MAY 2011


9-14thA large low pressure system brought scattered showers to the Western half of the nation on Monday, while the East saw a break in wet weather. A low pressure system strengthened as it moved off the Northern Rockies and into the Plains. Counter-clockwise flow around this wide system allowed for warm and moist air to pour into the Midwest from the Gulf of Mexico. This created a warm front that stretched from the Northern Plains, into the Great Lakes and Midwest. This system kicked up widespread scattered showers, with periods of heavy rainfall over the Upper Midwest. Most areas saw between 0.50 and 1.0 inches of rain, while Menominee, Wisconsin saw a mid-day total of 1.14 inches of rain. Moisture wrapped well around the back side of this system, which also pulled cooler air in from Canada. This allowed for more rain showers to develop across the Rockies, with high elevation snow showers. Parts of western Montana saw 1 to 2 feet of snow above 6,000 feet. The Central Rockies only saw light flurries with accumulation near 1 inch at high elevations of Utah and Colorado. The southern edge of this system created strong winds across the Southeast and Southern Plains. While conditions remained dry with low humidity, strong winds allowed for rapid fire spread. Thus, fire weather advisories have spread from western Texas and New Mexico to Colorado, western Oklahoma, and western Kansas. Strongest winds were reported at Ruidoso, New Mexico with gusts up to 61 mph.

A deep trough of low pressure supported a strong, cold Spring storm system that moved into the southern and central High Plains Wednesday afternoon. On the northern edge of this system, cold air supported a mix of valley rain and high elevation snow in Colorado and Wyoming. Winter Storm Warnings and Winter Weather Advisories remained in effect for western Colorado through the late afternoon. Meanwhile, warm moist air ahead of associated cold fronts increased atmospheric instability in the Central and Southern Plains and the Mid-Mississippi Valley. Bands of significant precipitation and intense thunderstorms developed ahead of these cold fronts from Iowa and Nebraska through Texas. Additional heavy rainfall and strong thunderstorms developed ahead of frontal boundaries in the Upper Great Lakes and affected areas of Wisconsin and northern Michigan. Storms from Texas across the Southern Plains to the Midwest and western Great Lakes had the potential to turn severe with large hail, damaging winds, frequent lightning, and tornadoes. As of this afternoon, a tornado was reported in Adams County, Nebraska, while numerous quarter to hen egg sized hail events (1.00 to 2.00 inches in diameter) were reported from Texas through the Upper Great Lakes. Damaging winds in Texas, Oklahoma, Missouri, Kansas, and Nebraska led to tree damage, downed power lines, and property damage. Elsewhere in the nation, severe weather was possible in the Carolinas with damaging wind and hail. In the West, a cold front approached the Pacific Northwest coasts and triggered light rain showers in the coastal areas of Washington and Oregon. Additional cloud cover and a few light showers reached into northern California.

15th-21stThe East Coast Saw another dreary day on Monday, while the Plains saw a sunny and warm day. A low pressure system remained relatively stationary as it spun over the Southeast and Mid-Atlantic States. Flow around this system pulled ample moisture onshore from the Gulf of Mexico and Atlantic Ocean, thus, a moist frontal boundary stretched along New England and the Northeast. At the same time, a cold front hovered over the Gulf states. These frontal boundaries triggered widespread scattered rain showers across much of the East Coast, with heaviest showers reported in the North. Albany, New York reported a mid-day total of 1.29 inches of rain, while Clarksburg, West Virginia saw 0.875 inches of rain. Behind this system, low pressure in the East was opposed by high pressure in the Plains. This pushed moisture away to the South, and allowed for sunny skies, dry conditions, and warm Spring temperatures to spread from the Dakotas and Upper Midwest to Texas. The North saw highs in the 60s, while the South remained in the 80s and 90s.
Meanwhile, Out West a low pressure system hovered just offshore of the West Coast. A wave of energy associated with this system moved over the Intermountain West and Northern Rockies, into southwestern Canada. This brought rain and high elevation snow showers to the Rockies. At the same time, another wave of energy and associated front approached northern California, which kicked up a few scattered showers across the Pacific Northwest.

 Fairly widespread clouds covered much of the northeastern quadrant of the nation Wednesday as a deep low pressure system sat over the Central Appalachians. Wrap around winds associated with this low ushered significant moisture into the Mid-Atlantic and southern New England. This translated into numerous rain showers with periods of heavy rainfall and thunderstorms throughout the day. Daytime heating increased atmospheric instability in the Upper Ohio Valley and the northern Mid-Atlantic, putting these areas at slight risk of severe weather activity with damaging wind, hail, and perhaps some tornadoes. Thus far, two events of quarter sized hail (1.00 inch in diameter) were reported in Randolph and Marion Counties, West Virginia. Flood Watches and Flood Warnings remained in effect for areas of West Virginia through Connecticut and western Massachusetts due to persistent precipitation. Additional on and off showers and thunderstorms developed in parts of the Great Lakes and the Ohio Valley. Behind the activity in the East, a strong jet dug across the West, while a strong Pacific storm stirred up areas of showers, high elevation snow, and thunderstorms from parts of central inland California through the Central and Southern Plains. Moist flow and daytime heating in the Central and Southern High Plains increased instability in these regions and created chances of severe weather with damaging wind, hail, and tornadoes.

