North American Weather (U.S.A & Canada)

[kold weather]

Looks like the first cold shot is heading down into central Canada right now, the 0z GFS progs thicknesses down to 531, not too bad at all and it would be cokld enough for snow IF the was any precip about.

GFS still going for that sort of set-up this morning whitefox. 850hpa temps get upto 13C with thicknesses getting upto 563. So you'd expect a warm-up tohugh its not quite as warm as the 0z yesterday suggested, maxes would probably be in the 12-14C range I'd guess.

Beyond that and real fun and games look like starting. A major cold shot comes down from the north as a Lp drfits eastwards and a HP comes in from the Pacific. This looks like being much of Canada's first major shot of cold thia Autumn with 850hpa temps down to about -10C in Winnipeg. Even more interesting is a open wave comes across the region on this run and IF that turns out to be anything close to accurate it would give a chance for a little snow in that region as well. Long way off yet and the details will need to be firmed up but it does look like at least a shot of cold is coming down from the Arctic, in such a shot the temps will have a hard time getting much above 1-2C.

By 180hrs the HP from the Pacific moves eastwards and sneds the cold shot towards E.Canada and gives them some cold, possible a LOT of snow for the far NE of Canada if this run is correct.

[WhiteFox]

GFS still going for that sort of set-up this morning whitefox. 850hpa temps get upto 13C with thicknesses getting upto 563. So you'd expect a warm-up tohugh its not quite as warm as the 0z yesterday suggested, maxes would probably be in the 12-14C range I'd guess.

Nice to see the blues starting to appear up there. It's surprising just how quickly they start to form up there once we get to November. Most of the solar radiation is gone, so apart from warm air being pushed up from the South or mixed in from the West it's downhill all the way to March...

Incidentally, a large warmup here in Chicago this weekend ahead of the next cold front; it's also been quite windy with winds gusting up to 40mph. We hit 24oC yesterday, and 27oC today; by Tuesday we're looking at about 15oC as a maximum. Of course, this is nothing compared to Denver.

Take a look at these observations for Denver, CO (mentioned by Paul Sherman):

20 20:53 N 33 G 41 10.00 Mostly Cloudy and Windy SCT026 BKN110 BKN180 46 34 29.68 1000.9

20 19:53 NW 13 10.00 Mostly Cloudy SCT050 BKN120 BKN200 66 20 29.56 994.5

20 18:53 W 22 G 31 10.00 Mostly Cloudy and Breezy SCT060 SCT120 BKN200 68 18 29.50 992.3

20 17:53 SW 18 G 29 10.00 Partly Cloudy FEW080 SCT140 SCT200 70 19 80 70 29.49 992.0

20 16:53 SW 20 G 25 10.00 Mostly Cloudy FEW080 SCT140 BKN200 76 15 29.49 991.3

20 15:53 NW 15 10.00 Mostly Cloudy FEW080 SCT140 BKN200 77 17 29.48 991.0

20 14:53 NW 9 10.00 Mostly Cloudy FEW080 SCT140 BKN200 80 19 29.48 990.2

From a high of 80oF yesterday, to light snow on Sunday morning, including a drop of 20oF (about 10oC) in the space of an hour (it would be interesting to see continuous graph; I'm wondering just how quickly that temperature actually fell!).

[kold weather]

I heard Toronto had a daily record yesterday with top temps of 25C, if so thats pretty impressive!

0z GFS this morning has slightly toned back the strength of the cold for next weekend but it still just about looks cold enough for snow providing it doesn't get downgraded anymore.

Anyway before then the warm-up still looks very much on for late this week in the Winnipeg region, 850hpa temps getting upto 15C for a time before the LP moves out of the way. I believe the fires in the far west of the USA are not being helped by the warm plume spreading in from the Pacific and this whole lot wil lspread eastwards displacimng the cooler air that is currently over C.Canada (Maxes progged at 10C, current temps are now 1C) Interestingly the height of the warm-plume comes overnight and by Thursday afternoon the colder air should be digging quite readily southwards. How cold?

Yet to be decided by the models it appears as they keep changing their tune.

