Wunderground.com - 1/28/13, Dr. Jeff Masters
Figure 1. Five-day predicted precipitation amounts for the period ending 7 am Saturday, February 2, 2013. Image credit: NOAA/HPC.
Is it spring or is it winter? The wild roller coaster ride of January 2013 weather continues this week, as Winter Storm Luna spreads snow, sleet and freezing rain across much of the Midwest and Northeast today, to be replaced by a spring-like surge of warm air nearly unprecedented in warmth and moisture for January. Temperatures in Oklahoma City have only reached 80° three times during January since 1890, but threaten to do so again today, and record-breaking high temperatures in the 70s are expected over much of Kansas and Missouri. Accompanying the exceptional January warmth will be near-record January moisture, as a flow of unusually moist air rides northwards from the Gulf of Mexico, where water temperatures are about 0.3°F above average.
Meteorologists use a term called "precipitable water" to discuss how much water vapor is in the atmosphere. Precipitable water is defined as how much rain would fall on the ground if one took a vertical slice of the atmosphere above a given location and condensed all the water vapor into rain. Precipitable water levels tend to be highest in the summer, since warm air holds more waver vapor, and can exceed two inches in the Midwest U.S. In winter, though, it is rare to see precipitable water values higher than one inch. However, current model runs are predicting that precipitable water values on Tuesday evening will be near record values for January over much of the Central U.S. The high moisture will lead to widespread rainfall amounts of 1 - 2" over the Midwest. These rains are likely to cause flooding problems in areas where the rain falls on frozen soils with a significant snow pack. Flood watches are posted for much of Indiana, Southwest Lower Michigan, and Northwest Ohio, as a result. Here are the record January precipitable water values for some selected upper-air observation sites, along with the forecast precipitable water values for Tuesday evening from the latest run of the NAM model (thanks to Nick Wiltgen of TWC for compiling this):
Detroit, MI: Record: 1.20" at 00Z 1/11/75. Forecast: 1.2"
Nashville, TN: Record: 1.50" at 12Z 1/21/59. Forecast: 1.1"
Little Rock, AR: Record: 1.91" at 12Z 1/13/71. Forecast: 1.5"
Lincoln, IL: Record: 1.35" at 12Z 1/12/60. Forecast: 1.3"
Accompanying the heavy rain on Tuesday will be the threat of severe weather. NOAA's Storm Prediction Center has placed portions of Arkansas, Louisiana, and Mississippi in their "Moderate Risk" region for severe weather on Tuesday. This is the first "Moderate Risk" forecast issued during 2013. Severe thunderstorms with damaging wind gusts and tornadoes are likely in the Moderate Risk area.
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