Sunday, October 28, 2007

Halloween Outlook

It's looking more likely that Halloween this Wednesday will be a chilly but dry evening. Models are indicating that Wednesday will start off blustery and cold with gusty northwest winds behind an intensifying low pressure system tracking into NW Ontario. This system could bring some rainfall to southern MB Tuesday night which may even mix with some wet snow overnight before ending early Wednesday morning. The rest of the day should see cloudy and windy conditions with below normal temperatures around +3C or so. A ridge of high pressure building in by evening should bring clearing skies as well as lighter winds to the Red River valley, but temperatures will likely be near the freezing mark by then. All in all, not a bad looking evening for the trick or treaters at this point. I will post updates as we get closer to Wednesday..

Saturday, October 27, 2007

Growing season officially ends downtown

It took awhile, but the 2007 growing season officially ended this morning for downtown Winnipeg, with the Forks weather station recording a low of -1C. This is the first freezing temperature at the downtown site since April 17th when a low of -0.4C was recorded, giving the downtown core a growing season this year of a whopping 192 days.. or over 6 months. This has been evident with the abundance of flowers and even some vegetable gardens still living in many areas of the city, especially downtown.

Contrast this to the Winnipeg airport site, which had a frost as late as May 27th (-0.1c) and as early as Sept 14th (-1.4c) for a growing season of only 108 days, almost half the length of downtown. This shows the large difference in nighttime temperatures between the more open rural areas around the egde of the city, and the more urbanized downtown core.

Here at my station in Charleswood, the official growing season lasted from Apr 26th to Oct 14th, or 142 days.. a good average for the city in general. This just goes to show how basing the growing season solely on the Winnipeg airport site can be very misleading!

Wednesday, October 24, 2007

Gusty south winds bringing milder air in..

Strong southerly winds over southern MB are bringing in milder temperatures tonight which will persist into Thursday. Those southerly winds are particularly strong over Winnipeg and the Red River valley tonight with gusts to 60 km/h due to funnelling effects up the Red River valley. This will keep temperatures from falling much below the 10 degree mark tonight.. our normal high for this time of year. On Thursday, gusty southerly winds in the morning will diminish by afternoon and switch into the northwest as a cold front moves through. Temperatures however will climb into the upper teens by early afternoon before the cooler airmass arrives by evening. Note that this same airmass produced record highs in the 25c range over southern AB and southern SK today.

Monday, October 22, 2007

Windy week ahead..

A weak weather system will track into central MB tonight and into northwest Ontario Tuesday morning. This system will bring a few showers through the northern interlake and central MB regions tonight possibly mixing with some wet snow in places. As the system tracks into northwest Ontario Tuesday morning, gusty northwest winds will develop behind the system over southern MB with northwest winds of 40 to 60 km/h possible through midday Tuesday.

By Wednesday a more potent system coming off the Pacific is forecast to track across far northern SK moving north of the MB/NU border on Thursday. This system is forecast to deepen into an intense storm over Hudson Bay on Thursday into Friday, with very strong northwest winds and blizzard conditions possible over the Hudson Bay coastline including Churchill and much of the Kivalliq region of Nunavut. South of this intensifying storm system, gusty south to southwest winds will bring milder conditions over the southern Prairies by Wednesday with temperatures climbing to the 20 degree mark over southern SK and southwest MB on Wednesday. Look for gusty southerly winds of 40 to 60 km/h or more over the Red River valley on Wednesday with highs in the mid teens. The milder weather will be short lived however as gusty northwest winds on the backside of the intense Hudson Bay storm drives cooler weather across the eastern Prairies for the end of the week.

Saturday, October 13, 2007


Skies finally cleared over Winnipeg early this morning after 8 straight days of clouds and gloomy weather. The cloud is still not that far away however this morning as the western edge of the cloud has moved just east of the city, with clouds persisting over southeastern Manitoba in areas like Steinbach and the Whiteshell. A disturbance in Saskatchewan will bring some cloud back in tonight into Sunday morning over the Red River valley, however this higher level cloud should clear out by Sunday afternoon.

Rob's Weekend Forecast for Winnipeg..

TODAY.. Morning fog patches with locally dense fog giving near zero visibility at times. Otherwise mainly sunny and a lot more pleasant today than recent days. Little or no wind. Highs around 14c.
TONIGHT.. Increasing clouds. Calm winds. Lows near zero.
SUNDAY.. Slight chance of a morning shower otherwise morning clouds giving way to sunshine. Light winds. Highs near 14C.

Wednesday, October 10, 2007

NOAA releases winter outlook

NOAA has just released their official winter outlook for the US. Their forecast calls for generally above normal temperatures over the US south and southeast and generally wetter than normal conditions over the Ohio Valley and Pacific Northwest. This is in response to the developing La Nina which would tend to produce below normal heights (trough) off the West Coast and above normal heights (ridge) over the southeast US with a storm track riding from the US west coast into the Great Lakes.

