Multi-Day Severe Weather Setup Leads to Tornadoes, Flash Flooding in Oklahoma

Matthieu Leave a comment

Early May is typically when the severe weather season really ramps up in the US Plains and this week has certainly lived up to that. The region has seen severe weather every day since Wednesday and is expected to see more today. A western troughing pattern has been dominant the past few days, allowing a strong southerly flow to take place in the lower levels of the atmosphere – advecting in plenty of moisture from the Gulf of Mexico located nearby. High levels of instability, coupled with enough shear to support supercells was in place.

[map autofit=”1″ disable_scrollwheel=”1″] [pin tooltip=”Bridge Creek”]Bridge Creek, ok[/pin] [pin]Norman[/pin] [/map]

The worst day of the outbreak tornado-wise occurred on Wednesday where 48 tornadoes touched down from Nebraska, all the way down to Texas. A particularly dangerous situation unfolded in Oklahoma as a supercell with a history of producing tornadoes moved northeast along I-44 and through the large city of Norman where it dropped a tornado, later rated EF-1. The same supercell also produced an EF-2 tornado near Bridge Creek, shortly before it dropped the Norman tornado. Tornadoes were not the only threat on Wednesday; significant rains fell across Oklahoma, including Oklahoma City, which saw trailing supercells hit the city and as a result severe flash flooding. One person died from the storms, while a few dozen were injured. Ditches became raging creeks that spilled their banks onto highways and residential areas. It’s not uncommon to see supercells drop 100mm of rain or more in an hour. Radar indicated that some areas just southwest of Oklahoma City saw over 250mm on Wednesday. Numerous stations in the area broke their daily rainfall records from this event. A state of emergency was issued in 12 counties as a result of the storms.

Chickasha Supercell
The tornadic supercell that hit Norman in its early stages, showing an obvious hook. (Source: Radarscope)
Oklahoma Flooding Rains
Storm total accumulation for Wednesday through 9pm shows areas of over 250mm (pink areas). (Source: Radarscope)

More severe weather is expected today as the trough shifts slightly eastwards. There’s a chance that today could be the second significant tornado day in less than a week in the Plains – Kansas, southeast Colorado and northern Oklahoma regions are under the gun. However, there are still a few uncertainties due to the models showing some mid-day convection possibly limiting the heating. The Storm Prediction Center had issued a moderate risk for the region as of Friday night. Regardless of what happens in the first half of the day, there will be severe storms; residents in the region will have to keep an eye on the sky for large hail, severe winds, torrential rains and even tornadoes!

Cool Weekend Ahead

Brad Leave a comment

Temperatures will remain well below normal through the coming weekend as unseasonably cool air becomes entrenched over the region behind the Colorado Low that brought rain to Southern Manitoba on Wednesday & Thursday.

Today will be a comparatively chilly day with temperatures struggling to climb to a high of just 7°C; this is around 10°C below the average high of 18°C for this time of year. The cool temperatures will be accompanied by gusty northwesterly winds of 30km/h with gusts to about 50km/h throughout most of the day. Skies will be fairly cloudy, but a few sunny breaks will manage to materialize through the day.

Tonight in the Red River Valley will bring cloudy periods and a low temperature dipping just below freezing to –1°C.

Saturday and Sunday will be fairly similar days with highs near 11 or 12°C and mixed skies as some cloud cover streams across the region from North Dakota. Winds will be relatively light out of the north at around 20km/h. Both Saturday and Sunday night will bring some cloud with lows in the 1–3°C range.

Cool Weather Persists Into Next Week

There’s nothing but bad news for those hoping for a quick rebound back to summer-like weather: it’s going to take quite a while for seasonal temperatures to return to the Red River Valley.

The GDPS clearly shows a trough of cold air remaining entrenched over Manitoba.
This image valid Monday morning from the GDPS shows a trough of cold air remaining entrenched over Manitoba. Image depicts 700mb temperatures.

Cooler-than-seasonal temperatures are expected to persist until the middle of next week thanks to the cold trough pictured above remaining stubbornly entrenched over the province. Long-range models are showing a return to seasonal warmth in the high teens for the second half of next week as an upper-level ride begins to build into the region, shunting the colder weather off to the east.

Colorado Low Brings Major Rainfall to Southern Manitoba

Brad Leave a comment

While Southern Manitoba has seen glancing blows from true Colorado Lows a few times over the past couple years, Winnipeg is in the middle of a multi-year drought with the last direct hit from a Colorado Low in memory occurring in November 2012.[1] Responsible for some of the biggest synoptic storms[2], Colorado Lows are a major weather system that often produce pretty much everything: thunderstorms, heavy rain, light showers, overcast & drizzly conditions, freezing rain, heavy snow and/or blizzard conditions.

