Convective Outlook Valid for Today and Tomorrow

Thunderstorm Outlook for Today

 

Regional Impacts

Isolated thunderstorms across parts of the Atlantic provinces today. Some of these storms could become more robust over northern NF and SE Lab.. the main threat are strong gusts possibly exceeding 70 km/h and heavier showers at a rate of 10-15mm/h.

 

Convective Discussion

At 12z the 500mb low was located over the mid-coast of Labrador with a thermal trough extending to the St. Lawrence Valley. This feature will slowly slide eastward today and along with a surface trough will become the focus for isolated pulse type thunderstorms during the afternoon especially over N portions of NF. All soundings across the region (except NS) were indicating a convective temperature ranging from 21 to 25 which should be reached fairly easily despite the limited sunshine.. with a couple of moisture axis maintaining Td’s above 16.. the result is MLCAPE between 500 to 800 J/kg. Under these conditions widespread Cu/TCU field is expected to grow during the afternoon and some of these cumuliform clouds should reach the next stage and evolve into CB’s with tops extending to 9 km, well below the tropopause which is lowering. Precipitable water analysis is showing 25-30 mm throughout the area, and as much as 35-40 over NS where stratiform cloud and embedded TCU’s are exiting.

 

 

Thunderstorm Outlook for Sunday

 

 

Convective Outlook Valid for Today and Tomorrow

Thunderstorm Outlook for Today

 

Regional Impacts

Potentially robust thunderstorms approaching severe limits over northernmost NB.. main treat is localised damaging wind gusts and some hail

Isolated elevated CB/ACB’s giving brief heavier showers over eastern Gulf of St. Lawrence, western NF/Lab

 

Convective Discussion

A frontal wave near Gaspé will continue to move NEwd giving widespread rain from eastern NS to Labrador, some elevated convection is associated with this feature and it should continue throughout the day. CLDN did indicate a few strikes over Nrn NS earlier and it continues over the Lower Quebec North Shore.

The main forecast problem today will be what happens in the wake of this system.. convective initiation is expected from the Beauce region to northern Maine.. a slightly cyclonic jet core is approaching from the Eastern Townships and is providing some extra support on the left-side exit which sits over northern NB/Chaleur region. Satellite imagery is showing the airmass transition currently occurring over northern Maine and western NB, although this new brand of air is more dry it has been historically quite buoyant. Convective temperature around 25 or 26 C, combined with dewpoints of 15 to 17 is enough to push SBCAPE above 500 or 600 J/kg. The drying in the mid-levels will certainly increase the downburst potential with modelled DCAPE values exceeding 700 J/kg. Some of the longer-lived storms could organize into a squall line but the deep layer shears are fairly high (45kt).

 

 

 

Thunderstorm Outlook for Tonight

 

Decaying thunderstorms over the Gulf of St. Lawrence region

 

 

 

Thunderstorm Outlook for Saturday

 

Surface / upper trough extending south from Labrador and a somewhat unstable airmass over Atlantic Canada

 

 

ECCC Convective Outlook Valid for THURS - THURS NIGHT - FRI

Thunderstorm Outlook valid for JULY 28^th:

 

Regional Impacts

Isolated non-severe thundershowers are possible across portions of NB today as an advancing feature approaches out of the Great Lakes basin.

 

Convective Discussion

The forcing for the weather today stems back across Ontario and Michigan. A northern branch of a jet streak is pushing into the Montreal area this afternoon, and a southern branch near New York City. Ahead of this system, the atmosphere is slowly destabilizing. Over most of the Maritimes, a weak thermal cap at 700mb still exists, and a significant dry layer from 700-500mb. This is the delineating feature of the day. A low pressure system on the Grand banks continues to produce strong thunderstorms over those marine areas today, near the surface trof. TS risk shifts further east in the overnight hours tonight with showers.

