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Severe Weather 101 – Severe Weather Awareness Week wrap up

Saturday, April 18th, 2015 8:30am MDT
Supercell thunderstorms like this can be beautiful - but they can also be deadly.  Do you know what to do when severe weather strikes?  (Stormscape Photography / FLICKR)

Supercell thunderstorms like this can be beautiful – but they can also be deadly. Do you know what to do when severe weather strikes? (Stormscape Photography / FLICKR)

Over the past week we have highlighted some of the severe weather hazards that we face in Colorado every spring and summer in our Severe Weather 101 series.  The dangers these present are significant and not to be taken lightly.

Tornadoes grab most of the headlines and certainly are a danger however others like lightning and flooding are more common and actually claim more lives.  We ask all of our readers to please, take the time to review these important articles – they could save yours and your family’s lives!

The National Weather Service has published a nice wrap up of Severe Weather Awareness Week that covers all the basics – see it below.  For more in depth information, please use the links at the bottom to view each article on our Severe Weather 101 series.  Be safe and be weatherwise!

PUBLIC INFORMATION STATEMENT
NATIONAL WEATHER SERVICE GRAND JUNCTION CO
600 AM MDT SAT APR 18 2015

SEVERE WEATHER AWARENESS WEEK IN REVIEW

Severe Weather Awareness Week in review…

Severe Weather Awareness Week in Colorado concludes today. During the past week we have presented information and safety rules for tornadoes, lightning and wildfires, floods and flash floods, straight-line thunderstorm winds, hail, and our warning programs.

We will now review some of the most important safety rules in our effort to build a Weather-Ready Nation.

Be weather-wise by staying informed on expected weather in your area. The National Weather Service is typically aware of the potential for severe weather many hours or even days before any severe weather watches or warnings are issued, providing forecast products to heighten your awareness. A Weather Story product is posted each day on National Weather Service Internet pages and Facebook pages which includes a map and text on possible hazardous weather expected within the next seven days.

A Hazardous Weather Outlook is also issued daily with information on possible hazardous weather through the next seven days. A watch is issued when conditions for severe weather or flooding become possible. A warning is then issued when life threatening conditions are imminent or occurring.

Tornadoes

Tornadoes can even strike in mountain areas.  In 2008 on August 23rd, this rope tornado struck Park County near Eleven Mile Reservoir.  Image courtesy Jerry Bivens.

Tornadoes can even strike in mountain areas. In 2008 on August 23rd, this rope tornado struck Park County near Eleven Mile Reservoir. Image courtesy Jerry Bivens.

The best way to protect yourself from tornadoes is to have a plan of action. The safest place to be if a tornado approaches is in a basement or safe room within a well-built structure, or in an underground storm shelter. If none of these options are available, move to a hallway or a small interior room on the lowest floor, usually this is a closet or bathroom. Get under a heavy piece of furniture or in a bath tub and cover yourself with blankets. Remember, the greatest risk of injury from tornadoes is from flying debris.

Modular homes and mobile homes, even those tied down, offer little protection from tornadoes. If a tornado approaches, leave those locations and seek safety in a nearby sturdy building or storm shelter.

If you are driving in open country and see a tornado, if time permits, the best thing to do is simply drive away from the tornado path. Do not take shelter beneath a highway overpass. Wind speeds may actually be higher in these areas and often become collection points for debris.

If you are caught outside and cannot seek shelter inside a sturdy structure, crawl into a culvert or lie down in a narrow ditch or ravine and cover your head. But remember that the worst place to be when a tornado threatens is outside in the midst of flying debris.

Lightning

Lightning usually kills and injures more people in Colorado than any other thunderstorm hazard. Lightning also causes many wildfires.

The best defense to protect yourself against a lightning strike is to plan ahead and avoid being caught where you might be vulnerable. Check weather forecasts prior to venturing out, especially if you are heading into the mountains. Plan outdoor activities early in the day before storms develop.

