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

The reason why the KS/NE border region has my attention has to do with the surface features setting up in the region. The surface chart below shows surface winds and moisture. We can see that the wind shift along the KS/NE border is indicative of a warm front setting up and there is a dryline bulge in the extreme NW corner of NE. These two regions of lift along with the backing sfc winds and increasing 850 LLJ pushing into the evening hours have me hopeful that there could be some storm development. Capping may be issue as well but forcing looks to be sufficient to overcome it late in the day. I will point out that the GFS is in the same general ballpark as the NAM, see second image.

Assessing the the 4 km NAM precipitation model clearly the KS/NE border region looks to break out but the western SD region does as well, likely in response to the stronger flow aloft. I have m doubts that moisture will make it that far north and storms may not pack the punch the 4km NAM seems to show. I am also keeping an eye on storms that may fire near the Ogallala, NE region as well, which look to fire along the dryline. There is no real evidence of a good push east of the dry line here thus these do have me wondering as well. But based on the analysis setting up in Valentine, NE to keep southern SD in play (near Mission) and southern, NE in play and keeping with the favoured target near the dryline/warm front intersect seems like a good compromise for now. Other factors influencing this are CAPE values of 2000-2500 J/kg possible and sfc-500mb bulk shear of 30-40 kt. Timing is a little late as per the forecast below but the 20-23 UTC time frame will likely see storms going.

Looking at Saturday May 15, I’m going to analyze the NAM very briefly. The reason why is mostly because I don’t agree with where the GFS is placing the surface low. Given that the base of the 500 mb trough is digging down into TX with stronger divergence over the west KS region, I feel that cyclogenisis near the CO/KA border is the more likely scenario, which is also supported by the latest SREF and 12Z ECMWF. See the first image below. The GFS and GEM seem to favour a most elongated area of low pressure with the main low center into northern SD. This is a little concerning but I think that the NAM solution has the right idea.

That being said then there are several targets likely for this scenario. Along the warm front through NE and into SD, the triple point in northeastern CO and northwestern KA, and along the dryline from Colby to Dodge City, KS. Given the leading edge of the southern 500 mb jet is pushing into the Colby region and that region sits between the right entrance of the northern branch of the 250 mb jet and the left exit of the southern branch. I’m going to target the Colby, KS region for as a tentative target for now.  

http://www.twisterdata.com/index.php?prog=forecast&model=NAM&grid=221&model_yyyy=2013&model_mm=05&model_dd=14&model_init_hh=12&fhour=36&parameter=RELV&level=500&unit=MB&maximize=n&mode=singlemap&sounding=n&output=image&view=large&archive=false

This bit of energy is looking to promote some cyclogenisis into the TX Panhandle region allowing for a dry line surge eastwards. The image below shows a weak dryline push to the southwest of the Childress, TX region. I know it isn’t very strong but the southeasterly surface winds and gradual upslope in combination with the large scale ascent from the upper low may just be enough to get things going. On top of that, there could be some outflow boundaries pushing back to the west from ongoing convection in eastern TX.

http://www.twisterdata.com/index.php?prog=forecast&model=NAM&grid=221&model_yyyy=2013&model_mm=05&model_dd=14&model_init_hh=12&fhour=36&parameter=DPTF&level=2&unit=M_ABOVE_GROUND&maximize=n&mode=singlemap&sounding=n&output=image&view=large&archive=false

In support of this we have great Sfc-500 mb bulk shear into the Childress area:

http://www.twisterdata.com/index.php?prog=forecast&model=NAM&grid=221&model_yyyy=2013&model_mm=05&model_dd=14&model_init_hh=12&fhour=36&parameter=SHRM&level=500&unit=MB&maximize=n&mode=singlemap&sounding=n&output=image&view=large&archive=false

And 850 winds show a descent LLJ pushing northward with not incredibly high but sufficient moisture within the 850 inflow.

http://www.twisterdata.com/index.php?prog=forecast&model=NAM&grid=221&model_yyyy=2013&model_mm=05&model_dd=14&model_init_hh=12&fhour=36&parameter=DPTC&level=850&unit=MB&maximize=n&mode=singlemap&sounding=n&output=image&view=large&archive=false

Storms will likely be moving relatively slow with a southwest storm motion. The weaker flow aloft may prevent some venting and thus HP storms or even updrafts being undercut by storm outflow is a cause for concern, but were here now and will give it a go. But needless to say looks like the Childress, TX may be a good tentative target, where the GFS/GEM look to want to fire off the dryline into west OK, will wait to see what 00Z data shows and progression of subtropical energy.

