Directional Winds & "Fronts" - WAFB 9 News Baton Rouge, Louisiana News, Weather, Sports

Directional Winds & "Fronts"

Question:

In all of my 65 years I have noticed an east wind is a very uncomfortable wind.  It seems to be much more uncomfortable than a north wind after a front, even though the north wind is a colder wind.  Is there a scientific basis for this phenomenon or is it just my imagination?  To give you a little scientific data, I live in Acy, Louisiana (a suburb of St. Amant) and Acy lies about 15 miles due west of Lakes Maurepas and connecting Pontchartrain. 
Lagniappe question: What exactly is a "front"?  Is it just a traveling boundary between two weather systems or is it something more?


Answer:

I suspect that your location relative to Maurepas and Pontchartrain can make a wintertime east wind rather uncomfortable because it is not only cool (although generally NOT as cold as a "north" wind), but also because it is moistened up as it passes over the relatively warm lakes (warm in the sense that very often the lake waters are MUCH warmer than the west-bound air flowing over them.)  Cool, damp air tends to feel "colder" to the skin than cool, dry air because as the moisture is evaporated on your skin, it produces a "chilling" effect (removes even more heat from your skin to evaporate the water).

I will try to keep the answer to you lagniappe question very simple and sort of one-dimensional. [This is a two-day lecture in my course at LSU!] A front is a boundary separating two different air masses - the contact point between the two.  You can think of the air masses as large domes of air that slide across the planet's surface, kind of like large flat blobs.  Within the air mass conditions are fairly similar.  These air masses can extend over 1000s (even tens of 1000s) of square miles.  But because of their unique characteristics (their temperature and moisture structure, for example), these air masses tend to avoid freely mixing with air masses in contact on their margins.  (The entire earth is covered by a "patchwork" of these air masses, each moving all the time.)
The primary differences in air masses for the Gulf Coast region are the "cold & dry" air masses from the N and NW  vs.  the usually "mild-to-warm & moist" from the S and SE (the Gulf). When the cold, dry air mass is advancing, the boundary between the two is a COLD front.  In this instance, the "mild & moist" air is lifted by the "cold & dry" air because "mild-to-warm & moist" is lighter than "cold, dry air."  Lifting the moist air eventually produces rain as the water vapor in the "moist air" begins to condense.  So, a COLD front represents cold, drier air replacing mild-to-warm, moist air at a location.
 
A WARM front is the opposite - mild/warm & moist air replaces cold, drier air at the surface.  The problem for WARM air replacement, however, is that it has to replace the cold air from the top down (because it is still lighter than the cold, dry air).  WARM front tend to move more slowly and tend to be less active from a weather perspective.
 
The front is the meeting point (at the surface) between the two air masses.  Cold, dry air acts like a bulldozer, undercutting the mild, moist air usually in place over Louisiana.  When the air masses are dramatically different, the COLD front lifting can occur very rapidly - resulting in t-storms.  Rapid uplift usually means t-storms.
 
Now it's important to remember that the air masses extend above the surface for considerable depth - upwards of 1-3 miles or more. While we almost never, ever mention the "elevated front" (the contact point between the two air masses at some height above the ground), this too can be important in terms of determining the weather action and severity.
 
I could go on for pages ... but that should be enough for you to chew on for a while!
 
Good questions!
 
Jay Grymes
Chief Meteorologist
WAFB Storm Team

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