Convective Outlook Valid for Today and Tomorrow

Thunderstorm Outlook for Today

 

No thunderstorms expected.

 

Regional Impacts

None.

 

Convective Discussion

The upper air pattern this morning shows two lows, one over northern Ontario and another one east of Newfoundland. In between, a ridge stretches from the Appalachians to James Bay. The airmass instability will produce fair weather cumulus over the Maritimes, and for Newfoundland the cloud cover will be more extensive giving occasional rain or drizzle.

Very little change is expected with these features during the next several days, although the ridge will attempt to build with limited success over western Quebec/Maritimes.

 

 

Thunderstorm Outlook for Wednesday

 

No thunderstorms expected.

 

Convective Outlook Valid for Today and Tomorrow

Thunderstorm Outlook for Day 1

 

Regional Impacts

Slight risk of a non-severe thunderstorm over eastern NS this afternoon, and western NF.

 

Convective Discussion

This morning upper air patterns shows an upper low over Labrador giving extensive cloud cover, also

An upper ridge extends north-south through Ontario to the southeastern US. The airmass between these two features is somewhat unstable, and this instability is found in the mid-levels. Large bands of alto-cumulus extend from southern NF to NS to PEI and then NB, and are producing scattered showers. Clear air prevails over western NS as the 500mb heights increase ahead of the upper ridge.

 

Forecast guidance is suggesting limited instability this afternoon over eastern NS and western NF, but the limiting factor will be the lack of bright sunshine over NS, and the relatively cool temperatures and dry air over NF. For this reason towering cumulus is mostly expected and the likelihood of deeper convection and the chance of any lightning is rather small.

 

 

Thunderstorm Outlook for Tuesday

No thunderstorms expected.

 

 

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Information on Threat Relationships

 

 

Threat	Rainfall Amount	Wind Gusts	Hail Diameter	Tornado Probability
Minor	< 25 mm	< 70 km/h	< 2 cm	Unlikely
Moderate	25 – 50 mm	70 –89 km/h	2 – 4 cm	Low
Severe	50– 100 mm	90– 119 km/h	4 – 6 cm	Moderate
Extreme	100 mm or more	120 km/h or greater	6.0 cm or greater	High
Risk of Thunderstorms: Thunderstorms that develop in this area will be less organized and will not likely meet warning criteria. Severe Thunderstorm Watches will not likely be required.
Slight Risk of Severe Thunderstorms: There is a low probability that weakly organized thunderstorms will develop, these thunderstorms may reach warning criteria. Severe Thunderstorm Watches may be required
Moderate Risk of Severe Thunderstorms: There is a moderate probability that organized thunderstorms will develop, thunderstorms are likely to reach warning criteria. Severe Thunderstorm Watches will likely be issued.
High Risk of Severe Thunderstorms: There is a high probability that well organized thunderstorms will develop, these thunderstorms are likely to meet or exceed warning criteria. Severe Thunderstorms Watches will be issued.

 

Convective Outlook Valid for Today and Tomorrow

Thunderstorm Outlook for Today

 

No thunderstorms expected.

 

Regional Impacts

None.

 

Convective Discussion

The upper air pattern this morning shows two lows, one over northern Ontario and another one east of Newfoundland. In between, a ridge stretches from the Appalachians to James Bay. The airmass instability will produce fair weather cumulus over the Maritimes, and for Newfoundland the cloud cover will be more extensive giving occasional rain or drizzle.

Very little change is expected with these features during the next several days, although the ridge will attempt to build with limited success over western Quebec/Maritimes.

 

 

Thunderstorm Outlook for Wednesday

 

No thunderstorms expected.

 

Convective Outlook Valid for Today and Tomorrow

Thunderstorm Outlook for Today

 

..Severe thunderstorm watch is in effect most of western New Brunswick .. Very dangerous thunderstorms are expected.

 

Scattered thunderstorms, some severe have the potential to produce heavy downpours, damaging winds, large hail and frequent lightning. There is a slight risk of a tornado.

 

Regional Impacts

New Brunswick: Initially western portions of the province will be affected by large clusters of thunderstorms advancing over the region from Maine. The threat of severe conditions is initially over central and northern portions of the province, but this area will likely spread east towards late afternoon and evening. At this point, the main threat is for heavy downpours with localised 25mm,  wind gusts in the 70 to 90 km/h range and hail of 2 cm or more. There are indications that the environment in which stronger and longer lasting storms could produce a small tornado   

 

Convective Discussion

This morning’s upper air data is showing a large upper trough advancing over the Great Lakes while an upper ridge is about to leave the Atlantic provinces. Between these two features a strong upper jet of 130 knots extends from the central Great Lakes to Labrador. Cold unstable air has reached western Quebec, and the low level thermal ridge and moisture axis now extends from the mid-Atlantic coast to the Notre Dame mountains and the lower St. Lawrence valley. At the surface, the frontal boundary extends from southeast Labrador to southern Quebec and then western NY. The front is expected to move across the Maritimes tonight with the wind finally shifting to north over NS Monday morning.

Scattered thunderstorms will form and become organised in bands during the afternoon, but the bands will be mostly parallel to the flow. But as a strong low level jet continues to inject moisture and temperatures reaches their maximum these clusters/bands will become stronger and persist long enough to become multi-cells which at that point will follow and eastward motion. With temperature/dewpoint of 30,18 CAPE values quickly jump to 1000 to 1500 J/Kg of energy which would be enough to push CB’s tops in the 10-15 km range. Some of the multi-cells storms could produce a tornado over areas near the international boarder in Madawaska county, the hodograph from Caribou is indicating some curvature in the low level winds, and the helicity values are expected to become sufficient. Further south, the strong storms will be producing very heavy rainfall of more than 25 mm, and potentially some large hail.  

 

 

Thunderstorm Outlook for Day 2

No convection expected

Convective Outlook for Today, and Tomorrow

Thunderstorm Outlook valid for Today – Sept 6^th, 2021.

 

Regional Impacts

Heavy rainfall and moderate winds are possible if discrete severe cells develop in NW areas of New Brunswick this afternoon. Risk of isolated non-severe thundershowers across rest of province and PEI.

 

Convective Discussion

With Pwats near 45mm in places, the greatest hazard today is heavy rain. As a large long wave trough sweeps through the region from ONT/QUE late this afternoon and evening, thunderstorms could be triggered in this unstable airmass. Mixed CAPE values are 500-1000J/kg, with 0-6k shear of near 40kTs. Storms are not expected to be widespread at this time as the timing will be slightly out of phase with the main LLJ. They are also not expected (at this issue time) to be more than marginally severe on the Canadian side of the border due to rainfall >25mm/hr, and possible gusts of 60km/h.

 

 

Thunderstorm Outlook valid for Tomorrow – Sept 7^th, 2021.

 

Regional Impacts

Non-severe embedded thundershowers forecast for many areas near the centre of the upper low.

 

Convective Discussion

This weather feature brings with it fall-like characteristics. The cool upper low aloft will be able to trigger a few lightning strikes within a general showery weather pattern. This is the last convective outlook issued by the ASPC Summer Severe Weather Support Desk for 2021.

 

 

Forecaster: TIRONE