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.

 

 

Convective Outlook Valid for June 10th, 2019

Convective discussion

This morning’s analysis is showing an upper cold low over the northeast coast of Newfoundland with a vast cloud deck extending southward to the south coast of the island. The upper air sounding indicates plenty of instability in the low to mid levels to produce widespread towering cumulus and showers. Limited daytime heating will produce enough energy (CAPE values between 250-500 J/kg)  to generate an isolated cumulonimbus over the areas where the southern edge of the cloud deck lies.

Regional impacts

Newfoundland and Labrador: Risk of isolated non-severe thunderstorms over Connaigre, Burin Peninsula, Clarenville and Terra Nova. Brief downpours, small hail and wind gusts 50 km/h.

New Brunswick: No thunderstorms expected.

PEI: No thunderstorms expected.

Nova Scotia: No thunderstorms expected.

Jean-Marc Couturier

Convective Outlook Valid for July 9, 2019

Convective Discussion

 

Only one area for potential TSRA is over NL and waters to the NE of the island. Upper level low and some PVA gave some elevated ISOL TSRA to parts of Newfoundland early this morning. Skies are beginning to clear somewhat, which could give way to some ISOL cells this afternoon. Modifying the 12Z tep from YJT could give between 200 and 300 CAPE, but the upper dynamics are weak. There could be slight 500 mb height falls which could lead to some cells. Freezing levels are low, so some small hail is a possibility if they develop. OTWZ nil sig wx for the rest of the region.

 

Regional Impacts

 

Newfoundland: ISOL cells are PSBL this afternoon.

 

Elsewhere: nil.

 

 

Jeremy

Convective Outlook Valid for July 8, 2019

Convective discussion

 

A couple areas show some potential for thundershowers/storms today. The first is a over the Quebec Lower North Shore. A weak trough near the surface could produce some TCU and am ISOL CB that could trickle into portions of the Great Northern Peninsula this afternoon.

 

The better area for possible storms is across SE QC this afternoon. WV imagery shows a good area of PVA east of James Bay that is advecting to the SE. Upper level troughing at 500/250 mb will give some weak divergence. There is also a decent jet at 250 upstream moving south of James Bay, and eventually curving towards the east, putting NRN NB/Gaspe in the left exit region (however the timing appears to be off just a little). Looking at KCAR and YZV, FZLVLs are below 10,000 feet, but PW is low as too the low level moisture. Shear, on the other hand, is pretty good. Expect strong gusty winds and small hail with the stronger storms this afternoon and into this evening. Given the decent dynamics, some cells will propagate over the GLFSTLAWR tonight.

 

Regional impacts

 

Newfoundland and Labrador: Risk for ISOL TSRA advecting from the Lower North Shore into the Northern Peninsula.

 

New Brunswick: SCTD non-severe storms are likely later today and into this evening associated with the PVA and upper level trough. Small hail and gusty winds are quite possible (conditions look ripe for some SVR storms in QC).

 

PEI: PSBL TSRA affecting portions of the island this evening as they move across ERN NB (good upper level forcing).

 

Nova Scotia: nil

 

 

Jeremy