Wasatch Weather Weenies

Hydrometeorological insanity prevails over the western U.S. as the monsoon goes out with a bang rather than a whimper.  A good rule of thumb for meteorology is to beware when the atmosphere is in outlier mode, and that is certainly the case this week as a monsoon trough amplified over the southwest and ridging built over the northwest, leading to a pronounced high-over-low pattern over western North America.  These features, along with the abundant moisture and the development of crest-level easterly to southeasterly flow across much of Utah and Colorado can be seen in the 0600 UTC (0000 MDT) analysis for last night. 0600 UTC (0000 MDT) 12 September 2013 Analysis of 700-mb geopotential height (contours), wind (barbs), and relative humidity (color filled at 10% increments beginning at 70%). Let's start in southern Utah where a flood warning now extends over a huge chunk of terrain from the high plateaus running down the central part of the state to the Colorado ...

As discussed in the previous post, the large-scale pattern we are currently in is one in which our weather is coming from the east rather than the west.  Thus, like George Costanza in Seinfeld, it is best to go against your instincts and "do the opposite." Case in point are the showers over the Salt Lake Valley this morning, which moved into the area from the southeast. It felt very odd this morning with a light steady rain falling, a relative humidity of 88%, and a dewpoint of 61ºF. Source: http://mesowest.utah.edu The trough responsible for the easterly flow and the showers is not in a hurry to vacate the Intermountain West.  It looks like it will give us unsettled weather through at least Saturday. Addendum @ 9:15 am: The photo below shows some beautiful lenticular clouds that formed in response to the SE flow across the central Wasatch.

"My name is George, I'm unemployed and I live with my parents."  The greatest pickup line ever?  Doubtful.  But it worked for George Costanza and perhaps it will work for you this week. The high-over-low pattern we will experience the next couple of days is one in which you need to resist every instinct you have about observing the weather.  Look to the west?  I think not.  With a high to the north and a low to the south, our weather will be coming from the east and the southeast.  Note, for example, the forecast flow at 700-mb (crest level, bottom left) and jet-stream level (upper left) in the NAM model forecast for 6 AM MDT tomorrow (Wednesday) morning. Source: http://weather.utah.edu The precipitation band forecast to be to our northwest (lower right) is not associated with an approaching cold front, but passed over Salt Lake from the south and southeast during the previous 6 hours of the NAM forecast.   So, do the opposite t...

With the passage of a weak trough and the penetration of our first (weak) gasp of flow from the northwest into northern Utah in many weeks, there's been a modest decline in humidity and clouds over the Salt Lake Valley today.  For example, the integrated precipitable water, a measure of the total water vapor within the atmosphere, declined late yesterday from just over 3 cm to something closer to 2.5 cm. Source: NOAA/ESRL Dewpoints at the Salt Lake City airport also declined somewhat from near 60 to something closer to the mid 50s. Nevertheless, the monsoon is nearly weakened, not defeated, and we are still seeing some deep convection firing up over the high topography to the south and southwest of the Salt Lake Valley, especially the Oquirrh, Stansbury, and Sheep Rock Ranges. Source: College of DuPage Forecasting where and how strong convection of this type initiates remains a major challenge for meteorology.  For instance, why is is that the convection is de...

With temperatures in the 60s, dewpoints near 60, and rain falling steadily from the sky, I slept like a baby last night.  I can't even remember the last time we had a long period of steady rain like this and it seems like a gift from heaven, although yesterday's stronger downpours unfortunately caused some flooding and debris-flow problems in wildfire-scared areas such as near Alpine .  Further, the delay of the Texas–BYU football game is a prime example of why major stadiums need to prepare and have a plan for participant and spectator safety during severe weather (as does the Broncos–Ravens game on Thursday night).  Even if the U is prepared, the BYU experience provides a learning opportunity to see what worked effectively and what didn't.  U officials should also have a look at Gratz and Noble (2006) , who provide a summary of lightning safety guidelines for large groups.  It's not a matter of if but when there is a thunderstorm, possibly severe, that impa...

It's been a long time since we saw large-scale northwesterly flow (yesterday's intense outflow event doesn't count - it was intense, but a small-scale feature and the winds quickly) but it looks like it is going to happen sometime late tomorrow or tomorrow night.  Note the northwesterly flow at 700-mb (crest level) in the GFS forecast valid 1200 AM Monday (see left hand panel). It will be interesting to see what kind of an airmass this ushers in.  Will it be dry and clear, or smoke filled?  Time will tell. If you will miss the monsoonal flow, you can just drive down to southeast Utah.  The trough never really pushes into that area and they remain mired in the monsoon.

I'm on a quick trip for a meeting at the University of Notre Dame and observed a gorgeous sundog during yesterday's sunrise at the Salt Lake City airport. Sundogs, also known as parhelia, are typically produced as light from the sun is refracted by ice crystals in cirrus clouds, as was the case above.  There is some decomposition of the light into a color spectrum, but the decomposition is not as dramatic as occurs with rainbows, which are produced by water droplets. The Atmospheric Optics site  run by Les Cowley is a good place to learn more about sundogs, halos, and similar phenomenon. The sites at Notre Dame are less dramatic and dominated by football.  I'm not a Notre Dame football fan, but did my best to grin and bear it. Not shown here is the hex I put on touchdown Jesus.