Looks 'Wetter' for Wednesday

They’ve had some heavy rains, strong storms and even some localized flooding in the northern parishes today, but for many of us in the WAFB viewing area, it has remained dry. True, we did have some passing showers and a few t-storms in our viewing area this afternoon, especially up along the LA/MS state line, but most of those were quick-moving and short-lived, producing little in terms of accumulations.

 

Even with today’s relatively quiet weather so far, we’ll keep a slight chance of rain in the evening and overnight forecast. We’ll also carry isolated showers in the forecast for the morning drive, then take Wednesday afternoon rain chances up to about 50-50.

 

 

The upper-level ridge that has been a dominating feature in our recent weather is finally breaking down. A cool front is sagging southward today and will stall over the northern half of our viewing area later tonight and early tomorrow. At the same time a series of mid/upper-level disturbances will continue to move west-to-east across the coastal states. Add in daytime heating and Gulf humidity and you can see why rain chances will be noticeably higher for Wednesday.

 

 

Somewhat surprisingly, however, the wetter pattern doesn’t hold on for long. We’ll drop rain chances for Thursday down to the 30% to 40% range, and drop it another 10% for Friday as a ridge attempts to become re-established over the eastern U.S. before the end of the work week. Heading into the weekend, we’ll keep isolated to scattered mainly-afternoon t-showers in the forecasts for both Saturday and Sunday.

 

Temps throughout the rest of the work week and into the weekend will run very near the norm for this time of year: low to mid 70°s for morning lows and low 90°s for afternoon highs.

 

 

Tropical Depression #2 (TD#2) continues to move over across Central America -- the latest position estimate puts the poorly-defined center over Mexico and not too far from the coastline to the Bay of Campeche. The current best-guess forecast track takes TD#2 over the southern Bay of Campeche by tomorrow and possibly remaining over the water until late Wednesday or early Thursday. Still, there is little opportunity for the depression to undergo much development before landfalling again on Thursday. Still, TD#2 may prove to be a proficient rainmaker for parts of Mexico, but the system offers no threat to U.S. interests.

Better Chances for Rain This Week

 

Titan9 Doppler was showing a few showers on Monday afternoon with a couple of t-storms in the WAFB viewing region, but all was mainly quiet across the immediate BR metro area as of 3PM. We’ll keep isolated showers in the WAFB area forecast for the rest of the afternoon and early evening, then ending soon after sunset. 

 

No doubt about it, summer heat has really kicked in this month! Today marks the 8th straight day with highs at 90° or above at Metro Airport (BTR) and for some of you that run of heat has been essentially rain-free. In addition, we’ve got returning to the 90°s just about all week long.

 

For the trivia buffs ... BTR averages about 19-20 days every June with highs of 90° or more. Today marks the 11th day at 90° or more for this June. Based on BTR records since 1930:

. . . the most June days at or above 90°: all 30 days during June 2006 and June 1960
. . . the fewest June days at or above 90°: only 4 days during June 1983 and June 1961

As we’ve seen the past couple of days, rain chances will remain on the low side -- say around 20% to 30% -- for Tuesday. Fortunately, the upper-level “heat ridge” that dominated our weather over the weekend is weakening and retreating a bit to the west -- that should allow for better rain chances by Wednesday into Thursday. Set rain chances for Wednesday and Thursday in the 40% to 50% range -- and for many, the gardens and lawns could use a little rain.

It looks like upper-level ridging will return as early as Friday, and the will mean a drop in forecasted rain percentages for Friday through the upcoming weekend. But for the time being, we aren’t yet anticipating a return of the mid 90°s for the coming weekend.

For the College World Series, the Tigers take on the UNC Tarheels in an elimination match-up on Tuesday at 2:00PM. The weather cooperates at T.D. Ameritrade Stadium for Tuesday afternoon: mostly sunny to partly cloudy, game temps in the low 80°s with winds light and ranging from the ENE to the ESE.

