RIM FIRE

I could not help writing a blog on this incredible fire burning just south of Lake Tahoe across the Sierra Nevada Mountains some 120 miles east of San Francisco.



Current Information on the RIM Fire:

Fire Size: 63,366 acres
Percent Contained: 1%
Nearly 2,000 fire personnel are working on this fire

The Rim Fire, as of Friday Morning, has burned more than 105,620 acres of forest. The fire has destroyed nine structures and has caused one injury. 

The fire is raging out of control dangerously close to Yosemite National Park. At this time, the U.S. Forest Service says there is currently no threat to Yosemite Valley, however, that could change in a hurry with a slight change in wind direction.

Current Drought Conditions across the western United States: Areas in ORANGE represent SEVERE drought conditons, areas in RED represent EXTREME drought conditions.

This fire is extremely hard to control due to the SEVERELY dry conditions and the rugged terrain. 

Incredible Satellite Imagery of the massive wildfire from space:

Photo taken by NASA's MODIS Satellite yesterday of the fire 

High Resolution Imagery Animation of the smoke visible from space:

Air quality, as expected, has really become bad across northwestern Nevada and northeastern California (area shaded in red represents where the air is unhealthy to breathe):

This fire has gotten so large that it is now actually making its own weather. The fire is burning so hot that it is actually forming its own dry thunderstorms. Hot air rises, that rising air carries water vapor and smoke into colder areas of the atmosphere aloft allowing for pyrocumulus (fire clouds) to develop. Those pyrocumulus clouds can actually produce their own lightning and gusty winds, however, no precipitation falls, therefore, adding even more fuel to the out of control fire. 

Good video explanation of how pyrocumulus clouds develop:
http://www.youtube.com/watch?v=diDkILlA4zs

Incredible Photos of the smoke from the fire:

Hopefully this fire will come to an end soon. However, as of right now it does not look good. With high pressure parked over the middle of the nation, winds will continue to stay strong out of the southwest across California (especially at the higher elevations).

Weekend Rain?

Hello everybody. The weekend is almost upon us; it is hard to believe how fast time flies. I just finished scanning all of the latest computer models and they are indicating a better chance for scattered tropical showers and thunderstorms over the weekend. 

I have my eye on an area of deep tropical moisture over the northeastern Gulf of Mexico right now that will quickly move east to Texas over the weekend. The higher moisture levels may be just enough, with daytime heating and a sea breeze, to generate some widely scattered heavy downpours over the area this weekend. Especially for areas from Austin to the south and east. I'm putting rain chances at 30% for both Saturday and Sunday in Austin. I'm putting those chances at 40% for areas south and east of Austin and 20% for areas north and west of Austin.

A large ridge of high pressure that is thankfully not parked over Texas is located just north and east of Texas right now. The clockwise flow of high pressure in the upper levels of the atmosphere will help to steer this batch of moisture over the northeastern Gulf of Mexico into Texas. Another benefit of the high being parked north and east of Texas is that air will be able to rise. Remember, you need rising air to promote shower and thunderstorm development. High pressure causes air to sink.

Unfortunately, this is not going to be a big rainfall event. Nevertheless, some lucky folks may pick up as much as an inch of rain under a heavy downpour while others may not even see a drop.

This is a look at forecasted moisture levels across Texas over the weekend. You can see that area of red across central and south Texas. That represents the higher moisture content. 

Sea Breeze

Hello everybody! Today will officially make day #24 of triple digit heat for the year here in Austin. The average number of triple digit temps for Austin is closer to twelve. At least we are nowhere near 2011's record shattering 90 days of temps at or above the century mark.

With this ridge of high pressure parked over our area, the air above us is forced to sink and compress. As the air compresses it heats up and dries out. During the afternoon hours, some of that dry air aloft is allowed to sink down to the surface. Therefore, allowing for temps to rapidly climb above the triple digit mark. Remember, the less moisture in the air, the easier it is for the air to cool off and heat up. 

As the temperature rises and moves away from the dew point temperature, which is basically an indication of how much moisture is in the air, the humidity drops and eventually the dew point temperature will fall as well. Also important to keep in mind is that the higher the dew point temperature, the more muggy the air. When the dew point temperature and the air temperature meet up, the atmosphere becomes saturated, meaning humidity is at 100%. Therefore, fog develops.

 

Let's take yesterday for example...we started the day at a warm and muggy 79°F with a dew point temperature of 72°F which gave us a relative humidity of 79%...by early afternoon the temperature had already soared to 102°F with a dew point of 65°F...you can see the dew point has already fallen from earlier in the morning...that combination gave us a relative humidity of 30%...by 6 p.m. we were sizzling at 104°F with a dew point of 56°F which gave us a relatively low humidity at only 20%. See the key factor too remember is that as an air mass heats up, it is able to hold more moisture. That dry air aloft is actually a saving grace because it allows for moisture levels in the afternoon to drop. Even though the temperature was 104°F it actually felt "cooler" with a heat index of 103°F thanks to the dew points in the 50s. If the air had not dried out in the afternoon and we stayed with a muggy 72°F dew point while we were at 106°F yesterday afternoon our heat index would have soared to 118°F!! That would have felt more like the coastal cities in Saudi Arabia this time of year.

