Friday, 29 November 2013

What's going on across the stratosphere?

With regard to any significant SSW occurring this winter, its looking very slim in DEC/JAN given the indices on the table this year. For +QBO, -PDO, N/- ENSO and years with the JAN SSN below 95 no significant warming's have even occurred since 1950 in DEC/JAN. In february their are a few exceptions, one begin 08-09 which had a strong East Pac ridge, definitely aiding in the wave 2 response. 00-01 is another example of this, although the PDO was neutral/positive and the QBO was transitioning from positive to negative. The common denominator in these two years is a strong Kamchatka PV lobe and bering sea/GOA ridging. Unless we see an uptick in the PDO/ENSO domains, or a quick downturn in the QBO by feb a major warming in the DJF period is going to be tough to come by. EP heat flux anoms are already starting off winter well below normal ever since the wave 1 response in late october. Our best shot will probably be a wave 2 warming in Feb if we can keep the EPO ridge consistent which becomes more likely given the +QBO/N ENSO and -EPO persistence. If this doesn't work out then their is always the FW question in March/April that should arise with a mean state similar to our current one. This SSW timing is much more favoured given the current setup and could have impacts on spring, especially with the warming ENSO region expected and a transitioning QBO index(favourable for high heights across the NAO/EPO region's).

Feb 2001
Feb 2009

Tuesday, 26 November 2013

Snowstorm Forecast Nov 26-27

Winter Storm Discussion

After a long summer, winter is back and so is snowstorm tracking across eastern canada. A low pressure area formed across the central gulf coast yesterday night and has since began its trek eastwards, now stationed across western NC according to noaa mesoscale analysis. Snow will begin to break out across the niagara region over the next few hours with snowfall moving into eastern ontario and southern quebec in the 7pm-10pm timeframe. The snowfall is expected to come in two waves, with a secondary low forming and riding along the east coast tomorrow bringing a reinforcing shot of precip to Eastern ON/QUE by tomorrow afternoon and evening. The heaviest snow is expected to fall southeast of ottawa and west of montreal in an area from east of kingston up towards saint jerome, the laurentian's and the eastern suburbs of ottawa. Over this area, a general 25-35cm's of snow is expected to fall, with isolated amounts in the 40cm range.

For the city of montreal itself, precipitation type will be a huge issue and likely a headache for EC and many forecasters across the area. Precip should start off as snow in the city with 7-15cm of snow likely before a change over to rain and maybe a brief period of ice pellets between 7am and 1pm. The east end will be seeing a longer period of mixing while the west island gets less. Higher elevations NW of the city should be the jackpot zone with all snow, nice isentropic ascent and a plethora of moisture available. After the change over to rain, another 5-12cm is likely in the afternoon/evening hours with a change over back to mostly snow occurring around the 12-2pm time frame. RGEM/GFS have this changeover a little bit earlier with only a brief period of RN/PL in the early morning hours. I am going with the RAP/NAM WRF/NAM/SREF consensus for now, based on surface analysis at the current time. For the GTA, looks like the heaviest precip will fall overnight, mostly in the form of 10:1 ratio snowfall. Expecting 2-9cm amounts over the city, with highest amounts over the east end(oshawa area). In terms of the ottawa valley, I am expecting a solid 15-25cm of snow with some isolated 30-35cm amounts over the east end. Perhaps ratios are a little bit better then 10:1, but not by too much.

With that being said here are my forecasted snowfall totals across eastern canada. Questions, comments ETC are encouraged.

Kingston: 20-30cm
Ottawa: 15-25cm
Montreal West Island: 12-25cm
East Montreal: 8-20cm
Belleville: 10-20cm
GTA: 2-9cm
Hamilton/Burlington: Trace-4cm
Niagara: 5-12cm
Quebec City: 8-18cm, locally 20cm
Trois Rivieres: 7-15cm, locally 15-20cm

Friday, 22 November 2013

Lake Effect Snow Outbreak for Southern Ontario

I thought that I would post my thoughts on this LES potential, now that Travis has shared some of his thoughts. I'm thinking that the flow align's a little bit further west then he is thinking. This outbreak looks like it has huge potential, greater then we have seen in a while. Params look to set up really nice as previously discussed. High Delta T values will set up some very intense squalls as extreme instability develops along side a very saturated BL, low shear values and continuing cold air advection through sunday morning.

