Friday May 17 & May 18 Chase Forecasts
Thursday, May 16, 2013 at 11:55 PM Next two days look to be coming together well and will focus on these days in the discussion here as a few long days on the road have me tired. First looking at the 500 mb flow for tomorrow afternoon there is some more appreciable flow come into the central/high planes with the main center of vorticity just west of the 4 Corners region. Not ideal but can still make for enough large scale ascent to get some cyclogenisis going. The 500 mb chart below shows better flow over the westerns portion of SD but what has my eye is the KS/NE border region:
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.
Chase Day 1 & D2 Prospect
Tuesday, May 14, 2013 at 1:15 PM We got back on the road today heading southwest out of Eureka, MO heading to Norman, OK for this evening to get into good position for our chase on Wednesday. After a quick analysis of the NAM/GEM and 00Z GFS things are looking a little more interesting for tomorrow. Both the GEM/NAM look to have a secondary shortwave which looks to pivot around the back main bit of subtropical energy that is pushing into western TX/OK. You can see it pushing into the extreme southwest corner of OK. (will only post links to images to keep data usage low):
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.
In support of this we have great Sfc-500 mb bulk shear into the Childress area:
And 850 winds show a descent LLJ pushing northward with not incredibly high but sufficient moisture within the 850 inflow.
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.
Chase 2013 Outlook: Some Prospects on the horizon
Friday, May 10, 2013 at 10:47 PM As our chase trip approaches, things are gradually starting look up. Although forecast models have been taking us on a roller coaster ride over the past few weeks, I am glad to see some consistency starting to break through between various model runs and between individual models. As it stands we are looking to depart on Monday May 13 to try and see what could come of a long shot setup but possibly some TX Panhandle magic into western OK. Although flow aloft is not ideal, CAP looks to be breakable and there may be a combination of some dryline forcing along with gradual upslope flow into the Panhandle. See images below. On top of that storm motion will likely be to the SW which was similar to the May 29, 2012 setup in western OK where gorilla hail was dropped in the Peidmont, OK region. I’m not convinced something of significance will come of it, but with the limited time we have I think we will chance it. I will also note that the ECMWF is also on par with this setup with a minor risk, but again cannot post the graphics from Accuweather Pro site so you will have to take my word for it.
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.
My 2013 Chase Season Outlook: Not all doom and gloom
Friday, May 3, 2013 at 6:46 PM Where are all the tornadoes this season? Well the answer to that in the short term is the awful dual (both eastern and western) rex blocking pattern setting up with an eastern and western cutoff lows forecast to develop over the coming days. The first image below is this morning’s 500 mb analysis which has the two areas forecast to transition to cutoff lows in the next few days. The second image is the NAM 500 mb forecast for May 5 which shows the two cutoff lows (circled in red). This pattern is not conducive to tornadoes as the eastern low and recent cold front passage has essentially shut down the Gulf not allowing for any moisture to surge into the planes as well as placing a stagnant upper flow which does not produce the needed wind shear for supercell storms and tornadoes.
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.
July 4, 2012 T-Strom Risk
Wednesday, July 4, 2012 at 12:11 PM 
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.