Convective Outlook Valid for Today , Tonight and Tomorrow

Regional Impacts…

 

Today

Labrador:  Chance of afternoon thunderstorms southeast.

NB/NS/PEI/NL:  None.

 

Tonight

NB/NS/PEI/NL/ Labrador:  None.

 

Thursday

NB/PEI/Labrador:  A chance of afternoon/evening thunderstorms.

NS/NL: None.

 

Convective Discussion…

A weak trough of low pressure tracking across Labrador will give a chance of non-severe afternoon thundershowers over sections of southeast Labrador today. On Thursday, some embedded thundershowers are possible across portions of New Brunswick and Prince Edward Island. If clearing occurs late in the day over extreme northwest New Brunswick then some surface based activity is possible. Another trough of low pressure tracking across northern Labrador will give a chance of non-severe afternoon thundershowers over sections of central and northern Labrador Thursday afternoon.

 

 

Thunderstorm Outlook for Today

 

Thunderstorm Outlook for Tonight

 

Thunderstorm Outlook for Tomorrow

Convective Outlook Valid for Today , Tonight and Tomorrow

Regional Impacts

 

Today

Labrador: 70-90 km/h gusts, 2-3 cm hail, risk of cold core funnels.

NS: 70-90 km/h gusts, 15-25 mm/h rainfall rates, ~1cm hail

NL/PEI : isolated to scattered thunderstorms

NB/Magdalen- QC:  None

Tonight

Labrador:  A chance of thunderstorms.

NB/NS/NL/Magdalen- QC: None.

Monday

Labrador:  chance of thunderstorms.

NB/NS/NL/Magdalen- QC: None.

 

Convective Discussion

A 3-4 SD vertically stacked cold upper low continues to slowly move east across Labrador. Near the centre of the upper low, an area of minimal vertical wind shear will yield the potential for widespread cold core funnel clouds across western Labrador with plenty of vertically slacked low level vorticity. Southeastern sections of Labrador will benefit from strong potential vorticity advection from the upstream deep upper low. This in combination with steeper lapse rates, lower freezing levels, linear shear profiles of 35-45 kts and daytime instability up to 1500 J/kg of SBCAPE will yield the primary hazard of significant hail in organized convection. The steeper low level lapse rates and cooler environment also presents a strong wind gust secondary hazard. Small hail is also possible across western NL, but weaker instability through the HGZ should keep this smaller in nature despite lower freezing levels.

 

On going clearing ahead of a weakening cold front across NS may also result in severe weather later this afternoon. Initiation is expected to be aided by coastal convergence at the surface with a sea breeze front in addition to the weakening cold front. Higher freezing levels and instability through the hail growth zone should keep any hail small in nature, however strong wind gusts may occur with significantly developed convection. PWATs appear to be slightly higher as well across NS near 35 mm, which would also present a near severe rainfall rate threat with organized convection.  

 

Tonight a chance of thunderstorms will be limited to the stronger dynamics near the upper low tonight as day time instability abates. Tomorrow a similar situation is expected

across south central Labrador, with any storms being dynamically driven given limited expected thermodynamics (MLCAPEs ~300-400 J/kg).

 

Thunderstorm Outlook for Today

Thunderstorm Outlook for Tonight

 

Thunderstorm Outlook for Tomorrow

 

Brennan

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