Mike's Blog Archive: June 2009

For much of the Denver Metro area the weather was great today, minus a few thunderstorms that developed far south of the city. There was plenty of sunshine, high temperatures, and calm winds. And even though there will still be a chance of thunderstroms throughout much of the week, especially on Wednesday, the warm weather will be of most interest. Temperatures will climb into the upper 80's and lower 90's across the Denver Metro area and most of the state.

The great weather is do to a high pressure system building into the region, allowing for mostly clear skies, ample sunshine, and with a slight southwest winds, temperatures reaching in to the upper 80's and 90's. Even as a weak cold passes through the state on Wednesday, conditions will still stay warm.

After all the rain from two weeks ago, warm, relatively dry weather is welcomed.

We will have at least one more day of heavy thunderstorms in Denver and across the eastern plains as the copious flow of moisture continues to move into the state all the way from Central America. This early appearance of the classic "summer monsoon" pattern is going to bring more slow moving thunderstorms this afternoon and evening. The ground is quite saturated with moisture, so flash flooding will be possible during the storms - especially in areas that have had heavy rain already this week.

Saturday will also be a pretty stormy day, but for a different reason. A cold front will slide into the state from Wyoming. This front will bring cooler temperatures, but the front will stall over central Colorado and help to stir up more stormy weather. Showers and thunderstorms will be likely again in the afternoon hours, especially over the northeast corner of the state.

Sunday will start to warm back up and there will still be some thunderstorms, thanks in part to all the humidity in the atmosphere from the recent rains. The front will begin to move back to the north and warmer air will return to the region. This warming trend will continue into Monday and Tuesday. The upper level winds will shift and become more westerly by early next week. This shift in the upper level winds will cut off the deep moisture from the tropics and should allow our weather to dry out. Rain chances will drop back to just a slight chance by early next week.

Here is a little more information about our summer thunderstorm threat...

The prime time for severe thunderstorms

June is almost over and boy what a month it has been, very wet and wild! Severe weather plagued many parts of Colorado bringing heavy rain, strong winds, hail and tornadoes. This June has been exceptionally wet; we have seen 4.86 inches of rain so far, a normal June we usually see around 1.44 inches of precipitation—so Colorado is well above average this month.

The reason for this pattern of cool and wet weather for much of the Midwest is due to La Niña, or a lack of it. According to Klaus Wolter of the University of Colorado- CIRES Climate Diagnostics Center NOAA-ESRL Physical Science Division, we have been under weak-to-moderate La Niña conditions since fall of 2008. These conditions continued through the winter keeping Colorado dry and mild. Over the past four weeks however El Niño conditions have emerged bringing us lots of wet weather for June.

Wolter says that our recent weather has many features of an early monsoon. It appears that similar conditions will continue for our area into early July. Wolter believes that eastern New Mexico to eastern Colorado will experience a slightly enhanced amount of precipitation for the next couple weeks.

It’s anyone’s guess if El Niño will become the dominant force on our weather for the next few months into Fall. However if El Niño is here to stay through the rest of the year we can expect a much wetter more snow filled winter for 2009.

If you would like to see more information from Klaus Wolter and his Executive Summary check out the Earth System Research Laboratory webpage.

For much of the Denver Metro area the weather was great today, minus a few thunderstorms that developed far south of the city. There was plenty of sunshine, high temperatures, and calm winds. And even though there will still be a chance of thunderstroms throughout much of the week, especially on Wednesday, the warm weather will be of most interest. Temperatures will climb into the upper 80's and lower 90's across the Denver Metro area and most of the state.

The great weather is do to a high pressure system building into the region, allowing for mostly clear skies, ample sunshine, and with a slight southwest winds, temperatures reaching in to the upper 80's and 90's. Even as a weak cold passes through the state on Wednesday, conditions will still stay warm.

After all the rain from two weeks ago, warm, relatively dry weather is welcomed.

We will have at least one more day of heavy thunderstorms in Denver and across the eastern plains as the copious flow of moisture continues to move into the state all the way from Central America. This early appearance of the classic "summer monsoon" pattern is going to bring more slow moving thunderstorms this afternoon and evening. The ground is quite saturated with moisture, so flash flooding will be possible during the storms - especially in areas that have had heavy rain already this week.