Georgian Bay
From late afternoon saturday into early the evening hours it looks like cells set up in a WNW fashion(collingwood/wasaga band south towards stayner, angus and Bradford/Newmarket) before shifting further to the SW once the flow shifts to the NNW by late evening into the overnight. This squall should be able to briefly move through the GTA/hamilton area's as well before building back to the West. These squalls should sit in this type of position through sunday morning with a band extending through meaford/collingwood and down towards shelbourne and perhaps as far east as alliston. Don't think areas east of barrie see very significant accumulations with this outbreak besides some weaker squalls after the immediate passage of the cold front saturday evening/afternoon. Barrie is in the 5-10cm zone. The squalls should build back to the NE sunday afternoon with the flow lining up in a more NW direction as the high moves through, but this will only last for a few hours before shear starts to rebuild.

Lake Huron

BL lapse rates should remain rather steep throughout tomorrow evening into the overnight and through sunday morning with some wavering of the band from more of a goderich, st mary's, tillsonburg position before shifting further south into the london/strathroy/lambton shores areas. Going to see this band waver considerably throughout the duration of the event as winds shift between these two positions. Thinking thundersnow is possible especially in areas North of London, may even get into the city, where 10-25cm is likely IMO.
Here is my Forecast Map. Thinking a trace-5cm is possible outside the blue zone with the area shaded in pink, including the GTA and hamilton.

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Wednesday, 20 November 2013

December Update

Contrary to any previous ramblings, I am all in for a below normal december based on the current look to the pattern. The NE pacific warm pool will help encourage strong ridging over the aleutians(we are seeing hints of this already with Ca air masses packing a punch from the prairies on east). We are already seeing record cold showing up across the NWT, AB and BC. The bering sea ridge will shift at times into the GOA(when tropical forcing is favourable) creating more of an el nino/la nina hybrid sometimes. Biggest risk right now is if the GOA warm pool backs further west which would have a tendency to shift the coldest anoms into the W and SW part of the continent(unlikely scenario at this point). 
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Indications are pointing towards a favourable GWO in Dec with +AAM dominating the 35-55N belt and easterly momentum dominating the subtropics. This will help encourage the MJO to move into more favourable phases. Roundy plots show this evolution just before christmas with a wave moving across the pacific in tandem with the active KW phase plot.
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In terms of the AO, it should stay predominantly on the positive side this winter with little in the way of any major SSW's unless we see a late winter final warming which could have implications on spring. An overall +NAO and +AO means that we can see some larger temp swings with more of a progressive pattern setting up on average. In terms of the +QBO, Neutral ONI and Smin induced -NAO pattern, we will need to see where the PV sets up in december to see if that theory can prove itself valid. Early indications have the upper vortex over the greenland/siberia area with most of the blocking confined to the bering sea. 

Saturday, 16 November 2013

Major Severe Weather Outbreak Looms

With a moderate risk out now from the SPC, the weather world is buzzing about the current severe weather outbreak on the way for the lower great lakes region. It has become apparent that a very significant outbreak of severe weather is on the way. Throughout the day today and into tonight, warm and moist air will be advected northwards through the ohio and tennessee valley's. Dew points are well into the 60's and even 70's across south texas based on current observed data. These readings will be transported well to the north due to strong forcing from the low level jet. 
By tomorrow morning temps are expected to reach 70f in the chicago and lafayette area's with 60's extending east towards detroit and columbus. This should provide ample moisture to set off discrete cells especially if skies can clear out ahead of the front. Surface-500mb bulk shear is in access of 50kts as well, with significant speed and directional  wind shear with height.

