Thunderwear recommended

Update: 4:20 pm. Severe storm warnings are now posted for southwest Cass, all of Crow Wing county (including Brainerd) and Kandiyohi county for large hail and potentially damaging winds over 60 mph. 1″ diameter (quarter-size) hail is being reported with some of these storms, there is a potential for hail as large as golf balls, large enough to damage roof tiles and ding automobile surfaces. Although conditions are marginal we can’t even rule out an isolated tornado somewhere in central or southern Minnesota through the early evening hours – no way to pinpoint precisely where a tornado might form, but there is a small risk. St. Cloud may see strong/severe storms between 4:45 and 6:00 pm, storms rumbling into the Twin Cities after 6:00 or so. Stay alert and be ready to hit the basement, or a small windowless room on the ground floor (away from outer walls and windows) if warnings are issued for your county. If the sky turns threatening DO NOT WAIT for sirens to sound or warnings to be issued for you to take action. Rely on good old fashioned common sense. Today will be the wettest, stormiest day for the next week. Dry weather prevails Wednesday through next Tuesday morning, unusually cool weather by Thursday giving way to a slow weekend warming trend as 80 returns Saturday and Sunday.

Update: 1:40 pm. Doppler Radar shows a line of intense thunderstorms developing rapidly well north and west of the Twin Cities metro. There is evidence of 3/4″ diameter hail in some of these storms near Wadena and Alexandria. If hail reaches 1″ in diameter (roughly quarter-size) warnings will be issued for specific counties acrdoss Minnesota, which is increasingly likely between 3 and 6 pm. Most of us will just see a heavy thunderstorm and gusty winds; a tiny percentage of the region may experience large, damaging, (ping pong-size) hail, wind gusts over 70 mph, even an isolated tornado can’t be ruled out in this moist, unstable, highly sheared environment. Stay alert and be ready to move to a safe place if warnings are issued for your county.

 

Update: 9:30 am. Doppler Radar out of the Twin Cities shows a large smudge of moderate/heavy rain tracking northeastward across central Minnesota. This weakening MCS, or “meso-convective system” is moving slowly, dropping significant rain in its wake. Some .50 to .75″ amounts are possible, a badly needed soaking for farms across central Minnesota. It looks like the heaviest rains may stay north of the Twin Cities, now in a moderate/severe drought. The environment remains ripe for isolated severe storms later today. The greatest risk: between 3 and 7 pm. Stay alert and check in often for possible watches and warnings.

 

Monday Almanac for the Twin Cities. High: 82, Low: 60. Precipitation: 0″ (35 degree low at International Falls!)

I’m starting to wonder if this is a sign of Minnesota summers-to-come. It’s always dangerous (and usually short-sighted) taking a current pattern and projecting it out – indefinitely – into the future, without some very strong science to back it up. Some of the perennial skeptics, the climate-change deniers, point out that global temperatures have cooled since 1998. That’s a distortion of the truth. It’s true that temperatures, worldwide, peaked during 1998, during an especially severe El Nino warming of the Pacific that had a domino effect around the planet. Nothing in nature ever progresses on a perfect straight line. There are always zigs and zags, ups and downs – the important question: what is the true trend? In spite of monthly and yearly aberrations, the “noise” in the atmosphere, what are global temperatures really doing? The graph below shows global temperatures (measured by satellite, land-based thermometers and ship reports) and the trend is still pretty hard to dispute, in spite of the fact that temperatures did, in fact, peak around 1998, and we’ve experience a few cooler years since 2007. Yes, the sun may be a factor (I don’t think the final verdict is in there) and I’m keeping an open mind, hoping deep down that anthropogenic (man-made) greenhouse gas releases aren’t the only factor. But so far I haven’t seen any reputable, peer-reviewed science on a large scale that would cause me to doubt that the warming we’re seeing in the global data isn’t “real”.

Greenhouse gases have spiked 38% since 1800 (no dispute about this) and to think, rationally, this won’t have any impact on temperature, is naive and short-sighted. Actions (usually) have consequences. To pretend otherwise is illogical, and potentially dangerous for future generations who may judge us fairly harshly. This is the greatest of global challenges: a slow-motion transformation with worldwide consequences, no easy solutions, requiring international agreements that require political compromise and changes in business and energy generation that won’t pay immediate dividends. There is no instant, capitalistic return-on-investment, and in a fast-paced business world more concerned about next quarter’s profitability it requires a level of faith and commitment that’s pretty rare these days. Climate change, not health care, may become the dreaded “third rail” of politics. We’ll soon see if our elected representatives (specifically the Senate) are up to the task.

Today will be unsettled with more clouds streaking overhead, and a growing risk/opportunity of bumping into something thundery and wet as the day goes on. Not all of the ingredients are present for a widespread severe weather outbreak, but there may be just enough moisture and instability for rising thermals of warm air to break through a weak inversion “cap”, accelerating upward into flat-topped, anvil-capped cumulonimbus thunderstorms. The entire state is under a “slight risk” of isolated severe storms.

