Convective Outlook Valid for Today, Tonight and Tomorrow

Regional Impacts

Today: Organized convection is occurring this morning offshore of Baccaro Pt, NS. Frequent lightning and heavy rainfall are the associated hazards. Pop-up shower risk in extreme western Labrador and northern NB - a few of these could be TCUs tall enough to create a few lightning flashes. No sig rainfall expected here.

Tonight: No thunderstorms forecast under stable conditions.

Thursday: Approaching trof brings risk of discrete cell thunderstorms in NB late day, and embedded thunderstorms across SW NS late day. These storms are not expected to be severe at this time.

Convective Discussion

Morning sounding at YQI remains very saturated at all levels, much like yesterday. But today’s limiting factor is a trigger. There isn’t really a strong forcing to create anything organized other than the shortwave offshore that is causing ongoing convection. TCUs in NB will remain unorganized and not overly tall, if they even develop. Similar setup in Labrador of weak dynamics. Tomorrow brings an approaching trof interaction late day that cools the column aloft after maximum daytime heating and will destabilize the column over the western Maritimes. However, it is fairly skinny cape for the time of year.

Thunderstorm Outlook for Today

Thunderstorm Outlook for Tonight

Thunderstorm Outlook for Tomorrow

Forecaster: Tirone.

Convective Outlook Valid for Today, Tonight and Tomorrow

Regional Impacts

Today: Embedded convection with the influential coastal troughing across NS – specifically the South Shore. Only hazards forecast are potentially high rainfall rates and lightning.

Tonight: Offshore deep convection continues, but slowly pulling away.

Wednesday: Pop-up shower risk in extreme western Labrador and northern NB. A few of these could be TCUs tall enough to create a few lightning flashes.

Convective Discussion

Pwats remain high this morning and early this afternoon across parts of NS, particularly the SW. Organized convection could bring locally very heavy rainfall. YQI sounding this AM is basically wet adiabatic from 900mb to the stratosphere. Caribou is much drier above 600mb as it is out of the tropical airmass. The depth of moisture is being closely monitored today and alerts will be issued if a storm back-builds or stalls over a particular region. The special weather statement continues to highlight the potential. The tropical dynamics pull off land this evening, but remain over the marine district tonight. Tomorrow is much quieter with minimal cape to work with, and a return to seasonal temperatures and humidity.

Thunderstorm Outlook for Today

Thunderstorm Outlook for Tonight

Thunderstorm Outlook for Tomorrow

Forecaster: Tirone.

Convective Outlook Valid for Today, Tonight and Tomorrow

Regional Impacts

Today: Isolated severe supercell structure is possible along colliding boundaries across western NB this afternoon. There is an elevated risk of rotation within these cells. Damaging winds, heavy rain, and hail are also NB hazards today. Across NS, storms are also likely to fire along “the spin” of eastern mainland. These cells are capable of producing moderate rainfall.

Tonight: With a tropical push of moisture and enhanced lift, scattered-numerous strong thunderstorms are forecast across mainland NS during the overnight hours. These storms bring a significant rainfall risk. A special weather statement has been issued to provide the public with advance notice of this event.

Tuesday: As the forcing pulls away over the marine district, embedded thunderstorms are still possible midday. The hazards are diminishing at this time.

Convective Discussion

--Potentially Impactful Next 24hrs--  There are 2 events that are shaping up to affect the Maritimes district. (Nfld and Labrador are quiet for this forecast period.)

1. Supercell development is possible in western NB this afternoon driven by high moisture and high shear. Pwats support deep convection, and there is a 65kt Jet supporting the activity. Effective shear is over 55kts at max daytime heating today. Sig tor and EHI flag tornadic potential, similar to yesterday but with stronger signals. This poses a wind risk, hail risk, and heavy rain risk. The yellow area on today’s outlook conveys this message. Alerts may be required. The dynamics upstream in Maine are being closely monitored at the typing of this report. Organized storms are also possible across inland NS – but these storms don’t have the same enhanced shear dynamics to work with. Mositure across NS is impressive this morning, dewpoints over 20, with fog patches.

