEFS showcases this shift in the pattern from a warm open to the month towards a much colder pattern very nicely. The GEFS has other model support, as well.
This is the type of dramatic shift in the overall pattern that not only threatens to “lock in” a colder than average regime, but potentially lead to plenty of wintry mischief to boot, and just in time for the holiday season.
There’s teleconnection support for the wintry shift, as well, leading to further confidence of a significant move towards cold, and potentially snowy/ icy, conditions as the true holiday and Christmas season approaches.
To summarize, while unseasonably quiet and mild conditions will rule in the short-term, Mother Nature sure seems to have an attitude of making up for “lost time” in the medium to longer range. This is the type pattern that we’ll have to monitor the potential of some sort of leader-follower scenario as the transition from warm to cold takes place, and given the blocky nature of the pattern, it sure seems like we’re heading into a busy time of things from a wintry perspective mid and late month.
Perhaps this will be the scene as Christmas time nears across the Mid West, including central Indiana? Time will tell…
Permanent link to this article: https://indywx.com/2017/11/27/warmth-dominates-now-but-a-cold-wintry-pattern-is-lurking-for-the-holidays/
Nov 09
“Block Ready To Rock?” Cold Pattern Developing Around Thanksgiving…
Model data continues to suggest a Greenland block will develop as we progress into late-November. This kind of pattern creates a “log jam” of sorts in the weather pattern and is the type pattern notorious for unseasonably cold regimes across our region. The overall agreement between various models raises our confidence in this pattern unfolding as Thanksgiving nears.
Such a pattern illustrated above, per the European ensemble (image 1) and the GFS ensemble (image 2), would help drill a tongue of unseasonably cold air through the northern Plains, into the Mid West, and across the East.
A look at the 00z teleconnections this morning shows 3/4 “big boy” drivers going to that cold look for late-November, as well:
We’ve been discussing early snow cover across Canada and the northern tier for weeks and how models would have to “correct” colder as they realize the air masses traveling over the snowpack won’t be able to modify as they normally would without that snowpack. The differences between this November and last are startling and show how the early snowpack is beginning to “feedback” on itself leading to early-season cold air.
2016 snowpack and temperatures anomalies through the first week of November:
2017 snowpack and temperatures anomalies through the first week of November:
Given the overall look to the pattern downstream, I anticipate the cold will continue to “press” and eventually overwhelm the pattern east as we progress through the second half of the month.
To close, we expect a developing Greenland Block to help drive an unseasonably cold late-November, including the Thanksgiving holiday. This is the type pattern that can also help generate early season wintry “fun and games,” however it’s far too early to be specific with any sorts of potential wintry events that may eventually come in this pattern. Stay tuned.
Permanent link to this article: https://indywx.com/2017/11/09/block-ready-to-rock-cold-pattern-developing-around-thanksgiving/
Dec 29
Shift Back To A Cold Pattern Awaits; What About Winter Storm Potential?
December-to-date is running colder than normal (to the tune of 2.2 degrees at IND), but the past (7) days has seen a flip in the frigid 1st half of the month.
December temperature anomalies, courtesy of Weatherbell.com.
Temperature anomalies the last 7 days. Courtesy of Weatherbell.com.
The “relaxation” is temporary. Modeling continues to advertise the recent “thaw” will give way to increasingly bitter times as we get deeper into the New Year. By New Year’s Day we note the positive heights continuing to establish themselves across Alaska and Greenland (cold and stormy signal). We also note the southeast ridge present, though to a lesser degree than over the past week.
By Day (10), the cold pattern is well established over the Lower 48. This is a coast-to-coast cold signal (heart of the cold centered over the west and central) depicted by the European ensemble, along with other modeling.
Teleconnections support a cold pattern returning.
The agreement amongst teleconnections is nice to see and ups confidence in the overall direction of where this pattern is heading in regards to colder than average times looming. The negative PNA correlates nicely with the SE ridge that continues to make itself heard from time to time over the next few weeks. It should also be noted that the phases of the Arctic Oscillation (AO) and North Atlantic Oscillation (NAO) become more of a factor for mid and late winter.
As far as storminess goes, we’ll have to handle those as they come. The overall pattern screams towards the idea of an active Ohio Valley to interior Northeast storm track as we move forward (continuing deeper into mid and late winter, as well). That doesn’t mean one or two storms won’t bypass our local region to the south, due to strong, cold high pressure north, but the mean storm track should put areas through the Ohio Valley in the “sweet spot” from a snow perspective throughout the majority of January, and the rest of winter, for that matter. Depending on the position and strength of the Greenland Block will have a lot to say about things. Needless to say, storms cutting NW into the central Lakes should be few and far between after the New Year. Speaking of storms, we have to continue to keep an eye on the second half of next week. At the time of this discussion, the threat is still beyond the 7-day period, but circle late next week and weekend for the potential of wintry “mischief.”