If thunderstorms threaten, seek shelter in a building or in an enclosed metal-roof vehicle, making sure all windows and doors are closed. Never seek shelter under an isolated tree. During thunderstorms, stay off corded telephones, away from electrical devices, and away from plumbing. Also get out of shower stalls, bath tubs, swimming pools and lakes when lightning is nearby.

You should wait at least 30 minutes after the last sound of thunder before resuming outdoor activities. When thunder roars…go indoors.

Floods and Flash Floods

The Big Thompson Flood in 1976 claimed the lives of 144 Coloradoans and serves to remind us of the dangers of floods. (USGS)

The Big Thompson Flood in 1976 claimed the lives of 144 Coloradoans and serves to remind us of the dangers of floods. (USGS)

When flooding or flash flooding is possible, you should remain alert and be ready to quickly evacuate to higher ground or climb to safety. Flash floods often occur suddenly and without warning. You need to follow some basic flood safety rules:

Do not camp or park your vehicle along streams and washes, particularly during threatening conditions. If you are near a river, be aware of water levels and be prepared to move to higher ground if river levels rise. Do not enter areas that are already flooded. If walking or fishing along a river, be aware that erosion from swift running water can cause river banks to collapse. Never let your children play around high water, storm drains, viaducts or arroyos.

Nearly half of all flash flood fatalities are vehicle related. While driving your automobile, look out for flooding at highway dips, bridges and low areas. Two feet of moving water will carry away most vehicles. Never attempt to drive across a flooded road. And be especially cautious at night when it is difficult to see flood dangers.

Strong Straight-Line Winds

Straight-line winds from thunderstorms, including microbursts, can become quite strong, even reaching speeds in excess of 100 mph in extreme cases. When thunderstorms approach, high winds can suddenly develop, causing things on the ground to become swift moving airborne missiles with a potential force to injure or kill. As with any thunderstorm, seek shelter before the storm arrives.

Hail

This is one of the largest recorded hail stones which is more than 7 inches in diameter and fell in Nebraska in 2003.  (NOAA)

This is one of the largest recorded hail stones which is more than 7 inches in diameter and fell in Nebraska in 2003. (NOAA)

Large hail can pose a danger to animals and people. Hail also produces considerable damage to crops and personal property each year in Colorado. Again, get indoors before thunderstorms arrive. A fall of small hail can suddenly change to a fall of very large ice missiles which can injure or kill. Make efforts to protect personal property before storms threaten.

Warning Notification

When thunderstorms threaten, tune to NOAA All-Hazards Weather Radio, The Weather Channel, or your local radio or television stations. Also check the Internet web site from the National Weather Service office serving your area. And if you have a relatively new cell phone you should receive Tornado and Flash Flood Warnings on your phone if you are in the area of the warning.

During threatening weather days, plan the actions you will need to take so that you will be prepared if dangerous weather conditions actually develop.

NOAA’s National Weather Service wishes you a safe severe weather season.

Severe Weather Awareness Week in Colorado concludes today. During the past week we have presented information and safety rules for tornadoes, lightning and wildfires, floods and flash floods, straight-line thunderstorm winds, hail, and our warning programs.

 

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Severe Weather 101 – Lightning and lightning safety

Friday, April 17th, 2015 10:00am MDT
This is NOT the time to be outside.  (michaeljames / FLICKR)

This is NOT the time to be outside. (michaeljames / FLICKR)

Of all the weather types associated with thunderstorms – hail, tornadoes, floods, etc – lightning is usually the most dangerous. In the United States there are an estimated 25 million cloud to ground lightning flashes each year and each one is a potential threat to life and property.

During the past 10 years there has been an annual average of 39 lightning fatalities in the United States. Last year, 23 people lost their lives due to lightning.

Colorado is ranked # 2 in lightning related deaths (2001 – 2010) so the danger this presents to life and property is very significant for us. It is interesting to note though that Colorado ranks only 32nd in the number of cloud to ground strikes over that same period. Which means, in short, we have fewer strikes than many other states and yet more deaths.

