Thursday, June 27, 2013

Sunny California

When I think of California I think of palm trees, In-N-Out Burger, and perfect weather. There is a reason for the perfect weather in California. A high pressure off the west coast usually dominates during the summer. High pressures are areas of sinking air. Sinking air inhibits cloud growth and also warms surface temperatures. However, a breeze from the ocean during the day, called a sea breeze, brings cool ocean air inland. Marine air is cool because water doesn't heat up as quickly as land. Water has a high specific heat and the water is churning. A perfect mix of cloudless days and a cool breeze keeps temperatures near the coast in the 70's.

Last weekend I swam in the Pacific Ocean for the first time. I've touched the Pacific several times before, but it's always been too cold to swim. Finally, I had my chance. Huntington Beach screams California: surfboards, volleyball, sand, and sun. My favorite part was swimming into the waves and letting the waves knock me over.

The weather seems too good to be true here. I need to remember that California is a big state. Below is an image from Mesowest showing the high temperatures on June 27, 2013. Temperatures were cool along the coast where there is a large marine influence, but step over the mountains and you're in the hot desert. Remember, California is also home to Death Valley, perhaps the hottest place in the United States! Most western states will experience 100 degree temperatures this weekend. I'll go to the beach again and enjoy 80 degrees.


Wednesday, May 15, 2013

bright band

Radar measures reflectivity. Reflectivitiy is proportional to the diamater of the partical to the sixth power dbz~(D)^6.

Snow and rain reflect different amounts of radiation. This causes problems to decide how much it is actually raining or snowing.

Melting snow can be very deceiving. When snow starts to melt it gets a watery shell around the flakes. To a radar beam it looks like a 10 cm rain drop.

Often this phenomenon is evident on radar in what is called a "bright band" where the radar shows a high echo but there are actually less rain that is thought to be there.


Hot day in the Midwest

Two weeks ago the Midwest had lots of snow. Yesterday, May 14 2013, the Midwest had broke record temperatures. It was HOT! Click the link to view a Mesowest profile of the day. Notice the winds coming from the southwest. Also, take a look at the humidity. It was very dry in the hottests areas.

Milwaukee Heat Burst


At 20:00 (8:00 PM) there was a sharp rise in temperature. This temperature rise is related to an increase in wind speed. The increased wind speed was caused by a heat burst. In a heat burst, virga evaporates, cooling the air making, and becomes more dense. The air suddenly sinks and compression causes adiabatic warming. At the surface, people experience sudden gusts of warm air.



Mesowest profile of temperature and wind in Milwaukee on May 14, 2013:
http://mesowest.utah.edu/cgi-bin/droman/meso_base.cgi?profile_id=pJGv1rH0902JSAza

National Weather Service description of the Heat Burst:
http://www.crh.noaa.gov/news/display_cmsstory.php?wfo=mkx&storyid=94614&source=0 

Virga and heat burst video (go to 8:00 PM)
http://f5.aos.wisc.edu/webcam_movies/latest_sunrise_to_sunset_northwest_640x480.mov

More about heat bursts:
http://www.crh.noaa.gov/oun/?n=heatburst_info


Monday, April 8, 2013

Downslope Windstorm

Northern Utah is waiting for another downslope windstorm. The National Weather Service, however, emphasized this wind storm will not be as strong as the storm in December, 2011. The GFS model for 04/09/13 at 03 UTC (6:00 P.M. local time) shows a large pressure gradient between Utah and Wyoming. This will induce high winds along the Wasatch Front as air plunges down the mountain side.
GFS 04/09/13 03 UTC: Sea Level Pressure and 3hr Precipitation

The NAM for the same time also shows a large pressure gradient. Below are the predicted surface winds at 03 UTC.
NAM HIRES, Northern Utah: 04/09/13 03 UTC: 10-m winds and 3hr Precipitation

Check out the Wasatch Weather Weenies blog for more about the downslope windstorm.