Convective Outlook Valid for Today, Tonight and Tomorrow

Regional Impacts

NS… Scattered thunderstorms today across southern Nova Scotia, with torrential downpours of 30 to 50 mm/h.

NB… Isolated thunderstorms possible this afternoon across northwestern New Brunswick with strong wind gusts and heavy downpours of 15 to 25 mm/h.

PEI… Isolated thunderstorm possible early this afternoon with heavy downpours of 15 to 25 mm/h.

NL… Isolated thunderstorms possible this afternoon across southern Labrador with heavy downpours of 15 to 25 mm/h.

 

Convective Discussion…

A cold front sweeping across the Maritimes is triggering thunderstorms across the region this morning, with this expected to continue into tonight as the front moves east. PWATs of 52 mm from the 12Z Yarmouth sounding indicate an extremely moist atmosphere ahead of the main front. An area of tropical moisture sitting off Cape Hatteras is being pumped north into the Gulf of Maine by a strong ridge over the southern Atlantic. A line of thunderstorms has developed along this stream of moisture this morning, and have already begun moving onshore into southwestern Nova Scotia. These storms will likely continue to move north and east as the day progresses, reaching the eastern shores of Nova Scotia tonight. Current guidance suggest the heaviest convection will remain along the Atlantic coast, however it is possible for some thunderstorms to continue further inland. Due to the high amount of moisture available today, the main threats with these storms will be torrential downpours of 25 to 50 mm/h, which will continue overnight along the Eastern Shore. Localized flooding will be possible with heavy showers and thunderstorms today.

In addition, some isolated thunderstorms are also possible over parts of New Brunswick and southern Labrador this afternoon closer to the upper low. Clearing skies here will allow SBCAPE to build up over 1000 J/kg by this afternoon and bulk shear is forecast to be extremely high but linear; upwards of 60 kts. Due to the high shear, it is possible that storms may struggle to get organized, however strong wind gusts and heavy rain are possible with any storms that do fire.

 

Thunderstorm Outlook for Today

Thunderstorm Outlook for Tonight

Thunderstorm Outlook for Tomorrow

Copp

Convective Outlook Valid for Today , Tonight and Tomorrow

Regional Impacts

Newfoundland… some thunderstorms giving locally 15 to 25mm possible.

NB… slight chance of thunderstorms today with low possibility of 15-25 mm rain and some strong winds. Overnight and tomorrow morning an enhance risk of heavy nocturnal rainfall for southern areas.

NS and PEI… Slight chance of TS today. Overnight and tomorrow morning an enhance risk of heavy nocturnal rainfall in vicinity of Bay of Fundy into central PEI. Could impact northern NS and the Annapolis Valley.

Convective Discussion

The subtleties of nailing down these convective outlooks continues to be a challenge as we move into the next couple of days. The high moisture content and unstable airmass will continue to linger until Friday when things begin to dry out somewhat. Most of the significant weather events over eastern Canada have been largely linked to the series of short-wave troughs that have been moving through, the system that impacted southern Ontario yesterday fortunately weakened as it approached the Maritimes overnight.  However, we are looking at a potential event overnight and early tomorrow as the large-scale upper trough begins to push east. We should be able to watch how the convection develops today over northeastern US, this should give us a clue to weather we are impacted by a nocturnal MCS or not however any messaging in term of alerts would likely be a very short notice if anything is warranted at all. It should be noted that high-res models like the HRRR have been somewhat useful in forecasting these nocturnal events, perhaps not in the sense that the locations are completely accurate, but the general occurrences have been pretty good.  The Day 1 night Outlook covers a large area yellow and represents the most probable location for intense storms but there is still some uncertainty in the exact location

For today newfoundland and Labrador will continue with there relatively active thunderstorm activity with some isolated and possibly more organized cells in NFLD, updrafts aren’t very strong but the moderate shear and high moisture content bring some concern for heavier rainfall amounts than individual cells might suggest. Keeping a close eye on radar rainfall estimates is likely the best approach. 

It seems likely that most of NB will have slight capping aloft which should initially make deeper cells unlikely until later today. Givin the decent shear, likely above 40 knots of bulk shear (0-6 km) and dry mid-levels some isolated severe storms are possible should things initiate sooner than expected.

