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

 

Convective Outlook Valid for July 12 2019

Convective discussion

 

A frontal trough is advancing over the Maritimes. Area soundings from this morning are showing moisture extending from the low levels to 7,000-10,000 m. A southerly 40kt low-level-jet is feeding moisture, but the air mass is stable in the mid-levels limiting any thunderstorm activity to areas where Dew point temperatures are 20 degrees or more  (south of a line from northern Gulf of Maine to Lurcher to NS South Shore). The low pressure centre will move out of the Maritimes late Saturday, and at that point it will begin to impact NF.

 

Further west, over southern Quebec/Townships and Maine Highlands, the residual low-level cloud deck is starting to break up. This general area will be the focus for surface-based convection this afternoon. This is also where a surface-based moisture tongue is aligned with the 500 mb thermal ridge. Large CAPE values in excess of 1000 J/kg are indicated by the forecast guidance but are likely over-done due to the extent of the cloud cover. However, once the mid-level destabilize numerous clusters of thunderstorms could initiate. Slow eastward moving storms could produce brief heavy downpours and wind gusts. This activity could potentially reach westernmost areas of NB late this afternoon or early this evening.

 

Regional impacts

 

Newfoundland and Labrador: No thunderstorms expected.

 

New Brunswick: Risk of late-day thunderstorms brief downpours and high wind gusts possible.

 

PEI: No thunderstorms expected.

 

Nova Scotia: Isolated elevated non-severe thundershowers.

 

 

 

Convective Outlook Valid for July 11 2019

Convective discussion

 

No thunderstorms forecast today. Gradual clearing is expected over Newfoundland with the upper low departing to the southeast. Upper ridge continues to build over the Maritimes.

 

Moisture ahead of a trough extending from northern Quebec to the Great Lakes is starting to spill over Maine/NB. Rain with a risk of thunderstorms will spread across western Lab, NB, PEI and mainland NS Friday.