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Multiple Systems Bring Heavy Showers, Thunderstorms and Flooding to Ontario

Updated: Apr 20, 2019

Due to the multiple systems over a span of 4 days, we have decided to split our forecast into two separate forecasts validations.
The first set of forecasts are valid until 2am on Saturday. The second set of forecasts will be valid from 2am on Saturday to Sunday at 8pm.

We are closely tracking a series of low-pressure systems which are expected to pass through portions of Ontario. The first system will begin to impact the region late Wednesday night and continue into Friday morning. The second system will begin to impact the region during the afternoon/evening on Friday and continue into the mid-late time frame on Saturday. Finally, this second system will bounce around the region with lingering showers into Sunday morning.

As the first system pushes into Southern and Northeastern Ontario late Wednesday night, moderate rainfall is expected to spread in Northeastern Ontario with a few patches of moderate rain across Southern Ontario. Local patches of thunderstorms are possible with some enhanced gusty winds and small hail also being possible. All storms will be non-severe. Into the morning hours on Thursday, the moderate rain will start to diminish with a mix of light to moderate rain showers across portions of Eastern and Northeastern Ontario with some patchy showers in Central Ontario. Some light to moderate pockets of snow and ice pellets may be possible in Northeastern Ontario extending near or north of Hearst, Fraserdale, and Manitouwadge. Isolated thunderstorms are possible in Central, Eastern, and Northeastern during this time. Into the early afternoon (12 to 2pm), scattered showers and non-severe thunderstorms are expected to move into the region and develop across Southwestern Ontario extending into Central and Eastern Ontario (Midland, Parry Sound, Algonquin, etc). The showers may be heavy at times with hail and gusty winds inside of thunderstorms. These thunderstorms will be along a cold front which will slide through the region throughout the afternoon and into the evening. Scattered showers and thunderstorms will be possible extending from the Quebec Border to the Michigan Border. The heaviest showers on Thursday will be from thunderstorms. In the early morning hours on Friday, the cold front thunderstorms will weaken due to a lack of daytime heating and another round of moderate showers will approach the region from the south. This system will push north during the day on Friday bringing widespread showers to the region. At times, the rain may change over to snow on the north edge of the system. There is some model disagreement on the exact location of this system, which, will change with the heaviest and most rain falls. The area of question extends from Sudbury/Manitoulin/North Bay south to Tobermory/Parry Sound/Deep River. This questionable area currently is unset on exact rainfall amounts as the system may not push as far north as originally expected. Into the afternoon and evening on Friday, the showers may develop into local thunderstorms across Southern Ontario. Moderate to heavy rain is expected. Into the early hours on Saturday, the thunderstorms and moderate to heavy rain will push east into Eastern Ontario with lingering showers across the GTA, Southwestern Ontario, Central Ontario and the Golden Horseshoe. In Northern Ontario, a system from Northern Manitoba will spread into Northwestern and Far Northern Ontario and will drop a quick 5 to 15mm of rain across the region before moving out later on Saturday and into Sunday. During the morning hours on Saturday, scattered showers may be possible extending from Kingston to Cornwall and across Southwestern Ontario. Throughout the day on Saturday into Sunday, local scattered showers are possible. The core of the rain will fall from Thursday to Saturday with lingering amounts from Saturday to Sunday.


Forecast Date 1: Valid from Thursday at 2am to Saturday at 2am.


Rainfall

Rainfall Forecast, for Southern Ontario. Issued April 18th, 2019.

Blue or '1':

Areas in the blue or marked with a '1' can expect less than 15mm of rain. This includes much of Northern Ontario including everything north and west of White River, Peterbell and Cochrane. Most areas should see less than 5mm. Areas from Atikokan extending northeast towards Jellicoe, Mammamattawa and Moosonee, as well as areas towards the south, could see rainfall totals between 5 and 15mm of rain.


Green or '2':

Areas in the green or marked with a '2' can expect between 15 and 25mm of rain. This includes portions of Northeastern Ontario such as Wawa, Timmins and Chapleau as well as Batchawana Bay, Ruel and Kirkland Lake. Most of these places should see rainfall totals near 15mm although a few local places may see amounts towards 20 or even 25mm of rain. Areas along the Quebec Border such as Kirkland Lake, Ruel, Gowganda and Temiskaming Shores may see local amounts higher than 25mm towards 35mm of rain. This is due to thunderstorms which may impact the region.


Yellow or '3':

Areas in the yellow or marked with a '3' can expect between 20 and 40mm of rain. This includes portions of Northeastern Ontario such as Sault Ste. Marie, Sudbury, Temagami, Manitoulin Island, Espanola, Monetville and Elliot Lake. Most of these places will see rainfall totals between 20 and 30mm of rain although local totals, especially near Monetville could climb to near 40mm. Thunderstorm activity may enhance rainfall totals.

