Convective Outlook Valid for Today, Tonight and Tomorrow

Regional Impacts

NL… Some scattered thunderstorms across central Newfoundland this afternoon. Main hazards are rainfall rates of 20 to 30 mm/h and wind gusts of 60 to 70 km/h.

NB… Elevated thunderstorms possible tonight with rainfall rates of 15 to 25 mm/h. Scattered thunderstorms over southern New Brunswick possible tomorrow with rainfall rates of 25 to 50 mm/h.

NS/PEI… Isolated thunderstorms possible tomorrow over northern and central Nova Scotia and eastern PEI. Main hazard is torrential downpours of 25 to 50 mm/h.

 

Convective Discussion…

Today, most of the convective activity will be associated with a trough moving through Newfoundland. Some clearing behind the initial convection this morning will allow MLCAPE values to rise to 1000-1500 J/kg by this afternoon. Bulk shear values near 30 kts will aid in organising this convection as it moves east through central Newfoundland this afternoon. One of the limiting factors today will be the amount of upper and mid level cooling, especially over southern Newfoundland. Thus the main area of interest this afternoon will remain in central and northern Newfoundland as the trough moves through. The main threat with these storms will be locally heavy downpours of 20 to 30 mm per hour, but strong wind gusts and some pea sized hail are also possible. A few isolated thundershowers are also possible over southern Labrador today, however these storms are not expected to become severe due to weaker dynamics and a lack of strong instability.

Tonight, the remnants of hurricane Beryl will approach New Brunswick. This system has a track record of being highly convective, with that trend expected to continue as it enters New Brunswick. While mid level instability is currently forecast to be quite minimal, PWAT values are expected to rise up to 50 to 60 mm tonight, so any elevated thunderstorms that develop along the warm front bring the risk of torrential downpours tonight. This risk will continue into tomorrow afternoon over eastern portions of the Maritimes. Strong southerly low level flow tomorrow afternoon over the Bay of Fundy will pump some additional moisture into the warm sector over southern New Brunswick. This will increase the risk for some higher rainfall rates here in any convection that does occur in the warm sector, with 25 to 50 mm per hour possible. This area will move east into parts of mainland Nova Scotia and possibly eastern PEI tomorrow evening. Some isolated thunderstorms are also possible over extreme northwestern New Brunswick early tomorrow evening, closer to the low center, though these are expected to remain non-severe.

 

Thunderstorm Outlook for Today

Thunderstorm Outlook for Tonight

Thunderstorm Outlook for Tomorrow

Copp

Convective Outlook Valid for Today, Tonight and Tomorrow

Regional Impacts

 

Today

NB/Labrador:  Scattered thunderstorms with some of them becoming strong, rainfall rates 25 mm/h, hail possible, and gusts 50-80 km/h.

NS/PEI/NL:  Isolated thunderstorms giving 15-25mm/h rain and brief strong wind gusts.

 

Tonight

NL/Labrador:  A chance of thunderstorms.

NB/NS/PEI/:  None.

 

Wednesday

NL/Labrador:  Isolated thunderstorms with rainfall rates 15-25 mm/h.

NB/NS/PEI: None.

 

 

Convective Discussion

 

An upper disturbance and cold front will approach from Quebec/Western Lab today, continuing to increase moisture and instability. Some high level cloud may inhibit the extent of daytime heating over New Brunswick, Newfoundland and central and southeastern Labrador, but CAPE values could still approach 1000J/kg for southeastern Labrador and Newfoundland. There is weak to moderate shear, so the bigger issue will be some training thunderstorms. Divergence aloft and the left exit of the 250mb jet, and moderate 0-6km shear will also aid in sustaining convection in multicell or possible bow line segments over southern Quebec and Maine. The timing of the incoming trough and warm 850mb temperatures is such that stronger convection may remain capped hold off over New Brunswick until later in the day, but elevated convection may persist overnight aided by a strong low level jet as the trough moves over the Gulf of St. Lawrence and into western Newfoundland tomorrow morning.

 

On Wednesday, the trough continues eastward over northeastern Newfoundland and southeastern Labrador. A weak feature is expected to move into western Labrador in the afternoon and may trigger non-severe thunderstorms. The humid air mass over the Maritimes will trigger some pop up TCUs but are not expected to breach the warm cap from 700-500mb.

