Convective Outlook Valid for Today and Tomorrow

Regional Impacts

New Brunswick, PEI, valley and northern Nova Scotia: There is a risk of severe thunderstorms today giving heavy rainfall, strong winds and small hail. Currently some storms producing heavy rain across northern NB. A few thunderstorms should form early this afternoon across the south. Scattered thunderstorms should develop later this afternoon across NS that could advect into PEI .

Southwestern Labrador: slight risk of a thundershower this afternoon and evening.

East of the Avalon: isolated elevated thundershowers.

 

Convective Discussion

There is a fairly decent chance in seeing some severe thunderstorms today across New Brunswick, Nova Scotia and PEI today giving heavy rain, strong winds and hail. There is a strong 250 jet placing the favourable areas in the left exit region, as well as some divergence. Divergence is also evident at 500 mb as the upper trough slowly approaches from the west, so heights will be falling a little as well. There is not as much low-level moisture as yesterday but still enough to add to the buoyant atmosphere. The 12Z KCAR tephi has a decent unstable profile, PWAT of 36 mm, a relatively low FZLVL (around 10,ooo feet) and about 35 knots of shear. The current storms affecting the northern half of NB is giving locally heavy rainfall. Modifying the sounding gives a mixed layer CAPE of around 1000. Mind you the shear will be decreasing through the day across northern NB, it will remain across southern NB, so strong storms giving wind gusts of around 80 km/h, heavy rain and hail of up to 2 cm are possible. For Nova Scotia, the issue right now in the favourable zone (valley and northern areas) is the mid level cloud cover. The 12Z YQI tephi has decent low-to-mid level lapse rates and shear of up to 35 knots. PWAT is the same as KCAR. Modifying it for a temperature of 31 degrees gives close to 1000 CAPE. So, much like NB there is a decent chance in seeing severe storms. The issue, as mentioned above is the current cloud cover. There is a back edge moving into the Gulf of Maine so I would expect cells to develop later this afternoon. Again heavy rain, strong winds and small hail are possible in the stronger storms. Some of these cells across southern NB and NS should progress into PEI later today.

 

A slight risk of a thundershower this afternoon and evening near Wabush/Labrador City  in the vicinity of the upper low.

 

Thunderstorm Outlook for Day 1

 

Thunderstorm Outlook for Day 2

 

Jeremy

Convective Outlook Valid for Today and Tomorrow

Regional Impacts

For Nova Scotia: there is a slight risk of a severe thunderstorm across portions of the eastern mainland into early this evening. The main threat is heavy rainfall. Some gusty winds are also possible but below warning threshold (90 km/h).

For New Brunswick: scattered thunderstorms are expected to develop this afternoon.

For Newfoundland: there is a risk of isolated elevated/nocturnal  thundershowers tonight

 

Convective Discussion

As mentioned above, there is a slight risk of a severe thunderstorm across the eastern mainland of Nova Scotia this afternoon. Looking at the parameters (MIST): we have the moisture with dewpoint temperatures into the low 20’s and a moist tongue at 850; the instability is there with model LI’s in the minus 5 to minus 8 range; analysis from the 12Z YQI and YAW tephis show 30-40 knots of shear in the 0-6 km level; and lastly a weak trough offering up a trigger mechanism once the convective temperature is reached early this afternoon. Upper air analysis doesn’t show much at 250 mb as the main jet is well to the north of NS. There is a 40 knot jet at 500 mb, but not really an indication of at least minimal falling atmospheric heights. The upper level trough at 500/700 is well to the west and won’t be a factor until D2 as it approaches Maine and New Brunswick. One thing noted on the 12Z tephis is the warm, stable air aloft. This will be the determining factor. Modifying the 12Z soundings for temperatures of 30, and dewpoints of 22 gives about 1000 mixed-layer CAPE. The MUCAPE is way overdone and ignored. I expect TCUs to form shortly after the lunch hour with isolated-to-scattered TS not long thereafter. Once again, the stability aloft may prevent any potential cells from becoming severe (25+ mm of rain in one hour).

 

Scattered cells are likely to develop across northern New Brunswick this afternoon…there is a very little chance in seeing anything close to severe limits. Locally heavy downpours can be expected.

 

Lastly, there is a risk of elevated convection tonight across southern Newfoundland.

 

Thunderstorm Outlook for Day 1

 

Thunderstorm Outlook for Day 2

Convective Outlook Valid for Today and Tomorrow

Thunderstorm Outlook for Day 1

 

Regional Impacts

New Brunswick: Heavy downpours for most of the province likely, with strong downdrafts and possibly a wet microburst. The main threat area is the southwest.