More severe weather developed across the Plains on Friday, as a low pressure system hovered over the Central U.S. Counter-clockwise flow around the system pulled warm and moist air in from the Gulf of Mexico, which produced a warm front that stretched from the Plains to the mid-Mississippi River Valley. At the same time, a cold front developed behind this system, and extended southward into the Southern Plains. The strong surge of moisture in between these two fronts allowed for severe storm development with heavy downpours, strong winds, and large hail. Rainfall totals ranged from 1 to 2 inches across Oklahoma and Missouri, with up to 3 inches in areas of severe thunderstorm development. Tinker, Oklahoma reported a mid-day total of 3.37 inches. Meanwhile, multiple reports of large hail came in from western Arkansas, as well as golf ball size hail reported in Goldthwaite, Texas. The northern side of this system allowed for periods of heavy rainfall to develop across Montana and North Dakota. Rainfall totals ranged from 1.0 to 1.5 inches, with no reports of severe storms. In the East, a slow moving low pressure system lingered over the Northeast, which pushed more moisture onshore from the Atlantic Ocean. This allowed for a few more showers to develop across the extreme Northeast. Rainfall totals remained less than a half of an inch.

In the Southeast, however, high pressure over the Gulf of Mexico brought another warm and dry day to the Gulf states. Warm temperatures, low relative humidity, and strong winds caused another dangerous fire weather day. Multiple fires broke out across southern Georgia and the panhandle of Florida.

The Mid-Mississippi River Valley saw another active weather day on Monday. A low pressure system that moved into the Great Lakes continued to push a strong frontal boundary southeastward. The system stretched from the Great Lakes, down the Ohio River Valley, over the Mid-Mississippi River Valley, and into the Southern Plains. Due to warm and moist air feeding this system from the Gulf of Mexico, more severe storms developed just ahead of this front. Rainfall totals ranged from 1 to 2 inches across most of Missouri, Arkansas, and eastern Oklahoma. However, heavier rain developed in areas of severe thunderstorms. Blytheville, Arkansas reported a mid-day total of 2.13 inches of rain. Large hail and damaging winds accompanied these storms with quarter sized hail reported in Lake Worth, Texas, and dime to quarter size hail reported in St. James Phelms, Missouri. Montevallo, Missouri saw strong winds with gusts up to 60 and 70 mph, which caused major damage to trees and power lines across the region. Meanwhile, the northern end of this system created widespread scattered rain showers from the Great Lakes to New England. Rainfall totals ranged from 0.5 inches to 0.75 inches from Michigan to Pennsylvania. Severe weather has not yet developed across the North.  Out West, a low pressure system continued on its eastward path over the Rocky Mountains. The system brought widespread scattered rain showers to the Northern and Central Rockies. In addition to Spring snow melt, these rain showers created flooding problems across Montana, Wyoming and parts of the High Plains. The back side of this system allowed for cloudy skies and cool conditions to linger across the Pacific Northwest, but rain showers have not developed.

The strong storm system, associated cold front, and jet stream that brought deadly tornadoes to Oklahoma, Kansas, and Arkansas moved eastward from eastern Kansas into Missouri on Wednesday. This system drew warm, moist air from the south northward, while the jet stream ushered cold air into the nation's mid-section as it streamed in from the southwest. This activity created warm and unstable conditions from parts of eastern Texas and northern Louisiana through the eastern Great Lakes. Atmospheric conditions were favorable for the development of severe weather with severe thunderstorms, potentially deadly tornadoes, large hail, and damaging wind. Strong thunderstorms, heavy rainfall, hail, high wind, and tornadoes formed ahead of the cold front in parts of Missouri, Illinois, and Indiana. Meanwhile, numerous bands of showers, heavy rainfall, and thunderstorms developed to the north of this low and to the north of another associated front stalled in the Ohio Valley, from Nebraska through Michigan. The Storm Prediction Center put areas from northern Louisiana through the eastern Great Lakes at slight risk of severe weather development. Areas from southern Arkansas and northern Mississippi across much of the Mid-Mississippi, Ohio, and Tennessee Valleys were placed at moderate risk. A high risk statement remained in effect for parts of northeastern Arkansas, western Tennessee, southeastern Missouri, southern Illinois, western and central Kentucky, and southern Indiana through the afternoon into the early night. A major tornado outbreak was anticipated over portions of the Mid-Mississippi and lower Ohio Valleys. In the West, a late season cold front swaths of clouds spreading across the Pacific Northwest, the Northern Intermountain West, and northern California as a late season cold front brought gusty winds, unseasonably cold temperatures, and a mix of light rain showers and high elevation snow showers to the Pacific Northwest and northern California. Wind Advisories were in effect for parts of inland California, Nevada, and inland Oregon. Winter Weather Advisories were in effect for the extreme southern Cascades range and northern Sierra Nevada mountains.

A strong storm system over the Upper Midwest lifted northward into Canada Tuesday and the associated cold front from Minnesota to the Southern Plains advanced eastward. As a result, showers and thunderstorms developed along and ahead of the front from the Upper Midwest to the Southern Plains, and then eastward onto portions of the Great Lakes and Ohio Valley. In particular, severe thunderstorms developed over parts of the Mississippi Valley and Great Lakes, with hail and damaging winds.  Out West, a low pressure system off the coast started to move eastward Tuesday and produced rain showers and isolated thunderstorms over the Pacific Northwest and Parts of Northern California.   Elsewhere, rain and isolated thunderstorms fired up over the coasts of Carolinas and far southern tip of the Florida Peninsula.  Temperature wise, another hot and humid day prevailed across much of the South , Southeast and Mid-Atlantic as high pressure continued to build over the region. Well above average temperatures appeared over the central Appalachians and lower Great Lakes Tuesday afternoon. Heat index values reached to 100 to 105 over parts of the Appalachians and Mid-Atlantic and 95 to 100 over the lower Great Lakes and Southeast.

Jim G. Munley, jr.

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