Sunday December 15 2024 Forecast (8:17AM)

71 Comments

DAYS 1-5 (DECEMBER 15-19)

A large high pressure area sat overhead overnight and it got cold! Sunrise temperatures sat in the 10s for most of the region, with some lower 20s in the urban centers (heat island effect) and over the outer part of Cape Cod (surrounded by warmer water). The high pressure area starts to drift off toward the east today and as it does so our sunshine will become more limited as high to mid level clouds increase from the west ahead of an approaching low pressure area. At the same time an evolving weak onshore air flow will cause some lower clouds to come in from the ocean in eastern areas. Tonight, clouds collect and consolidate from both sources, and Monday is expected to be a cloudy day as a weak low pressure system approaches. This system will have cold enough air to work with so that some light snow can occur over inland areas, and eventually some freezing drizzle / rain, while closer to the coast I’d expect mainly a rain event. However, this system will also be running into a lot of dry air and falling apart as it moves in, so it’s quite probable that the precipitation is nearly insignificant for much of the region. Monday night, a more southerly air flow takes over with increasing moisture so expect a thicker overcast with spotty drizzle and patchy fog to form, and then as a larger area of low pressure begins to pass north of our region, a frontal boundary will be dragged eastward across the region, bringing with it widespread rain showers for Tuesday morning. This system will be moving right along and we’ll dry out that afternoon into early Wednesday. The next low pressure wave on its heels will spread clouds back in on Wednesday with a batch of rain (that can begin as mixed rain/snow for some interior areas) later Wednesday and early Thursday (which can end as mix/snow for some areas) as colder air returns.

TODAY: Sunshine becomes less abundant as clouds increase. Highs 33-40. Wind variable up to 10 MPH.

TONIGHT: Becoming cloudy. Lows 25-32. Wind variable to S under 10 MPH.

MONDAY: Cloudy. A period of light snow to mix inland and mix to rain coast. Some potential for icing from freezing rain/drizzle away from the coast. Highs 35-42. Wind variable up to 10 MPH.

MONDAY NIGHT: Cloudy. Fog patches. Chance of drizzle. Temperatures 35-42, slowly rising overnight. Wind SE to S up to 10 MPH.

TUESDAY: Mostly cloudy with rain showers likely morning to midday. Clouds break for intervals of sun afternoon. Highs 46-53. Wind S 5-15 MPH, shifting to W with higher gusts.

TUESDAY NIGHT: Clearing. Lows 25-32. Wind W 5-15 MPH.

WEDNESDAY: Clouding over. Rain arrives by late-day, may be mixed with snow initially interior locations. Highs 40-47. Wind variable up to 10 MPH.

WEDNESDAY NIGHT: Cloudy. Rain likely. Areas of fog. Lows 36-43. Wind NE 5-15 MPH.

THURSDAY: Cloudy start with rain ending, possibly mixed with snow. Clouds decrease thereafter. Highs 38-45. Wind NE to N 10-20 MPH.

DAYS 6-10 (DECEMBER 20-24)

Opportunities for snow or snow showers about 3 times (every other day). Temperatures below normal. We’ll be in a trough position here, and medium range guidance has trouble handling “pieces of energy” and therefore presents inconsistent representations of what can happen on run-to-run simulations. That’s why these are talked about as non-specific opportunities until each “chance” gets closer.

DAYS 11-15 (DECEMBER 25-29)

A temperature moderating trend with a couple of rain/mix/snow chances.

71 thoughts on “Sunday December 15 2024 Forecast (8:17AM)”

  1. EDITORIAL COMMENT: So all over social media as usual concrete answers are given about the weather from people who look at “the models” but don’t actually understand what they are looking at. You’d think after all this time, those folks would understand what model guidance actually is, and what it’s actually meant to do, but they don’t. They act as if each run of the guidance IS the answer. No. No. NO. You’re not going to get concrete answers from computer model simulations. It’s not possible. You try to tell these folks that, and they just block or ban you. Who wants to hear from the experts? What do we know? They and their brainwashed, non-rational-thinking followers will tell you they don’t need to hear from us because their “weather person” is always spot on, and better than us. News flash: Wrong.