If nothing else at least you got GFS FI, which is for UK standards very cold, 850hpa temps get down to -16C and the thickness of 511, if that were to come off we'd be seeing maxes probably around -4-6C I'd guess. Very cold but probably not too far away from average in November.

Looks like rain is finally going to make it into the SE states as well, they do need it quite badly, esp as the La Nina favors a SE ridge!

Edited October 22, 2007 by kold weather

[Coopsy]

High's here in southern Alberta look set to reach 19oC due to the southerly winds, ahead of a high coming in from the Pacific. The it looks set to tumble for a few days. By mid to late week prob 0oC for ddaily high, not sure about any snowe though, unless the winds turn to an easterly and give some upsloping

Interesting to note that snow levels here in the eastern rockies are much lower than this time last year. In fact the ski slopes opened for a weekend in early November last year, not sure its gonna happen this year. No recorded snow in the town here so far this season

Amazing warmth in C/S Ontario with highs prob touching 25/26oC today

Incidently, its was 21oC at 11pm last night in Toronto, for late October that amazes me. You could be having a bbq on the deck and still be warm in a t-shirt

[WhiteFox]

Anyway before then the warm-up still looks very much on for late this week in the Winnipeg region, 850hpa temps getting upto 15C for a time before the LP moves out of the way. I believe the fires in the far west of the USA are not being helped by the warm plume spreading in from the Pacific and this whole lot wil lspread eastwards displacimng the cooler air that is currently over C.Canada (Maxes progged at 10C, current temps are now 1C) Interestingly the height of the warm-plume comes overnight and by Thursday afternoon the colder air should be digging quite readily southwards. How cold?

Yet to be decided by the models it appears as they keep changing their tune.

Ensembles showing good agreement for a spike to 15oC for 850s in Winnipeg. Interesting to note that the spike is not so pronounced further south. Anyway, after the spike something a bit closer to seasonal norm looks likely, but no real agreement on a pattern change to cold by any means. Ten day forecast is currently going for 4oC on Tuesday and 2oC on Wednesday next week in Winnipeg (average is 5-6oC).

Further East, New York remains about or just above average, with max temps ranging from 16oC to 21oC over the next few days. FI starts next Tuesday and becomes steadily more random thereafter. Could be a decent cold shot, or a warm plume! Such are the vagaries of the Atlantic Seaboard...

[Roger J Smith]

Very strong cold front coming through the prairies on Thursday -- temps will tumble down by 15-20 degrees in a few hours with this, and watch for very strong wind gusts from W to NW.

The southern CA fires are fanned by east winds called Santa Ana winds, this is the common set-up for major fire activity in Oct and Nov with strong high over Utah-Colorado, and east wind gradient enhanced by the topography. These winds are downsloping so they get additional warmth and dry out further, winds yesterday were gusting 70-100 mph in exposed locations from the ENE. The fires are becoming mega-severe and the San Diego region in particular faces a major evacuation alert.

Meanwhile, the low which is crossing western Canada will end up moving northeast towards Greenland and playing a big role in how the confusing situation over Europe resolves. If it moves far enough north and west, it could be a factor in tilting the flow and permitting a split in the ridge to open the floodgates for cold air from Greenland. If it takes a more southerly track, it will probably just keep the mild southwest flow in place over the central to eastern Atlantic.

Retrograde action seems likely very soon, and I think this low will in fact head north eventually near Baffin Island and help to get something more active going over Europe.

[kold weather]

Its interesting whitefox that a few of the GFS ensembles are going for soemthing colder around 10 days time in the east which may need to be watched.

Before then as Roger said quite a large cooldown set to occur during Thursday. 850hpa temps get upto an impressive 16C during Wednesday eveing which wil no doubt lead to a fairly mild day for the Winnipeg region. Its overnight that a strong cold front dips down and brings in colder air with winds changing from SSW to NNW. This airmass is a lot colder then the present one with thickness getting below 528mbs and also 850hpa temps down to -7C though there won't be much in the way of precip about. Quite abit of cloud cover expected till the winds shift to a drier westerly directionearly on Saturday with a fair chance of an air frost. Maxes during this quick cold snap look like being around 4-5C IMO then on Sunday a SSW as a strong high (1040mbs) transfers eastwards to the south of winnipeg.

