Convective Outlook Valid for June 29th, 2019

Convective Discussion

Modifying the 12Z Caribou sounding to the convective temperature of 24 deg gives 830 J/kg of CAPE. There is 35 knots of 0-6 km shear. The shear is unidirectional and is all above 3 km. At Caribou, the shear from 0-3 km is very low so based on this sounding, squall lines are unlikely. There is a strong 80 knot jet in the upper levels over the southern Maritimes as indicated by the 12Z sounding at Yarmouth. However, over NS and PEI, CAPEs are low so severity is not expected. The prog sounding for 18Z over western Labrador indicates that with daytime heating to the forecast high of 19 deg, convective initiation would give up to 800 J/kg of CAPE. Shear over western Labrador is low, so only pulse storms are expected if they form.


 As is often the case, the challenge today is the amount of sunshine this afternoon to trigger the convection. At 11 am there is still a lot of cloud cover over the areas outlined as potential for convection. For NB where there is a slight risk of conditions approaching or meeting severity, the most likely scenario is for strong storms to form over srn QC and then advecting late this afternoon or this evening over the province.

Regional Impacts

 

Maritimes…

Risk of thundershowers over most of NB, mainland NS, slight risk PEI. Possible wind gusts and small hail over NB

Newfoundland and Labrador…

Risk western Labrador.

 

Stephen Hatt
Forecaster
ASPC 

Convective Outlook Valid for June 28th, 2019

Convective Discussion

Convection today will be surface based with generally low CAPE’s. Highest CAPE will be northwestern New Brunswick this afternoon where up 700 J/kg is possible. Elsewhere CAPEs are in the 200-400 J/kg range. The dew points are generally in the 12-16 deg range and upstream dew points are similar. 0-6 km shear is low and in the 20-25 knot range. There is a strong 250 mb jet (60-80 knots) extending from southwestern Quebec to southwestern Nova Scotia. Otherwise mid and upper level winds are quite light over Atlantic Canada (30 knots or less). 500 mb temperatures are fairly uniform across eastern Canada at about -15 deg, so little change in stability aloft is expected.

Regional Impacts
Maritimes…
Risk of thundershowers over most of NB and western NS.

Newfoundland and Labrador…
Slight risk extreme western Labrador.

Stephen Hatt
Forecaster
ASPC

Convective Outlook Valid for June 28th, 2019 Day 2 Outlook

Convective Discussion for Friday, June 28, Day 2 Outlook

The upper trough that is digging over Quebec will move eastward tonight and will over the Maritimes on Friday. Mid level temperatures on Friday will drop a few degrees and more insolation is expected. In addition, an upper level jet over southern Ontario will move eastward over the western Maritimes on Friday. Heavy downpours of rain, small hail and wind gusts are possible

Regional Impacts

Maritimes…

New Brunswick, western Nova Scotia.

Newfoundland and Labrador…

None expected.

Stephen Hatt

Forecaster

ASPC

Convective Outlook Valid for June 27th, 2019

Convective Discussion

Conditions are generally unfavourable for convection over Atlanta Canada today. However, there is lots of instability and dynamics over the St. Lawrence River this morning that will slowly advect eastward. Over this region, there is a moist tongue of dew points in excess of 16 deg and warm temperatures of 20 deg or higher. There is an east-west 250 jet over southern Ontario and a north-south 250 jet extending from western Maine into eastern Quebec. There is also a digging 500 mb trough with diffluence ahead of it. There is a possibility that some cells with high precipitable water could creep into extreme northwestern New Brunswick later today giving heavy downpours.

Regional Impacts

Maritimes…
Western New Brunswick.

Newfoundland and Labrador…
Slight risk western Labrador.

Stephen Hatt

Forecaster

ASPC

Convective Outlook Valid for June 26, 2019

Convective discussion

Basically there is a risk of non-severe thundershowers for the western Maritimes. Currently there is a nearly stationary low near James Bay with a frontal trough extending from it southeast over Maine. This trough is nearly stationary with little dynamic upper support. There is also very little moisture west of the main feature. There is some weak detstabilisation in the mid levels, with a 500 mb thermal trough well east of the 700 mb trough thisch continues down to 850 mb. There is also some moisture near and below 850, with a moist tongue over northern Maine extending toward  Northwest New Brunswick, and mid level clouds are moving away to the east. If and when the stratus breaks up there may be enough heating to produce some thundershowers.

In the Gulf of Maine a nearly stationary broad weak low is triggering some  embedded which  moving towards southwestern  Nova Scotia. There cellc should not go much east of the tri-county area.

For Thursday, indications are for a slow progression into Labrador and across the western Maritimes.

Regional Impacts

Nova Scotia: Slight risk for this afternoon into this evening and overnight for non-severe thundershowers.

New Brunswick: Slight risk for evening and overnight for non-severe thundershowers.

Newfoundland, Labrador, and Prince Edward Island: None for today and tonight. Overnight into early Thursday morning there is a slight risk for western Labrador.

Doug Mercer