Saturday, 6 September 2014

Spetember 9-11th Severe Weather Potential

Hello everyone and welcome back to the Severe Weather Centre. I've been keeping a close eye on the models lately and have been quite impressed with some of the severe weather parameters for this upcoming Wednesday across MI,IN, IL, OH and S On. Subtropical moisture will get drawn from Norbert's circulation off the West coast of Mexico in addition to an upper level low which is expected to spin off the B.C coast for several days. Note the two features on the latest run of the GFS(18z initialization).

By Monday evening this upper level low will come inland, crossing the Northern California coast and taking a track through the rockies and up towards Lake Superior. This will try to partially phase with an area of vorticity currently located across Nunavut, which will cause anomalous deepening of the low pressure area for this early in the fall. The euro goes as deep as a 982mb low centre near Sault St Marie Wednesday night while the GFS/CMC are a little faster and weaker with the SLP centre, albeit still very impressive.

18z GFS

12z Euro

 This deep low pressure area creates a very impressive kinematic environment with a 45-55kts LLJ across parts of MI, IN and NW OH. This jet strengthens even further after sundown with a 60-65kts jet max across S On late wednesday evening.

GfS model 850mb wind field valid 6z Thursday 

Really impressive low level speed/directional wind shear in a sounding near guelph, On. Notice the strong clockwise turning, small T/td spreads and extreme water loading/saturation.
 The sounding lacks instability and steep mid level lapse rates, however.

 These winds will be accompanied by a 90kts upper level jet streak nosing SE with strongly backed sfc flow out ahead of the front. PWAT values are in access of 2" across a widespread area.
GRR had this to say in this afternoon's discussion. Very interesting.


CAPE's do appear to be lacking on most of the models, with a general 500-1000j/kg on most modelling across IN/IL with little to no CAPE further NE. This, along with timing are going to be huge players for S On as a faster vort ejection will increase the chances of a more significant outbreak although super cells will likely continue well after sundown as the low level wind fields continue to intensify. Keep in mind, the models due tend to underestimate WAA at this range so a trend upwards in the instability department is likely as we edge closer to the event. Right now, I'm in agreement with the SPC outlook in terms of the areas likely to be effected. If modelling continues showing the dynamic's it has been showing, a dangerous situation is possible for S On from Windsor through the GTA, including much of SW Ontario. On the other side of the border Michigan, NW Ohio and Indiana are at risk of severe weather. Primary threats appear to be high precip super cells with strong winds, flooding potential and possible tornadoes. I'll keep you posted on twitter in the days ahead!

Monday, 18 August 2014

Preliminary Winter 2014-15 Ramblings

I did some analog searching yesterday and found out some interesting trends and observations for this winter. As a base state I searched for years since 1950 that contained weak-moderate el nino's, easterly QBO shear at 30mb and 50mb heading towards a negative peak late in the winter (FMA period). A strong NE pac warm pool in the fall was the third piece of criteria I looked for giving an H5 pattern like so (note this is not my analog set for this winter, I am just playing around).

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What I realized is that there are two main group's with 86-87 and 91-92 extremely warm over the CONUS and the three remaining yrs having your typical evolution with a -EPO and strong NE pac high with a '13-'14 like downstream response. I still need to do further research regarding 86-87/91-92 but from what i've gathered so far the warmth of 91-92 was a result of the extremely high sun spot activity and weak siberian high in October. 86-87 may have been a result of the QBO increase mid winter and negative AMO preventing heights rises near greenland.

Group 1:
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Group 2:
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Dividing the original set into only the Smax years with increasing solar(left) or decreasing solar(right) have some implications:
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The typical reaction from some mets would be to automatically go with a -NAM/SAM state when a nino/-QBO combo presents itself in wintertime. The composite above debunks those expectations and proves that other factors are at work here. Coming into this winter solar activity will be a key factor in addition to the el nino positioning and atlantic SST pattern. Looking at nino yrs with -QBO shear, Smax and decreasing solar heading into winter you still see the NAO predominantly positive in the DJF period. In my case study -NAO months occurred only 22% of the time in the decreasing years, with increasing solar years averaging a -NAO more often (66% of the time) when their is no isolation for ENSO positioning (i.e modiki v.s classic). 

What this tells me is that solar trends this fall are important but must be coupled w/ enso positioning in order to make a good forecast. In addition to this, north atlantic SST's and siberian pressure patterns will be key in determining the winter AO/NAO. These indices will not be so clear cut and NAO volatility is likely this winter because of all these factors(I don't think the NAO will be predominantly negative but closer to neutral/weak positive in the means). The benefit of having the NE pac warm pool is that even if the NAO waits until late to go negative which can happen in nino's, you can still have a very interesting pattern, especially for the interior. 

