General summer chat

[LetItSnow!]

 B87 

2 hours ago, B87 said:

Why would April 2021 synoptics produce average days if they occurred in June

Interesting question so this is my attempt to answer it with the best of my knowledge. The temperature guesses are mostly for England.

The end of March spell with comparitive anomaly for the end of May and the synoptics would have likely produced a couple days in the low 30s, probably the 30-33C region, maybe challenging the record.

The 1st of June would have been a transitional day with hot air still over the south so down there probably another day in the high 20s/low 30s but a cold front moving S/SW within the high. The 2nd would have been a cooler and fresher day though probably some residual warmth in the mid 20s. Probably not much in the way of rain with that front and just quite cloudy.

The 3rd to the 8th wouldn't have been a complete horror show. The 3rd and 4th probably would have been mostly pleasant with temperatures widely in the high teens/low 20s and sunny spells with some cool nights. The northerly push would have seen unusually cool air so I imagine the weather front would lead to some impressive convection so some big storms rumbling southward. I think there would have been snow in the far north on high ground. Widely nights would have been very chilly and some local air frost wouldn't be out of the question, definitely single digits for most if not all. Days, depends on cloud etc but probably low to mid teens for most though London may have been in the 17-19C range with sunny spells.

The 9th to the 12th probably would have been very thundery but unusually cool with a northerly flow but flabby troughs around the place. I imagine temperatures in the teens with the 11th probably seeing widespread thunderstorms breaking out, especially across the SE due to weak pressure from a trough to our SE. A very common 1980s summer set up - cool and violenty thundery.

The 13th to the 18th would have seen the high pressure lead to warm days but probably some cold nights at first with any leftover cool air so local ground frost for sure and single digit minima, but with the June sunshine under an anticyclone temperatures would be in the low 20s quite quickly but with nights remaining cool.

The 19th to the 26th would turn very warm, maybe even fairly hot as uppers increased and the flow turned south-easterly. There may have been some rogue thunderstorms in the far south-west and temperatures would probably climb at least into the upper 20s, particularly on the 23rd, 24th and 25th.

The 27th to the 30th would have turned thundery as a weak trough developed over the country as lower heights pushed north, so a proper 1980s style thundery breakdown. Probably lots of severe thunderstorms on the 27th and 28th making way for a cool and very cloudy closing days with weak north-easterlies and perhaps more showers and storms but more scattered. 

No doubt would have been cooler than average even by the 1961-1990 average and I imagine still with a bigger anomaly by night. I do think the month would have likely reached 30C+ either on the 1st or between the 23rd to 25th, but probably only like 30-31C with an outside chance of just like 28-29C.

 

Sorry if off topic but it was a fascinating concept to me lmao.

Edited April 8 by LetItSnow!

[Addicks Fan 1981]

From what @Tamara said in some archive model thread forums may 2007 actually had a positive AO but when we came into the summer AAM collapsed dramatically.  It was the same year where we had el niño to la niña transition, we had an east QBO in tandem with negative zonal winds blowing across the troposphere aligning with the weak sea ice and subsequently produced the poor summer it did.   

For may 2006 there was a lot of northern blocking but also a lot of robust wave activity so when we turned the calendar month to June it generated high AAM and a generally great summer up until August with the heat at its peak in July.    

Edited April 8 by Addicks Fan 1981

[summer blizzard]

 B87 A lot of synoptics from April 21 would result in a different temperature profile. April was still early enough that a slight inversion was present. 

The 1st-4th would likely feature a high durinal range and temperatures close to average. 

The 5th-12th would be quite cool but potentially damp with a stronger sun to spark showers. 

The 13th-19th would feature a west-east split but generally products temperatures close to or above average. 

The 20th-26th would draw mostly south easterlies and be warm.

The 27th-30th would be cool and damp or even wet. 

So the first 12 days may be on the cool side but the 13th-26th would be warmer than average securing a warm month. 

[Summer8906]

15 hours ago, WYorksWeather said:

Not sure about necessarily duller/cloudier than average or wetter than average - there's not a clear trend that way. What might be more true is a slowing down in the pattern, in the sense that you're more likely to get one month that is clearly better than the other two, rather than a generally mixed and changeable summer.

That's true, and 2019 was basically like that. Poor June, settled July, poor first three weeks of August, mostly dry and fine for a month from around August 20, and then five or six months of constant rain before the very dry spring 2020.

[Summer8906]

 summer blizzard I think the big difference would be that in June, the showers would be more widespread and severe, as you imply, due to stronger solar heating.

Often slack northerlies in June (when they occur, which isn't so often) produce some really big showers, some severe with hail and frequent thunder.

