A potent upper-air pattern will create extreme instability across the Southwestern Prairies Thursday. A surface trough will slice through the summer air offering a trigger for explosive thunderstorm development in the unstable atmosphere.
Winds at the surface out of the southeast and upper-level winds from the southwest suggest a well-sheared warm sector. The strongest surface heating will remain just south of the border. In spite of that, ample moisture delivery, temperatures falling aloft, effective shear, and plenty of energy will provide a breeding grounding for severe thunderstorms Thursday.
Thunderstorms will develop across Southern Alberta and Northern Montana around 2 pm. Trans-versing northeastwards throughout the afternoon and evening, Initial storm develop may feature discrete cells and bowing segments; a threat for large hail, damaging winds, and an isolated tornado is possible. As progression into the evening continues, a powerful nocturnal complex of thunderstorms known as a Mesoscale Convective Complex (MCS), may develop. These convective weather systems are notorious producers of damaging winds, intense frequent lightning, large hail, and localized flooding in torrential downpours. Moreover, these systems are known to persist well into the pre-dawn hours.
HAZARDS: 90-110km/h wind gusts, 2-5cm hail, torrential rainfall, frequent lightning, and an isolated tornado.
We will be monitoring the thunderstorms throughout Saskatchewan and Alberta attentively on Thursday. Be sure to closely monitor watches and warnings throughout the afternoon, evening and overnight. We will be issuing another forecast for severe thunderstorm risk in Saskatchewan, Friday. The risk depends greatly on the evolution of thunderstorms Thursday into pre-dawn Friday.
HEAVY RAINFALL CONTINUES WEST OF EDMONTON
Much of the focus is rightfully centered around substantial thunderstorm risk further south, but appreciable rainfall amounts along the Highway 16 & 40 corridor is worth mentioning. This region has already seen very-heavy rainfall over the last several days. Another 50-75mm is on tap between Hinton and Edmonton, through Friday.
A sudden surge of warm, summer-like air will herald in the risk of thunderstorms across the Lower Great Lakes. These thunderstorms may turn severe; capable of producing damaging winds & hail across portions of Southern Ontario.
SURGING TEMPERATURES, THUNDERSTORMS & RAIN
An area of low-pressure will transverse through the Midwestern United States towards Ontario, throughout the day Sunday. Ahead of the system, temperatures will surge into the mid-20s and humidity readings into the low-30s. Near the Lake-shore, cooler conditions are expected.
Showers are expected before midnight tonight, lasting into the pre-dawn hours. Persistent rain-showers and embedded thunderstorms are expected for Central Ontario – mainly East of Georgian Bay. Sunny breaks are anticipated through the morning hours, allowing for some instability to build before the arrival of a cold front.
At this point, it appears the setup will feature two potential waves of thunderstorms. The primary wave will consist of a complex of heavy rain showers with embedded thunderstorms impacting Southern Ontario between 4-10 pm. Initiating at approximately 4 pm in Windsor and exiting Eastern Ontario by 11 pm. Risks include: torrential downpours, lighting and isolated damaging winds. A potentially stronger second round of thunderstorms (along an advancing cold front) may happen on Sunday evening/overnight, across Extreme Southwestern Ontario. There is some uncertainty regarding the evolution of thunderstorm development. If thunderstorms do develop, risk factors include: hail and isolated damaging wind gusts.
Across Northern Ontario, a large swath of heavy rainfall is expected. Local rainfall totals nearing 50mm is anticipated.
Our forecasting team is vigilantly monitoring a powerful low-pressure system expected to form North of the Texas Panhandle late this evening. The upper-level disturbance originating out of California, will coincide with a favorable setup for an explosive storm development. Read more about Panhandle Hooks’ here.
Did you know? It was an infamous Panhandle Hook which sank the SS Edmund Fitzgerald on November 10th, 1975.
This storm will feature strong winds, blizzard conditions, heavy rainfall, thunderstorms, and shifting ice-conditions across the Great Lakes. Almost everyone in Eastern Canada will feel the effects of this powerful storm. Read more to gain insight on how this storm may impact you.
BLOCKBUSTER BLIZZARD EAST OF LAKE SUPERIOR
Our forecast team is closely monitoring a soon-to-be rapidly strengthening Panhandle Hook, sagging into the Texas Panhandle. Gathering abundant gulf moisture before trekking towards the Upper Great Lakes. The storm will experience the most intensification while tracking Northeastwards through the Upper Midwest (United States), towards Lake Superior & Northern Ontario. Coinciding with an expanding strong to damaging wind field.
Confidence is considerable for a high-impact Low for regions N and NE of Lake Superior with likely 30cm or more of blowing snow contingent with 60km/h+ wind gusts. The heaviest snowfall will likely be 30-40km inland from the immediate Lake Superior shoreline. This is bad news (or good new depending on your prerogative), when considering how much snow has already fallen across this region. Some are running out of places to even put the snow.