As for our day 2, based on the forecast, we can see sufficient flow from about the OK Panhandle up into northwestern KS and then even into northwestern NB. This does cause concern as the NB region looks to have the better flow aloft but at the same time looks unlikely that sufficient moisture will make it that far north. So for now will keep the CO/KS /OK border regions the prospect for D2 with a close eye on how NB will pan out...Might have to make a long haul.

http://www.twisterdata.com/index.php?prog=forecast&model=NAM&grid=221&model_yyyy=2013&model_mm=05&model_dd=14&model_init_hh=12&fhour=60&parameter=WSPD&level=500&unit=MB&maximize=n&mode=singlemap&sounding=n&output=image&view=large&archive=false

After that the May 17 through to May 21 could be an active period through the Central planes. May 17 and 18 looks a little on the fence as capping could be an issue but there will be some potential for some upslope storms in CO and maybe a bit of dryline action in the OK Panhandle on the 17 and some dryline action possible in west KS or maybe even NB on the 18. Again concerns being capping and the 500 mb chart below shows a pretty good ridge over the most of the region on both days. But moisture return will likely be sufficient and with westerly flow aloft divergence should be sufficient as well, although little weaker on May 18.

After this looks like what could be the better bit of action picks up on May 19 as the trough ejects just east of the 4 Corners region, as shown below on 500 mb chart. Sfc moisture return here will likely be decent with the deeper trough setting in and the sfc chart below shows dryline potential in northwest OK and southwest KS, and possibly some action in the vicinity of the warm front along the KS/NB border. After this the trough is relatively slow moving which would give way to another potential chase in central OK on May 20 and the ECMWF continues to dig the trough south giving another possible chase day in the TX/OK border region on May 21, but will play this by year. At this point I am just happy to see the models pick up on some good chase prospects.

That being said the May 19 setup is also reinforced by the ensembles, namely the GEFS and NAFES, as well as the ECMWF ensemble mean. The firs image shows the GEFS ensemble means, the trough is not as deep as the operational run and that is because some members do show some ridging in place, thus a little concerning still but like that at least the mean shows a trough pattern. The NAFES is a little more aggressive showing a slightly deeper trough but the tilt is a little on the positive side thus signaling questionable moisture return and capping issue. But at this point, as in my previous post, there is optimism here and hope that the latter part of May will become a little more active.

One of the main reasons for this blocking pattern and split flow regime can be attributed to the PNA index (Pacific North American Pattern). Simply but it describes the state of the Aleutian low which is a semi-permanent feature in the North Pacific. Ideally we would like to see this index in the negative which promotes western trough pattern, but is currently positive and is forecast to remain so into the middle parts of May, as seen in the graphic below from the climate prediction center. This positive phase usually means split flow pattern and western ridge (i.e. the current pattern).

There is however some relief in sight possibly in the May 8-10 time frame as the western cutoff low ejects eastward and brings along with it a descent amount of energy as seen by the area of enhanced winds through south central Texas and southern Oklahoma at 500 mb as shown below (GFS 500 mb forecast for evening of May 9)

Along with this pattern develops a weak surface low into southwest Kansas and promotes a good return of Gulf moisture with a dryline ejecting westward into TX panhandle along the OK border. On the plus side to, the upper level flow pattern will also promote a good amount shear thus making for a favorable supercell environment. The images on the left shows surface winds and moisture return to the planes, and the one on the right is the surface to 500 mb bulk shear. Unfortunately the ECMWF is not as optimistic with the setup and still continues to show no moisture return from the gulf and a lower amplitude upper trough. Also, we will not be able to make this setup as we still have work commitments and Dayna needs some dental work done.

After this period looks like things shut down once again as a ridge pattern takes hold again which is indicated by pretty much all key models here being the GFS/GEFS ensemble/NAEFS/ECMWF opp run and ensemble mean. But not all is lost here, and for time sake I will jump over a little bit of detail. But from May 15 onward things begin to look encouraging among the GFS operational model/GEFS and NAEFS ensemble. Below is the last panel of the GFS operational run form 12Z today and the area circled is of interested to me as it shows an area of substantial energy out over the Pacific and has been signaling so over the past couple days now. Although the current ridge over the west may be discouraging the energy pushing east I believe may be the turnaround come the latter part of May.

Even more encouraging about this trend is both the GEFS ensemble mean and NAEFS ensemble (shown below in respective order) have also continued with the increased energy over the Pacific tracking eastward. What I find a little more encouraging still is that both the ensembles show a persistent western trough and have continued to show increased Pacific energy tracking eastward. The one caveat is the western trough shown does not have a favorable orientation, but at this point I will take it.

