Thursday April 29 2021 Forecast (8:27AM)

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DAYS 1-5 (APRIL 29 – MAY 3)

A frontal boundary will be spending most of its time in or at least close enough to have significant impact on the weather in the southeastern New England region (aka the WHW forecast area) during this entire 5-day period. It’s already played havoc with my own forecast made just yesterday morning, within hours of me posting it, when it became sunnier and warmer than I thought just a few hours in advance. I don’t think too many people will complain about a nicer spring day than had been expected, so there is that! My idea had been that today would turn out like yesterday did, and yesterday would have been more like today is likely to be. I don’t think I’m going to get surprised with nice weather today though, as the overcast will be hanging around and there will be an increasing chance of rain showers as we go through the day, so that by later this afternoon wet weather is pretty widespread across the region. This in response to the third in a series of disturbances / low pressure waves riding along the frontal boundary, which separates Canadian coolness from springtime warmth to the south. Model indications have been that if we’re going to bust into the warmer air on the other side, that we may have to wait until Monday, but yesterday that was a day 6 forecast, and do I need to repeat how those can go? Today’s guidance is not so sure about the Monday warmth, with some models “deciding” that the frontal boundary is going to stay down to the south. From a pure temperature forecasting standpoint, this could make a difference of at least 20 degrees in the temperature at some locations. Just for an example, a warm push on Monday with a west or southwest wind could drive Boston’s temperature toward 80, while being on the other side of the boundary with an east or northeast wind could hold them closer to 55 or even lower, depending on cloud cover. So not only does the forecast challenge include timing and coverage of any precipitation, but also taking into account temperature and wind direction based on the forecast position of that front. Rewind a bit to Friday. After today’s general onshore flow keeps it cool, we get “milder” for a while as the wind flow shifts to a strong land breeze during Friday, with many areas breaking 60 for high temperatures. But did you notice I said “precipitation” and not just “rain” earlier? Yes, there is a reason. On Friday, when the third disturbance pulls away from the region, it will be intensifying and there will also be a lot of cold air aloft with an upper level disturbance that still has to make its way through the region. A lobe or two of energy rotating around the back side of the departing low will create some showers, and these can fall as rain, mix, or snow during the late night hours of Friday and early morning of Saturday. This will likely be dependent on elevation and/or intensity of precipitation. So while it’s highly unlikely anybody will see accumulating snow, it is distinctly possible that parts of the region may see very early May flakes. During the day Saturday we’ll see nothing more than a passing additional rain shower in a few locations, otherwise it should be dry but breezy and rather chilly for the start of May. Many times when we have a day like that, the next day is likely to be tranquil and somewhat milder as high pressure builds in. Nope. Not this time. This is such a fast-moving pattern right now and the frontal boundary is not getting that far south of us Saturday that it’s ready to be pulled back northward Sunday by another approaching disturbance. It’s going to be tough to time this one for a couple days, until we get closer. Some guidance has it moving more rapidly than other guidance. But the idea is that Sunday will likely feature a fair amount of cloudiness and possibly the threat of some light rainfall at some point. And this leads us to the day 5 dilemma for Monday. A faster-moving disturbance would drag the boundary back to the south during Sunday and yet another approaching disturbance from the west could push it back to the north Monday, at least giving us a shot at getting into the warm air. A slower-moving disturbance would drag the front back to the south as it departed Sunday night into Monday, making it more likely we’d be on the cooler side for Monday. This is one of those times when I am just going to say I have no idea how this is really going to play out yet, so I’ll write the forecast below to cover this uncertainty as best I can and then re-evaluate for the next update. That’s about all I can do from a forecasting standpoint right now…

TODAY: Cloudy. Isolated to scattered rain showers through early afternoon. Scattered to numerous rain showers becoming widespread by late day including a slight chance of thunderstorms. Areas of fog. Highs 48-55 eastern coastal areas and Cape Cod, 56-63 elsewhere. Wind E up to 10 MPH.

TONIGHT: Cloudy, areas of fog, widespread rain showers with a chance of thunderstorms evening. Mostly cloudy with scattered rain showers overnight. Lows 45-52. Wind E up to 10 MPH evening, N 5-15 MPH overnight.

FRIDAY: Variably cloudy. A passing rain shower possible. Highs 58-65. Wind NW 10-20 MPH but gusting 30-40 MPH at times.

FRIDAY NIGHT: Variably cloudy. A passing rain or snow shower possible overnight. Lows 35-42. Wind NW 15-25 MPH, higher gusts.

SATURDAY: Sun/cloud mix. A brief rain shower possible. Highs 52-59. Wind NW 10-20 MPH with higher gusts.

SATURDAY NIGHT: Mostly cloudy. Light rain possible overnight. Lows 40-47. Wind variable 5-15 MPH.

SUNDAY: Mostly cloudy. Slight chance of rain. Highs 52-59. Wind variable 5-15 MPH.

SUNDAY NIGHT: Variably cloudy. Slight chance of rain. Lows 43-50. Wind variable to W 5-15 MPH.

MONDAY: Partly sunny. Highs 60-67 southern NH and northern MA, 68-75 to the south except cooler parts of South Coast. Wind variable to SW 5-15 MPH.

