Convective Outlook Valid for August 6, 2019

Convective Discussion

 

There are residual low clouds associated with a departing low pressure system east of Newfoundland. Elsewhere across the Atlantic provinces, the upper ridge continue to prevail today preventing any convective cloud to form.

Two upstream systems may impact the parts of the region in the medium term:

A frontal wave over northwestern Quebec will advance towards western Labrador tonight and Wednesday bringing a slight risk of thundershower;

Another frontal wave, over the Gulf stream will push a humid air mass over Nova Scotia offshore waters bringing scattered thundershowers along with a chance of downpours and locally gusty winds.

 

Regional Impacts

 

Newfoundland: Nil

 

Labrador: Slight risk of thundershowers early Wednesday

 

NB and PEI: Nil

 

NS: Downpours and higher gusts near thundershowers for offshore waters

 

 

Jean-Marc

 

Convective Outlook Valid for August 5, 2019

Convective Discussion

 

At the surface, a cold front stretches north-south over eastern portions of Newfoundland. An upper cold low will remain parked over the lower Quebec North Shore today, eventually moving east of Labrador Tuesday.

A cluster of lightning associated with the cold pool persists this hour over southeastern Labrador, and this activity is expected to continue well into the afternoon. An upper trough extending southward from the upper low along the west coast of the island will move across central regions this afternoon triggering isolated thundershowers ahead of it. The main threat with these storms is brief heavy downpours and gusts up to 70 km/h.

 

Tranquil weather conditions are expected across the rest of the Atlantic provinces this afternoon.

 

Regional Impacts

 

Newfoundland: potential for brief heavy downpours (20 mm) for northern, central and eastern regions of the island

 

Labrador: potential for brief heavy downpours (20 mm) over southeastern regions

 

NB, NS and PEI: Nil

 

 

Jean-Marc

 

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