Convective Outlook Valid for Today and Tomorrow

 

Thunderstorm Outlook for Today

 

Regional Impacts

NB: Isolated thunderstorms over southern areas.

NS: Isolated thunderstorms possible over inland areas of central mainland NS.

PEI: None

NF&Lab: Isolated thunderstorms over southeastern Labrador.

Marine waters: Isolated embedded thunderstorms over marine areas south of Newfoundland.

 

Convective Discussion

 

Surface based convection is possible over central areas of mainland NS and parts of southern NB as afternoon temperatures rise into the mid to high 20s. However, CAPEs over both areas are quite low as the profile is forecast to be quite warm in the 500-700 mb layer. There is very little shear over these areas of potential convection as a weak upper trough moves over NS and NB. The 500 mb winds are forecast to be in 5 to 10 knot range over NS and 20 knots over NB. So any thunderstorm cells that do form will be short lived and vertical. The threat is locally heavy downpours.

 

An area of rain and potential embedded convection south of NS and NF today will persist today and tonight as the upper trough will persist south of NS and slowly weaken. Isolated thundershowers are possible. However, lightning activity hasn’t occurred recently.

 

Surface based convection is possible over southeastern Labrador. Although CAPEs are not expected to huge, there is a lot of shear (50 to 60 knots sfc to 500mb). Also the upper 250 mb jet is over the region and is about 100 knots.  Based on this scenario, severe conditions with gusty winds and hail can’t be ruled out if thunderstorms occur. The shear may be too strong for cells to organize and may be torn apart before they can form.  There have been a few lightning strikes to the west of this region this morning.

 

 

 

 

Thunderstorm Outlook for Sunday

 

Regional Impacts

NB: None

NS: None

PEI: None

NF&Lab: None

Marine waters: Isolated embedded thunderstorms over marine areas south of Atlantic Canada.

 

Convective Discussion

 

Thunderstorms are not expected over land areas of Atlantic Canada on Sunday. Although lifted indices are forecast to be in the -2 to -4 range over parts of NS and NB, the profiles are dry and there is a subsidence inversion near 700 mb. The inversion is a result of a weak upper ridge moving in from the west.

 

Elevated convection within a band of moderate to occasionally heavy rain south of Atlantic Canada remains possible as the upper trough persists offshore and gradually weakens. Lift in this area of rain is from about 850 mb.

 

Convective Outlook Valid for Today and Tomorrow

Thunderstorm Outlook for Today

 

Regional Impacts

NB: None

NS: None

PEI: None

NF&Lab: Isolated thunderstorms over western Labrador possible.

Marine waters: Isolated embedded thunderstorms over marine areas south of Nova Scotia.

 

Convective Discussion

 

Surface based convection is possible over western Labrador this afternoon. Maximum unstable CAPEs are around 900 J/kg. Shear is decent, at about 30 knots and is unidirectional from the SW. The 250 mb jet over Goose Bay at 12Z was 90 knots. However, the upper jet is positioned south and east of the area where initiation is most likely to occur. The threats of thunderstorms if they occur are heavy downpours and gusty winds. Warning criteria conditions are not expected.

 

Elevated convection within a band of moderate to occasionally heavy rain south of NS is possible. Lift in this area of rain is from about 850 mb. This area of rain and embedded convection is ahead of a slow-moving upper trough. Severe conditions are not expected.

 

 

Thunderstorm Outlook for Saturday

 

Regional Impacts

NB: None

NS: Isolated thunderstorms possible over inland areas of mainland NS.

PEI: None

NF&Lab: Isolated thunderstorms over southeastern Labrador and southeastern Newfoundland possible.

Marine waters: Isolated embedded thunderstorms over marine areas south of Newfoundland.

 

Convective Discussion

 

Surface based convection is possible over inland areas of mainland NS as afternoon temperatures rise into the mid to high 20s. However, CAPEs are quite low as the profile is forecast to be quite warm in the 500-700 mb layer. There is very little shear over this area of potential convection as the aforementioned upper trough moves over NS on Saturday. The 500 mb winds are forecast to be in 5 to 10 knot range. So any thunderstorm cells that do form will be short lived and vertical. The threat is locally heavy downpours.

 

The area of rain and embedded convection south of NS today is expected to shift eastward on Saturday as the upper trough moves eastward. Isolated thundershowers over southeastern Newfoundland are possible. Severe conditions are not expected.

