Convective Outlook Valid for Today and Tomorrow

Regional Impacts:

 

Today

NB/NS/PEI/NL/Labrador: A chance of non-severe thundershowers.

 

Tonight

Labrador: A chance of non-severe thundershowers.

NS/NB/PEI/NL: None

 

Sunday

NB/Labrador: A chance of non-severe thundershowers  

NS/PEI/NL: None

 

Convective Discussion:

 

A warm and humid air mass prevails throughout the region. A 30kt southwesterly LLJ and a supportive vorticity centre is giving thundershowers over areas of Newfoundland today. Generally MLCAPE values range from 500-1000J/kg however a clear lack of a trigger or a supportive upper jet should allow the main threat to be downpours. PWAT values near 40 mm maintain the downpour threat that has been in existence for the last few days in areas where the cells are training or slow moving.

 

Thunderstorm outlook for today:

 

Thunderstorm Outlook for Tonight

 

Thunderstorm Outlook for Tomorrow

Convective Outlook Valid for Today and Tomorrow

Regional Impacts

NB: Isolated non-severe thunderstorms possible over the northern half of NB this afternoon, rainfall up to 10 mm.

NS & PEI: A few embedded thunderstorms with locally heavy downpours of 15 mm,  possibly up to 30 mm over eastern NS.

NL: Isolated thunderstorms over southeastern Labrador, and Northern peninsula, and possibly over central portions of the island,  rainfall up to 10 mm.

 

Convective Discussion…

Warm and humid air mass prevails throughout the region, with the exception of Labrador where dewpoint temperatures are less than 15. The main area of interest today is along a 30kt southwesterly LLJ which is pumping moisture into an axis running from south of Halifax through eastern regions of mainland NS, and then to the northeastward to the Northern peninsula of NF. A deep instability layer above 850mb with tops extending to 9-10 km is analysed on the Shearwater sounding, generally MUCAPE values range from 500-1000J/kg. The LLJ and the presence of areas of vertical velocities at 700mb will likely enhance rainfall processes over the previously mentioned area today. A 75kt southwesterly upper jet also will also support some of the convective cells that forms. Over southern NB and western-most regions of NS, warming is expected in the mid-levels today which will prevent low level instability from extending vertically.

 

Thunderstorm Outlook for Today

 

Thunderstorm Outlook for Tonight

 

Thunderstorm Outlook for Tomorrow

 

Convective Outlook Valid for Today, Tonight, and Tomorrow

Regional Impacts

NB: Organized thunderstorms possible over NW NB this afternoon, 0 to 1 cm hail and locally heavy rain of 20 to 40 mm possible.

NS & PEI: Isolated thundershowers with locally heavy downpours of 10 to 15 mm.

NL: Slight chance for an embedded thundershower over southern Labrador, locally heavy downpours are the main risk.

 

Convective Discussion…

The main area of interest today is along the NB/Maine border. A shortwave currently over western Maine will slowly push east, which will provide ample lift for convective activity this afternoon. A 100 kt southerly 250mb jet sitting over western NB will aid in the development of organized thunderstorms, pending the clearing of low level cloud over northwestern NB. Models have been under-forecasting cloud cover here, and if things do not clear out this afternoon, thunderstorm activity will be limited. If cloud does begin to clear this afternoon, surface based CAPE values may exceed 1000 J/kg; this in combination with 20-30 kts of 0-6 km shear will support the development of organized thunderstorms. The main threats would be 0 to 1 cm hail, locally heavy downpours of 20 to 40 mm, and convective gusts up to 70 km/h. The risk here will be entirely dependant on whether or not the low level cloud clears out enough to allow surface temperatures to rise into the low to mid twenties, allowing for surface based convection to initiate.

 

A few lightning strikes are also possible over parts of NS and PEI today, as a 55 kt 500mb jet sits over the region. This will allow for some isolated embedded convection, with locally heavy downpours being the main threat. This risk will remain overnight before the jet begins to push east tomorrow morning.

