Another active day in terms of severe storms is set to take shape across the country tomorrow particularly in southern ON and in AB/W’rn SK. The water vapour image below shows the two upper level lows that will be responsible for these active days, the one currently located off the coast of BC and the other along the WY/MN borders. By late tomorrow afternoon the GFS/GEM/ECMWF have the western low still situated on the Vancouver Island region and the eastern impulse just tracking into IA/WI region. Reason why I am showing the GFS, as just mentioned, there is great agreement on the forecast position of these impulses among the cluster of models indicated and the NAM is the outlier among the group, not by much but enough that it will make some difference down the road.

Investigating the 500 mb wind forecast shows a good balance of divergence and diffluence over central to eastern AB which will lead to cyclogensis in the lee side of the Rockies by the afternoon and strong divergence over southern ON which will continue to push the low up from the US by late afternoon/evening.

Below is my forecast analysis for tomorrow evening/afternoon across the area of interest but in the section below will break the discussion into the two areas of interest. Note that the regions circled in purple are general risk area, and area outlined in pink show tornado risk areas.

Ontario

At the surface there is a low pressure system that will be pushing toward and slide along or just south of the northern shore of Lake Erie. There will be a warm front associated with this low and will follow a similar track just ahead of the low center. In south central ON Lake Breeze (LB) convergence will also be setting up with the Huron/Georgian Bay/Ontario lake breeze fronts converging roughly around an area outline by Kitchener-Minto-Orangeville. The warm front and lake breezes will be the main region of focus for any surface based convection tomorrow afternoon and evening. Within the LB zone SFCAPE values are forecast to reach the 500-1000 j/kg range and MUCAPE values near the warm front in southwestern ON are forecast to reach the 500-1500 j/kg range through the afternoon/evening. There will be ample shear present across the region but will make note that vectors with the LB region a perpendicular to the LB fronts which will lead to more isolated updrafts where as shear vectors in the vicinity of the warm front are more parallel thus leading to more messy convection with multiple slitting cells. However, forecast hodographs across much of the area do show veering with height, and even more so in southwestern ON. All factors combined would suggest that the LB region will likely see a few isolated cells go up, possibly supercell modes, and through southern ON expect multiple modes with embedded rotating updrafts. Greatest tornado threat looks to be along and just south of the warm front from Simcoe to Windsor, and a small risk in the LB region. Important Note: LB region will greatly depend on how much cloud cover persists through the late morning hours to allow for suitable destabilization through the day.

Alberta/Western SK

All factors discussed above will lead to low developing to the northwest of the Edmonton region roughly near the Slave Lake region. Front he region a triple point will setup with the warm front extending east toward Cold Lake, AB, the cold front extending west northwest toward Fort St. John, and a dryline extending south along or just east of the QE 2 corridor to the US border. Within the region east of the dryline and south of the warm front SBCAPE values are forecast to reach the 1000-1500 J/kg range by mid afternoon, bulk shear values expected to range from 40-60 kts, and forecast hodographs indicate veering with height, should all contribute to mainly isolated updrafts and a few supercells. The issue will be how much cloud cover will linger through the morning. If there is sufficient clearing by late morning-mid day, the region just NW of Edmonton would see the largest risk of tornadoes particularly through the late afternoon and evening as the 850 mb LLJ really begins to ramp up. At the moment general consensus appears that initiation will likely take place between 20-22 UTC (2-4 pm MDT).

A quick analysis this afternoon is showing the possibility of a few severe storms this afternoon/evening for extreme southeaster MB, particularly the area outlines by the TCH from ON to Winnipeg, south from Winnipeg along Hwy 75, and the US border over to Lake of The Woods.

