Upper impulse currently tracking its way through NE’rn BC into NW’rn AB will push into south central SK tomorrow afternoon and will bring with it the risk of severe weather to the province. The trough is rather compact but the SREF_H5 as shown below shows a subtle trough with subtle height falls within the SE corner of the province which should help with overall ascent within the warm sector. This will be key as there does appear to be some capping issues the forecast, will touch in this in a second. Further helping the scenario is the 500 mb jet core will pass through the southern portion of the warm sector with the left exit of the 250 mb jet within the same vicinity. This will also prove to be very beneficial as this will greatly enhance cyclonic shear and help increase deep layer shear.

Monitoring the forecast track of the surface low over the past few days there has been some disagreement with how far into SK the low would track and how far north the warm front would push. The GEM/GFS/ECMWF have been pretty consistent with the low tracking through central SK forecast to be just north of Yorkton by Sunday afternoon, the H5_SREF also supports this scenario. The NAM however keeps the low along the SK/US border with the warm font sitting just S of the Hwy 23 corridor through MB. I have chosen to reject this scenario for the time being as it is the large outlier. With the trough pushing in, it should allow for the warm front to push N, but can see that the 18Z NAM from today is beginning to trend with the general models trend. But cannot discount the possibility of the front not pushing as far N with the amount of synoptic precipitation forecast for central SK the cold air from this could prevent a good northern surge of the warm air. I will use the 18Z NAM for surface forecast analysis as I think it is starting to have the right idea. I suspect to see storms initiate near the 21 UTC-00UTC (2:00 pm-5:00 pm CST) along the cold front near the Hwy 35 corridor just E of Regina and also along the dryline/cold front intersect near the Weyburn area as well. This region could see the best low level dynamics to see some good suprcells. Storms will track E at first and as they get rooted in the boundary layer track SE to SSE.

There is however some bust potential, and this can once again be attributed to a pretty stout CAP that is forecast to be in place through the afternoon as indicated by the forecast sounding within the warm sector. But as discussed above the saving grace is the upper height falls should help to mix that out, good forcing along the front and dryline (particularly near the intersect of the  two) and good evapotranspiration from crops which is often underforecasted by models. Looking at Sfc-500 mb bulk shear of 50-70 kt, sfc-850 mb bulk shear of 25-30 kt, and veered hodographs through a deep layer looks possible that organized supercell structures are likely along with the risk of a few tornadoes. Tornado risk will increas as storm track E where an S-SE 850 mb LLJ will help further enhance low level shear. Main risk area appears to be Yokton, Weyburn, Estevan, Carnduff, SK and into Brandon, Russell, Pipestone MB. As storms push into S central MB expect them to congeal into more of a line as the cold front overtakes the dryline. But this can all amount to nothing if that CAP wins giving nothing but scattered unorganized convection.

Certainly an active afternoon weather wise is in store for SK. Water vapor imagery this morning is showing the upper low and associated short wave along with a 500 mb 60-70 kt jet ejecting out of the Rocking into AB which will bring an enhanced risk of severe weather for SK. Along with the 500 mb flow is a jet core at 250 mb is forecast to develop in the southwestern portion of SK this afternoon and being to nose into the warm sector which will really act to enhance upper level divergence.

At 850 mb there will substantial southerly low level winds with the main 30-40 kt LLJ axis to the immediate east of the cold front which will gradually strengthen to a 50-60 kt LLJ through the evening for the eastern part of the province. These low level winds will contribute to ample low level shear with Sfc-850 mb bulk shear ranging from 20-40 kt and Sfc-500 mb bulk shear values of 50-70 kt. This is resulting in extremely veered hodographs within a deep layer and large amounts of streamwise vorticity within inflow winds. Parameters within this range will most certainly yield strong rotating updrafts and isolated supercells with a tornado risk. I would even go as far to say that there is a risk of a couple long tracked and possibly violent tornadoes.

