Wednesday, November 18, 2015

The Weather This Week - All Sorts of Crazy

The weather system currently crossing the country has produced an astounding amount of interesting and severe weather so far, from torrential rain to tornadoes and blizzard conditions.

The system came ashore along the west coast on Sunday and strengthened over the western U.S on Monday. The surface low began to become organized over the Rockies as the deep upper level trough developed a cutoff over the southwest U.S. Cold air on the west side of the system, warm, moist air streaming northward on the east side, and strong winds aloft combined to produce a volatile atmosphere.

500 millibar map (~20,000 ft) for November 16, 6:00 p.m.
Surface weather map for Tuesday, November 17, 2015 at 6:00 a.m. CST
Early in the day the Storm Prediction Center identified an area from northern Texas into Nebraska as in a Slight Risk for severe weather, with a smaller Enhanced Risk over northwest Texas and western Oklahoma.
Convective Outlook for Tuesday, November 17 issued at 8:00 a.m.CST

Meanwhile, a Blizzard Watch was upgraded to a Blizzard Warning over eastern Colorado, including the Denver area. Later in the day Tornado Watches were issued covering areas from the Texas Panhandle into Nebraska. In Colorado areas in the Blizzard Warning were only 90 miles or so from other parts of Colorado in a Tornado Watch.

24-hour snowfall ending the morning of November 17. The orange-red area in southwest Colorado is 15-18 inches

Supercell thunderstorms did eventually develop during the late afternoon and evening from northwest of Amarillo, TX to west of Dodge City, Ks, and further north into Nebraska. A number of large tornadoes were spawned by these storms. One tornado near Pampa, TX produced EF-3 damage. Surveys are being conducted on other tornadoes that touched down. In western Kansas nine tornadoes touched down, including one which was on the ground for 78 minutes and 51 miles and produced EF-3 damage near Kismet.

Storm reports from 6:00 a.m. 11/16/2015 to 6:00 a.m. 11/17/2015

The tornado outbreak that occurred Monday night from western Texas into far southern Nebraska was very rare for the west-central Plains in November. This may have been the greatest number of tornadoes on a given November day so far west in the Plains dating back to 1900.

Cold, wind, and snow came in on the heels of the severe weather. Twelve to 18 inches of snow fell in northwestern Kansas, with lesser amounts in western Nebraska. Howling winds spinning around the intensifying low pressure system whipped up the snow creating blizzard conditions from the eastern plains of Colorado into western Kansas. A large portion of Interstate 70 in eastern Colorado and western Kansas was closed due to the dangerous conditions on Tuesday.

48-hour snowfall accumulation ending the morning of November 18, 2015. 12 to 18 inches of snow were  reported by observers in western Kansas.

Today, winds were the big news from the the Rockies and northern and central Plains east through the Midwest. This occurred as the central U.S. low pressure system intensified as it merged with another low that moved in the the Pacific Northwest yesterday. This Pacific system produced damaging winds across Washington state. Today winds gusted in excess of 100 mph in a few locations in Colorado, 94 mph in Boulder and the National Center for Atmospheric Research, and 77 mph in Fort Collins where CoCoRaHS headquarters is located.

Surface map at 3:00 p.m. CST November 17. The Central Plains low is starting to intensify. The system that merged with it today can be seen over Washington and British Columbia.

 The amount of moisture being transported by the central U.S. storm system was phenomenal. There was a conveyor belt of atmospheric moisture from the Gulf of Mexico north to Hudson Bay in Canada.
Water vapor satellite image On Tuesday, November 17 at 11:15 a.m. CST. The pink and blue colors indicate moisture, while the orange and red colors depict dry air. The west side of the upper level trough is clearly seen along the Rockies, as is the center of the closed low over Texas and Oklahoma panhandles.

On Tuesday evening the NWS Quad Cities office (Iowa/Illinois) reported a record high amount of precipitable water for November, 1.50 inches, measured by the evening atmospheric sounding. This moisture, along with the strong lift generated by the intense low pressure system aloft resulted if copious amounts of precipitation from Texas to Illinois, and east through the Gulf States. Three to four inch amounts were common from southern Missouri south to Louisiana and east through Mississippi.

Today the severe weather focus was in the southeast U.S., and this afternoon tornadoes touched down in the Florida panhandle and near Atlanta, GA.

Surface map at 3:00 p.m. CST Wednesday, November 18.

On Thursday the low now over the Northern Plains will be near the southern end of Hudson Bay, while the front pushes slowly off the east coast, and most of the country should see some quiet weather for 24 hours or so.

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