Convective Outlook Valid for Today , Tonight and Tomorrow

Regional Impacts

 

Today

None forecast.

 

Tonight/Tmrw Morning

Moderate to heavy rain shower activity with embedded thundershowers advances into the SW marine district.

 

Sunday

NS/NB/PEI : Heavy rainfall is forecast to develop and persist throughout the day. Local torrential downpours are the main concern, enhanced further by embedded thunderstorms. Areas at greater risk are marked in yellow.

 

Convective Discussion

High pressure is beginning its exit from the Maritimes today, giving way to a complex moisture feed developing off the US Eastern Seaboard. This weather maker will be the story for the Maritimes from Sunday into Tuesday. Pwats within are forecast to be over 60, which will lead to heavy rainfall and potential flooding concerns locally. Embedded thunderstorms will enhance totals further. A yellow area has been depicted for now showing upwards of 100 mm. Rainfall rates of near 30mm/hour are possible in this airmass. Unfortunately the airmass can’t advance very quickly through the area with the ridge remaining stubbornly positioned over Nfld for the period. Synoptic weather warnings will be used to alert the public of this developing weather situation.

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

LAB: A chance of thundershowers.

NS/NB/PEI/NFLD: None.

 

Tonight

NS/NB/PEI/NFLD/LAB: None.

 

Saturday

NS/NB/PEI/NFLD/LAB: None.

 

Convective Discussion

A departing upper low over northern Labrador with an associated surface trough will track across eastern labrador this afternoon. MLCAPE values are expected to be 250-500 J/kg and the effective shear will be 10 to 20 knots so any thundershowers will be weak in nature. On Saturday, an area of high pressure will move across the region so convection is not expected.  

Thunderstorm Outlook for Today

Thunderstorm Outlook for Tonight

Thunderstorm Outlook for Tomorrow

 

Convective Outlook Valid for Today, Tonight and Tomorrow

Regional Impacts

Today

LAB: Chance of scattered thunderstorms across eastern Labrador this afternoon with small hail, strong wind gusts, and locally heavy downpours.

NL: Chance of an elevated thundershower over the Avalon today with locally heavy downpours.

NS/NB/PEI: None.

Tonight

NS: Slight risk of an isolated thundershower overnight over northern Cape Breton.

NB/PEI/NL/LAB: None.

Tomorrow

LAB: Chance of scattered thundershowers across central and eastern Labrador tomorrow with gusty winds and locally heavy downpours.

NL: Slight risk of an isolated thundershower over central Newfoundland in the afternoon.

NS/NB/PEI: None.

 

Convective Discussion…

This morning, an upper low sits over northern Quebec with two troughs extending south. The first trough reaches from the Labrador Sea down into the Avalon Peninsula, then south into the Atlantic. Some lightning activity was observed in this trough overnight as it moved east across Newfoundland. The risk for an elevated thundershower continues early this afternoon for the Avalon, but the trough will slowly move east out of the region by this evening. A few brief heavy downpours will be possible in these thundershowers due to some high precipitable water over the area, with 41 mm observed on the 12Z St. John’s sounding this morning. Storms aren’t expected to become too organized here today however, due to a lack of instability in the weakening trough, but some marginally severe rainfall rates are possible due to the high precipitable water. Elsewhere, the second trough is slowly moving east and extends from the upper low through central Labrador, and down into the Gulf of Maine. Some thunderstorms are expected to trigger along this trough later this afternoon over eastern Labrador, where MLCAPE is forecast to rise near 750 J/kg in addition to a diverging 500 mb jet approaching from the southwest this morning. Some storms may become organized due to effective shear of 30 to 40 kts, but none are expected to reach severe criteria. PWATs over the area are forecast to be around 20 to 25 mm, so rainfall is not a primary concern. DCAPE close to 700 J/kg however could produce some strong wind gusts in the more organized cells.

Tonight, the second trough in question will continue to move east, extending down into the Gulf of St. Lawrence. A 250 mb jet will approach from the west, to lie over the surface trough overnight, which could spark up a brief thundershower or two. These cells could impact parts of PEI and northern Cape Breton overnight and into early tomorrow morning, but the risk remains low at this time. By tomorrow afternoon, both the jet and the trough will sit over central Newfoundland. MLCAPE is expected to remain near 500 J/kg here tomorrow, with the models showing some cloud cover lingering into the late morning. If this cloud is able to clear out a bit quicker than forecast, instability may be able to rise a bit higher but confidence is low at this time. Nonetheless, the risk does exist for an isolated thundershower or two over central Newfoundland tomorrow afternoon which could produce brief heavy downpours and some gusty winds. There is also the risk of some scattered thundershowers over central and eastern Labrador tomorrow afternoon around the upper low as it spins out over the Labrador Sea. Instability is expected to be lower here though, 250 to 500 J/kg MLCAPE, so the risk remains fairly low.

 

Thunderstorm Outlook for Today

Thunderstorm Outlook for Tonight

Thunderstorm Outlook for Tomorrow

Forecaster: Copp

Convective Outlook Valid for Today, Tonight and Tomorrow

Regional Impacts

Today

NB/LAB: Slight risk for some isolated thunderstorms over northwestern New Brunswick and western Labrador late this evening with small hail, gusty winds, and locally heavy downpours.

NL: Chance of an elevated thundershower over western Newfoundland today with some locally heavy downpours.

NS/PEI: None.

Tonight

NL/LAB: Slight risk for an elevated thundershower overnight.

NB/NS/PEI: None.

Tomorrow

LAB: Chance for some scattered thunderstorms over southeastern Labrador with small hail, gusty winds, and locally heavy downpours.

