Some September rain for parts of Northern California, but no sign of a wet fall

Filed in Uncategorized by on September 23, 2014 351 Comments

Recent weather recap

While the weather in Northern California has been relatively unremarkable over the past couple of weeks, this was definitely not the case in Southern California. One of the most intense heatwaves in recent memory baked the Southland for an extended period of time, and was accompanied a impressively humid airmass (it certainly didn’t resemble California’s typical “dry heat”). Numerous daily temperature records were broken over the course of this warm spell, new wildfires broke out, and Southern California broke its all-time energy consumption record due to the added burden from cooling appliances.

Palm trees in San Diego burst into flames after being struck by lightning during a wild thunderstorm in midst of record heat wave. Photo by Kit Corey.

Palm trees in San Diego burst into flames after being struck by lightning during a wild thunderstorm in midst of a record heat wave. Photo by Kit Corry.

Partly driven by this record heat were widespread mountain and desert thunderstorms in the southern part of the state, which brought localized flash flooding. A handful of much more unusual (but highly localized) convective events also affected coastal and valley regions in certain parts of California. One of these was the rather spectacular thunderstorm in the San Diego area on September 16, which occurred in conjunction with remnant moisture from former East Pacific Hurricane Odile. These localized (but very intense) storms brought significant wind damage, exploding palm trees, and a torrential mid-afternoon downpour to downtown San Diego. Another somewhat surprising thunderstorm outbreak occurred this past weekend over the Southern Sacramento Valley and Northern San Joaquin Valley and adjacent foothills, but precipitation in this case was quite light and impacts were mostly limited to a pretty lightning display and a few (fortunately small) wildfire starts.


Rain headed for Northern California, but…

A fairly deep trough (for this time of year) is currently approaching California from the northwest. A deep surface low tied to this trough is producing heavy precipitation and powerful winds over the open ocean, but is expected to weaken considerably and move well to the north of California before making landfall. The trailing front will nonetheless be quite moist, and may be capable of producing substantial, soaking precipitation of up to 1-2 inches along the North Coast. Because the front will be weakening rapidly as it moves southeastward across the state, however, precipitation totals elsewhere will be drastically less than on the North Coast, tapering quickly to around a tenth of an inch along the I-80 corridor (including Sacramento and San Francisco). Thus…while most of the major population centers in NorCal will probably see some raindrops out of this, significant precipitation away from the North Coast is unlikely.

An impressive offshore storm system will weaken drastically before approaching the California coast later this week. (NOAA/SSD)

An impressive offshore storm system will weaken drastically before approaching the California coast later this week. (NOAA/SSD)

Unfortunately, substantial precipitation is also unlikely in the vicinity of the King Fire, which has burned nearly 100,000 acres of thickly forested land between I-80 and US-50 on the western slope of the Sierra Nevada. Additionally, strong southerly winds in advance of the cold front tomorrow and early Wednesday will lead to extreme fire danger and the risk of rapid fire spread once again (a Red Flag Warning is now in effect). While light precipitation on Wednesday/Thursday will help to temporarily reduce fire danger, the forests of NorCal are so dry that gains from such light precipitation are unlikely to last more than a few days.


No wet fall on the horizon

The most recent CPC precipitation outlook calls for below normal precipitation this fall in Northern California.

The most recent CPC precipitation outlook calls for below normal precipitation this fall in Northern California.

Numerical models suggest that a dry pattern will return to all of California by late this weekend and probably continue through the first week in October. Dynamical and statistical models currently now suggest a modest signal for a drier-than-average fall, especially in Northern California. Consistent with this, the newly-updated September-November precipitation outlook from the Climate Prediction Center calls for an increased chance of below-normal precipitation. Of course, what happens in the fall months does not necessarily have any bearing on what happens closer to the peak of the rainy season (during January-March)–and at least a couple of the seasonal forecast models currently foresee fairly wet conditions for the middle of winter. Again, though, as I’ve emphasized before: seasonal forecasts for California precipitation are not particularly good (skillful) out beyond a couple of months, so for now we’ll just have to wait and see.


The Blob Abides;” El Niño still trying to gain foothold 

The region of exceptional, record-breaking ocean warmth in the northeastern Pacific Ocean that has been in place now for over a year continues to be a prominent feature. “The Blob,” as it has come to be called, does appear to be linked (in one way or another) to the Ridiculously Resilient Ridge. As long as this region of extremely warm water remains in place, the risk of enhanced West Coast ridging will probably remain elevated. This is possibly one of the reasons why coupled model simulations are projecting a relatively dry fall across Northern California.

"The Blob" is clearly visible in this recent SST anomaly plot. (NCEP/PSD/ESRL)

“The Blob” is clearly visible in this recent SST anomaly plot. (NCEP/PSD/ESRL)

At the same time, El Niño conditions are still percolating in the Pacific. The most recent Kelvin wave continues to propagate eastward across the Pacific basin, and will probably enhance SST anomalies once it reaches the West Coast of South America. Coupled models are still calling for the likely emergence of a weak El Niño event this winter (or, less likely, a moderate one). The warm equatorial SSTs that define El Niño may interact in unusual ways with the record-warm North Pacific this winter, so possible atmospheric teleconnections (and implications for California rainfall) are not entirely clear at this point. However, it does now appear that the kind of “slam-dunk”, powerful El Niño event that might have given us high confidence in a wet winter is simply not in the cards.

