Convective Outlook Valid for Today and Tomorrow

Regional Impacts

Local rainfall amounts of 20 mm for central sections of NF today.

 

Convective Discussion

 

This morning the low at 500mb/surface are located over Cabot strait and continue to move eastward passing east of the Avalon tonight. Ahead of these features, several curving bands of rain are detected by NF radar. Satellite shows colder cloud tops along the south coast and over central regions, but the Stephenville sounding shows that the instability is limiting vertical development to embedded ACC which could still give higher rainfall rates periodically during the day. There has not been any lightning activity detected by CLDN or GLM over the region since last night and none is anticipated for the rest of the day. The low feature will exit NF after midnight.

 

For Tuesday, the RDPS is indicating an area of potential instability west of Nain, but this activity will likely be limited to the 850-700mb level due to a mid-level inversion.. Otherwise dry conditions are expected Tuesday and Wednesday as an upper ridge builds over Atlantic Canada.  

 

*Note that National Monitoring has an open ticket on the lightning sensor at Wabush Lake. They are unable to access the equipment since yesterday (June 18)

 

Thunderstorm Outlook for Today

 

Convective Outlook Valid for Today and Tomorrow

Regional Impacts

Locally heavy downpours giving 15-25 mm for areas affected by thunderstorms.

 

Convective Discussion

 

After a bout of intense lightning activity overnight things are expected to be somewhat less intense today. Some thunderstorms will continue over Nova Scotia and possibly into southern New Brunswick and PEI later in the day. Updraft potential is not expected to be very high however some favourable dynamics are like to organise the convection into multicell clusters, with some upper support before the upper jet exits the region later today. Locally 15-25mm is expected, slightly less than the rainfall rates than the ~25mm/hr that we saw overnight. Some small hail is possible with the lowering freezing levels but it should well below warning level.

 

Thunderstorm Outlook for Day 1

 

Thunderstorm Outlook for Day 2

 

Mel Lemmon

Convective Outlook Valid for Today and Tomorrow

Regional Impacts

 

Nova Scotia and Southeastern New Brunswick… Locally heavier embedded rainfall, frequent lightning possible tonight.

 

Convective Discussion

 

A vertically stacked low pressure system will gradually make its way across Nova Scotia over the next couple of days, bringing unstable air along with it.  Aloft a weak cyclonic jet ahead of the upper low could be a contributing factor to support some vertical motion over the next couple of days but otherwise the thermodynamics are not overly favourable for development of severe thunderstorms. There will be very little surface based CAPE with this system with thunderstorm imitating above 850 mb for most of the period. Most unstable CAPE in general will remain below 500 J/kg, with low to moderate deep shear. Precipitable water values will be in the 30-40mm, this coupled with potential updrafts could lead to locally heavier rainfall rates approaching 25mm/hr.

 

Thunderstorm Outlook for Day 1

 

 

Thunderstorm Outlook for Day 2

 

 

Mel Lemmon

Convective Outlook Valid for Today and Tomorrow

Regional Impacts

 

Maritimes: Scattered thunderstorms today, with some discrete cells possibly reaching severe limits for moderate hail, and rain. (Funnel clouds are possible).

NL: Embedded thundershowers within a greater area of showers/rain.

 

Convective Discussion

 

Dynamics at play over Newfoundland today include a trough line generating instability over the island. Precip is likely to be in the rates of 5-10mm, and these cells are moving quite quickly to the north. Winds gusts locally may reach near 60 to 70 km/h. Both CAPE and Shear are much more favourable for thunderstorm development over portions of the Maritimes. In SW NS, ML CAPE of 500-800 is present, and convective trigger temps will easily be surpassed with the cloud holes that are developing this morning. In central and SE NB, MLCAPE is 760-1000 J/kg, with Effective Shear of 25-30kts in the lower levels. Lapse rates of -6 were analyzed this morning, as the upper low feature continues to destabilize this air mass. SFC dew points of 12-16 are observed as the morning fog burns off. This upper trof is very important to watch as it sweeps through the AOR this afternoon. Helicity values (similar to those near Hants county yesterday) will be present near Moncton and Shediac late this afternoon. As such, there is a *non-zero chance of a funnel cloud or non-supercell tornado* in this area. However – the chance is very low, and it is not included on the graphical depiction because of the low likelihood and low severity. Watches will be used to alert the public if required. Another advancing trough will bring a line of convection up from the south Saturday evening, over the marine areas and affecting NS’s south and Acadian shores.

 

Thunderstorm Outlook for TODAY

 

Thunderstorm Outlook for TONIGHT

 

 

Thunderstorm Outlook for SATURDAY

 

 

Forecaster: J. TIRONE/ASPC

Convective Outlook Valid for Today and Tomorrow

Regional Impacts

NB, NS, and PEI: Scattered thunderstorms today and tomorrow, some of the stronger storms could produce heavy downpours 10 to 20 mm, and possibly higher.

NL: None, deeper instability limited to the west of a line from Fermont/Lab City to Lake Eon to Chevery.

 

Convective Discussion…

A surface and upper low over Maine will move east today, reaching the Gulf of St. Lawrence tonight. The upper low will then weaken and open up over Labrador. Moisture associated with these features will continue to produce widespread showers with embedded thundershowers with forecast guidance suggesting CAPE of 250 J/kg or less, however as the day progresses, insolation from breaks in the cloud cover and the cold temperatures aloft will increase the depth of the instability with surface-based CAPE values expected to reach 500 J/kg. Under these conditions this deeper convection will produce locally heavier showers 10-20 mm, some small hail < 1cm, and wind gusts to around 60 km/h. Generally the shear is weak, except over NS where current soundings indicate 0-6km values above 20 kt which might produce weakly organised convective cells.

 

A series of weak low pressure systems will extend from NY state to Atlantic Canada on Friday. Low level moisture/fog will give way to isolated thunderstorms during the day.

 

 

Thunderstorm Outlook for Today

 

Thunderstorm Outlook for Tonight

 

 

Thunderstorm Outlook for Friday