Convective Outlook Valid for Today and Tomorrow

Regional Impacts: Today- primarily lightning in eastern Labrador and much of central Newfoundland with a secondary hazard of convective gusts to ~70 km/h in central Newfoundland. Lightning will be a hazard later this evening in western Labrador.

 

Tonight- Lightning for much of NB, with hail greater than 1 cm, heavy downpours and wind gusts greater than 70 km/h possible before noon in NW NB. Isolated lightning over western Labrador.

 

Tomorrow- scattered to isolated lightning for most of NB, PEI and NS. West to Northwest NB at greatest risk hail greater than 2cm, wind gusts ~90 km/h and heavy downpours. Much of western and central Labrador will again see lightning as a primary hazard.

 

Convective Discussion: Today weak vorticity advection in conjunction associated with a upper trough will yield the risk for lightning in eastern  Labrador and much of central Newfoundland. As a building upper ridge advects eastward lapse rates will become less favourable for eastern Labrador later in the day. Given the lower surface dew points,  profiles suggest storms that do develop over Newfoundland will be fairly high based, yielding the potential for gusty convective winds to ~70 km/h. The potential for small hail cannot be ruled out entirely with a relatively low hail growth zone, despite skinny CAPE profiles. Western Labrador will likely be subjected to some isolated storms that are currently ongoing in central Quebec as instability continues to build eastward with the upper ridge continuing to advect towards Newfoundland.  

 

Tonight a strong LLJ of ~35-40 kts will be the focal point for elevated convection for much of NB into western Labrador. Enough instability looks to remain in NW most NB for some surface based  convection to develop prior to the Friday noon hour. These storms will initially be able to work with MLCAPES of up 750 J/kg with strong linear shear profiles with bulk shears up to 40 kts ahead of an approaching cold front. This gives rise to the potential for severe weather rather early in the day on Friday, primary hazard appear to be marginally severe hail, strong gusty winds and heavier downpours given PWATs of ~30-35mm. Storm motion will be relatively quick at 30-40 kts, limiting excessive rainfall despite the high moisture being advected into the region.

 

Tomorrow elevated convection will continue to advect eastward with the progression of the strong LLJ, additional solar insolation should increase the amount of energy storms have to work with ahead of the cold front in western NB. Again linear shear profiles, with fast easterly storm motion gives rise for a wind hazard with gusts ~90-100 km/h. Severe hail with MLCAPES ~1000 J/Kg is also a possibility. Storm mode should primarily be linear, although there is a slight chance of a discrete supercells at the base of the cold front from central Maine to west-central NB. Here a non-zero tornado threat could exist if low level wind profiles end up being southeasterly rather than southerly. Right now confidence and probability is too low to note outside of this discussion.

 

Thunderstorm Outlook for Today

 

Thunderstorm Outlook for Tonight

Thunderstorm Outlook for Tomorrow

 

Convective Outlook Valid for Today and Tomorrow

Regional Impacts

 

New Brunswick /Labrador: Slight risk in portions this afternoon and Thursday night.

Nova Scotia/PEI/Newfoundland: Nil.

 

Convective Discussion

 

Weak surface based convection is possible this afternoon but ML cape values near 300 J/kg and wind shear near 20 kts will limit any potential to just isolated showers and a risk of non-severe thundershowers.  A risk of embedded non-severe thunderstorms late Thursday evening ahead of an approaching trough.

 

Thunderstorm Outlook for Day 1

 

 

Thunderstorm Outlook for Day 2

 

Convective Outlook Valid for Today and Tomorrow

 

Regional Impacts: NS/NB and Labrador: Lightning, and downpours are the hazards of concern today.

 

Convective Discussion: up to 500  J/kg of MLCAPEs will yield isolated non-severe storms in western NS/NB where clearing is anticipated to occur. Bulk shears will initially be rather low but will increase to ~ 20 kts later this afternoon, however the thermodynamics will become less favourable later in the day as a TROWAL rotates in from the NE stabilizing the atmosphere. From a jet dynamic standpoint this region is also briefly in the left exit region of a 120kt jet max early this afternoon before it advect eastward over the western marine district.  Slightly greater instability of ~500-600 J/Kg MLCAPEs in the terrain in southern Labrador will also see some isolated pulse storms with low bulk shears and slow storm motion of ~10 kts or less.  Elevated convection giving lightning over the southeastern marine district will continue along the leading edge of the upper trough today.

 

Two areas of thunderstorms possible tomorrow, primarily in the terrain along the northwestern Labrador Quebec border, and in northern NB. In Northern NB inverted V-profiles could yield some gusty winds in TCU showers, but instability is marginal once mixed for a reasonable dew point and may not yield much in the way of lightning.

