Convective Outlook Valid for July 23, 2019

Convective Discussion.

 

There is a slight risk of TSRA across CNTRL LAB today in conjunction with an approaching upper area of low pressure, and associated troughing in the middle and upper-levels. The closest TEP to try and analyze was YVZ, but it’s likely too far downstream. However adjusting for a surface temperature of 24 and adding a little moisture in the low levels could produce and few hundred joules of CAPE. Very little in the way of shear so I would expect just some ISOL pulse cells. SAT pix is showing some clearing skies so would expect convection to initiate once the Tc has been reached…early to mid afternoon.

 

A nearly stationary trough of low pressure south of NS and NL will continue to produce some SCT TS through today and tonight. The TEP out of KCHH has a 50+ LLJ at 850 mb, which is a little discerning. It wouldn’t take much to mix that wind to the surface. The afternoon marine forecast for waters south of NS will included PSBL wind gusts near thunderstorms. The SE Avalon may get clipped with some embedded TSRA tonight (say from St. Shott’s up through Cappahayden)…but it’s a marginal risk at best. PW is in the order of 40 to 50 (from the YQI TEP) so areas where there are no TS could see very heavy rains today and tonight (NS and SE NL). OTZ quiet weather for the rest of the region.

 

Regional Impact.

 

CNTRL LAB: risk for non-severe TS this afternoon.

 

NS and SE NL: LCL HVY RA today and tonight…with slight risk of TSRA for the SE Avalon tonight.

 

Elsewhere: nil sig wx.

 

 

Jeremy

Convective Outlook Valid for July 22, 2019

Convective Discussion.

 

Not a whole lot on the go today after a day of storms across NS yesterday. There is a fairly stationary trough/cold front sitting south of NS that will produce the occasional TS through the course of the day. 12Z surface analysis shows a weak waves along the front SE of the Great Lakes. Guidance moves that feature towards SW NS later tonight…so there could be some ISOL elevated TSRA after midnight.

 

The feature worth mentioning is an area of vorticity (observed on WV imagery) currently to the NE of Anticosti Island. This lobe is moving generally eastward and could produce some ISOL convection today. This area is also in the vicinity of the left exit region of a strong 250 mb jet.

 

Regional Impacts.

 

Newfoundland: PSBL ISOL TSRA in association with the area of PVA at 500 mb.

 

Nova Scotia: ISOL elevated TSRA PSBL after midnight tonight down across portions of SW NS.

 

Elsewhere: NIL SIG WX.

 

 

Jeremy

Convective Outlook Valid for July 21, 2019

Convective Discussion

 

The focus for severe weather today will be regions adjacent to southeastern Maine, and also inland portions of western Nova Scotia where hot and humid conditions prevail. Strong thunderstorms have migrated from Quebec over Maine this morning and are now entering Charlotte county in southwestern NB. These clusters of thunderstorms have a history of producing hail the size of a ping pong ball. The latest radar presentation suggests that these clusters are becoming better organized and are beginning to look more like early stages of squall lines. One of these features extends from Oromocto Lake to St. Stephen, and another one stretches NE-SW upstream from Bangor.

 

Convection should initiate during the first half of the afternoon over inland areas of Nova Scotia. The best forcing is expected over western regions but any storms that form could migrate to other regions of the province during the later part of the day. Buoyancy will increase throughout the afternoon and some of the forcing mechanisms will become better aligned. Using a Ts of 34 and Td of 24 is enough generate CAPE values in excess of 1500 J/kg pushing the lifted index to -5 or less. These large cumulonimbus would then become long-lived in this moisture-rich environment where deep layer shear of 30-40 knots are expected.

 

Regional Impacts

 

New Brunswick…For southernmost regions, strong thunderstorms with clusters of frequent lightning, widespread downpours, hail and locally severe winds.

 

Nova Scotia…For western regions, strong thunderstorms with clusters of frequent lightning, widespread downpours, hail and locally severe winds.

 

Newfoundland and Labrador…Isolated non-severe thunderstorms over southeastern regions.

 

PEI…None

 

 

Convective Outlook Valid for Month Day Year

Convective Discussion

 

A strong upper level jet stream (150 knots) runs from the Southern Prairies-Northern Ontario-Central Quebec-and then drops southeastward over the Gulf of St. Lawrence and then south of Newfoundland. Cloudy and cool conditions prevail in the airmass northeast of this feature, while hot and humid conditions prevail southwest of it.

This mornings upper-air soundings from CAR GYX and YQI are showing strong capping around 600mb, and a definite lack of forcing mechanism in the upper levels. The hot humid conditions will not be enough to trigger surface-based convection this afternoon. For this evening and overnight, some airmass thunderstorm activity from the lower Great Lakes and Northern New England may reach Maine and spread into western NB.

Regional Impacts

 

New Brunswick…Risk of a thunderstorm with localized downpours this evening and overnight

 

PEI and Nova Scotia…None

 

Newfoundland and Labrador…None

 

 

Convective Outlook Valid for July 19th, 2019

Convective Discussion

 

A short wave trough is approaching New Brunswick from central Quebec today. An increasingly more hot and humid air mass is also approaching the region this afternoon over western New Brunswick as winds begin to shift to the southwest on the  backside of a ridge of high pressure. This trough is expected to bring showers and thundershowers to northern New Brunswick this afternoon and continue to track eastward towards Nova Scotia and western Labrador by tomorrow morning.

 

The air mass will become increasingly warmer in the low levels which will lead to further instability this afternoon. As the trough approaches northwestern New Brunswick, 0-6km wind shear will increase somewhat but remain moderate, with divergence aloft and the approach of a strong 250mb jet to help maintain convection. Only modest CAPE values of 200-500 J/kg are expected, except perhaps for extreme northwestern New Brunswick which could exceed 500 J/kg. It is expected that multicellular storms will be the dominant type of convection with brief heavy downpours and strong wind gusts possible with some cells possibly developing stronger lines of convection over northwestern New Brunswick this evening. Freezing levels remain high enough that hail is not expected to be a main threat with cells that develop today.

 

Regional Impacts

 

New Brunswick…Lightning, locally heavy rainfall amounts, and brief strong wind gusts are possible for northern and central New Brunswick this afternoon and evening.

 

PEI and Nova Scotia…Scattered showers with the slight risk of a thundershower maintaining into the late evening possible.

 

Newfoundland and Labrador…None

 

 

Roberta McArthur