In the tropics, the National Hurricane Center “upgraded” the vigorous tropical wave located over the Gulf of Honduras (NW Caribbean) to Tropical Depression #2 (TD #2). TD #2 is moving inland across Belize, headed towards northern Guatemala and the Yucatan. Given that it is moving over land, development is not an issue in the short term. However, the forecast guidance does take the system into the southern Bay of Campeche by Tuesday or Wednesday. At that point, conditions appear somewhat favorable for development -- and the National Hurricane Center currently shows the system briefly achieving tropical storm strength before its final landfall in Mexico. If TD #2 were to become a tropical storm, it would be named Barry.

A couple of other disorganized tropical waves are evident over the open tropical Atlantic, but none show imminent signs of organization.

Temps Remaining Above-Normal This Weekend

By Jay Grymes & Steve Caparotta

Warmer-than-normal weather will persist for at least another three or four days -- afternoon temps in the 90°s coupled with an abundance of Gulf humidity will continue to push daily maximum Heat Index readings above 100° for many WAFB neighborhoods right through the weekend. 

Our forecast for Friday and the weekend remains virtually unchanged.  Mid/upper-level ridging will be the primary controller for our weather for Friday and Saturday, with the ridge starting to flatten (weaken) late Saturday into Sunday.  For most of us, hot-and-humid with little in the hopes of a cooling shower will be the rule for the next few days.

Although the guts of the upper ridge remains in place, it still looks like that “cool” front we’ve been advertising this week will indeed slide south during the latter half of the day Friday into early Saturday as a “backdoor” cool front.  Don’t expect much of a change though -- the front will add a few percentage points to rain chances on Friday and produce a very modest drop in dew points and the morning low for Saturday, but that’s about it.  Expect highs in the mid 90°s for both days.

We’ll go with a 20% rain chance on Friday, with only spotty showers for Saturday. 

As we mentioned, the outlook calls for a weakening of the ridge by Sunday.  Now we are not talking about a major change, but a less robust “cap” on the atmosphere which should allow for a few afternoon showers.  So let’s be generous and say isolated showers -- uh, maybe -- for Sunday afternoon. 

The forecast for next week stays on the “drier” side, with rain chances generally around 20% through the week.  But we also expect those daytime highs to back down into the low 90°s rather than the mid 90°s through the work week - - not a big change, but worth noting nonetheless.  And after a run of mid 90°s, low 90°s may not seem so bad?

As for the tropics, there are a couple of waves -- one to the east of the Lesser Antilles and another in the SW Caribbean -- but neither is showing any real threat for development at this point.

Heat & Humidity Combine for Added Discomfort!

-- Jay Grymes / WAFB Storm Team

 

Afternoon temps in the 90°s coupled with an abundance of Gulf humidity will continue to push the Heat Index readings up to near or even above 100° for most WAFB neighborhoods just about every day this week.

 

As you know, the Heat Index represents the perceived ‘feels like’ temperature for humans and is often referred to as the “apparent temperature.” The Heat Index (HI) is a subjective measure that makes a number of assumptions about the state of an individual, including type of clothing, the amount physical activity, even the person’s size and weight. The HI, therefore, is a reference number, a guideline, designed to approximate what one would “feel” given a combination of temperature and humidity under light winds and shaded conditions. And remember, the “apparent temperature” can increase by as much as 10° to 15°F under direct mid-day sunshine.

 

The human body has a built-in “cooling system” -- perspiration! Yet we fight perspiration constantly throughout the South Louisiana summer. It may not seem to make sense, but sweating is actually designed to cool the body. How? Heat is removed from the body by the evaporation of sweat -- it’s the same as the effect when you dab your skin with rubbing alcohol. The alcohol quickly evaporates, pulling heat out of your skin through the evaporation process and leaving you with a cooling sensation.

 

So why doesn’t the sweating process work better? Because of the normally high water-vapor content in our south Louisiana summer air -- our high humidity.

 

The more humid the air around us, the less efficient the perspiration/evaporation process. And when the air is very humid, the opportunity for our sweat to evaporate can go to near zero -- and then say hello to that sweat-soaked shirt!

