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A Windy Day to Mark Arrival of Warmer Air

October 12, 2012April 3, 2015 Brad Leave a comment

Winds will pick up today out of the south as warmer air finally begins to push it’s way into Southern Manitoba. By this afternoon, strong winds will be in place over the Red River Valley and temperatures will finally climb out of the single digits under an extensive cirrus cloud deck.

NAM-based model Skew-T Log-P diagram for the central Red River Valley valid at 21Z this afternoon.

Winds will pick up by early this afternoon as a warm front pushes across Southern Manitoba. Sustained wind speeds will increase to 50-60km/h, with strong gusts on top of that; mostly around 70km/h, but the potential exists for gusts as high as 80-85km/h.

The picture above is a model-based skew-T log-P diagram which shows how temperature (red line) and moisture (green line) change with height in the atmosphere over a single location. Up the right-hand side of the chart are wind barbs, which represent the wind speed & direction at that height in knots. Each full tick mark is worth 10kt, a half tick mark is worth 5kt, and a filled triangle is worth 50kt. On the left hand side, the pressure is marked from 1000mb (the surface) to 100mb (about 16km off the surface). In the skew-t log-p diagram above, we can see a strong 20kt flow out of the south with an unstable layer from the surface to about 875mb. Within this unstable layer, near the inversion, winds increase to 45kt. Since it’s within mixing distance of the unstable layer, it’s entirely possible that those strong winds could be mixed down to the surface.

Temperatures will climb to about 10°C today, but with that strong wind it’s going to feel a little cool out there this afternoon. The winds will taper off this evening as things cool off, and then we’ll enter into a fairly pleasant weekend.

We’ll be under the influence of a weak low pressure system through the weekend, however unlike most systems, very little precipitation will occur near the system; instead most of the precipitation will be displaced northwards, into the high Interlake region, where frontogenetic forcing is stronger. What that means for us, fortunately, is that we’ll see relatively light winds through the weekend, a mix of sun and clouds and daytime highs in the low-to-mid teens. Overnight lows will be bumped up a little bit from the -3 to -5°C range to just at or above 0°C.

This weekend will be a pleasant break from the cold. Best to get out and enjoy it too; next week looks to bring multiple systems that could bring us some more rainy, windy weather.

September Marks a Return to Seasonal Weather

October 10, 2012April 3, 2015 Brad Leave a comment

September closed out with a few beautiful days, bringing a month that had a bit of a cool start back to seasonal conditions. As for whether Winnipeg continued it’s 14-month above normal streak, that depends on which average you use. If you’re partial to the 1971-2000 means, then yes, we’ve extended the streak to 15 months. If you use the 1981-2010 means (which are the ones we use here at AWM), then unfortunately, our streak has come to an end.

September 2012 Summary

2012 departure from normal (or monthly anomaly of) temperature. The year-to-date mean is also plotted.

September 2012 closed out with an average temperature of 12.6°C, 0.28°C below the the 1981-2010 normal of 12.9°C. At -0.28°C below normal, the month of September ended Winnipeg’s above-normal streak at 14 consecutive months¹. The warmest day in September 2012 came near the end of the month on the 29th when the mercury climbed to 29.6°C, a mere 0.4°C off the record for that day of 30°C set in 1905. No new daily high record temperatures were set this September. The coldest night was the night of September 22/23 when the mercury dropped to -7.1°C. This broke the previous record low for that night of -6.1°C set in 1879 and was 1.2°C off the record coldest night in September of -8.3°C, set on September 29, 1899. In total, just the one record low temperature was set this September.

2012 departure from normal (or monthly anomaly of) precipitation. The year-to-date total is also plotted.

September continued the significant precipitation deficit when compared to the normal. Usually we see about 48mm² in September, but this year we saw a mere 4mm of precipitation. Receiving less than 10% of our normal rainfall for the month continues the precipitation deficit to 4 consecutive months in Winnipeg.

In other miscellaneous September statistics:

We finished the month with 0 days above 30°C, but 7 days at or above 25°C.
September 2012 did not break the top 50 warmest Septembers on record.
Despite our practically non-existent precipitation for the month, we still nearly quadrupled the record driest September of 1948, where only 1.3mm fell.
Our 4mm precipitation total for the month was only 2.5% of the precipitation that fell in the record wettest September of 1872, when 156.2mm fell.