This highlights the fact that, quite frankly, folks here in Colorado are not aware of the dangers lightning presents and they do not take proper steps to protect themselves. One of the great things about Colorado are the outdoor activities we all enjoy, but there comes a time when we need to head indoors.

» Click here to read the rest of Severe Weather 101 – Lightning and lightning safety

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Wet, cool weather to linger Friday and through the weekend

Friday, April 17th, 2015 5:39am MDT

Ah yes, springtime in Colorado. The mountains are seeing heavy snowfall, here along the Front Range we have seen some snow but now have rain, out on our eastern plains severe thunderstorms will be possible.  The unsettled conditions will remain with us over the three day period and in fact, other than a brief break toward the middle of next week, cool and wet weather may be the norm for the next couple of weeks.

For today in Thornton, temperatures warmed a bit in the pre-dawn hours, enough to see our precipitation change to rain versus snow.  As of this writing the past 24 hours have brought 3.9” of snowfall and a healthy 1.27” of liquid precipitation.

We will see that precipitation total climb today with rain expected throughout the day. It should ease some this evening.  It wouldn’t be surprising to hear some thunder, especially in the afternoon.  Temperatures are going to remain cool with highs in the mid to upper 40s.  Overnight tonight some light showers, perhaps with just a bit of snow will be possible.

Temperatures warm on Saturday to the mid-50s.  Skies will remain mostly cloudy though and there will be at least a chance of showers throughout the day.  Some thunder will again be possible in the afternoon.

The early morning hours of Sunday may see a minimal rain / snow mix.  There will then just be a slight chance for a sprinkle during the daytime hours.  Temperatures again remain cool and winds breezy.

For the extended period, we do expect to start drying out Monday and Tuesday and Wednesday should see a rebound to above normal temperatures and dry conditions.  However long term models indicate a series of systems after that with overall cooler and wetter than normal conditions expected through the end of the month.

Stay warm and dry this weekend and of course keep an eye on http://www.thorntonweather.com/ for all the latest.

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Severe Weather 101 – Hail and Wind

Thursday, April 16th, 2015 5:25am MDT
Straight line winds can be as damaging as a tornado.  This image is from a park in Tennessee.  (NWS)

Straight line winds can be as damaging as a tornado. This image is from a park in Tennessee. (NWS)

During the spring and summer months in Colorado, a wide array of severe weather can strike. Tornadoes may grab all the headlines, but straight line winds and hail can do a great amount of damage in their own right – and they are more common.

Straight line winds are winds out of a thunderstorm and are classified as severe when they hit 58 mph. These winds can reach tornado and hurricane force and as a result, cause property damage and can injure and even kill animals and humans.

These winds are usually the result of air cooling rapidly due to precipitation or evaporation. As the cooler air is heavier than the surrounding warmer air, it rushes downward, accelerating toward the ground and spreads out as it hits, much like pancake batter being poured onto a griddle.

» Click here to read the rest of Severe Weather 101 – Hail and Wind

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Winter-like conditions return for Thornton’s Thursday

Thursday, April 16th, 2015 5:24am MDT

The spring storm we have been talking about has begun to make itself felt with colder temperatures and the first flakes falling in Thornton.  Cold and precipitation are a certainty but the details are still difficult to pin down.

Skies today are going to be cloudy across the board.  Temperatures in the early morning hours were pushing freezing but not falling a few degrees short of the mark.  We will warm during the day to a high of around 43 degrees or so.

It is the mercury readings that are going to play a key role in determining what form precipitation takes today.  Right now we are inclined to think that for much of the time it is going to be too warm for snow and rain is more likely.

Some light shower activity will be possible through the morning with it falling as snow initially then transitioning to a rain / snow mix as things warm up.  Minimal snow accumulations during the day today are expected in the Thornton area – likely a half inch or less.  Much will melt as soon as it hits the ground.

Tonight brings better chances for precipitation but again, temperatures are the problematic wildcard in determining snow vs rain.  Rain looks to be most likely from the evening until about midnight when a transition to all snow can be expected with colder temperatures.  Again though, any overnight accumulations are expected to be light (less than two inches).