Saturday will also be a pretty stormy day, but for a different reason. A cold front will slide into the state from Wyoming. This front will bring cooler temperatures, but the front will stall over central Colorado and help to stir up more stormy weather. Showers and thunderstorms will be likely again in the afternoon hours, especially over the northeast corner of the state.

Sunday will start to warm back up and there will still be some thunderstorms, thanks in part to all the humidity in the atmosphere from the recent rains. The front will begin to move back to the north and warmer air will return to the region. This warming trend will continue into Monday and Tuesday. The upper level winds will shift and become more westerly by early next week. This shift in the upper level winds will cut off the deep moisture from the tropics and should allow our weather to dry out. Rain chances will drop back to just a slight chance by early next week.

Here is a little more information about our summer thunderstorm threat...

The prime time for severe thunderstorms and tornadoes in Colorado is in early to mid June. At that time, the upper atmosphere is still a little bit chilly, but the surface is quite warm. This creates an unstable situation in the atmosphere as the warm air near the ground can quickly "bubble up" through the colder air above - think of a hot air balloon rising. Our mountains exacerbate this situation as they act as "heating elements" up there at about 12,000 feet or so. The sun quickly heats the ground up there and the ground then heats the air. This warm air rises quickly through the cool, thin alpine atmosphere and can form small puffy cumulus clouds by mid-morning. As the heating continues, those innocent little clouds blossom into small thunderstorms by lunchtime. In the early afternoon, those storms begin to have an "attitude" and often chase climbers off the peaks by 2 or 3 PM. The upper level winds then push these storms out onto the plains, bringing Denver and the Urban Corridor a round of rumbles by mid afternoon. Those thunderstorms keep rolling off to the east and whip up severe weather over the high plains of Colorado and may even stay intact late into the night as they roll all the way across Kansas.

June is the peak time for tornadoes thanks to the fact that we often have strong upper level jet stream winds. These winds help to create rotating thunderstorms called "supercells". These monster storms can last for hours and can spawn a dangerous combination of flooding rains, large hail, deadly lightning and tornadoes. Supercell thunderstorms that develop over Colorado often move hundreds of miles and may still be causing damaging weather all the way to the Mississippi River.

About 90% of the 40-50 tornadoes that occur in Colorado in an average summer happen east of I-25. The flatter terrain on the plains is more conducive to the development of supercell thunderstorms - the mountains tend to disrupt the rotating motion of the storm. Most of our tornadoes occur in the late afternoon or early evening and we have very few late at night. This is due to our higher elevation - the atmosphere tends to cool and stabilize more quickly here than it does in the Midwest or over the southern plains where late night severe weather is common.

There is a great website that can really give you high resolution precipitation reports. Check out the Community Collaborative Rain and Hail Study - also know as COCORAHS! This program was developed over a decade ago by Nolan Doesken, the Colorado State Climatologist. There are now over 6,000 volunteer weather watchers in the COCORAHS system nationwide. To learn more and to check the latest rainfall numbers for your neighborhood, just click COCORAHS INFO.

Thursday featured another round of big boomers late in the afternoon. Once again today, there was plenty of flooding and hail with the storms that developed. The hardest hit areas were the southern and eastern portions of the Denver area

At DIA, the daily dose of thunderstorms has boosted the June precipitation total at DIA to 4.35 inches. This pushes our June rainfall to nearly an inch and a quarter above average. So far, June 2009 is the 6th wettest on record. The wettest June on record for Denver was in 1882, when 4.96 inches of rain fell during the month.

For the year to date, Denver has now officially recorded 9.87 inches of precipitation. This figure is 2.05 inches above average for the year so far. Compare that figure to the 7.48 inches of total precipitation for all of 2002 - Denver's driest year on record. We certainly seem to have emerged from the most recent drought.

Light winds are swirling around a large high pressure system that is now anchored over the central United States. Moisture is flowing into the southwestern United States all the way from Mexico. This type of weather pattern is actually more like the annual "monsoon flow" that we see in late July and August. This seasonal shift in the wind pattern tends to bring the slow moving thunderstorms that drop a couple inches of rain and caused flash flooding. Current indications are that we will see more of this pattern over the next several days - so get ready for more super soakers.

