Convective Outlook Valid for August 4, 2019

Convective Outlook.

 

There are a couple areas of concern today: one over central NL and the other along portions of NS. First in NL, elevated morning convection giving locally heavy downpours should weaken in the coming hours. If things clear in the SW after lunch there is plenty of CAPE (1000 j/kg or more) so cells could fire fairly quickly and move northeastward through the afternoon and into the evening. Based on the 12Z YJT tephi the shear is low, but freezing levels are fairly low as well. Could be some strong wind gusts and small hail, but the main threat would be torrential downpours with 25 mm/h possible.

 

Now for NS. After analyzing things from the surface to 250 all the ingredients are there for a potentially stormy afternoon (of course, from experience working the desk this not always pans out). There is a 90 knot 250 mb jet observed in YQI placing NS in the left exit region. There is a strong 50 knot jet along SW NS with an approaching upper trough to the west, with 40-50 knots of shear along with falling atmospheric heights. There is also an approaching 700 mb trough. Sat pix shows plenty of sunshine to aid convection at the moment (need to keep an eye on some mid-level cloud sneaking into SW regions). There is a thermal ridge at 850 pushing into the province and an approaching surface cold front, that at 12Z, was analyzed to be somewhere near western and northern portions of the province. Dewpoint temps should be in the upper teens this afternoon proving the moisture. There were a couple severe cells in NB yesterday with Tds several degrees cooler, so confidence is fairly high that we see a couple strong storms this afternoon and into this evening. In addition, CAPE values could be up around 1500 j/kg. The instability won’t be that strong as LI’s will be around -4, but with all the other ingredients, this shouldn’t be of concern as a limiting factor at all. Torrential downpours and strong winds are the main threats…though some small hail is also possible.

 

Regional Impacts.

 

Newfoundland: potential for very heavy downpours with cells today across central regions of the island…25 mm/hr.

 

Nova Scotia: potential for very heavy downpours and strong winds from Queens County through to Pictou and Antigonish (including all counties along the ATL coast of NS) as well as Cape Breton.

 

PEI: slight risk of a thundershower for eastern portions of the Island.

 

NB/LAB: nil.

 

 

Jeremy

Convective Outlook Valid for August 3, 2019

Convective Discussion.

 

There are a couple areas today that run the risk for some thunderstorms. First is across WRN/CNTRL LAB where an upper trough will produce some TCU and SCTD CBs this afternoon. There is very little shear and lack of moisture, but freezing levels are fairly low. Some small hail is a possibility. SAT PIX is showing the cloud breaking up which will aid their development.

 

The second area will be across NRN/CNTRL NB this afternoon and into this evening. KCAR is showing decent shear (40-45 knots), but is lacking low level moisture. Also modifying for a convective temperature of 27 only gives a few hundred J/KG of CAPE. An upstream upper level trough will help to initiate some convection after lunch. Given the dry air below 700 mb, there could be some modest dry microbursts in the stronger cells. Right now severe storms are not expected…and just a slight chance in seeing near severe storms this afternoon and into this evening. Local downpours are also possible along with small hail. Later tonight, some of the convection may slide south and eastward affecting SRN NB and parts of PEI.

 

Regional Impacts.

 

Labrador: scattered non-severe cells this afternoon for central and western regions.

 

New Brunswick: scattered storms this afternoon and evening for central and northern portions of the province. Gusty winds and small hail with some cells.

 

PEI: risk of seeing a TRSA tonight as convection drifts eastward from NB.

 

Nova Scotia/Newfoundland: nil.

 

 

Jeremy

Convective Outlook Valid for August 2nd, 2019

Convective Discussion

 

A couple of upper level disturbances are affecting Labrador today, while a trough continues to pull east of Newfoundland. Convection has been ongoing over eastern marine waters from the southern Grand Bank northeastward towards Funk Island Bank this morning and is expected to pull east of the marine waters this evening. With the aid of some coastal convergence and slight cooling aloft, southeastern Labrador could see some thundershowers this afternoon. Freezing levels are fairly low but there is still a decent amount of precipitable water so heavy downpours and small hail is possible.