It'll be this high that will introduce a cool-down to the far north of the states and also E.Canada.

[icy toes]

Well. Just returned this morning from our week in New York. The weather was unbelievable - mid to high-70s all week. It even hit 80 on a couple of occasions. I think some records were broken last week. The humidity was really noticeable during the first half of the week. It made sight-seeing really draining, as we walked everywhere. The subway was a no-go area for us as it was like walking into an oven. How New Yorkers cope with that heat when it's really hot, god only knows. Thank god the carriages are air-conditioned.

A big line of storms that brought tornadoes to some parts of the US on Thurs/Fri didn't really hit NYC. We had some light showers, while some parts of the state got 4-5 inches. Shame, really, as it looked for a while we were going to be in the firing line of some spectacular storms. When we left New Jersey at lunchtime yesterday we were basking in some gorgeous weather. Imagine the shock this morning when we landed at Heathrow and found ourselves scraping the ice of the windows!! Even as I'm typing now it's only reached 7 deg. Brrrr!

All in all a fantastic trip, made even better by the unseasonably hot weather.

[WhiteFox]

The southern CA fires are fanned by east winds called Santa Ana winds, this is the common set-up for major fire activity in Oct and Nov with strong high over Utah-Colorado, and east wind gradient enhanced by the topography. These winds are downsloping so they get additional warmth and dry out further, winds yesterday were gusting 70-100 mph in exposed locations from the ENE. The fires are becoming mega-severe and the San Diego region in particular faces a major evacuation alert.

Relative humidity was down to 8% in some areas affected by the Santa Ana winds yesterday; that would make your skin dry!

This airmass is a lot colder then the present one with thickness getting below 528mbs and also 850hpa temps down to -7C though there won't be much in the way of precip about. Quite abit of cloud cover expected till the winds shift to a drier westerly directionearly on Saturday with a fair chance of an air frost. Maxes during this quick cold snap look like being around 4-5C IMO then on Sunday a SSW as a strong high (1040mbs) transfers eastwards to the south of winnipeg.

It'll be this high that will introduce a cool-down to the far north of the states and also E.Canada.

Each successive cold front tends to bring a colder airmass at this time of year. It's great! Winnipeg is probably like elsewhere I've been over here; there may be an air frost, but a hoar frost is unlikely. In winter you can look outside on a beautiful sunny day and easily trick yourself into thinking it's summer...until you step outside of course!

Well. Just returned this morning from our week in New York. The weather was unbelievable - mid to high-70s all week. It even hit 80 on a couple of occasions. I think some records were broken last week. The humidity was really noticeable during the first half of the week. It made sight-seeing really draining, as we walked everywhere. The subway was a no-go area for us as it was like walking into an oven. How New Yorkers cope with that heat when it's really hot, god only knows. Thank god the carriages are air-conditioned.

Humidity? In October? Don't visit between June and September if you thought October was bad! When the air temperature is in the nineties and the dewpoint mid-seventies then you really feel it!

You're right about the subway, although I still use it. In mid summer I break into a sweat as soon as I go down the stairs. The trains themselves are an oasis of cool at that time of year.

Severe storms are unusual in New York; they tend to die out somewhat over New Jersey. Sometimes they make it across, but nowhere near as bad as upstate or further West.

[Coopsy]

Extremely strong winds here in the past 12 hours, many trees down, roads blocked and cars damaged. Strong chinooks to blame I believe, 100km/h winds. However the plus was that at 11pm last night the temperature was 14oC, balmy for these parts

[kold weather]

Yeah i'm not surprised by the hoar frost given there probably isn't as much moisture as there is here.

12z GFS looks pretty amazing for Wednesday-Thursday, looks pretty warm for the time of year with a really impressive shot of hot air from the south, 850hpa temps on this run upto 16C with maxes progged at 18C!

As you say once that clears away the 12z GFS gives repeated shots from the north each getting colder and colder. On Saturday this run gets the thicknesses down to 524mbs and I think maxes aren't going to get much higher then 4-5C like I said earlier...just a shame the airmass is fairly dry with pretty high pressure values, getting upto 1030mbs at one point.