    Also, you’re not even going to get concrete answers from the professionals about the detailed weather for 8 to 10 days from now. Why? Because we’re honest when we say it’s not possible.

    Stick with the sources that will lead you in the best direction when it comes to knowing what to expect. Not sure who that is? Hint: It’s not them. 😉

    (Yes I realize everybody here already knows this, but feel free to share this with folks you think don’t.) 🙂

    Reply

    1. I avoid social media as a rule and certainly when it comes to weather. What I do most is inform family, friends and colleagues about terrible forecasting and hype. Sometimes it’s hard to persuade them. I have a family member who said to me, “So I understand we’ll be having a white Xmas.” 🙂 🙂 🙂

      Reply

      1. I am now up to about 5 messages from people about the “massive blizzard on Christmas” that was initiated by one YouTube “forecaster” who is known for this type of thing. Find one model run that shows something, hype it to the maximum, just to get views. For what? If you need that to feel important, than it’s time to do a serious self-evaluation. Harsh-sounding? Yup. Sorry? Nope.

        The level that these people are influencing society’s perception on what we (people like me) do is disturbing.

        Reply

  2. Of note: Both 3km NAM and HRRR (most recent available info) shows most of Monday’s precipitation drying up before it has a chance to fall.

    Reply

  8. Good morning and thank you TK.

    btw nice rant and I totally agree. I can understand how frustrating it must be for one in your profession.

    Reply

  9. 19 here thus morning. Hadi lives about a mile from me and he reported 16 2. Could there be that much of a fifference? I suppose it is possible, but I more suspect sensor accuracy specifications is the answer.

    Reply

      1. Did you check the specs? My temperature sensor
        is accurate to +/- 0.5 degrees F.

        I believe you gave me the make of your equipment and I checked on line and it was accurate to +/- 2.5 degrees F.
        IF that is so, it is a huge difference and likely explains the discrepancy. But I can’t be sure you model is actually that same accuracy as the one I looked up. Curious if you have checked.

        I have another sensor that is only accurate to +/- 2.5 degrees and if I have the sensor side by side, you should see the difference. it is a joke and so much so, I removed the
        one with that was less accurate and no longer use it.

        Reply

  10. Once again, a correction to make, so if any of you see this happening out on social media, you can comment appropriately if you wish to.

    I’ve seen several comments on various platforms already about how unusual it is for California to have tornadoes and even more so, because it’s winter.

    Wrong and wrong.

    The state of California averages 11 tornadoes per year. About 80% of these occur from December to March.

    Reply

      1. It was the first tornado warning issued for that very spot. But when you consider the size of California, there’s nothing unusual about that statistic.

        They wouldn’t have mentioned it if it was in the middle of nowhere.

        It will get more attention because it was in a location where more people live. From a media standpoint that makes sense because no one else is really going to care about one in an area with basically no population.

        But again that it makes sense from a media standpoint because they’re going to want to report stuff more upfront that it takes place where people are.

        Reply

        1. I agree that an incident in more populated areas gets attention. San Francisco is a major area and I’d be disappointed if a first were not mentioned.

          Reply

  12. Thanks, TK

    A brisk 13 this morning, now up to a very nice 26!

    We’ve picked up a one minute and two seconds later sunset since last Monday! 🙂

    Reply

        1. Meteors were back last night, but not as frequent as the night before. All in all it was a great Geminid shower despite the moon!

          Reply

  15. And one final comment regarding tornadoes, per my colleague who gives me lots of great info…

    2024 was the 4th highest tornado count for the country but well shy of the record set a decade ago. What was absent was strong tornadoes. In fact, it’s now been nearly a dozen years since the last EF-5 in the US.

    The reason for the increased count for weaker tornadoes is simply continued improvements in detection and far fewer missed occurrences now compared to even just 5 or 10 years ago, and most certainly before that as well. We don’t get more tornadoes “now” vs. “then”, we just “see” them better. Better tech + more people watching.

    Reply

  16. I feel like in occasionally peeking at the NAO, PNA and AO teleconnection projections, the models are most struggling with the AO outlook right now.

    They’ve been consistent slightly positive on NAO, consistent on a slightly more positive PNA, but the AO is waffling.

