Wednesday, March 11, 2009

Winter weather discussion for Memphis

Just got off a conference call with the National Weather Service in Memphis. The Winter Storm Watch will be changed to a Winter Weather Advisory for Shelby, Tipton, and Crittenden counties (including West Memphis, Memphis and suburbs, Covington, and Munford) and will be in effect from 4am-10pm Thursday. A Winter Weather Advisory will also be in effect for Fayette County (including Somerville and Oakland) from 7am Thursday to 1am Friday. The Winter Storm Watch for DeSoto County (including Southaven and Olive Branch) will be cancelled. An updated Mid-South Warnings map will be available after the advisories are issued.

Forecast discussion
This will definitely be a borderline case for the city of Memphis as the freezing line (32 degrees at the surface) is expected to be right along I-40 by mid-morning. Temperatures prior to that will be above freezing, and temperatures throughout the remainder of the day will remain in the 32-34 range. Precipitation will move into the area before dawn as rain, helping to cool the temps down as it falls. A warm (above freezing) layer of air will exist above the surface, causing precipitation to melt as it falls. However, near the surface, sub-freezing air will help to re-freeze at least some of the precipitation.

Therefore, for Memphis, I expect rain to start mixing with sleet sometime around the morning rush-hour (7-9am). After 9am, we will likely be seeing more sleet, and possibly freezing rain (ice), than rain. Precipitation should begin to taper off around lunchtime or early afternoon and could become a light snow/sleet mixture at that time. See the NWS graphic above for the expected precipitation types and amounts.

Accumulations are expected to be perhaps as much as 0.2" of ice in the northern parts of the metro area, while southern areas may be half that. Up to an inch of snow and sleet is possible on top of the ice during the late morning through afternoon hours. Roads will initially start off OK due to recent warm temperatures, but in locations that see moderate freezing precipitation, bridges, overpasses, and secondary roads could become slick by mid-day. Links to road conditions are available in the sidebar of this blog.

I will update this as necessary throughout the event and, of course, you can check the MWN Forecast for more information at any time. As I have done in the past, I will also attempt to post any metro school closings on this blog.

No comments: