MID-LATE WEEK STORM TO SPREAD RAIN, THUNDER FROM EAST TEXAS TO MIDWEST

Forecast water-equivalent precipitation — 7 AM Tuesday to 6 PM Saturday

Low pressure over the southern Plains early Wednesday is forecast to intensify and move to near Chicago by early Thursday, spreading rain and thunderstorms from E Texas to the Great Lakes. This system may produce strong enough rising motion in the atmosphere to change rain to wet snow across parts of the metro area on Thursday.

FORECASTS SUGGEST A GENERAL ABSENCE OF WINTRY WEATHER THROUGH MID-FEBRUARY

The flow of mild, Pacific-origin air that has overspread much of the nation is likely to continue for much of the next two weeks. Beyond that, heading into the latter part of the month, there are signs of a colder regime becoming established. However, by the end of February average high temps are already topping 40 degrees. Increasing sunlight and lengthening days make extended periods of snow cover or extremely low temps unlikely.

Mild temps to dominate through mid month — forecast mean temp departure from normal (valid February 11 to 16)

Warm pattern may begin to break down by late February — forecast mean temp departure from normal (valid February 16 to 21)

THE EFFECT OF SNOW COVER ON NIGHTTIME TEMPERATURES

4 AM CST observed temperatures and infra-red satellite imagery taken 4:36 AM Monday

On clear nights, snow cover radiates outgoing terrestrial radiation more efficiently causing lower surface temperatures. The lighter gray shades over Wisconsin and northern Illinois reflect these lower readings.

EFFECT OF SNOW COVER ON DAYTIME TEMPS

3 PM CST observed temps and visible satellite imagery

During the day snow cover reflects rather than absorbs most incoming sunlight resulting in lower surface temperatures. If temps are above freezing, cooling over snow cover is compounded by melting. The change of state from a solid to a liquid requires an absorption of energy. This further inhibits daytime warming.

MILD PATTERN HAS NATION’S SNOWPACK IN RETREAT

Map showing extent of observed snow cover on Monday, January 27th when 54.7% of the country was snow covered.

Map of U.S. observed snow cover one week later, on Monday, February 6th. Snow coverage had shrunk to 36.1%.

FORECAST FOR FRIDAY AT 5:30

Secondary low pressure may develop in moderately colder air Friday following Wednesday night/Thursday rain and produce an area of wet snow

FULL-DAY TEMP DEPARTURES FROM NORMAL

Overall milder than normal pattern to persist through mid February