 

The dew point temperature is one of our better indicators of the humidity level of the air. (You may recall that when the air temperature and the dew point temperature are equal, the relative humidity is at 100%.) The higher the dew point, the more water-vapor being held by the air. For Baton Rouge, summer season outdoor dew points are routinely in the low to mid 70°s and can climb into the upper 70°s to near 80° when conditions are right. By comparison, air-conditioned locations often will try and maintain an indoor dew point temperature below 60°. (To get a sense of what this means in terms of humidity, to go from a dew point temperature of 60° to a dew point of 75° requires that the amount of water vapor in the air must nearly double!)

 

For Baton Rouge, a somewhat typical summer afternoon will see outdoor air temperatures climb into the low to mid 90°s with dew point temperatures in the low to mid 70°s – no doubt about it, that combination is unpleasant to say the least! For example, a combination of an air temperature of 95° with a dew point of 75° yields a Heat Index of 107° -- considered “Dangerous” when one is exposed to that kind of heat for prolonged periods without relief. Of course, on individual days it can get even hotter and more humid for the Red Stick. What’s more, there are a number of days during just about every summer when the Heat Index stays in the triple digits for several hours. In fact, we sometimes see these extreme heat days come back-to-back-to-back.

 

 

The bottom line: heat can be a killer. In fact, some estimates suggest that, on average, 300 or more Americans die each year as a direct or indirect result of extreme heat.

More Heat, Less Rain Ahead

The upper-level ridge over the west-central U.S. continues to slowly ease its way to the east, increasing the strength of the “cap” over Louisiana. Remember, by a “cap or “lid,” we are referring to high pressure in the mid- to upper-levels of the atmosphere. This cap not only suppresses cloud development (and therefore inhibits rainfall), but also promotes sinking air. Sinking air must warm as it descends, so the sinking process actually adds heat to the lower-levels of the atmosphere.

 

 

We’ll stay warmer-than-normal and mainly dry through the rest of the week. Red Stick residents should plan on muggy mornings with patchy fog and sunrise temps in the low to mid 70°s while afternoon highs under mostly-sunny to partly-cloudy skies reach the mid 90°s.

 

These won’t be record afternoon temps but still take care in the heat, especially when under the direct sunshine. Remember, the mid-day sunshine can add as much as 10° or more to the “feel” of the air ... and that’s before we consider the Heat index impact of our traditional summertime humidity.

 

Now, okay ... a handful of you will still see a passing afternoon shower just about every afternoon this week. Even as the upper-level ridge sets-up right over top of us towards mid-week, there are still going to be a couple of pop-up places where the rising air punches high enough through the upper-level cap and produce a localized shower. The Gulf air mass at the surface is obviously very warm and very moist, and warm-and-moist air is, by definition, unstable and quick to rise.

 

Think of it like this: with the abundance of low-level unstable air, some fraction of it is going to find a “weakness” in the overhead cap. Almost like the fork holes your mom puts in her pie crust to let some of the steam out while it bakes. So yes, we could see a couple of blips on the Titan9 radar just about every afternoon this week, but they will be few and far between for the next few days.

 

We’re watching the potential for a “backdoor” cool front to slip southward and try to make it to the Gulf Coast on Friday. Signals are a bit mixed at this point, but given the time of year, the odds of the front pushing into and through the WAFB viewing area are on the low side. Still, the front could get close enough to put a crack in the atmospheric cap, and the closer the front gets the better the potential rain chances on Friday afternoon.

 

 

For now, I’m thinking that the front won’t make it this far south and only gets close enough to increase rain chances to about 20% for Friday afternoon. Not much of a big deal, really, and that would still be rain chances lower than normal for this time of year. Of course, we’ll keep an eye on the forecast developments with this scenario over the coming days.

 

Another day passes and we remain quiet in the tropics.

Getting Drier -- and hotter -- this week!

Jay Grymes / WAFB Storm Team

 

Titan9 Doppler was showing a few showers on Monday afternoon with a couple of stronger t-storms to the south and east of Baton Rouge, with most of the action loosely linked to the afternoon “sea breeze.” We expect all of that action to die-down as we head into the evening and go to mainly fair skies overnight.