Note the very dynamic upper level jet streak that is going to be penetrating this warm sector. SRH values will likely be above 350 near Chicago with EHI values >3 ripping right through the chicago metro area. The cells along the cold front will most likely stay discrete as they move through the Chicago area before organizing into a squall line setup over Michican, Ohio and S ON.

 This means that we see an elevated tornado threat across IL,IN, and KY before it transitions to mostly a damaging wind threat over OH/ MI and ON. The tornado threat will still translate east as meso-vortices can form along the front and jet dynamics remains very favourable for rotating thunderstorms. Peak Gusts to 115km/hr are possible along the intensifying front, as the surface low deepens below 980mb.

Stay safe out their this sunday! Will continue to update blog when needed.

Sunday, 3 November 2013

Solar/QBO Research

 I have been investigation the solar/QBO relationships a little bit closer recently. The HT theory is that when you have a solar max/+QBO, SSW's become more frequent especially in february unless you have a +PDO/el nino in which they often happen earlier. I decided to do some research on this relationship.

Looking back at years since 1953, with a +QBO state and a monthly mean JAN SSN over 95 we notice that 6 out of 12 cases have a major SSW event in feb. Another 4 years have an SSW in JAN with only 2 in december. Whats important to note is that all the years with major december warmings had +PDO states and half the jan warming's had +PDO states as well. Also important is that no +QBO/smax years have even not seen a major SSW event, which is pretty striking.

Looking back at all years since '53 with a +QBO and low to moderate solar(JAN SSN below 95)

We learn that 14 out of 25 cases have no major SSW events all winter.... with just 3 out of 25 years having a SSW in DEC or Jan. These 3 years all had +PDO's. Another 6 out of 25 years in the data set had SSW in March or April, with no real PDO trends. There were also 2 years that had major Feb warmings.

So heres what we can pull out of this research:
1. In +QBO/Smax years SSW's are favoured in Jan/Feb and have always occured at least once per winter when the SSN is above 95 in january.

2. You are much more likely to see a SSW's in DEC when the PDO is positive or their is an el nino if the QBO is positive and SSN in high.

3.When the QBO is positive and winter SSN is low to moderate then you will most likely not see a SSW and if you do it becomes more likely to become a FW in march or april. Only seldom do you see a DEC/Jan/Feb warming and it helps to have a +PDO or el nino.

If solar flares continue to occur and the 30 day SSN continues to rise, we have a better chance at seeing a mid to late winter SSW and subsequent AO dip. This may be one of the only factors that can get us out of the overall +AO regime as many indices have been pointing to a stronger then normal vortex. If solar activity drops off again, its going to be very tough to see a SSW or sustained -AO period until March/april.

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Friday, 1 November 2013

Latest Analysis On The Stratosphere

Some interesting trends developing with regards to the stratosphere....

The vortex has began to quickly strengthen after a strong wave 1 warming and EAMT surge last week. Upper stratospheric temps are now returning to below normal levels as solar activity ramps up. Been looking more into stratospheric analogs for the upcoming winter, based on a -PDO, neutral ONI and +QBO state. Best years include 78-79, 01-02, 90-91, 61-62 and 66-67. With these analogs we saw a tendency to see early winter Canadian warming's with December 78 and 66 showing this response.
Dec 1978 warming at 10hpa:
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Tropospheric response shows a very anomalous alaskan block with CPF evident from siberia to NA. There was also a very strong -VE anomaly across western europe/ east asia with a gradient pattern look for the UK.
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In Dec 1966 the CW response was greater across the mid and lower levels of the stratosphere with a similar 500mb setup afterwords. Notice how the western siberian block becomes dominant with mean troughiness across the mid latitudes.
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In terms of other years in the dataset, 61-62 had no Major SSW events and 90-91 had a Major late winter warming with a classic wave 1 response. In the 01-02 season, despite several significant disruptions to the upper vortex, it was tough for these warm anoms to down well, which made minimal impact on the surface pattern until spring.

