Issued at 1:04 PM CDT, Tuesday, June 19th, 2012
-Visible satellite image from 1:15pm CDT: Warm front pretty much sits over the Twin Cities early This Afternoon. Hot, clear, and capped airmass south of the warm front. Elevated convection continues to form north of the boundary from Westcentral to Northeast Minnesota.
At 12pm low pressure of 998mb was over Southeast South Dakota with a well defined warm front extending east of that low through Southcentral Minnesota.
The atmosphere along and south of that warm front was already very unstable early This Afternoon with CAPE of 2000-3000 j/kg per meso-analysis.
Showers and thunderstorms have been developing all Morning and early Afternoon well north of the warm front across the Northern half of Minnesota as there is plenty of elevated instability to support thunderstorm development on the cool side of the warm front.
Short term model guidance continues to show numerous showers and thunderstorms affecting Northeast Minnesota and Northwest Wisconsin into Tonight. The models do differ somewhat as to where the heaviest corridor of rain will setup, but it appears that Central and Northern and Northeastern Minnesota have the best chance for excessive rainfall totals through Tonight.
-A tremendous amount of moisture will be available for a thunderstorm to tap into. Dewpoints in the 60s and 70s into Central-Eastern Minnesota with PWS from 1.50-2.00″ and 850mb dewpoints of around +16C. The strongest thunderstorms could easily put down a quick inch or two of rain, and if your area gets underneath training of storms for a few hours, rainfall totals could exceed 3-4″ by late Tonight. Flash flooding is a real concern in parts of the Northland.
-As I pointed out earlier, there should be no shortage of instability for thunderstorms Today and Tonight. CAPE of 1000-2500 j/kg should remain in place with Lifted Indices of -3 to -8C. Much of the instability in our area is expected to stay elevated though, as the warm front will likely stall out near Interstate 94 in Central Minnesota, or perhaps a tad more to the north. With the warm front staying just south of our area, the chance for surface based thunderstorms and tornadoes will be lower, although there’s still a potential that Crow Wing, Southern Aitkin, Pine, and Burnett Counties could get awfully close to the warm front by late This Afternoon/Evening…If that happens, then supercells and a chance of a tornado would increase.
-The amount of wind shear will be on the high side across the Northland with 0-6 KM Bulk Shear and Effective Bulk Shear of 30-50 knots. In addition, 1km Helicity will range from 150-350 m2/s2. This will certainly support a risk of elevated supercellular thunderstorms with a large hail and wind damage threat.
-People living in Northeast Minnesota and Northwest Wisconsin will want to monitor the weather Today and Tonight. Severe thunderstorm watches, warnings, and flood warnings may be issued at times by the National Weather Service.
-Remember a severe thunderstorm or tornado WATCH means conditions are favorable for severe thunderstorms in and close to the watch area. Go about your business, but keep an eye to the sky and have a way to be notified should a warning be issued.
-A warning means that severe weather is imminent or already occurring.
-When thunder roars get indoors!!!
*15z RAP model temperature forecast valid at 7pm This Evening. Notice the wind barbs, a good indicator of where the front will be This Evening. By looking at the winds, it would appear the warm front would make it into Central-Eastern Minnesota by early This Evening.
*15z 1km Helicity forecast valid for 7pm This Evening. 100-150 m2/s2 is usually enough to spin up tornadoes. This Evening we have values nearing 300 m2/s2 right along the warm front. The question is will the CAP break as 700mb temps will be in the +12 to +14C range in Central-Eastern Minnesota thru late This Afternoon…If the cap breaks, storms could explode near the warm front.
*Favorable mid level winds will be in place for storm organization. SW winds of 35-50 knots at 500mb.
*850mb winds are more from the S, so the wind direction changes with height, this could lead to rotating supercells This Afternoon and Evening.
*Tornado risk per Storm Prediction Center. These maps are for Today/Tonight.
*Large Hail potential
*Damaging Wind potential
*Watch and Warning map per National Weather Service Duluth, Minnesota.
Green=Flash Flood Watch
Orange=Severe Thunderstorm Warning
Tim
Canon T3 12.2MP Digital SLR Camera with 18-55mm f/3.5-5.6 IS II Lens –
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