Convective Outlook Valid for Today, Tonight, and Tomorrow

Regional Impacts

 

Today:

NS/NB/PEI/NL: None.

 

Tomorrow:

NS: Embedded thunderstorms on Friday in western NS, locally heavy downpours of 30-60 mm.

NB: Scattered thunderstorms on Friday along the Fundy coast on Friday, locally heavy downpours of 30-60 mm.

PEI: Isolated thundershowers possible on Friday, locally heavy downpours of 10-20 mm.

NL: None.

 

Convective Discussion…

Not much going on today in terms of convective weather, although a few lightning strikes are possible over the Atlantic ocean, south of Sable Island.

 

The main story will be with an incoming stream of tropical moisture tomorrow. Rain and some isolated thunderstorms are forecast to move into the Maritimes by tomorrow morning along a warm front, before more organized convective activity along the cold front will move through Nova Scotia and southern New Brunswick on Friday evening into Saturday night. PWAT values will build to near 60 mm by Friday afternoon for Nova Scotia and southern New Brunswick, with ample mid-level instability upwards of 500-750 J/kg allowing for some organized convection along the cold front by Friday evening. Storms are expected to be more isolated Friday morning and afternoon, before becoming more organized on Friday evening and overnight into Saturday as the 250 and 500 mb jets approach the Maritimes. The main threat with these storms will be locally heavy downpours of 30-60 mm. Rainfall rates in excess of 25 mm/h are possible.

 

Thunderstorm Outlook for Today

 

Thunderstorm Outlook for Tonight

 

Thunderstorm Outlook for Tomorrow

 

Copp

Convective Outlook Valid for Today, Tonight, and Tomorrow

Regional Impacts

NB: Isolated thundershowers possible over NW NB this afternoon. Locally heavy downpours of 10-15 mm.

NL: Isolated thundershowers possible over western Labrador this afternoon. Locally heavy downpours of 10-15 mm.

NS & PEI: None.

 

Convective Discussion…

A few areas of interest exist today, however no severe weather is expected. The first area is associated with a small, weak embedded upper low moving through the St. Lawrence river valley. This upper low will approach NW NB this afternoon bringing the chance for a couple isolated thundershowers. While SBCAPE values of around 750 J/kg are forecast, this number may be too high as extensive cloud cover is present over the area of interest. In addition, a lack of bulk shear (10-15 kts) should prevent any severe potential. As such, the main hazard with these cells will be locally heavy downpours of 10-15 mm. 

The second area of interest is within an upper trough moving into western Labrador this afternoon. Although bulk shear values are forecast to increase to 30-40 kts this afternoon, meager CAPE values of 250-500 J/kg should keep convection non-severe, with the main risk being locally heavy downpours of 10-15 mm.

 

Thunderstorm Outlook for Today

 

 

Thunderstorm Outlook for Tonight

 

 

Thunderstorm Outlook for Tomorrow

 

 

Copp

Convective Outlook Valid for Today , Tonight and Tomorrow

Regional Impacts

Interior Newfoundland and Northern New Brunswick.. Low probability of isolated showers or thunderstorms giving 10-15mm.

Southern NS.. 25-25mm possible in embedded thunderstorms.

 

Convective Discussion

Overall instability is somewhat diminished from yesterday which doesn’t bode well for thunderstorm potential, however many areas likely received 10-15 mm yesterday which is similar to todays potential for some showers. No severe thunderstorms are expected in the general airmass thunderstorms and the main focus of interest is with the broader synoptic area to the southwest of NS. Most of the potential for high rainfall should pass just south of NS but rainfall rates of 25-35mm could just clip southwest parts of the province tonight. However this system seems to have less potential for heavy downpours when compared to some of the recent systems which tended to have significant convection and thunderstorm activity, most of that type of weather will remain further to the south. This system does have high precipitable water values approaching 50mm but the instability is not expected to be significant, these weaker updrafts are less likely to realize the full potential rainfall rates, nevertheless some uncertainty remains and this system could track slightly further north than expected.

 

Thunderstorm Outlook for Today

 

Thunderstorm Outlook for Tonight

 

Thunderstorm Outlook for Tomorrow

Convective Outlook Valid for Today , Tonight and Tomorrow

Regional Impacts

Maritimes.. Isolated thunderstorms giving 20mm rain with small hail and gusts to 50 to 70 km/hr possible.

NF.. Embedded thunderstorms with amounts 20-40 mm.

 

Convective Discussion

There are two main areas of concern once again, that associated with the low, and the unstable airmass behind that system. The system will likely impact some areas of Newfoundland with amounts in the 20 to 40mm in the heaviest areas of rain. This system is likely to be slightly weaker than is was as it passed over Nova Scotia which saw some amounts over 50mm. Over the Maritimes there are a couple factors coming together that could make this a possibly impactful day. Overall CAPE values are moderate with mixed layer values near 1000 J/kg, and sfc dew points approaching 20C. PW values are somewhat less than they have been but still sufficient for thunderstorms producing moderately heavy rainfall. In addition the dynamics are somewhat favourable with mid level wind shear values above 30 knots and some low level helicity in the vicinity of the surface trough. Later this afternoon the upper level jet could also aid in the development of severe storms over eastern NB.

 

It should be noted that although updraft are weak, there is some potential for severe weather to occur and it is unlikely albeit not impossible that waterspout or land spout tornado could occur along some coastal waters including the Northumberland Straight and Cape Breton shores.

 

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 and PEI.. Showers and thunderstorms possibly giving 25mm, small hail.

NS.. Showers and thunderstorms, possibly intensifying tonight, 15- 25mm today. Possibly exceeding 25 mm tonight.

NL.. Possible isolated thunderstorm over southwest Labrador.

 

Convective Discussion

A low pressure system will slowly make its way across the Maritimes today, passing over southern Newfoundland tonight. Instability aloft will trigger deeper convection across mainland NS today and overnight. This system is expected to move with enough speed that a prolonged period of heavy downpours are not expected, however shorter lived periods of heavier rain perhaps lasting over an hour could bring upwards of 25mm, with rainfall rates of up to 40mm per hour possible.

Over NB most of the potential for intense thunderstorms will be associated with thunderstorms that will initiate over Maine and Southern Quebec today.  Surface CAPE values over 1500 J/kg are expected across Maine and some intense storms could move over western NB later in the day. Dynamics are somewhat favourable for organised convection with approximately 35 knots of deep shear. The outlook maybe slightly conservative with the risk, however watches could be issued if organised thunderstorms form in Maine, with the expectation that some stronger cells could track over NB.

 

Thunderstorm Outlook for Today

 

 

Thunderstorm Outlook for Tonight

 

Thunderstorm Outlook for Tomorrow

 

 

Mel Lemmon