 

Thunderstorm Outlook for Day 1

 

Thunderstorm Outlook for Night 1

 

Thunderstorm Outlook valid for JULY 29^th:

 

Forecast for Friday is widespread showers/fog/drizzle/and risk of TS embedded for NS and PEI along advancing frontal feature. Sfc moisture is expected to converge well ahead of the trof’s arrival. With proper jet support, storms in central NB may become severe. Gusty winds can be expected as the storm mode seems to favour squalls/multi-cell dynamics. However, the catch is that shear may actually be too high. Values near 50kTs could rip storms apart before they can grow to mature heights. This will be monitored extensively in next 24hrs. 0-6k shear values near Montreal at 18z today will be important forecaster information.

 

Thunderstorm Outlook for Day 2

 

Forecaster: TIRONE

ECCC Convective Outlook Valid for Today, and Tomorrow

Thunderstorm Outlook valid for JULY 27^th:

 

Regional Impacts

Isolated non-severe thunderstorms along an advancing frontal feature across the Avalon early today. Additional isolated non-severe thundershowers are possible in the interior of Nfld as air mass modifies slowly.

 

Convective Discussion

The main forcing is the broadly sweeping cold front that continues to trundle eastwards. Directly behind the front remains slightly unstable so in clear skies a pop up shower is possible later this afternoon. Dynamics are not favourable for any significant hazards other than lightning. Across Labrador, there is a strong thermal cap at 700mb and it is quite dry in mi-levels. Low-cloud will also create quite a hindrance. Across the Maritimes, this 700mb cap is even stronger as can be easily deciphered on Caribou and Yarmouth’s soundings this AM. Stable, sunny, relatively dry conditions are the Wednesday forecast here. No TS risk tonight.

 

Thunderstorm Outlook for Day 1

 

Thunderstorm Outlook for Night 1

 

Thunderstorm Outlook valid for JULY 28^th:

 

Northern tier of New Brunswick, largely terrain driven, will de-stabilize slightly adding the risk of late afternoon pop-up showers and thunder. Severe hazard criteria is not expected to be met by these single-cell storms. Skinny CAPE values at best are near 300J/kg, with minimal shear in the background environment.

 

Thunderstorm Outlook for Day 2

 

Forecaster: TIRONE

Convective Outlook Valid for Today and Tomorrow

Regional Impacts

 

NL: isolated thunderstorms with locally heavy downpours and strong winds

Labrador: isolated to scattered thunderstorms with locally heavy downpours and small hail.

Southern and eastern marine regions: strong winds and heavy downpours

 

Convective Discussion

 

A low pressure system over western Labrador will slowly move eastward today and weaken, while a cold front that moved off of Nova Scotia this morning will continue eastward across the marine slope waters and north across Newfoundland today. This front is currently being maintained  over the slope waters by favourable upper dynamics the assist of a strong 250 mb jet axis over Nova Scotia and strong bulk shear of 45KT. The upper levels beyond 500 mb are warm based on the Stephenville sounding but that should degrade some with a cold trough this afternoon depending on breaks in cloud cover to increase surface based heating to further destabilize the air mass. Thunderstorms currently over southern portions of Newfoundland could continue or reignite this afternoon.

 

Some convection is expected for southern Labrador south along a elongated trough axis where the thickness ridge will move to the northeast. Some clearing this morning will also help to increase instability in the area where CAPE values are indicating near 1000J/kg. Storm are expected to be non-severe multi-cell type but with little bulk shear, there is the possibility of heavy downpours and small hail given lowering freezing levels.

 

Thunderstorm Outlook for Day 1

 

 

Thunderstorm Outlook for Day 1 Night

 

Thunderstorm Outlook for Day 2

 

Weak short wave trough moves into Newfoundland. Any surface based heating over inland areas could trigger some non-severe convection that will move to the northeast during the day. Although precipitable water will be lower than today, with values still near 30 mm and CAPE values near 500 J/kg, there could be some local heavy downpours and brief wind gusts.