Then the GFS keeps Central Canada in a cold set-up for the rest of the run with some really cold values developing, thickness drops down to 514mbs which is pretty cold and impressivly low if you compare to British values!

[WhiteFox]

Yeah i'm not surprised by the hoar frost given there probably isn't as much moisture as there is here.

Then the GFS keeps Central Canada in a cold set-up for the rest of the run with some really cold values developing, thickness drops down to 514mbs which is pretty cold and impressivly low if you compare to British values!

First sign of the sub 500 thicknesses for Northern Canada way out in FI:

And the -20s nudging in:

Won't be long until Winnipeg is tasting them!

[Roger J Smith]

It was very balmy here today (Tuesday) at about 20 C with a warm sun and by late afternoon a lot of spreading contrails and other high cloud. The front is now just to our west and should blow through here around 15z. CC, you will get it around midnight or a bit later, should be quite a blow again. Looks to me like southern AB and SK will hit 24 C then fall to near freezing as this goes through on Thursday. Mentioned to another forum member who went to Churchill in northern MB that they could see a snowstorm up there Thursday evening, Winnipeg I would say will start out near 8 C on Thursday morning and fall to -8 C by Friday morning. Could be some of those thin lines of snow squalls I was mentioning as the Manitoba lakes are still about 12 C. The 516-dm thickness you all love to see is heading south, but of course, here there is nothing but land (and a lot of small lakes) in its path so it's worth -20 C instead of the -5 C you're lucky to wring out of it in February.

[Coopsy]

Not sure if my temp gauge is wrong but it read 14oC at 8am this morning, amazing

Gorgeous sunnny and warm day here today, we might even see a 20oC before the blast of northerlies hits tomorrow

EDIT: Just out in the car at 12:30 pm and the temp was 19oC

[kold weather]

Quite an interesting FI from the 12z GFS today and for the first time looks like a sustained cold spell with increasingly lowering thickness as cold building up in the arctic finally starts to head southwards in a sustained fashion. Indeed the 12z run also gives a real chance for some light snow by early November, indeed deep FI actually has a fairly decent snow event for Winnipeg, nothing too severe but a couple of inches which would in turn help the temps to plummit greater in any future cold shot.

[Coopsy]

Temps at 2:30 pm yesterday topped out at 20oC, then the cloud and wind picked up and by 5pm it was 14oC and raining. By 10 pm it was 10oC and raining and by 7am the next morning it was 0oC and snowing with about 1 cm covering after the cold fron thad moved through.

Day time highs today about 4oC, a very different contrast in 24 hours

[kold weather]

Yeah seems like a similar thing happened across much of centraol Canada yesterday. Winnipeg yesterday maxed out at 20C under a pretty impressive warm set-up though that has now been replaced by a colder set-up from the WNW with temps in Winnipeg hovering around 0C. Colder air now starting to dig down into that region with the 0z GFS showimng thickness getting down to 525 and also 850hpa profiles down to -8/9C. That should mean maxes probably in the region of 3-5C IMO. Interestingly the 0z GFS laos gives some patchy showers for the region and given the temps, if this is the case then some light snow showers are quite possible on Saturday. It's going to be one to watch just in case something does happen.

[Coopsy]

Does anyone know the impact a strong La Nina would have on western canada weather this year? For southern Alberta here, the fall has been rather 'zonal' with frequent westerlies coming in from the pacific, with the odd northern flow as the high pressure comes in. Just wondering if I can expecta lot of chinook winds as a result?

[kold weather]

To be honest I'm not all that sure how much of an impact and difference between a mod/strong (hard to say how La nina will come out to be honest) however given the west is exposed to the Pacific is pretty likely to play a rather large role.

Anyway Winnipeg going for another warm-up over the next 12hrs as they move into a small warm sector in the LP heading ENE which is lifting thickness upto round 555-558mbs with current temps already upto 14-15C i can only imagine maybe getting a 16C before the cold front starts to drive through in about 12-15hrs time and when that happens there will probably be quite a sharp drop in the temps.