Now the new Monthly ECMWF came out and through mid-May it looks rather disorganized and sloppy but after May 20 it gets pretty active. The one downside is that it looks to keep things in the mid to high planes region which would greatly have moisture issues and the other is into June it hints to want to really get some western trough. The new ECMWF ensemble control run on the other hand paints a very good picture from May 15 onward with a few good prospects and from May 18 onward begins to show a very deep trough begin to dig in near the 4 corners region. Now you will have to take my word on this since I used the Accuweather Pro site to look at the ECMWF data and they do not allow the images or links to be posted. So I can say with some amount of certainty that the early part of May will be pretty inactive, with a few obscure events possible, but from May 15 onward I believe things will take turn to a more active pattern. Here’s hoping.

Looks like three areas of concern for today, and those region are circled above green the weakest, yellow stronger storms, and red the area where the worst of the storms will be today. Starting in SW'rn ON, there is un upper level vorticity maxima currently near the Sault Ste. Marie region tracking southward. This upper disturbance along with the frontal boundary will make for a few thunderstorms this afternoon. CAPE values look high enough for some storms to reach sever limits with soundings supporting some strong straight line winds and LCL's look to be a little elevated.

Area from Kingston up to Quebec city looks pretty good with the main upper jet passing through the warm sector which should provide some extra kick to the system. Shear vectors are oriented as such that isolated updrafts will be supported and low level shear looks to be supportive of a few supercells. Hodographs are indicating though mostly splitting modes and thus not likely no real organized supercells will get going. CAPES are high enough though to provide a good hail risk and chance for some strong winds and likely see some severe storms through the Ottawa, Cornwall areas and down into Kingston.

The greatest risk for today is in NW'rn ON from Fort Francis across to the Lake Superior shore line. Here strong upper level jet and low level flow and moisture will provide enough fuel for strong thunderstorms. Some of which a on going through the MB area. All parameters here looks to support strong thunderstorms with the risk of some large hail, winds, and even an isolated tornado is possible. The greatest tornado threat is in the MN but regions right along the U.S. border (as outlined above) cannot rule out the risk of a brief tornado.

The low is currently located near Charron Lake, MB just west of the elbow of Ontario. From here a warm front extends across northern Ontario currently in Pickle Lake and across to Kapuskasing and Timmins. The cold front is currently sitting right along the MB/ON borders from Charron Lake and extends down into MN along the ND and SD borders. As the low and wave progress ENE through today, the cold front as well as regions near the low centre will see thunderstorms develop throughout today and into the evening. The NAM/WRF surface forecast here shows the wave does not progress much during the day but does begin to surge ENE through the overnight period. Therefore there is a dual wave that develops overnight with the primary wave in ON and a secondary cold front in southern MB. With MLCAPES forecast to be between 2000 - 2500 J/KG in northwestern ON and between 400-600 J/KG in central MB there will be two primary areas for thunderstorms development. 1. The Interlake region in MB where heavy downpours and large hail are the main threat. 2. In northwestern ON where regions along the the cold front (from Fort Frances across to Thunder Bay and up to Big Trout Lake) where weakly veered hodographs and shear vectors parallel to the cold front will make for fast moving splitting cells with some supercells in the area. Also regions along the warm front will see some convection as well where hail and heavy downpours are the main threat. As the 850 mb low level jet strengthens this evening expect storms to increase in intensity and thus bringing in the threat of a few isolated tornadoes. The largest threat for tornadoes looks the be in the region outlined by Sandy Lake, south to Goose Lake, then east to Pipestone River Provincial Park. The peak tornado threat will be between 8 pm and 2 am local time. Storms that do initiate will progress NE at about 30 to 50 knots and continue through the overnight period, but gradually decrease in strength as they push NE.

Starting aloft however for tomorrow, models (NAM-WRF/GEM/GFS) agree on a strong 250 mb jet nosing into the southeastern SK and southwestern MB through the afternoon/evening period and again at 500 mb same group of models indicating a strong jet axis into extreme southeaster SK and southwestern MB. Because of this scenario we end up with a deepening vorticity maxima aloft and enhanced large scale ascent across much of the prairies.

But this causes some issues now near the surface. With this rapidly deepening upper low, the surface low will occlude at a much faster pace thus leaving the possibility of having the warm sector pinched off before it even reaches the border. If this is the case then tomorrows severe weather potential goes virtually to 0. Current guidance however still indicates a warm front should extend from Winnipeg across to the ON/MN border just south of Thunder Bay. A cold front will extend from Winnipeg down through east central ND, into northwestern SD, and into northern CO. A trowal will then extend from Winnipeg up into north central SK around Prince Albert National park. The analysis was derived from the NAM/WRF 00Z surface forecast for Sunday June 10 (or the afternoon of June 9). Thus the southeastern corner of MB from Winnipeg to Kenora, ON and across the warm front boundary, a well as the portion of SK and MB which sit along the trowal are the focus areas for severe convective weather tomorrow afternoon. Note that both the GEM/GFS do have the triple point slightly north and west of the NAM/WRF, but given the rapid intensification of the upper low and vorticity center, I prefer the NAM/WRF solution here.