At the surface there is a low currently sitting in eastern AB near the Oyen region with a warm front pushing NNE’wrd into SK and cold front pushing across south central AB, this low is forecast to track NE’wrd and end up near the Prince Albert region this afternoon. Within the warm sector of due points are forecast to range from 18^oC-22^oC which is on the extreme end and will be plenty to give LCL height within the 500-1000 meter range, but still think with shear and shear vector orientation along with ample upper level divergence supercell modes will likely remain classic in nature. CAP is expected to hold on until around 20 UTC (1:00 pm CST), where forecast soundings begin to show CAP erosion and CAP gone by 21-22 UTC (2-3 pm CST). Thus I believe initiation could be as early as 1:00 pm CST along and just west of Hwy 2 from Prince Albert – Moose jaw – US border and track ENE with storm motion about 20-40 km/h. With this type of environemt could see supercells mature within 30-40 min of initiation thus yielding a tornado threat through the afternoon for central SK and late afternoon/evening for eastern SK. All factors considered the area to the east of Hwy 2 will see the risk of isolated supercells and tornadoes with the highest risk between the TCH and Yellow Head Hwy.

Here is a slightly larger version of the map above withou the text just so its a little more clear:

Looking at water vapour imagery this evening, can see that there is another short wave trough embedded within the broad upper low/500 mb flow pushing in through southern BX this evening. This shortwave is forcast to push into south central SK tomorrow afternoon/evening which will bring the risk of severe weather for the extreme southeastern portion of SK and southwestern MB. Along with this short wave is 500 mb wjet core of 50-55 kt and a 250 mb jet core of around 100 kt which will help provide ample upper level divergence within the unstable air mass.

At the surface a low which is currently developing in northern MT/southern AB associated with the upper shortwave is forecast to track along the US/Can border and be located roughly between Estevan, SK and Minot, ND by tomorrow afternoon. Most models are in good agreement with where the low will be located the real disagreement comes with where exactly the warm front will be placed. By the looks of the 500 mb flow being a little more zonal I would think that the NAM solution having the front roughly along the TCH seems to be the more valid solution as opposed to the GEM/GFS idea of pushing the warm front into the interlake region. But will emphasize that where the front is located will make all the difference as to where the severe weather threat exists for tomorrow as all the instability needed will follow in behind the warm front along with very rich theta-e air. Within the warm sector the good flow aloft will bring 40-50 kt of surface to 500 mb bulk shear, south easterly 850 mb winds will make for about 20 kt of sfc to 850 bulk shear, and 2000-3000 J/kg os SBCAPE looks to be enough to get rotating updrafts. Low level shear will also be enhanced in the vicinity of the warm front also, thus any storms that do initiate, is they manage to anchor to the warm front there would be a tornado threat. One issue I do see is how ongoing convection tonight in SK will affect day time heating and that shear vectors are not exactly in a favourable orientation to allow for real discrete cells. Soundings also show a little bit of a CAP issue once again but hodographs are favourably veered within a relatively deep layer. Thus I believe convection will be rather messy tomorrow afternoon (initiate be around 3-5 pm CDT) but within the mess embedded mesos/supercells are possible and even a brief tornado. The purple region indicates general t-storm risk area and green shows where I think rotating storms are possible along with a brief tornado risk. Green region includes Brandon, MB, Moosomin, SK, Estevan, KS.

For comparison sake, here is the GFS sfc forecast for the same period, it is very similar to the GEM thus I'll just show the GFS forecast. This this were to verrify with the frontal postion then Winnipeg and Portage La Prairie would also be included within the green region and the lake breezes would become more of a facotor with possible additional initiation ahead of the main line.

We currently have a pretty deep trough bringing some severe storms to the central portions of Alberta, is this same system that forecast to push into Saskatchewan tomorrow which will bring another severe weather risk to the province. Starting at the upper levels we have a relatively strong 500 mb low that will be ejecting into northern AB with a strong wind max ejecting around the base of the low into SK. Along with that there is a 120-135 kt jet core that will also be ejecting into the southern to central portions of SK. There is some discrepancy among models as to where the exact positioning of these upper features will be located but in the grand scheme of things that should not affect the overall setup. There will still be ample upper level divergence, but there is some agreement on where the main diffluent region will be in eastern SK which will help things along.

