Tuesday, June 2, 2015

Hot, Mainly Dry Weather Continues

By Jay Grymes & Steve Caparotta

June 2nd WAFB First Alert Quickcast:

warm (hot?) afternoons ahead with highs near or above 90°  
- mainly dry through the weekend
- morning minimums show a very slow rise through the week

Our break from the wet weather pattern that dominated much of the past eight weeks or so will continue.  Upper-level ridging anchored over the Southern Plains will persist at least through the upcoming weekend and likely into next week.

With Louisiana positioned on the eastern flank of the high-pressure dome, we will continue to be dominated by ridge-driven subsidence as well as a northerly-to-northwesterly flow aloft.  The subsidence will inhibit afternoon vertical development of thundershowers while northerly winds will keep help keep dew points in the 60°s through the next couple of days, at least.

During early June, dew point readings typically average around 70° or more for the Red Stick.  Remember, dew points give us an indication of the amount of water vapor in the air.  Now a  dew point difference of 67° and 70° may not sound like much, but air with a dew point of 70° has better than 10% more water vapor in it than air just three degrees cooler!  That’s a notable difference in water vapor content, and can be the difference between feeling “not bad” and “muggy.”

The lower dew points -- along with mainly fair skies at night and in the early morning -- have allowed morning lows to slip down into the mid and upper 60°s the past couple of days, and we expect more morning lows in the upper 60°s at least through Friday.

Of course, upper-air ridging adds to the daily warm-up in two ways: (1) by reducing the cloud cover, we allow more sunshine to heat the surface and cause a faster morning and mid-day rise in temperatures, and (2) sinking air from above (subsidence) warms as it descends due to compression (the pressure getting higher as you get lower in the atmosphere, and the higher pressure means squeezing the air molecules, causing them to warm). 

Our Baton Rouge forecast calls for highs near or above 90° for most or all of this week and through the weekend.  By the way, while we note that the air for much of this week may be slightly “drier” (lower dew points) than normal for early June, afternoon Heat Index values will still run from roughly 2° to 5° above the air temperature during warmest hours of the day.

So what about rain?

Even under the effects of persistent ridging like we are expecting this week, spotty afternoon and early evening showers can’t be completely ruled out, although they are likely to be brief appearances.  At this time of year, a few small blips can be expected on Doppler radar on even most of the driest days, although these showers tend to be very short-lived.  Bottom line: whatever does develop this week isn’t likely to last too long, and may even provide a brief and welcomed break from the mid-afternoon heat.

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