The fiercest winds will not correspond with the heaviest snowfall rates. Still, inland locales such as Timmins & Kapuskasing will still have to contend with extensive blowing & drifting snow. Especially, once the low tracks into Quebec, with colder air and stronger gusts arriving on the backside of the low.
There will be a line of mixing of wintry precipitation likely from Sault Ste. Marie to Sudbury to the QC border. Including a brief period of ice pellets and rain-showers.
WIDESPREAD DAMAGING WINDS ACROSS SOUTHERN ONTARIO
Temperatures will begin to surge above freezing across Southwestern Ontario, as early as, late Saturday evening. Double-digit temperatures & strong Southwesterly winds will advance throughout the Southern half of the Province throughout the morning & afternoon. Rain-showers and even a risk of elevated thunderstorms is expected. Proceeded by, a sharp cold front & plummeting temperatures.
We anticipate extensive blowing snow and poor-visibility East of Lake Huron late Sunday evening through Monday. Avoid all unnecessary travel in the red highlighted area on our wind impact map.
The supportive track and strength of the low will herald in a significant damaging wind threat across Southern Ontario. The strongest winds could peak as high as hurricane force (120km/h), along the Northeast shore of Lake Erie. We anticipate wind gusts over 100km/h across Prince Edward County, and East of Lake Huron. Peak wind gusts will likely reach or exceed 90km/h across the rest of Southern Ontario.
The sudden onset of warm air, rainfall, and extreme wind gusts will bring treacherous ice conditions across the Great Lakes. Ice shoves may be damaging to infrastructure along exposed shorelines. If you participate in winter activities such as, ice fishing or snowmobiling, it would be a good idea to remove your ice hut from the Great Lakes. Avoid snowmobiling until ice conditions improve.
A NEW COASTAL LOW BOMBS OUT AS IT TRACKS THROUGH THE MARITIMES
The powerful storm sweeps through Quebec on Sunday, and will subsequently phase into a strong ‘weather bomb’ south of Yarmouth. Potentially, deepening below 970mb (967-969mb).
While the exact phasing & extend of warm air advection is not entirely set-in-stone, it appears the heaviest swaths of snowfall will likely be off the Gaspe Peninsula shoreline and into the North Atlantic, thereby mitigating what could have been 2 or more feet of snow.
Southern New Brunswick will likely experience a rain/snow/wintry mix. With amounts totaling near 10cm. Amounts increasing to 20-30cm across the Northern extent of the Province. Pockets of heavier enhancement, accompanied by similar conditions is expected across Extreme Southern Newfoundland
Timing Western New Brunswick – Late Afternoon Sunday Most of New Brunswick – Sunday Evening Nova Scotia – Sunday Mid Evening PEI – Sunday Overnight Newfoundland – Monday
Hardest Hit Gaspe (35-45cm) Bathurst (25-35cm) Edmundston (30-35cm) Campbellton (30-35cm) Extreme Southern Shoreline of Newfoundland (25-40cm)
DANGEROUS BLIZZARD CONDITIONS STRETCH FROM JAMES BAY THROUGH NORTHERN QUEBEC
A major blizzard is on-tap for much of Northern Quebec. The worst of the treacherous conditions will be felt across the mouth of the Rupert River, Southeast of James Bay. Where rural communities can expect winds over 90km/h combined with 15-25cm of freshly fallen snow. Extensive blowing/drifting snow & near-zero visibility is expected. Isolated communities across Central & Northern Quebec may become cut-off, briefly.
Isolated severe thunderstorms expected today (Sunday, June 10th) in Saskatchewan & Manitoba.
Isolated severe thunderstorms are expected to develop in Central and Eastern Saskatchewan beginning by the mid-afternoon and persisting well into the evening hours in Western Manitoba.
We have highlighted an area in orange where the greatest risk develops. Regions is yellow can expect primarily non-severe showers and thunderstorms. Note: this risk continues into Western Manitoba.
Risk factors associated with these thunderstorms include: large hail, torrential rainfall, frequent lightning, and damaging wind gusts in excess of 100km/h.
Much cooler and less humid conditions are expected for Monday.
Severe thunderstorm risk for today expected in the orange section of our map.
A surface low will decent across Southwestern Saskatchewan early in the morning Sunday. The first low has led to rain and heavy thunderstorms in Southwestern areas of the province early this morning. At the same time, a secondary low pressure center/vort max will be deepening as it approaches Western Saskatchewan during the afternoon. A trough in the Jet-stream will be progressing Eastwards across Saskatchewan during the period.
A eastward progressing front associated with the deepening low-pressure system, will act as a trigger from the mid-afternoon through the late evening – across Central and Eastern Saskatchewan.
Deep moisture transport aided by a 30-40kt low-level Jet out of the Southeast will result in dew-points in the high teens. Concurrently, temperatures will likely rise into the high 20s. Convective Available Potential Energy (CAPE) will likely build above 2000 J/KG across the warm sector, providing plentiful energy for strong thunderstorms. Warmer air aloft (a “cap”) will have to erode before storms can erupt – perhaps after peak energy.