At the same time the low starts to deepen quite neatly and that strengthens the pressure gradient so expect an increase in terms of winds on Wednesday and the same deepening also drags down some much colder air down from the north which the models have been progging for the last 7-10 days, though granted its nowhere near as potent nor as large as the GFS forecasted. I wouldn't be at all surprised to see the precip on the back edge turn to wet snow like it did a touch last time, the atmosphere is that bit colder then last time with the colder air just a touch sharper at coming in as well so I feel there is a chance of this occuring though not sure it'll amount to all that much. GFS progging 850hpa temps to drop quite decently and thickness drops to 524. The GFS appears to be forecasting a further trough to head in behind the cold front later in Wednesday and IMO this will probably be of either sleet and snow with it becoming progressivly more snow like it as the day goes on and while it may lead to a breif cover I don't think they will lead to much IMO.

The 12z run does get very interesting towards FI with a very potent cold plunge by UK's standards heading into the area but probably pretty bog standard by C.Canadas standard!

[Nick F]

Does anyone know the impact a strong La Nina would have on western canada weather this year? For southern Alberta here, the fall has been rather 'zonal' with frequent westerlies coming in from the pacific, with the odd northern flow as the high pressure comes in. Just wondering if I can expecta lot of chinook winds as a result?

Normally La Nina tends to lend to a -ve PNA pattern (i.e. a trough over Western Canada) with cooler/colder and wetter weather over Western Canada during winter, the -ve PNA tends to bring stronger zonal winds over N America, so stronger chinook winds East of the Rockies may well occur more frequently this winter. However, there will tend to be brief +ve PNA episodes too with a ridge over Western Canada and a more amplified flow with a decrease in upper westerlies, a +ve PNA looks like developing next week in fact. But a -ve PNA is more likely to persist during La Nina.

[WhiteFox]

The 12z run does get very interesting towards FI with a very potent cold plunge by UK's standards heading into the area but probably pretty bog standard by C.Canadas standard!

It's still there on the 18z, but less pronounced on the control run:

Warms up again quite quickly after that on the majority of the runs. Probably looking at an ice-day for the coldest part of that run. I'm in Helena, Montana at the moment, and the colder air arrives here first on Monday (albeit slightly warmer) and it gives us maximum forecast temperatures of 3oC with snow showers. Incidentally, it's forecast to get down to -4oC here tonight; that feels cold because it's early in the season - -2oC was cold enough yesterday morning!

As for the East Coast, New York is currently running at a record high temperature for October. Forecasters estimate that the final temperature will come in 0.1oF below the current record of 63.8oF which was set in 1947. The cold shot forecast for Winnipeg arrives in New York a bit later on, moderated obviously. This will come as a shock if it makes it; 850hPA down to about -8oC with thicknesses about 516:

[Coopsy]

Normally La Nina tends to lend to a -ve PNA pattern (i.e. a trough over Western Canada) with cooler/colder and wetter weather over Western Canada during winter, the -ve PNA tends to bring stronger zonal winds over N America, so stronger chinook winds East of the Rockies may well occur more frequently this winter. However, there will tend to be brief +ve PNA episodes too with a ridge over Western Canada and a more amplified flow with a decrease in upper westerlies, a +ve PNA looks like developing next week in fact. But a -ve PNA is more likely to persist during La Nina.

Thanks Nick, I appreciate the response

[WhiteFox]

Agreement starting to appear for the cold front for next week. Winnipeg ensembles showing a short, sharp shock for next Tuesday/Wednesday:

A high of -2oC for Tuesday and -1oC for Wednesday is forecast before just climbing above freezing on Thursday. Dry air though, so no snow in sight...

The cold air spreads south and East. Incidentally, it seems to linger the longest in the East; ensembles show New York staying below -5 for four days. It sill still be comfortable above freezing there of course!

[Roger J Smith]

TS Noel is predicted to become a powerful extratropical low moving NNE across Newfoundland on Sunday night and Monday, the NHC guidance shows 60kt sustained winds with higher gusts. This implies a central pressure well down around 955 mbs, so something to watch in the next few days to see if this verifies.

[Coopsy]

A rogue shower appears on the radar to be well organised, 30 minutes of heavy snow now. All roads, pavements and grass covered. I will try and get a picture when it gets light (its 8:48 and its still dark, roll on the clocks going back this weekend)