Rainfall Forecast, for Northern Ontario. Issued April 18th, 2019.

Orange or '4':

Areas in the orange or marked with a '4' can expect between 30 and 60mm of rain. This includes all of Southern Ontario including portions of Northeastern Ontario near North Bay and Mattawa. Almost all of Southern Ontario will see rainfall totals at or near 30mm with amounts towards 40mm being likely. Rainfall totals in local places and in a few areas of concern such as Windsor/Essex County, Eastern Ontario, the shores of Lake Huron and Georgian Bay and Central Ontario have the best risk as seeing rainfall amounts towards 50 or even 60mm of rain. Due to the strong snowpack into Eastern and Central Ontario, this raises major concerns for flooding. Thunderstorm activity may enhance rainfall totals. With thunderstorms, there may be pockets of even 70mm throughout this region.


Red or '5':

Areas in the red or marked with a '5' can expect between 40 and 80mm of rain. This includes portions of Algonquin Park extending south into Muskoka/Parry Sound region as well as the Haliburton, Bancroft and Renfrew County regions. Most places should see at or near 40mm with rainfall totals as high as 60mm seeming possible. Local totals to 80mm are possible, therefore, the upgraded risk level to a level 5. Due to the strong snowpack into Eastern and Central Ontario, this raises major concerns for flooding. Thunderstorm activity may enhance rainfall totals. If the thunderstorms set up over the same region as the moderate to heavy system rain, rainfall totals near or actually over 80mm are possible.


NOTE: Depending on the exact track of the second system, rainfall totals may be pushed further north into Northeastern Ontario (40 to 80mm moves towards North Bay, 30 to 60mm moves into Manitoulin Island, etc) if the system travels further north than currently expected. This message will be updated if this change will take place.

Forecast Date 2: Valid from Saturday at 2am to Sunday at 8pm.


Rainfall

We have decided to not include due to the low rainfall risk.


We are expecting less than 10mm for areas extending from Tobermory across to Britt and North Bay.


We are expecting less 10 to 25mm for areas south of that line. Local amounts towards 35mm are possible from Prince Edward County extending northeast to Renfrew including everything east of that line.

Flooding and the Snowpack

The Ministry of Natural Resources and Forestry have issued a flood watch for Ontario.


Alongside the ministry, there are multiple conversation authorities which have issued flood watches and warnings and watershed condition statement. A full list can be found on their website.


In their summary, they state, "A Colorado low merging with a Texas low is forecast to move in tonight (Wednesday evening) bringing significant precipitation, mostly in the form of rain, across the Province. The precipitation will begin Wednesday evening where 15 to 25 mm is forecast along the shores of the upper Great Lakes. The system is forecast to slide south on Thursday and drop 15 to 30 mm of rain across a large swath of central and southcentral Ontario. Rainfall is forecast to persist into Friday with 15 to 30 mm forecast across a large swath of southcentral, south and southeastern Ontario.


The system is forecast to die out on Saturday but may still produce up to 20 mm in southwestern Ontario. Thunderstorms associated with this event are possible and may produce and additional 5 to 10 mm in isolated areas.


Totals across a broad swath of south and central Ontario in the range of 30 to 50 mm are forecast with higher amounts possible in isolated areas.


High winds associated with system in the range of 30 to 35 km/hr with stronger gusts up to 45 km/hr are forecast across the lower Great Lakes.


Daytime high temperatures are forecast in the 0 to 10 degrees Celsius range across most of the north of the Province over the next five days with forecasted highs in the 5 to 15 degree Celsius in the south. Night-time low temperatures are largely forecast to stay at or below 0 degrees Celsius in the northern part of the Province and remain at or above 0 degrees Celsius in the southern parts of the Province.


Mid-April snow surveys show a continuing snowpack in central and northeastern Ontario ranging from 100 to 200 mm of snow water equivalent in central Ontario and 100 to 250 mm in northeastern Ontario. These values are above average to well above average for this time of year."

National Operational Hydrologic Remote Sensing Center : NOAA : Current Snowpack (April 17th, 2019)

The attached image above indicates the current snowpack which across Central and Eastern Ontario, including Northeastern Ontario sits around 50 to 100cm with local amounts as high as 150cm of snow.


National Operational Hydrologic Remote Sensing Center : NOAA : Current Snowpack Liquid Totals (April 17th, 2019)

In this next attached image, this indicates the current snowpack liquid totals which across Central and Eastern Ontario, including Northeastern Ontario sits around 2 to 10". This snowpack is rich of upwards of 250mm of liquid on top of expected rainfall amounts.


Flooding is possible along river banks/river flood planes and in low-lying areas.


#TurnAroundDontDrown

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