Friday, February 24, 2012

Staying Cool This Weekend

By Jay Grymes & Steve Caparotta
As expected, the front slipped through during the early morning hours, wetting a few streets for the morning drive and prompting a quick drop in both air and dewpoint temperatures as it moved through.  Friday’s high temp of 73° occurred around 2AM, with temps dropping from 70° at 7AM to 63° at 8AM.  And the dewpoint temperature -- a measure of moisture in the air -- has plummeted from the upper 60°s ahead of the front (rather humid for February) down to the upper 20°s this afternoon.
As of 4PM, Titan9 Doppler radar is still showing a broken band of light rain across southeast Louisiana, with that band slowly moving to the east and SE.  Some of those radar returns are probably not reaching the ground given the very dry (low dewpoint) characteristics near the surface.
Mostly cloudy skies this evening will show slow, steady improvement overnight, with fair skies expected by Saturday’s sun-up.  The clearing skies, “dry” air and light north-to-NE flow will mean a chilly start to the day -- look for sunrise lows in the upper 30°s for many neighborhoods along and north of the I-10/12 corridor.
Clouds will be returning to the area through the day on Saturday, as a mid/upper-level disturbance along the southern Texas coast tracks to the east and ENE across the Gulf.   High and mid-level clouds will be the main impact from this feature, but we can’t rule out spotty showers for Saturday afternoon and evening, especially for the coastal parishes.
In fact, we’ll keep a 20% rain chance in the forecast for early Sunday.  As the core of the disturbance continues to the east through the day, we should see some improvement into Sunday afternoon.  But the Canadian air mass that is moving into our area this evening stays pretty much in control of our weekend temperatures, with highs in the low 60°s for both days.
We’ll begin a warm-up on Monday, with 70°s for highs on the board for much of the upcoming work week.  And we’ll also work rain chances back into the forecast for Tuesday through next Friday.
Here’s a little food for thought:
After a dry start to the winter, many of us have experienced a “wet” run recently.  As you may recall, we’ve talked at length about the recent persistence of La Niña conditions and how La Niñas serve as a good forecasting tool in anticipation of dry weather for this time of year.  In fact, since the 1950s, roughly 75% to 80% of past La Niñas were associated with dry winter/springs across south Louisiana. 
Many of you have seen more than enough rain in recent weeks, and we’ve even seen a few rivergage sites go into flood.  Yet the reality is that the majority of communities in the WAFB region are still reporting below-normal rainfall for the period of November 1 through today.  Closer to the coast, a number of sites are well-below normal for the 4-month period, with a few locations reporting less than half their normal rainfall for the period.

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