Convective Outlook Valid for Today , Tonight and Tomorrow

Regional Impacts

Today.

Scattered thunderstorms for western NB and portions of NS this afternoon and evening. Main threat is torrential downpours, but strong wind gusts are also possible in the stronger cells. There is a chance of a strong to severe thunderstorm for the eastern mainland. Storms should be non-severe for western NB.

 

Tonight.

Isolated thunderstorms possible for NS, PEI and portions of NB. Main threat is torrential downpours.

 

Sunday.

Isolated thunderstorms possible for Cape Breton. Main threat is torrential downpours.

 

Convective Discussion

There are a couple features that will impact the region today – a weak trough that’s currently stretching from the Cape Cod area into southwestern NB and an upstream short wave trough currently over southern Quebec. The aforementioned trough could be the catalyst for an isolated strong to severe thunderstorm this afternoon/evening for a portion of eastern NS. The 12Z tephi out of YQI looks decent and adjusting the surface temp and dewpoint results in a mixed CAPE close to 1000 J/KG. There is also decent shear of around 35 knots. Of course there is PLENTY of low level moisture as we continue to be plagued with very high humidity near the surface (PWAT just shy of 50 mm at YQI). The instability is modest as well so we just need some sunshine to fire off a storm or 2. Upstream SAT PIX does show some openings in the overcast ST/SC deck but also some fairly fast approaching mid-level cloud in the gulf of ME. Given the recent flooding in areas of NS there is somewhat heightened awareness today in the event we see cells develop. The one saving grace would be the forward motion of the convection as the mean flow would have it moving eastward at 60-70 km/h. Rainfall rates of up to 50 mm/h look possible. The issue would be if we see any training/back-building of cells. We shall see…

 

The second feature mentioned above is already producing some storms upstream. As the short wave approaches ME and western NB we expect to see some scattered thunderstorms this afternoon and into this evening. Locally torrential downpours seem to be the main concern.

 

There could be some isolated convection tonight and into Sunday morning for eastern NB, NS and PEI as that same short wave moves across the MRTMS. And given what we are seeing at this hour in southern QB there is a chance that Cape Breton sees a isolated cells Sunday afternoon as the short wave just exits the region.

 

Thunderstorm Outlook for Today

 

Thunderstorm Outlook for Tonight

 

Thunderstorm Outlook for Tomorrow

 

Jeremy

Convective Outlook Valid for Today, Tonight and Tomorrow

Regional Impacts

Scattered thunderstorms are forecast over extreme SW-ern NS late today, as well as the potential for isolated marginally severe thunderstorms from Windsor through to Collegeville area today. More organized thunderstorms are forecast over western NB where partial clearing is forecast to occur. The main hazard for the day is heavy rain.

 

Convective Discussion

Complex “tropical-like” dynamics at play today for 3 main forcings for convection each with individual hazards associated. A front in Labrador may spark a few lightning strikes as it transits through over the next 24-hrs.

1. Western NB: MUCAPE values near 1000 could (with a strong enough forcing) even overcome the cap that exists at 500mb, leading to gusty winds and heavy rain. PWATS in this area with actual dew points near 20 at 45mm today.

2. An area of potential instability exists from Kings county through to Guysborough county late this afternoon. The forcing here would be a sea breeze type front. If this materializes, dew points are near 22 and PWATS close to 50 so rain is the main hazard.

3. A frontal feature streaming up from the U.S. eastern seaboard is feeding in moisture and buoyancy causing non-severe thundershowers – Shelburne area likely to be in this moisture feed this evening. Saturday morning the rain hazard exists again in central NS marked in yellow on the overnight graphic. Models are not in perfect agreement on placement, but there is a consistent signal again for decent rain rates (greater than 30mm/hr). These local areas have a high vulnerability/sensitivity based on rainfall that has fallen in the last week.

The rest of Saturday sees generally improving conditions for NS, with pop-up showers across much of NB, PEI and in eastern areas of Nfld. Sunday’s dynamics as humidity builds back into the Maritimes is not a clear picture at this point.

 

Thunderstorm Outlook for Today

 

Thunderstorm Outlook for Tonight

 

Thunderstorm Outlook for Tomorrow

 

Thunderstorm Outlook for Sunday

 

Forecaster: TIRONE

Convective Outlook Valid for Today, Tonight and Tomorrow

Regional Impacts

NS/NB… Scattered thunderstorms possible today. Main hazard is torrential downpours of 25 to 50 mm/h.

PEI… Isolated embedded thunderstorms possible this afternoon. Main hazard is locally heavy downpours of 15 to 25 mm/h.

