Convective Outlook Valid for Today and Tomorrow

Day 1 Thunderstorm Outlook

 

Regional Impacts

For New Brunswick...

There is a slight chance that severe thunderstorms could develop giving strong wind gusts and potentially heavy downpours.

Elsewhere..

A slight chance of embedded thunderstorms giving locally heavier rainfall.

 

Convective Discussion

Overall there is not of lot of instability in the airmass but with cold air advection aloft and some daytime heating surface based CAPE’s should exceed 500 j/kg by this afternoon over New Brunswick. In terms of the dynamics, conditions are very favorable ahead of the approach cold front that will pass over New Brunswick today, with about 50 knots of deep shear to support supercell development. In addition there will be convergence and enhanced low level vorticity along the front. It is possible that supercells could develop with the potential to produce bowing segments leading to strong surface winds. Watches may be required should organized storms begin to develop.

 

Threat Table for reference

Threat	Rainfall Amount	Wind Gusts	Hail Diameter	Tornado Probability
Minor	< 25 mm	< 70 km/h	< 2 cm	Unlikely
Moderate	25 – 50 mm	70 –89 km/h	2 – 4 cm	Low
Severe	50– 100 mm	90– 119 km/h	4 – 6 cm	Moderate
Extreme	100 mm or more	120 km/h or greater	6.0 cm or greater	Elevated
Risk of Thunderstorms: Thunderstorms that develop in this area will be less organized and will not likely meet warning criteria. Severe Thunderstorm Watches will not likely be required.
Slight Risk of Severe Thunderstorms: There is a low probability that weakly organized thunderstorms will develop, these thunderstorms may reach warning criteria. Severe Thunderstorm Watches may be required
Moderate Risk of Severe Thunderstorms: There is a moderate probability that organized thunderstorms will develop, thunderstorms are likely to reach warning criteria. Severe Thunderstorm Watches will likely be issued.
High Risk of Severe Thunderstorms: There is a high probability that well organized thunderstorms will develop, these thunderstorms are likely to meet or exceed warning criteria. Severe Thunderstorms Watches will be issued.

 

Day 2 Thunderstorm Outlook

Convective Outlook Valid for Today and Tomorrow

Hello All,

 

Although we have had an active start to the week with respect to severe weather today marks the official start of the ASPC’s Summer Severe Weather Desk. We have decided to include the Day and the Day 2 outlook in this one email, unless this proves to challenging due to the weather. If you have any comments about the format we are open to suggestions and feel free to contact me at mel.lemmon@canada.ca.

 

 

 

Regional Impacts

 

For Newfoundland and Labrador..

Heavy downpours and strong wind gusts nearing warning criteria are possible for western Labrador. Most areas are more likely to see weaker storms with less frequent or isolated thunderstorms.

 

For New Brunswick..

Strong thunderstorms are possible this evening with activity possibly extending into the overnight hours. Frequent lightning and some downpours less than 15 mm are possible. However should storms develop earlier in the day severe cells are possible over western parts of the province.

 

Convective Discussion

 

A significant low pressure system just west of Labrador will be the main driver of convective weather for the next couple of days. This low will move eastward today and along with the low the cold front extending southwest into southern Quebec and eastern Ontario will also begin to track eastward. The most favourable thunderstorm dynamics will be just ahead of the cold front that will extend into western Labrador by this evening. However CAPE values for Labrador will be low and not expected to exceed 500 J/kg. There is a significant amount of deep shear and lower level shear which could lead to supercells and bowing segments which could generate strong surface gusts. The probability of this is scenario is low but careful attention will be paid to the satellite and lightning detection to monitor thunderstorm development.

 

Over New Brunswick Cape values may exceed 1000 j/kg however the lack of a trigger could push back thunderstorm potential well into the evening as thunderstorms initiate well ahead of the cold front over New England and eventually move over New Brunswick. There is a low probability that a severe thunderstorm could impact the region but the most likely scenario is that thunderstorms will occur late after maximum daytime heating with weakened updrafts.

 

 

 

 

Mel Lemmon

Convective Outlook for Today and Tomorrow

 

For today…

 

Regional Impacts

 

Heavy downpours and strong wind gusts can be expected in thunderstorms over northern parts of New Brunswick this afternoon. Wind gusts may exceed 70 km/h and the heaviest downpours are forecast to be around 25mm.

 

Over Newfoundland embedded thunderstorms could continue giving locally higher rainfall amounts.

 

Convective Discussion

 

Another active day of thunderstorms is expected across northern New Brunswick with CAPE values in excess of 1000 j/kg. The dynamics are not quite as favourable today with deep shear values of about 25 knots from the 12Z sounding at KCAR. The is some drying at midlevel’s which could lead to strong downdrafts possibly exceeding 70km/hr over northern area and could possible approach warning levels of 90 km/hr.

 

 

 

For tomorrow…

 

At this point there is not a high probability of severe weather due to the low CAPE however dynamics will be increasing through the day leading to a risk of some severe weather for western Labrador and northwestern New Brunswick.

 

 

Mel Lemmon

Convective Outlook Valid for Today and Tomorrow

 

Regional Impacts

Thunderstorms are forecast to develop this afternoon over northwestern New Brunswick and spread eastward into the evening. Heavy downpours can be expected with rainfall amounts possibly exceeding 25 mm in the heaviest thunderstorms. Wind gusts may occur but are not expected to approach warning criteria. Some small hail is possible.

 

Convective Discussion

The primary concern is heavy rainfall due to the high amounts of available moisture content. Deep wind shear values are generally less than 30 knots and long lived supercells are not expected. It is possible that storms could become weakly organised into a mesoscale convective system but rainfall will remain the primary concern.

 

 

 

For Thursday, rainfall remains the primary concern, however stronger wind gusts can be expected.

 

Mel Lemmon

Convective Outlook Valid for May 27, 2020

 

Regional Impacts:

 

We are expecting thunderstorms for northern New Brunswick tomorrow afternoon and continuing into the evening.  Heavy downpours and small hail are possible, but a this time strong winds look less likely.  A more detailed discussion will be issued tomorrow.

 

Jennifer Kowal