Another thing that i've found is that all of my analog years except 51-52 actually had a WB nino and I don't think that it's just a coincidence that all these yrs had a strong GOA warm pool in the fall. Since this is strongly the case again this year we may be headed down that modiki/more blocky road as well, especially if we see a more poleward then normal u wind line as we get into the fall. But again, even if it becomes a modiki, its no clear cut relationship w/ solar still a mystery.

In summary my prelim thoughts are as follows:1) I am favouring a slightly positive NAO this winter
2) More research needs to be done regarding why the 91-92 and 86-87 years differed so much from the other years in the analog set, especially in terms of NE Pac high strength. If we share too many similarities with these yrs in the fall, a very warm winter could be possible(less likely scenario at this point).
3) Weak ridging along the SE coast is likely this winter, with coldest departures displaced NW of the east coast into the plains and GL's.
4) Weak-Moderate nino is favoured given the downwelling phase of the OKW expected in the near future
5) AMO is likely to remain negative but keep an eye on the sneaky +SST anoms in the davis straits
6) PDO is expected to stay positive as we head towards winter
7) Leaning closer to an el nino modiki as opposed to a classic nino setup
8) An interior storm track is more likely overall
9) Warmer then normal conditions expected along the west coast in addition to dryness. 

Tuesday, 24 June 2014

Why will El Nino turn out potentially weaker then expected?

After expectation's were very high coming off a record breaking oceanic kelvin wave this past spring, tides have turned in the ENSO department with the prospect's of a strong el nino dwindling. Below are some of the factors I am looking at regarding ENSO:

1) Solar flux has dropped at or below 75 for the first time since november after a double peak this winter/spring period signifying a long and weak cycle. This should have some implications on ENSO this upcoming fall/winter.

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2) Despite negative 200mb CHI propagation into the central/eastern pacific this week, any WWB's over the WPAC are expected to remain weak/stationary over the next week. This displays that even period's which favour el nino strengthening are failing to produce major changes to the subsurface anomalies.
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3) Cooler than normal subsurface SST's have replaced the strong downwelling OKW that formed in the early spring period.

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4)AAO/Atlantic circumpolar wave forcing has helped keep the western IO cool while SST's in and around the maritime continent are well above normal. This makes it very difficult to keep the SOI predominantly negative. SOI values are expected to remain negative through early July with a reversal to positive values expected after ~7/3 as the MJO wave propagates east.

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5) A weak K/O current this spring means the JJA "summertime" AO anomaly should remain predominantly positive correlating to this SST anomaly setup.

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6) Underwater currents have shifted to an easterly anomaly after it was initially suspected that the base state of the pacific changed to a mean westerly anomaly as a result of the mega downwelling OKW in the spring. Obviously that claim was proven false.
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For these reasons i'm expecting a weakening and retrograding el nino anomaly as we head into winter. In the end, moderate ENSO strength is likely IMO in the trimonthly ONI dataset (+1.0 to+1.5c peak). Any questions/comments, feel free to shoot away in the comment section below.

Sunday, 22 June 2014

Are back to back Nino's on the way?

Looking at years following at least three winters with negative ONI conditions and at least one winter with ONI values <-1.00 for 3 or more trimonthly periods we get the following years as past analogs.

1957-58(Moderate El Nino) and 1958-59(Warm Neutral)

SST anomalies from 1957-58 on the right and 1958-59 on the left

1976-77(Weak/Moderate El Nino) and 1977-78(Moderate El Nino)

SST anomalies from 1976-77 on the left and 1977-78 on the right

1986-87(Moderate El Nino) and 1987-88(Moderate El Nino)
1986-87 on the left and 1987-88 on the right

2002-03(Moderate El Nino) and 2003-04(Warm Neutral)

1918-19(Moderate El Nino) and 1919-20(Weak El Nino)

1911-12(Moderate El Nino) and 1912-13(Cool ENSO Neutral Conditions)

As you can see, all of these setup's have a secondary el nino(sometimes considered warm neutral) that is weaker in terms of anomalies when compared to the first nino. The 1911-12 and 1912-13 couplet is the only exception, with ENSO neutral conditions occurring in the second winter(1912-13).

Now comes the question whether the current pattern we are in is considered a period of 3+ years with cooler then normal ENSO conditions. Unlike most negative ONI periods including 1 or more la nina events, trimonthly ONI managed to spike at or above +0.5c for two trimonthly period's in the fall of 2012. Although by official standards this is not considered an el nino, it can significantly alter the global climate system. The question for me was if I could find a good analog to see if it made a difference to the ENSO state following a long cool ENSO period with an el nino year afterwords. After some research, the mid 1930's matched up pretty well. Below are the ONI values in this period courtesy of Bob Tisdale. Note the long period of negative ONI values from late 1932 through mid 1939. This period included several spikes into warm neutral conditions(similar to the 2012 period) although official nino status was never met. Coming out of this period was not only a double nino, but a triple nino.

