December 20, 2018
Summary: There was a wide range in temperatures this afternoon, everything from the low 60s where fog and low clouds were absent to only 49 degrees at Lemoore where fog and low clouds were persistent. Variable high clouds are also streaming in from the west/southwest which should inhibit fog formation tonight until at least the early morning hours when dew points and temperatures match.
Upper level high pressure which was off the southern California coast this morning is migrating southeastward just off the northern Baja, California coast this evening. This will allow a weak wave of low pressure to move through Friday, however no precipitation is expected. There will be plenty of cloud cover tonight and Friday, though. Over the weekend, a westerly flow will zip across the eastern Pacific. Embedded within this flow are weak waves of low pressure which will move in from time to time. Any active weather will be confined to northern California. Of course, with a westerly flow, temperatures will be relatively mild.
Speaking of mild, while the valley was in the 50s and low 60s, temperature at Tehachapi soared to 70 degrees, illustrating the strong warm air inversion.
A cold low will drop southeastward Christmas Eve into northern California. Depending upon model of choice, this could turn out to be an inside slider where much of the energy moves into the western Great Basin with weaker dynamics over California. Or, it could come barreling through central California Christmas Eve night and Christmas morning with a good chance of light rain from Fresno north and a chance of light showers south of that line. This system will be followed by another low which will move through the 27th. Precipitation is not anticipated with this system, but behind it the winds aloft will turn north/northwesterly or perhaps simply northerly.
Models from the 29th through the first few days of January are indicating a strong upper high will be off the Pacific coast while a low carves out over the Four Corners region. This will spread colder and drier air into the region, but one piece of good news is the fact the high will not build far enough to the north to introduce cold, Arctic air. Even so, some frost nights can be anticipated, especially the last few days of this year and the first few days of next year, unless fog and low clouds take over which would largely reduce the chance of cold nights.
Forecast: Variable cloudiness tonight. Mostly cloudy Friday. Variable cloudiness at times Saturday through Monday with areas of night and morning clouds and fog. A chance of showers, especially Monday night, south of Fresno County and mainly after midnight. Light rain will be likely from Fresno County northward Christmas morning with a small chance of showers in the afternoon. Mostly cloudy Christmas night and Wednesday morning with areas of low clouds and fog. Mostly clear to occasionally partly cloudy Thursday with areas of night and morning fog.
Short Term:
| Madera 40/58/41/57 | Reedley 41/59/42/57 | Dinuba 39/57/41/57 | |
| Porterville 37/60/41/58 | Lindsay 36/60/40/58 | Delano 41/61/43/59 | |
| Bakersfield 45/62/46/58 | Taft 46/62/46/58 | Arvin 38/63/43/58 | |
| Lamont 41/62/44/59 | Pixley 39/59/42/57 | Tulare 38/58/42/57 | |
| Woodlake 38/59/42/57 | Hanford 40/61/43/57 | Orosi 37/59/41/58 | |
Winds: Winds will be generally at or less than 6 MPH through Sunday with periods of near calm conditions.
Rain: Dry weather will continue probably through most of Christmas Eve. There seems to be two solutions showing up on models this afternoon. One solution is a low driving in from the Gulf of Alaska, through northern California then into extreme western Nevada. The other is for the low to move into through northern California and right into central California late Christmas Eve night and Christmas morning. The best chance of precipitation will be after midnight Christmas Eve and the first half of the day Christmas Day with a small chance of showers Christmas afternoon. I still want to use the wording “chance of light showers” south of Fresno County as the front will dry up as it moves southward. Dry weather will return Wednesday and, if models are correct, will continue through the first five days of January.
Frost Discussion: All locations will be above 32 degrees tonight and each night through this coming Wednesday. The air mass following the Christmas storm will be colder but not excessively so. Daytime highs should fall back to near seasonal with overnight lows for the most part dropping into the 30s. all of this hinges on cloud cover and fog conditions. A northerly flow will develop from the Pacific Northwest down into California the 29th through the first couple days of January. This may lead to some frost nights, but as we get closer to the last week of the year, models look milder than they did several days ago. For now, even though we may have some frost nights, it does not look like a critical situation will develop.
Next report: Friday morning/December 21