Autumn air awaits behind a big cold front; Karen's effects on the Mid-South

As we discussed a couple of days ago, confidence in the weekend forecast has been lower than we like to see it, mainly due to Tropical Storm Karen moving into the Gulf Coast region as a cold front pushes through the Mid-South. The overall scenario is starting to come into focus however, and it appears that the cold front will have the most influence on our weather this weekend, with Karen contributing indirectly.

Daytime Saturday - Unsettled

With a warm and humid airmass in place, and the front approaching, the Mid-South is positioned to start seeing scattered showers and possibly a thunderstorm as early as Saturday morning. A few models are trending towards a chance of rain in the morning, then possibly a break in the afternoon, before the main rainmaker - the cold front - arrives late Saturday evening. Even given those trends though, I'm hesitant to remove all rain chances during the PM hours on Saturday given the warm, humid airmass in place and model solutions like the one below.

While most storms that form Saturday will be sub-severe, the Storm Prediction Center has placed the Mid-Mississippi Valley south to Memphis in a Slight Risk for severe storms.  The main threat will be a few strong wind gusts embedded in storm cells.  So, for those of you with Saturday plans in the Memphis/Tunica areas, it would be a good idea to have your umbrellas or rain ponchos handy. Any storms that pop-up could have some brief heavy downpours and lightning, as well as an isolated high wind threat.

SPC places the Mid-Mississippi Valley south to Memphis in a Slight Risk of severe weather for Saturday.

High-res NAM model forecast radar between 3-7pm Saturday, indicating possibility of scattered thunderstorms.
Click for larger image. Graphic courtesy WeatherBell.

Saturday night - Wet

As for the bug kahuna - the fall cold front and it's associated low pressure system are responsible for a heavy dumping of snow over the northwest and north-central U.S., as well as severe storms in the Midwest, proving it's potency. It will get hung up just a bit as it sweeps towards the Mississippi Valley on Saturday thanks in part to Tropical Storm Karen's approach in the northern Gulf of Mexico.  Karen will be pushed from coastal Louisiana across the central Gulf by the upper-level trough trailing the front before being absorbed by the front as it moves into the Deep South and Mid-Atlantic. Click here for more information on Karen from the MWN Tropical page.

Scattered thunderstorms will be likely along and just ahead of the front as it moves through the Memphis metro in the 7pm-midnight timeframe Saturday night. Trailing the front, periods of rain (possibly heavy) will last much of the night Saturday night. The excess rain will be due in part to Gulf moisture riding up over the front from Karen. Depending on the speed of the front and Karen's exact track, showers may linger into Sunday morning in the Memphis area.

Precip totals projected by the NWS through Sunday 7am. Click for larger image. Courtesy WeatherBell.

Next week - Autumn!

The best news with this cold front is the cool Canadian high pressure behind it. Much of next week will see sunny skies and temperatures that fall into the 70s for highs and 50s for lows.  In fact, some cooler spots may see 40s on Monday and Tuesday mornings! Temperatures will moderate slowly through the week but after above normal temps and humidity this week, it will be a welcome change, just in time for Shelby County Schools fall break! You can find the complete MWN Forecast for the weekend and next week here.

Tuesday AM projected low temps (GFS model) - near 50 in Shelby County! Click for larger image. Courtesy WeatherBell.

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