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About this time of year, the weather map shows a red L, usually south of Las Vegas.  Unlike the other red Ls on the map, cool temperatures and precipitation are not in the offering.  

For more and a first-guess forecast, go below the fold.  And if anybody here wants to disagree, please feel free to!

The Colorado River Valley is among the hottest areas in the United States during the summer, with temperatures often exceeding 110 degrees.  As I write, much of it is under an excessive heat warning, a perverse achievement in a region where 95-105 degrees is normal this time of year.  

The strong heating of the valley and the desert plateaus that surround it is strongest near the surface during the day, but temperatures several hundred meters above the surface are the highest at night.  


Fun Fact #1:  If temperatures rise as you gain altitude, a "temperature inversion" is said to exist.  The air below the inversion is very stable and, absent strong winds, any pollution emitted under the inversion will stay there.  

Fun Fact #2:  Meteorology instructors and models like to track 850 mb temperatures since they do not vary with diurnal heating.  If surface temperatures in early June over Des Moines are 56 F at 7 am and 78 F at 7 pm, chances are that the weather over Des Moines did not change.  Chances are also good that the temperature at 850 mb remained around 54 F all day.  Given the same temperatures at the surface and a 5 F rise in 850 mb temperatures, it's safe to assume that interesting weather took place over Des Moines (the nature of which must be determined from other sources like satellite photos and damage reports from points west...)

Anyway, Dr. Teresa Bals-Elsholz at Valparaiso University made a drawing that I've modified and reproduced below on the right.  On the left is an idealized map of the lower Colorado Valley, with Lake Mead/Las Vegas to the north, the Imperial Valley to the west and the Gila Valley to the east.  

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If you heat a column of air, it expands.  Thus the distance between the 925 mb pressure level and (say) the 700 mb pressure level increases.  (This evenings's NAM model would probably draw a 500 mb isobar where I drew a 700 mb isobar).  The drop of the 925 mb isobar indicates where a thermal low can be located.  Like any low in the Northern Hemisphere, air around it circulates counterclockwise.  

Next month, throw in some mid-level moisture carried over from the Gulf of Mexico as the Bermuda-Azores high punches westward over the Deep South (maybe).  Perhaps add outflowing moisture from tropical systems farther south next month and moisture from a warming Gulf of California (likely!).  Fold in some flow around the thermal low, and the monsoon hits Arizona.  

And now, an amateur forecast for yKos

Thursday:  Low 79, High 104
Friday:  Low 81, High 106
Saturday:  Low 78, High 103
Sunday:  Low 78, High 101

To get this forecast, I looked at the GFS model 850 mb temperatures, added about 11 C for the high (seemed to work this weekend) and subtracted 2 C for the low (past behavior suggests a 13 C difference between max and min in Las Vegas when relatively hot in June -- I don't know if a real forecaster would take that into consideration).  
The NWS predicts brisk upper 90s for Friday and Saturday, 101 on Thursday and 100 on Sunday.  Of course, 4-7 days out the models may be spectacularly wrong, but 90s or 100s in Vegas in early June are near certainties.  

Not that I'm bitter, but next weekend looks like another round of sunshine and seventies near Chicago.  

Originally posted to Yamaneko2 on Sun Jun 04, 2006 at 10:37 PM PDT.

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Comment Preferences

  •  yikes...that's hot! (1+ / 0-)
    Recommended by:
    Yamaneko2

    I guess I'm prepared:)

    I just bought some lovely skirts and cute capri's for the occasion:)

  •  Aww Crap! (0+ / 0-)

    I had my Weather widget set to Las Vegas and was very pleased when the forecast showed the mid-80s for this week. After reading this diary I double-checked and saw that it was set to Las Vegas, NEW MEXICO!

    It's gonna be 107 degrees tomorrow in Las Vegas, NEVADA!!!!!!

    And don't tell me it's a DRY heat! You can stuff your dry heat when the soles of my sneakers are melting onto the pavement!!

  •  Cool! (1+ / 0-)
    Recommended by:
    Yamaneko2

    Mother Nature bats last.

    by pigpaste on Sun Jun 04, 2006 at 11:27:08 PM PDT

  •  Vegas is nice (3+ / 0-)
    Recommended by:
    Ted Hitler, mrd in nyc, Yamaneko2

    ...until about the end of April.  

    I'm already on my way there.  Like an idiot I'm riding the southern route out.  It'll be 100 in west Texas by noon and still in the high 90's when I arrive in Roswell, New Mexico about dark.  The next two days from there to Vegas will be cookers, too.  I hope the old Harley holds up.  I'm packing a lot of extra drinking water and have lots of sunscreen.  

    Chicago is sounding pretty sweet right now.