    I think only a couple days ago, the outlook was for a slightly negative AO and now, it’s for a slightly positive AO.

    I think that’s why in the medium and long range projections, the models seem to be trending away from sustained cold in the medium and long range.

    Reply

    1. All it takes is a very small error in the short range which translates to much larger errors the further out in time you go. This is the main reason why I repeatedly remind everybody everywhere about the limits of guidance.

      These are only dealing with actually existing elements of meteorology once – the initalization. From there, everything is a projected based on what we know about the atmosphere. And we’ve surely mis-estimated some things, probably most things, by at least a little bit. This is what leads to model error with increases as time increases. 🙂

      Reply

    1. The surface temperature should be above freezing by 10AM. I couldn’t rule it out, but it may end up a case where nothing is falling from the sky, so there is nothing to freeze on any surfaces anyway.

      Reply

  19. 12z ensemble mean for ECMWF model continues to deliver a modest snow to SNE prior to Christmas. Up a tiny tick from yesterday.

    Reply

  20. Thanks TK! The upcoming Friday-Saturday (12/20-12/21) is interesting for SNE snow potential. Not a perfect setup at the moment, flow is a little progressive. Probably a situation where a negative (or at least less positive) NAO could help. But definitely would not count out the possibility of widespread accumulating snow in that window…

    Substantial warming/moderating trend for the Northeast heading towards Christmas and through at least New Year’s, as TK’s forecast has indicated. That’s Pacific-driven as NorCal and the Pac NW get drenched.

    But the first half of January could turn very interesting for the East as Northwest/Alaska blocking likely returns…

    Reply

  21. A bit ironic, I was actually vacationing in the Napa area this past week. Which was beautiful by the way, it’s off-season for them but was lucky to have a stretch of several great weather days, which is hard to do this time of year. Not to mention lower prices and greatly reduced crowds! Flew home from SFO on Thursday evening. One day later, the city got a tornado warning and measured wind gusts over 80 mph. Could’ve stayed behind to storm chase 😛

    The weather in California has been very interesting this fall/early winter. Northern California is off to one of its wettest starts to the rainy season on record, and will build on that the last 10 days of the year. But Southern California has missed out time and again, and we’re still dealing with wildfire issues as you’ve probably seen. And that’s unlikely to be remedied through the end of the year. It’s a big state obviously, but that dichotomy is pretty wild.

    Reply

    1. Hi WxWatcher. You sure have had some crazy weather out your way. Hopefully, 2025 will settle for you.

      If we dont see you here until after the holidays, Merry Christmas.

      Reply

  23. Crazy video of a tornado earlier from the Target parking lot in Scotts Valley, CA:

    https://x.com/bushmantribe/status/1868080145099329952?ref_src=twsrc%5Etfw%7Ctwcamp%5Etweetembed%7Ctwterm%5E1868080145099329952%7Ctwgr%5E340d79e3a92b20e16b8f7e170584b111b02082b2%7Ctwcon%5Es1_c10&ref_url=https%3A%2F%2Fwww.americanwx.com%2Fbb%2Findex.php%3Fapp%3Dcoremodule%3Dsystemcontroller%3Dembedurl%3Dhttps%3A%2F%2Ftwitter.com%2Fbushmantribe%2Fstatus%2F1868080145099329952%3Fs%3D4626t%3DNn9Cx92_8118fPdhHPdJHw

    Reply

  26. Thank you for your check-in and comments today WxWatcher! As always, very nice to see you here and I always appreciate your valuable input!

    Reply

  27. HRRR trend to keep a few patches of light snow together into our region tomorrow, while the rain is what dies out and never really gets in at all, until tomorrow night when it’s just patchy drizzle, followed by a 6 hour period of rain showers from pre-dawn to slightly after dawn Tuesday. A couple days ago I said I expected that to trend to a “glorified frontal passage”. Well, it’ll be a frontal passage, but hardly glorified, more like almost a non-event. 😉

    I agree with WxW’s comments above, which you’d have gathered from my blog discussion today anyway. More cold coming, then an end-of-month moderation.

    Reply

  31. I have not measured but I would say looking out the window about an inch to an inch in a half with a glaze of ice on top of that.

    Reply

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