Thursday, August 28, 2008

Summer's last hurrah?

It looks like the fine summer-like weather we've enjoyed through much of August will close out the month this weekend with another round of summer-like warmth, especially over SE MB. But as if on queue, a sharp cold front will move across southern MB late Sunday or Monday bringing in much cooler and wetter weather just as the calendar flips to September. The details..

An upper ridge will build over southern MB on Saturday giving us a fine start to the Labour day weekend. Saturday will see plenty of sunshine across southern MB with temperatures in the mid to upper 20s along with increasing southerly winds.  This upper ridge is forecast to build over Ontario over the long weekend, while cooler unsettled weather moves in over the western Prairies. The dividing line between these two airmasses will set up right through southern MB on Sunday along a cold front that is expected to drop southward across the Interlake and stall from southwest MB through Winnipeg into the Pinawa area.  There will be a dramatic temperature difference across this front with summerlike temperatures of 27-30C to the south and east, and more fall-like temperatures of 20C to the north and west along with clouds and a chance of showers. Current forecasts for Winnipeg call for a high of 30C on Sunday, but I'm a little skeptical we'll get that high with that Interlake front so close to us (major bust potential Sunday because of this front). I think areas south and east of Winnipeg will have a better chance of seeing 30 degree temperatures on Sunday (including the Whiteshell, Lake of the Woods and the southern Red River valley), while places like Grand Beach through Gimli to the Riding Mtns will be considerably cooler on Sunday (highs only near 20C).

For holiday Monday, models indicate this cold front will sweep through southern MB, bringing in cooler weather for all areas but the extreme southeast along with a good chance of rain, possibly heavy in parts of southwest MB into the Interlake.  All in all, looks like the best bet for a warm dry long weekend will be toward the SE corner of the province (e.g. Whiteshell, Lake of the Woods and southern Red River valley), while cooler and wetter weather moves in by Sunday to areas further north and west (especially SW MB through the Interlake). As always.. stay tuned…the forecast for this long weekend will be a tricky one.   


  1. Yes today is a very nice start to the long weekend!!!
    Let's hope that it keeps up!
    Do you think that August will come out as a ABOVE average month for a change???

  2. As of yesterday, the average daily temperature for August at Winnipeg airport was 19.4C.. almost a full degree above normal (normal 18.5C) With warm weather for the next 2 days, we should finish around the same mark, so yes, August will be our first month since January that has finished above normal. This would also make August the warmest month of the year.. beating July by a full degree (July 2008 average 18.4C) August definitely salvaged the summer of 2008!

  3. Still looking like a tough call regarding the holiday weekend forecast.. especially here in Winnipeg. That frontal trough will be right through the Red River valley on Sunday and Monday separating warm air to the east from cool wet weather to the west. Bottom line.. if you're at Lake of the Woods, you'll have a great long weekend weatherwise. If you're at Clear Lake, it'll be all downhill after Saturday. In between.. we'll be battling it out between the warm and cool air both Sunday and Monday.

  4. Latest guidance shows that frontal trough will stall right through Winnipeg on Sunday and Sunday night, perhaps even move slightly north of us as a warm front early Monday before it pushes east of Winnipeg during the day Monday. As I mentioned before, there is a considerable "bust" factor in temperature and precipitation forecasts over southern MB for Sunday and Monday, particularly over Winnipeg and SW Manitoba near the frontal trough where summer weather to the south and east battles fall weather to the north and west. Current forecast highs of 27-31C on Sunday and Monday could easily be 5-10c cooler depending on the actual position of the trough. Watch for thunderstorms and heavy rain along and north of the trough as well Sunday night into Monday.

    Note that we should definitely be in the cooler air by Tuesday.. that forecast high of 25C on Tuesday in Winnipeg is likely 5-10C too high as computer guidance is being fooled by warm temperatures aloft.

  5. Watch out for hurricane gustav...

    Not only is it forecast to brush New Orleans as a major hurricane, but it may also alter our weather for awhile after it makes landfall.

    P.S. Maybe a chance of severe storms on Sunday in South-Eastern Manitoba?

  6. Impressive and persistent southwest flow the next few days. Flow regime will be almost unidirectional making training/heavy rain a possibility as was mentioned.

    There will be chance for elevated storms to fire along the front and the edge of the midlevel cap tonite... possibly affecting Winnipeg by early Sunday morning.
    Strong, well defined low level jet will cause deep gulf moisture to surge northwards tonite.

    If debris clouds clear out of areas just SE of the stalled front... things could get quite unstable for surface based convection tomorrow during the day. SB CAPE of 1500 J/Kg is progged to converge with high 3 km helicity values of near 500 m^2/s^2 in vicinity of front.

    Very good set up on Sunday nite as the southerly LLJ cranks up again ahead of the upper distrubance. Finally the main 500 MB low passes over on Tuesday giving a chance for a cold, steady rain.

  7. Well they do have a severe thunderstorm watch out for just north of the city!
    Maybe some storms tonight!

  8. Well it looks like that some thunderstorms are finally starting to form in western Manitoba!
    Maybe they will a slight chance that the storms could make into the Winnipeg area tonight!

