Position of polar jet stream keeping Jack Frost at bay

PGEweather@pge.comDecember 8, 2012 

For many years,  our daughter, Chloe, played soccer during the fall and winter months. Customarily, our family showed up at the appropriately named “Atascadero Freeze” soccer tournament. This tournament is held in December, and my daughter’s games usually started at 8 in the morning. 

I remember one early- morning game when the icy grass didn’t crack under our shoes as we walked across the bleached-frozen fields. The colder temperatures seem to put everybody in the holiday spirit. After the tournament, we always ventured across Monterey Road and cut a Christmas tree from Hidden Springs Tree Farm.

This year, the Atascadero Freeze tournament is to be played next weekend — Dec. 15 and 16. Who knows, the kids may very well play on frost-free fields this year. You see, the federal Climate Prediction Center in Maryland is predicting that above-normal temperatures will continue through the end of the month for San Luis Obispo County.

Hard to believe, but the last time it dropped below freezing in Paso Robles was Nov. 14. Since that time, overnight lows have remained above freezing.  Normally, Paso Robles’ mean low temperature is 33.3 degrees during December. So far this month, the mean low temperature is an unusually balmy
49.6 degrees. 

San Luis Obispo hasn’t dropped below freezing at all this fall. So far this month, San Luis Obispo’s minimum temperature has averaged 52.7 degrees; normally it’s 42.0 degrees.

One of the key reasons for this warm weather is the position of the southern branch of the polar jet stream. Two areas of high pressure, one over the north Pacific and the other over Greenland, have forced the jet stream far to the north. Meteorologists refer to these jet stream changes as the North Atlantic Oscillation and Pacific North American pattern.

This has kept most of the frigid Arctic air mass north of the United States-Canadian border, resulting in an unusually warm December in the Lower 48 states. Already, more than 2,000 high temperature records have been broken during the first part of this month. Many East Coast cities are nearly 20 degrees warmer than normal.

Unfortunately, if you happen to live on the north side of the polar jet, you’ve been dealing with bone-freezing temperatures.  Fairbanks, Alaska, has seen temperatures drop to nearly 40 degrees below zero. The burg of Chicken, Alaska, reached a low of
42 degrees below zero earlier this month.

Closer to home, another factor in our abnormally warm temperatures was the large 964-millibar storm that set up shop in the Gulf of Alaska in late November. The storm produced persistent southerly winds for days on end that brought warm and moist air from the southwestern Pacific. This air mass produced mild temperatures and significant rain in Northern and Central California. Brandy Creek, near Redding, recorded 23.4 inches of precipitation. A little north of San Luis Obispo County, Mining Ridge along the Big Sur coastline reported 17.38 inches of rain, while Cal Poly finished with 3.31 inches.

Another factor that’s kept minimum air temperatures warmer in the North County has been the night and morning low clouds and fog that have developed in the wake of the recent storm. These clouds have acted like a blanket and prevented much of Earth’s heat from radiating into space, keeping overnight lows warmer. 

This week’s northeasterly (offshore) winds will dry the atmosphere and produce clear skies, allowing the overnight temperatures to cool. Since weather records have been kept, there has never been a December in the North County in which the temperature hasn’t dropped below freezing. And I’m sure Jack Frost will reappear soon.

Weather report
The Eastern Pacific high will strengthen to 1,032 millibars off Point Reyes and will remain nearly stationary through tomorrow. Combined with the Eastern Pacific high will be an area of high pressure over the Great Basin. This will produce night and morning northeasterly (offshore) winds. This offshore flow will produce hazy to clear skies, a dry atmosphere and mild daytime temperatures through Tuesday. 

Today it will reach the mid-70s in the coastal valleys and along the beaches. North County will warm to the mid-60s.  Overnight lows will drop to the 40s along the beaches and in the coastal valleys.

North County will finally see temperatures reach the freezing point by Tuesday morning.

The ridge of high pressure that has kept the Central Coast dry since last week will weaken as a result of an upper-level trough that will move over Northern California. The associated cold front will pass over San Luis Obispo County on Wednesday with increasing southerly winds, clouds and scatted rain showers. The relatively cold air associated with this system is not likely to result in any significant rainfall. However, snow levels in the Sierra will lower to between 2,500 and 3,000 feet.

Daytime temperatures are also expected to be below-normal with the warmest locations forecasted to be in the upper 50s to mid-60s on Wednesday.  The cool and unsettled pattern may continue through next weekend with a potential for widespread precipitation coming toward the beginning of the following workweek.

Surf report
Today’s 4- to 6-foot northwesterly (310-degree deep-water) swell (with an 8- to 11-second period) will remain at this height and period through Tuesday.

An intense 949-millibar storm with hurricane force winds developed near the western Aleutian Islands on Saturday.  A 3- to 5-foot northwesterly (290-degree deep-water) swell (with a 19- to 21-
second period) from the storm will arrive along our coastline later  Monday into Tuesday and will increase to 5 to 7 feet (with a 15- to 17-second period) Wednesday. This northwesterly (290-degree deep-water) swell will further build to 6 to 8 feet (with an 11– to 14-second period) Thursday, decreasing Friday. 

Seawater temperatures
Seawater temperatures will range between 57 and 59 degrees through Friday.

Seasonal safety
PG&E encourages its customers to keep safety in mind as they decorate their homes and trees in the coming weeks. The following holiday lighting safety tips will help to reduce the risk of fire and injury.

• In addition to being shatterproof and shock resistant, LED lights produce almost no heat, making them safe to touch and greatly reducing the risk of fire.

• Look up and live. Before stringing outdoor lights, check for overhead power lines. Never place yourself or any object in a position that risks contact with a power line — the result can be fatal.

Look up before raising ladders or other objects. Keep at least 10 feet away from overhead lines.

• Before stringing lights on outdoor trees, make sure tree limbs haven’t grown into or near power lines. Branches, trees and even the ground adjacent to a tree can become energized when trees contact power lines.

• Make sure lights are approved for outdoor use. Never use indoor lights outdoors.

• Follow the manufacturer’s limits for the number of light strings that can be safely connected together.

• Check all strands for cracked or broken plugs, frayed insulation or bare wires. Worn cords can cause fires, so discard damaged sets of lights.

• Route cords inside your home so they won’t trip anyone. Don’t place them under rugs, furniture or other appliances. If covered, cords can overheat or become frayed, increasing the risk of fire.

• Always turn off decorative lights — indoor and outdoors — when leaving the house and before going to bed.

• Do not place your tree near a heat source such as a fireplace or heat vent. The heat will dry out the tree, making it more susceptible to fires caused by heat, flame or sparks.


Send in questions
If you have any questions or comments about weather or this column, I would love to hear from you. You can also subscribe to my daily weather forecast by emailing me at PGEweather@pge.com.

John Lindsey’s column is special to The Tribune. He is a media relations representative for PG&E and longtime local meteorologist.

The Tribune is pleased to provide this opportunity to share information, experiences and observations about what's in the news. Some of the comments may be reprinted elsewhere in the site or in the newspaper. We encourage lively, open debate on the issues of the day, and ask that you refrain from profanity, hate speech, personal comments and remarks that are off point. Thank you for taking the time to offer your thoughts.

Commenting FAQs | Terms of Service