Convective Outlook Valid for June 30th, 2019

 

Convective Discussion

 

Today we are looking at a few different areas of convective activity, an area of low pressure slowly moving south of Nova Scotia and surface based convection for this afternoon over interior areas of Newfoundland and Labrador.

 

An upper level low over southern Quebec will be slowly drifting southeastward today and align with a surface low pressure system which is developing southwest of Nova Scotia and will drift eastward this afternoon. Elevated thunderstorms have already been firing up over southern Maine and have slowly drifted towards the western marine areas and western Nova Scotia. There has also been quite a bit of convection over the extreme southern slope waters of the Maritime marine district associated with the low’s warm front. That general area of convection is expected to round up the eastern and northern side of the low affecting parts of eastern Nova Scotia this evening and overnight. The main threat with this convection today and overnight will be heavy downpours. There is not much wind shear aloft to drive convection along that develops and precipitable water values are ranging from 30-35mm. There could be some localized areas of 30-50 mm mainly over extreme western Nova Scotia and parts of Cape Breton. There is also some upper level support being on the left exit of a strong 250 mb jet and a cold pool at 500mb over central Quebec tracking to the southeast. Some late afternoon convection is also possible over northwestern New Brunswick associated with the upper level low, especially if they get some clearing this afternoon.

 

For Newfoundland and Labrador, the main trigger for thunderstorms this afternoon will be daytime heating as well as slight cooling in the upper levels enhancing instability. Goose Bay sounding required a convective temperature of 20C with 300 J/kg of CAPE. There is very little shear however so only non-severe pulse type storms are expected west of Goose Bay giving brief gusts and locally heavy downpours. Similarly over Newfoundland, the main risk for any convection will be over interior areas where maximum daytime heating is likely with temperatures expected to reach 23C, combined with slight troughing in the upper levels.

 

Regional Impacts

 

Maritimes…

Locally heavy downpours over western Nova Scotia and Cape Breton. Isolated downpours and brief gusts over northwestern New Brunswick.

 

Newfoundland and Labrador…

Risk of locally heavy downpours and brief gusts over central Newfoundland and central/western Labrador.

 

 

 

Roberta McArthur

 

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