If hot summer weather is your favorite - get ready to sizzle this week, especially today. Colorado is on the western edge of a big high pressure system that is simply a huge bubble of hot air that covers much of the central United States. High temperatures will soar into the 90s to low 100s over the Central and Southern Plains, all the way to the Great Lakes today.

High temperatures will hit the low 90s in the Denver Metro area today. Average high temperatures for this time of year are into the low to mid 80s. Thunderstorms will be scattered about this afternoon and evening, but the atmosphere is actually rather stable, despite the hot surface temperatures. This is due to the fact that the air aloft is also quite warm, acting like a lid or cap on thunderstorm development.

Tomorrow, a weak cold front move into northern Colorado and bring the opportunity of more thunderstorms into the Denver Metro area Wednesday afternoon. Looking to the end of the week, the weather looks to cool off a bit back into the mid 80s as a second cold front moves through the area on Friday.

With all of the hot temperatures, it is important to remember to drink plenty of water and rest periodically if you are doing work outside. If possible, try to avoid working outside during the hours of 10:00 A.M. and 2:00 P.M. The reason that it is recommended that you avoid outside work during these hours is that the sun is the highest in the sky and the most direct rays reach the Earth during these hours. Imagine a flashlight pointing straight down on the ground; the rays of light are more intensified and confined to the same spot. As the sun sinks lower into the sky it is like moving that flashlight to an angle, the rays are open and less intense in the same area.

The UV index for Tuesday is 12, so be sure to protect your skin by wearing a hat and putting on sunscreen when going outside. An index of 12 is categorized as extreme, so if you do plan on soaking up some rays and work on that tan, be sure to use sunscreen.

Are you prepared for this severe weather season? Now is the time to get your 24/7 Weather Alert Radio, and be ready when severe weather strikes!

Storm chasing is best left up to the pros and you can follow along as these storm chasers capture the awesome power of nature by going to the storm chasers blog on the Storm Chasers Blog.

You can get free weather text alerts directly to your phone, just click on weather text alerts on the top of the weather page.

Colorado has been stuck in a very active severe weather pattern for quite some time. It finally appears that we will catch a much needed break as we head into the weekend. This should make all the dads out there very happy! The severe weather that we have been experiencing lately is not unusual for Colorado this time of year. With the clashing of air masses in the atmosphere this can be a very volatile time across our state.

The upcoming weekend will see the official arrival of Summer, the actual time of the June Soltice is 11:46 PM MDT on Saturday. The weather will feel a bit more like summer over the next 5 to 7 days as we will gradually transition from the stormy weather pattern to a warmer and drier regime early next week. Over the next 24-48 hours, there will still be some thundery weather, but the risk of severe storms will be lower.

Some of the storms that we have endured in recent weeks have been a special type of thunderstorm called a "super cell". These storms are unique due to their rotation that can reach to the ground and become a tornado. Most tornadoes form from these large rotating thunderstorms. These monster storms tend to develop ahead of cold fronts that push southward from Canada across the central U.S. As the fronts sag into the warm and humid air that covers the southern plains, the colder air wedges under the warm air, creating lift. The lifted air rises up to form thunderstorms that can rapidly grow to heights of 40 to 50 thousand feet above the ground.

As the storm pushes high into the sky, it reaches into the jet stream - the band or river of fast moving air that flows around the world. It is the increase in wind speed with height that causes the thunderstorm to begin a large, slow counterclockwise rotation. This rotating thunderstorm is what is classified as a "super cell".

Once the super cell storm develops, the best analogy for thinking about how the tornado forms is to think of a figure skater doing a spin. The skater starts with their arms out, and is rotating rather slowly. As the skater brings their arms in, the rotation begins to speed up. In physics, this is called "the conservation of angular momentum". The rotation gets faster and faster as the size of the rotating column grows narrower. This is a very simplistic description, but eventually this narrow rapidly rotating column of air will drop to the ground as a tornado.

Are you prepared for this severe weather season? Now is the time to get your 24/7 Weather Alert Radio, and be ready when severe weather strikes!

Stormchasing is best left up to the pros and you can follow along as these stormchasers capture the awsome power of nature by going to the stormchasers blog on the denverchannel.com www.thedenverchannel.com/stormchasersblog/index.html

For more information, check out the 24/7 Weather Alert Radio Webpage!

You can get free weather text alerts directly to your phone, just click on weather text alerts on the top of the weather page.

