A day after a devastating EF-3 tornado struck several communities in northeast Montana, parts of Minnesota and Wisconsin have been experiencing yet another round of rough weather.  Damaging wing reports have been widespread this afternoon and evening for areas north of Minneapolis and in Wisconsin in the Michigan Upper Peninsula border region; this is perhaps a welcomed blessing on a day that looked to be ripe with tornadic potential earlier on. A number of Minnesota-based chasers have been streaming this live today, and will continue to do so as storms continue into the overnight.

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A long-track tornadic supercell moved across extreme northeast Montana yesterday evening, producing several tornadoes across this sparsely populated wheat country.  Sadly, two fatalities were reported west of Reserve, MT in Sheridan County from one particularly large and violent tornado produced by this storm.  Initially, two supercells developed around 23z in the vicinity of a triple point near the Saskatchewan Border, with the eastern storm becoming dominant later on as a dryline feature surged east along and south of an E-W oriented warm front.  The first cell likely produced before being cut-off from the instability by the surging dryline and/or RFD from the intensifying eastern cell.  This complex surface pattern can be seen in the two radar images below, showing both cells at 5:38 pm MDT, and the dominant eastern cell after the western one evaporated by 7:11 pm MDT.

A large, violent tornado touched down at around 6:15 pm MDT several miles west of Reserve, MT, and was reportedly on the ground for over a half hour, causing significant damage west of town.  A damage survey is scheduled for data by Glasgow NWS, and I wouldn't be surprised if we have another EF4 on our hands this season.  If I didn't have a dissertation to finish, I likely would have started this chase just north of the border in SK, so likely would have missed everything if the border crossing took too long.  I would seriously give any of our best chases this season just to be on this supercell from yesterday.  I'm obsessed with these subtle, late-season setups!!!  Once I finally graduate tornadoes like these will never again go un-chased..

Despite strong southeasterly upper-level wind shear, Bonnie still made landfall in South Florida as a weak tropical storm with maximum sustained winds of 35 knots.  As seen in the IR image at left, most of the convection is north of the center of circulation, with only the most robust rain bands producing tropical storm-force winds.  Given the 30-50 knots of 300-200 mb flow above Bonnie and over the eastern Gulf of Mexico, there is very little convection to the southeast of the circulation, so conditions should improve rather quickly today over southeast FL...especially given the fairly quick forward speed of around 16 knots to the west-northwest.  The RUC analysis at left shows the strongly southeasterly shear between a strong antcyclone over the eastern U.S. and slow-moving upper-level low in the Gulf of Mexico that is currently ripping Bonnie apart, and will continue to do so when the center moves out over the Gulf.  This shear will prevent Bonnie from strengthening despite the warm ocean waters, and may even cause a weakening below tropical storm strength prior to landfall in southeast Louisiana early Sunday morning as indicated by a majority of the models.  Still though, the GFDL intensifies Bonnie to a moderate tropical storm strength after re-emergence over the Gulf of Mexico, with maximum sustained winds of 45 knots at landfall, especially to the north and northeast of the center given the expected continuance of southeasterly shear.  Therefore, the NHC has issued tropical storm warnings across southwest Florida for today, and from the extreme western Florida Panhandle through most of southeast Louisiana for Saturday night and early Sunday.  TVN storm chasers will likely be streaming live video of Bonnie at landfall (assuming everyone isn't in SD chasing the anticipated tornado outbreak), so be sure to check out the Live page over the next few days!

One month after the historic June 17th tornado outbreak ravaged the state, forecast models show an impressive combination of wind shear and high instability coming together over central and southern Minnesota late tomorrow afternoon, meaning the area could again endure another round of what has been an extended period of  tumultuous weather. A strong surface low is projected to develop over the west-central part of the state by mid-afternoon tomorrow, bringing south-southeasterly winds and moisture into central Minnesota by tomorrow evening. At the same time, a mid-level short-wave trough is expected to be entering the area, which, when combined with the high instability, will create a highly dynamic environment ripe for intense thunderstorm development. A few question marks remain with the forecast, one of those being how long storms will be able to remain discrete. Right now it would appear as though cells will fire over southwest Minnesota late tomorrow afternoon, then merge relatively quickly into a larger-scale complex. If this happens, the chances for tornadoes will diminish, but the threat for widespread extremely damaging winds will become a huge concern for areas of southern MN, including the Minneapolis metro area. However, if thunderstorms are able to remain discrete for any considerable amount of time, the threat for strong tornadoes will increase dramatically. Either way, residents should definitely remain alert to changing conditions tomorrow afternoon. The usual crew from Minnesota will be streaming live once again -- we're very fortunate to have such a dedicated group of chasers in the northern Plains this season! As with all of the live streamers, they play a critical role in helping the NWS and local media with the ground-truth they need to warn the public -- this in addition to allowing everyone else who can't chase see what's happening, of course!

A widespread severe weather outbreak is a near certainty this afternoon and evening over eastern MN into WI extending south into northern IA, as a strong trough strengthens even further to the northwest of the Great Lakes Region.  A 40-50 knot low-level jet will pump 70s dewpoints northward and contribute to strong low-level shear to the east of a cold front currently surging into western MN, and deep layer shear will be more than sufficient for supercells.  It looks like there will be a classic "bimodal" structure to the severe weather geography today, which means the strongest storms and highest chances for tornadoes typically reside in two areas - one to the north and one to the south.  Indepedent of Lakes Superior and northern Lake Michigan being a huge obstacle, I would probably chose the northern mode over northern WI into the eastern MN arrowhead, where low-level shear will be maximized and storm motions will be more perpendicular to the cold front allowing them to move off the boundary and into the favorable environment.  However, the heavily forested areas near the Great Lakes are very difficult chase terrains, so the southern mode over southeast MN into northeast IA might be the ideal target.  While the environment looks very favorable for tornadoes in the southern mode, the only concern I would have if chasing the southern target up there (the dissertation is destroying my late season storm chasing) would be an unfavorable southwest-to-northeast boundary orientation given a near-parallel storm motion, which could cause any supercells that form to merge and quickly become an outflow dominant MCS.  Nevertheless, it will be interesting to see how this severe weather event evolves, and to watch the live video from streamers in the field!  I'm definitely not used to watching potential tornado outbreaks from my home computer...NOT EASY!