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What may end up occurring this year is we either see a significant warming early on in the winter or no major warming's at all until Late feb into April. The stratosphere looks increasingly vulnerable to some sort of early winter response, especially if we see the MJO moving into phases 4-7 by DEC. This would help force an EAMT surge with bering sea troughiness and possibly a wave 1 response.

If their is no DEC warming, a Final warming event would be favoured with a heightened HT effect coming into play this year. This would become most likely if the monthly SSN drops off and we can get help from tropical forcing as KW's upwell warmth over the western Tropical PAC. The ENSO modelling is honing in on this type of situation, although the -PDO forcing will try to resist any FW attempt's. Many factors are coming into play here but the two period's to watch closest this winter look to be Dec and late winter in the SSW department. 

Monday, 28 October 2013

Stratospheric Ramblings

The current state of the atmosphere is such that we saw a pretty robust MJO wave over the west pacific. This, combined with building pressure over asia, has helped produce a burst of west pacific typhoons over the last two weeks. This has triggered a positive feedback loop as these typhoons have distributed latent heat and negative potential vorticity anomalies downstream. This has helped pump the west pacific ridge and contributed to a strong bering sea trough( -EPO/WPO pattern). So why does this have any significance in relation to the strat? Stagnant bering sea troughiness and a very potent EAMT event(trigerred by tropical forcing over the W Pac) has really helped trigger a wave 1 response over NE siberia. Mean H5 pattern in the last 7 days shows the -WPO/-EPO setup.

Currently, the stratosphere is in a strengthening state which it should be at this time of year. As the heat source(EAMT + W PAC typhoons) for this warming fades, the vortex should rebuild stronger then it was before. -AAM anoms propagating equatorward will also help rebuild the vortex, with a potentially long period of a +AO coming up. In any case, it is a good sign to see such a strong fight against the vortex in a west QBO year. I suspect this won't be your typical +QBO year as we are in a westerly shear phase which promotes more pertubations to the vortex. In addition, we have a more poleward the normal 0 u line, with a greater then normal build up of ozone over the north pacific. These factors should make a major warming easier this winter.

The analog years I have been using for the stratosphere are 85-86, 01-02, 80-81, 90-91 and 08-09 which all have a neutral ENSO state(with the exception of 08-09), a +QBO shear phase and low solar activity. All these wintera had some form of a SSW event with the exception of perhaps 85-86 which didn't make as much of an impact at the surface. I'll give 2001 and 2009 as examples, with a 2-3 wk lag for the peak H5 response.
2009: compday.Ck0LXBcuJI.gif   H5 Reflection:compday.it2zFiklwJ.gif
Notice how the cold signal is muted across NA while their is a very strong -VE anomaly across western europe.
2001 had the opposite pattern with warmth in W europe and cold anoms across NA:
500mb setup 2-3 weeks later


If we look at all +QBO shear years, without isolating for solar or ENSO we get the following H5 setup. The important feature to note is the strong East PAC ridging and bering sea trough which would help promote a mid/late winter wave 1 response as well. The euro monthlies have also been hinting at strong GOA ridging, which combined with aforementioned factors make a good case for a SSW this winter.

So the point being made here is that you can see significant SSW's in downwelling +QBO years, especially when other factors are favourable for development. Although significant SSW's can occur, placement of the coldest anomalies at 500mb will only favour some locations across the N Hem, whether its europe, asia or NA.