Sunday marked the 8th day in a row for severe weather across region. Over the past 8 days, we've observed more than 10 tornadoes and 60 hail storms occuring across northeastern Colorado. On Sunday, a funnel cloud was observed at the Colorado Rockies baseball game, forcing the game into a weather delay and the fans and spectators to be evacuated from the stands for an hour.

Some of the same will be expected for today across the Denver Metro area. Conditions are very favorable for severe weather. This is mainly due to the warm moist air near the surface and the relatively cold, dry air higher up in the atmosphere. These are some of the main ingredients needed for severe weather.

This late spring reminds me of June 1991, where the atmosphere was very moist and warm, allowing for numerous thunderstorms to develop on a daily basis. It was my first season in Colorado and my old friend, Bill Kuster and I were so busy in the weather office that I thought I would never see my wife and children!

So when will we get a break?

For now it seems that thunderstorms will start right back up for this afternonon. As we head into the mid-week, conditions will turn less favorable for severe weather and at the same time warming into the 80's, a ridge of high pressure will begin to move in to the region. We should get some rather pleasant weather midweek, before some severe conditions come back later in the week and for the weekend.

The daily dose of thunderstorms will continue today, making it the fifth straight day with weather worries for residents along the I-25 Corridor. The stationary weather front that has been draped over Colorado will again serve as a focus for thundery weather this afternoon. Some of these storms will become severe and produce the terrible trifecta of heavy rain, large hail and isolated tornadoes.

As a meteorologist, I am reminded of Bill Murray's 1993 movie "Groundhog Day". Each morning the alarm would go off and and Murray's character "Phil" would awake to see the exact same weather and go through the same motions day after day after day.

Yesterday's storms really hammered the Greeley area. Large hail and heavy rain damaged crops in Weld County. Many residents could smell onions after the hailstorm as the smashed crop was quite aromatic. Some farmers are hoping that if the weather dries out a bit, they will have time to replant crops and still get them to harvest in the fall.

Here is some more information about tornadoes...

Most tornadoes in the United States occur in the central plains, with the greatest likelihood of twisters in the southern plains around Kansas, Texas and Oklahoma. Colorado lies of the western fringe of "Tornado Alley", but our state still averages between 30 and 50 tornadoes per year.

The peak season for tornadoes is in the spring and early summer. From March through June, about 70% of all the tornadoes in a year will occur. This is due to the fact that the weather patterns that are needed for tornado development are most common in the spring and early summer.

Most tornadoes form from large rotating thunderstorms called "super cells". These monster storms tend to develop ahead of cold fronts that push southward from Canada across the central U.S. As the fronts sag into the warm and humid air that covers the southern plains, the colder air wedges under the warm air, creating lift. The lifted air rises up to form thunderstorms that can rapidly grow to heights of 40 to 50 thousand feet above the ground.

The storm pushes high into the sky, reaching into the jet stream - the band or river of fast moving air that flows around the world. It is the increase in wind speed with height that causes the thunderstorm to begin a large, slow counterclockwise rotation. This rotating thunderstorm is what is classified as a "Super Cell".

Once the super cell storm develops, the best analogy for thinking about how the tornado forms is to think of a figure skater doing a spin. The skater starts with their arms out, and is rotating rather slowly. As the skater brings their arms in, the rotation begins to speed up. In physics, this is called "the conservation of angular momentum". The rotation gets faster and faster as the size of the rotating column grows narrower. This is a very simplistic description, but eventually this narrow rapidly rotating column of air will drop to the ground as a tornado.

Tornadoes are classified by the wind damage that they cause. The scale was developed by Dr. Ted Fujita from the University of Chicago. Dr. Fujita based his "F scale" on a 0 to 5 basis for tornadoes. On February 1, 2007, a team of meteorologists and wind engineers updated the Fujita scale which is now known as the "Enhanced Fujits Scale (EF)". The EF0 is a weak tornado, while the EF5 storms are the most powerful winds ever observed on Earth.

