Convective Outlook Valid for Today , Tonight and Tomorrow

Regional Impacts

 

Today:

NS: Widespread rain in the east with localised heavier showers with amounts up to 25 mm / isolated thunderstorms

NB: Slight risk of a thunderstorm SE

NL&LAB: Risk of a thunderstorm / widespread rain with embedded heavier showers along the southwest regions with amounts up to 50 mm

 

Tonight:

NB NS PEI: None

NL&LAB: Slight risk of a thunderstorm south coast

 

Sunday:

NB NS PEI: None

NL&LAB: Risk of thunderstorms eastern portions of the island

 

 

 

Convective Discussion

 

An upper low north of Sept-Iles with a trough extending to NB / Gulf of Maine will slowly swing eastward today and tonight,  eventually leaving NF coast Monday. At the surface, the low pressure is located NE of Anticosti island with a cold front extending to southern Maine. Elevated moisture content continues to be supplied  in the warm sector by a 40kt southerly LLJ, precipitable water values in the axis Sable-Cabot Strait-NF west coast are exceeding 45mm. YJT tephi from this morning indicates enough instability to support ACC/ACB with tops between 7-8 km. Over the Maritimes the airmass is beginning to dry but the instability and humidity is just enough to support one or two surface-based CB’s, based on the Shearwater modified tephi (24,18) Cape values could reach 300-400 J/kg LI -2 accompanied by strong deep layer shear 0f 30-40kt. A cyclonic 90kt upper jet stretching from southern NE to NF would also provide some extra forcing over NS.

 

Thunderstorm Outlook for Today

 

 

Thunderstorm Outlook for Tonight

 

 

 

Thunderstorm Outlook for Sunday

 

 

 

 

Convective Outlook Valid for Today, Tonight and Tomorrow

Regional Impacts

 

Today:

NS&PEI: Scattered heavy downpours. Strong wind gusts are also possible for western NB in the evening.

NB: Isolated heavy downpours and strong wind gusts for western NB in the evening.

NL&LAB: None

 

Tonight:

NS&PEI: Scattered thundershowers giving locally heavy downpours.

NB: None

NL&LAB: Isolated heavy downpours for southwestern Newfoundland.

 

Sunday:

NS: Isolated heavy downpours over eastern areas.

NL&LAB: Isolated heavy downpours for southern Newfoundland.

 

 

Convective Discussion

 

A trough of low pressure extends over the Maritimes northeastward into central Labrador giving heavy downpours at times. The trough will slow down today as it gets blocked against a ridge of high pressure east of Newfoundland and a building ridge over central Quebec. This will increase the threat of training showers or thunderstorms this afternoon and overnight, enhanced by a 40KT LLJ which will be slowly tracking along the Atlantic coast of NS. Rainfall rates of 25 to 50 mm per hour are possible as precipitable water increases over the Maritimes but there is uncertainty in the amount of lightning expected versus just tropical downpours, which will make rainfall amounts highly variable. Areas of southern New Brunswick, aided by topographic enhancement in strong southerly winds, have already seen total rainfall amounts of 50 to 90 mm overnight and this morning. Meanwhile, a trough over southern Quebec will shift southeastward into Maine and western New Brunswick this afternoon and evening. Although there is increasingly favourable dynamics in that area under the left exit of the 250mb jet and effective shear near 30KT, CAPE remains fairly weak. The strength of any thunderstorms that do develop will be conditional on if  cloudiness and showers from this morning clear. At this time, thunderstorms that do develop may not maintain for long, but there is still a small risk of organization into lines where strong wind gusts are possible.

 

For Sunday, the trough weakens as it slowly pulls eastward. Heavy downpours are possible for much of Newfoundland and southeastern Labrador. Where clouds clear out in the afternoon in Nova Scotia, convection may develop along the spine and drift southeastward.

 

Thunderstorm Outlook for Today

Thunderstorm Outlook for Tonight

 

 

 

Thunderstorm Outlook for Sunday

 

Forecaster: McArthur

 

 

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