Should temperatures be colder than expected today and tonight, snow numbers could go up.

The good news is that no matter what form the precipitation takes, it will help alleviate the bone dry conditions we have been seeing lately.  Further, the mountains and foothills areas above 7,000 feet are going to see a significant shot of snow which should help supplement some of the snowpack that has been lacking.

Our Winter Weather Briefing Page has all the latest.

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Severe Weather 101 – Floods and Flash Floods

Wednesday, April 15th, 2015 6:15am MDT
The Big Thompson Flood in 1976 claimed the lives of 144 Coloradoans and serves to remind us of the dangers of floods.

The Big Thompson Flood in 1976 claimed the lives of 144 Coloradoans and serves to remind us of the dangers of floods.

For much of Colorado, floods and flash floods present a grave danger to life and property. These usually are the result of one of two things – spring snow melt occurring rapidly or a severe thunderstorm. Colorado is very susceptible to flash flooding and these occur somewhere every year in the state.

The waters from flash floods can move with extraordinary speed and strike with little or not warning.  Their force can be extremely destructive and when coupled with trees, dirt, rocks and other debris they carry downstream, they are deadly.

Flooding is the number one weather killer in the United States.

» Click here to read the rest of Severe Weather 101 – Floods and Flash Floods

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Cooler, unsettled weather Wednesday; Snow possible tonight

Wednesday, April 15th, 2015 5:59am MDT

Our recent sunny, mild weather takes a break today as we begin a period of cooler and wetter weather.  As things develop today, we will see an increase in clouds and possibly some showers later but most action doesn’t begin until tomorrow.

For today look for partly clear skies initially but then cloud cover will increase leading to mostly cloudy skies for most of the day.  With a strong pressure gradient in place, winds will again be breezy, particularly this afternoon and evening when gusts to 30mph will be possible.  Temperatures will be topping out in the mid-50s.

We may see some light shower activity after about 3:00pm and lasting into tonight.  Any precipitation will initially be in the form of rain but as a cold front moves in this evening and temperatures drop, snow becomes possible after midnight.  At this time we’re not expecting any overnight accumulation.

The eventual track and speed of the low pressure system continues to be a bit of a mystery and as we have said repeatedly, that is going to be the determining factor in just how much precipitation northeastern Colorado gets.

We do expect our weather to be impacted through Friday, possibly into Saturday.  A decent shot of snow between Thursday afternoon and Friday PM is certainly possible but we won’t really have a good feel for the outcome for another 24 hours or so.

A Winter Storm Watch has been issued for the central and northern Colorado mountains but no advisories are in place for lower elevations (yet).

As always, our Winter Weather Briefing Page is your one-stop shop for the latest.

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Severe Weather 101 – Tornadoes and tornado safety

Tuesday, April 14th, 2015 6:40am MDT
Last year's Windsor Tornado highlights the very real danger twisters present in Colorado.  Do you know when to do when one strikes?

The 2008 Windsor Tornado highlights the very real danger twisters present in Colorado. Do you know when to do when one strikes?

One fact that may surprise those new to Colorado is that we are actually on the western edge of the infamous Tornado Alley. This large swath of land comprises much of the nation’s midsection and is a unique place as the United States sees more tornadoes than any other place on earth. In fact, tornadoes have been recorded in all 50 states including Alaska and Hawaii.

Closer to home, Colorado sees our share of these storms. In fact, one metro area county – Weld County – holds the distinction of being the “tornado capital of the world.” With 252 tornados from 1950-2011, no single county in the nation has had more tornadoes! Adams County is number two in the state and isn’t far behind with 156 over that same period.  Granted these numbers are skewed a bit simply due to the sheer size of those counties, but it does serve to highlight the real danger that tornadoes present.

Even here in the metro area tornadoes are a real danger. The Thornton area was struck in 1981, one of the worst tornadoes to strike the Denver area in history. At 2:30 p.m. this tornado touched down and by 2:45 p.m., the tornado had hit Thornton City Hall. The tornado’s destruction sent 53 injured people to hospitals, 25 homes were destroyed and 239 structures were damaged.