A cold front/occluded front is slowly progressing eastward through the southern portion of the province this afternoon which will act as the primary trigger for surface based convection. Along with this front is a strong 250 mb jet streak which is in the 90-100 kt range and 500 mb vort max forecast to reach the southern tip of Lake Manitoba late this afternoon/evening (first image below), which will aid in overall ascent ahead of the front. Furthermore, CAPE values are forecast to reach the 750-1000 J/Kg range, in combination with 35-40 kt deep layer shear, the environment for extreme southeastern MB may become conducive to a few severe storms and even a supercell is possible given shear profiles. Main threats will be wind, rain, and moderate hail. A tornado threat will be minimal as any convection will likely initiate too late to really feed off the daytime heating. The second map shows forecast analysis and the circled region is the main risk area where I think strongest storms will be possible late this afternoon and evening.

Things look to be shaping up tomorrow afternoon for what could be a pretty active day in terms of severe weather for southwestern Saskatchewan and southern Alberta.  Starting with the upper levels there is a strong 500 mb jet core with a strong area of vorticity ejecting out of the Rockies tomorrow afternoon which will be the main driver for a low to develop along the SK/AB border and enhance the severe weather threat. Furthermore there is a strong 250 mb jet core also ejecting eat from the Rockies (see last panel for 205 winds) with the left exit region forecast to be over the warm sector of the low tomorrow afternoon which will supply amble upper level divergence.

These factors mentioned above will contribute to the low developing near the North Battleford, SK region through the day tomorrow with a warm front extending through south central SK, a cold front pushing south through Alberta and a weak trough/dryline pushing east through southern AB into southwestern SK. CAPE values (instability) within the region between the trough/dryline and warm front is forecast to reach the 1000 J/Kg mark by the late afternoon with about 30-35 knots of shear. Shear vectors will be mostly perpendicular to the trough/dryline as well as warm front thus leading to mainly isolated updrafts. Forecast hodographs within the southwestern SK region show good backing winds with marginally veered profiles with height which should contribute to weakly rotating updrafts and possibly organized supercell structures. Thus all factors combined looks like storms may initiate along the SK/AB border mid to late afternoon and become more organized as they push into SK. Looks like main threats will be winds and hail which could reach marble sized. The tornado threat at the moment does seem pretty low but best chance at a brief tornado would be along the Hwy 4 corridor from North Battleford, through Swift Current, and down to the US border. Along the cold front into AB would expect mainly line and bowing segments with a few areas of strong straight line winds and hail mainly along and south of Hwy 9.

Been a little while but many late nights and early mornings have kept me from being able to update as often as I would like. Had a few slow days in terms of chasing with the exception of May 24. Not much promise was held for the day but was able to capture a wicked display of atmospheric vorticity (spin) within the bare bone updrafts near the Holyoke, CO region. Essentially the LP storm at first was showing the bare bone structure of what a supercell is made up of and was an awesome display of the complex dynamics involved within a supercell thunderstorm. Eventually the storm become the tornado warned storm that went through the Chase County NE region but night fall and low viz prevented us from being able to spot any tornadoes (although none were confirmed regardless) but was able to get one of the best lightning shows to date. Video and pictures found here:

http://www.severeweatherdiaries.com/photography/storm-chase-2013-chase-day-9-vortices-lightning-in-colorado/

http://www.severeweatherdiaries.com/stormchase2013/

Onto the forecast for the next two days; which appears to hold some promise one again. For today flow, although moderate at best, is beginning to return to the central planes. Below shows the 250 mb flow and we can see that there is a branch of the Polar jet begging to push its way into the eastern CO and western KS regions. Morning analysis shows that this jet streak is currently entering the 4 Corners region and the 12Z NAM has initilized this feature well. It is this jet streak that will be the focus of energy for todays setup.

At 500 mb we can observe a weak shortwave that is pushing into the eastern CO region which will be enhanced some by the 250 mb jet and will help with overall ascent within the northwestern section of KS and south central/western part of NE.

