Tag: Nocturnal

Rain Returns to the Red River Valley

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While July has been a wonderful summer month (perhaps a little too wonderful at times), my lawn and my wallet are both ready for some cooler weather and some rain.  The cooler weather certainly has arrived; was anyone outside yesterday?  Even with the wind it was wonderful!  And, fortunately for my tomato plants, it looks like some rain is on the way as well.  Read on to find out the details!


16:15Z Daytime Multispectral Composite Satellite Image

The upper ridge that brought near-record Humidex values to Southern Manitoba earlier this week has finally moved off towards the east, which has allowed the upper trough situated along the B.C. Coast to begin moving inland.  As it migrates eastwards, it will spawn two low pressure centres: one over Central AB and a second one that will move through Montana and along the North Dakota/South Dakota border.  This will result in a rather complicated setup come Saturday morning with a surface low pressure system anchored to the upper low over Central AB with a secondary surface low pressure system anchored to a shortwave rounding the upper trough across the ND/SD border, with an elongated surface trough connecting the two.


GEM-REG Fri. July 22 12Z Model Run valid Sat. July 23 @ 12Z; 3hr. QPF + MSLP

In short, this setup will bring with it two bouts of precipitation.  The first will arrive through the morning hours on Saturday.  It’s exact placement is still quite certain, as it will be produced by nocturnal convection along a 30kt southeasterly low-level jet.  As the evening progresses today, it will become quite a bit clearer as to where exactly the thunderstorms will track.  That being said, it’s quite likely that areas near the international border will see 10-15mm of rain tomorrow morning with a few embedded thunderstorms as this system passes by.  Currently, it looks as if it’s up in the air as to whether or not it will reach as far north as Winnipeg, however I suspect we’ll see a sprinkle or two tomorrow morning.  I certainly won’t dismiss the possibility of a good shower or thunderstorm here tomorrow morning with local amounts around an inch, though!

After that, the upper trough will begin to swing in during the afternoon, and that will bring with it a band of rain that will track through in the late afternoon and evening, bringing an additional 10-15mm to what has fallen already.


Total Accumulated Precip. from the 12Z GEMREG Fri. July 22 valid 12Z Sun. July 24 (Sunday Morning)

All in all, most of the RRV should see 0.75-1.25 inches of precipitation tomorrow distributed between two distinct rain events: relatively early in the morning and late in the afternoon.  Cloudy skies will likely dominate between the two events, limiting our daytime high to only about 20°C.

After this system clears out tomorrow evening, we should have a few nice sunny days with highs in the mid-twenties.  The next chance for rain looks like Tuesday evening, when a weak system moving through brings the slight chance of some late-day showers or thunderstorms.

Unsettled Weather in Store Next Week

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Having broken the 30° barrier another time in the 2010 summer, summertime sun will give way to more unsettled weather next week.

A weak cold front will pass across Southern Manitoba tonight, bringing with it a very slight chance of showers (most likely nothing) and moving us into a cooler airmass for tomorrow, which should be a mostly cloud day.

By Monday morning, a warm front (shown above in the 850mb temperatures) will be positioned SW-NE across Southern Manitoba, extending from a surface low positioned in central North Dakota.  For several days, as the low moves northeast along the baroclinic zone, scattered showers will ride along the warm front.  Each night, there exists a potential for non-severe nocturnal thunderstorms in the RRV and east near the intersection of the warm front and a weak 850mb jet extending up into Southern Manitoba.  Most of the energy associated with the 850mb jet will remain in the states, so I don’t think that any severe weather will be on tap.

Get out and enjoy tomorrow, Sunday through Wednesday will be cooler (think low 20’s for highs) and rather unsettled, with mainly cloudy skies with occasional sunny breaks and showers lurking around during the days, with areas of organized precipitation occurring overnight. on Sunday night and Monday night.

Slight Chance of Thunderstorms Tonight, Then Cooler

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So, once again, the possibility of severe thunderstorms exists through the RRV this afternoon and into the overnight period; but how likely are they?

The various models are hinting at it:

The Canadian GEM-REG Model Output

The US GFS Model Output

The US NAM Model Output

Both the GEM-REG and GFS are showing convection over the RRV tonight, however the NAM keeps the convection almost exclusively in the states.

For us, I would lean towards a few showers tonight with maybe a thunderstorm, however I won’t completely rule out the current forecast of showers & thunderstorms.  The models have traditionally pushed the 850mb jet too far N pretty much every day, so colour me suspicious of real convection moving into the RRV (remember Tuesday night?).

The most likely scenario will be convection developing near the triple point of the low & fronts in ND this afternoon, then moving NE and just clipping SE MB.  If, however, the warm front manages to push into extreme southern Manitoba, there could be a higher likelihood of thunderstorms tonight.  Some convection may initiate in or just to the west of Winnipeg by late afternoon due to daytime heating that could become severe, however that would most likely die off as the sun goes down.

All in all, for Winnipeg, I’d say there was a 60% chance of showers or thunderstorms early this evening, and a 40% chance of thunderstorms overnight.  Ultimately, we won’t know what it will look like until things start happening in 4 or 5 hours from now.

After today, a cold front sweeps through Southern Manitoba on Friday and will bring us into a cooler regime with dewpoints in the high single digits to low double digits, and daytime highs in the low twenties.  In my opinion, a refreshing change from the sticky conditions we’ve had the past few days.

Severe Thunderstorms Tonight

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Environment Canada has issued a severe thunderstorm watch for most of southern Manitoba for this evening. A few thoughts on the coming hours…

For Southwestern MB:

The main threat for severe storms should end this evening. High temperatures and dewpoints combined with daytime heating have contributed to a favourable environment for severe thunderstorms. These ones should primarily be driven by the sun, so once the sun starts going down, so too should the intensity of the storms.

For the Red River Valley:

The main threat for severe storms will continue through the evening as an 850mb jet pushes up out of North Dakota into the RRV. The main threat with these storms will primarily be rain. The storms are developing on the nose of the 850mb jet, just downwind of an area of moisture convergence, so as the evening continues, the storms will have more and more moisture to work with. This, combined with the fact that storms will most likely be training (multiple storms moving in rapid succession over the same area), will result in some areas in the RRV getting large quantities of rain. My initial estimate would be that some areas will receive total amounts of 70-90mm locally, however it could potentially be higher than that. Most areas will probably receive on average 15-25mm of rain.

Other threats from these storms will primarily exist during the evening hours when they still could be surface based. If any storms can develop by themselves this evening, there’s a slight chance they could become supercells given the SSE flow through much of the RRV. If that is able to happen, then there would be a chance of large hail (my estimates would be quarter to loonie sized) and strong winds (90+ km/h). Give the backed surface flow, there would also be a very slight chance of a supercell becoming tornadic, but the overall setup doesn’t look to favourable for that; you never know what storms will do when working with 3000+ joules of CAPE, though.

This MCS will stick around for a good portion of the night, resulting in a widespread wet and noisy evening for many residents in Southern Manitoba.