Monsoon news: ‘All monsoons are caused by temperature differences between the land and the sea’ — Peter Shelton

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From The Watch (Peter Shelton):

The North American monsoon arrives every summer about this time, and blessedly so, following a baking-hot June with its smoke and fires and nervous fireworks bans.

The term monsoon comes, of course, from the famous Indian monsoon weather pattern that drenches much of the Asian subcontinent like clockwork every (well almost every) year. The root is an Arabic word, mausim, which means “wind-shift.” Sailors on the Arabian Sea noticed centuries ago that dry northeast winds in the winter suddenly turned southwest during the summer, bringing with them torrential rains. A similar wind-shift drives our mid-summer pattern.

All monsoons are caused by temperature differences between the land and the sea. The Indian summer heats the vast Rajasthan Desert. Ours is similarly driven by the hot, dry Sonoran/Mojave complex, stretching from western Mexico to eastern California. As the deserts heat up in June and July, surface low-pressure forms over Arizona triggering the wind-shift and sucking moisture up from the south. You can see it on the satellite pictures: moisture pumping northward from the Gulf of California.

The pattern starts along Mexico’s tropical Pacific coast and builds gradually to the north. When the plume bumps up against the high country, daytime convection builds those towering cumulus clouds, and the rainy season begins. In Asia, the barrier is the great Himalayan Range. In Arizona, the Mogollon Rim serves the same lifting/cooling function. When the moisture finally reaches Colorado (near the northern limit of most monsoons) the southern mountains especially present an impressive rain-generating barrier.

Parts of Mexico and Arizona receive 80 percent of their annual rainfall in July and August. Nearly a quarter of Telluride’s yearly total falls courtesy of the monsoon. As important perhaps as the wetting of the soil is the cooling of the psyche, the relief felt by flowers and wild things and the humans who tramp among them…

The worst days were the result of mesoscale convective complexes (MCCs). These super-size groupings of cells organize into monster storms capable of dropping furious amounts of water. These are the cells that cover Hwy 145 in red mud, that wash thousands of tires into the Uncompahgre River.

This is what happened on July 31, 1999, in the Dallas Creek drainage west of Ridgway.

An MCC got stuck between the Uncompahgre Plateau and the Sneffels Range and dropped about three inches of rain in three hours. Little Dallas Creek, which was flowing at a lazy 130 cubic feet per second the day before, leapt up to 3,960 cfs on the 31st – almost eight feet above flood stage. The flood took out bridges and hayfields and rural roads for miles around.

From the National Weather Service Pueblo office:

MONSOON RAINS BRING SOME RELIEF IN THE DROUGHT FOR PORTIONS OF SOUTHERN COLORADO…

SYNOPSIS…UPDATED

THE ONSET OF THE SOUTHWEST MONSOON HAS BROUGHT SOME MUCH NEEDED AND BENEFICIAL RAIN TO PORTIONS OF SOUTH CENTRAL AND SOUTHEAST COLORADO…WITH WIDESPREAD PRECIPITATION TOTALS BETWEEN 3 AND 4 INCHES RECORDED ACROSS THE SOUTHEAST MOUNTAINS SINCE THE BEGINNING OF JULY. THIS MOISTURE…HOWEVER…HAS NOT BEEN AS MUCH OR WIDESPREAD ENOUGH ACROSS THE REST OF SOUTH CENTRAL AND SOUTHEAST COLORADO TO BRING ANY LONG TERM RELIEF TO THE DROUGHT GRIPPING THE REGION OVER THE PAST TWO YEARS.

WITH THIS IN MIND…THE CURRENT US DROUGHT MONITOR INDICATES IMPROVEMENT IN THE DROUGHT ACROSS THE SOUTHEAST MOUNTAINS AND NOW DEPICTS SEVERE DROUGHT (D2) CONDITIONS IN PLACE ACROSS MOST OF CUSTER COUNTY…EXTREME SOUTHWESTERN PUEBLO COUNTY….WESTERN AND CENTRAL PORTIONS OF HUERFANO COUNTY AND EXTREME WESTERN LAS ANIMAS COUNTY.