Due to the intense heating over central Texas our air pressure at the surface drops...remember, heat RISES, and RISING AIR produces LOW PRESSURE. Since water does not warm anywhere near as quickly as land, an area of higher surface pressure sets up over the Gulf of Mexico. High pressure always flows to low pressure, therefore, every summer evening after a very hot day, the winds crank up out of the south and southeast and replenish our area with sticky gulf air. Because air has been being lifted across central Texas all day due to the extreme heat, air over the gulf moves in to fill its place.

Take a look at today's latest high resolution forecast model dew point temperature analysis...the blues are dry air and the yellows and oranges are humid air. Watch how we start out muggy, dry out during the afternoon and end up muggy again overnight.

Back on Monday evening you can see the sea breeze in action according to hourly weather updates out of Camp Mabry. At 7 p.m. it was 100 with a dew point in the 50s with no wind. At 9 p.m. it was 94°F with a dew point in the upper 60s and a strong southerly wind (that was the sea breeze that moved through).

Saharan Dust

Saharan Dust heading to Texas? Believe it or not, it's possible! Matter of fact, it has already happened a couple of times this summer. Two days ago NASA's MODIS satellite photographed a massive dust storm pushing east off of the northwest coast of Africa with origins in the western Sahara Desert. Strong winds in that region this time of year frequently pick up large amounts of fine dust particles and strong easterly trade winds frequently carry that large cloud of dust and dry air across the Atlantic and into North America. This layer of dry, dusty air suppresses tropical storms and hurricanes from developing. Therefore, expect a quiet couple of weeks ahead in terms of tropical activity in the Atlantic. This massive cloud of dust and dry desert air is known as the SAL (Saharan Air Layer).

Massive Dust Storm moving off the coast of Africa (Image taken: July 30, 2013...MODIS)

Incredible animation of the dusty dry air moving across the Atlantic. The yellows, reds, and pinks indicate that dry dusty air. It is amazing to see just how much dust is crossing the Atlantic and at how fast it is traveling.

Information below was taken from Dr. Jeff Masters' WunderBlog
 
How dust affects hurricanes
Saharan dust can affect hurricane activity in several ways:

1) Dust acts as a shield which keeps sunlight from reaching the surface. Thus, large amounts of dust can keep the sea surface temperatures up to 1°C cooler than average in the hurricane Main Development Region (MDR) from the coast of Africa to the Caribbean, providing hurricanes with less energy to form and grow. Ocean temperatures in the MDR are currently 0.7°F above average, and this anomaly should cool this week as the dust blocks sunlight.

2) The Saharan Air Layer (SAL) is a layer of dry, dusty Saharan air that rides up over the low-level moist air over the tropical Atlantic. At the boundary between the SAL and low-level moist air where the trade winds blow is the trade wind inversion--a region of the atmosphere where the temperature increases with height. Since atmospheric temperature normally decreases with height, this "inversion" acts to but the brakes on any thunderstorms that try to punch through it. This happens because the air in a thunderstorm's updraft suddenly encounters a region where the updraft air is cooler and less buoyant than the surrounding air, and thus will not be able to keep moving upward. The dust in the SAL absorbs solar radiation, which heats the air in the trade wind inversion. This makes the inversion stronger, which inhibits the thunderstorms that power a hurricane.

3) Dust may also act to produce more clouds, but this effect needs much more study. If the dust particles are of the right size to serve as "condensation nuclei"--centers around which raindrops can form and grow--the dust can act to make more clouds. Thus, dust could potentially aid in the formation and intensification of hurricanes. However, if the dust acts to make more low-level clouds over the tropical Atlantic, this will reduce the amount of sunlight reaching the ocean, cooling the sea surface temperatures and discouraging hurricane formation (Kaufman et al., 2005.)

Incredible forecast model showing where the dust layer should be over the coming days provided by NOAA's Visualization Laboratory using the NOAA NGAC Aerosol Model. Some of that dust is likely to make it to Texas sometime next week! When that happens our skies turn a milky, hazy color instead of blue and sunsets take on a characteristic red glow. Of course, the dust in the air will put air quality levels in the moderate category. Therefore, those that are sensitive to dust and allergens will need to limit time spent outdoors or just avoid outdoor activity altogether. 

 http://www.youtube.com/watch?v=F3Q8Sh2AjPo

As for our weather here in central Texas over the next 7-10 days, expect more of the same. With high pressure directly overhead air is forced to sink. When air sinks it compresses and heats up. That sinking air combined with our dry ground is the perfect combination to give us day after day after day of triple digit heat. You can think of high pressure as a big shield over Texas keeping rain out.

New drought report just put out today shows that 97% of the state of Texas is in drought. Unfortunately new forecasts out today also show our drought persisting into the fall.

HEAT RELIEF?
 
Don't get excited yet, because it is August and it is a long way's out, however, long range forecast models are showing a cool front pushing into Texas late next week or next weekend that may help to push highs back into the lower to middle 90s for a couple of days. However, because of that front we may see extremely HOT temps in the 104-108°F range by the time we get into the middle to end of next week ahead of the front.