 

Surface based convection is possible over southeastern Labrador. Although CAPEs are not expected to huge, there will be a lot of shear (50 knots sfc to 500mb). Also the upper level jet is forecast to move over the region. Based on this scenario, severe conditions with gusty winds and hail can’t be ruled out.

 

 

 

Convective Outlook Valid for Today and Tomorrow

Thunderstorm Outlook for Today

 

Regional Impacts

NB: None

NS: None

PEI: None

NF&Lab: None

Marine waters: Isolated thunderstorms developing tonight over southwestern waters, then spreading northeast.

 

Convective Discussion

The main features this morning are a 500mb upper low south of New England with a southeasterly upper jet ahead of it as indicated by Yarmouth and Shearwater soundings. At the surface, a frontal boundary extend from the back of the upper low, mid-Atlantic coast of the US, to southern Quebec, and then to Labrador. Several low pressure centres are analysed along the front, but the main centre appears to be just north of the Ottawa Valley where several clusters of lightning strikes are detected . Another area with lightning activity is over the Gulf Stream, southeast of Nantucket. Over time, a push of cold air aloft currently over James Bay will catch up with the frontal band over northern Quebec and Lab, while a new upper low emerges over the Maritimes. This new system will drive a swath of very moist air over all of the Atlantic provinces which will eventually connect with the advancing frontal boundary producing some heavy rain. Isolated thunderstorms will likely occur near the upper low, and along the front.

 

 

Thunderstorm Outlook for Friday

 

Isolated thunderstorms ahead of an upper low over CB and southwestern NF, and along a frontal system advancing over Labrador.

 

 

Convective Outlook Valid for Today, Tomorrow and Friday

Regional Impacts

NB: None

NS: None

PEI: None

NF: None

Labrador: Isolated thunderstorms possible over northwestern sections later today into this evening.

Marine waters: Isolated thunderstorms for Laurentian Fan and East Scotian Slope by later today into this evening.

 

Convective Discussion: Two areas of focus for convection today. The primary area of concern will be over northwestern Labrador where surface based convection initiating in north-central Quebec will move eastward towards a QS upper ridge positioned over central Labrador. Any convection will become elevated and more isolated as it moves towards this region, as upper level dynamics become less favourable. Nevertheless an isolated strike cannot be ruled out entirely with marginal MUCAPES of ~200 J/kg. The second area of convection will be located to the east of a cut-off low over the eastern slope waters. Here convection is expected to be elevated forced by decent instability  (MUCAPES ~500 J/Kg), and a strong LLJ (~30-35 kts at 850 mb). However it should be isolated in nature given that the best synoptic ascent will be located well to the SW (near the cut-off low). Over the next two days this area of concern is expected to gradually advect west-northwest, and convection should increase in frequency from isolated to scattered as PVA becomes more aligned with the area of instability and the LLJ. Continued moisture advection to the from the subtropics will cause PWATs to rise into the mid 40s by Thursday evening, so if elevated convection does manage to make it to land, rainfall rates will become a primary hazard.

 

Thunderstorm outlook for today:

 

 

Thunderstorm outlook for tonight:

 

 

Thunderstorm outlook for Thursday:

 

 

Thunderstorm outlook for Thursday night into Friday:

 

 

 

Convective Outlook Valid for Today and Tomorrow

Regional Impacts

NB: None

NS: None

PEI: None

NF: None

Labrador: None, isolated thunderstorms possible over northwestern sections on Wednesday.

Marine waters: Isolated Thunderstorms over southwestern Grand Banks. Isolated thunderstorms for Laurentian Fan and East Scotian Slope by Wednesday evening into Thursday.

 

Convective Discussion: Upper trough in the process of being cut-off to the south of the Maritimes as heights rise in Labrador. To the east of this feature moist unstable profiles and a moderately strong 850 mb jet can support isolated elevated convection over the southwestern Grand Banks.

As this cut-off feature retrogrades to the southwest, the instability associated with this jet structure will gradually advect westward allowing for isolated convection over Laurentian fan and the East Scotia Slope on Wednesday night into Thursday respectively. On Wednesday afternoon northwestern most Labrador has profiles that support elevated instability on the order of 300-500 J/kg however a sufficient triggering mechanism may be lacking as a warm front remains well to the east over north-central Quebec. Regardless an isolated strike cannot be ruled out, especially if this feature advects eastward faster than advertised by our current guidance.  

 

Thunderstorm outlook for today:

 

 

Thunderstorm outlook for tonight:

 

Thunderstorm outlook for Wednesday:

 

 

Thunderstorm outlook for Wednesday Night and Thursday: