Convective Outlook Valid for Today , Tonight and Tomorrow

Regional Impacts

 

Today

NB/LAB: Scattered thundershowers.

NS/PEI/NFLD: None.

 

Tonight

NS: Chance of thundershowers.

NB/PEI/NFLD/LAB: None.

 

Monday

NS/NB/PEI: Embedded thundershower risk.

NFLD/LAB: None.

 

Convective Discussion

A trough stretching from western Labrador to the St. Lawrence River Valley will likely spark some non-severe thundershowers over northwestern New Brunswick and central Labrador today.  MLCAPE values are expected to be near 500 J/kg and the shear will be 20 to 30 knots. Current soundings indicate a layer of warm air above 500 mb which should keep storms from reaching severe status. The main hazards with any storms will be small hail, strong wind gusts, and locally heavy downpours. On Monday, a low developing in the trough will give a risk of embedded thundershowers across the Maritimes. Localized downpours are possible with any thundershowers that develop.

Thunderstorm Outlook for Today

Thunderstorm Outlook for Tonight

Thunderstorm Outlook for Tomorrow

 

Convective Outlook Valid for Today, Tonight and Tomorrow

Regional Impacts

Today

LAB: Scattered thunderstorms possible today capable of producing small hail, strong wind gusts, and heavy downpours.

NS/Newfoundland: Chance for some elevated thundershowers today over Cape Breton and southern Newfoundland with some locally heavy downpours.

PEI/NB: None.

Tonight

LAB: Some isolated thundershowers possible overnight over northern and western Labrador.

NS/NB/PEI/Newfoundland: None.

Tomorrow

NB: Chance of some isolated thunderstorms over northwestern New Brunswick in the afternoon and evening with small hail, strong wind gusts, and locally heavy downpours.

LAB: Some scattered thundershowers possible through the day over central Labrador capable of producing some locally heavy downpours.

NS/PEI/Newfoundland: None.

 

Convective Discussion…

Two areas of interest are in play today. The first is associated with an upper low between Cape Breton and southern Newfoundland, and the second associated with an elongated trough extending from the northern Labrador Sea down into southern Quebec. Some isolated thundershowers have already been observed this morning with this first feature along the Eastern Shore of Nova Scotia. The upper low will slowly move northeast, reaching the Avalon Peninsula overnight. Due to the amount of cloud cover over this area of interest, convection is expected to remain elevated through the day as some scattered thundershowers move into southern Newfoundland. MUCAPE values of 250 to 500 J/kg are forecast, with effective shear in the 15 to 25 knot range allowing some of these thundershowers to be sustained through the day. The main risk with these cells will be heavy rainfall rates of 20 to 30 mm per hour. This low will move east over the Atlantic tonight. The second feature over Quebec and Labrador has already produced some scattered thunderstorms, which are expected to continue through the day and into this evening. MLCAPE is expected to build near or above 1000 J/kg by early this afternoon over western Labrador, in addition to some moderate jet support providing effective shear in the range of 20 to 30 knots by late this afternoon. This should allow some cells to become organized this afternoon and into this evening, with the main hazards being some heavy downpours, strong wind gusts, and small hail. This trough is moving very slowly to the northeast which could ramp up some of the rainfall totals over the area. This risk will extend overnight and into tomorrow, but without daytime heating only a few isolated non-severe thundershowers are expected overnight.

Tomorrow, the same trough will likely spark some non-severe thundershowers over central Labrador, with MLCAPE expected to be much lower (250 to 500 J/kg) due to enhanced cloud cover over the region. However, the environment over northwestern New Brunswick is expected to ramp up by the mid-afternoon as the trough moves into the St. Lawrence river valley. Clear skies during the morning and early afternoon here should allow MUCAPE values to build to 750 to 1000 J/kg. This in combination with effective shear values of 20 to 30 knots could lead to some organized thunderstorm development in the mid-afternoon over northwestern New Brunswick. However current model tephigrams indicate a layer of warm air above 500 mb which could keep storms from reaching severe status. The timing of the trough will also play a role in when convection triggers, so there is still some uncertainty here tomorrow. The main hazards with any storms that do fire will be small hail, strong wind gusts, and locally heavy downpours.

 

Thunderstorm Outlook for Today

Thunderstorm Outlook for Tonight

Thunderstorm Outlook for Tomorrow

Forecaster: Copp

Convective Outlook Valid for Today , Tonight and Tomorrow

Regional Impacts

Today:

Lab: Risk of a thundershower giving moderate wind gusts and rainfall rates.

NL: Risk of a thundershower giving moderate wind and rainfall rates, along the southern coasts.

NS: Risk of a thundershower inland.

NB/PEI: NIL.

Tonight:

Lab: Risk of a thundershower giving moderate wind gusts and rainfall rates.

NS/NB/PEI/NL: NIL.

Tomorrow:

Lab: Risk of isolated thundershowers giving moderate wind gusts and heavy rainfall.

NS/NB/PEI/NL: NIL.

Convective Discussion

The low-pressure system from yesterday is currently located to the southeast of Nova Scotia. This system is still giving embedded showers and thundershowers with isolated cells giving rainfall rates near 25 mm/hr. As this system progresses, model guidance is indicating that a lot of the forcing will diminish throughout the day. However, there is a cool trough that is forecast to move through the Maritimes, which will mainly act as a trigger for isolated thundershowers over mainland Nova Scotia; predominant areas of concern would be the higher terrain. Over Labrador, there is a decaying ridge of high pressure, and looking at satellite imagery, there is a clearing of mid to upper-level cloud along with a burning off of mist throughout much of the region. CAPE values are rising to near 1,000 J/kg because of this clearing trend. Daytime heating will act as a trigger and initiate some isolated thundershowers.

Tonight into tomorrow, a frontal system will approach Labrador from Northern Quebec today and affect Labrador tonight into tomorrow. There are some timings issues for this frontal system as it approaches, as such hazards are on the lower side. If the system progresses slower and maintains intensity, then tonight there is less confidence in thundershowers tonight and hazards could be more intense for the tomorrow period. Current guidance is giving an early afternoon of approximately 1,500 J/kg of Mixed Layer CAPE (MLCAPE) with shear values remaining around 15KT. If this system moves slower than it will be more likely that the jets will move through at a more effective timing, allowing shear to increase, which would lead to better organization of convection.

Thunderstorm Outlook for Today

Thunderstorm Outlook for Tonight

Thunderstorm Outlook for Tomorrow

Forecaster: Lambert

Convective Outlook Valid for Today , Tonight and Tomorrow

Regional Impacts

Today:

NS/NB/PEI: Risk of thunderstorms giving moderate wind and heavy downpours.

Lab: Risk of thundershowers.

NL: Nil.

Tonight:

NS/ PEI: Risk of thunderstorms giving heavy downpours.

Lab: Risk of thundershowers, mainly over higher terrain.

NB/NL: Nil

Tomorrow:

Lab: Risk of thunderstorms giving moderate wind, heavy downpours and a risk of small hail.

NL: Risk of thunderstorms along the southwest coast.

NS: Risk of a thundershower.

NB/PEI: Nil

Convective Discussion

A Low off the southwest coast of Nova Scotia is having its frontal wave sheared apart, which is allowing for a complex setup for today and into tomorrow. Looking at water vapour imagery, along with upper-air soundings, we can see that the main cold front is back towards the US Eastern Seaboard; meanwhile, the upper jets have sheared off from the low centre as the trowel wraps through Nova Scotia and New Brunswick, creating a dry slot. Along with the synoptic setup, there is vorticity advection affecting Northwest New Brunswick, and a departing ridge over Labrador, which is allowing for topography-induced troughs to develop. With this setup, we are seeing Precipitable Water values (PWAT) nearing 50mm, along with CAPE values hovering around the 500 J/kg mark. As such, going forward with this setup, it is most reasonable to use the Most Unstable CAPE (MUCAPE) values, to which we are seeing a swath of MUCAPE values between 500-1000 J/Kg around the Maritimes and Labrador.

Tonight, the disconnected frontal wave from today will progress eastward, allowing for some isolated thunderstorms to persist in the overnight hours for the Maritimes. For Labrador, there is a risk of thundershowers overnight; This drier air could allow for some thunderstorms overnight, though there is more uncertainty with this.

Tomorrow, remnants from today’s frontal wave will likely stay just to the southwest of Newfoundland, and model guidance indicates that convection will struggle to move inland. For Labrador, there is a stronger low-pressure system moving through Northern Quebec and Southern Baffin Island, which model guidance suggests a cold front could extend from Ungava Bay to Southern Quebec. The warm sector will enter Labrador with this frontal system, bringing a slight risk of hail, moderate winds, and rainfall. As this system progresses, the risks could change, as there are some timing uncertainties.

Thunderstorm Outlook for Today

Thunderstorm Outlook for Tonight

Thunderstorm Outlook for Tomorrow

Forecaster: Lambert

Convective Outlook Valid for Today , Tonight and Tomorrow

Regional Impacts

Labrador… Risk of thunderstorms today across western and central areas – may approach severe limits briefly in the Churchill Falls area today with gusty winds and heavy downpours.

Nova Scotia…  Chance of thundershowers in the overnight tonight with shower activity arriving from the SW. This risk extends eastwards in the day on Thursday. Moderate rainfall is the only hazard being forecast over land areas.

New Brunswick… Risk of an isolated thunderstorm near the Quebec border in the afternoon on Thursday.

Convective Discussion

The synoptic pattern is slowly advancing to the east in the next 24 to 48hrs. This brings a change in the weather across the Maritimes.

Ample surface moisture is in place today(dew points near 19), and effective shear(30kts) in the vicinity of the 2 forcings is good. The delay in anything getting going is simply the pace of the trigger itself. In Labrador, the trof will spark up this afternoon and may bring gusty winds and decent downpours. Small hail is also possible but shouldn’t exceed 1.5cm. Offshore from NS over the southwestern marine district, severe storms are possible and may form a decent line bringing gusts to near 90km/h. This will be monitored in case Squall watches or Warnings are required (depicted in yellow). As the low continues to wrap further and slowly advance east tonight, the thundershower risk moves into Nova Scotia. But it is forecast to be embedded in the overall greater shower activity (depicted in grey). It’s very warm at 700mb and quite dry in the upper levels this morning(Yarmouth sounding). Going to take some time to moisten the entire column to support any lightning activity. By tomorrow afternoon, the 100kt southerly jet at 250mb is just east of Halifax and situated as such that severe weather is not being forecast over any land areas. The orientation is not conducive this time.

Thunderstorm Outlook for Today

Thunderstorm Outlook for Tonight

Thunderstorm Outlook for Tomorrow

Forecaster: Tirone.