Moving down to 850 mb we can see there will be a relatively strong 850 mb LLJ which is forecast to strengthen through the evening and overnight hours which will help with overall low level shear values. At the moment the 12Z data indicates sfc to 850 mb shear values to be somewhere within the 20-40 kt range which is suitable for good low level rotation along with 30-50 kt of sfc-500 mb shear. Based on the upper level winds there is no shortage of shear.

At the surface there is currently a cold front tracking across AB which will begin to push its way through N'rn SK along with a dryline in the southern portion through tomorrow. It is this dryline that will be the main focus for storms tomorrow afternoon. The stronger 500 mb flow will alow for the dryline to surge this far west. Ahead of the cold front CAPE values are forecast to reach extreme values between 3000-4000 J/kg with the GEM even going as high as ~4400J/kg in the Regina region. But examining forecast soundings do reveal on problem for any storms that fire (see sounding above), and that is a very large layer of dry air aloft and a titanium CAP. Looking at the CAP forecast field we can see a weakness within the CAP right along and near the dryline but ahead of it within the real good air the CAP is extremely strong. All factors considered I still think there is the risk for some storms but they are likely going to be extreme isolated and relatively short lived. Given that air aloft is so dry once the ambient moisture is used my primary storms, they will likely choke off and die. Thus I believe there will be the risk of some very isolated supercells with initiation between 2-4 pm CST near Regina and a few storms along the cold front in NW'rn SK some could be severe. But feel as though LCL heights will limit the tornado threat even with the amount of streamwise vorticity within forecast soundings. Current convective models do indicate though the areas from Mellville northward will be more favourable for longer lasting storms with more surface based convection. Some major cities in the pink region are Regina, Moose Jaw, Weyburn, Estevan, and Yorkton.

And if you think I'm crazy saying there is a dryline there here is NAM 30mb mean due points and sfc streamlines:

There will be a pretty substantial risk today in southern Alberta for a few supercells this afternoon. Watervapour imagery this afternoon (first image) shows a pretty large trough that is forecast to push into AB this afternoon, and has in fact began to do so as I’m writing this. This trough will begin to develop a low within the southern portion of the province where a warm front will begin to push northwards along with a weak cold front and stationary boundary setting up along the foothills (second image). The air along this boundary is forecast to see SBCAPE values well into the 1500-2000 J/kg range with up to 2500+ J/kg south of the warm front. Bulk shear values within the region are forecast to be 35-40 kt with 40-50 kt (third image) near the Medicine Hat region and forecast hodographs do indicate low level veering of the winds but mainly within a shallow layer. Thus there appears to be a broad risk are for convection (purple) but the pink region is where I think the greatest chance for supercells are. This region includes Calgary, south along QE2 to Lethbridge and region just to the west of the QE2, and over to Medicine Hat. The Medicine Hat region is lowest probability at the moment since there is a pretty strong CAP in place and storms may struggle some to get going. On top of that shear vectors more parallel to the warm front would suggest very messy type convection here. Furthermore forecast soundings in the region show that storms in this region will be rather elevated and thus render more of a strong damaging wind threat with some large hail.

The QE2 corridor from Lethbridge to Calgary is of peak interest this afternoon. Storms are forecast to fire along the foothills this afternoon, and satellite imagery is already indicating pretty decent cumulus development as that trough surges eastward. The strongly backed winds along with the veered wind profiles plus amble instability will likely be enough to get supercells. Veered profiles aren’t very deep but are such in the lowest levels that a brief tornado is possible. I expect storms will initiate within the next 2-3 hours with the most dangerous region being from Calgary-Lethbridge and along the QE2 corridor.