2012-01-30

The high latitude Eurasian Anticyclone of January-February 2012 A strong blocking anticyclone developed over northern Russia in late January 2012. As the anticyclone strengthened, a closed 5640m ridge with near 3 above normal height anomalies over northern Russia. At the surface an anticyclone developed with a closed 1060 hPa and at times a closed 1064 hPa contour. This massive deep anticyclone transported warm moist air into the Arctic, producing warm conditions and rain in the Spitsbergen Islands to near 80 degrees north latitude. But the high impact, if not historic, weather event occurred to the south where the strong easterly flow on the southern flank of the anticyclone pushed arctic air into eastern, central and eventually Western Europe. The cold air resulted in over 150 weather related deaths by 2 February 2012. The winter of 2011-2012 had been relatively mild for most of Europe. As the cold air surged westward, it brought snow and temperatures fell to near normal then to well below normal. The mild conditions were rapidly replaced by harsh winter conditions. As the cold weather swept into Western Europe it brought snow to Rome, Italy for the first time in 26 years. Temperature fell below -32C (-26F) over portions of Eastern Europe. This paper will document the anticyclone and the cold episode that affected much of Europe over the period of 30 January through 3 February 2012.and its impacts. The focus is on the use of anomalies to analyze this and similar high impact weather events. Forecasts from the NCEP GFS and GEFS are presented to show the value of using climate data in the forecast process to better anticipate extreme weather events.

2012-01-22

Gulf States Severe weather and Tornado Event of 22-23 January 2012 Abstract: A mid-tropospheric trough moved across the Rocky Mountains and into the Plains on 22 January 2012. As the wave moved eastward it pulled a plume of deep Gulf moisture into the Mississippi Valley. Precipitable water anomalies of 3 to 4 above normal were present in this moisture plume along with a strong 850 hPa jet. The shortwave flooded much of the eastern United States with warm air and triggered a severe weather event in the Mississippi Valley with 247 severe reports on the 22 of January. Severe thunderstorms were observed in the deep moisture plume ahead of the wave and attendant cold front. Severe storms were observed from southern Arkansas to Indiana. Tornadoes were observed as far north as Tennessee but the focus of this January tornado outbreak was from Arkansas to Alabama. The event produced 264 severe weather reports over the two days to include 50 tornadoes. Of the 50 tornadoes, 26 were observed in the State of Alabama, which experienced two deadly tornadoes. The 26 tornadoes in Alabama surpassed the event of 10 January 1975 when there were 13 tornadoes in Alabama. This paper will document the historic tornado and severe weather event of 22-23 January 2012

2012-01-21

A deep trough over northern western North America and a ridge over the eastern Pacific brought a strong 250 hPa jet and a surge of deep Pacific moisture into the western United States from 18-22 January 2012. Reports of over 16 inches of precipitation were observed in the mountains of southern Oregon. Many areas of California had heavy rain or snowfall. The combination of the cold air over western Canada and Alaska and the surge of moisture produced snow in Washington State. Before the ice storm began, the Seattle area had 10-20cm of snowfall. Heavy snow impacted the higher elevations. Farther south and at lower elevations heavy rain dominated. Strong Pacific jets and moisture surges are often associated with El Niño conditions. However, such events can and clearly do occur during El Niña winters. This event was observed during a La Niña winter. This paper will document the West Coast heavy precipitation event of January 2012. The NCEP GEFS precipitation forecasts show that the GEFS did well in predicting the potential for heavy rainfall and the impact of the Pacific moisture plume into the mountains of the western United States.

2012-01-17

Abstract: A strong cold front ripped across the Midwest and into the northeastern United States on 17 January 2012. Unseasonably warm moist air ahead of the front provided moisture and added instability. This resulted in widespread severe weather mainly before 1800 UTC in the Ohio Valley and another widespread convective wind severe event in the eastern Great Lakes. Overall, there were 165 reports of severe weather, including 14 confirmed tornadoes, on 17 January 2012, a relatively high number of severe reports for mid-winter. Southern Indiana and Kentucky were particularly hard hit with 10 verified tornadoes which based on the 1950-2011 climatology is an historic event. The region averages about 0.37 tornadoes per year during the month of January. Other big tornado events in this region included 3 tornadoes in 1964 and 1997, 5 tornadoes in 2008 and 6 tornadoes in January 2006. This paper will document the historic tornado and severe weather event of 17 January 2012.

2012-01-05

The first part of the winter of 2012 will be remembered in many part of the United States as a warm and snowless winter. The combined effects of a persistent La Niña and a positive NAO likely were contributing factors. The MEI was a modest 0.97 for the month of December 2011 but the AO at 2.28 was second only to 2006. The pattern produced a generally warm period over the eastern United States for the month of December 2011. At the end of December 2011 and into early January 2012 an unusually large ridge developed over the western United States. This produced a period of warm weather, breaking many high temperature records from the West Coast to the plains. The sharp ridge pushed a 5820 m contour over the southwest and amplifying the pattern, allowing cold air into the eastern United States. As the western half of the United States basked in unseasonal warmth, the eastern United States briefly experienced the coldest weather of the winter of 2011-12 to date. This paper will examine the conditions associated with the western United States warm up to include some large scale Teleconnections data. Standardized anomalies are used to characterize the pattern. Forecasts from the NCEP 75 and experimental 55km GEFS are used to show that this unusual event was relatively well predicted.

2012-01-03

A deep, fast moving cyclone produced a high wind event across portions of Northern Ireland and Scotland on 3 January 2012. The central pressure bottomed out around 952 hPa based on the United Kingdom Met Service surface analysis. The strongest wind occurred south of the cyclone in the relative cold air mass, north and west of the strong southerly flow in the warm air. Similar to other oceanic cyclone events, the strongest winds were associated with only light or showery precipitation. The cyclone was relatively well predicted by numerical models and ensembles, however, the intense winds south of the cyclone in the cold air were not as well predicted. This mesoscale feature, associated with winds over about 80 mph was not so well predict. Forecasters, using pattern recognition identified this as a “sting jet” and correctly alerted the public for the potential for strong and damaging winds. Identifying and recognizing the pattern and probabilities is more important than names assigned to the phenomena. No debate on the name of the phenomena is offered here. Standardized anomalies were used to assess the strong winds and the overall intensity of the system. The strong winds disrupted transportation, damaged homes, and interrupted power in northern Ireland, Scotland and portions of England. The higher and more damaging winds were farther to the north, closer to the passage of the deep oceanic cyclone. Shapiro-Keyeser Cyclone Ensembles anomalies.