North American Monsoon 2007

[Ilya Neyman]

Looking over at the latest GFS progs after the last in a series of Pac NW troughs blows on through the Monsoon High may finally start to get going. This is most likely to occur during the first week of July, which is, climatologically speaking, the time for that to happen.

Granted, the GFS has been forecasting the ridge to build north and become established for now through the new week earlier, and in all reality the trough looks to dominate but it is believable that the deep troughiness could finally break down heading into July.

 

[Chris Bethurum]

I've noticed a general lessening of monsoon thunderstorm activity that makes it into the Los Angeles basin in recent years. I can remember some really good stuff just about every year 10-20 years ago, with one September 2nd event that had to be borderline severe.

During another event I witnessed two lightning strikes on airliners approacing LAX on the Civet profile decending through aproximately 10,000 feet. Tops were above 400. Bases appeared to be 80-100.

The last I recall seeing monsoon lightning around here was while returning from the Reno Air races by light aircraft in 2005. I'm looking forward to the more frequent return of towering cumulus over the San Gabriel and San Bernardino mountains.


As I kid spening quite a bit of time visiting family in Tucson during the 80s I saw some pretty exhilirating stuff.


Kudos to Mr. Faidly on the use of CCW when one can get one. Some states are on the wrong side of reality. Reality in how our government protects our safety an soverignty in a rather unaccountable way is becoming alarming. Do something about it so we don't have to bring up discussions of thuggery and lawlessness when it comes to chasing weather in our border states. It's time for serious messages to be sent. If not now, when?

 

[aaron.burkham]

This will be my first year starting lightning photography, ive found a couple good spots to start at in the vail area, i do need gear though, i was thinking a regular 35mm to start with, i know there is a whole lot more to it but i will figure it out as i go.

 

[Warren Faidley]

First "weak" towers of the season went up today over areas just south of Tucson. Looks like storms might begin as early as Monday - Wednesday.

Warren

 

[Greg Campbell]

I've been watching Warren's brave little storm for the past few hours while waiting to escape work. It's hanging together somehow, and is even spitting some pretty lightning. With a near-full moon to illuminate the scene, my first chase of the year is on!

 

[Charles Kuster]

The monsoon also usually starts here in mid July. On one hand, it brings us much needed rain which lowers the fire danger. It also brings us the best hail chances for the entire year (max= .5" ). However, I generally don't like the monsoon. Every day is the same. Sun in the morning followed by rain in the early afternoon. I really like thunderstorms, but these are generally very weak and it usually just ruins most of the day for any outside activities. At least we won't have to worry about fires as much when it comes.

 

[Mark Farnik]

In Colorado, the Monsoon usually begins about a week to ten days after it begins in California, Arizona and New Mexico. The average start date is between July 10th-July 20th, as Charles noted in his post. The typical end date is around August 20th-August 30th. The monsoon varies in length from year to year, sometimes just hanging around for two to three weeks and other times lingering for six to eight weeks.

What is most interesting to me about the monsoon in Colorado is that it has two facets; the mild mannered sun in the morning, rain in the afternoon pattern which is predominantly in the mountains in foothills, and then the sun in the morning, vicious HP supercells in the afternoon pattern on the plains.
Colorado, without a doubt, gets its worst weather during Monsoon season. Killer flash floods, gorilla hail, tornadoes and furious lightning storms are all significant threats. Colorado's worst weather disaster, the Big Thomspon Canyon Flood of 1976, occurred during the monsoon. Colorado's worst hailstorm, the infamouse "7-11" hailstorm, demolished roofs, windows, cars and trees from Estes Park to Colorado Springs on July 11, 1990. Colorado's deadliest tornado also occurred during the monsoon 83 years ago on August 10, 1924 near the town of Thurman where 10 people were killed in a farmhouse by a lunchtime tornado. In more recent years, significant monsoon tornadoes include the Last Chance F3 of July 21, 1993; the Dailey F3 of July 5, 2000; and the Riverside Reservoir F2 of July 21, 2000.
Our homestead has been struck by tornadoes twice during the monsoon; an F2 on July 29, 1980, and another F2 on July 21, 1993 (it occurred in the same outbreak as the Last Chance tornado).

 

[Paul Stofer]

We've got a monsoon going on here in Texas.. Man, wish the rain would stop.

 

[aaron.burkham]

First "weak" towers of the season went up today over areas just south of Tucson. Looks like storms might begin as early as Monday - Wednesday.