2. Tonight brings even more moisture into the equation, from the remnants of what was once Tropical Storm Chantal interacting with a longwave nearly-stationary trof. This stream of juicy air is entering our AOR this evening. As such, Pwats soar over 65 in places, and columns are fully saturated by midnight. The main hazard tonight is heavy rainfall. The yellow area on tonight’s graphic depicts this risk area. KF Rainrate products are depicting hourly rainfall rates of 60 mm/hr. This seems potentially too high. But it cannot be fully ruled out. The system has tropical influence and a history of producing locally very heavy downpours. If storms are training or slow moving, then higher precip amounts are possible. Forecasters will be paying close attention to this tonight.

Thunderstorm Outlook for Today

Thunderstorm Outlook for Tonight

Thunderstorm Outlook for Tomorrow

Forecaster: Tirone.

Convective Outlook Valid for Today , Tonight and Tomorrow

Regional Impacts

Labrador … A few thunderstorms possible along cold front today, heavier showers and some wind gusts possible.

NFLD… No thunderstorms expected.

NB…Thunderstorms this possible this afternoon and this evening, locally heavy downpours and strong wind gusts are possible.

NS and PEI… Some thunderstorms could affect PEI and northern NS this evening.

Convective Discussion

Unsettled weather will continue over the next few days. An approaching cold front is expected to trigger some surface-based convection today over Labrador and into New Brunswick. While instability in Labrador is not particularly high, the fast-moving upper trough may destabilize the atmosphere more than models currently suggest. Some gusty winds may be possible in stronger cells, but they are expected to remain below warning criteria.

Over New Brunswick, strong wind shear, high moisture, and moderate CAPE could support the development of some intense cells. With strong linear shear in place, cells are expected to move quickly — roughly east to southeast at 25–30 knots — which may help limit the overall heavy rainfall potential. However, rainfall rates could still be very high, with some potential for localized flash flooding.

Although some convection is possible this afternoon, the more likely scenario is for deeper convective cells to move into western parts of the province by early this evening. If severe thunderstorm alerts are issued they would likely be later in the day.

Thunderstorm Outlook for Today

Thunderstorm Outlook for Tonight

Thunderstorm Outlook for Tomorrow

 

Mel Lemmon

Convective Outlook Valid for Today, Tonight and Tomorrow

Regional Impacts

Today: Some scattered thunderstorms possible across Atlantic Canada today. Main hazards are locally heavy downpours, small hail, and some strong wind gusts.

Tonight: Risk of some isolated thundershowers tonight through the central Maritimes. Locally heavy downpours are the main hazard.

Tomorrow: Some scattered thunderstorms possible over central Newfoundland tomorrow afternoon. Main hazards are locally heavy downpours, small hail, and some strong wind gusts.

Convective Discussion…

A cold front that moved through New Brunswick yesterday continues to produce some thunderstorm activity over the Gulf of St. Lawrence and eastern PEI this morning. Bulk shear values over 40 knots here under the 500 mb jet will aid in sustaining these storms through the day with land impacts likely to only be felt in the Magdalen Islands and northern Cape Breton early this afternoon, and extreme western Newfoundland later this evening. Heavy downpours are the main risk with these storms due to some higher PWAT values over 35 mm here, though some small hail is also possible with the strongest cells.

In addition, an upper low centred over northern Maine this morning will track into southern New Brunswick early this afternoon and continue to move east through the day. Modest MLCAPE values of 500 to 1000 J/kg through southern New Brunswick and central/eastern Nova Scotia will support the development of some thunderstorms out ahead of the upper low, in areas of enhanced vorticity advection. Bulk shear values are a bit lower than yesterday here, in the 25 to 35 kt range, which should limit storms from becoming severe or very long-lived. PWAT values in the 20 to 30 mm range and low freezing levels hint at the risk for some locally heavy downpours and small hail. Some of these storms may sustain themselves overnight around the upper low centre as it moves through the central Maritimes. Tomorrow, a similar environment is in place for central Newfoundland with the same upper low forcing convection.

Thunderstorm Outlook for Today

Thunderstorm Outlook for Tonight

Thunderstorm Outlook for Tomorrow

Forecaster: Copp