 

 

Thunderstorm Outlook for Today

 

Thunderstorm Outlook for Tonight

 

Thunderstorm Outlook for Tomorrow

 

 

Roberta McArthur

 

 

Convective Outlook Valid for Today , Tonight and Tomorrow

Regional Impacts…

 

Today

Labrador:  Scattered thunderstorms gusts 50-70 km/h and brief heavy showers 15mm/h.

NB/NS/PEI/NL:  None.

 

Tonight

Labrador:  A chance of thunderstorms.

NB/NS/PEI/NL:  None.

 

Tuesday

NB/Labrador:  Widespread thunderstorms with some of them becoming strong, rainfall rates 15-25 mm/h, hail possible, and gusts 50-80 km/h.

NS/PEI/NL: None.

 

Convective Discussion…

 

The airmass between James Bay and Labrador has become very unstable this morning ahead of an approaching upper level disturbance. At this point, the instability is triggered by 500 dam heights fall amplified by straight sunshine. In terms of dynamic support, A cyclonic jet over the Quebec far north is slowly descending, while a 40kt SWly low-level-jet is pumping moisture and energy into the mix. Surface CAPE values in excess of 1000 J/kg, LI of -4 and (increasing) 0-6 km shears of 25-35kt, will help support long-lived clusters.  

 

Fair weather cumulus along with warm and humid conditions are expected over the rest of the region.

 

For Tuesday, precipitable water will be on the increase and the upper disturbance and weak cold front will approach from Quebec/Lab and set the stage for the next round of thunderstorms. Current forecast guidance is suggesting the possibility of strong convective features but confidence is only starting to increase. This activity will likely occur during the peak daytime heating period of the day.

 

 

Thunderstorm Outlook for Today

 

 

Thunderstorm Outlook for Tonight

 

 

Thunderstorm Outlook for Tomorrow

 

Convective Outlook Valid for Today , Tonight and Tomorrow

Regional Impacts…

 

Today

NB/Labrador:  Scattered afternoon thunderstorms. A chance of becoming severe over NB.

NS/PEI/NL:  None.

 

Tonight

Labrador:  A chance of thunderstorms late Monday morning.

NB/NS/PEI/NL:  None.

 

Monday

NB/Labrador:  A chance of afternoon thunderstorms.

NS/PEI/NL: None.

 

Convective Discussion…

A trough of low pressure tracking across Labrador will give scattered afternoon thundershowers over portions of Labrador. Cape values are near 500 J/kg so any cells that form are no likely to be severe. Over New Brunswick, surface based thundershowers that could become severe are possible this afternoon. There are no real surface forcing mechanisms but Cape values are 500-1000 J/kg and shear is linear at 40 knots.  There is the potential for heavy rain at times as PWAT values are near 30 mm. There is also a supportive right entrance to an upper level jet to give support.

 

 

Thunderstorm Outlook for Today

 

Thunderstorm Outlook for Tonight

 

Thunderstorm Outlook for Tomorrow

Convective Outlook Valid for Today , Tonight and Tomorrow

Regional Impacts…

 

Today

NB/NS/PEI/NL:  A chance of thunderstorms.

Labrador:  None.

 

Tonight

NB/NS/PEI/NL:  A chance of thunderstorms.

Labrador:  None.

 

Sunday

NB/PEI/Labrador: A chance of thunderstorms. Over New Brunswick, surface based storms will may give severe weather in the afternoon.

NS/NL: None.

 

Convective Discussion…

A trough of low pressure tracking across the Maritimes will give a chance of embedded thundershowers for those areas today. There is the potential for heavy rain at times as PWAT values are 30-50 mm. Surface based thundershowers are possible this afternoon over portions of Newfoundland but the CAPE values are less than 500 J/kg so they should stay non-severe. On Sunday, surface based thundershowers are expected over most of New Brunswick and portions of Labrador. Over Labrador the CAPE values are expected to be less than 500 J/kg so non-severe cells are expected. Over New Brunswick, CAPE values near 1000 J/kg and shear of 30-40 knots will help support possible severe thunderstorms.

 

Thunderstorm Outlook for Today

 

Thunderstorm Outlook for Tonight

 

Thunderstorm Outlook for Tomorrow