Warm, breezy weekend
June 14, 2007
Sunny skies, breezy conditions and a slow cooling trend is in store through the weekend. Watch for the afternoon and evening westerly winds which will blow in the 15 to 25 mph range with stronger gusts. Highs for Friday will rise into the upper 70s to lower 80s then lower a few degrees for Saturday and by Sunday. Overnight lows will range from the upper 30s to near 50 depending on your location.
Have you ever wondered what the PNA pattern is that you will hear TV weather forecasters talk about? PNA is short for Pacific North America pattern. It is complex but in simple terms is the set up of upper-level high pressure and upper-level low pressure. It is most pronounced in the winter months but does exist to some extent year round.
The positive phase consists of upper level high pressure over the Eastern Pacific or western states with corresponding upper level low pressure over Hudson Bay in Canada and the eastern states. This is also known as the Hudson Bay low. This positive phase keeps our area dry during the winter months with few exceptions. The negative phase of the PNA pattern is the opposite with lower pressure over the west and higher pressure over the east at upper levels. The corresponding weather pattern shift also takes place with colder and wetter conditions in the west and warmer, drier weather in the east during the winter months. The summer reflection of the PNA usually produces hotter, thundery weather for us during the positive phase and cooler, windy and drier weather during the negative phase with some exceptions.
— Simon Smith is an observer for the National Weather Service. He lives in South Lake Tahoe. He can be reached at firstname.lastname@example.org.