 

Thunderstorm Outlook for Day 1

 

 

Thunderstorm Outlook for Day 2

Convective Outlook Valid for Today and Tomorrow

Thunderstorm Outlook for Today

A few near-severe thunderstorms are possible over parts of NB. Isolated non-severe thunderstorms for southern Maritimes and Labrador

 

Regional Impacts

NB: Northwest..Scattered thunderstorms developing upstream and migrating over the region with downpours likely, rainfall rates could result in amounts of 30 mm or more. Any longer lasting storms have the potential to produce small hail and wind gusts in excess of 70 km/h. Likelihood of thunderstorms is minimal over the northeast.

South NB, PEI, and NS.. rain spreading throughout with isolated embedded thunderstorms producing heavy downpours, rainfall amounts through Tuesday could exceed 50 mm locally.

Lab: Slight risk of a thunderstorms between Wabush and the power line towards Sept-Isles

 

Convective Discussion

The analysis this morning is showing a couple of interesting features, the first being a rather large cold pool associated with a 500mb low over Northwestern/central Quebec, and the second is a frontal disturbance currently east of Cape Cod and advancing towards the Maritimes. Widespread showers continue to spread across southern NB and northern NS. Radar is also detecting strong echoes in northern NB and the Lower St. Lawrence, however Lightning flashes have diminished since mid-morning but will likely increase once again this afternoon as the cold pool advances towards the St. Lawrence, Bands of Towering cumulus are currently forming over the Eastern Townships of Quebec and the Saguenay. In terms of dynamics for the afternoon, there is a departing cyclonic upper jet, advancing surface/upper trop with a moderate southerly flow ahead of it. In behind the trough there is a 30 westerly LLJ punching through the Highlands of Maine. The limiting factor for significant vertical development of convective cloud is the lack of strait sunshine, in fact Satellite is showing extensive cloud cover as far west as the Beauce, including Maine (north and south).  

The most likely scenario will be for surface convection initiation to occur over the Lower St. Lawrence, Beauce and Maine north woods.. and then migrate east of the provincial/international border during the middle to late part of the afternoon. As for the mode of convection, the deep layer shear values will also be limiting (< 30kt) but using a convective temperature of 22 / dewpoint of 14 would suggest MLCAPE of 500 J/kg  with CB tops above 10 km with a possibility of some isolated tops above 12km making some of the more persistent clusters near-severe. The main threat would be torrential downpours, but hail of up to 1cm and winds of 70km/h are also likely. We will defer until early afternoon before making a final decision on a severe thunderstorm watch.

The other area of concern is related to the frontal system, a large area of cold cloud top is currently advancing over the western marine district and there are at least three fairly active convective clusters embedded in that system. The steering flow aloft is south to southwest which could help in spreading heavier rain over NS.

Over NF an upper ridge will prevail today, as indicated by the dry conditions in both soundings from Stephenville and St. John’s. Satellite imagery shows open cellular Cumuliform cloud developing over Labrador and because of the diffluent flow aloft and the cold pool to the west - a few thunderstorms are likely. Goose Bay sounding is very dry in the low levels but if surface warming is maximised then there is a good possibility of strong wind gusts due to downdraft currents.

 

Thunderstorm Outlook for Tuesday

Slight risk of a thunderstorm over western NB, and also central and western Lab

 

Convective Outlook Valid for June 12th and June 13th, 2022

Thunderstorm Outlook for Day 1

Isolated tstorms producing local downpours today for New Brunswick and parts of coastal NS with slight risk of severe thunderstorms producing heavy downpours.

 

Regional Impacts

Risk of localised heavy downpours for New Brunswick and parts of coastal Nova Scotia.

Risk of non severe thundershowers for southern Newfoundland.

 

Convective Discussion

Isolated thunderstorms a possibility today across New Brunswick and parts of coastal Nova Scotia.  Generally conditions are unfavourable for severe t-storm formation.  The area is not dynamically in a favourable location, low level max winds are only around 20 kts, precipitable water is only around 25 mm, low level Td’s are around 12C and vertical motions look to be inhibited at around 500mb.  However, some coastal convergence along eastern NB and parts of NS could push parcels above the 500mb cap which could result in local heavy downpours especially since they will be slow moving or stationary.  Also, forecasts highs are around 26 degrees.  If actual highs go a few degrees warmer, then it may be enough thermodynamic lift to get past the 500 mb cap and produce some local heavy downpours. 

 

 

Thunderstorm Outlook for Day 2