Tuesday July 20 2021 Forecast (7:28AM)

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DAYS 1-5 (JULY 20-24)

The sunshine is back to start today, but it’s got a smoke screen – a high altitude one via Canadian and western US wildfires – nothing all that unusual for this time of year though. We’ll feel a bit of heat today today as we’re in a very warm air mass with moderate to high humidity. This may help fuel a couple isolated late day showers or thunderstorms, mainly west and north of Boston, which may still be around tonight as a disturbance moves through from the west. This sets up a potentially interesting day tomorrow, as a broad trough moves across the region with embedded disturbances, good for up to a few rounds of convection producing showers and thunderstorms. Some of the storms could potentially be strong to severe, so we’ll have to keep an eye on this during the day, anywhere from late morning to early evening. This system pushes off to the east at night, and we get a visit from Canadian high pressure bringing us the nicest day we’ve had in a while on Thursday. The next disturbance passes through the region Friday, but this one looks fairly weak and will only bring the chance of a few passing showers, mainly during the first half of the day as it stands now. Another area of high pressure brings nice weather back for Saturday.

TODAY: Smoke-filtered sun, eventually some clouds, and the chance of a late-day shower or thunderstorm mostly well north and west of Boston. Highs 80-87, cooler Cape Cod. Dew point upper 60s. Wind W 5-15 MPH.

TONIGHT: Variably cloudy with a chance of a shower or thunderstorm during the evening, then partly cloudy with patchy ground fog overnight. Lows 61-68. Dew point lower 60s. Wind W under 10 MPH.

WEDNESDAY: Variably cloudy. Episodes of scattered to numerous showers and thunderstorms. Some thunderstorms may become severe. Highs 76-83. Dew point middle to upper 60s. Wind W 5-15 MPH, variable and potentially stronger around storms.

WEDNESDAY NIGHT: Partly cloudy. Lows 57-64. Dew point falling to middle 50s. Wind NW 5-15 MPH.

THURSDAY: Mostly sunny. Highs 76-83. Dew point upper 50s. Wind NW 5-15 MPH.

THURSDAY NIGHT: Partly cloudy. Lows 58-65. Dew point middle to upper 50s. Wind W under 10 MPH.

FRIDAY: Partly sunny. Chance of showers, mostly morning through midday. Highs 73-80. Dew point near 60. Wind W 5-15 MPH.

FRIDAY NIGHT: Mostly clear. Patchy ground fog lower elevation areas. Lows 55-62. Dew point falling to middle 50s. Wind NW up to 10 MPH.

SATURDAY: Mostly sunny. Highs 76-83. Dew point upper 50s. Wind W 5-15 MPH.

DAYS 6-10 (JULY 25-29)

Westerly flow overall. Disturbances with shower chances somewhere in the July 25-26 and later July 27-28 time frames, but most of the time rain-free – a considerably drier pattern than recently. Temperatures near to below normal.

DAYS 11-15 (JULY 30 – AUGUST 3)

Overall pattern keeps us in a west to northwesterly air flow, with no major heat, temperatures near to slightly below normal, and a drier overall regime with fewer shower chances.

56 thoughts on “Tuesday July 20 2021 Forecast (7:28AM)”

  2. Thanks TK.

    I once heard a PSA on the radio that 90% of wildfires are started by humans. Who’s going to argue with Smoky? 😉

    Still looking forward to DAYS 6 and beyond with more refreshing Canadian air and much less rainfall hopefully. I believe that Logan is only ~2” away now from the 1921 record (11.69”). I suppose it could be broken in one strong storm tomorrow?

    1. I love these. Thanks, Tom. You can see the layer in the sky. I was out for a few minutes and my eyes are itching.

      1. I like them too ! The modern day satellites have such improved detail. Hopefully, come Thursday, the smoke will get pushed south of us.

  13. From the NWS office at Norton re: tomorrow

    Wednesday…

    The approaching shortwave will generate lift over the region, while
    convective parameters will be more unstable than today. CAPE will be
    around 1500 J/Kg and possibly 2000 J/Kg. Total-totals will be in the
    mid 50s. LI values will be quite impressive at minus 5 to minus 8.
    Light wind at the surface but 35 kt at 500-mb, so expect at least
    some shear for storm organization. Finally, PW values will be 1.5 to
    1.75 inches, while this is not excessive for mid-July, it is
    certainly above average. We note that SPC has the region in a
    Marginal Risk for severe. WPC yesterday had the region in a Marginal
    Risk for excessive rainfall

    1. JJ, I think there is a reasonable chance it will be upgraded to slight based on the NWS discussion I posted above. Those parameters look decent enough to me. If not at the 1:30 PM update, then the next one or certainly tomorrow AM.
      We shall see.

  15. You might be right JpDave. One thing to look forward to once we get through tomorrow the rest of the week the dew points drop to more comfortable levels and this haze from these western wild fires will be gone.

  16. The version of the ECMWF that runs out to 46 days gets updated on Mondays and Thursdays. On yesterday’s update, there isn’t a single day between now and the end of August where more than 3 of the 51 members have Nashua reaching 90. In fact, August 4 and 14 are the only days with 3 out of 51, the rest of them are 2 or less. If you use Boston instead of Nashua, August 2, 6, 14, and 15 are the only days when 2 of the 51 ensemble members have Boston hitting 90, the rest of the days are 1 or 0. It doesn’t have that many cool days either, with most of the members having highs in the 70s or 80s nearly every day.

