Thunderstorms and Snow

Although the thunderstorms that rumbled through the South today were tame in comparison to last week's batch, the large storm system dominating the middle of the country still caused some problems. In particular, Minnesota was subjected to blizzard conditions that shut down mail delivery in some areas.



Other areas dealing with late season snow included Calgary, Alberta and even all the way down to western Kansas. And then there are the extreme seasonal snowfall totals that have accumulated, such as in Spokane, WA, Vail, CO, and Concord, VT.

High Water on the Big Muddy

With levels continuing to rise on the lower Mississippi River, the most extensive river flooding in11 years is now developing. Although the probable opening of the Bonnet Carré Spillway would give protection for New Orleans, other river towns are beginning to feel the impact. The Corps of Engineers has heightened monitoring of levees, and there has been a breached private levee today in the area of the Morganza Spillway.

Mississippi Cleaning Up

The cleanup from Friday's storms in Jackson and central Mississippi continues, and will for a while.

Initial storm reports are now available from the National Weather Service.

A Stormy Day in the South

Last night Little Rock, Arkansas had major damage from a tornado.

Today the squall lines marched across Mississippi. All of this stormyness was in the warm moist air a few hundred miles ahead of a cold front. Even at 12Z (7:00 AM) this morning, the upper air soundings were showing unstable air across the region, with CAPE of 666 J/kg at Jackson and 1375 at Shreveport (which was already near the squall line). The severe winds of the squall line came through the Jackson Metro area around 12:30 this afternoon, resulting in widespread damage. The ASOS at Hawkins Field in Jackson recorded the following report of 47 kt wind gusts before apparently losing power:

KHKS 041729Z 28035G47KT 1 1/4SM HZ SQ FEW036 BKN046 BKN070 24/17 A2994 RMK AO2 PK WND 26047/1728 PRESRR P0002

Earlier this morning, the surface charts provided a good example of potential problems in frontal analysis due to squall lines, outflow boundaries, and rain-cooled air.


For the most part, the fronts and air masses are easily identified in the RUC Theta-e analysis, including the relict cool air mass to the east of the Appalachians. The important point to note is that the low Theta-e air mass extending from northern Louisiana to Ohio is due to low-level rain-cooled air behind the squall line.
In east-central Texas the visible satellite imagery showed a dramatic shadow from the anvil of a complex of severe storms. Overshooting tops were also fairly pronounced in the morning sunlight.



Here is the radar reflectivity showing the squall line approaching Jackson:


And a close-up of the Doppler velocity just before the strongest winds reached JSU, showing storm-relative winds in excess of 50 kt:

Weather Roundup

Strong winds associated with a southerly buster (cold front) caused widespread damage in much of Australia. There was a dramatic rescue from the snow in Keswick Ridge, New Brunswick (Canada). And snow removal costs in northern Maine have prompted calls for federal disaster declarations.

NOAA Air Resources Lab

NOAA's Air Resources Lab (ARL) is the primary NOAA branch dealing with research on air quality and chemistry issues. Offices are located in Maryland, Tennessee, Idaho, North Carolina, and Nevada. Particular emphasis in recent years has been on urban meteorology and applications for homeland security. In recent years, JSU has worked with ARL on atmospheric dispersion studies and data collection, in concert with the UrbaNet project. Another prominent project of ARL has been the East Tennessee Ozone Study (ETOS). The NOAA/ATTD DataViewer is an effort to dynamically mesh meteorological data with a Geographic Information System (GIS).

A Mighty Long Rope

Tracking a cold front with satellite imagery is easiest when there's a rope cloud. Formed by the sudden uplift of moist air to the Lifting Condensation Level (LCL) by the hydraulic head of a surface density current, rope clouds are linear features that rarely produce significant precipitation. In some cases they may also be associated with thunderstorm outflow boundaries or mesoscale fronts. Usually their position will correspond very well with the location of the surface discontinuity, although this can vary some in cases like "tipped over" fronts where cool water surface temperatures inhibit the surface front. In some cases kinks or intersections of multiple rope clouds can help to localize uplift sufficiently to initiate thunderstorms. Generally the low cloud top height and narrow scale of rope clouds make them much easier to see with visible imagery than with infrared. An example over Florida was studied by Seitter and Muench in 1985.

Today there is an unusually long rope cloud feature, spreading in a pretty much continuous line from Ontario to Texas. The position of the cold front can be identified also in New Mexico, by the presence of upslope stratus. Comparison with the RUC analysis of equivalent potential temperature confirms the strong density discontinuity. The decreased gradient across the front in West Texas is related to the presence of a short dryline feature in northeast Mexico. A weak outflow boundary from the prefrontal convection extends across from San Antonio to southern Mississippi.