2012 So Far

Year-to-date temperature anomaly, by month, for 2012 (red) compared to the other 139 years on record for Winnipeg, MB, with the five warmest years (orange) and five coldest years (blue) noted.

As mentioned before, September’s deviation of -0.28°C from normal has brought an end to the above-normal conditions of 2012. Until September, every single month this year had been above-normal. Looking again at our Winnipeg temperature anomaly climatology, we can see that despite our slightly below-normal September average, we’ve managed to still remain the most above normal (by a hair) that we’ve ever been. Things still look to be on track for us to end up in the top 5 warmest years ever and we’ll keep updating each month to see where we end up.

Rest of 2012

As mentioned last month, sea ice in the Arctic is at a record low, which while it hasn’t prevented us from getting the odd cold outbreak, still looks to have the potential to reduce the strength/onset of the Hudson Bay arctic vortex that sets up and maintains a cool, northwest flow over the Eastern Prairies. While a month ago it also looked like El Niño was going to help us possibly see a warmer-than normal winter, over the past couple weeks the El Niño signal in the Eastern Pacific has significantly weakened. This means that any large-scale hints towards what sort of winter we’ll see are becoming rather muddled and no strong signal currently exists.

Based on 1981-2010 normals. Winnipeg sits at 15 months above normal if using the 1971-2000 normals. ↩
The normal precipitation for September is 47.6mm. ↩

Slowly Improving Weather in Store

October 10, 2012April 3, 2015 Brad Leave a comment

The weather will slowly improve over the next couple days as some warm air begins to slowly push across the Prairies.

3hr. cumulative precipitation from the RDPS for late this afternoon.

Today will remain mostly cloudy across Southern Manitoba with two main features to pay attention to. The first feature is a low pressure system that will slide from Southern Saskatchewan into North Dakota, bringing with it a chance of showers through southwest Manitoba through the morning and into the early afternoon. The second feature will be a trough slumping southwards through the Interlake into the Whiteshell. The southern extent of this trough will move through the Red River Valley in the late afternoon and evening, and as it enters the area, a few scattered convective showers or flurries will develop along it and move through the region. Whether we see rain or snow will depend on the exact timing of the system and what the temperature is; either way, accumulations will fairly insignificant and the showers likely won’t be widespread. Daytime highs will be around 6°C this afternoon.

After these systems pass, we’ll see skies slowly clear out overnight as temperatures drop to around the -3°C mark. A ridge of high pressure begins working it’s way into Manitoba; skies will remain mainly sunny as temperatures slowly climb. Tomorrow we should see daytime highs around 9°C through the Red River Valley, and increasing up to around 11°C for Friday. We’ll see a mix of sun and clouds on Friday as a weak system brings some cloud through the Red River Valley as it passes through central Manitoba.

The weekend looks relatively average, with no indications so far that any significant precipitation events are in store for us over the next week.

Gloomy Thanksgiving Monday

October 8, 2012April 3, 2015 Brad Leave a comment

This Thanksgiving will be nothing like last year’s (which featured temperatures in the twenties), as rain and wet snow make for a rather miserable holiday Monday.

Total precipitation accumulation for Monday's system

The GEM model shows generally 10-20mm of precipitation over Southern Manitoba

A low pressure system sliding south-eastward through Manitoba on Monday will be responsible for the precipitation, with rain beginning to move into Southern Manitoba early Monday morning. Temperatures on Monday will be cool, but generally not cold enough for snow with values hovering in the mid single digits during the daytime. By evening there will be a changeover to snow in some areas, mainly portions of Western Manitoba, as colder air is pulled down from the north. Areas in the Red River Valley can expect a bit of wet snow late Monday evening into the overnight period, but with surface temperatures remaining above zero, no notable accumulation is expected. Total precipitation accumulations will generally range from 10 to 20mm across Southern Manitoba by early Tuesday.

Unfortunately, conditions will improve little for Tuesday. It will be a chilly start to the work-week as cold air pulled down by the previous day’s low pressure system will not allow temperatures to climb much higher than the mid single digits at best. Monday’s low pressure system will have departed by Tuesday morning, so no more significant precipitation is expected (save for perhaps a few scattered showers or flurries). At this point models keep us in the single digits for Wednesday as well, so even normal weather will continue to elude us.

The late week period looks to remain fairly miserable, with temperatures staying stuck in the single digits. No more significant precipitation is expected later this week.

A Weather Moment

Author: Brad