Imagery of Developing Colorado Low
This satellite image from early this morning shows the developing Colorado Low over…Colorado. Who would have thunk?

Today will see the arrival of a Colorado Low that will dominate the weather over Manitoba for the coming few days. Southern Manitoba will escape most of the nasty weather associated with this system with just rain expected – albeit a fair amount – while Northern Manitoba gets slammed with heavy snow, freezing rain and strong winds.

Wednesday

Wednesday
24°C / 15°C
Increasing cloudiness then showers with the risk of a thunderstorm

Today will be a relatively pleasant day despite the imminent arrival of the Colorado Low. While today will start off with a little bit of sunshine, high cirrus will move in through the morning with thicker cloud arriving this afternoon. Winds will be out of the south to southeast at around 30–40km/h with some gustiness on top of that. Shower activity – with the risk of thunderstorms – will work its way northwards out of the Dakotas through the day into the Red River Valley. Temperatures will be quite mild with highs around the 23–24°C mark.

Heading into the evening, main band of showers associated with this system will spread across Southern Manitoba bringing rain with a slight chance of an embedded thundershower to the region. Rainfall amounts through the Red River Valley will likely be highly variable thanks to the convective nature of the precipitation; in general the “safe” guess at this point is somewhere in the 15–25mm range…or so. I don’t believe amounts will be much higher than that, but depending on a whole bunch of factors, amounts could end up in the 5–10mm range instead. Unfortunately, with such highly convective systems, these things are almost impossible to forecast until much closer to the event, so we’ll be providing updates in the comments below as well as on Twitter and Facebook. The showers will persist through the night as the temperature dips down to around 14 or 15°C.

Thursday

Thursday
17°C / -2°C
Showers

Tomorrow will be a fairly wet day with more shower activity, potentially quite heavy at times, lasting much of the day before finally beginning to taper off in the evening. Our high temperature will only be around 17°C with some light southerly winds flipping to the northwest in the afternoon to around 40km/h. Rainfall amounts, again, could be quite variable thanks to the convective nature of things and exactly how the system matures.

RDPS Forecast Precipitation Accumulations by Thursday Evening
The RPDS weather model is bullish on convection and producing over 2″ of storm-total rainfall for the Red River Valley. This is likely too much.

There are really two possible outcomes:
1. General rainfall amounts near 10mm with convective amounts once again near 20–30mm in the Red River Valley. This would assume a general “rainy” area with embedded convective storms.
2. Very little rain as energy reconsolidates around a low developing in North Dakota and precipitation pushes off to our south and east.

I don’t think Plan #2 is particularly likely, but it should be noted. Again, we’ll provide updates heading forward below in the comments as this entire system becomes a more developed.

The gusty northwesterly winds will taper off in the evening as the precipitation moves out. Expect the temperature to drop to a very chilly –2°C.

Friday

Friday
8°C / -3°C
Mainly sunny and cool

Friday will be a pretty benign day marked by temperatures well below normal for this time of year as our high struggles to climb to 8°C with an Arctic ridge building into the region. Winds will be breezy out of the northwest at around 30km/h making for a chilly day all around.

Clear skies will continue on Friday night as the temperature dips to around –3°C.

  1. I checked through our archives and chatted with a few other people, and that seems to be the general “last hit” agreement. Feel free to leave a comment if you can recall one more recently.  ↩
  2. Synoptic storms are large low pressure systems that impact across hundreds to thousands of kilometres, unlike convective storms which impact small areas.  ↩

Nice Start to the Week, Then Some Rain

Scott Leave a comment

This week will start out very nice, with temperatures in the twenties. However, a strong low pressure system will move in toward the middle of the week, bringing more unsettled conditions.

Monday

Today will be a great day in southern Manitoba. Temperatures will be near the 20C mark with sunny skies and light winds. There isn’t much else to say, enjoy the weather!

Tuesday

Tuesday will be another very nice day as temperatures climb into the low twenties, once again under mainly sunny skies. Winds will be from the south-east at about 20 km/h.

Wednesday

Wednesday will remain warm, but more unsettled conditions will begin to take hold in southern Manitoba. An approaching low pressure system is expected to bring rain showers to southern Manitoba late in the day and into Wednesday night. This system may bring us more significant precipitation on Thursday, but it is too early to speculate on potential rainfall amounts.

Long Range

It looks like we’ll see cooler weather late this week into the weekend as a much cooler air mass gets pulled down from the north. This push of cool air will result from the departure of this week’s low pressure system. Long range models suggest we’ll return to above-seasonal conditions at some point next week.