    80W-71S
    The most un-American thing you can say is, "You can't say that." -G. Keillo

    by Eddie Haskell on Sun Jun 04, 2006 at 11:27:31 PM PDT

    •  Are you really hoggin' it to Vegas? (1+ / 0-)
      Recommended by:
      Eddie Haskell
      •  Yes (2+ / 0-)
        Recommended by:
        mrd in nyc, Yamaneko2

        Developed a rear jug rocker box leak about Joplin, MO, though.  Not serious, but it sprays about three tablespoons of oil all over the chrome every couple hundred miles. Not even enough to drip on the ground, but still, ugh. Phoning ahead to Vegas HD dealer so they have gaskets and all in stock when I arrive.  I also need to find a place to change to straight 50W tomorrow.  I think the heat will be too much for standard 20W50 oil.  The old scooter doesn't really like 80mph all day when it's a hundred degrees.  Likes idling around in traffic in those temps even less.

        I'm afraid I didn't pack any khakis and a blue blazer; hope the yKos wardrobe police won't get on my ass too much.

        80W-71S
        The most un-American thing you can say is, "You can't say that." -G. Keillo

        by Eddie Haskell on Sun Jun 04, 2006 at 11:43:26 PM PDT

        [ Parent ]

        •  Bit of a warning (0+ / 0-)

          In the Desert Southwest, elevation and geography often mean more to the weather than those funny red and blue lines on the weather map.  Las Vegas is at 2000' elevation while Bullhead City, AZ is at about 800'.  107 F in Las Vegas becomes 114 F on the Colorado River's shore.  

          You probably also know that cooling breezes stop cooling at high temperatures...

  •  Any hope for wind (chill)? (1+ / 0-)
    Recommended by:
    Yamaneko2
    In California, the Central Valley heats up, the hot air rises to above 5000 feet, forming a vacumn near the ground, which sucks air (in the form of wind) into the valley, resulting in afternoon winds noticably in  San Francisco and sometimes in Santa Barbara. In the early evening as the sun sets, the valley cools, and in SF around 7:30 in the summer, the wind stops. If the marine layer has been pulled in by the vacumn of the valley, then SF gets fog.

    In Las Vegas, conditions are very different from the simplistic suck of the central valley, and I don't know much about it. So, is there any opportunity for wind and therefore chill, say in the Grand Canyon or any where nearby?

    What the president says is executive privilege is nothing but executive poppycock. Senator Sam Ervin

    by sailmaker on Sun Jun 04, 2006 at 11:32:38 PM PDT

    •  Higher elevation is your friend. (1+ / 0-)
      Recommended by:
      sailmaker

      Typically, for every kilometer you rise, you lose 9.8 degrees Celsius in perfectly dry air, somewhat less in moister air (down to about 5 C in saturated air, not an issue in southern Nevada in June).  Thus the forecast that predicts 107 F for Las Vegas (elevation about 2000') also predicts 72 F at 10,000 feet not far west of the city.  It also predicts thunderstorms.  

      I'm sure that locals (particularly those who were born in the area before widespread AC) and tourist information centers will be able to give you tips on avoiding the heat without huddling in AC.  

      Incidentally, wind does not imply chill when temperatures exceed 100 F.  In humid conditions, it implies greater heat stress.  I don't know how well the evaporation of sweat counteracts getting cooked by 105-degree breezes in the desert, but I'll repeat advice that I often hear to carry water.

  •  I forwarded to my dad, the climatologist (0+ / 0-)

    He'll be joining me in Vegas and I'm sure he'll enjoy your diary, as I did.

    "Americans can always be counted on to do the right thing - after they have exhausted all other possibilities." Winston Churchill

    by LondonYank on Mon Jun 05, 2006 at 12:01:55 AM PDT

  •  It only matters (0+ / 0-)

    if the air conditioning breaks down.

    •  Praying to the Freon Gods? (0+ / 0-)

      Believe it or not, a friend and neighbor of mine installed the current cooling system in the Riviera.  I will give him a hard time if it is hot in there.

      I am coming down from the Strait of Juan de Fuca, where it has been nice and cool all week.  For Pacific Northwesterners, the concept of an outdoor pool is intriguing, to say the least.  

      "An inglorious peace is better than a dishonest war." - Mark Twain

      by skwimmer on Mon Jun 05, 2006 at 07:08:49 AM PDT

      [ Parent ]

  •  love your weather diaries (0+ / 0-)

    I'm a weather nerd myself.

    Never chase a lie. Let it alone, and it will run itself to death.

    by terrypinder on Mon Jun 05, 2006 at 05:34:45 AM PDT

    •  Thanks! (0+ / 0-)

      It's a passion of mine as well, although at this stage I'm still a rank amateur whose forecasts often stink.  

      Coming soon are diaries on real Doppler radar and the carbon cycle.  If I can fold progressive politics into it, so much the better (though I suspect progressive politics addresses imbalances in the carbon cycle more readily than detecting tornadoes.)

  •  Effective temperatures (1+ / 0-)
    Recommended by:
    Yamaneko2

    With afternoon relative humidity around 10% (normal for Vegas in June), the sensible temperature (temperature you actually feel) will be about five degrees cooler than the thermometer reading.  On the other hand, direct sunshine can add up to fifteen degrees to the sensible temperature.  Do your running around out of doors in the early morning hours (if you can get up that early) or in the evening after sunset.  

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