Station ID: KMSP Lat: 44.88 Long: -93.22
NAM Model Run: 0Z JUL 14, 2009

Forecast Hours: 0hr 6hr 12hr 18hr 24hr 30hr 36hr
Sfc Prs(mb): 987.2 988.2 985.5 982.2 978.3 978.2 978.7
Mean SLP (mb): 1016.7 1017.8 1015.5 1011.5 1007.5 1007.5 1008.4
2m agl Tmp (F): 76.9 62.6 64.8 74.2 69.5 69.2 66.4
2m agl Dewpt(F): 46.6 47.2 50.2 63.9 67.2 68.7 64.6
2m agl RH (%): 33 56 58 69 92 98 94
10m agl Dir: 102 121 147 168 145 200 273
10m agl Spd(kt): 4 7 11 15 16 8 10
6hr Precip (in): 0.00 0.00 0.00 0.02 0.40 0.04 0.00
AccumPrecip(in): 0.00 0.00 0.00 0.02 0.43 0.47 0.47
Sfc CAPE (J/kg): 0.0 0.0 0.0 0.6 44.6 838.8 89.3
Sfc CINH (J/kg): -0.5 0.0 -0.6 -13.9 -14.3 -51.2 -160.7
0-3km Hel(J/kg): 90.2 143.3 181.8 221.1 541.5 194.2 81.8


NAM model run from Monday evening, with a 24 hour prediction showing a high “helicity” value for 7 pm this evening (541.5) suggesting strong wind shear aloft, enough to get a few isolated thunderstorms “spinning”, which may in turn lead to large hail, even an isolated tornado.


Meteorologists looks at many factors when gauging the risk of severe weather, including something called “helicity”, which is the potential for thunderstorms to spin, rotate. This is what Doppler Radar does so well: it detects mutating thunderstorms that spin; these are the (rare) storms most likely to sustain warm updrafts over the course of many hours. Usually a thunderstorm self-destructs, rain and hail-cooled air snuffs out the warm updraft and the storm fizzles. But when there is considerable “wind shear” (changing wind speed and direction with altitude) thunderstorms can spin, in essence protecting the warm updraft, sustaining a storm over the span of many hours, generating enough “vorticity” (spinning energy) to spin up nature’s most violent updraft: the tornado. Large hail is often a strong tip-off that a storm updraft may be severe enough to spin up a tornado. Anything larger than golfball-size gets my attention. Most tornadoes are usually preceded by a few minutes of large hail. Skies often brighten, rain and hail tapers, it almost looks like the storm is over, but then, at the rear of the storm, in the southwestern quadrant, a rotating “wall cloud” lowers to the ground. It’s here that a tornado is most likely to form, at the tail-end of a hail-producing, rotating thunderstorm.

Amazing file photo of a dramatic wall cloud, with obvious strong rotation. Here is where a tornado is most likely to form.

One of the problems with Doppler Radar: only 20-30% of all spinning thunderstorms go on to spawn a tornado; it’s almost impossible to determine WHICH rotating storms will go on to drop a tornado, so as a result the NWS tends to over-warn when it comes to tornadoes. Many times they’ll issue a warning based on just Doppler returns. Their confidence level goes up dramatically if they receive confirmation from professional storm spotters on the ground, specially-trained SKYWARN spotters who communicate in to local Civil Defense and National Weather Service employees. It’s great to have Doppler data, but only a human being, literally out in the field, can CONFIRM that a given, spinning storm is actually giving birth to a deadly tornado. BTW the NWS is always looking for more SKYWARN spotters – they give special classes and if you have a strong interest in weather and want to volunteer in your community you should look into it. It’s a great group of people (all weather fanatics!) and these men and women are on the front-line, the eyes and ears of the National Weather Service, an integral part of the warning process that saves so many lives every year.


To go to SKYWARN’s local home page and learn more about the organization and upcoming classes click here.

Latest SPC Outlook for Tuesday. There is a 30% probability of severe weather (1″ diameter, quarter-size hail and/or wind gusts > 58 mph) within 25 miles of any location within the red hashed area.

WRF/NMM Model Output for 7 pm this evening. The models can’t detect individual thunderstorms or even delineate precisely where bands of storms will set up. In this kind of a convective, showery pattern some towns/farms may pick up as much as 1″ of rain, while 5 miles away nearby neighborhoods see little more than .05″ of precipitation. As an average I think many of us will see anywhere from .20 to .35″ of rain later today and early tonight.

500 MB Winds for 7 pm Monday evening. This graphic shows wind speeds roughly 18,000 feet above the ground, outlining the “jet stream” (shaded in green). The yellow regions show the fastest winds within the jet core, what meteorologists refer to as “speed maxes”. One of these speed maxes passing overhead can create an environment where storms are more likely to ignite late in the day. Overall this is a pattern more typical of mid or late September than mid July, the jet core some 200-400 miles farther south than usual for mid summer. Why? Great question – wish I had a great answer.

No comments yet

Leave a Reply