Tuesday, November 26, 2013

Clearing, Staying Chilly on Wednesday!

By Jay Grymes & Steve Caparotta

We spent the night waiting for a chillier air to arrive ... but it just didn’t happen for Baton Rouge.  In fact, morning temps at Metro Airport (BTR) ended uprising between midnight and 5:00am rather than falling, only to start to drop again when the morning rains arrived.
Although there were breaks in Tuesday’s rains, the clouds, the northwest winds and the steady temps in the 40°s made for a day that was even drearier than Monday.  As we hinted yesterday, rains tapered off after the morning and many of you had a prolonged run of rain-free hours through the middle of the day.  
Yesterday we described a double-barreled rain event for today, with the first round of rain tied largely to the surface low passing to our south from west-to-east with energy from the southern branch of the jet stream.  That would be followed by a second round of showers tied to the upper-level low that was positioned over Texas on Monday.  That gameplan appears to have been on-target, with wet weather moving back into the area this evening.

It all clears out of the viewing area before sunrise, giving us a dry Wednesday morning commute.
So what about that talk of a frozen “wintry mix?”  Chances are still fairly low, but we still can’t entirely rule out the potential that keen-eyed viewers up along and north of the LA/MS state line might see a brief shot of sleet or even a couple of ice pellets.  Note that the window of opportunity is small -- only a handful of hours -- and seems limited to the evening hours before midnight.
Not to worry: even those that might see a “winter mix” won’t have to deal with accumulations nor should it be an issue for the Wednesday morning drive.
So we say “goodbye” to the rain and open Wednesday with mainly clear skies at sunrise, but we’ll be trading the rain for more cold.  Many of you to the north and east of Baton Rouge will awaken to a light freeze for Wednesday morning -- indeed, some metro BR neighborhoods could see frost and a brief light morning freeze although we’re officially posting 33° for the forecast low at Metro Airport.  Later in the day, even with the sunshine, Wednesday stays chilly with highs topping out in 40°s for the third straight day.
But it gets MUCH colder for Thursday morning!  We’re going with a low of 25° for the Red Stick on Thanksgiving morning with lows dipping into the low 20°s along and north of the LA/MS state line. That has prompted the National Weather Service to issue Freeze & Hard Freeze Warnings for most of the area late Wednesday night into Thursday morning.

Cold?  Boy, you bet … Baton Rouge’s record low for November 28th is 23°, set back in 1938. We’ll get uncomfortably close to the record!
The Thanksgiving morning freeze will extend all the way to the coast.  And remember, in many cases the duration of the freeze is more important and more damaging than the actual low temperature.  For the time being, we’ll go with BTR temperatures at or below freezing for roughly 10 hours or so.  For WAFB communities along and north of the LA/MS state line, durations could exceed 14 hours!
Remember, double-digit freeze durations are more than enough to damage the tender vegetation, so take precautions.
But what about those exterior pipes?  For most outdoor pipes up against the side of the house, this is not likely to be a pipe-busting freeze.  But for those living north of the I-10/12 corridor, you should consider wrapping any exterior pipes that have a history of freezing.
And needless to say, our area strawberry farmers as well as local gardeners with young, outdoor citrus need to set-out the protective ‘blankets.’
Assuming that BTR drops to 25° or lower for Thanksgiving morning, when was the last time we had a freeze like this?  Metro Airport dipped to 26° on March 3rd -- the coldest day of 2013 thus far.  If BTR drops to 25° or below, we have to go back to January 2011 to find a day as cold or colder.
Now understand that a low of 25° for Baton Rouge is not all that uncommon: there have been more than 300 days with lows of 25° or below since 1930 (84 years).  In fact, over those 84 years, there have only been 10 years without at least one day when the minimum dropped to 25° or below for BTR.   Yet somewhat interestingly, 4 of those 10 years have occurred since 2005.
While we’ve seen a handful of “25° free” winters of late, not all recent winters have been ‘warm’ throughout -- for BTR, there were 7 days in January 2010 with lows at or below 25° and 9 days during the 2010-2011 winter with lows of 25° or below.
So, a 25° low may not be all that rare for Baton Rouge, but a 25° reading during November is uncommon for the Capital City.  To put in into perspective, the statistical “average first freeze” for Baton Rouge doesn’t occur until the last week of November -- generally right around the Thanksgiving holiday and rarely more than a light to moderate freeze.
(By the way, our first freeze for this season was almost two weeks “early,” with BTR briefly slipping to 32° on the morning of the 13th.)
Since 1930, there have been only 14 November days with minimums at or below 25° for Baton Rouge.  Three of those days were in November 1938 and two more occurred during November 1976.  That leaves just 9 November occurrences over the remaining 82 seasons -- or roughly once every 9 years, on average, that BTR has a November morning at or below 25°.
By the way, the last time Metro Airport’s thermometer dipped to 25° during November was back in 1992, so that statistic suggests that we were a long overdue.
For the trivia fans, the earliest 25° or below reading Baton Rouge was 22° on November 15, 1940.  And the all-time lowest November reading for BTR?  21°, recorded on November 30, 1976.
Thankfully, temps will climb into the 50°s for just about everyone under sunny skies by Thanksgiving afternoon, providing a much-welcomed thaw.  Most WAFB communities can expect another freeze for Friday morning, but the Friday freeze won’t be nearly as cold nor as prolonged.  Then we’ll head into a warming trend through the weekend.  Expect dry weather throughout the Thanksgiving weekend with highs back into the 60°s for Saturday and approaching 70° for Sunday.

Rain is back in the forecast by Monday, just without the freezing temperatures this go-around! 

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