Atlantic Convective Outlook Valid for Today and Tomorrow

Thunderstorm Outlook for Today, June 20^th.

 

Regional Impacts

Isolated non-severe thundershowers are possible over the Gulf waters as well as offshore over Laurentian fan. These cells are expected to be embedded in showers being driven by the upper trof. Only a few lightning strikes are forecast in the risk areas.

 

Convective Discussion

The upper low is still the dominant weather forcing for today. Not much has changed since yesterday, other than sfc temperatures cooling further in NB. As a result, the atmosphere although saturated/moisture rich in the low levels is fairly stable. Shearwater this AM is moist yet stable up to 9,000ft. Much more of a springtime fog/drizzle airmass regime than a summer severe weather day. East of CYQY, there is even thermal ridging above 700 to prevent anything further. And, back to the west, the airmass is far too dry (across Maine).

 

 

Thunderstorm Outlook for Tomorrow, June 21^st.

 

Regional Impacts

No thunderstorms expected at this time.

 

Convective Discussion

Atmosphere continues to stabilize further as upper low fills. Forecast highs quite cool across Atlantic Canada for first day of summer.

 

 

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END/ASPC

Convective Outlook Valid for Today and Tomorrow

Thunderstorm Outlook for Today

Isolated non-severe thunderstorms

 

Regional Impacts

NB: None

NS: Towering Cumulus cloud over northern regions possibly giving a brief shower

PEI: Towering Cumulus cloud possibly giving a brief shower

NF: None

Marine waters: Isolated Thunderstorms over northern Gulf of St. Lawrence today, and south coast of NF tonight.

 

Convective Discussion

Current satellite imagery is showing an Upper / Surface Low pair over Maine / NB producing extensive cloud cover and occasional rain. At the surface, a warm front extends from the low northeastward to great northern peninsula of NF. The intersection of this feature with a strong southerly low-level jet will continue to support isolated non-severe thunderstorms over the northern Gulf of St. Lawrence. A strong southern flow of moist air prevails over NF ahead of the upper low feature and it is producing pockets of heavy rain along the west coast.

The strong southerly flow has been advecting very stable air in the mid-levels which is favoring a corridor of dry air over central NS this morning. The sounding at Shearwater has a very strong inversion at a height of 3-4 km which will likely limit the amount of vertical development of the cumulus cloud. In fact, a max temperature of 24 (and dew point of 10) only renders about 200 J/kg of MUCAPE, however topographic features such as the Cobequid Mountains could potentially provide the necessary lift for an isolated tall TCU/CB.

 

 

Thunderstorm Outlook for Monday

 

No thunderstorms expected

Convective Outlook Valid for Today and Tomorrow

Thunderstorm Outlook for Today

 

Regional Impacts

New Brunswick: Scattered thunderstorms with brief heavy downpours, Hail of 2 cm, and wind gusts to 80 km/h

Nova Scotia: Numerous Strong thunderstorms with Hail of 2 cm or more, heavy downpours and wind gusts to 90 km/h

PEI: Hail 1 cm or more, heavy downpours and wind gusts 70 km/h or more

Newfoundland: Chance of a thundershower late in the day and tonight in the southwest

Labrador: Turning much colder with brief heavy showers, no thunderstorms expected

 

Convective Discussion

An upper low over Maine will advance over the Maritimes today and remain in place on Sunday. A cold trough extends southeastward from the low and will be rotating over the region today.. this will be the focus for convective initiation. Strong surface heating over NS-PEI-Ern NB will further contribute in the destabilization of the environment, and modified soundings can easily push mixed layer cape values between 500-1000 J/kg with a temperature/dewpoint combination of 25/15. This very buoyant air mass will produce CB with tops to 7 or 8 km and max overshooting tops to 12 km especially over regions along the Northumberland Strait. The early morning soundings were also indicating deep layer shear strong enough to support multi-cellular clusters with some capable of producing damaging wet macrobursts. The main threat will be large Hail, torrential downpour and damaging winds.  

 

 

Thunderstorm Outlook for Sunday

 

Slight risk of a thunderstorm over eastern Maritimes.

Convective Outlook Valid for Today and Tomorrow

Regional Impacts

 

New Brunswick: Hail 1 cm or more, heavy downpours and wind gusts 70 km/h or more today and Saturday

Nova Scotia: Hail 1 cm or more, heavy downpours and wind gusts 70 km/h or more Saturday

PEI: Hail 1 cm or more, heavy downpours and wind gusts 70 km/h or more Saturday

Newfoundland: Chance of a thundershower tonight in the southwest

Labrador: Chance of a thundershowers today and Saturday

 

Convective Discussion: A cold front will track across western New Brunswick this afternoon and eastern New Brunswick on Saturday. Falling heights ahead of an approaching vorticity max is occurring this afternoon. Lots of cloud around today which may limit the severe potential over western New Brunswick. Today over western New Brunswick, PWAT values of 30-35 mm, linear shear near 30 knots and Cape of 500-1000 J/kg are expected. The CAPE is very cloud dependent and so the severe weather potential all hinges on that.  On Saturday lots of sun is expected in the noted area which will likely produce small hail, downpours and gusty winds.  PWAT values of 30-35 mm, linear shear of 20-30 knots and Cape of 500-1000 J/kg are expected.

 

Thunderstorm Outlook for Day 1

 

 

Thunderstorm Outlook for Day 1 Night

 

 

Thunderstorm Outlook for Day 2

 

 

 

 

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