EF0 - up to 85 mph - light damage EF1 - 86 to 110 mph - moderate damage EF2 - 111 to 135 mph - considerable damage EF3 - 136 to 165 mph - severe damage EF4 - 166 to 200 mph - devastating damage EF5 - above 200 mph - incredible damage

About 70 % of the annual average of 1000 tornadoes nationwide are classified as EF0 or EF1. About 28 % of all tornadoes fall into the EF2 or EF3 category. Only about 2% of all tornadoes are classified as EF4 or EF5. Often a severe weather season will come and go without a single EF5 tornado reported. However, about 80% of all tornadoes deaths are the result of the EF3, EF4 and EF5 tornadoes. These storms are much less common, but much more dangerous.

Tornadoes are not named like hurricanes are, but the strong or deadly tornadoes are usually remembered for the town or location that they affected. For instance, the infamous "Xenia Ohio Tornado" of April 1974, or in Colorado, the "Limon Tornado" in June of 1990, the "Holly Tornado" in 2007 and last year's "Windsor Tornado".

Perhaps the single worst tornado on record was the great "Tri-State Tornado" of March 1925. This huge tornado started in southeastern Missouri and tore a path of destruction all across Illinois, before ending in western Indiana. The twister covered a distance of 219 miles and was on the ground for over 3 hours. In the days before adequate warnings, the storm caught everyone off guard. The Tri-State Tornado killed 689 people, injured over 2,000 and caused 17 million dollars in damage - a very large figure in 1925!

In Colorado, the peak season for tornadoes is in early June. At that time, the almost daily dose of thunderstorms can easily rise up to the jet stream level and begin to rotate into a super cell. These storms tend to form along the Front Range, roll over the Denver metro area and then really get severe over the eastern plains of the state. About 90% of all Colorado tornadoes occur east of I-25. Although tornadoes can form in the high country, the rough terrain tends to disrupt the rotation needed to form a super cell.

In my 30 years in meteorology, I have been through many tornado watch and warning situations. In 1984, I walked through a small town in southern Wisconsin, named Barneveld, just hours after it was ripped apart by what was then called an F5 tornado. Only one time have I seen a tornado, as most of the time I am right here in the 24/7 Weather Center issuing warnings and weather updates, so I do not get much of a chance to chase these storms. However, we do have a crew of storm chasers that go out in search of these deadly weather events and you can follow along with them as the blog for us here at Channel 7.

Tornadoes have done some very unusual things. The powerful winds can pick up a railroad locomotive, lift a water tower off the ground, and drive blades of grass into walls just like a hammer and a nail. At the same time, there have been reports where tornadoes have picked a refrigerator off the ground, tossed it several hundreds of yards, dropped it back on the ground and not even broken an egg inside the refrigerator!

Tornadoes usually form on the back edge of the thunderstorm cloud, meaning that most of the storm has already passed overhead. Often the rain, hail, thunder and lightning have mostly gone by and then the tornado occurs. That is why you will often see the sky looking very bright behind the tornado - a dramatic contrast to the very dark funnel. After the tornado, the sky often quickly clears as the storm moves away. There are, however, no hard and fast rules for tornados, so sometimes the twister occurs in the midst of a large area of thunderstorms, so after the tornado occurs, it just rains and rains.

The Denver Metro area and the surrounding suburbs have experienced a wide range of severe weather, anywhere from quarter-size hail to several tornadoes. These severe storms have caused significant damage to many cars and buildings in the Metro area, especially to the southeast of Denver in Aurora, CO, where the Southlands Mall sustained significant damage to its buildings. Some mall patrons' vehicles were turned over or damaged as well. Fortunately, as of 5:00 pm today, there were no reported injuries.

Today's severe weather was caused by a cold front passing through Northeastern Colorado from the north. This cold front clashed with the relatively moist, humid air across the region, with this moist, humid air serving as fuel for the severe storms.

Heading into the early evening hours, the chances of severe weather decrease significantly, and overnight conditions will become relatively tranquail, with mostly cloudy skies and temperatures dropping into the mid 40's. The next several days will bring mostly cloudy skies and chances of afternoon thunderstorms. Daytime high temperatures will reach into the mid 70's and lower 80's.

After a pleasant Saturday, a moist and unstable air mass will settle over Colorado, and this will leave us with slightly cooler temperatures and a good chance for storms in the afternoon hours, some possibly becoming severe.

Highs are expected to reach the low 80s Saturday, with a little bit of a cool off for Sunday and a front passes through from the north.