    In terms of rainfall, it’s drier there too. For Boston, by the end of August, the mean of the 51 members is about 5.5″. Between 25% and 75% of the members range between about 4-6.75″. For Nashua, the mean is around 6.25″, with the 25-75% range around 4.75-7.75″.

      1. I found dry and low humidity! Flew to Denver this morning now on the way to Colorado Springs. Tomorrow Heading to Philmont Scout Ranch in New Mexico for a 12 day, 57 mile trek with my sons Boyscout troop. Be dodging monsoon t-storms first few days anyway.

        1. Awesome! Enjoy. By any chance might you be hiking by Taos? That area is absolutely beautiful.

  21. This might play a role for thunderstorms tomorrow.
    Tweet from Paul @weatherwiz

    (1/2) The potential is there for numerous damaging wind/hail reports Wednesday but one major key may be position of a surface or pre-frontal trough. If surface winds are more westerly that will limit convergence & coverage of thunderstorms.

    (2/2) Should the surface winds remain more SW or even SSW…greater coverage of thunderstorms. Of course, early morning sun is a factor too. Any activity tonight could help lay boundaries for tomorrow as well.

  22. Started next camping adventure down around Taunton for a handful of days and seemingly bullseye for tomorrow’s storms, etc. Of course ….. storms are like dogs, they sense fear 🙂 🙂 🙂

  23. It’s been awhile since wildfire smoke has mixed down to the surface at this concentration.

    The last time I remember it this notable at ground level was July 2007.

  24. From NWS Boston
    *** Strong to Severe Thunderstorms Wed Afternoon & Evening ***
    *** Damaging winds, Large Hail & Localized Flooding Possible ***
    *** Greatest Risk CT/RI & south of I-90, esp I-95 corridor ***

  25. 18z NAM 3km version is high as a flipping kite. No good. Buhbye.

    If it’s right about tonight’s convection coverage, and the lack of tomorrow’s in favored areas, I may struggle to ever doubt it again. 😉

  26. Translation keep an eye to the sky tomorrow afternoon as some areas could see a nasty thunderstorm???

    1. Yup. But as time goes on I’m thinking coverage won’t be all that great. Low coverage, possible high impact event.

  27. The smoke is even a bit thicker down here in NJ than up where most of you are. You can (faintly) smell it at ground level here. I would have to say it’s the worst smoke day I’ve ever experienced.

    Tomorrow’s setup looks pretty interesting. Unusually good dynamics for this time of year. Could see some big wind and hail producing cells. I think the SPC’s slight risk area looks really good; maybe things end up favoring the southwestern portion of the risk area (CT, NYC, NJ) a little more? But we’ll see. Also interested to see if there’s any notable effects of the smoke on convection tomorrow. It may be thick enough to promote some convective inhibition, though I don’t think it’ll be a big factor.

    1. I was wondering that myself (smoke inhibition).

      What do you make of the 18z 3km NAM (specifically for SNE)? In my opinion, O.T.L. big time.

      1. I think OTL also in terms of the total dearth of convection. I’ve been leaning away from the 3km NAM and towards the HRRR this year, with generally (though not always) favorable results.

        However, based on the timing of the front, I would definitely favor southern/eastern areas for the best chances. I also think the evolution of the ongoing convection over upstate NY/northern New England will be a factor. There will probably be remnant outflow boundaries around tomorrow.

        Kind of a complicated forecast! But always gotta be mindful when you have a stronger forcing/higher shear day like tomorrow.

  28. WxWatcher I get the impression from reading your comments and seeing some of the comments from meteorologists on twitter that are some favorable factors for severe weather but also some negative ones. It doesn’t look widespread severe weather to me but there could be a few spots that get hit tomorrow with damaging wind hail and heavy rain. NWS Boston was mentioning atypical for July to see a mid level trough go from positive tilt to neutral to negative at comes across the region.

    1. Yes, the nature of the trough is the key part of the unseasonably favorable dynamics. But like you said, it’s definitely a “pros and cons” forecast (of course, that’s often the case). If the front was coming through 2-4 hours slower then I’d really be sold on a big severe weather day.

      One thing I don’t think will factor in much if at all tomorrow is excessive rain/flash flooding. I don’t see much of a tornado threat either, unless a discrete cell is able to interact with a remnant outflow boundary. But both damaging winds and large hail are likely to be in play.

  29. FYI everyone – the Southern New England Weather Conference will be virtual again this year. We’re going to hold it on line on Saturday morning November 13.

    Dr. Louis Uccellini will be talking about snowstorms (he literally wrote the book on them), as well as some of the things the NWS will be doing.
    David Vallee will be talking about the 30th anniversary of Hurricane Bob.
    We’ll have someone from NHC presenting.
    We’ll have a Winter Outlook presentation
    We’ll also have a panel discussion with reps from the NWS/Private Sector/ Broadcast/Academia

    I’ll have more details for you after I get the website updated this weekend.

    (If you didn’t know, I’ve been on the planning committee for the conference since it’s inception 20+ years ago and I run the website for it).

  30. Tough air to breathe out there, at least if you’re exerting yourself. Combination of high humidity and the haze/smoke.

  31. JPDave, looks like we will be several miles East of Taos, NM. We will be hiking around Cimarron. We’re down near the Air Force Academy at the moment in Colorado Springs. It’s a three hour drive to Cimarron NM. Truly beautiful countryside!

    1. On one of our nights we will be camping at 11,000 feet! The scouts are excited of the upcoming adventure. We’ve been preparing the last few months and also hiked Mt Washington and Lafayette loop trail the last couple weeks. I’m proud of what they’ve accomplished!

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