So what would be some potential effects of a double el nino if analogs hints verify?

1) A temporary spike in global temperatures.

2) Longer lasting temporary +PDO regime within a multidecadal -PDO phase. This means a relief from  drought conditions that currently exist over the SW and southern plains states.

3) Strength of ENSO in the 2015-16 winter could dictate the H5 pattern across the eastern U.S(stronger events correlate to very cold temperatures east of the rockies e.g 77-78 and 69-70 while warm neutral events correlate to warmth e.g 03-04).

4) Continued below normal ACE/tornadic activity over the next 2 years with a significant spike to follow.

Questions and comments are encouraged in the section below. You can tweet me with your questions, @blizzardof96.

Thursday, 19 June 2014

Early Thoughts on Winter

Few comparisons I made on twitter this morning, using an ONI base state between +0.7 and +1.5c. All el nino/-QBO years are on the right with nino/+QBO years on the left. We should be in a -QBO shear phase this DJF nearing the -QBO peak late winter. Note how the -QBO years tend to have a pretty strong -NAO block with lower heights surrounding the block and a -SAM/+PDO state in the means. Whether solar activity increases or decreases heading into winter will be very important as you run the risk of ending up similar to 91-92 although it's definitely not a guarantee either way.

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The PDO dataset is also pretty interesting with the positive years on the right. I am expecting the PDO to remain positive through next winter as the nino continues to gradually strengthen. This is consistent with the NMME/JAMSTEC suite's. Note how PNA and EPO ridging is stronger in the +PDO years and the state of the NPAC is completely opposite. This tends to favour areas further SE for the heavy snow's(mid atlantic and southern parts of the Northeast) as it takes any nina component out of the pattern.

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The few things i'll be monitoring besides solar:

1) Positioning of the NPAC warm pool. If it can retrograde, look for the storm track to want to shift further west. If it continues to shift East into a more classic +PDO horseshoe position, as I am expecting, the mid atlantic will be more favoured in terms of storm track/snow interests.

2) The warm SST's off the east coast tend to pump up a stronger SE ridge like 51-52 saw in the December-January period. 

3) Keeping an eye on the positioning of the nino. Currently favouring a slightly west based nino although it could very well end up providing more basin wide like forcing.

4) We just came out of a long lasting la nina period. ONI spikes coming after at least a double nina look like this with no ENSO sorting:
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5) SLP pattern across N Siberia in October. This goes hand in hand with SAI feedbacks, which looks at snow cover growth in october over southern siberia.

Below are Positive AO El nino december heights at 250mb with Oct SLP anoms on the left. Notice the negative SLP anomaly across N Siberia and the response across North America.
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-AO years are completely opposite in December. 8 of those 10 +AO December years remained persistent with a +AO in January as well. In feb it mattered little as troughiness still dominated over the northeast/great lakes. Any questions about the upcoming winter? Feel free to shoot me a question in the comment section below or you tweet me @blizzardof96.

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Monday, 19 May 2014

Summer 2014 Outlook Part 1

The time has come, the time that we wait all year for. The summer season is upon us and many are wondering what is in store for parts of north america this upcoming summer.  This season, I decided to break my outlook up into two parts, with part two coming out sometime before the start of June. The discussion below(part 1) deals with a case study I have been wondering about regarding vastly different H5 pattern's among different East based or basin wide el nino events. The "going rule" that most people usually go by is that East Based nino's involve a North Pacific high that is based further west then WB nino's which brings down the PNA overall and pumps the SE ridge.  In addition, East Based nino's tend to force a stronger South-American hadley cell which curbs any North Atlantic blocking. This assumption is usually correct but significant year to year variability is present so that one cannot just say WB nino's are always cold and EB nino are always warm east of the rockies. In the discussion below I will go into detail on what factors you can look for when differentiating between a warm and cold EB/Basin wide nino event.

First off, I want to get a clear picture on where we are headed in the ENSO department before delving any further. Right now, the state of the pacific is undergoing significant change. Warm water continues to invade the ENSO domain, especially across eastern and central areas. Nino 1+2 has surged to 1.3c above normal as of today's update while nino 3.4 is at 0.4c above normal.