DAYS 6-10 (MAY 4-8)

Oh goodie! More uncertainty as it appears we’ll have a frontal boundary in our vicinity much of the time. Best chance of “warm” is very early in the period, otherwise leaning cooler with episodes of unsettled weather.

DAYS 11-15 (MAY 9-13)

Overall pattern similar, frontal boundary tends to hang nearby with episodes of unsettled weather and variable temperatures averaging not that far from normal.

34 thoughts on “Thursday April 29 2021 Forecast (8:27AM)”

  7. Good morning and thank you TK.

    In short, the weather will be typical Spring Time in New England. 🙂

  8. Thank you, TK.

    Any time I see the word “snow” in a forecast, I like it. My mother bought a wooden sign that says “Snowbound.” Upon my Mom’s passing, I put it above the entrance to my apartment. It reminds me on those sultry days in July that snow is only 4 months away.

  10. Yup, forecast is already going down the tubes today too. The numerous showers are about 6 hours ahead of any guidance, and even much faster than I would have guessed by looking at radar trends. This is a “can’t win” slump. It’ll end eventually. 🙂

    1. As long as your right about Saturday. Around the 5 pm timeframe for Duxbury today do you see it raining hard enough to cancel an estimate

  11. TK, you’re being quite hard on yourself. Your forecast is based on guidance from models and interpretation of that data PLUS your experience as a met. You do a great job. No forecast is perfect. in fact, if all forecasts were perfect it would be a very dull world.

    1. I agree. But I think this is important. There are t least two lessons here that I like to hear TK help with. First, if you make a mistake, say so. I love when a person can do that. It is why I like to try and talk things through if there is a disagreement. And honestly, I’m praying I can say I made a mistake with some of my covid beliefs. Second, it is a great way to teach that even the media Mets can make mistakes but those mistakes do not take away from their talent …..OR their knowledge.

  12. Interesting piece from the NWS on temperature scales

    US National Weather Service Boston MA
    YotnrSpuslesortferdaiy at e12dh:0nssosrc0de oPeSeuMcds ·
    #WeatherKnowledgeWednesday Virtually every county on earth uses the Celsius temperature scale. The Celsius scale was named after Swedish astronomer Anders Celsius. Since 1743 the Celsius scale has been based on 0 °C for the freezing point of water and 100 °C for the boiling point of water. The U.S. is one of very few counties to still use the Fahrenheit scale. The Fahrenheit scale was developed by physicist Daniel Gabriel Fahrenheit in 1724. The Fahrenheit scale is now usually defined by two fixed points: the temperature at which pure water freezes into ice is defined as 32 °F and the boiling point of water is defined to be 212 °F, both at sea level and under standard atmospheric pressure. The Fahrenheit scale was the primary temperature standard for climatic, industrial and medical purposes in English-speaking countries until the 1960s. In the late 1960s and 1970s, the Celsius scale replaced Fahrenheit in almost all of those countries—with the notable exception of the United States and in certain cases, the United Kingdom—typically during their general metrication process. Scientists, such as meteorologists, use degrees Celsius or a third temperature scale known as kelvin. The Kelvin temperature scale was named after the Belfast bon William Thomson, 1st Baron Kelvin. Unlike the degree Celsius and Fahrenheit, the Kelvin is not referred to or written as a degree. The kelvin is the primary unit of temperature measurement in the physical sciences, but is often used in conjunction with the degree Celsius, which has the same magnitude. In meteorology, most of the computer models that aid forecasters in weather prediction are coded in Kelvin. The Kelvin scale uses zero as its null point, and on the Kelvin scale, pure water freezes at 273.15K, and it boils at 373.15K. A forth temperature scale is the Rankine scale, which is named after the Glasgow University engineer and physicist Macquorn Rankine, who proposed the scale in 1859. Just like the Kelvin scale, zero on the Rankine scales is absolute zero, but a temperature difference of one Rankine degree is defined as equal to one Fahrenheit degree, rather than the Celsius degree used on the Kelvin scale. Here is a link to a temperature unit calculator that will convert between all four of the temperature scales along with additional information on the formulas for the temperature conversion script.
    https://www.weather.gov/epz/wxcalc_tempconvert

  15. In a rare lucid moment, I have something to be shared with TK.
    Even a broken clock is right 2 times a day.
    So….I suggest you keep issuing the same forecast every day and at some point, you will break your slump.
    I know…..I should go back to my cave. Lol.

  17. My goodness did this thing ever bring it with rain in an area that badly needed it!

    Underestimated that, but so what. Between the good weather yesterday and the beneficial rain today, it’s kind of a win-win, even if the forecast was an oops-oops. 😉

  19. Soaking rain here in Back Bay for many hours. Ducks are very happy, I’m sure.

    JPD, thanks for sending the picture of the full moon, and the information on temperature scales. Love temperature scales.

  21. Will be really interested to see some rain totals here in andover, it rained heavily almost all day.

    1. I’m seeing 1,75 and just over 3 inches on two of the Wunder sites

      And I thought we were doing well with 0.68

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