Convective Outlook Valid for Today and Tomorrow

Regional Impacts:

 

Today

NL: Rainfall rates 25-35mm/hr, wind gusts 70-80 km/h.

 

Tonight

None

 

Tuesday:

NB: isolated lightning.

 

Convective Discussion:

Significant instability exists across Newfoundland today. A 25/18.5 modified 12z RAOB from Stephenville yields a MLCAPE of 1000 J/kg, providing ample energy for storms to develop. Nevertheless effective shear of 20-25 kts should limit storm structure to the pulse variety. Moisture is quiet abundant with PWAT ranging from 35-45mm, giving a primary rainfall rate hazard this afternoon with storms that develop. Steep lapse rates from 900mb to the surface and widespread MLCAPEs in excess of 1000 J/kg present a secondary wind hazard, especially if shear ends up being locally enhanced (allowing for the odd storm to take on some super cellular characteristics).  Hail is anticipated to be small if it occurs due to a high HGZ and lower shear values.

 

Thursday:

Another upper trough moving through Ontario today will weaken and move eastward into northern NB tomorrow. Ongoing moisture advection throughout the day in southwest flow ahead of the upper trough should allow for some free lift late in the afternoon. Bulk shears of 30 to 40 kts in combination with MLCAPES up to 750 J/Kg could yield some stronger storms, however there remains some uncertainty in terms of the timing of upper trough.

 

 

Thunderstorm outlook for today:

 

Thunderstorm outlook for tonight:

 

 

Thunderstorm outlook for Thursday:

 

Convective Outlook Valid for Today and Tomorrow

Thunderstorm Outlook for Today

 

Regional Impacts

Labrador.. numerous strong thunderstorms expected with downpours giving rainfall rates of 20+ mm/h, wind gusts 70 to 90 km/h, and hail. Some of the storms could reach severe limits and a watch has been issued for the Churchill Valley, including the Churchill Falls townsite.

NB.. Strong thunderstorms producing downpours giving rainfall rates of 10-20 mm/hr, gusts 60-80 km/h.

NF.. risk of a non-severe thunderstorm over western sections

NS and PEI.. risk of a non-severe thunderstorm

 

Convective Discussion

A surface cold front over the St. Lawrence Valley will move across Labrador and New Brunswick this afternoon. This feature is the focus for convective activity today. Thunderstorms have already been reported in western Labrador, and the expectation is for the storms to become numerous during the afternoon. The left exit of an approaching cyclonic upper jet will support the potential for severe thunderstorms over central Labrador. Also, in the warm sector the regional model is indicating the presence of a curved, but generally longer-live cells will likely form into organized clusters/lines. Over NB where midlevel support is not as solid, MLCAPE of ~1000 J/kg and effective shear of 30-35kt could be enough to support strong thunderstorms with convective wind gusts, there is a slight chance that some of these storms could approach the supercell category.

 

Thunderstorm Outlook for Tonight

 

 

Thunderstorm Outlook for Wednesday

Convective Outlook Valid for Today and Tomorrow

Regional Impacts

Today..

Newfoundland and New Brunswick… Slight risk of thunderstorms giving locally heavy downpours.

NS, PEI and Labrador… No thunderstorms expected

 

Tomorrow..

Labrador… Severe thunderstorms possible with heavy rain and strong wind gusts.

New Brunswick… Thunderstorms could give locally heavy downpours.

NS, PEI and NFLD… Low probability of thunderstorms.

 

 

Convective Discussion

There is a low probability of thunderstorms over the Atlantic region today a slight risk over interior parts of newfoundland and western New Brunswick. There model seems to be underdoing the surface dew points so it is possible that the cap at 700 may be overcome with daytime heating and surface convergence. Overall updrafts in thunderstorms should not be very strong with surface CAPE values generally under 500 J/kg and wind shear values not overly favourable for organised convection.

 

Tomorrow dynamics will become more enhanced wind shear and an approaching cold front that also act to enhance convection, the environment should support organised convection. There is a slight risk of severe thunderstorms over Labrador with strong gusts possible in some storms, however it is possible that could cover and rain may subdue any severe thunderstorms.  Over New Brunswick the risk will be somewhat more significant than today with more moisture and a better triggering mechanism, but weak updrafts could be the limiting factor and severe thunderstorms being only a slight possibility.

 

Thunderstorm Outlook for Day 1

 

Thunderstorm Outlook for Day 2

 

Convective Outlook Valid for Today and Tomorrow

Regional Impacts

Labrador… Slight risk of weak thunderstorms over eastern areas.

Elsewhere… No thunderstorms expected today.

 

Convective Discussion

Dynamics look somewhat favourable for the development of weak thunderstorms early this afternoon for eastern Labrador, however the conditions become less favourable later this afternoon so the conditions will not likely build through the day. If thunderstorms do develop the will likely not persist very long and be fairly quick moving. No significant rain nor severe weather is expected with these storms should they develop.

 

For tomorrow potential area of thunderstorm activity will likely expand but the likelihood is still quite low with a relatively dry airmass that will make convection difficult to get going. It is possible that some coastal convergence could be sufficient to get enough lift to initiate thunderstorms. However with weak updraft potential no significant convection is expected.

 

ML

 

Thunderstorm Outlook for Day 1

 

 

Thunderstorm Outlook for Day 2

Convective Outlook Valid for Today and Tomorrow

Thunderstorm Outlook for Today

 

Regional Impacts

Isolated thunderstorms across parts of the Atlantic provinces today. Some of these storms could become more robust over northern NF and SE Lab.. the main threat are strong gusts possibly exceeding 70 km/h and heavier showers at a rate of 10-15mm/h.

 

Convective Discussion

At 12z the 500mb low was located over the mid-coast of Labrador with a thermal trough extending to the St. Lawrence Valley. This feature will slowly slide eastward today and along with a surface trough will become the focus for isolated pulse type thunderstorms during the afternoon especially over N portions of NF. All soundings across the region (except NS) were indicating a convective temperature ranging from 21 to 25 which should be reached fairly easily despite the limited sunshine.. with a couple of moisture axis maintaining Td’s above 16.. the result is MLCAPE between 500 to 800 J/kg. Under these conditions widespread Cu/TCU field is expected to grow during the afternoon and some of these cumuliform clouds should reach the next stage and evolve into CB’s with tops extending to 9 km, well below the tropopause which is lowering. Precipitable water analysis is showing 25-30 mm throughout the area, and as much as 35-40 over NS where stratiform cloud and embedded TCU’s are exiting.

 

 

Thunderstorm Outlook for Sunday