NB/NS/PEI/NL: None.

 

Convective Discussion…

This morning, a disorganized elongated trough extends south from the Labrador Sea into the Atlantic waters south of Nova Scotia. Scattered thunderstorms in this trough have persisted overnight as it approaches western Newfoundland and southern Labrador, with this risk expected to continue through today. These storms are likely to stay elevated due to a thermal ridge between 750 and 800 mb evident on the 12Z Stephenville sounding, but an advancing shortwave near Cape Breton within the trough should keep scattered thundershowers going through the day. Weak MUCAPE values near 500 J/kg and effective shear of 10 to 20 kts will keep anything from becoming severe today over western Newfoundland, but some brief heavy downpours are possible with PWATs near 40 mm observed this morning at Stephenville. Elsewhere, a large trough over central Quebec will continue to move east this afternoon, reaching northwestern New Brunswick and western Labrador late this evening. A large capping inversion is present around 700 mb over New Brunswick, which is likely to keep any storms from firing this afternoon ahead of the trough. Good shear is in place (30 to 40 kts effective) and some clearing of the low level cloud is evident this morning which could help bump MLCAPE values upwards of 750 J/kg but this is unlikely to erode the cap. Due to the timing of the trough, thunderstorms aren’t expected to fire until late this evening, but by that point daytime heating will begin to shut down. The risk here today is low, but if anything is able to break the cap before the trough arrives it will have the potential to produce some gusty winds, small hail, and some heavy downpours.

Tonight, an elevated thundershower or two is possible over central Newfoundland as the first trough continues to move northeast and out over the Labrador Sea by tomorrow afternoon. The second trough impacting western Labrador and northwestern New Brunswick today will bring a similar risk for some scattered thunderstorms over southeastern Labrador tomorrow as it gradually moves east. A similar environment to today in the west is expected here, with the risk of some small hail, gusty winds, and locally heavy downpours.

Thunderstorm Outlook for Today

Thunderstorm Outlook for Tonight

Thunderstorm Outlook for Tomorrow

Forecaster: Copp

Convective Outlook Valid for Today, Tonight and Tomorrow

Regional Impacts

Today

NS/PEI/NB: Chance for some scattered thundershowers today across mainland Nova Scotia, eastern PEI, and southeastern New Brunswick with some gusty winds and locally heavy downpours.

LAB: Chance of an isolated thundershower along the Labrador coast this afternoon.

NL: None.

Tonight

NS/PEI/NL: Chance for some elevated thundershowers overnight.

NB/LAB: None.

Tomorrow

NB/LAB: Risk of scattered thunderstorms over northwestern New Brunswick and western Labrador late in the day tomorrow with small hail, gusty winds, and heavy downpours.

NL: Chance of an isolated thundershower over western Newfoundland through the day with locally heavy downpours.

NS/PEI: None.

 

Convective Discussion…

This morning, a weakening upper low sits over central Labrador, with an elongated trough extending south from the Labrador Sea into the Maritimes, where a weak surface low sits off the southwest coast of Nova Scotia. This surface low will be the main driver for convection today, with a few lightning strikes already observed offshore. Current model guidance already has some clearing over southeast New Brunswick and PEI, leading to forecast MLCAPE values of 750 to 1000 J/kg over this area, but persistent low level cloud cover over most of the Maritimes has held on this morning and the longer it sticks around, the less likely MLCAPE values are to build over 500 J/kg. Thus, most of the convection is likely to occur around the low center (where the best MUCAPE is available) as it slowly moves northeast through the day. Weak effective shear (~20 kts) is likely to keep storms from becoming organized, but due to the slow moving nature of the trough, as well as high PWATs (44.6 mm on 12Z Yarmouth sounding), some slow moving cells could drop some near-severe rainfall rates of up to 20 mm per hour over mainland Nova Scotia. Elsewhere, the upper low in Labrador could spin up some isolated thundershowers this afternoon. A bit more clearing is evident here which should allow some instability to build ahead of the upper low. Once again though, a lack of effective shear (15 to 25 kts) and some weak lapse rates will likely keep anything from becoming organized, but a few lightning strikes are possible.

Tonight, the surface low south of Nova Scotia will continue to move northeast to lie near PEI by late tomorrow morning. A slight chance of some elevated thundershowers are possible to the north and east of the low as some better jet support moves in from the West tonight. By tomorrow afternoon, the low will be approaching Newfoundland, which brings the risk for some elevated thundershowers to the western half of the island and southern Labrador. Weak lapse rates however keep the risk quite low but with similar PWAT to Nova Scotia today, some heavy downpours of 10 to 20 mm per hour are possible in any storms that do fire.

Late in the day tomorrow, a trough will approach from Quebec, bringing the risk for some scattered thunderstorms over northwestern New Brunswick and western Labrador. There is a lot of uncertainty with regards to initiation here, the first being the timing of the trough which is currently forecast to enter New Brunswick tomorrow evening. A large CAP is also evident between 700 and 500 mb which will likely keep storms from firing tomorrow afternoon ahead of the trough. Cloud cover could also pose an issue for convective initiation, with some hi-res guidance hinting at low level cloud lingering into the afternoon over most of New Brunswick. This would drastically limit MLCAPE from building during the day, severely limiting the environment storms can fire in. Given enough clearing tomorrow and if the trough moves through early enough, the risk does exist for some small hail, strong wind gusts, and locally heavy downpours across northern New Brunswick and western Labrador.

Thunderstorm Outlook for Today

Thunderstorm Outlook for Tonight

Thunderstorm Outlook for Tomorrow

Forecaster: Copp