In response to these factors above we can see here that there is a developing low within the CO/NE/KS state intersections with a dryline pushing into the western KS region which also extends up into WY and through to southwestern KS. The primary focus here will be near the lows center where a triple point looks to setup on the KS/NE border just south of the McCook, NE region. To the east of this dryline of forecast to be a moisture latent airmass with rich Theta-e values and surface based CAPE forecast to reach near the 4000 J/kg values. Again capping will be somewhat of an issue but may help the cause by allowing only the better storms to remain discrete, organized, and not bee interfered with by weaker disorganized storms. The GFS for the most part in agreement with the NAM in terms of upper flow but synoptically at the surface the GFS is favouring a slight westward bias in the setup of the dryline/triple point. Thus   the target for now remains broad and would be between the I-80 (from North Platte, NE to Lexington, NE) and I-70 (from Colby, KS to Hays, KS) Corridors with a focus near the Norton, KS region whihc seems to be the most central point within the target region. There is also a possibilty of a blue sky bust today if the dryline is not strong enough lacking some convergence near the sfc.

For May 27 the western trough continues to dig with increasing flow over the planes from at the 250 and 500 mb levels. Of interest here is the jet nosing into the western planes and the region of enhanced 500 mb flow over the central KS region.

Again in response a surface low develops within the central KS region with triple point developing near or just west of the Great Bend, KS region. It is also encouraging to see that the GFS/NAM are in relatively good agreement here once again with the GFS having a light westward bias and north with triple just south of the Hays, KS region but not far off. Again deep moisture and even better Theta-e values have this day a little more promising but CAP will be a little stronger. With all factors combined I feel the CAP will break and again will help to allow only stronger storms to persist and thrive as there should be minimal “crapvection”. This will think that the Great Bend region is a good tentative target for now.

We had a very hectic but good chase yesterday. We began our chase on the supercell that eventually pushed its way into Hays, KS. Before we followed into Hays we decided to break off from it since it looked pretty undercut and the RFD was very cold and knew it likely would not produce much. The cell to the south near Rozel/Larned, KS got going and looked rather good so we headed south. After hearing multiple reports of tornadoes and seeing the images we didn’t think we would make in time. But we got on our west road toward the meso and alas there it dropped a beautiful cone tornado that lasted for about 10-15 minutes with a smaller satellite tornado that briefly dropped to out east. It was a great chase today

Today is a really good setup once again. We have a secondary shortwave trough rounding the long wave through today which should push into the Texas Panhandle/southwestern KS today. This area to the immediate east will be the area of interest for this afternoon’s initiation:

http://www.twisterdata.com/index.php?prog=forecast&model=NAM&grid=221&model_yyyy=2013&model_mm=05&model_dd=19&model_init_hh=12&fhour=09&parameter=RELV&level=500&unit=MB&maximize=n&mode=singlemap&sounding=n&output=image&view=large&archive=false

Currently there is an outflow boundary with a NW to SE orientation sitting in northeastern OK this morning, but most mesoscale models have it mixed out through the afternoon due to the stronger southerly synoptic flow, but still something to keep on eye just in case it lingers. Essentially at the surface we have a cold front that will drop south through today in KS and intersect with the dryline just south of Wichita, KS. Winds out ahead of this region are southerly but I suspect that in response to the frontal intersect and the added vorticity from the 500 mb short wave mentioned above, there is likely a mesoscale low feature to develop here. That should provide better backed winds in the region and give a greater tornado risk. Not to mention the 3500-4000 j/kg of CAPE which is forecast to be uncapped by 21-00 UTC should help things along just fine. Thus a target of around Ponca City, OK will be ideal for today for initiation along the frontal intersects and keeps us in the vicinity off the outflow boundary. Below first link is to Sfc winds and moisture, second shows CAPE forecast.

http://www.twisterdata.com/index.php?prog=forecast&model=NAM&grid=221&model_yyyy=2013&model_mm=05&model_dd=19&model_init_hh=12&fhour=12&parameter=DPTF&level=2&unit=M_ABOVE_GROUND&maximize=n&mode=singlemap&sounding=n&output=image&view=large&archive=false

http://www.twisterdata.com/index.php?prog=forecast&model=NAM&grid=221&model_yyyy=2013&model_mm=05&model_dd=19&model_init_hh=12&fhour=12&parameter=CAPE&level=SURFACE&unit=none&maximize=n&mode=singlemap&sounding=n&output=image&view=large&archive=false