December 16, 2020
Summary: Clouds are beginning to increase ahead of a robust low pressure system. The parent low is located just off the Washington coast with a strong cold front stretching almost into the subtropics.
The Pacific Northwest and northern California will be the recipients of a short lived atmospheric river of air for significant amounts of rain over the northern 1/3 of the state. The cold front and upper air support will weaken rapidly as the cold front marches down the valley Thursday morning. light showers should reach Fresno County by roughly dawn then spread southward into Kings and Tulare Counties by Thursday morning and late morning, if any precip is left, in the valley portion of Kern County. The usual northwesterly push of air will follow as the storm moves into Nevada Thursday night.
As the air is lifted by the Kern County mountains and the southern Sierra Nevada, a low cloud deck will develop, covering most of the eastern and southern portions of the valley through Friday morning. as a relatively cool, dry air mass moves in, those clouds will dissipate by midday Friday.
A flat zone of upper level high pressure will take shape over the eastern Pacific and will build eastward over California and into the interior west through the weekend and the early part of next week. The main forecast challenge will be increasing amounts of morning fog and low clouds, possibly persisting through the day in some areas, especially Sunday and Monday.
We’re still studying the pattern beginning Tuesday of next week and lasting through the Christmas holidays. The latest version is a sharp ridge of upper level high pressure building along the coast, stretching all the way into southern Alaska and northwest Canada while a winter storm dives into the interior west. This storm will be the leading segment of a polar air mass which will dive into the Rockies and the Midwest by Christmas Eve. If this afternoon’s models have a good handle on this, this air mass will remain east of central California. Keep in mind, we’re still several days out and there will be changes on projections as we move forward day to day.
One thing is pretty much a given after tomorrow, and that’s the fact that the chance of rain after tomorrow is extremely low and will be for at least the next week and possibly longer.
Forecast: Increasing cloudiness tonight. light showers becoming likely from Fresno County north before sunrise, spreading into Kings and Tulare Counties during the early morning hours and Kern County by late morning. showers ending Thursday afternoon. Mostly cloudy Thursday night into Friday morning, clearing Friday afternoon. Mostly clear to occasionally partly cloudy Friday night through Wednesday with extensive fog and low clouds nights and mornings, possibly persisting into the day in some areas by Sunday.
Short Term:
| Madera 41/57/34/55 | Reedley 42/57/34/56 | Dinuba 40/57/33/54 | |
| Porterville 41/58/34/56 | Lindsay 40/57/33/55 | Delano 42/58/35/55 | |
| Bakersfield 42/57/40/56 | Taft 47/57/47/54 | Arvin 42/57/39/56 | |
| Lamont 42/58/40/55 | Pixley 41/58/34/55 | Tulare 40/57/33/54 | |
| Woodlake 41/57/34/55 | Hanford 42/58/35/55 | Orosi 40/57/34/54 | |
Winds: Winds this evening will be light. Late tonight through Thursday evening, winds will be mainly out of the northwest at 8 to 15 MPH with local gusts to near 25 MPH north of Kern County and mainly along the west side. Winds will diminish later Thursday evening. Winds Friday and Saturday will be generally at or less than 10 MPH late mornings and afternoons and less than 5 MPH nights and early mornings with extended periods of near calm conditions.
Rain: Light showers will spread as far south as Fresno County after about 4:00am or so then will spread into Kings and Tulare Counties during the early to mid morning hours and Kern County generally after 10:00am. This is a fast moving system, so showers will end from northwest to southeast during the early to mid afternoon hours. Rainfall amounts will be light with this system, ranging from.10 to .25 in eastern Fresno and Madera Counties, possibly a tenth or two over much of Tulare county and about a tenth of an inch or so in Kings County and probably just a few hundredths over the valley portion of Kern County. It’s possible some drizzle will continue near the base of the Tehachapi into Thursday evening, otherwise dry weather will prevail Thursday night. models show basically another blocking ridge pattern developing this weekend which will more than likely last at least a week, and quite possibly longer.
Frost: All locations will be above 32 degrees both Thursday and Friday mornings. The air mass moving in on a northwesterly flow behind tomorrow’s cold front is more or less typical of mid December. From Saturday and each morning through the middle of next week, where the skies are mostly clear and conditions are generally fog free, upper 20s and lower 30s will be possible in river bottom or other typical low spots. The main challenge will be fog and low clouds and how widespread they become. It’s possible we could see a multi-day fog regime beginning this weekend where widespread morning ground fog lifts into a low overcast with only partial afternoon clearing. If that pattern sets up, we would see chilly afternoons but above freezing overnight lows. Typically under this pattern, we would approach each night one by one, but certainly nothing dangerous is ahead for several days.
Yes, indeed, I’m still closely monitoring the pattern beginning the 23 and lasting beyond Christmas. If some of this afternoon’s models hold water, we would see a sharp ridge of high pressure over and along the west coast, building way up into southern Alaska and northwest canaca while a strong winter storm develops over the Rockies. If this configuration holds true, the arctic air mass would remain from the Rockies eastward with central California continuing to have dry weather but with extensive fog issues from day to day. I’m keeping my fingers crossed that this pattern holds.
Next update: December 17/am