SST change since 4/16 is listed below, via the CPC. Notice significant warming of Eastern ENSO regions with slight warming across nino 3.4 and nino 3. This sudden SST warming off South America is a result of an anomalously strong downwelling Oceanic Kelvin Wave(OKW) that formed in February and is continuing to propagate eastwards in the Tropac. This OKW was so strong that it actually modified the base state of the Pacific, causing sub-sfc currents to favour a mean westerly direction. It also helped weaken the upwelling OKW that is following it so that it only acted as a slow down to the upcoming nino instead of denting the anomalous sub-sfc warm pool. For these reasons, I am favouring a high end moderate or low end strong el nino which is on the higher end of the model guidance currently.

Sub Surface Temperature anomaly loop via NOAA
With that in mind I am expecting an east based event in June which slowly transitions to basin wide as we head towards july/august.   For the purpose of this outlook I will be examining years that are EB/Basin wide as that is our expected ENSO positioning this JJA. Bolded/underlined are the years with above normal 500mb height anomalies in the means east of the Minnesota to Texas corridor. Most years did vary from month to month. For example, 1957 had a cold august while June and July were much above normal temperature wise in the east/lakes. I was pretty pleased with my dataset, as even though the sample size was small the numbers were pretty even (4 above normal, 5 below). Beforehand, I did note that there was no conclusive trend with PDO, AMO and solar when related to both dataset's which means that other factors are at work here.

a) East/Basin wide events listed below, with solar mins and maxes noted

East: 1997(Below Normal)  *Smin
East: 1983(above normal)
East: 1972(below normal)
East: 1957(above normal) 
Basin Wide: 1987(above normal)  *Smin
Basin Wide: 1991(above normal) *Smax
Basin Wide: 1965(below normal)  *Smin
Basin Wide: 2009(below normal) *Smin
Basin Wide: 1982(below normal)  *Smax

200mb height anomalies for the JJA period
Group a) which included the below normal EB/BW Nino years. Notice how circumpolar troughs dominate the 30-80N region with slightly above normal heights over the Tropical Pacific.
Group b) Well above normal heights were present along the equator with a strong Great lakes ridge and -PNA pattern.

500mb Omega Anomalies

Colder then normal EB/BW El nino years

 Notice the very strong forcing between the dateline and ~120W in addition to strong African uplift. Weak negative Omega anomalies were present across the northern and Western IO. 

In the above normal EB El Nino years, IO forcing was significantly stronger and extended further east both South and North of the equator. African forcing was significantly weaker then the other group of year as the AEJ(African Easterly Jet) was displaced south in the means.

So how can we actually tell whether this year is headed towards the above normal years(enhanced IO forcing, -PNA, weaker African forcing and +NAO) or the opposite pattern. One thing we look for is persistence as the atmosphere loves to repeat itself, even with changing indices. Below is the H5 pattern for the above normal years in MAM. Notice a very similar type of pattern as noted above.
A strong upper level trough is present across the southern Bering Sea and Sea of Okhotsk in addition to a strong eastern U.S ridge/SW trough.
In the below normal years note the very strong bering sea high which is exactly opposite of dataset 1. This is a very encouraging signal as it makes it easier to differentiate between years that will take path a) or b) as the correlation is high.

OLR Anomalies
In the below normal years tropical forcing was strong across the Southern IO and the African sector in addition to off equator forcing near hawaii. This favours below normal temps across Eastern NA as it weakens the East Asian Hadley cell, increases East Asian cyclogenesis and strengthens the downstream North Pacific high. Also notice how -OLR anomalies extend west of the dateline.
In the above normal years many aspects of tropical forcing are similar(Positive OLR over the central and northern indian ocean). The main difference is that the forcing over the central/eastern tropical pacific is based right along the Equator while the below normal years had more subtropical uplift. The -OLR anomalies also don't extend as far west once you get beyond the dateline.

So how has this year looked so far? If we take a look at tropical forcing notice how -OLR anomalies are virtually non existent across Indonesia.  Notice how Tropac forcing is weaker(more consistent with the below normal years) and also extends further West of the dateline(consistent with the below normal years).

At H5 a Strong North Pacific high, -WPO and tendency for strong East Asian troughiness is in place. This also mirrors the below normal years. 
The West Pacific jet packet amplified anomalously as well.
To conclude part 1, I am expecting this year to behave similar to group A or the Basin wide/East Based nino years that have below normal temps in the JJA means over the Eastern midwest, great lakes, ohio valley and eastern CONUS while the western CONUS enjoys above normal temperatures. In subsequent updates, I will go into further detail regarding the month to month/regional breakdown with precipitation and temperature analysis. I will also talk about some of the closer analogs that I am looking at, in addition to other factors such as the QBO, PDO and solar activity. Any questions, comments etc are more then welcome and I will try to answer them as soon as possible. You can tweet me @blizzardof96 with questions as well.