Convective Outlook Valid for July 17th, 2019

Convective Discussion

 

There is the potential for marginally severe thunderstorms to develop for parts of Atlantic Canada as a trough of low pressure swings through the region today and overnight.

 

A low pressure system over northern Quebec will move into Labrador by this evening. A cold front extends southward from this low and will track through all of the Atlantic provinces today into tomorrow morning. The primary concern for severe weather today will be ahead of and along the cold front as it moves over parts of central Labrador and central New Brunswick this afternoon and evening.

 

For New Brunswick, there will be plenty of low level moisture with dew points already reaching 20C and precipitable water values approaching the low 40s in southern Maine and over southwestern Nova Scotia. There is an area of showers starting to push into western New Brunswick but the cloud already over the area may inhibit some daytime heating. Looking at areas father north which have had clearer conditions as well as the Caribou 12Z sounding, convective temperatures near 28C are expected to be reached. CAPE values could reach the  1000-1500 J/kg range. Wind shear is mainly unidirectional but moderate enough to sustain potentially severe lines of convection with strong wind gusts possibly reaching 90 km/hr and heavy downpours. Freezing levels are quite high at 14,000ft but given the high CAPEs there could also be the risk for small hail <2cm.

 

Convection has also begun to initiate over northern Quebec and is expected to continue into central Labrador. The precipitable water values are not as high nor is the mid level shear but the freezing levels are lower so there is the risk for small hail.

 

 

Regional Impacts

 

 

New Brunswick…Locally heavy rainfall, frequent lightning, small hail and strong wind gusts possible early this afternoon into this evening.

 

Nova Scotia and Prince Edward Island…Locally heavy rainfall and  brief wind gusts possible this afternoon and evening.

 

Labrador… Locally heavy rainfall, frequent lightning, small hail and strong wind gusts possible early this afternoon into this evening.

 

Roberta McArthur

 

 

 

 

 

Convective Outlook Valid for July 16th, 2019

Convective Discussion

 

A broad upper low over Newfoundland and eastern Labrador will slowly drift to the northeast today. A more concentrated area of convection this morning over the southeastern Grand Banks will continue off to the north and east this afternoon. With some partial clearing this morning over central and eastern Newfoundland and Labrador, convective temperatures are expected to be reached along with a bit of cooling aloft which will further destabilize the atmosphere and help to generate some convection this afternoon. CAPE values in to 200-500 J/kg range along with some weak to moderate shear and sufficient low level moisture will help to sustain convection. With freezing levels  below 10,000ft, some small hail along with locally heavy rainfall is not out of the question.

 

Meanwhile, a more potent low pressure system currently over James Bay will be advancing eastward over northern Quebec today with a trough of low pressure extending southward. A warm front will begin to affect parts of western Labrador this evening and overnight with some embedded thundershowers along it. Some embedded thundershowers are also possible early tomorrow morning for western Labrador with a very slight risk over western New Brunswick as the trough of low pressure associated with the low pressure system continues to advance eastward.

 

 

Regional Impacts

 

Labrador…

Locally heavy downpours, small hail and brief strong wind gusts are possible this afternoon over parts of central and eastern Labrador.

 

Newfoundland…

Locally heavy downpours, small hail and brief strong wind gusts are possible this afternoon over parts of central and southeastern Newfoundland.

 

Maritimes…

No convective weather expected today. However, a very slight risk of an embedded thundershower is possible early tomorrow morning over western New Brunswick with locally heavy downpours.

 

Roberta McArthur

 

 

Convective Outlook Valid for July 15th 2019

Convective Discussion

 

A chance of thunderstorms over much of Atlantic Canada.

 

There a few distinct areas for potential thunderstorm development today for the Atlantic Provinces. Overall we are looking a moderate amount of moisture with greater than 25 mm of precipitable water with weak cape (< 300 J/kg) and giving weak vertical velocities. The potential for severe weather is quite low, however, some locally heavy showers are possible giving 15 to 20mm of rain. There a small chance that Maritime thunderstorms could become organized giving a slightly higher potential for heavy downpours, due to training or clustered convection.

 

Longer lived storms are possible over eastern Newfoundland where the dynamics are more favorable with moderate shear and decent dynamics. These thunderstorms will not be surface based and this will limit the potential for severe weather there is a high amount of moisture but the storms will be moving quickly. 15 – 20mm is possible.

 

Regional Impacts

 

Labrador…

Low risk of garden variety thunderstorms though the interior regions. A higher potential area of convection will move into western Labrador this evening. Small hail < 10mm and wind gusts near 30 knots are possible.

 

Newfoundland…

Garden Variety thunderstorms with a possibility of 15-20mm should higher topped storms develop. Embedded thunderstorms east are unlikely to produce any severe weather however

 

New Brunswick and Nova Scotia …

Garden Variety thunderstorms with a possibility of 15-25 mm should organized  storms develop.

 

 

 

 

 

Mel Lemmon

Convective Outlook Valid for July 14th, 2019

Convective discussion

 

Severe thunderstorms expected across New Brunswick today and possibly over parts of Nova Scotia and western PEI. 

 

Conditions are lining up nicely today for thunderstorms, some of which could be severe.  Diffluence aloft will help enhance convective activity.  An upper trough tracking over western New Brunswick will bring PVA to the area and a bit more cooling aloft to an already rather cool upper atmosphere.  Good moisture at the lower levels will help fuel thunderstorms.  0-6 km wind shear is around 30 to 35 knots which should be enough to help maintain longer lived storm cells.  The limiting factor today is that there is a lot of mid level moisture which could inhibit some stronger cell growth.  Satellite shows partial clearing in the area so CAPE values of 500-1000 J/kg are possible with higher amounts possible over the orange threat area where the timing of the trough this afternoon coincides with max heating.  The trough will help kick these thunderstorms and it is slow moving so heavy local rainfall is the main threat.  Strong, gusty winds and small hail are also possible.  The threat weakens this evening with the setting of the sun.

 

Regional impacts

 

New Brunswick: Heavy local rainfall is the main threat but strong, gusty winds and small hail also possible.

 

PEI: Western areas -> Heavy local rainfall is the main threat but strong, gusty winds and small hail also possible.

 

Nova Scotia: heavy local rainfall possible along the valley and east.

 

Newfoundland and Labrador: non severe expected over western Labrador.

 

Barrie MacKinnon

 

Convective Outlook Valid for July 13th, 2019

Convective discussion

 

Risk of non-severe thunderstorms over New Brunswick with small possibility of a severe thunderstorm. 

 

Partially clearing skies over New Brunswick with decent low level moisture  and weak surface convergence could produce thunderstorms over the area this afternoon and early evening.  Slight cooling aloft during the afternoon with marginal shear at around 30 kts and  some upper diffluence could be enough to maintain isolated severe thunderstorms with locally heavy downpours and strong, gusty winds but this threat is marginal. 

 

Regional impacts

 

New Brunswick: Thundershowers with small risk of a severe thunderstorms producing locally heavy downpours and strong, gusty winds.

 

PEI: Risk of non-severe west.

 

Nova Scotia: No thunderstorms expected.

 

Newfoundland and Labrador: No thunderstorms expected.

 

 

Barrie MacKinnon