Might a June version of April 2021 have produced, for a while, something like the middle part of June 1987, which was notable for cool weather featuring sunny starts and heavy thundery showers during the afternoon and evening before clearing overnight?

The more sunny, anticyclonic phase of April 2021, from about the 15th-25th (IIRC) would probably end up being warm by day in June, as you also say, perhaps around 23C max, like many days in June 1996. It's rare for it to be both sunny and cool once we get to June.

Finally the month would end with a cool and showery NE-ly type, probably with more cloud overall than the earlier showery phase - leading us into our alternate-reality July, which would be the worst since at least 1988.

I'd suspect a June version of April 2021 would still end up being cool, especially at night, but less so.

Overall an interesting month with the only unsettled weather the slack showery type. I didn't actually mind the middle bit of June 1987 as it was at least interesting, though I disliked the first week and the period around the solstice which were dull and damp.

(EDIT: sorry, just seen @LetItSnow!'s post which more or less comes to the same conclusion! I would disagree on any 30s though: the uppers were pretty cool throughout April 2021 so I'd expect an absolute max of 25 or so, during the sunniest phase).

Edited April 8 by Summer8906

[LetItSnow!]

 Summer8906 Late March and the 1st had 10C uppers and late March had seen near record level temperatures, so in June I’d imagine the equivalent would be uppers around 15C which still would be present on the 1st which is why I think in the south in that synoptic pattern the temperature would be somewhere around 27-31C

[raz.org.rain]

 

[WYorksWeather]

CFSv2 also looks pretty good for high pressure. Only August has any sort of low signal, and especially June has a very strong high pressure signal.

Precipitation also not too bad. Maybe June and August better in the north, July better in the south?

Temperature wise still a very strong signal for a very warm and/or hot summer.

Anyway, something to ponder. Add a large pinch of salt of course since it is the CFSv2!

[damianslaw]

 WYorksWeather These warm temp anomaly forecast maps are shown for every season nowadays, nothing new. Can't remember last time average or below shown, mind last cold season was Spring 21, so they've been right, just a case of how deep the reds are nowadays.

Edited April 10 by damianslaw

[reef]

 WYorksWeather urgh, not another June with constant easterlies. We had 14 hours of sunshine in the first 10 days here last year. At least its the CFS so it'll probably be wrong.

[WYorksWeather]

 damianslaw Yep, I prefer to treat the yellow as default mild. The red though is quite something even in our christmas pudding - that's 1-2C above the 1991-2020 average. Though summer averages haven't risen as much, that is a strong signal for a very warm or hot June and July, at this range.

Anyway, we'll just have to wait and see what happens as we get a bit closer. Key points I suppose will be how much the ground dries out through the rest of April and May, which will have an impact on the temperature ceiling.

[WYorksWeather]

 reef To be fair, I guess it does very much depend on how the averaging works. You could have an average position of the high to the NE but that might mask a lot of variation.

 

[raz.org.rain]

More on the positive NAO developments

 

[Greyhound81]

Has the hottest day of any year ever been in May?  I think it would be almost impossible, even if the summer is very poor.

I know the warmest day of any year has been in September a few times (including last year).

 

Edited April 11 by Greyhound81

[summer blizzard]

Before anybody gets overly excited it's worth remembering that the AO values are normally close to neutral in summer and that +/-1 months are rare. The polar vortex is net easterly regardless of what happens until late August. 

[B87]

June 2024 will obviously be worse than June 2023, but will July and August also manage to be worse than last year?

[Weather Enthusiast91]

I am going for a washout June this year, with the summer improving as the season goes on. So August will be the best month for summery and useable weather, with the hottest day of the year recorded at Heathrow early in the month.

Edited April 21 by Weather Enthusiast91

[B87]

I think all 3 months will be cooler by day, wetter and cloudier than normal.

[Addicks Fan 1981]

 Weather Enthusiast91 the CFS begs to differ from what you are suggesting and if we have a good second half of may that will determine our june/july pattern.   

[I remember Atlantic 252]

Sept probably best month, think most agree about horrible June

[summer blizzard]

Anecdotal but for a lot of recent developing La Nina's, it's July that the trades in the Pacific suddenly pop up raging. Probably related to the timing of the monsoon season or something creating a downstream wavelength that can be amplified. 

[B87]

 summer blizzard What would that do for us?

[summer blizzard]

 B87 Strong trades around the dateline (easterlies) typically strengthen the mid-lattitude jet in response (stronger westerlies) and suppress AAM. 

It's why a lot of people tend to think that La Nina produces less favourable summers for the UK.

[B87]

 summer blizzard So after a fairly horrendous run since last July, it will continue through into autumn at least?

[raz.org.rain]

 B87 not necessarily, and I wouldn't say particularly likely at this point.