January 27 - 29, 2014 Winter Storm Discussion

Some important, key considerations with regard to the type of wintery precipitation hinges upon WHEN the precipitation will begin for New Orleans.

Here before me, I have 1 solution showing as soon as early Tuesday morning; then another showing 12 Noon Tuesday, 1/28, to 12 Midnight late Tuesday night; a 3rd solution showing 6 PM Tues evening to 3 AM, Wed. Morn; and a 4th suggestion between 3 PM and 9 PM, Tuesday afternoon & Tuesday night.

I think, the sooner the precipitation starts, as in that 1st one, early Tuesday morning, will have a better chance to increase the freezing rain / icing potential. Later in the day, will allow temperatures to climb above freezing, although not much, and so then the icing threat becomes de-emphasized, since colder temperatures aloft will work-in Tuesday evening & beyond.

In order to have the icing and freezing rain, surface temperatures have to be 32° and below.

Everyone would prefer what I'd call a "cleaner" storm that produced snow & sleet, vice the freezing rain & ice.

I believe the snow potential for southshore will have to hold-off until Tuesday evening & beyond, when temps. aloft are shown cool aloft, closer to freezing as shown by C-Gem & your Gfs.

The single most important element differentiating THIS next one for Tuesday & Tuesday night, 1/28, is MORE measureable QPF amounts. Gfs keeps a lot of the moisture hugging along the coast & in the Gulf of Mexico. Several other solutions bring it ashore, generating measureable precipitation.

As the way I see it from Nam's 12Z solution, a full-on major ice storm is advertised in that solution, after inspecting the thermal profile structure aloft. Nowhere near the 0.83" it generates for New Orleans would be needed, either. Its solutions showing 7°C temps at 850 mb and 4° at 900 mb during the time it's precipitating would not support sleet nor snow during the daylight hours Tuesday; instead it'd be rain & freezing rain on Tuesday.

Since all the other models hold-off the precipitation until Tues. Afternoon & Tuesday night, and since the others are also considerably COLDER aloft, in their thermal profiles, than Nam, then these other solutions would support sleet & snow for a wider area of Southeast Louisiana, than the last one did, on Friday, 1/24.



-- cyclogenesis