 

A weak low pressure area currently south of James Bay will continue tracking to the southeast. A trough extending southeast of the low will bring some isolated showers to northern New Brunswick this evening and overnight. At this time the dynamics do not look favourable to initiate any surface based thundershowers as there is a considerable cap at 950mb based off the Caribou sounding to overcome.

 

Regional Impacts

 

Labrador…Lightning, locally heavy downpours and small hail are possible for southeastern Labrador.

 

Maritimes and Newfoundland…None

 

 

 

 

Roberta McArthur

 

 

 

Convective Outlook Valid for August 1st, 2019

Convective Discussion

 

Another active day for the Atlantic provinces today. A trough stretching from central Labrador to southwestern Nova Scotia will slowly progress eastward this afternoon. Along and ahead of the trough, moisture remains high with dew points in the 18-20 degree range. Along with some solar insolation and a slight increase in 0-6km shear, thunderstorm development will likely initiate this afternoon and continue into the evening. There has already been some elevated convection this morning over Newfoundland that will continue to push to the northeast. There is a thicker cloud band with isolated showers stretching the Gulf of St. Lawrence toward southwest Nova Scotia. Should this cloud break up this afternoon, surface based CAPE values could range from 1500-1800 J/kg over parts of mainland Nova Scotia and central Newfoundland. Surface based convection is expected to initiate early this afternoon over the spine of Nova Scotia and central Newfoundland. The main risk with these storms will be heavy downpours (25-50mm), especially over Nova Scotia and central to northeastern Newfoundland where some training of thunderstorms may occur. There is also the risk of hail (1-2cm) and strong wind gusts.

 

Central Labrador will also continue to see come elevated embedded convection associated with an upper level low over northern Quebec. Locally heavy downpours and small hail are possible.

 

For southern marine areas, there are a couple of low pressure centers that are tracking from West Scotian Slope to the southern Grand Banks. Some isolated convection is expected to continue today. Some strong wind gusts to 30KT are possible under thunderstorms.

 

Regional Impacts

 

New Brunswick… Mainly southern New Brunswick could see lightning and locally heavy downpours.

 

Nova Scotia…Lightning, heavy downpours (25-50mm where training may occur), small hail and strong wind gusts.

 

PEI…Lightning, heavy downpours , small hail and strong wind gusts are possible.

 

Newfoundland…Lightning, heavy downpours (25-50mm where training may occur), small hail and strong wind gusts.

 

Labrador… Lightning, heavy downpours , small hail and strong wind gusts are possible.

 

 

 

Roberta McArthur

 

Convective Outlook Valid for July 31st, 2019

Convective Discussion

 

This could be a very active day for much of the Atlantic Provinces with the main focus of energy being over New Brunswick and possibly spreading into western PEI. In general there will be a weak surface trough from western Labrador then through New Brunswick which will help aid in the thunderstorm initiation. For most of the Maritimes there are high CAPE values between 1000-2000 J/kg and very high levels of moisture, this will lead to a high probability that heavy down pours will occur. Over Newfoundland and Labrador updrafts will be much weaker however with the high moisture content of the airmass locally heavy rain is still a possibility. Over New Brunswick the wind shear is sufficient to organize some storms, longer lived thunderstorms can be expected with a low chance of supercell and bow echo formation. Should stronger storms develop strong wind gusts 70-90 km/h and hail of 2-4 cm is possible.

 

Over Nova Scotia dynamics are not as favorable however there is a chance that back building thunderstorms could develop along the spine of nova scotia.

 

Regional Impacts

 

New Brunswick… Heavy Rain 25-50mm in heaviest thunderstorms, Hail 2-4 cm and wind gusts 70-90km/hr.

 

Nova Scotia… Heavy Rain 25 mm, locally higher amounts in back building thunderstorms.

 

PEI… Heavy Rain 25-50mm in heaviest thunderstorms, Hail 2-4 cm and wind gusts 70-90 km/hr over western areas possible.

 

Newfoundland and Labrador… Locally heavy downpours 20mm, small hail possible over western Labrador.