A tornado watch is currently in effect for eastern North Dakota, extreme northern South Dakota and extreme western Minnesota as a large, potent trough makes its way into the northern Plains this afternoon. Initial convective development has been in the form of discrete storms, with a dominant storm moving slowly east-northeast from near Jamestown generally toward Fargo. Later this evening the storms are expected to become more clustered, and eventually grow into a MCS which would likely impact western Minnesota into early tomorrow. By tomorrow afternoon, intense discrete or quasi-discrete storms are expected across southern MN, northeast IA and western Wisconsin; wind shear is expected to be very strong in a moderately unstable environment, especially over western Wisconsin, so strong tornadoes and very large hail are of particular concern tomorrow afternoon. The northern Plains chasers will likely be out in force later today and especially tomorrow, so be sure to follow their chase by accessing the Live page!

A very large tornado watch has been issued for all of eastern ND ahead of a cold front marching through the Northern Plains, with a tornado warning just issued at around 4 pm CDT for Barnes County, ND as a cluster of HP supercells has been gatherning strength.  Conditions appear favorable for tornadoes, and especially large hail, for much of eastern ND this afternoon and evening as a 35-45 knot LLJ is punching north ahead of the advancing cold front co-located with extreme instability (3000-4000 J/kg CAPE).  The SPC has outlined much of eastern ND into northwest MN with a 10% area for tornadoes, and a "30 hatch" area for large damaging hail given how the warm sector has recovered today from earlier convection.  While the trend has been for clusters of HP storms, I wouldn't be surprised if this cluster went nuts as the afternoon progresses into evening, especially given the favorable environment feeding these supercells shown on the 21Z RUC analysis.  As seen here, the latest RUC analysis is showing a nose of 4-5 0-3 km EHIs feeding into the Barnes Co area associated with the LLJ nose, and an outflow boundary/warm front that could locally enhance the low-level wind shear for these storms to work with.  As this storm moves east, the RUC is showing the LLJ to strengthen toward 00z, and as we lose a little heating and the weak cells die out, I wouldn't be surprised if only a few dominant, tornado-producing, and relatively classic supercells remain.  Bill Doms and Eric Whitehill are currently streaming live video of these tornado-warned supercells (click here), so be sure to check out how these cells are materializing in real-time!

Hurricane Alex slammed the western Gulf Coast on June 30, officially making landfall as a category 2 storm along the central Tamaulipas, MX coastline. Areas to the north in extreme south Texas experienced hurricane winds and an impressive storm surge, captured in this incredible video by seasoned hurricane chasers Jeff Gammons and Jim Edds! Alex became the second most-powerful June hurricane on record -- perhaps a sign of things to come, as NOAA forecasters have predicted a highly-active hurricane season. Alex also caused major problems in eastern and central Mexico with it's inland progression, where several deaths were reported after an estimated 12-20" of rain fell.

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A fairly active severe weather pattern appears to be shaping up for the end of June and early July across the northern Plains of Montana, the Dakotas as well as across the Canadian border in Alberta, Saskatchewan and Manitoba, Canada. Supercells capable of tornadoes will be possible today (June 29) over extreme northern Montana into Alberta and Saskatchewan as a large trough digs into the northern Rockies, while a surface low is anticipated to take shape right on the MT/AB/SK border. Moderate to high instability should be able to build over this area tomorrow afternoon, with surface dewpoints possibly reaching into the mid to upper 60s well into northern SK by 00z tomorrow!  Severe thunderstorms should be expected over an area from Great Falls, MT to Edmonton, AB to Saskatoon, SK, with the best tornado potential appearing right along the AB-SK border late tomorrow evening. On Wednesday the threat will shift east into the Dakotas and Manitoba. We're also keeping an eye on the tropics, as Alex makes its way toward the Texas Gulf Coast; a number of live streamers will be active, so be sure to follow them on the Live page! 

A potent jet streak is currently passing over the Northern Plains, with a warm front extending from southeastern SD into southern MN, setting the stage for explosive supercell development over this area by peak heating. The latest RUC is showing 0-1 km EHIs of 7-8 along the warm front by 00z, which is likely a little over-estimated but still more than conducive for strong tornadoes.  CAPE values of 5000+ over this area as very high dewpoints pool along the boundary will result in intense updrafts and massive hail in persistent supercells.  All models are showing relatively early convective initiation by 20-21z, given the weak capping inversion, with elevated convection already marching through southeast SD toward the reservoir of strong instability.  The HRRR is showing multiple supercells along the warm front in southern MN by 00z, gradually morphing into a derecho and surging southeastward toward the Great Lakes Region.  The SPC has already issued a tornado watch from southeast SD into southern MN, with the discussion mentioning an elevated supercell currently just east of Huron, SD that is expected to become surface-based with a significant tornado threat developing as it tracks along the warm front into southern MN.  The greatest tornado threat will be between 21 and 00z as the low-level jet increases, but before the storms merge into an MCS.  I wouldn't be surprised there are over a dozen tornado reports this afternoon into evening...  TVN already has several live streaming teams in the field, so be sure to check out the Live Video page throughout the day! http://chase.tornadovideos.net/pages/full_screen

Quelle: TornadoVideos.net