  9. Nice storm northeast of Erickson moving to the northeast. Tops over 16 km with rotation noted. This frontal trough will become even more active Sunday evening/night with heavy rain potential over Riding Mtn/Interlake areas.

    Forecasts still calling for a high of 31C in Winnipeg for Sunday.. which is possible, but highly tenuous based on the proximity of that frontal trough. As mentioned before, best bet for 30C temperatures will be south and east of Winnipeg, less chance north and west of the city.

    Regional temperature guidance giving highs on Sunday of 31C in Portage and Gimli, 28C in Brandon, and 29C in Melita, even though forecasts show northerly winds developing in these areas north of the frontal trough. Look for highs some 5-10C cooler than models suggest in these areas.

    Note also that Monday's high for Winnipeg has been lowered to 23C from 27C with showers forecast. That makes the forecast high of 25C for Tuesday with "rain" highly unlikely, given we will be well into the cool air by Monday night. As noted earlier, models are getting fooled by the warm temperatures aloft leading to overly optimistic temperatures on Tuesday. Highs of 15-18C look more likely for Tuesday.

  10. Morning analysis shows frontal trough has set up pretty much where expected.. from west of Pilot Mound through Portage to south end of Lake Winnipeg. In fact, the CWB mesonet shows the trough is just east of a Elie to Stonewall to Patricia Beach line. North of this boundary, winds have shifted into north or northeast which will keep temperatures some 5-10C cooler than areas south of this line today. Forecast high for Brandon was lowered from 28C to 22C for today. Likewise, Gimli's high of 31C has been knocked down to 28C.. which may still be about 5C too high.

    For Winnipeg, we may luck out and stay in the warm sector with our southerly winds.. in which case, we could see 30C this afternoon. However, the frontal trough will be close enough that we may get back-doored by cooler air to our north. It could be a case where St Vital hits 31C and Stonewall hits 24c today!

    I'm surprised that the forecast for Winnipeg is calling for a high of 30C for Monday (up from 23C yesterday afternoon). The frontal trough will be swinging through us tomorrow with clouds and showers/tstorms.. Morning temperatures in the low
    20s may actually fall in the afternoon. Don't be surprised to see that forecast high drop significantly.. much like what happened in the forecast for Tuesday (forecast high of 25C is now down to 13C!!)

  11. While we're enjoying a last taste of summer, check out what's happening out west on the Banff webcam.. SNOW!

    As for us, looks like we've clouded over here in Winnipeg with a lot of low level cloud in the mixing zone along the sharp frontal trough lying through southern MB. That may rob us of our 30 degree day today. As expected, 30C+ temps south and east of Winnipeg this afternoon in the sunshine, while areas north and west of us stay around 20-23c in the cooler air.

  12. Did Winnipeg hit an overnight high low this morning? It looks like the low was around 21C.

  13. Sunday 4PM temp comparisons. S. MB. What a contrast!

    Brandon Airport Cloudy 17
    Carberry 17
    Carman 32
    Dauphin Airport Cloudy 16
    Delta Marsh 20
    Emerson Sunny 32
    Fisher Branch 18
    Gimli Harbour 19
    Gimli 21
    Gretna 33
    McCreary 16
    Melita 20
    Oak Point Marine 19
    Pilot Mound 31
    Pinawa 30
    Portage Southport Airport 23 Roblin 17
    Shoal Lake 15
    Sprague 31
    Swan River 15
    Winnipeg Airport Mostly Cloudy 29

  14. Weird being on the interface of the cold and hot air the entire day in Winnipeg. Cloud line bisecting the city ... almost stationary low clouds to the NW and clear sky to the SE.

    The warm sector remained capped today.. the elevated storms formed well north of the trough where mid level temps were cooler. Going to be interesting to see what happens convection wise tonite. Front does not move appreciably until tomorrow during the day.. so where will the storms form tonite?

  15. That list nicely shows the dramatic temperature contrast across this frontal boundary. People heading up to Gimli or Grand Beach today expecting 30 degree weather would have been disappointed! Here in Winnipeg, the southerlies kicked in again late today allowing us to hit that 30 degree mark over most of the city...although Doppler radar was indicating the frontal trough lying across the north perimeter this afternoon with temperatures only near 25C north of there (such as Stonewall)

    Attention now turns to the potential for thunderstorms bringing heavy rain along and north of this frontal trough tonight.. mainly over SW MB through the interlake where persistent storms may train over the same area bringing heavy rainfall amounts.

    By the way, I see the forecast high for Winnipeg on Monday has been dropped again to 23c as the frontal trough moves through us.. down from that puzzling high of 30C earlier today. Enjoy those warm conditions this evening before the change to fall starting tomorrow!

  16. as of 5:00 pm (at the airport), we hit another 30 degree day!
    if you round it, it is 31, but technically, it is actually 30.7 degrees.
    and a note, the suspected rain (north perimeter) is actually a glitch with the radar. however up into the Dauphin area, it looks like that there is some rain firing up there.