Warren

I saw those on the way to work today, cant wait for this to get started

 

[Jim Means]

GPS PW Image of 2006 Monsoon onset in California

I thought people might be interested in these images of precipitable water that I made that show the onset of last year's monsoon in California and Nevada. These are "hot-off-the-press" images that I've created for my thesis research and are precipitable water derived from GPS signal delays. They're a little bit hard to see because I had to reduce them for this forum, but the blues represent low PW, the greens medium PW and the red are high (~1.5"). I have a higher resolution animation of a week's worth of these images created every 3 hours. In the animation you can see how the moisture spreads from southeast until all of California is covered. The ones I've uploaded here are the beginning and end of the sequence (June 21 and 27 of 2006), and clearly show the change in the moisture field over a fairly short time period.

 

[Chris Bethurum]

I'm a bit in the dark over the images and some of the numbers you mention. I assume precipitable means available in the atmosphere to fall as precipitation, wheather it reaches the ground or not?

You mention the images being snapshots taken every three hours. Is it safe to assume the red (1.5") area between the Salton Sea and the Sea of Cortez shows a thunderstorm in progress or at least clouds capable of dropping that much water on the ground below if the atmosphere were to put all of it's water on the ground? The greening of the images just indicates more water in the atmosphere and presumably higher humidities on the surface on average?

I live in the LA basin immediately southwest of that deep blue (dryest) blue blob in the Mojave Desert in the first image. I mentioned earlier in the thread, the LA Basin has received less monsoonal precipitation in recent years than what I would call normal. There was an event I remember in late July that created what I would call record or near record heat indexes in the basin. Temps during the day were in the low 100s but the humidity seemed like it had to be around 50%. Some thundershowers came through and kicked up a dust storm from east to west though most of the basin received little or no rain.

 

[Jim Means]

Precipitable water (PW) is how much water vapor is contained in the atmosphere from top to bottom--it is what you would see on the ground if it could all be condensed out. Larger PW values are one indicator (although not always a great indicator) of potential for convection. In Southern California I've found that if the PW is less than about 0.9" there is not much chance for mountain convection, while if it's greater than 2" it will almost certainly figure out a way to convect. It's one of the standard numbers that you'll see on balloon soundings. For example, I just looked at the soundings on the College of DuPage website (http://weather.cod.edu/analysis/analysis.raob.html) and see that San Diego has a PW of 0.70" and Miami has a PW of 2.06". So just looking at those numbers I'd say there's potential around Miami but not much hope around San Diego.

So on the maps I was showing, taken one week apart, the first image shows PW of less than 0.5" over most of the state, while a week later the PWs have increased by over 50% across the state and in the southeastern deserts things were getting quite juicy. The cool thing about the images I'm starting to produce is that unlike the balloon soundings I'll be able to produce them 8 (or maybe even 24) times a day instead of twice, and also they're higher resolution than just about any other plots of PW that you'll see--oddly enough that's because there are so many earthquakes in California!

 

[Greg Campbell]

It looks like S. Az might see a spike in the DPs Monday, but then more dry, hot, miserable weather immediately follows.

I've reached the June Madness stage - I'm sick and tired of being hot 24/7 and never want to see the #!%^$% sun again. Bring on the frigging weather already!

-Greg

 

[Chris Bethurum]

Jim

Thanks for the info. Out of curiosity, what are the highest PW reading that can be seen? Can you get usable readings if you send a balloon up through a thunderstorm or is it only something that can be done in clear air or clouds that are relatively stable?

I've heard VIL described to me as 'vertically integrated liquid' a figure determined by a radar cross section of a storm and shown in some of the weather software available. If so, can this be converted into a figure like PW? I would assume in dense thunderstorm PW would be measured in tens of inches?

On a side note I believe I heard a report of rainfall on the order of 16 inches in an hour and a half during recent central TX storms. Is this possible? I can imagine that much in a really bad 24 hour period, but 1.5 hours?? Is this legit or just more of the exageration so often found in the media?

 

[Jim Means]

Chris,

I guess the highest PW reading you could have would be when the air is saturated at every level for whatever the temperature profile is. The highest ones I recall seeing were associated with tropical cyclones and were about 3 inches. Here is a link to measurement in one such case http://www.fsl.noaa.gov/media/hotitems/2004/04Sep10.html, when TS Frances passed over Florida--they also used GPS to measure this. The rainfall can greatly exceed the PW because the wind can keep bringing in moist air to replace the rained-out air. 16 inches in an hour and a half is extreme, but not impossible--I think the world record hourly rainfall is about the same order.

I'm not an expert on VIL, but I know that is radar measurement of liquid water in a column, so it differs from PW, which is a measure of water vapor. Launching weather balloons in thunderstorms is not recommended (not to say it doesn't happen), because of the dangers associated with lightning and highly flammable hydrogen.