EXCEPTIONAL (D4) DROUGHT CONDITIONS REMAIN DEPICTED ACROSS MOST OF THE SOUTHEAST COLORADO PLAINS AND INCLUDES SOUTH CENTRAL AND SOUTHEAST PORTIONS OF EL PASO COUNTY…CENTRAL AND EASTERN PORTIONS OF PUEBLO COUNTY…CENTRAL AND EASTERN PORTIONS OF LAS ANIMAS COUNTY…AS WELL AS ALL OF CROWLEY…OTERO…KIOWA…BENT…PROWERS AND BACA COUNTIES.

EXTREME DROUGHT (D3) CONDITIONS CONTINUE TO BE INDICATED ACROSS EXTREME NORTHEASTERN CUSTER COUNTY…EASTERN HUERFANO COUNTY AND WEST CENTRAL PORTIONS OF LAS ANIMAS COUNTY. EXTREME DROUGHT (D3) CONDITIONS REMAIN DEPICTED ACROSS MOST OF FREMONT COUNTY…MUCH OF TELLER COUNTY…MOST OF THE REST OF EL PASO COUNTY AND THE REST OF PUEBLO COUNTY. EXTREME DROUGHT (D3) CONDITIONS ALSO REMAIN INDICATED ACROSS EXTREME SOUTHWEST MINERAL COUNTY.

SEVERE DROUGHT (D2) CONDITIONS CONTINUE TO BE DEPICTED ACROSS SOUTHERN CHAFFEE COUNTY…EXTREME WESTERN FREMONT COUNTY…NORTHERN TELLER COUNTY AND EXTREME NORTHWESTERN EL PASO COUNTY. SEVERE DROUGHT (D2) CONDITIONS ALSO REMAIN ACROSS THE REST OF MINERAL COUNTY…AS WELL AS ALL OF SAGUACHE…RIO GRANDE…CONEJOS…ALAMOSA AND COSTILLA COUNTIES.

MODERATE DROUGHT (D1) CONDITIONS REMAIN DEPICTED ACROSS THE REST OF CHAFFEE COUNTY AND LAKE COUNTY.

MORE INFORMATION ON THE US DROUGHT MONITOR CLASSIFICATION SCHEME CAN BE FOUND AT: WWW.DROUGHTMONITOR.UNL.EDU/CLASSIFY.HTM

SUMMARY OF IMPACTS…UPDATED

THE VERY DRY CONDITIONS ACROSS THE STATE CONTRIBUTED TO THE START OF SEVERAL NATURALLY CAUSED AND HUMAN INDUCED WILDFIRES OVER THE PAST FEW MONTHS…INCLUDING THE BLACK FOREST FIRE…WHICH HAS BECOME THE STATES MOST DESTRUCTIVE WILDFIRE ON RECORD…WITH NEARLY 500 HOMES DESTROYED.

WITH THE ONSET OF THE SUMMER MONSOON…AREAS IN AND AROUND THESE NEWLY CREATED AND OTHER RECENT BURN SCARS ACROSS SOUTH CENTRAL AND SOUTHEAST COLORADO…HAVE ALSO EXPERIENCED DESTRUCTIVE FLASH FLOODING DUE TO THE LOSS OF VEGETATION AND THE DEVELOPMENT O HYDROPHOBIC SOILS CAUSED BY THE FIRES.

HOWEVER…THE BENEFICIAL MONSOONAL RAINS HAS PROVIDED SOME SHORT TERM RELIEF TO THE AREA…WITH SEVERAL LARGE MUNICIPAL WATER PROVIDERS EASING OR HAVING PLANS TO EASE THE STRICT WATER RESTRICTIONS IMPLEMENTED THIS PAST SPRING…INCLUDING DENVER WATER AND COLORADO SPRINGS UTILITIES.

THE STATE HAS SETUP THE FOLLOWING WEBSITE TO GIVE INDIVIDUALS INFORMATION ON WHAT THE CURRENT WATER RESTRICTIONS IN THEIR SPECIFIC COMMUNITY ARE: WWW.COH2O.CO

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