For the northern Plains/southern Prairies.. there is essentially an equal chance of either below/near or above normal conditions this winter.. i.e. a non-forecast. In other words, there is no clear signal how this year's La Nina will affect the southern Prairies one way or the other. If indeed the general synoptic pattern sets up as described above, then there would be a greater likelihood of below normal temperatures this winter over the Prairies, especially the western Pariries, with perhaps above normal snowfall over the eastern Prairies closer to the storm track.

Here in Winnipeg, our last extended La Nina occurred from mid 1998 to early 2001. During those winters,

1998-99… generally warmer than normal.. especially February and March.
1999-2000.. Generally much above normal..with near normal January. (snowcover was gone here by end of February)
2000-01... A real see-saw winter. Third coldest December on record, followed by a mild January then cold February
2001-02.. Generally warmer than normal, cold March

So as you can see, La Nina doesn't necessarily equate to a cold winter here, at least in the eastern Prairies. One also has to consider the remarkably low Arctic sea ice cover recorded this year (an all time low), which presumably would tend to delay the onset of deep and persistent Arctic airmasses in the far north. That could mean a delayed start to winter over the Prairies, before colder than normal conditions set up for the latter half of the winter, mainly over the western Prairies. If that storm track is further north, then Alberta could see a snowier than normal winter with storms off the Pacific, with above normal temperatures more likely over the eastern Prairies.

A TV meteorologist in the US has produced an analog map showing temperature/precip anomalies based on previous La Nina years back to 1950. It supports above normal temperatures in the southeast US, and colder than normal temperatures over the north/northwest US including the southern Prairies.

So there are hints that perhaps we'll see colder than normal conditions at some point this winter, but there are also conflicting signals that reduce confidence in this outlook, especially in light of warming trends in our winters over the past decade and this year's record low Arctic ice cover.

NOAA will update their winter outlook on October 18th and Nov 15th.

Where's the sun?

It's been a dreary few days over Winnipeg and Southern MB with generally overcast skies and cool conditions, as well as that washout of a Thanksgiving Monday. Our last sunny day was last Thursday (Oct 4th) which helped boost temperatures to 18C. Since then, afternoon temperatures have generally been stuck between 5 and 10c under overcast skies. Here in Winnipeg we had some brief sunny breaks Sunday morning (7th) otherwise, it's been overcast since last Friday. But that isn't unusual for this time of year as cool air begins flooding over the Prairies with still relatively warm ground and open lakes providing low level moisture. As a result, quite often you can get several days of cool cloudy weather during these months even in high pressure ridges (known as "dirty" highs in these cases) We're in such a period right now, and it looks like we'll stay cloudy through Friday before we get a better chance of some sunshine this weekend.

Sunday, October 07, 2007

Significant rain possible over SE MB Monday

A new storm system developing over Minnesota will track into Northwest Ontario Monday and intensify. Significant rain is expected to develop on the northwest wide of this storm system, affecting much of southeast MB and the Red River valley Monday including Winnipeg. 20 to 30 mm of rain is possible over southeast MB with little or no rain expected west of the Red River valley. In addition, it will be quite cool as northwest winds tap some colder air aloft, bringing temperatures down to the 5c mark by afternoon. A good day to stay inside and enjoy some Thanksgiving leftovers!

Thursday, October 04, 2007

Thanksgiving weekend outlook

A slow moving complex area of low pressure developing over the central American Plains will give a mixed bag of weather over southern MB this holiday weekend. Models have been struggling to find a consistent solution with this upcoming system, which explains the large swings and flip flops in the forecast this weekend. Initially it appeared as if this system would bring a prolonged period of rain over southern MB through the weekend. It now looks like much of the rain will fall over southern SK and southwest MB Friday into Saturday before moving into the rest of southern MB Saturday night into Sunday. At this point, the bulk of the weekend rain is expected through southwestern MB and the interlake (perhaps 20 -30 mm), with lesser amounts expected over the Red River valley and southeast MB (5-15 mm)

Saturday looks interesting as the storm system sharpens over the US midwest sending a pronounced warm frontal tough towards southern MB. This warm front will mark the leading edge of much warmer air which will be surging north into North Dakota and Minnesota on Saturday. The front may push into extreme southeast MB on Saturday with 25C temperatures possible along the US border. At this point, it appears Winnipeg will stay on the cool side of this front with temperatures in the mid teens. However if the front pushes far enough north Saturday afternoon, Winnipeg may get into the low 20s (as current forecasts suggest) The frontal trough will move east Saturday night into Sunday with showers and possible thunderstorms over southern MB with locally heavy rain possible. Another system threatens showers for Monday.

Summing up.. unsettled Saturday with showers over southwest MB and the interlake - drier with a warming trend over southeast MB. Showers and thunderstorms Saturday night with locally heavy rain possible. Showers ending Sunday. A few showers possible Monday. Have a good long weekend whatever the weather!

Rob's Obs humidity/dew point values

I installed a new temperature and humidity sensor on my Davis weather station today.. hopefully that will give more reliable humidity and dew point values now. So far values look good, but I will continue to monitor over the next few days to make sure readings are reliable.