 

Tuesday will begin with a few clouds and sunrise temps in the low 70°s for metro BR. We’ll go to partly cloudy skies for the afternoon, with rain chances on Tuesday at less than 20%. 

 

It looks like the main weather story for Tuesday and the rest of the work week will be about the heat. Our forecast is calling for highs in the low to mid 90°s across metro Baton Rouge for Tuesday, with highs on most days this week up around the mid 90°s. Factor in the humidity and we’re talking about peak afternoon Heat Index numbers climbing into the triple-digits just about every day this week.

 

At the same time, we’re calling for a run of “mainly dry” days, with rain chances for most WAFB neighborhoods running at under 20% each day right into the weekend.

 

 

Why the “hot-and-dry” spell? As you know, in the summertime, the two go hand-in-hand. Reduced cloud cover means less chance for rain and more direct solar heating. 

 

Our forecast for the next couple of days calls for upper-level ridging (high pressure in the mid to upper levels of the atmosphere) to take charge and persist right into the weekend. Ridging suppresses cloud development and actually causes the upper-levels to sink towards the surface -- literally pushing downward from above. This downward motion effectively puts a cap on the lower levels of the atmosphere, minimizing the ability to hot, humid air to rise (and to develop into clouds).

 

 

The cap isn’t always perfect, so some rising still can occur, allowing for occasional, spotty showers. But the upper-level ridging and resulting cap means little or no chance for rains like we saw over the weekend -- at least not for the next several days, and probably not through the weekend.

 

So get ready for some serious summer season heat all week long.

 

So far so good in the tropics -- all remains “quiet” there.

Storms Remain Possible Overnight

By Jay Grymes & Steve Caparotta

Although most of the Baton Rouge metro area stayed dry today, we’ve seen some very active weather all around us.  A outflow boundary (a mini 'cool front' produced by earlier storms to our north) is moving through the WAFB region this afternoon and evening, and upper-level divergence (increasing winds aloft) has aided the lift and taken advantage of the warm, moist and unstable surface air, fueling the storms that have developed.

We’ve seen a handful of Severe T-Storm Warnings posted this afternoon for areas to the east, southeast and south of metro BR, with the storms generally moving to the southeast at 15-20 mph.

In addition, we’re getting some signals from short-term meteorological models, including our in-house “PrecisionCast” RPM, that we could see some additional showers and storms extending into the evening and overnight.  We’ll keep rain chances at about 30% through the night and early morning, with lows in the 70°s.  Don’t be surprised to be awakened tonight by rumbles of thunder!

We’re also maintaining that 30% rain chance through Friday afternoon -- not great news for the LSU Tigers and Oklahoma Sooners and the fans of the NCAA Super Regional, but it could be worse.  We’re not worried about an all-day rain, so they should be able to get the 6:00 PM game in even if they have to deal with a delay.

We’re posting 20% to 30% rain chances for Saturday and Sunday -- again, not ideal for the Super Regional schedule.  But it is summer in south Louisiana, and if you live here you know that this is just what summer is supposed to be like.

Monday looks like the day with the best rain chances over the upcoming 7 days, with a somewhat drier outlook for the remainder of next week.  Of course, drier often means warmer, and that’s just what we expect for Tuesday through Thursday next week:  lows in the low to mid 70°s, highs in the low 90°s and a humid air mass that makes the afternoons feel like the mid to upper 90°s.

As for T.S. Andrea ... she intensified more than expected last night and earlier today.  The 4PM NHC Advisory shows a tropical storm with peak sustained winds of 65 mph -- rather impressive for the first storm of the season and for a storm that looked poorly-organized and sheared just a day ago.  As expected, Andrea headed into Florida, making landfall along Florida’s “Big Bend” at 4:40 PM.  Andrea is expected to accelerate tonight and tomorrow, reaching the Carolinas by Friday afternoon and becoming ‘post-tropical’ by late Friday or early Saturday.  Andrea has produced some pockets of heavy rain and some wind damage in the Sunshine State and preliminary reports indicate ‘she’ has spawned a dozen tornadoes over the Florida peninsula.