Convective Outlook Valid for Today and Tomorrow

Regional Impacts

Isolated non-severe thunderstorms over New Brunswick and Southern Labrador. Stronger storms will likely occur over Maine, and could move close to western New Brunswick.

 

Convective Discussion

There are a couple of upper features this morning supporting convective development throughout the day.  An upper low just west of Labrador with its associated cold pool will maintain unstable conditions over areas from Wabush to Churchill Falls and Goose Bay. Spotty lightning has been detected throughout the morning especially in the area between Wabush and Sept-Isle, and also between Smallwood reservoir and Goose Bay. MLCAPE in the order of 300 to 500 J/kg will support development of individual cells capable to produce brief downpours - small hail - and gusts of around 60 km/h.  

A thermal trough extends southward from the cold pool to Maine and then to Long Island. Two jet branches will intersect with the trough, one of those is oriented west to east along the lower Quebec North Shore, and the second branch is pushing southward over the St. Lawrence Valley moving into Maine where the most unstable upper air profiles were found this morning. Gray, Maine shows MLCAPE values of around 1000 J/kg and lifted index of -2 to -4. This is an area were multi- cell development is likely during the afternoon due to the incoming northwesterly jet intersecting with the trough, providing extra support to these storms sustained by deep-layer shear values of about 30 knots. While the bulkier action will remain west of New Brunswick, weaker non-severe storms will likely develop over the province.

 

Thunderstorm Outlook for Day 1

 

 

Thunderstorm Outlook for Day 2

Convective Outlook Valid for Today and Tomorrow

Regional Impacts

 

A risk of thundershowers for western Labrador today. Thundershowers have already popped up northeast of Sept-Iles.

 

Convective Discussion

 

Marginal cape values of 400-500 J/kg and shear of 20-30 kts are expected for western Labrador today. Supportive upper flow and vorticity will yield a risk of thundershowers with some daytime heating this afternoon/evening.

 

 

Thunderstorm Outlook for Day 1

 

 

 

Thunderstorm Outlook for Day 2

 

Convective Outlook Valid for Today and Tomorrow

Regional Impacts

Multiple thunderstorm cells developing during the afternoon over central and southern NB, the main threats are heavy downpours and damaging winds.

 

Convective Discussion

Today, the focus for organized convection will be along a cold front currently extending east-west across Gulf of St. Lawrence and northern NB. Isolated pulse-type thunderstorms will develop ahead of the front during the afternoon and into the evening. Some of these storms could become better organized and turn  into a multicell arrangement especially over central and southwestern regions. The dynamics over the area are minimal, but moisture below 700mb is plentiful and mixed-layer CAPE approaching 1000 J/kg should be enough to produce fairly robust storms. The Caribou upper air sounding from this morning is showing a layer of dry air above 700mb which would suggest a threat of high wind gusts.  

By the end of daylight hours the front will reach northern NS and will begin to weaken as it continues to slump southward during the night.

 

 

Thunderstorm Outlook for Day 1

 

 

Thunderstorm Outlook for Day 2

 

 

Convective Outlook Valid for Today and Tomorrow

Regional Impacts

Valley/northern Nova Scotia, western New Brunswick, central Newfoundland: there is a risk of non-severe thundershowers this afternoon and into the evening.

Southeastern Labrador: a very slight chance of a thundershower this afternoon from any development in Quebec that may drift into the region.

 

Convective Discussion

There are several areas that may see some isolated cells this afternoon. Over the “spine” of Nova Scotia, the valley and northern regions, isolated cells are likely to develop this afternoon as skies are starting to clear. The PWAT is close to 30 mm from the YQI TEP, and CAPE values of to 500 J/kg are possible. As has been the case for several days there is an abundance of moisture near the surface with dewpoints around 20 degrees in many places. There is not much of a trigger, mostly some orographic lift would be needed to initiate convection. There is little wind shear so weak pulse storms giving locally heavy downpours are possible. Over western areas of New Brunswick some isolated cells are likely this afternoon and into the evening under the influence of that persistent upper level low over New England. The KCAR TEP doesn’t look that promising based on the 12Z balloon ride. But the PWAT is 30 mm. Absolutely no shear so weak pulse storms are possible, with locally heavy downpours. For central Newfoundland there is a slight risk of afternoon and evening thundershowers in association with an approaching trough of low pressure. Increasing wind shear could give some gusty winds in some of the potential cells. But overall the risk is pretty low for seeing a CB. Lastly there could be an isolated cell roll into southeastern from the Lower North Shore of Quebec.

 

Thunderstorm Outlook for Day 1

 

Convective Discussion

I won’t go into much detail at this point in time, but there is a slight risk of a severe thunderstorm producing heavy rain, small hail and strong wind gusts across western New Brunswick Thursday afternoon and into the evening hours. A strong cold front will be pushing southward through the day, temperatures near 30 degrees with high dewpoints and increasing shear is all evident on numerical guidance. MUCAPE of over 1000 J/kg is possible by mid to late afternoon. Some isolated cells are also possible over the slope waters south of Nova Scotia and the southern Grand Banks of Newfoundland.

 

Thunderstorm Outlook for Day 2

 

Jeremy

Convective Outlook Valid for Today and Tomorrow

Regional Impacts

Labrador: some isolated thundershowers expected today associated with a southeastward moving trough of low pressure. Gusts to 70 km/h are possible.

Central/eastern/northeastern Newfoundland: a slight chance of late afternoon and evening thundershowers.

Maritimes: a chance of thundershowers today and tonight in association with a fairly stationary upper level low.

 

Convective Discussion

Labrador:

There is a fairly strong 700-500 mb jet descending from Ungava Bay area (YVP has about 55 knots of shear based on the 12Z tephi). A surface frontal zone could trigger some isolated cells this afternoon and into this evening as daytime highs hit the upper 20’s to low 30’s. PWAT at YVP is close to 40, but the air mass is moving into a drier zone, so heavy downpours shouldn’t be an issue at this time. Given the dryness below 700 mb at YYR, some wind gusts in cells is a possibility. Right now gusts to 70 seem reasonable.

 

Central/eastern/northeastern Newfoundland:

There is a weak area of instability laying across the aforementioned areas on the island. Given the latest sat pix skies appear to be clearing so there is a risk of isolated cells this afternoon and into this evening. 12Z YJT tephi is not particularly interesting, but with enough solar insolation CAPE could reach 300. Given about 15 knots of 0-6 km shear, weak pulse cells are expected.

 

Maritimes:

Lastly, the stubborn upper area of low pressure west of the MRTMS. Yesterday the guidance was suggesting potential for some heavy downpours given PWAT was above 40mm and in an area of modest divergence aloft, but there was next to nothing. Lots of activity over the marine areas, but nothing at all over land. So given the history of the upper low only a slight risk of a TSRA is expected, and this would mainly apply to Nova Scotia tonight. Not included in the risk zone is northwestern New Brunswick. If given enough surface heating an isolated cell is possible. Right now I am expected mostly TCUs.

 

Thunderstorm Outlook for Day 1

 

Convective Discussion

The greyed area is a combination of the leftover upper low that will be weakening somewhat and the approaching frontal trough over Labrador. With the increasing shear associated with the trough some gusts to 70 km/h are possible over southern Labrador (of course where only the caribou roam).

 

Thunderstorm Outlook for Day 2

 

Jeremy