 

Thunderstorm Outlook for Today

 

Thunderstorm Outlook for Tonight

 

Thunderstorm Outlook for Tomorrow

Copp

Convective Outlook Valid for Today, Tonight, and Tomorrow

Regional Impacts

NS and NB: Embedded thundershowers today with locally heavy rain, 20 to 40 mm along Atlantic shores of NS and south-central NB.

NL: Isolated embedded thundershowers possible over central Labrador this afternoon, local rainfall amounts 15 to 25 mm.

PEI: Isolated thundershowers possible this afternoon, locally heavy rain of 10 to 15 mm.

 

Convective Discussion…

As an area of high pressure sits east of Newfoundland, a quasi-stationary trough extends from the US east coast through the St. Lawrence river valley, and into northern Labrador. This pattern in combination with a 40 kt low level jet is supplying ample moisture over the next few days across Atlantic Canada. MUCAPE values of 500 to 750 J/kg and 40 kts of 0-6 km shear will allow for some sustained embedded convection today along Atlantic shores of NS, as well as in south-central NB. The main threat with these storms will be locally heavy rainfall, with 20 to 40 mm possible in areas of convection. This threat will persist overnight along the south shore of NS.

 

A weak shortwave will move into southern Labrador this afternoon, providing ample lift for some organized convection between Labrador City and Goose Bay with 40 kts of 0-6 km shear. The main threat with these thundershowers will be locally heavy rain, with 15 to 25 mm possible.

 

Tomorrow, a shortwave will approach northern NB from the west. This, in combination with 20-30 kts of 0-6 km shear and surface-based CAPE values of 1000-1250 J/kg will allow for a line of organized convection to form over northern Maine. Main threats with these thunderstorms will be 0 to 1 cm hail, and locally heavy rain of 20 to 40 mm. There is still some model disagreement on the speed at which this shortwave will approach NB, so the risk area may need to be extended to the southeast as models gain a better handle on the system.

 

Thunderstorm Outlook for Today

 

Thunderstorm Outlook for Tonight

 

Thunderstorm Outlook for Tomorrow

 

Copp

Convective Outlook Valid for Today and Tomorrow

Regional Impacts

NB and NS: Risk of an embedded thunderstorm, bands of heavier showers giving 10 to 20 mm today

Lab: occasional rain spreading over western Lab, amounts less than 10mm today

Rest of NF and PEI: none

 

Convective Discussion

Surface low over south-central Ontario with inverted trough extending towards northern Quebec. Surface warm front extends from the Low to southern Quebec-southern Maine-South shore of NS. A high pressure area now sits east of NF. The biggest change in the past 24 hours is the northward and eastward propagation of the increasingly moist air mass that has been sitting over the Maritimes. A strong southerly low-level-jet 30kt will maintain the supply of moisture with calculated precip. water from the upper air soundings indicating values in the 35-45 mm range.. this trend is expected to spread into NF&Lab today and tonight. The cloud deck mostly consists of overcast layers from near or at the surface extending up above 9-10km. While the extensive cloud cover will make it difficult to get enough surface heating to initiate convection, in their current state, soundings from YQI and YAW show plenty of instability (MUCAPE of 300 or 400 J/Kg) for embedded CB’s with tops up to 7-9 km. Deep layer shear values are a solid 35kt which might help sustain the convection over the Gulf of Maine until the clusters reaches the Fundy region later today. A few public forecast regions have been identified with the greatest potential for high rainfall rates/amounts during the next 48H, some of the forecast guidance is indicating amounts as high as ~100 mm.. but an average of the main deterministic models indicates a medium probability of 40 to 60. Regardless of the numbers, the maximum amounts will be driven by convective bands and it would be fairly difficult to identify which location/county will receive the most.

 

 

 

Thunderstorm Outlook for Today

 

 

Thunderstorm Outlook for Tonight

 

 

Thunderstorm Outlook for Wednesday