Convective Outlook Valid for Today , Tonight and Tomorrow

Regional Impacts

 

Today

NB/Labrador: Isolated of  thunderstorm.

NL/NS/PEI/Magdalen- QC:  None

Tonight

Labrador:  A chance of thunderstorms.

NB/NS/PEI/:  None.

Sunday

NB/NS/NL/Labrador:  isolated to scattered thunderstorms, 10-15 mm/h rainfall rates, small hail, wind gusts ~70 km/h.

Magdalen- QC: None.

 

Convective Discussion

Focus of thunderstorms today will be mainly across Labrador with potential vorticity advection ahead of a slow moving upper low centered over western QC.

Surface instability - MLCAPE is rather meager for the 30-40kts of bulk shear, but strong dynamic forcing and higher MUCAPE will likely produce elevated storms and lightning among showers.

South of this feature a cold front will gradually cross the St. Lawrence valley and move into northwestern NB later this evening giving a chance of thunderstorms.

Tonight dynamics will remain more or less status quo across Labrador, but the focus of lightning will be more confined to the upper low with less surface instability overnight.

 

Tomorrow convection will again be focused near the upper low across much of Labrador (to be centred near Churchill Falls), with some stacked low level voracity cold core funnel clouds are possible across western Labrador…

although unlike to be observed given the population density.

Further east instability will have a better opportunity to build during the day ahead of the cold front across southeast most NB, most of PEI, NS and western NL. MLCAPEs up to 750 J/kg will be sufficient in places with 35-45 kts of bulk shear to yield organized convection.

Lower PWATs (25-30mm) than what has been observed most of the summer to date on significant convective days should limit the rainfall rate hazard. On the other hand lower freezing levels and the drier air could yield small hail and gusty winds.

 

Thunderstorm Outlook for Today

Thunderstorm Outlook for Tonight

Thunderstorm Outlook for Tomorrow

 

Brennan

Convective Outlook Valid for Today, Tonight and Tomorrow

Regional Impacts

NL… Slight risk for some isolated thundershowers in parts of Labrador today and tomorrow. Heavy downpours possible.

NS/NB/PEI… None.

 

Convective Discussion…

As a ridge of high pressure builds into the Maritimes today, any lightning activity will be isolated to parts of Labrador, under the upper trough. Meager MLCAPE and weak bulk shear values lead to a low risk for any thunderstorm development today, however brief heavy downpours are possible with any storms that do develop.

Tomorrow, a cut-off low will swing into western Labrador, bringing a slightly greater chance for thunderstorms. More favourable dynamics are in place, but once again meager instability may hinder more organized storms from developing. Some isolated torrential downpours are possible in thunderstorms tomorrow, however this risk remains low.

 

Thunderstorm Outlook for Today

Thunderstorm Outlook for Tonight

Thunderstorm Outlook for Tomorrow

 

Copp

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