NL… None

 

Convective Discussion…

A strong moisture plume from the remnants of Hurricane Beryl will move across the Maritimes today, bringing the risk for some scattered thunderstorms to parts of Nova Scotia and New Brunswick. A few thunderstorms have already developed in Maine this morning and have moved across the international border into New Brunswick. Watches have been issued for southern New Brunswick, and will likely be expanded into Nova Scotia this afternoon. This risk for severe storms will continue into this afternoon, especially along the Bay of Fundy, where good low level moisture flow will help fuel storms that fire along the 500 mb jet as it slowly moves east. One of the big challenges today however will be achieving sufficient instability. Models have backed off on MLCAPE values, likely due to increased cloud cover over the southern Maritimes, as well as the stalling of the thermal trough over New England. This should keep the risk for severe weather over and around the Bay of Fundy, though given sufficient clearing, there is a slight risk that some severe storms could fire in southwestern Nova Scotia. Dynamics will not be an issue today, with bulk shear values of 45 to 50+ kts. PWAT values have been observed to be between 50 to 60 mm based on the 12Z Yarmouth and Gray soundings. As such, the main hazard with any storms today are torrential downpours of 25 to 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

NL… Some scattered thunderstorms across central Newfoundland this afternoon. Main hazards are rainfall rates of 20 to 30 mm/h and wind gusts of 60 to 70 km/h.

NB… Elevated thunderstorms possible tonight with rainfall rates of 15 to 25 mm/h. Scattered thunderstorms over southern New Brunswick possible tomorrow with rainfall rates of 25 to 50 mm/h.

NS/PEI… Isolated thunderstorms possible tomorrow over northern and central Nova Scotia and eastern PEI. Main hazard is torrential downpours of 25 to 50 mm/h.

 

Convective Discussion…

Today, most of the convective activity will be associated with a trough moving through Newfoundland. Some clearing behind the initial convection this morning will allow MLCAPE values to rise to 1000-1500 J/kg by this afternoon. Bulk shear values near 30 kts will aid in organising this convection as it moves east through central Newfoundland this afternoon. One of the limiting factors today will be the amount of upper and mid level cooling, especially over southern Newfoundland. Thus the main area of interest this afternoon will remain in central and northern Newfoundland as the trough moves through. The main threat with these storms will be locally heavy downpours of 20 to 30 mm per hour, but strong wind gusts and some pea sized hail are also possible. A few isolated thundershowers are also possible over southern Labrador today, however these storms are not expected to become severe due to weaker dynamics and a lack of strong instability.

Tonight, the remnants of hurricane Beryl will approach New Brunswick. This system has a track record of being highly convective, with that trend expected to continue as it enters New Brunswick. While mid level instability is currently forecast to be quite minimal, PWAT values are expected to rise up to 50 to 60 mm tonight, so any elevated thunderstorms that develop along the warm front bring the risk of torrential downpours tonight. This risk will continue into tomorrow afternoon over eastern portions of the Maritimes. Strong southerly low level flow tomorrow afternoon over the Bay of Fundy will pump some additional moisture into the warm sector over southern New Brunswick. This will increase the risk for some higher rainfall rates here in any convection that does occur in the warm sector, with 25 to 50 mm per hour possible. This area will move east into parts of mainland Nova Scotia and possibly eastern PEI tomorrow evening. Some isolated thunderstorms are also possible over extreme northwestern New Brunswick early tomorrow evening, closer to the low center, though these are expected to remain non-severe.

 

Thunderstorm Outlook for Today

Thunderstorm Outlook for Tonight

Thunderstorm Outlook for Tomorrow

Copp

Convective Outlook Valid for Today, Tonight and Tomorrow

Regional Impacts

 

Today

NB/Labrador:  Scattered thunderstorms with some of them becoming strong, rainfall rates 25 mm/h, hail possible, and gusts 50-80 km/h.

NS/PEI/NL:  Isolated thunderstorms giving 15-25mm/h rain and brief strong wind gusts.

 

Tonight

NL/Labrador:  A chance of thunderstorms.

NB/NS/PEI/:  None.

 

Wednesday

NL/Labrador:  Isolated thunderstorms with rainfall rates 15-25 mm/h.

NB/NS/PEI: None.

 

 

Convective Discussion

 

An upper disturbance and cold front will approach from Quebec/Western Lab today, continuing to increase moisture and instability. Some high level cloud may inhibit the extent of daytime heating over New Brunswick, Newfoundland and central and southeastern Labrador, but CAPE values could still approach 1000J/kg for southeastern Labrador and Newfoundland. There is weak to moderate shear, so the bigger issue will be some training thunderstorms. Divergence aloft and the left exit of the 250mb jet, and moderate 0-6km shear will also aid in sustaining convection in multicell or possible bow line segments over southern Quebec and Maine. The timing of the incoming trough and warm 850mb temperatures is such that stronger convection may remain capped hold off over New Brunswick until later in the day, but elevated convection may persist overnight aided by a strong low level jet as the trough moves over the Gulf of St. Lawrence and into western Newfoundland tomorrow morning.

 

On Wednesday, the trough continues eastward over northeastern Newfoundland and southeastern Labrador. A weak feature is expected to move into western Labrador in the afternoon and may trigger non-severe thunderstorms. The humid air mass over the Maritimes will trigger some pop up TCUs but are not expected to breach the warm cap from 700-500mb.

 

 

Thunderstorm Outlook for Today

 

Thunderstorm Outlook for Tonight

 

Thunderstorm Outlook for Tomorrow

 

 

Roberta McArthur