re: Tornado! Large PDS Watch Issued for Portions of LA & MS

SPC is specifically mentioning the possibility of a tornado outbreak.



Day 3 Convective Outlook CORR 1 NWS Storm Prediction Center Norman OK

0241 AM CST Sun Nov 27 2022 Valid 291200Z - 301200Z

...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF THE LOWER TO MID MISSISSIPPI VALLEY... CORRECTED FOR WORDING

...SUMMARY...
Severe thunderstorms with wind damage and tornadoes, along with some hail, will be possible from the Sabine River Valley and lower Mississippi Valley north-northeastward into the mid Mississippi Valley on Tuesday. A significant severe-weather event will be likely across parts of the region.

...Lower to Mid Mississippi Valley/Sabine River Valley/Eastern Ozarks...

A highly progressive upper-level trough will move quickly into the southern and central Rockies on Tuesday. Ahead of the system, a broad 40 to 60 knot low-level jet will transport low-level moisture northward across east Texas and the lower Mississippi Valley, where surface dewpoints should reach the lower to mid 60s by midday. In response to moisture advection and surface heating, moderate instability is forecast to develop by early afternoon across much of east Texas and Louisiana. Isolated to scattered convective initiation will be possible in the early afternoon from near the instability axis eastward across the lower Mississippi Valley. A severe threat will be possible with this activity.

Moisture will continue to advect northward into the eastern Ozarks and mid Mississippi Valley during the late afternoon and early evening. This will set up a broad corridor of moderate instability across much of the lower to mid Mississippi Valley. As the upper-level trough approaches from the west, the low-level jet is expected to strengthen into the 50 to 70 knot range by early evening. This combined with increasing deep-layer shear, associated with an approaching southern Plains mid-level jet, will make conditions very favorable for severe thunderstorms across the lower to mid Mississippi Valley. NAM forecast soundings along the axis of strongest instability, from northeast Louisiana into eastern Arkansas, by 03Z Wednesday have MLCAPE in the 1500 to 2000 J/kg range, with 0-6 km shear in the 60 to 70 knot range. This combined with a long and looped hodographs, with 0-3 km storm-relative helicities in the 400 to 500 m2/s2 range, will be favorable for supercells and tornadoes. A few strong tornadoes will be possible with the more dominant supercells that remain discrete.[b/] The most favorable area for strong tornadoes may develop along the western edge of the low-level jet, as is forecast by the ECMWF, from eastern Arkansas into northwest Mississippi and western Tennessee. [b]A tornado outbreak will be possible across parts of the lower to mid Mississippi Valley, if the current forecast parameters, such as instability, deep-layer shear and low-level shear remain at current forecast levels.

In addition to the tornado threat, the potential for wind damage will likely increase during the evening as storm coverage and the chance for cell interactions increase. Mid-level lapse rates are also expected to be steep, which should support a hail threat with the more intense cells. The extent of moisture return will determine how far north-northeast the severe threat develops. At this time, it appears that at least some severe threat will be possible during the evening and overnight period as far north as southern Illinois and southwest Indiana. A categorical upgrade will be possible in later outlooks. ..Broyles.. 11/27/2022

Just surprised that this area for severe weather isn't shifted East into Alabama for the next day. We almost always follow severe weather to the West with severe weather in Alabama.

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My money was on Delta starting this thread being that he's in the orange again.

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I’ve a long alcohol and football induced thanksgiving weekend I haven’t been paying attention

Tuesday morning, afternoon, or evening for Lafayette/Baton Rouge/Covington? Got some travelers along those regions.

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patiently await the tales of the many felonious crimes you undoubtedly committed over that time.

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Other than driving back home taking back roads from the bar drunk last night, none.

00z HRRR has mischief in mind. This is around 1pm Tuesday.

Sounding from around the Alexandria area at the same time.

The high here tomorrow is only 70, I’m having a hard time seeing daytime heating causing enough instability for a moderate risk. Seems temps usually have to get near 80 to get that level of severe

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The high here tomorrow is only 70, I’m having a hard time seeing daytime heating causing enough instability for a moderate risk. Seems temps usually have to get near 80 to get that level of severe

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Cool season setups are typically more shear driven vs big CAPE but there will be plenty of CAPE tomorrow. The parameter space is high end.

While we won't really have a line form, the most obvious failure mode right now would be a messy storm mode. There's a cap, but not a great one. So, if storms start firing early like the trend is, maybe they can crowd each other.

I think that could definitely help on the northern extent. Farther south, though, I'm not so sure. The environment only gets better as the evening progresses, and some of those storms, as modeled, would be relatively in the clear.

It will also be interesting to see if we get some boundaries working from the early storms that really amplify what fires up later. That would be a localized matter that you wouldn't know until the storms are rolling.

Either way, it looks to be multiple rounds of storms starting early afternoon and continuing well into the night/early morning.