Convective Outlook Valid for July 26 2019

Convective Discussion:


Thunderstorms are unlikely over Atlantic Canada today due to very dry conditions and subsidence in the mid levels over the Maritimes and Newfoundland. The subsidence inversion in the 700 to 600 mb layer should suppress any convection exceeding that layer. These conditions are the result of a large surface high over southern areas and an approaching upper level ridge today and tonight. Showers are likely later today over southeastern and central Newfoundland. However, the dry air and subsidence aloft should prevent any TCu’s that form from obtaining sufficient height to become CB’s.


Over Labrador, relatively warm air aloft and cool air in the low levels will give a profile too stable for deep convection. In addition, mid-level cloud and moisture will suppress solar insolation.


Regional Impacts:

Maritimes: none.

Newfoundland: Scattered showers, thundershowers unlikely.

Labrador: none.

Marine areas: none. 

Convective Outlook Valid for July 25 2019r

Convective Discussion:

A slight chance of thundershowers over northern Labrador and for the southern border between Labrador and the Quebec border. Over southernmost sections of the Scotian Shelf and the southern Grand Banks occasional thundershowers.

Today a broad trough will be moving into Labrador from the west as a trigger, with some associated cooling aloft and weak destabilisation. The main inhibitor is again a lack of moisture. From 850 mb and higher there is precious little moisture, and at the surface the dew points are near 10 C or less.  PWATs over and upstream of Labrador are only near 17 mm. Now there is some low to mid level cloud moving in , which may supply the necessary moisture. Topographic forcing may help a little north and south, as previously mentioned. Impacts will be mainly some gusty winds , followed by  some brief heavy showers,  Freezing levels are again below 9000 ft, so there is a slight chance for small hail.

For the Maritimes there is little upper forcing, low shear near 20-25 kts, PWAT less than 20 mm, and low to moderate dew points. For Newfoundland the shear is higher as is the PWAT in the southeast, but upper forcing  is again limited. Finally , Stephenville and St. John’s tephis, show a moderate cap in the west and a strong cap in the east.

For offshore waters, high SSTs near the North Wall of the Gulf Stream will trigger some thunderstorms, further north isolated embedded convection is possible,

Regional Impacts:

Maritimes and Newfoundland: none.

Labrador: low chance for non-severe convection for northern Labrador and the southern border.

Marine areas: occasional non-severe thunderstorms over the southern Scotian Shelf, as well as the southern Grand Banks.

Doug Mercer

Convective Outlook Valid for July 24 2019

Convective discussion:

Non-severe thunderstorms possible for Labrador, western New Brunswick, and most southern offshore waters. Severe is likely near Geroges Bank, where squall warnings are in effect.

Currently there is a trough extending over southwestern forecast waters, which currently have SSTs above 26 C.  This is giving CAPEs near 2500-3000 J/kg, and wind gusts in excess of 40 kts are likely. PWAT is in the 50 mm range. But 0-6 km Shear is low, near 20 kts. So these are multicells organised along the weak trough moving though. While SST’s drop gradually farther east, there are still SSTs near 20 C  for  southernmost parts of Laurentian Fan and the Grand Banks

For western New Brunswick the main limiting factor is moisture. PWAT is near 20 mm, at 850  mb dew points are near or less than 8 C, and surface dew points are less than 16 C. While there is a strong  upper jet over the province, it is not well placed for any significant lift. There is a weak trough over the southern part of the province, and some low level moisture is advecting in from southern Maine. Conditions are clear with come Cu setting up. Based on this there is a chance for isolated thundershowers this afternoon and ending this evening, with the highest chance in the south.

For Labrador there is a QS low near Ungava bay with a trough extending south crossing western areas moving towards the coast, giving weak lift enhanced a bit near the trough. A slowly approaching deep thermal trough from the west will help destabilise things,  and the aforementioned upper jet is over southernmost Labrador. The left exist is a bit too far east, but may enhance things along the border range in the south, and maybe south of Lake Melville near the coast. Limiting factors are again low PWAT amounts near 20 mm, and  low dew points. Excpect non severe thundershowers with some moderate wind gusts. With freezing levels generally below 8500 feet, small hail is possible.

Regional Impacts:

Labrador: non-severe thundershowers are expected this afternoon into this evening. These’s a chance of near severe cells near the southern border of Labrador.

Western New Brunswick: slight chance of thundershowers this afternoon.

Slope waters  extending to south of the Avalon Peninsula: For western slope waters just south of the main discussion area, squalls are likely for western areas. Elsewhere non-severe embedded thundershowers are expected.

Doug Mercer

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