Permanent link to this article: https://indywx.com/2016/12/29/shift-back-to-a-cold-pattern-awaits-what-about-winter-storm-potential/
Nov 10
A Word (Or Two) On Where We Think This Pattern Is Going…
Before we get into the updated thinking on the pattern, lets review what we have out:
- Step-down process to cooler/ colder weather begins in mid-November.
- Thanksgiving-Christmas period, as a whole, turns wintry and is snowier than average.
- Our complete 2016-2017 Winter Outlook can be found here.
The first week of November has featured an incredibly warm start to the month. (Image courtesy of MRCC).
Speaking of warmth, 2016 has been a very warm year.
(The cold of 2014 seems so long ago…)
Back to present. We’ve targeted the middle part of November to finally beginning “bucking” the recent warm trend. This won’t happen overnight and will be a battle of back and forth, initially. Thus, the “step-down” label. To be clear, November, as a whole, will finish much warmer than average. It’s virtually impossible to counter the incredibly warm start. That said, we do anticipate “jabs” of colder air working in here over the next couple weeks. For instance, this weekend will feature lows in the 20s for most and highs not making it out of the 40s Saturday afternoon. (The average low and high at IND Saturday are 37 and 54).
Despite being in a weak La Nina, the pattern is taking a while to respond. Remember, we’re coming off one of the strongest El Ninos on record. Until we slow the PAC jet, significant, long-lasting, changes won’t occur. We can lean on the AAM (Atmospheric Angular Momentum) forecast for clues as to when this may occur. You can read more about the AAM here. My fellow local weather compadres, Michael Clark, Ed Valley, and Kirk Hinz have also written/ blogged extensively about the AAM and resulting impacts.
When we look at the AAM forecast (above), we note the westerlies may begin to slow (indicative of the negative values) in the 8-10 day period. This is crucial and, simply put, has to happen for the pattern to begin shifting into more of a position to allow sustained cold to enter the equation. We want to reiterate that this, in and of itself, doesn’t create the cold, but instead allows the pattern to begin shifting away from the Nino-like (warm) regime into more of a La Nina pattern, as a whole. – Hey, you have to start somewhere.
If we can finally get the westerlies to slow, other elements are in play that could (and should) lead to a colder pattern as we move forward. Our (3) big teleconnections are in a position favorable for cold for mid/ late November, into early Dec.
Additionally, the EPO is forecast negative off the GEFS and EPS. (Images courtesy of Weatherbell.com).
Again, this is a cold signal. (Image courtesy of Madusweather.com).
The ensemble data is also beginning to key-in on higher heights (blocking) developing over the top. Notice the significant changes in the overall look to the pattern between now and days 11-16. (Images courtesy of Weatherbell.com).
In summary, and in the face of *most* seasonal data that is screaming warm, warm, warm, we still don’t have any significant changes to our overall thinking of “step-down” mid-November giving way to more sustained wintry-like conditions in the overall sense from the Thanksgiving-Christmas period. Time will tell and only the Good Lord knows what the future holds, but we’ve done far too much work and research to throw the “game plan” in the trash before the game even begins…
Permanent link to this article: https://indywx.com/2016/11/10/a-word-or-two-on-where-we-think-this-pattern-is-going/
Jan 02
Overwhelming Evidence On Mid Month Cold…
The step-down cold pattern early January is ongoing, but we’ve been clear with our thinking of even colder air invading around mid month (Jan 10th-20th time period). We wanted to…
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Permanent link to this article: https://indywx.com/2016/01/02/overwhelming-evidence-on-mid-month-cold/
Dec 05
Warm Late Next Week; Active Times Loom For The 2nd Half Of December…
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Permanent link to this article: https://indywx.com/2015/12/05/warm-late-next-week-active-times-loom-for-the-2nd-half-of-december/
Dec 01
Welcome To Meteorological Winter…
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Permanent link to this article: https://indywx.com/2015/12/01/welcome-to-meteorological-winter/
Nov 28
Iron Bowl Saturday: December Rambles…
This is a special day in the McMillan house. Iron Bowl Saturday only comes around one day a year… Needless to say, the Auburn flags have been on the vehicles since Wednesday, we’re decked out in our orange and blue, and game faces are on for this evening’s matchup. WAR EAGLE!
