Convective Outlook Valid for Today and Tomorrow

Thunderstorm Outlook for Day 1

 

Regional Impacts

 

For Eastern Newfoundland…

No significant impacts are expected do to thunderstorm activity today, some locally heavier embedded showers in thunderstorms and occasional lightning might affect the forecast.

 

Convective Discussion

 

For today there will be sufficient moisture and instability east of the most of the public areas to generate occasional embedded thunderstorms just ahead of the 250 jet that is slowly swinging northeastward today.

 

The dynamics are coming together for tomorrow with the upper level jet becoming a supporting factor for the development of Thunderstorms. Central Newfoundland is currently the most likely area to be impacted with a low potential for severe storms. Low level moisture could be the limiting factor but areas of enhance low level convergence could see some thunderstorms develop.

 

Thunderstorm Outlook for Day 2

Convective Outlook Valid for Today and Tomorrow

Thunderstorm Outlook for Day 1

 

 

Regional Impacts

Widespread rain across NS, rain also across Labrador mixing with some snow in the west. Scattered shower activity across the rest of the Atlantic provinces.

 

Convective Discussion

Vertically stacked low near Anticosti Island at 12z with an east-west orientated frontal wave over Labrador. Cold front has moved past Newfoundland with pressure rises of about 4mb in behind between 9-12z over eastern portions of the island. The airmass has dried out significantly behind the frontal feature but it remains fairly unstable as indicated by the YJT sounding. In this unstable environment, bands of TCU with tops to 15,000ft or more will develop giving scattered showers. Note that surface based CAPE values of more than 250 J/kg are attained simply by warming the surface to 16C, so in this context the development of a small CB with tops over 22,000ft is not out of the question over west-central and northern Newfoundland this afternoon. The latest satellite imagery is showing more and more breaks in the cloud which could be the key to the last point.

Further away from the low, and around the cold pool aloft we find a couple of troughs, one over the Saint. Lawrence Valley and another one over NS where overcast stratiform conditions with widespread rain will prevail, the Shearwater sounding shows some instability between 5,000 to 10,000ft which will result in localised heavier rain with these embedded TCU’s.

Over NB, The airmass is quite dry but small warming of the surface will produce bands of TCU’s with tops between 12,000 to 14, 000ft and spotty showers.    

 

 

Thunderstorm Outlook for Day 2

 

Convective Outlook Valid for Today and Tomorrow

Thunderstorm Outlook for Day 1

 

Regional Impacts

Burin and Avalon Peninsulas of Newfoundland: showers heavy at times giving amounts near 50 mm.

 

Convective Discussion

This morning’s 12z analysis is showing the 500mb upper cold low anchored off the South Shore of Nova Scotia. Some convection is evident on the Satellite pictures south of the low and the Scotian slope, and lightning is limited to areas south of 40N. East of the low, very strong southerly winds are pushing a moisture plume originating from around 35N all the way to the Gulf of St. Lawrence and Newfoundland. The 12z sounding from YJT is showing nimbostratus up to 27,000ft and precipitable water of 35mm. The YYT sounding is showing a 50 knot low-level-jet and layers of instability in the mid-levels suggesting ACC’s which could result in rainfall rates of 10mm or more per hours later in the day and tonight. The probability of thunderstorm is not zero over NF, but the risk was left out of the outlook. The very moist airmass will continue to move northward over southeastern Labrador today and tonight.

 

Thunderstorm Outlook for Day 2

Convective Outlook Valid for Today and Tomorrow

Thunderstorm Outlook for Day 1

 

 

Regional Impacts

Burin and Avalon Peninsulas of Newfoundland: slight chance of embedded thundershowers, which may give some gusty winds over land.

Maritimes including marine waters: nothing significant expected.

 

Convective Discussion

Basically the same reasoning as for Sunday. There was some convection well south of Newfoundland last night, but no threat resulted for the island. The low/trough is basically stalled near and south of the Cabot Strait, and will gradually intensify and drift north. CAPE’s are marginal or non-existent with current guidance, but could become strong enough to fire off a cell or two if the models are off a little. If so, it will probably be over eastern Newfoundland in onshore flow, where the shear is weak enough (near 30-35 kts) to allow TCus or CBs  to develop. Over western Newfoundland the shears are 65+kts, eliminating the chance for CBs.

 

 

Thunderstorm Outlook for Day 2

 

 

Burin and Avalon Peninsulas of Newfoundland: slight chance of embedded thundershowers, which may give some gusty winds over land. Barely possible.

 

Convective Outlook Valid for Today and Tomorrow

 

Thunderstorm Outlook for Day 1

 

Regional Impacts

 

Southern Avalon Peninsula and marine waters to the south and southwest: Chance of embedded thundershowers this afternoon into the overnight period. No significant impacts expected.

 

Convective Discussion

A cold front from a weak low on the Gulf of St. Lawrence will slowly move east today and will then stall south to southwest of Newfoundland on Monday. North of the low and west of the cold front conditions will quickly dry out, and as the ridge to the west moves in convection will be inhibited, with thunderstorms unlikely. Embedded thundershowers near Georges banks will move east over slope waters today, and may approach the Avalon this afternoon and again overnight as the storm stalls and intensifies. CAPE’s are expected to be low,  well below 500 J/kg. In addition the deep layer shear will be too strong southwest of Newfoundland, shearing off the cells, but will drop a bit towards the Avalon allowing a chance for some isolated thundershowers and possibly gusty winds over land.

 

Thunderstorm Outlook for Day 2

 

Slight chance of embedded thundershowers continuing into Monday for eastern and northern Newfoundland. No significant impacts expected.