Stay tuned for an upcoming comprehensive California Weather Blog post on the California drought and the Ridiculously Resilient Ridge, which will be posted on September 29th!



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  • C M

    We had a similar mega heat wave at the beginning of October 2012 but the rest of the month turned out to be cooler and wetter than normal.

  • raindog

    Such an odd storm. We had over an inch of rain since yesterday from wrap around moisture from the northeast out of the Nevada desert. Mt Lassen still white. Looks like some convection now developing north of me up near Burney Basin and more to the northeast headed this way. This storm keeps hanging on, love it!

    • Bandini

      I’ve been shocked by how much precipitation we’ve received since Thursday. It has rained all day yet again, just clearing a bit now. Very happy with the all this moisture.

      • raindog

        I cant believe how much precip this storm has brought to us. Last Wednesday when I was watching the storm come in, I was hoping we’d get a half inch. Now we are up over 3 inches Since Thursday. This is one fantastic storm.

        • Bandini

          I know. It seems that they were calling for roughly .25 or less, especially in regards to what would fall on the King Fire. Talk about over-shooting the mark. I don’t have a rain gauge here at my place but I would make a modest guess of 1.5 – 2 inches or so. I think the King Fire received right around that amount as well. They’re calling it 87% contained but I’d expect it to be even better by tomorrow.

          • inclinejj

            We should only pay the TV weather people on days they get the forecast right! Ha

  • craig matthews

    Making up for the June gloom we didn’t get earlier this year. Low over western NV is drawing in a hefty marine layer. Feels like a late spring storm here too.

  • Utrex

    4.4 earthquake in South Dos Palos

    • lightning10

      Hold on to anything you can. Been one of the more active years for quakes. Then again its been quite since the early 90’s

    • Bob G

      Never knew about this

  • Bandini

    Another day of soaking rain, what a system this has turned out to be. Headed up a little higher and got blasted with snow, fun stuff.

    • rob b

      Looks great, hopefully we see the good storms around mid October to lay a good base for the Winter.

      • Bandini

        That would be great. Last year there wasn’t a true base until February when the upper mountains got 3-5 feet or so with that warm storm.

  • lightning10

    Such a nice day to be watching the Charger game. To bad they could have one of the warmest games in a long time if it gets as warm as some of the models are showing. It could be a lot warmer then the last heatwave.

    • BlackRoseML

      It least it would not be as humid as before. Jax suck.

  • SBMWill

    ECMWF and GFS both weakening the ridge for the weekend and GFS showing weak troughing over southern bight. Once again it seems much could change 168 out.

  • C M

    Unusual situation in South San Jose; sky is completely covered with dark ominous looking clouds and it’s 81 degrees out like we’re going to have a thunderstorm or something. Normally, when it’s this cloudy, temperatures rarely exceed 70 in the Bay Area.

    • Yep. It is completely cloudy and dark.

      • C M

        Unfortunately looks can be deceptive; no thunderstorms or even showers on radar or in the forecast. Any chance of a surprise within the next few hours?

        • Nothing on the radar but it really looks like it will rain. But I’m not really sure. I thought it was supposed to be sunny and 80 degrees today? Lol

          • C M

            the temperature is right though. It feels muggy.

  • Bandini

    Good news from Inciweb regarding the King fire:

    Total Personnel 4,420Size 97,099 Acres
    Percent of Perimeter Contained 89%
    Fuels Involved Heavy timber, steep terrain
    Significant Events: After 4 days of precipitation with accumulations of 1-3 inches, fire spread has been halted, however heat remains in the heavier fuels and in the heavy duff sheltered from the rain under the dense timber canopy. As the weather turns warm and dry over the next several days, expect to see an increase in fire activity and smoke production; however spread potential is extremely low, doe to the successful suppression efforts.

  • Boy…the ECMWF and GFS are currently in excellent agreement that a dramatic warm-up will occur this week and continue for the foreseeable future. This event could be rather impressive, including coastal areas and NorCal.

    • Dan the Weatherman

      NWS San Diego is forecasting highs in inland Orange County to be near 100 or just above for late next week. I really hope we don’t see any more extreme heat like this for the rest of this year after this next episode is over.

      • Sunchaser

        and ACCUWEATHER showing rain middle of the month,,,wow who to believe?

        • Bob G

          Accuweather removed rain from the Mid October forecast at least for my area of the Central Valley

          • Brett

            It’s showing rain in my forecast in Folsom for the weekend after this one.

    • Yep. This is unbelievable. I hope this is just temporary.

    • Kamau40

      Yep, that’s right!! Looks like an offshore flow for early next week will be developing as well.