One common myth is that tornadoes don't strike metropolitan areas.  This has been disproved many times including here in Colorado in 1982 when an F2 tornado struck Thornton.  Image courtesy the City of Thornton archives.

One common myth is that tornadoes don’t strike metropolitan areas. This has been disproved many times including here in Colorado in 1981 when an F2 tornado struck Thornton. Image courtesy the City of Thornton archives.

The most well known tornado outbreak in the metro area occurred on June 15, 1988. Five tornadoes resulted in seven injuries and damage in excess of $15 million.

We all of course also remember just seven years ago when the town of Windsor, not far from Denver, was struck with an EF-3 tornado that claimed one life and destroyed and damaged hundreds of buildings.

The greatest threat for tornadoes occurs during late spring and early summer when you have a combination of heat and moisture in the lower atmosphere. Here in Colorado, tornadoes are frequent from May through August with June being the most active month.

However, there is no hard and fast rule for when tornadoes strike, as Colorado witnessed on March 29, 2007 when Holly, Colorado was struck by an EF-3 tornado with winds of 165 mph. Two women lost their lives as a result of that event and 160 homes were damaged.

Colorado ranks 10th in terms of the number of tornadoes with 1,911 events from 1950-2011. One good thing is that our high altitude and drier air do make it harder for the monster supercells that spawn the biggest tornadoes to form. Most of our tornadoes are small and short lived. Further, thanks to the wide open spaces of the eastern half of our state, many strike sparsely populated areas. This is reflected in the fact that we rank 38th for tornado related deaths.

» Click here to read the rest of Severe Weather 101 – Tornadoes and tornado safety

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Tuesday brings one more unseasonably warm day, cooler weather comes tomorrow

Tuesday, April 14th, 2015 5:37am MDT

Thornton is set to enjoy another day with temperatures well above normal today.  That however changes Wednesday as cooler temperatures arrive and precipitation becomes likely later.

For today the forecast doesn’t look entirely unlike yesterday – although a bit warmer and a bit more wind.  Skies start out sunny and then a few clouds arrive giving us mostly sunny skies by late morning.  The mercury will be climbing as we head for a high temperature reading in the mid-70s.  Winds start out light but then are expected to pick up this afternoon with some gusts to 25mph possible.

The dry, windy conditions have prompted a Red Flag Warning for much of the eastern plains, including the eastern half of Adams County.  Extreme caution is advised across the area as fuels are very dry and with the wind it wouldn’t take much for a fire to get out of hand.

Looking ahead…  Flip a coin.  That is about where we are at on determining which way the approaching storm system is going to track.  Models are still not in agreement so it may be another 24 hours before we really know what is in store.

For right now we are calling for temperatures a bit below normal Wednesday, much depending on the timing of the arrival of a cold front.  We’ll have a chance for showers at various points tomorrow, particularly in the afternoon.  Overnight tomorrow and into Thursday morning a rain / snow mix will be possible.

How much precipitation?  Tough to call and we aren’t going to throw a number on it yet.  Our fear is that the bulk of this system is going to be diving south and if it does, it takes our precipitation with it.  We will just have to continue to monitor its progression and try to get a better feel for where it is going to go.

As always, http://www.thorntonweather.com/ is the place to go for the latest.

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April 12 to April 18: This week in Denver weather history

Monday, April 13th, 2015 5:40pm MDT
This Week In Denver Weather History

April 12 to April 18: This week in Denver weather history

A look back at this week in Denver weather history shows quite the variety of weather conditions.  We have seen everything from high winds and snowstorms to hail, thunderstorms and sub-freezing temperatures.

From the National Weather Service:

7-12

In 1959…snow falling over a 5-day period totaled 20 to 30 inches just east of the mountains…while over the plains blizzard conditions closed schools and blocked highways. The second big storm in two weeks dumped 16.4 inches of snowfall on Stapleton Airport with the most…11.6 inches… Occurring on the 8th. East winds gusted to 37 mph on the 9th. Temperatures dipped into the single digits on the mornings of the 7th and 12th when 7 degrees were registered. The cold temperatures caused streets to glaze with ice…resulting in the death of a pedestrian who was struck by a car in Denver. Three people died from heart attacks while shoveling the heavy…wet snow.

