Convective Outlook Valid for Today and Tomorrow

Regional Impacts:

 

Today

NL: Wind gusts 70-90 km/h, hail 2-3 cm, rainfall 15-25mm, scattered to frequent lightning.

 

Tonight

None.

 

Tuesday

None.

 

Convective Discussion

An anomalous cold upper low located over central Labrador (more common in early spring rather than summer) is giving rise to a strong upper jet of ~ 130 kts east of the Avalon this morning. Here the Newfoundland is in a favourable region of synoptic lift given its proximity to the left exit of the this quick upper jet. On water vapour this morning a potent vorticity centre was located to the west of Stephenville, this feature is expected to round the southern periphery of the upper low (located over Labrador)  and move eastward towards Terra Nova providing ample PVA as it does so. Aloft lapse rates are also expected to steepen, with 500-700mb temperature differentials anticipated to increase from 14-15 C to 18-19 C later this afternoon. The biggest question mark remains the amount of instability later this afternoon, Canadian guidance seems to be the most bullish in supporting a T/Td spread of 22/14 yielding 1500 J/kg of SBCAPE. This level of instability given the high shear environment (35-50 kts of bulk shear), and 0-3km SRH values of 100, would support supercell development between Gander and Clarenville. However foreign guidance is consistently drier, supporting SBCAPEs under 1000 J/Kg (maxing out at 800 J/kg) giving some uncertainty. Nevertheless a small area of dew points in the low teens did exist on the 12z analysis this morning SE of Gander, so one cannot discount the RDPS/GDPS solution all together. Storm motion is expected to be ENE at 30-40 kts, with any supercells moving to the right in an easterly motion. The primary threat with storms today is expected to be hail given the unseasonably low HGZ with the cold upper trough, linear hodographs, and steep mid level lapse rates. A wind hazard also exists, especially with any supercell RFD adding to the quick storm motion. Rainfall over any given location will be limited by the progression of storms today, and the lower PWATs of ~20-23mm associated with the unseasonable cool upper air mass in place. A tornado threat was ruled improbable given little directional shear in the 0-1 km layer (not much in the way of low level backing), despite LCLs being under 1 km.

 

Thunderstorm outlook for today

 

 

Thunderstorm outlook for tonight

 

 

Thunderstorm outlook for Tuesday

 

Convective Outlook Valid for Today and Tomorrow

Regional Impacts

 

Today

NB: Scattered strong thunderstorms.

NS/PEI/NL/Labrador: isolated thundershowers.

 

Tonight

None.

 

Monday

NL/Labrador: isolated thundershowers

NB/NS/PEI: None.

 

Convective Discussion

A cold front is basically stalled over southern NB but will drift across NS tonight. There is a lot of shear (40 to 60 knots and linear) and the cape is 500 J/kg or less. The shear is likely too strong for the cape but for areas near the front today (southern NB) some enhanced activity is possible. PWAT values of 25 mm will give downpours. Guidance is suggesting hail near 1 cm and low freezing levels near 9000 feet. Dry mid levels support the model guidance of wind gusts to 40 kts.

 

Garden variety pop-up thundershowers are possible on Monday for Nfld/Lab.

 

 

Thunderstorm Outlook for today

 

 

 

 

 

Thunderstorm Outlook for tonight

 

 

Thunderstorm Outlook for Monday

 

 

Convective Outlook Valid for Today and Tomorrow

Regional Impacts

 

Today

NB: Scattered strong to severe thunderstorms.

Labrador: isolated to scattered thundershowers in the west.

NS/PEI/NL: isolated thundershowers.

 

Tonight

MRTMS: None.

Labrador: isolated thundershowers.

 

Sunday

NB/NS/PEI/Labrador: isolated thundershowers

NL: None.