That being said, a quick look at the 500 mb chart above shows a ridge axis through eastern MB thus which may lead to some capping issues. Given 700 mb temps and CIN forecast, the cap will be breakable more the extreme southeastern portion of MB. Along the trowal however there is virtually no cap present, with 700 mb temperatures around the 3 to -1 degree C mark, thus there is a stronger potential for more vigorous convection with an even greater hail threat, but at the same time will make for a convective mess. Because of this there appears to be two regions of interest for strong tornadic thunderstorms tomorrow. A look at 850 mb flow and MLCAPE forecast will help reinforce the reasoning behind why this is. There are two main axis of strong low level flow indicated on the 850 mb forecast, the obvious axis through southeastern MB/northwester ON and the secondary axis through east central SK. The axis through SK appears to be a result of a secondary low spinning up along the trowal in response to strong cyclonic shear due to the 250+500 mb jets. In both areas forecast soundings indicate strongly veered hodographs thus rendering both the warm sector and areas along the trowal conducive to tornadoes. Thus two areas of focus for tomorrow where people should be aware and on the look out for severe weather: 1. Southern MB from Brandon across to northwestern ON along the Trans Canada and south along hwy 71. 2. From Portage la Prairie along hwy 16 northwest to Yorkton, SK and up to north-central SK to area east of Prince Albert National Park. Areas which I believe the most conducive to tornadoes are the Steinbach, MB area and regions just east of the Prince Albert National Park. Along with the tornadic threat is a large hail threat where greater than golf ball sized hail is possible for southeastern MB and up to golf ball sized hail possible for region in north central SK. Keep in mind however, these are regions I feel the worst could happen and that most of the people in MB and eastern SK need to be alert tomorrow since the entire region is prone to severe convective weather. That includes strong straightline winds, large hail, and tornadoes.

Today we blew off the risk in southeastern Texas as we would have to race the rapidly progressing gust front spit out by the MCS that plowed trough Kansas and Oklahoma last night. With shear parameters and the setup it was not worth chasing a linear mess and follow the front all the way to the Gulf. May 30th's chase turned out for the better as we were able to get on a rapidly intensifying supercell just northwest of Guthrie, TX. It popped up behind the main line and we suspect it initiated by the convergence along the outflow boundary from a large supercell to its southeast and the dryline. The inflow was nuts and had us driving through blinding dust storms as we tried to race ahead of it. Still unsure if it produced a tornado due to all the dust obscuring out view but it dropped some massive hail near Guthrie that we were able to play with after.

June 1, 2012 Forecast

Tomorrow looks to be marginal right now but if CAPE values can get up into the 3000 j/kg range we may be in business. Aloft the flow is marginal but is still on the lower end of what is suitable for severe thunderstorm development. The one down side is that we will once again be dealing with a northwest flow, but I'm not complaining since it has been producing for us this season. What I'm interested in as the 500 mb wind maxima shown here for tomorrow afternoon which is rounding the base of the main jet axis into the northeast portion of the Texas Panhandle. As this feature round the Rockies there should be some mesoscale stretching which could lead to enhanced vorticity and weak lee cyclogensis. 

Low level flow, particularly at the 850 mb level is pretty weak until about 00Z in through the northeast Panhandle region but by 03Z and around sunset the  low level flow should strengthen sufficiently to enhance low level shear. It is for this reason that the large CAPE will be needed, to be able to tap into the minimal shear initially close to initiation along stationary boundary between weak lee cyclone in eastern New Mexico and outflow from ridge sitting in southwestern MO. The resulting stationary boundary will extend from Wichita Fall, TX up to Amarillo then into northeastern NM will be the trigger for initiation as seen below. The CAPE maxima looks to establish itself in the vicinity of this boundary thus peaking my confidence that there should be supercell modes, this is further reinforced by veered hodographs in the vicinity of the boundary. Later in the evening as upper impulse strengthens and MCS should develop. The NAM/WRF and 4 km WRF precip models both indicate a precip maxima in the northeast portion for the Texas Panhandle with the 4 km WRF precip model keeping isolated supercells by 00Z with moderately rotating updrafts, as shown in the final image. Thus target for tomorrow Pampa, TX.