9-12

In 1901…rain changed to snow and totaled 10.8 inches in downtown Denver over the 4 days. Northeast winds were sustained to 28 mph with gusts to 31 mph on the 11th. Temperatures hovered in the 30`s.

10-12

In 1997…a pacific storm produced heavy snow on the 10th and the 11th in and near the foothills with 6 to 8 inches at Louisville and turkey creek canyon…5 inches at Morrison… And only 3.5 inches at the site of the former Stapleton International Airport. Northeast winds gusted to 24 mph at Denver International Airport. The storm also brought unseasonably cold weather with 5 new temperature records equaled or broken. Record low temperatures of 8 and 6 occurred on the 11th and 12th. Record low maximum temperatures of 20…19…and 30 occurred on the 10th…11th… And 12th respectively. This was also only the second time on record that the temperature had failed to reach the freezing mark for 3 consecutive days in April.

10-14

In 1927…post-frontal rain on the 10th changed to snow on the 11th and continued through the 14th. Snowfall totaled 8.5 inches from precipitation of 1.28 inches. North winds were sustained to 26 mph with gusts to 29 mph on the 13th.

11-12

In 1876…heavy snow began during the late afternoon of the 11th and continued through the night. Light snow ended around mid-morning of the 12th. The amount of snow was not measured…but precipitation totaled 0.70 inch… Which would be around 7 inches of estimated snowfall. Strong winds accompanied the heavy snowfall.

In 1896…post-frontal light rain changed to light snow overnight…but totaled only a trace. Northeast winds were sustained to 45 mph with gusts as high as 62 mph on the 12th.

In 1991…a strong pacific storm dumped heavy snow across metro Denver with amounts of 6 to 15 inches at lower elevations and up to almost 2 feet in the foothills west of Denver. Snowfall reports included: 21 inches at Idaho Springs…19 inches at Aspen Springs…15 inches in Arvada… 14 inches at Rollinsville…10 inches in Boulder… 8 inches in Aurora…and 7.3 inches at Stapleton International Airport where northeast winds gusted to 24 mph on the 11th.

12

In 1906…north winds were sustained to 52 mph in the city.

In 1916…post-frontal north winds were sustained to 40 mph with gusts to 42 mph. Light rain also occurred.

In 1964…strong gusty winds raked metro Denver. Wind gusts estimated to 60 mph or higher caused widespread damage to buildings and power lines. Blowing dust closed some roads. A wind gust to 46 mph was recorded at Stapleton International Airport.

In 1967…microburst winds gusted to 51 mph at Stapleton International Airport.

In 1982…wind gusts to 60 mph were reported in and near the foothills. Wind gusts to 44 mph were recorded at Stapleton International Airport.

In 1987…snow fell over metro Denver… Causing traffic tie-ups on the roads and at Stapleton International Airport where some flights were delayed for 90 minutes. I-25 south of Denver was closed for a time due to numerous traffic accidents. While only 4.2 inches of snow fell in Denver… Foothills to the southwest received 6 to 12 inches of snow. North winds gusted to 33 mph at Stapleton International Airport where the maximum snow depth on the ground was only 2 inches due to melting.

12-13

In 1922…post-frontal rain changed to heavy snow… Which totaled 7.0 inches in downtown Denver. This was the second snow in 3 days. North winds were sustained to 29 mph with gusts to 31 mph on the 12th.

In 1993…heavy snow occurred in the foothills northwest of Denver with 21 inches recorded at the Eldora Ski Area. Only 1.9 inches of snow fell at Stapleton International Airport where northeast winds gusted to 32 mph on the 13th. Most of the precipitation from the storm fell as rain across the city with 0.62 inch of precipitation measured at Stapleton International Airport.

» Click here to read the rest of April 12 to April 18: This week in Denver weather history

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