Convective Outlook Valid for Today and Tomorrow

Regional Impacts

Today..

Newfoundland and New Brunswick… Slight risk of thunderstorms giving locally heavy downpours.

NS, PEI and Labrador… No thunderstorms expected

 

Tomorrow..

Labrador… Severe thunderstorms possible with heavy rain and strong wind gusts.

New Brunswick… Thunderstorms could give locally heavy downpours.

NS, PEI and NFLD… Low probability of thunderstorms.

 

 

Convective Discussion

There is a low probability of thunderstorms over the Atlantic region today a slight risk over interior parts of newfoundland and western New Brunswick. There model seems to be underdoing the surface dew points so it is possible that the cap at 700 may be overcome with daytime heating and surface convergence. Overall updrafts in thunderstorms should not be very strong with surface CAPE values generally under 500 J/kg and wind shear values not overly favourable for organised convection.

 

Tomorrow dynamics will become more enhanced wind shear and an approaching cold front that also act to enhance convection, the environment should support organised convection. There is a slight risk of severe thunderstorms over Labrador with strong gusts possible in some storms, however it is possible that could cover and rain may subdue any severe thunderstorms.  Over New Brunswick the risk will be somewhat more significant than today with more moisture and a better triggering mechanism, but weak updrafts could be the limiting factor and severe thunderstorms being only a slight possibility.

 

Thunderstorm Outlook for Day 1

 

Thunderstorm Outlook for Day 2

 

Convective Outlook Valid for Today and Tomorrow

Regional Impacts

Labrador… Slight risk of weak thunderstorms over eastern areas.

Elsewhere… No thunderstorms expected today.

 

Convective Discussion

Dynamics look somewhat favourable for the development of weak thunderstorms early this afternoon for eastern Labrador, however the conditions become less favourable later this afternoon so the conditions will not likely build through the day. If thunderstorms do develop the will likely not persist very long and be fairly quick moving. No significant rain nor severe weather is expected with these storms should they develop.

 

For tomorrow potential area of thunderstorm activity will likely expand but the likelihood is still quite low with a relatively dry airmass that will make convection difficult to get going. It is possible that some coastal convergence could be sufficient to get enough lift to initiate thunderstorms. However with weak updraft potential no significant convection is expected.

 

ML

 

Thunderstorm Outlook for Day 1

 

 

Thunderstorm Outlook for Day 2

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