Convective Outlook Valid for Today , Tonight and Tomorrow

Regional Impacts…

 

Today

NB/NS: Risk of severe thunderstorms with heavy downpours, strong wind gusts and small hail.

PEI/Labrador:  Chance of thunderstorms.

NL:  None.

 

Tonight

NB/NS/PEI/NL/Labrador:  Chance of thunderstorms.

 

Monday

NB/NS/PEI: Risk of severe thunderstorms with heavy downpours, strong wind gusts and small hail.

NL: Risk of severe thunderstorms with heavy downpours.

Labrador:  Chance of thunderstorms.

 

Convective Discussion…

A slow moving upper low with a surface reflection persists over northern Quebec today. The associated cold front extends from southeastern Labrador into northern New Brunswick. Ahead of the front, dew points in the low 20C will continue today and into tomorrow. Shortwaves will move through the region today and tomorrow with weak troughing also helping to initiate convection. The following are occurring near and ahead of the front….CAPE values of 10000-2000 J/kg, precipitable water 40- 50 mm, shear near 30 kts. Over New Brunswick the slow moving front may produce severe weather however there is a lot of cloud which is leftover from previous convection in New England. This will potentially inhibit afternoon convection by suppressing the daytime high temperatures. Supporting the convection however is the favourable right entrance of a high level jet. Over Nova Scotia a weak surface trough moving up the Atlantic coastline may initiate convection.

 

Thunderstorm Outlook for Today

 

Thunderstorm Outlook for Tonight

 

Thunderstorm Outlook for Tomorrow

Convective Outlook Valid for Today, Tonight and Tomorrow

Regional Impacts

 

Today:

NB…Some thunderstorms possibly severe for northern regions with locally heavy downpours of 25 mm/h, small hail and strong wind gusts.

NS…Heavy downpours in thunderstorms with rainfall rates of 25 to 50 mm/h over western and central regions.

LAB…Scattered thunderstorms over central and southeastern regions with locally heavy downpours, small hail and moderate wind gusts.

 

Sunday:

NB…Slight risk of severe thunderstorms with heavy downpours, strong wind gusts and small hail.

NS/PEI…Risk of thunderstorms with locally heavy downpours.

LAB…Slight risk over southeastern Labrador.

 

Convective Discussion

As an upper low stalls over eastern Hudson Bay, shortwaves will move through the region over the next several days. A broad trough continues over central and eastern Labrador and southwestward into northern New Brunswick today while a second shortwave moves across Nova Scotia and the southern marine waters today. Lightning has been consistent this morning over the Gulf of Maine with quite high rainfall rates. There is a risk of elevated convection and locally heavy downpours for western Nova Scotia and southern Maritimes waters as this wave continues eastward. Precipitable water over the region based on the YQI morning sounding is near 50 mm.

 

Convection could be organized over the Gaspe Peninsula southward into northern New Brunswick this afternoon given increasing moisture under a southwest flow in the afternoon with upwards of 1500 J/kg of MLCAPE, but upper dynamics are expected to be weak to moderate with bulk shear of 20 kt. Multicells are possible with brief strong wind gusts, locally heavy downpours and small hail being the main threats. Convection could be near severe over southern and central Labrador as well if the surface cap

 

For Sunday, a shortwave moves across eastern Newfoundland and Labrador while another wave begins to track into the Maritimes in the evening. Depending on cloud cover, widespread risks of thunderstorms are possible during the afternoon. There is ample energy with over 1200J/kg with the hot and humid air mass persisting over the region, but also an increase in dynamics with 30 to 40 of bulk shear with an approaching upper jet over central Quebec, but there will likely be a warm nose near the surface to overcome. For now central and southern New Brunswick may have the highest potential for reaching severe thunderstorm criteria.

 

Thunderstorm Outlook for Today

 

Thunderstorm Outlook for Tonight

 

Thunderstorm Outlook for Tomorrow

 

 

Roberta McArthur

 

Convective Outlook Valid for Today, Tonight and Tomorrow

Regional Impacts

 

Today:

NL/LAB… Some isolated thunderstorms possible in parts of central and eastern Newfoundland as well as western Labrador today. Locally heavy downpours of 10 to 20 mm/h.

NB…Risk of thundershowers in western New Brunswick with 10 to 20 mm/h rates.

NS/PEI… None.

 

Saturday:

NB…Some thunderstorms possibly severe for northern regions with locally heavy downpours of 25 mm/h, small hail and strong wind gusts.

LAB…Scattered thunderstorms over central and southeastern regions.

NS…Embedded thunderstorms possible with locally heavy downpours of 10 to 20 mm.

 

Convective Discussion

For today, a shortwave trough continues eastward across Newfoundland today while a broad trough moves across Hudson Bay into Central Quebec and western Labrador this evening. MLCAPE over central Newfoundland of 500 J/kg, bulk shear of 20kt and further cooling at 500mb could see some convection maintain in the afternoon. High precipitable water near 45 mm remains over the region, so locally heavy downpours are the main risk. Some TCUs in showers are possible for the Maritimes this afternoon under a hot and humid air mass. Precipitable water is around 30 mm but mean wind is rather weak, so any convection that develops may also give locally heavy downpours. There is a risk of a thunderstorms mainly where MLCAPE could reach 1000 J/kg over northern New Brunswick with a weak trough approaching from the west. There is only a slight risk that TCUs could breach the warm 500-700mb cap currently over Nova Scotia along the Annapolis Valley with the help of some sea breeze convergence.