The chance of showers and thunderstorms will increase late Sunday afternoon and evening with increasing low level moisture over the northeast plains. Showers will continue late Sunday into Monday with the passage of an upper level weather disturbance and surface cold front. Cooler temperatures and relatively stable conditions can be expected on Monday with a chance of showers and thunderstorms throughout the day.

Severe Weather can strike at anytime and early June is the peak of Severe Weather Season, now is the time to prepare for such events. There are many precautions to take to ensure the safety of yourself and family. Having a 24/7 Weather Alert Radio is one way to obtain the information immediately when danger is headed your way.

In fact! The 7 News Weather Team will be at the King Soopers in Bennett, Colorado Saturday June 6th to help you set up your weather alert radio. This is a great opportunity for your family, friends, and co-workers to get a weather radio and be ready when severe weather strikes. See you there!

For more information, check out the 24/7 Weather Alert Radio Webpage! You can get free weather text alerts directly to your phone, just click on weather text alerts on the top of the weather page.

Severe weather season is upon us!

Colorado sits on the western edge of "tornado alley", which is coincidentally the location of the most tonadoes in the world. The Eastern plains, including the Denver metropolitan area, is a prime location for supercells to form. June supercells tend to spin off these violent twisters we call tornadoes. Not only are these supercells known for producing tornadoes, but dangerous lightning and large hail.

Fortunately, tornadoes occuring in the month of June have not claimed any lives. However, the intense lightning that accompanies these tornadoes, have caused many fatalities. In Colorado it is more likely to be injured or killed by lightning than any other weather phenomena. Hail, another severe weather threat, can cause extensive damage to property and is most notable during the early summer months.

Now is the time to prepare for such events. There are many precautions to take to ensure the safety of yourself and family. Having a 24/7 Weather Alert Radio is one way to obtain the information immediately when danger is headed your way.

In fact! The 7 News Weather Team will be at the King Soopers in Bennett, Colorado Saturday June 6th to help you set up your weather alert radio. This is a great opportunity for your family, friends, and co-workers to get a weather radio and be ready when severe weather strikes. See you there!

Tuesday has been full of moisture! Storms were experienced across Colorado, and precipitation totals were high for many areas. Otis: 3.69 inches Aurora: 1.84 inches Littleton, Fort Collins: 1.22 inches 24/7 Weather Center: 1.07 inches

The gloomy weather that brought this moisture may not have been desired, but it will be extremely beneficial to the state. With the atmosphere and soils now holding large amounts of moisture, temperatures will rise toward the end of the work week. This coupled increase in moisture and temperature will bring a greater chance for severe afternoon storms to the Front Range this weekend. We are not in the clear as far as storms go, but our temperatures will rise back into the 70s and 80s instead of dwindling in the chilly 50s. The March-like weather will be leaving and it might finally start to feel like summer.

With the wet weather, it is a good time to turn off your automatic sprinkler system. No point in having it running in the middle of a rainstorm. If we get the predicted heavy rains, you can actually give your system several days off. This will save water in the our reservoirs for the hot, dry periods and will actually help your lawn. The roots will grow deeper and stronger with less frequent watering, especially after a period of wet weather.

As we transition from this more moist spring air to warmer more dry summer weather we have our greatest chance for severe weather. Late May into early June is the peak of severe weather season so be prepared! An easy first step in your weather safety plan is to pick up one of our 24/7 Weather Alert Radios! For more information, check out the 24/7 Weather Alert Radio Webpage! You can get free weather text alerts directly to your phone, just click on weather text alerts on the top of the weather page.

A cool and unsettled weather pattern has developed over Colorado to start the month of June. The past weekend featured some warm temperatures, but also some big thunderstorms with heavy rain and hail. The next two days will be cooler, but even wetter as showers and thunderstorms will be likely, with even some snow in the higher mountain areas.

A cold front will slip across Colorado tonight and bring some unseasonably chilly weather to the area for Tuesday. Highs will only be in the 50s in the Denver area on Tuesday, with 40s in the northern mountains. The snow level should drop to around 10,000 feet Tuesday, so take the winter jacket if you are planning to drive in the mountains.

The atmosphere is pretty well chocked full of moisture. Computer models indicate that we will receive a good soaking in the next 48 hours. One to two inches of rain will likely fall over much of the Front Range Foothills and the I-25 Corridor. This will come in the form of heavy thunderstorms Monday evening and just plain rain on Tuesday.

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