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Forecast

Christmas afternoon update/2018

Christmas Day, 2018/pm

Summary: It’s a rather blustery Christmas afternoon  in portions of the valley.  Winds are generally between 15 and 25 MPH with gusts to near 30 on the west side and from Fresno County northward.  Even in the typically wind sheltered locations, breezy conditions are prevailing.  This same northwest flow is generating a considerable amount of upslope cloudiness against the north facing slopes of the Kern County mountains and along the Sierra Nevada foothills.  The northwest flow will continue tonight and Wednesday, regenerating lower level clouds along the eastern and southern flanks of the valley, at least into Wednesday morning.  Skies will clear along the west side where somewhat drier air is making some inroads.

 

The combination of cloud cover and wind conditions will maintain above freezing conditions tonight, although if winds die off and skies clear, especially towards the central and northern areas, lows could dip below freezing.  On Thursday, a colder low will drive southeastward into the Great Basin, possibly spreading some cloud cover over the valley for Thursday morning and maintaining temperatures generally in the low to mid 30s.

 

Behind this low will be a north and eventually northeast flow, driving colder and drier air into central California.  One of two scenarios will play out.  Number one is these winds could blow over the top of the valley, which occurs occasionally, allowing fog and low clouds to take over.  In this case, temperatures would remain in the 30s at most locations.  Number two is a rather gusty northerly wind will blow down the Sacramento Valley then into the western San Joaquin Valley, eventually scouring out the valley of the fog and low clouds.  This would result in lower dew points and temperatures would be in the 26 to 28 degree range in the traditional cold spots, and 29 to 31 elsewhere.  For now, it would appear the coldest mornings, if this pattern develops, would be Saturday and Sunday.

 

Models now place a cut off low off the central coast Monday, too far off shore to have much of an impact.  New Year’s Eve and New Year’s Day will see this feature farther out to sea, not bothering anyone but a few squid out there.

 

My Christmas present to you this afternoon is to possibly eliminate the chance of a cold air mass diving down the western U.S. the first few days of January.  Latest models show the westerlies breaking into the Pacific Northwest and even British Columbia, preventing polar air masses from moving southward.

 

Forecast: Partly to mostly cloudy tonight through Wednesday morning along the east side and the southern portion of the valley.  Mostly clear to partly cloudy on the west side.  Mostly clear Wednesday afternoon and evening.  Becoming partly cloudy Thursday and Thursday night.  mostly clear to occasionally partly cloudy Friday through Sunday and cold with areas of night and morning clouds and fog.  Partly cloudy Sunday night and Monday.  Mostly clear Monday night through New Year’s Day with areas of night and morning fog.

 

Temperatures: Lows tonight will range in the mid 30s to the lower 40s.  highs Wednesday will warm into the low to mid 50s.  lows Wednesday night will range in the mid to upper 30s.  Highs Thursday will warm into the low to mid 50s. 

 

Next report: Wednesday morning, December 26