December 23, 2018
Summary: A solid low overcast remains, based between 2,200 and 2,700 feet. The northern half of the valley has cleared with some clearing in western Fresno County and Merced County. I anticipate this overcast will hang in there for much of the night, although clearing may begin late tonight and for sure tomorrow morning as an approaching low and associated cold front move into northern California Christmas Eve and into central California Monday night and Christmas Day. Models are a bit more bullish this afternoon on possible rainfall amounts. This is discussed below.
Behind this system, a north/northeast flow will wrap around the western edge of low pressure which will develop over southern California. This will move somewhat colder and drier air into the valley, although I have seen cases where the flow actually goes over the top of the valley, leaving fog and low clouds at the bottom of the valley. For this forecast, we’ll go with partly cloudy skies Wednesday afternoon through Thursday. On Thursday, a second system will dive into the Great Basin, reinforcing somewhat colder and drier air into central California. In all likelihood, this will lead to frost nights Friday through Sunday of next week.
There is some good news on the pattern for the first week in January, or at least possibly anyway. Some models are now showing a flat zone of upper level high pressure over the eastern Pacific instead of that big ridge into Alaska. Model projections have the high several hundred miles off the central coast, putting California in a northwest flow which will make a huge difference in frost potential. This, of course, would be a much milder scenario, one which would favor fog and low clouds on the valley floor. Still, this is a switch from several days of modeling that had pointed to a possible freeze pattern. So, we’ll just have to wait and see if this new projection takes hold or if we flip back to the old pattern.
Forecast: Low overcast tonight with possible clearing after midnight. Increasing cloudiness Monday with rain becoming likely Christmas Eve night into early Christmas Day with a chance of a few lingering showers lasting into the afternoon. Mostly to partly cloudy Christmas night through Wednesday morning. Variable cloudiness at times Wednesday through Thursday with patchy morning fog. Mostly clear to occasionally partly cloudy Friday through Sunday with areas of night and morning fog and low clouds possible.
Short Term:
| Madera 41/59/46/54 | Reedley 43/60/46/55 | Dinuba 42/58/45/54 | |
| Porterville 45/60/46/56 | Lindsay 42/60/45/56 | Delano 45/61/47/57 | |
| Bakersfield 48/61/47/56 | Taft 46/61/46/57 | Arvin 46/60/47/57 | |
| Lamont 45/61/47/56 | Pixley 46/61/46/55` | Tulare 43/58/45/55 | |
| Woodlake 43/58/45/55 | Hanford 42/59/46/55 | Orosi 40/59/45/56 | |
Winds: Winds tonight will be generally at or less than 6 MPH with periods of near calm conditions. Later Monday, winds will be out of the southeast at 5 to 15 MPH, continuing well into Christmas Eve night. winds Christmas Day will be out of the northwest at 10 to 20 MPH at times with locally stronger gusts, mainly in western Fresno and Kings Counties. Winds Tuesday night will decrease to 5 to 10 MPH with light winds returning Wednesday with the possible exception of the far west side which may observe locally gusty north to northeast winds.
Rain: The stage is still set for a west Santa Claus Christmas Eve. Precipitation will spread down the valley Christmas Eve with periods of rain lasting into early Christmas morning. A few lingering showers may persist into the afternoon, mainly in the mountains of Tulare and Kern Counties. Dry weather will return Tuesday night and will continue for the remainder of the year. Models still show a very dry pattern for the first week in January.
Frost Discussion: All locations will be above freezing tonight and Monday night. It’s possible some areas could observe low to mid 30s Wednesday morning in areas that happen to clear out. The best possibility of that would be from Fresno County north and along the west side. A second weather system will dive into the Great Basin Thursday, possible spreading variable amounts of cloud cover over the valley, however this will create a northeast flow aloft. Surface high pressure will then take over over the Great Basin, creating an off shore surface flow.
This, in theory, will move colder and drier air down the valley for possible lows in the 26 to 29 degree range Friday through Sunday of this week. However, experience has taught me that there are occasions where these winds blow over the top of the valley, leaving the lower 2,000 feet undisturbed. This would trap moisture, usually in the form of fog and low clouds, on the valley floor. If this occurs, it would spell milder nights.
There is certainly more hope on this afternoon’s models in alleviating a possible freeze threat. Some models have switched gears. Instead of showing a massive high building into Alaska and northwest Canada, a much flatter high is shown, creating a northwest flow over California rather than north or northeast. This is a complete change from the past few days, so it will be interesting to see if this milder pattern continues on paper or whether we move back to a possible freeze pattern the first week in January.
Next report: Monday morning/Christmas Eve