Is it spring or is it winter? Wild roller coaster of temperatures for the U.S.

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.


Figure 1. Five-day predicted precipitation amounts for the period ending 7 am Saturday, February 2, 2013. Image credit: NOAA/HPC.


Figure 2. 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.

Dangerous air pollution episode finally eases in Utah
As I blogged about last week, clear skies, light winds, and a strong temperature inversion combined to create a dangerous air pollution episode in Northeast Utah in Salt Lake City and surrounding regions. However, over the weekend, a surge of warmer air and rain pushed into Utah, breaking up the temperature inversion, and bringing an end to the week-long pollution episode. In Salt Lake City, fine Particulate Matter less than 2.5 microns in diameter (also called PM 2.5) peaked at 59 micrograms per cubic meter on Saturday, nearly double the federal standard of 35 micrograms per cubic meter (averaged over 24 hours.) But by Sunday morning, PM 2.5 levels fell below 35 micrograms per cubic meter for the first time in over a week, allowing the city to finally breathe a little easier. In nearby Provo, Utah, the pollution had been much worse, with 24-hour average PM 2.5 levels more than triple the federal standard on Thursday morning, at 132 micrograms per cubic meter. On Sunday, air pollution levels in Provo also fell below the federal standard for the first time in over a week. With the forecast calling for snow through Tuesday and strong westerly winds building in, pollution levels should stay out of the red zone for at least the first part of this week. Brian Moench, an anesthesiologist and president of Utah Physicians for a Healthy Environment, estimates that poor air quality contributes to 1,000 to 2,000 premature deaths each year along Utah's Wasatch Front.


Figure 3. Observed air quality in North Provo, Utah, January 23 - 28, 2013. 24-hour average fine Particulate Matter less than 2.5 microns in diameter (also called PM 2.5) levels (black circles, top image) were in excess of the 35 micrograms per cubic meter U.S. standard (orange line) during the first part of the period, and peaked at 131 micrograms per cubic meter--more than 3 times the Federal standard--Thursday morning. The wind speed at the surface never rose above 6 mph (lower image, black dots) while the pollution was in excess of the federal standard, but on the 27th, the wind rose to 10 mph, helping flush out the pollution. Image credit: Utah DEQ.

Jeff Masters