  17. 7 PM Temp Comparison CYWG - CYPG
    Portage: +20 NNW 23
    Wpg A +30 S 26G39

    Amazing contrast!

  18. Even more amazing!

    Dauphin MB is 12 C
    Winnipeg is 30 C
    as of 8:00 pm.

  19. Gotta admire Mother Nature's sense of timing.. cold front came through here just around midnight as the calendar was flipping to Sept 1st. Temperature dropped from 26 to 21c in one hour. We're now down to 16C and probably won't recover too much today or the rest of the week for that matter. Welcome to September!

  20. Environment Canada states that heavy rain is persisting along a cold front in western Manitoba!
    I'm confused!
    Did the cold front not cross us last night in the city with that huge temperature drop!
    Is there another cold front????

  21. Daniel..

    The area of rain is occurring behind the surface cold front.. what we refer to as "post frontal" precipitation. Basically, the surface cold front has surged well ahead of the upper frontal zone (at 850 mb and above) which is supporting the main axis of precipitation. This means that the cool air we have at the surface is fairly shallow, since we're still in the warm sector aloft. This is one of the reasons why models can overestimate surface temperatures in these situations since they get fooled by the warm temperatures aloft and don't account for the "undercutting" cool air at the surface (as exhibited by yesterday's 30 degree forecast for today, when we're at 16)

  22. I see environment Canada has put out a new forecast calling for a risk of a severe thunderstorm

  23. Severe thunderstorm watch issued for the city of Winnipeg!
    It seems like one of those days where is could just be a steady rain and drizzle .... not severe thunderstorms!
    Where are the dynamics for severe thunderstorms????

  24. I don't know...

    Yesterday I didn't know where the dynamics for severe storms were in Western Manitoba either. There was no CAPE in those regions, only shear. Same situation today West of the RRV. In the Steinbach area it is 26, with a dewpoint of 22, so you can see the dynamics here. I guess the moisture must be coming from aloft....although there is still no CAPE in those regions according the the SPC's Mesoanalysis.

  25. is it me or does it look like there is a whole lot of rain coming!

    That rain band with all the thunderstorms embedded looks like it could easily dump 50 mm of rain , even in the city of Winnipeg!
    I mean that rain band is NOT shifting very far eastward with all that rain coming up from the south!

  26. I think they included Winnipeg and the Red River valley in the watch due to the possibility of heavy rain with a lot of convection developing to our southwest behind the front moving to the northeast. Heavy rain is one of the criteria for severe thunderstorms.

    The better threat for stronger individual thunderstorm cells with large hail and damaging winds is over far southeast MB in the warmer more humid air. Note that SPC has a slight risk of severe storms over extreme NE ND and northern MN as well.

  27. Keep in mind.. as Rob described very well... that surface conditions are not necessarily indicative of what is going on higher up in the atmospheric column. Surface conditions can be stable (cloudy, cool) but air lifted from above the frontal inversion can be quite unstable (warm, moist). Elevated storms can still be severe, producing frequent lightning, heavy rain and large hail. In cases of elevated instability it is good to look at MUCAPE (most unstable CAPE), which I believe calculates the largest CAPE generated by lifting a parcel from many different pressure levels. (Rob please correct me if I am wrong)

  28. Interesting temperature contrast across the city at 3 PM. 16 degrees at the Airport and 21 on my non-official thermometer in the southeast corner of the city. Just a bit farther south and east, according to the Manitoba Agriculture Web site, it's 26 degrees in St Pierre and in Steinbach.

  29. It was 26 before the storm came through Steinbach, and the dewpoint was 23. The temperature/dewpoint is now 24/23.

    I picked up a quick 8.8mm with that storm, and a max rain rate of 69.0mm/hr.

  30. EC issued a tornado warning..moments ago

  31. recorded 21.0mm of rain here in E. Transcona up to time of posting with this last band of rain and thunderstorms that started around 3:30-4:00ish. Had some real nice cloud to ground lighting here as well, seems to have calmed down for the time being...

  32. At my station in Steinbach the average high in August was 26.0, and the average low 13.9. That is a full degree above average on the high, and two full degrees on the low. August helped salvage the summer, but June and July are really the most exciting months...

    I would guess that severe weather reports are way below average this year. If it wasn't for those cold-core tornadoes we probably would have only had 2 or 3 tornadoes this year, which is only a third of average. That possible tornado near La Broquerie today may boost the supercellular type twisters.

    Hopefully September will be kind, but the current forecast doesn't look that way.

    P.S. Because of the warm temperatures in SE MB today, my station is averaging 27.0 for a high in September...that will soon change. The highest dewpoint this year was also recorded today, at 23 can't be common for the highest moisture reading to be in September!

  33. Poor Farmers up north!
    They are just getting hammered up north with very heavy rain!
    Rob any rain fall amounts from your station???
    Oh by the way.... did anyone see how many tropical storms there are right now!!

  34. I know the weather network's 14 day long range can't be relied upon, but they are saying below normal temps into the middle of September. Could be a long, long winter. Can you say seasonal anxiety disorder?