Friday, December 20, 2013

Severe Storms Possible Saturday

By Jay Grymes & Steve Caparotta

Short Term Highlights:
The big story over the next 24-36 hours will be the severe weather threat. Most WAFB viewers from Baton Rouge northward will be under a  “Moderate Risk” for severe weather while the remainder of the viewing area is under a “Slight Risk.” The critical risk window will be from Saturday afternoon into the pre-dawn hours Sunday. All the rains end on Sunday, with clearing underway by Monday.

Christmas Week Quickcast:
Sunshine returns by Monday and extends through Thursday, and the days will have a winter-like feel, especially Christmas Eve and Christmas Day. Some WAFB neighborhoods along and north of the I-10.12 corridor could see a light freeze on one or both of those two mornings. Afternoons under the sunshine will be comfortably cool.


The Rest of the Weather Story:
Our primary weather focus is on the severe weather potential for Saturday night into the earliest hours Sunday. Models are suggesting a squall line ahead of an advancing cold front that will generate strong to severe thunderstorms as it moves from west-to-east across the viewing area. The greatest threat for severe weather will extend across the Baton Rouge metro area and adjacent areas to the north, northwest and west of the Capital City.

The main severe weather threat will be in the form of damaging winds, but we want to point out that there is the potential for isolated tornadoes. Additionally, forecast models have come into much better agreement over the past 24 hours with regard to the timing of the stormy weather and frontal passage.

We’ll go with a mainly-dry but very muggy start to Saturday, with sunrise temps in the mid to upper 60°s. Areas of fog -- some locally-dense -- will be an issue for some communities, but the morning winds will be running in the 10-15 mph range, sufficient to minimize any concerns for widespread fog development. As a result, we do not anticipate a regional Fog Advisory for inland locations, although fog could be a real nuisance nearer to the coast and along larger waterways.

We’ll go with scattered showers and t-storms developing during the afternoon, well ahead of the cold front. Coverage will increase through the afternoon and into the evening as we await the main energy associated with the forecasted squall line. Right now we anticipate the west-to-east moving squall line to hit the BR metro area during the late evening hours (say, after 9PM) and push through the New Orleans metro area sometime closer to midnight. Some rains could linger into the early, pre-dawn hours of Sunday morning before ending.

The guidance is hinting at a trailing boundary -- essentially a secondary cold front -- that moves through the region on Sunday. While this looks like a “dry” front, it will have enough moisture to keep a decent deck of clouds around through much of Sunday. Some of the clouds could linger into early Monday before a cold and dry Canadian air mass finally moves into the lower Mississippi Valley for Christmas Week.

We’ve already mentioned the cold mornings for Christmas Eve and Christmas Day, with a slow warming trend that runs into Thursday. In the extended outlook, our next cold front arrives on Friday, producing another dip in the daily temperatures. However, Friday’s front will have only limited moisture to work with, so any rains will be isolated in nature and limited in amounts.

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