 

For tomorrow, the broad trough continues over central and eastern Labrador and southwestward into northern New Brunswick. Convection could be organized given increasing moisture under a southwest flow in the afternoon with upwards of 1200 J/kg of MLCAPE, but upper dynamics are expected to be weak to moderate with bulk shear of 20 kt. Some organization of convection is possible into multicells are possible with brief strong wind gusts, locally heavy downpours and small hail being the main threats for northern New Brunswick. A second shortwave moves into New England tonight and into the Gulf of Maine by early Saturday into southwestern Nova Scotia. There is a risk of elevated convection and locally heavy downpours for Nova Scotia and southern Maritimes waters with an increasing 40kt 850mb jet as this wave continues eastward.

 

Thunderstorm Outlook for Today

 

Thunderstorm Outlook for Tonight

 

Thunderstorm Outlook for Tomorrow

 

 

Roberta McArthur

 

Convective Outlook Valid for Today, Tonight and Tomorrow

Regional Impacts

NS/NB/PEI… Some scattered thunderstorms possible over the central Maritimes today. Heavy downpours of 20 to 30 mm/h possible.

NL… Some isolated thundershowers possible today and tonight. Heavy downpours of 10 to 20 mm/h possible.

 

Convective Discussion

A broad upper trough will be the main focus for convection today across Atlantic Canada. A few isolated thundershowers are possible over parts of Newfoundland and Labrador this afternoon, however the main focus will be in the central Maritimes, where a few weak embedded shortwaves slightly increase the potential for some organized thunderstorms to develop today. 49.4 mm of PWAT was measured at the 12Z Yarmouth sounding this morning, with this number forecast to reach 50 to 55 mm across portions of western and central Nova Scotia, southeastern New Brunswick, and PEI this afternoon. Due to the high amount of low level cloud cover over the region, convection will rely heavily on upper level forcing today. There is a 500 mb jet over the area of interest, however it is quite weak, so convection may initially struggle to become organized until the 250 mb jet begins to intensify off the coast of Nova Scotia later this afternoon. With 20 to 30 kts of bulk shear today, the severe risk is low and storms are not expected to be long lived, however any thunderstorms that develop will have the potential to produce torrential downpours of 15 to 25 mm/h due to the high PWAT over the area.

As the upper trough moves east tonight, the risks exists for some embedded thundershowers over western Newfoundland overnight. Heavy downpours of 10 to 20 mm/h will be possible here, maybe higher over areas with topographic enhancement.

 

Thunderstorm Outlook for Today

Thunderstorm Outlook for Tonight

Thunderstorm Outlook for Tomorrow

Copp

Convective Outlook Valid for Today, Tonight and Tomorrow

Regional Impacts

NL… Some strong thunderstorms possible in parts of northern and central Newfoundland today. Main hazards are torrential downpours of 20 to 30 mm/h and strong wind gusts of 50 to 80 km/h.

NB… Some isolated thunderstorms possible over extreme northern New Brunswick this afternoon. Heavy rainfall of 10 to 20 mm/h possible.

NS/PEI… None

 

Convective Discussion

Two areas of interest exist today, the first being triggered by a weakening shortwave currently near the Strait of Belle Isle, the second being triggered by a broad upper trough over central Quebec, extending down into New England. The shortwave moving into western Newfoundland already has a history of lightning activity, with this expected to continue as it moves across northern Newfoundland today. MLCAPE is expected to build today in central Newfoundland as clear skies will allow surface temperatures to climb ahead of the approaching feature. In addition, decent dynamics (30 to 40 kts of bulk shear) will aid in sustaining some organized convection today across this region. This shortwave is forecast to weaken slightly as it traverses east across northern Newfoundland, however PWAT values of 40 to 45 mm may produce some torrential downpours of 20 to 30 mm per hour. Some strong wind gusts of 50 to 80 km/h are also possible in convection here today.

The second feature being monitored will approach western Labrador and parts of northern New Brunswick later this afternoon. Although MLCAPE values are forecast to climb above 500 J/kg, weaker bulk shear (15 to 25 kts) keeps the risk for any organized thunderstorms low. Low level cloud cover this morning is also expected to limit the available CAPE in northern New Brunswick, as such the risk for thunderstorms is lower here than in western Labrador, where clear skies are allowing CAPE to better build. The broad nature of this upper trough should keep the risk for any severe weather near nil due to the lack of shear and cold air advection. Nonetheless, some brief heavy downpours of 10 to 20 mm/h are possible in any thunderstorms here today.

Tomorrow, this upper trough will move into central New Brunswick. Again, bulk shear values remain quite low (10 to 20 kts), however PWAT values are expected to climb upwards of 45 mm by tomorrow afternoon over the southwestern Maritimes. Torrential rainfall rates of 15 to 25 mm/h will be the main hazard here in any thunderstorms that do develop here.

 

Thunderstorm Outlook for Today

Thunderstorm Outlook for Tonight

Thunderstorm Outlook for Tomorrow

Copp