Convective Outlook Valid for Today, Tonight and Tomorrow

Regional Impacts

 

Today:

None

 

Tonight:

NB/NS/PEI: Isolated thundershowers giving locally heavy downpours

NL&LAB: None

 

Saturday:

NB/NS/PEI: Scattered heavy downpours, especially into the evening hours. Strong wind gusts are also possible for western NB in the evening.

NL&LAB: None

 

 

 

Convective Discussion

 

Moisture from a frontal boundary advancing across central Quebec extending into central Labrador will combine with a short wave trough over New England which will push northeastward tonight into Saturday over the Maritimes. Some of this moisture has some tropical influence stemming from the remnants of Tropical Storm Hilary as it rounded a quasi-stationary ridge of high pressure over the central US. The upper levels are warm over Labrador today and given the current could cover, afternoon temperatures may not be high enough to break the cap. There could be a slight lightning risk, but regardless, some vigorous TCUs and isolated heavy downpours are expected today.  Another ridge of high pressure over Newfoundland and southeastern Labrador will suppress any convection today.

 

As the southern trough moves into the Maritimes tonight and into Saturday, the risk of isolated thunderstorms increases. Precipitable water of 40-50mm will also spread into Nova Scotia and the Gulf of St. Lawrence. The trough over the Maritimes on Saturday will slow down as it gets blocked against the ridge east of Newfoundland. This will increase the threat of training showers or thunderstorms especially for Saturday night. Rainfall rates of 25 to 50 mm per hour are possible but there is uncertainty in the amount of lightning expected versus just tropical downpours which will make rainfall amounts highly variable. Meanwhile, the trough over central Quebec will shift southeastward into Maine tomorrow afternoon. Increasing CAPE and effective wind shear over that area could see some convection organize into lines and move into western New Brunswick by the evening.

 

Thunderstorm Outlook for Today

 

Thunderstorm Outlook for Tonight

 

Thunderstorm Outlook for Saturday

 

Forecaster: McArthur

Convective Outlook Valid for Today, Tonight and Tomorrow

Regional Impacts

NS, Cape Breton, eastern PEI: Thundershowers and showers this afternoon.

Western Labrador: Weak unorganized convection and showers tomorrow near the upper low center.

 

Convective Discussion

A frontal feature is transiting Nova Scotia now bringing showers and weak thundershowers to many areas of the province. This forcing will move offshore later today. Environmental shear has degraded quite a bit since the front cut thru NB earlier. Cape Breton (nearer the low center) still has 15-20kts of 0-6k to work with early this aft. This is where the most lightning activity is expected in the next 2hrs. Pwats are 35 in the model and 32 on actual soundings. However, cells are moving at a good pace, leading to only 5-10mm in the heaviest pockets of rain. Alerts are not likely today. Tomorrow is calmer behind the front in the less humid and cooler air mass. Labrador may see a few lightning strikes tomorrow simply due to proximity to the low feature. Severe weather is not expected.

 

Thunderstorm Outlook for Today

 

Thunderstorm Outlook for Tonight

 

Thunderstorm Outlook for Tuesday

 

Forecaster: TIRONE.

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