Convective Outlook Valid for Today , Tonight and Tomorrow

Regional Impacts

 

Today

Western Lab: isolated thunderstorms possible this afternoon and evening.

Eastern NL: elevated embedded thundershowers possible giving locally torrential downpours.

 

Tonight

NB/PEI: isolated thundershowers possible overnight and into early Monday morning.

 

Convective Discussion

 

A couple weak features will give the chance of thunderstorms today – one being the current trough slowly crossing NL and the other being the upper low/trough near western Lab. The 12Z tephi out of YYT has close top 50 mm PWAT indicating a super moist atmosphere, so any TCU or CBs that develop will drop locally torrential rainfall amounts in a short period of time. That would be the only concern to speak of today. There has been a little history of isolated lightning with this trough so one would expect the odd lightning strike anytime this afternoon and into this evening. The second feature near western Lab also has shown a little history of TS development, so isolated cells are possible especially this afternoon and early evening. We are getting late in the season for surface-based convection up at those latitudes but there is still enough solar insolation to support them.

 

Lastly the guidance has been hinting at possible convection in NB and perhaps PEI overnight tonight and early Monday associated with a short wave trough/surface cold front. Could be an isolated cell over NS Monday afternoon that is not currently depicted in the 36 hour prog.

 

Thunderstorm Outlook for Today

 

Thunderstorm Outlook for Tonight

 

Thunderstorm Outlook for Tomorrow

Jeremy

Convective Outlook Valid for Today , Tonight and Tomorrow

Regional Impacts

NB… Showers or thunderstorms with small hail giving 15-20 mm. funnel clouds possible in vicinity of coastlines.

NF… embedded thundershowers giving 25mm.

 

Convective Discussion

Well another day another passing trough of low pressure that will bring heavier embedded thunderstorms and showers to some areas. Areas in Nova Scotia saw up to 75mm of rain, despite the fact that the thunderstorm activity was somewhat less than past events. Rainfall rates could still be around 25mm per hour, with a slight chance of a thunderstorm. Behind this feature and ahead of the upper low, New Brunswick could see some thunderstorms or deeper showers giving heavy rainfall rates. These will likely be quite isolated in nature but there may be some enhancement over north areas. Cape values are generally low, less than 500 J/kg of mixed Cape and low freezing levels, giving small hail likely around 1 cm. There is some risk of funnel cloud formation near shorelines where some extra surface convergence is present, it is possible that some rotation could be very close to the surface. It should be noted that weak updrafts are not likely to produce severe or strong surface rotation or winds. No alerts are expected but it is possible that alerts could be issued if cells come in stronger 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

 

Today:

NS: Embedded thunderstorms this evening west of Halifax, heavy downpours of 30-60 mm.

NB: Risk of embedded thunderstorms along the Fundy coast this evening, heavy downpours of 30-60 mm. Chance for an isolated thunderstorm in extreme NW NB this evening, locally heavy downpours of 25-50 mm.

PEI: Chance for embedded thundershowers to move into PEI before midnight, locally heavy downpours of 10-15 mm.

NL: None.

 

Tonight:

NS: Embedded thunderstorms along the Atlantic coast between Halifax and Cape Breton Island overnight, heavy downpours of 25-50 mm.

NB & PEI: Slight chance for embedded thundershowers overnight, locally heavy downpours of 10-15 mm.

NL: None.

 

Convective Discussion…

An upper low over southern Ontario this morning will slowly move east, interacting with a stream of tropical moisture off the eastern seaboard today. Embedded thunderstorms have been observed over New England and to the southeast of Cape Cod this morning. These storms will move northeast today, reaching the southwestern shores of the Maritimes by this evening. Ample jet support wrapping around the aforementioned upper low will aid in sustaining this convection as it approaches the Maritimes, and is expected to persist along the Atlantic coast of NS tonight. The 12Z Yarmouth sounding this morning indicated precipitable water values of 50 mm, with this number expected to build to 60-65 mm over much of NS this evening. With a high volume of moisture in the atmosphere, any significant instability could lead to torrential downpours in the area of interest. Currently, MUCAPE values are forecast to build upwards of 500-750 J/kg by this evening along the Atlantic coast. With these numbers in mind, torrential downpours will be the main threat, with 30-60 mm and rainfall rates upwards of 25 mm/h possible. These amounts may end up being higher if the mid-level instability increases, depending on how much upper and mid-level cold air wraps around the upper low over Ontario, so this will be something to closely monitor.

 

A second smaller area of interest closer to the upper low exists in extreme NW NB. Here, an isolated thunderstorm may develop over Maine where stronger dynamics are present, however significant instability may be a challenge to reach. Thus, there is only a slight risk for severe weather, with the main threat being locally heavy downpours of 25-50 mm.

 

Thunderstorm Outlook for Today

 

Thunderstorm Outlook for Tonight

 

Thunderstorm Outlook for Tomorrow

 

Copp

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