Thunderstorm Outlook for Today

Thunderstorm Outlook for Tonight

Thunderstorm Outlook for Tomorrow

 

Mel Lemmon

Convective Outlook Valid for Today , Tonight and Tomorrow

Regional Impacts

NB.. Heavy downpours possible in thunderstorm, slight chance of significant wind gusts.

NS and PEI... Potential for thunderstorms to develop this afternoon with heavy downpours.

NFLD and Labrador... Isolated thunderstorms could produce local downpours.

Discussion

This will be short discussion as thunderstorms are already moving through some areas. This line below may serve as the trigger for severe weather later this afternoon for NB. There is some potential for a weak mesoscale system to develop which could lead to heavy rain and some stronger wind gusts. As of right now a lack of solar insolation could also somewhat limit this potential, therefor the worst areas for severe weather treat will likely be further east.

In Nova Scotia and into PEI where surface temperatures are going to be slightly warmer and the total precipitable water values are around 50mm there will be better chance for local flooding should thunderstorms develop.

NFLD will likely continue to get similar thunderstorms to what they have had over the last few days with isolated or somewhat loosely organized areas giving up to 25mm or so of rain.

Today

Tonight

Tomorrow

Mel Lemmon

Convective Outlook Valid for Today , Tonight and Tomorrow

Regional Impacts

Newfoundland… Some isolated thunderstorms today and nocturnal thunderstorms tonight. Up to 25mm in thunderstorms possible.

 

Labrador… Isolated thunderstorms today and tomorrow, locally heavy downpours possible.

 

New Brunswick… Slight risk of isolated thunderstorms today. Some thunderstorms tomorrow with amounts possibly reaching 50mm/hr rainfall rates for southeastern areas. Northwestern areas 25mm possible in thunderstorms.

 

PEI… Possible thunderstorms tomorrow with rainfall rates possibly reaching 50mm/hr.

 

Nova Scotia.. Possible thunderstorms tomorrow with rainfall rates possibly reaching 50mm/hr most likely for central and northern areas.

 

Convective Discussion

A few interesting features will contribute to the convective potential over the next couple of days, first and foremost the high moisture content covering much of the region, which will aid in heavy downpours in even weaker thunderstorms. For today the shear isn’t conducive to organised convection and severe weather with a predominately zonal flow, in general any thunderstorms that do develop should be fairly isolated. However a trough/weak frontal zone currently over Anticosti will impact Newfoundland tonight possibly causing Thunderstorm activity to linger overnight.

 

A shortwave tough approaching from southern Ontario has the potential to trigger heavy downpours tomorrow. The total precipitable water (TPW) values are likely to be near 50mm and the airmass will be quite unstable ahead of the shortwave trough. If thunderstorms develop heavy rainfall can be expected, and alerts may be required, although not all models agree with this assessment. However unlike some of the recent convective rainfall events this feature should progress through more quickly, but multiple cells could still impact some areas.

 

The dynamics will continue to improve into the middle of the week as the upper trough gradually approaches from the west, but the low level moisture may be somewhat depleted leading to potentially weaker updraft potential.

 

Thunderstorm Outlook for Today

 

Thunderstorm Outlook for Tonight

 

Thunderstorm Outlook for Tomorrow

 

Mel Lemmon

Convective Outlook Valid for Today , Tonight and Tomorrow

Regional Impacts

Today.. Isolated Thunderstorms giving some locally heavy downpours up to 25 mm, some stronger gusts possible.

 

Convective Discussion

The most favourable dynamics have shifted to lie just of the coast of Nova Scotia, in terms of upper support for prolonged and organized convection that will continue to diminish through the day. However there is still a decent amount of moisture in the atmosphere and surface dew point temperature will be in the high teens or even 20 C in some areas. Thunderstorms started early over eastern areas where a week trough was able to help trigger some smaller thunderstorms. As daytime heating continues there will be a slight chance of thunderstorms developing over areas including SW Newfoundland and NW New Brunswick. Moderate Cape could potentially lead to some heavier downpours and gusty winds. Wind gusts are not expected to be at warning level but if deeper thunderstorms develop it there may be a slight risk.

 

Dynamics will become more significant over the next couple days with a chance of organised convection on Tuesday. More details can be expected as we move into the shorter range.

 

Thunderstorm Outlook for Today

 

Thunderstorm Outlook for Tonight

 

Thunderstorm Outlook for Tomorrow

 

Mel Lemmon