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Martell: La Nina Signals Strengthen

09:50AM Feb 18, 2014



The following content was provided by meteorologist Gail Martell of 

U.S. weather anomalies: Midwest cold and Southwest drought resemble La Nina

Midwest corn fields are buried beneath a thick layer snow, 12-18 inches deep, in the wake of fresh snowstorm yesterday. Moderating temperatures are predicted this week , compacting and melting a portion of the thick snow. Chicago, Illinois, is expecting 40 F for 3 consecutive days, before a fresh polar air mass descends into the Midwest later this week. Widespread flooding is anticipated from the rapid snow melt. Thick snow is not apt to disappear entirely as cold temperatures would resume by Friday.

Winter La Nina Weather Pattern

Cold winter weather has dominated for many weeks, punctuated by bitterly cold Arctic outbreaks. The Great Lakes were 90% frozen over in mid February, the source of one-fifth of the world's fresh water. It has been 20 years since such widespread ice has occurred.

Record Drought Southwest United States

The lower 48 states experienced the 5th driest January on record. The Southwest United States reported record drought. This was very damaging for livestock grazing, reducing forage and creating a need for supplemental feed.

US Precipitation Past 60 Days

Drought has spread from the Southwest United States into the Great Plains, threatening hard red winter wheat. Oklahoma has received less than half of normal rainfall this winter, the US second largest wheat state. West Texas rainfall was "much below" to "record low" in January, the 3rd top bread-wheat state in the nation. January drought extended across the lower Mississippi Valley into the Deep South, affecting Arkansas, Louisiana, Missouri and Alabama.

What is causing the harsh winter weather? Upper Midwest cold and Southwest drought are linked to a strengthening La Nina signal. Sea surface temperature anomalies went from +0.4 C to -0.3 C from December to January. The La Nina is known as the "cool episode" from the cooling equatorial Pacific seas it causes in the eastern equatorial sea.

La Nina Template

Midwest winters are cold with the La Nina effect as the polar jet stream carves out a cold trough over the north-central United States. The Canadian prairies also experience harsh, cold winters with La Nina. The southern tier of the United States becomes very dry when the La Nina occurs. This is due to a very weak subtropical jet stream. The southern jet stream is the main source of winter precipitation, typically in southern United States. Midwest winters are stormy and wet east of the Mississippi River with the La Nina effect. Dryness often develops in the western corn belt.

The La Nina weather anomalies just described are a close match with the current conditions.

Winter Drought Hard Red Wheat

Would the La Nina signal continue? Australia and US climate experts predict neutral conditions for the near term but anticipate some warming of the equatorial Pacific sea into the northern Hemisphere spring (Australian fall). Much stronger and persistent La Nina cooling is required in the equatorial Pacific sea in order to change attitudes on the possibility of a full blown La Nina.