Another Taste of Autumn

A nice batch of showers and thunderstorms are rolling across the area as I type this update...much needed rain as parts of western KY & northwest TN are in moderate drought conditions.

 

The cold front and associated area of low pressure responsible for bringing today's showers and storms will press on to the east tonight, and most of the precipitation should be out of the area shortly after midnight.

The big story with this system will be the drastically cooler air that pushes in as a big dome of Canadian high pressure takes over in the wake of the front. 

You'll notice a big difference in temperatures as early as tomorrow morning, when lows could drop into the upper 40's across portions of southern IL & southeast MO, if skies can clear out quickly.  Tomorrow afternoon, temperatures will struggle to reach 70 with a blustery north wind expected.  Then tomorrow night, it's not out of the question that a few spots could flirt with record lows, as temperatures fall into the mid 40's.  The record for Thursday night/Friday morning at Paducah is 44 degrees.

By Sunday, the center of high pressure will drift east into New England...

With the return flow, winds from the south will pump some warmer air back into the region for the end of the weekend and first of next week.  This will also bring moisture back into the region, possibly setting us up for some scattered showers and thunderstorms by the first of the week.  More on that in the next few days.

La Nina Returns

While our overall weather pattern will remain fairly quiet for the immediate future, a look way ahead to the upcoming few months reveals that things may grow to become pretty active again over the winter and spring months, thanks in part to the return of La Nina.  La Nina...the "female" counterpart to El Nino, is an overall cooling of the waters of the central and eastern Pacific Ocean.  A recent look at sea-surface temperatures in the Pacific show that this climatic setup has returned.

Of course, there are a number of other atmospheric factors that will ultimately determine how our weather unfolds over the winter and spring months, but usually this type of setup brings wetter than average conditions to the Ohio Valley.  La Nina was certainly a contributing factor during last winter's record snowfall across parts of the central U.S., the record flooding across our region last spring, as well as the record number of tornadoes in April.  This will be a story worth following over the coming months, and could lead to more volatile weather during the more active months to come.  The official NWS winter outlook will arrive in mid-October, so it will be interesting to see how this plays into their predictions.  To read more about the latest La Nina information, check out this link:

http://www.noaanews.noaa.gov/stories2011/20110908_lanina.html

Windy Labor Day & Problems From Lee?

Hey there...hope you are enjoying your Labor Day weekend!  What a big change over the past 24 hours!  After nearly reaching 100 degrees yesterday, we held steady in the 70's today, with plenty of clouds and scattered showers associated with moisture from Lee and the cold front that moved across the area.  Tonight, a look at the surface map shows the front pretty much through the entire region, and the cooler, drier air moving in from the north.

With high pressure behind the front, and lower pressure at the center of Lee, our region will be stuck in a pretty big pressure gradient tomorrow, leading to a breezy Labor Day.  A Lake Wind Advisory is in effect for Monday, with NNE winds of 10-20 mph, gusting as high as 30-35 mph, with the strongest gusts the farther south you go.  And a big question mark for tomorrow will be how quickly we clear out. With moisture streaming north from Lee, it may take most of the day for clouds to clear out east of the Mississippi River.

Looking ahead, since the last post there have been some changes in the forecast models' idea of how the remnants of Lee will impact our weather picture this week.  It's a rather complicated situation with multiple variables, so some tweaking may occur to the forecast over the next few days.  As Lee begins to wind down and become post-tropical, it will be phased into the existing cold front that is moving through our area, and will move northeast along that front.

At the same time, Hurricane Katia is still slowly churning northeast across the Atlantic, headed in the direction of the east coast.  As you can see below, it still appears that Katia will not make landfall, but will get a little too close for comfort.

 

Ultimately, by mid-week it looks like the remnants of Lee will develop into what we call a cut-off low...an area of low pressure that is not connected, or "cut off", from the steering currents of the jet stream.  These features typically hang around for a few days, and lead to cloudy, cool, and sometimes rainy weather.  And with Katia approaching from the east, this system will effectively block other features, such as this low, from moving east, at least until Katia exits the picture. Here's what that looks like on the model chart by Wednesday morning:

Notice the "L" surrounded by circles over MS & AL?  That's our cut-off low.  Here's the surface chart for the same time period:

Notice the purple over the Local 6 area?  That indicates light rainfall over our region.  All of this is has been hinted at by one or two of the models for a few days, but today just about all of the models came into agreement on this scenario, which led to some big changes to the forecast for this week.  I went ahead and kept things mostly cloudy for Wed.-Sat., with daily 30-40% chances for rain, and slightly cooler temperatures.  We'll see how this whole thing plays out.....if Katia's track diverges, then the forecast will have to be adjusted as well.  Stay tuned.