Marginal wind shear and helicity readings, little veering with height, and a high LCL is expected to limited any tornado activity despite a south-easterly surface wind. The south-easterly flow and storm mode/track may allow for “training” – which heightens the threat for localized flooding.
Environment Canada (PASPC) has issued a map highlighting Southeastern Saskatchewan and Western Manitoba in a “moderate” risk for severe thunderstorms. Primary hazards include: 110km/h wind-gusts and 3-5cm hail. NOTE: these maps are still in the experimental stage.
Near the low center (which is expected to exist in the North Battleford corridor), a soaking rainfall and heavy thunderstorms is expected. This activity should remain non-severe. Rainfall amounts of 15-35mm are expected.
The risk for severe thunderstorms continues Eastwards into Manitoba. Reloading again, for Manitoba and Northwestern Ontario on Monday.
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For the first time in the 2018 season, a risk of widespread thunderstorms across Ontario could occur on Friday, May 4th, 2018 – some potentially severe.
During Friday morning, many regions across Southwestern, Southern and Central Ontario will experience widespread moderate rain: an isolated non-severe thunderstorm cannot be ruled out. As the morning and day progresses, conditions will become drier, sunny at times, more humid and potentially lead to some severe thunderstorms. The severe thunderstorms that do occur will bring mainly a wind threat.
A somewhat secondary line of isolated severe thunderstorms could also sweep into eastern sections of the Niagara region as a linear set-up of storms will form near upstate Pennsylvania and western New York state; where this line of storms exactly forms will be incredibly relevant for this region. Should it form quickly and near the CAN/USA border (as current atmospheric parameters suggest), the region will be impacted; a formation more eastwards will reduce the risk and impact substantially, to virtually nil.
Potential Severe-Threat Timing
Afternoon to early evening from west to east.
Scientific Analysis The greatest risk for isolated severe thunderstorms can be depicted in the ‘darker orange region’.
A slight risk for isolated severe thunderstorms can be depicted in the ‘lighter orange region’.
Mainly non-severe thunderstorms can be depicted in the ‘yellow region’. One or two severe thunderstorms cannot be ruled out in this region, particularly along HWY 402, HWY 403 near Brantford and HWY 401 near the London-Woodstock corridor. Later on Friday, it is possible along eastern sections (ex. Kingston to Brockville and 50-60km east of Ottawa), an isolated severe thunderstorm is also possible.
Sufficient atmospheric energy at the immediate surface, as well as, 100mb and 300mb above the surface (SB, ML and MU CAPE) could be adequate to lead to severe thunderstorms. While energy is not astronomically high, and lower in comparison to the more traditional summer months, relatively strong dynamic forces should act as a sufficient trigger for isolated severe thunderstorms. Convective inhibition (CIN) at the surface as well as 100mb above the surface (ML-CIN), should reduce the risk of severe thunderstorms, and thunderstorms all together along the immediate northern shoreline of Lake Ontario: this will lead to cells rapidly weakening as they form near or just east of Lake Huron and usher eastwards. A relatively moderate lifted index (LI) will aid in dynamic instability leading to the greatest threat of isolated severe thunderstorms particularly near or just inland of Lake Huron and SE Georgian Bay. Storm relative helicity (SR) remains weak at the 0-1km threshold, and slightly stronger at the 3km threshold; this will allow for an increased threat of isolated severe thunderstorms in more of a linear format (although not encompassing a large area). Cyclonic updraft at the surface is virtually non-existent at the 0-1km threshold thereby limiting any tornado touchdown to virtually nil.
Other parameters including: Bulk Richardson Number, Cross-Totals, Total-Totals, Thompson Index and shear at the high atmosphere (6km) support isolated severe thunderstorms; although not super-cells; witha risk for strong wind gusts mainly to 90-100km/h as being the primary threat.
Non-conducive lapse-rates and wet-bulb zero (WBZ) coefficients will mitigate the hail risk overall to pea-size to nil.
Precipitable water (PWAT – surface to 300mb) is somewhat low for ‘torrential downpours’, therefore, residents should be spared a ‘flooding risk’ as typical with some severe thunderstorms.
Ultimately, the deepening of the approaching low-pressure system will be well-timed with strong uni-directional winds aloft, 500mb height-falls, and a jet-streak. Further, a sharp cold front is expected to eject through Southern Ontario between ~2-6pm thereby providing a trigger for these thunderstorms.
Across much of Southern Ontario, residents can expect winds gusting to 80km/h for many regions and locally up to 100km/h, irrespective if regions see thunderstorms or not.
Tie down loose patio furniture, patio umbrellas and chairs.
Remember, summer thunderstorm forecasts – severe and/or non-severe – represent a plausible scenario based on extensive weather calculations, parameters and up-to-date atmospheric data. Nothing is for certain, but outlines a possible or likely scenario based on the aforementioned points.
Please stay tuned, as we at TCW are monitoring this situation attentively.
Drive safe and always be alert during hazardous conditions.