Convective Outlook Valid for Today and Tomorrow

Regional Impacts

For New Brunswick.. Heavy Downpours and winds gusting to 70km/hr are possible in thunderstorms.

 

For Labrador.. In addition to the heavy rain, downpours in thunderstorms and gusts to 50 km/hr are possible in thunderstorms.

 

Convective Discussion

The amount of available moisture available today is very high with precipitable water values between 40 and 50mm for most of the region. The main synoptic feature is the trough of low pressure that is moving through Labrador and eastern Quebec today. The trough should be sufficient to trigger some thunderstorms over Labrador but updrafts should remain weak enough that severe thunderstorms are unlikely, however there is still a slight possibility of severe storms and the situation should be monitored. Over New Brunswick slightly stronger updrafts will increase the potential for severe thunderstorms with mean layer capes between 1000 – 1500 j/kg. Thunderstorms are likely to move into the area this afternoon, and with low level shear values exceeding 30 knots there is some potential for organized convection. Watches may be required.

 

Thunderstorm Outlook for Day 1

 

 

Thunderstorm Outlook for Day 2

 

Convective Outlook Valid for Today and Tomorrow

Regional Impacts

Thunderstorms likely in western Labrador giving heavy downpours of rain and possible small hail. Gusty winds up to 40 knots are possible.

Non-severe thundershowers possible in western New Brunswick.

 

Convective Discussion

There is lots of low-level heat and moisture to give energy for convection in Atlantic Canada. However, cloud cover and low CAPEs are limiting factors in the Maritimes.

 

The best chance for significant convection today is in western Labrador. There is upper level dynamics with a 50-60 knot jet at the 250 level. The 0-6 km shear if about 40 knots. If there is sufficient sunshine as a trigger, the CAPE is between 1000 and 1500 J/kg in the extreme west and about 500 J/kg east of Churchill Falls.

 

Thunderstorm Outlook for Day 1

 

 

Thunderstorm Outlook for Day 2

 

Convective Outlook Valid for Today and Tomorrow

Regional Impacts

Western Labrador: risk of afternoon and evening thundershowers.

Northern New Brunswick: Risk of afternoon and evening thundershowers.

 

Convective Discussion

Isolated thundershowers are expected to form over western Labrador this afternoon in association with a trough of low pressure moving into the region from Quebec. La Grande tephi shows decent shear but somewhat of a cap in the mid-upper levels. PWAT is around 36 mm. Expected non-severe cells to develop with locally heavy rainfall and gusty winds.

 

There is also the risk of a thundershower this afternoon and evening across northern New Brunswick. KCAR tephi shows 500+ CAPE but very little shear. There is also the lack of a trigger so if cells do develop they will be slow moving. PWAT is around 35 mm so heavy downpours would be the main concern. Looking at both the YQI and YAW soundings it will be quite difficult to generate CBs in NS. However local areas of convergence could generate an isolated cell.

 

Thunderstorm Outlook for Day 1

 

Thunderstorm Outlook for Day 2

Convective Outlook Valid for Today and Tomorrow

Thunderstorm Outlook for Day 1

 

Regional Impacts

New Brunswick and Prince Edward Island: Slow moving non-severe thunderstorms developing this afternoon, with local heavy downpours and gusty winds. Near the Bay of Chaleur a slight chance for severe wind gusts, and a possibility of 2 cm hail this afternoon.

Labrador: continuing non-severe thunderstorms, tapering off this evening, with local heavy downpours and gusty winds.

 

Convective Discussion

A deep upper low over the northern Labrador Sea has two associated troughs, on extending from the low southwest to southwest of  Labrador, with some associated PVA. And a second roughly north-south trough over the eastern Gulf of St. Lawrence, again with some PVA. For the second trough there is a deep inversion, inhibiting significant convection for Newfoundland.  For Labrador the profiles are good for CAPE maxing between 500-1000 J/kg this afternoon, and reasonable PWAT possibly exceeding 25 mm, but with shear on the low side around 15-25 kts. While freezing levels are near 9500 ft at Goose Bay, the low shear argues against a separation of updraft and downdraft, possibly inhibiting hail growth. The main impacts should be heavy downpours and some brief strong gusty winds.

 

For most of New Brunswick there will be airmass convection, with decent moisture (PWAT near 30 mm and surface dewpoints in the 17-20 C range and some low level strauts burning off), good insolation after the cloud clears, shear in the 25-35 kt range, and surface based CAPEs possibly nearing 1000 J/kg this afternoon. Freezing levels in the south are too high for hail at about 15,000 ft, but in the north they are about 11,500 ft, which given the CAPE and the shear, gives a possibility for hail. In the Bay of Chaleur a weak jet and PVA may enhance conditions enough for near severe gusty winds, and a slight chance for 2 cm hail.

 

 

 

Thunderstorm Outlook for Day 2

 

 

 

Convective Outlook Valid for Today and Tomorrow

Regional Impacts

New Brunswick: mainly non-severe thundershowers this afternoon into this evening for most of the province. In the northwest marginal severe thundershowers with the highest threat for gusty winds and local heavy downpours.

Nova Scotia: non-severe thundershowers this into this evening and overnight for most of the province.

Labrador: non-severe thundershowers this afternoon into this evening, with a second batch possible overnight.

 

 

Convective Discussion

 

There is currently a deep upper ridge east of Labrador with a trough just west of it over Labrador. This will move east this afternoon into this evening, just west of the trough there will be a jet approaching  with the left exit region over northwestern New Brunswick by this evening. Finally there is a surface frontal  trough moving in from the northwest this afternoon and then moving across Nova Scotia tonight.  There’s also weak destabilisation aloft between a thermal ridge over Labrador and a weak thermal trough east of James Bay. We have some good insolation this afternoon and ample low level moisture, with 850 dew points 12-14 C, surface dew points in the 16-20 C range and PWAT in the 30-40+ mm range being maintained by a southwesterly flow. The shear is fairly low, around 20-25 kts currently.  

 

So mainly multi-cells getting organised eventually along the approaching frontal trough, some heavy downpours with gusty winds likely, and a low chance of hail with freezing levels in the 12,000 ft range. The chance for severe wind gusts may be enhance if a squall line or derecho forms this evening. The trough will also probably keep convection going well into the evening.

 

Thunderstorm outlook for day 1

 

 

 

 

Thunderstorm Outlook for Day 2