Nova Scotia: Poissibly a similar situation to New Brunswick, but mainly for the Cobequids and the west inland for the worst impacts.

Prince Edward Island: Scattered thundershowers possible, with local heavy showers and gusty winds.

 

Convective Discussion

There’s a cold front from north of the Gaspe and extending southwest over northwestern Maine, slowly moving in this afternoon . There’s ample low moisture in the warm sector with PWATs near 45 mm, a moist tongue over southern New Brunswick, and a dry layer at 700 mb near and behind the cold front. Bulk shear is 40+ kts, but there is little storm relative helicity. This argues for multicells with the front as an organising feature.  There’s already some weak prefrontal lines approaching the northwest, and conditions should intensify this afternoon, with some cooling aloft as a thermal ridge moves east of the porvince and we get some daytime heating. A diffluent flow aloft associated with an upper low to the northwest should also help.

 

For Nova Scotia conditions will occur later this afternoon or this evening with the approach of the low. Conditions should moderate into this evening.

 

 

 

Thunderstorm Outlook for Day 2

 

 

Convective Outlook Valid for Today and Tomorrow

Thunderstorm Outlook for Day 1

 

Regional Impacts

New Brunswick and western Nova Scotia: Depending on cloudiness, possibility of thunderstorms east and severe thunderstorms west, with heavy downpours the greatest threat, followed by gusty winds.

Northern Newfoundland and southeastern  Labrador: chance for non severe thunderstorms,

 

 

Convective Discussion

The synoptic situation is similar to yesterday, with a low near Hudson Bay and a second over the Labrador Sea, with an extended east-west trough between them and over Labrador. This also produces slight ridging over Quebec and New England.  For Newfoundland and Labrador there is some support for non-severe convection near the Strait of Belle Isle.  Some weak PVA from a jet right exit, combined with daytime heating may give a few cells. PWAT is only about 20 mm., but CAPEs in excess of 200 J/kg with a slight chance of 500 J/kg are possible.  Gusty winds and brief heavy showers are the main issues, with a slight chance for hail with YYR having freezing levels below 8000 ft.

 

For the Maritimes things are trickier. Cloudiness will be the key. There’s some upper support from a 500 mb jet near southwestern New Brunswick with some associated lift, with plenty of moisture below 700 mb. PWATs range from 40-60 mm, with surface dewpoints near 20 C,  and 850 dewpoints up to 15 C , with a moist tongue poking into southern New Brunswick. If things clear, CAPEs of up to 1000 J/kg or maybe higher are possible. Freezing levels near 15,0000 ft suggest large hail is unlikely. Very heavy rainfall is the largest risk, followed by gusty winds that may reach warning level, and finally some small hail. For the rest of New Brunswick and parts of Nova Scotia, the impacts will be somewhat weaker, but rainfall followed by winds as the main risks.

 

 

Thunderstorm Outlook for Day 2

 

Convective Outlook Valid for Today and Tomorrow

Thunderstorm Outlook for Day 1

 

Regional Impacts

New Brunswick: Possibility of non-severe thundershowers in the northeast if the thick cloud there burns off this afternoon. Possibility of Severe thundertorms in the extreme southwest if the cloud deck moves away or burns off,  with high wind the largest risk, followed by heavy downpours.  

Newfoundland: thunderstorms beginning this afternoon with possible heavy downpours, especially with the slow movement of the cells.

 

Convective Discussion

 

For Newfoundland: there’s a low of the coast of Labrador  from 250 mb down, with some upper dynamic support with PVA approaching western Newfoundland.  There’s some good moisture with dewpoints of up to 17 C and PWATs near 24 mm, with most of it below 850 mb, Shear and storm motion is relatively low,  suggesting plenty of time for rain to accumulate, and mean layer CAPEs suggest possibly reaching or exceeding 500 J/kg near and west of Gander, if they can get some clearing. Small hail is also possible, with freezing levels around 10-11,000 ft.

 

For New Brunswick:  there are some good ingredients, especially in the far southwest, but the big inhibitor is cloudiness.  The most likely place for convection is in the northeast, where things may start clearing this afternoon, but with non-severe cells likely. The general ingredients are near 50 kts of shear, PWATs in the 30-45 mm range, with surface dewpoints near 19 C and 850 dewpoints near 13 C moving in from the west.  If things clear in the north, CAPEs could reach 200-500 J/kg.  Gusty winds and local heavy downpours are the main threats, but the cells should move fast enough to limit therainfall from any given cell.

 

For the southwest the main risk would be wind gusts possibly reaching warning level, followed by local heavy downpours. Again, this is assuming some surface insolation this afternoon.

 

 

Thunderstorm Outlook for Day 2