As we get set to flip the calendar to December, we wanted to post some latest thinking.
Let’s take a look at the latest teleconnections. As we’ve been talking, there’s a lot of “noise” in model land, including conflicting signals. The positive NAO and AO argue for warmer than average conditions, while the positive PNA suggests chillier than normal times should prevail.
We wanted to post the latest model predictions of each teleconnections, courtesy of Weatherbell.com. Additionally, courtesy of madusweather.com, here’s what each teleconnection “phase” would normally lead to in December.
NAO
AO
PNA
Simply based on the teleconnections, you would build a December forecast that would lean more warm than cold, as the short term positive AO and NAO should trump the positive PNA. As we look at the month, as a whole, the AO and NAO are forecast to trend more neutral, while the PNA remains solidly positive. Does this suggest colder air, relative to normal, would invade mid and late month? – Certainly something to watch.
Additionally, the latest Southern Oscillation Index (SOI), has begun to take a negative hit. This is after weeks of positive SOI values- relative to the base state.
While it takes a while to impact the pattern, locally, this negative hit does suggest mid and late month could be a bit more interesting from a wintry perspective. We shall see.
The CFSv2 remains very consistent on a warm month, relative to normal, particularly across the northern tier.
While we can’t post the European weeklies here, the latest run suggests colder, and stormy times around Christmas week. Now, we should also note the overall performance of the Weeklies hasn’t been as accurate compared to normal over the past few months, but it’s another interesting trend to keep an eye on.
The MJO will begin the month in Phase 3 before going into the “wheel house.” All-in-all, we don’t get a “hat tip” from the expected monthly MJO forecast, with the exception of Phase 3 to begin (warm phase).
To sum up: Long range forecasting is always a gamble. Only the good Lord knows what the future holds. That said, there are times when we feel more confident about our long range, monthly outlooks, more so than normal.
We’ll lean warmer than normal for December (+ 1.5 at IND), and this really plays into our Winter Outlook (slow start expected with the emphasis on the cold and snow mid and late winter), but that doesn’t mean we’re expecting a “boring” month. Keep in mind November has been both warmer AND snowier than normal, with a very busy 2nd half of the month.
We’ll have plenty of challenges to handle as we rumble through the month no doubt, but we expect the positive AO and NAO to trump the positive PNA to start to the month. As we progress into mid and late month, we’ll have to be on alert for potential impacts of that significant SOI hit to open the month. We’ll also keep the Weeklies in check to see if the colder, stormy look Christmas week remains. It’ll be fun, as always.
To close, here’s one more emphatic WAR EAGLE from our home to yours! 🙂
Permanent link to this article: https://indywx.com/2015/11/28/iron-bowl-saturday-december-rambles/
Mar 04
Warm Up Coming…
After a long and cold winter, many are excited about hearing of the prospects of a warm up and first true taste of spring.
While the European data has totally bought in to the impressive “spring fling” next week, the GFS isn’t as excited of the potentially warmer times. Case in point, the GFS and European couldn’t be in more different camps for mid and late next week. Where the GFS has low/ mid 40s for highs the European has low/ mid 60s for highs. What’s 20 degrees amongst friends?!
Wild model swings and disagreements are common when pattern changes are taking place. While we might not get as warm as the Euro. would imply, it’s a safe bet we’ll be considerably warmer than the chilly GFS readings.
Note the AO and NAO strongly positive through the next 10-15 days. This is the time of the year when these teleconnections can impact our region’s weather in the most significant way. Both of these are warm signals taken at face value.
Note the pattern flip to a “flat” ridge by Day 10, indicative of the milder times ahead.
However, by Day 15 we notice the Alaskan ridge redeveloping. This is NOT a signal for warm weather across our part of the region, as the steering currents would tap available cold air and direct it south into the Mid West and Ohio Valley.
So, what do we take from this? We’re going to warm next week without question. While the extent of the warming is up for debate, the overall milder times for a 5-7 period is a good call at this point. On the flip side, we’re not ready to buy into the idea that spring is here for good just yet. The building Alaskan ridge by the end of Week 2 would imply a cold close to March, and potentially continuing into early April.
Another item to keep a close eye on the upcoming 4-6 weeks? Those NAO and AO signals. Should they remain predominately positive this time of year then it’ll be exceptionally challenging to get any sort of cold pattern to lock in for more than a day or two.
Permanent link to this article: https://indywx.com/2015/03/04/warm-up-coming/