Monday, 21 October 2013

Positive Arctic Oscillation Increasingly Likely To Start Off Winter

We are seeing a pretty strong -AAM anomaly propagating equatorward currently which helps support a +AO/+NAO pattern. The GEFS consensus keeps the index positive all the way into mid november.
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This type of pattern means a stronger vortex and a northerly displaced jet. Luckily a strong piece of the polar vortex is expected to park over eastern canada through early november. This may be caused, in part, by the neutral enso/+QBO regime which favours a cooler late oct into early nov period for the east. We have seen a wave 1 response across the bering sea area which has also helped bring the chill, along with an active east asian jet.
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What this also means is a recovery of the vortex is likely to occur by mid november, with a potentially positive AO regime setting up through early winter. The SAI/OPI has been the opposite of last year with a sharp negative trend in snow cover since early october. Ridging is expected to continue south of 60N across siberia so I would expect this trend to continue with snow cover ending off at near normal levels.
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If we look at the 10 most positive AO winters we find the following SLP setup near the north pole. Notice the -MSLP anomalies near siberia.
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This year we have seen below normal MSLP across northern siberia as well.
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The likely scenario IMO is the AO index remaining on the positive side through much of november and december with a SE ridge in the means and the core of cold/ winter storms aimed towards the midwest. This does not mean we cannot see a wintry pattern along the east coast, especially for new england, and the northern tier. Dec 07 is a good example of this. The +AO game is risky though as we will need to depend on a -EPO and favourable pacific setup to deliver the goods. The pattern does look ripe for a SSW event by jan/feb with a more poleward 0 line in the mean wind department as well as a large ozone build up from previous ENSO warming. This will likely play a role in hampering the AO state by Jan-March. 

Saturday, 19 October 2013

Tracking Strong Coastal Storm

The GFS and ECMWF are in pretty good agreement right now with the overall setup of this storm. The euro has a weak coastal low developing of the NJ coast before major intensification occurs once it reaches the gulf of maine/Atlantic canada.

 Right now the euro ensemble spread has a weaker surface low, with a more neutrally titled trough/ weak frontal wave developing. The devil will likely be in the details, which the OP euro would likely pick up on first.

Euro ENS has little spread in the guidance:
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To get a stronger storm for the interior northeast, we need to see the trough go negative a little bit earlier. The current NAO forecast argues for a spike towards neutral in this time frame which would help pump heights off the SE coast, and perhaps encourages a further west/stronger storm. It doesn't look like the I-95 corridor has a good shot at snow, although higher elevations in the interior could potentially see something. Given the more amplified nature to the pattern, I am keeping an eye on this although the euro ENS solution is probably best for now unless the euro OP trends the other way over the next few runs.
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Updated Winter Maps/Indices Forecast on Preliminary Winter forecast

Just want to give a heads up to everyone that I have updated my december, january and february temperature and snowfall forecasts. I have also updated the indice forecasts. Check it out if you have a chance and don't forget to leave any  questions or comments you may have.

November Warmer.... core of cold shifts west

A +AAM transport has occurred over the pacific basin during the past 10-15 days... which has aided in the development of a very warm pattern east of the rockies.
We saw this pattern at 200mb since october 1st:
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The poleward AAM transport was well established during this timeframe. I added a red arrow to illustrate this event better. This pattern favours eastern IO convection which has been helping enhance the west pacific tropical "flare up".
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Now this is where it gets interesting... the GEFS has a very strong MJO wave moving into phases 8/1. This pattern usually coincides with negative EAMT and frictional torque anoms. We are seeing the opposite pattern currently.
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Given typical progression of the GWO, what should happen next is an increase in easterlies between 30N-30S, eastern u.s troughiness favoured for the rest of october and an MJO wave moving towards phases 7,8 and 1 for the first half of november. This shifts the core of the coldest air over the northern rockies and interior west, with some intrusions into the great lakes/midwest at times. An increase in convection is likely over the central pacific/dateline area given the pattern. Euro weeklies/JMA agree with this overall pattern evolution. If a CCKW can coincide with the GWO, this would help increase confidence on developing convection over the central pacific. Keeping a close eye on the wave developing between 60-120E. Lets see if the euro shifts to this type of MJO setup... right now the ensemble members are all over the place with the ENS mean parked over the null phase.

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