 

Convective Discussion

An approaching cold front will track across New Brunswick later today and Nova Scotia on Sunday. There is a fair amount of shear (30 to 40 knots and linear) and the cape is 500-1000 J/kg. Additionally, areas of western NB and southern Labrador are in the favourable left exit region of an upper level jet. PWAT values of 25-35 mm will give downpours. Guidance is suggesting hail of 1-2 cm. Dry mid levels support the model guidance of wind gusts to 50 kts.

 

Garden variety pop-up thundershowers are possible on Sunday. Cape values due not look very high but shear is high and my be too strong to maintain cells.

 

 

Thunderstorm Outlook for today

 

 

Thunderstorm Outlook for tonight

 

 

Thunderstorm Outlook for Sunday

 

Convective Outlook Valid for Today and Tomorrow

Regional Impacts

 

Today

NB: isolated thunderstorms in the northwest.

Labrador: isolated thundershowers in the west.

NL: isolated embedded thundershowers over the Grand Banks.

 

Tonight

MRTMS: isolated thundershowers.

Labrador: isolated thundershowers.

 

Saturday

NS/PEI: scattered thundershowers

NB/Labrador: scattered strong (nearing severe) thunderstorms.

 

Convective Discussion

An approaching trough of low pressure  which was analyzed near the St. Lawrence river valley will likely trigger some isolated thunderstorms in northern ME this afternoon that will advect into NW NB as the day progresses. There is a fair amount of shear (close to 40 knots and linear) so could be some gusts to 70 km/h in some of the heavier cells (assuming they develop). But don’t really expect severe storms today as the more favourable dynamics remain further upstream for now. There is some lightning in QB that may make it to the Wabush/Lab City area this afternoon but that looks pretty marginal at best. Weakening upper level low could still give some isolated CBs to the Grand Banks today.

 

That same trough feature could give an isolated thundershower tonight across the MRTMS as cloud top cooling could help things a little. But certainly nothing to write home about.

 

The more favourable dynamics appear to be in store for Saturday based on latest computer models. I will not delve into details since that notion can change. Right now strong winds, small hail and heavy downpours are possible in some areas in the stronger cells. PWATs could be very high across parts of the MRTMS so high rainfall amounts in a short period of time may occur even outside the moderate (yellow) risk areas.

 

Thunderstorm Outlook for Day 1

 

Thunderstorm Outlook for Friday night/Saturday morning

 

Thunderstorm Outlook for Saturday afternoon

Convective Outlook Valid for Today and Tomorrow

Regional Impacts

NB: downpours and scattered lightning

NS: downpours and scattered lightning most of mainland

PEI: Isolated lightning western half

NF: None

Labrador: Isolated lightning Eagle River region

Marine waters: Scattered lightning eastern marine district into southwestern Grand Banks. Isolated lightning near Anticosti. Isolated lightning western Northumberland strait.

 

 

Convective Discussion:  Generally unstable with an upper trough over the Maritimes providing steep mid tropospheric lapse rates. Shear will be minimal today with slow storm motion initially easterly at 5-10 kts becoming southeasterly later in the afternoon into the early evening. Given slow storm motion and PWATs into the upper 20mm, the primarily hazard today will be downpours over the Maritimes. In eastern Labrador over meager instabilities of ~300 J/kg aided by a deformation zone on the western periphery of the upper trough may allow for the odd strike, however bulk shears in excess of 40 kts may prove to be too much to allow for convection to reach heights sufficient to generate lightning. Differential heating near the deformation zone may also allow for the odd strike near Anticosti island. Much of the southern/eastern Marine district remains in a moist unstable environment, with PVA from the upper trough continuing to trigger scattered thunderstorms. This region of instability is expected to slowly advect east with the upper trough, giving continued scattered convection over the next 36 hours.

 

On Canada day (tomorrow), little thunderstorm activity is expect. However storms may move into northwestern NB from eastern Quebec in the early evening hours as a cold front moves towards Atlantic Canada.

 

Thunderstorm outlook for today:

 

 

Thunderstorm outlook for tonight:

 

 

Thunderstorm outlook for Friday (Canada Day):