Convective Outlook Valid for Today , Tonight and Tomorrow

Regional Impacts

Newfoundland… Some isolated thunderstorms today and nocturnal thunderstorms tonight. Up to 25mm in thunderstorms possible.

 

Labrador… Isolated thunderstorms today and tomorrow, locally heavy downpours possible.

 

New Brunswick… Slight risk of isolated thunderstorms today. Some thunderstorms tomorrow with amounts possibly reaching 50mm/hr rainfall rates for southeastern areas. Northwestern areas 25mm possible in thunderstorms.

 

PEI… Possible thunderstorms tomorrow with rainfall rates possibly reaching 50mm/hr.

 

Nova Scotia.. Possible thunderstorms tomorrow with rainfall rates possibly reaching 50mm/hr most likely for central and northern areas.

 

Convective Discussion

A few interesting features will contribute to the convective potential over the next couple of days, first and foremost the high moisture content covering much of the region, which will aid in heavy downpours in even weaker thunderstorms. For today the shear isn’t conducive to organised convection and severe weather with a predominately zonal flow, in general any thunderstorms that do develop should be fairly isolated. However a trough/weak frontal zone currently over Anticosti will impact Newfoundland tonight possibly causing Thunderstorm activity to linger overnight.

 

A shortwave tough approaching from southern Ontario has the potential to trigger heavy downpours tomorrow. The total precipitable water (TPW) values are likely to be near 50mm and the airmass will be quite unstable ahead of the shortwave trough. If thunderstorms develop heavy rainfall can be expected, and alerts may be required, although not all models agree with this assessment. However unlike some of the recent convective rainfall events this feature should progress through more quickly, but multiple cells could still impact some areas.

 

The dynamics will continue to improve into the middle of the week as the upper trough gradually approaches from the west, but the low level moisture may be somewhat depleted leading to potentially weaker updraft potential.

 

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.. Isolated Thunderstorms giving some locally heavy downpours up to 25 mm, some stronger gusts possible.

 

Convective Discussion

The most favourable dynamics have shifted to lie just of the coast of Nova Scotia, in terms of upper support for prolonged and organized convection that will continue to diminish through the day. However there is still a decent amount of moisture in the atmosphere and surface dew point temperature will be in the high teens or even 20 C in some areas. Thunderstorms started early over eastern areas where a week trough was able to help trigger some smaller thunderstorms. As daytime heating continues there will be a slight chance of thunderstorms developing over areas including SW Newfoundland and NW New Brunswick. Moderate Cape could potentially lead to some heavier downpours and gusty winds. Wind gusts are not expected to be at warning level but if deeper thunderstorms develop it there may be a slight risk.

 

Dynamics will become more significant over the next couple days with a chance of organised convection on Tuesday. More details can be expected as we move into the shorter range.

 

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.

Scattered thunderstorms for western NB and portions of NS this afternoon and evening. Main threat is torrential downpours, but strong wind gusts are also possible in the stronger cells. There is a chance of a strong to severe thunderstorm for the eastern mainland. Storms should be non-severe for western NB.

 

Tonight.

Isolated thunderstorms possible for NS, PEI and portions of NB. Main threat is torrential downpours.

 

Sunday.

Isolated thunderstorms possible for Cape Breton. Main threat is torrential downpours.

 

Convective Discussion

There are a couple features that will impact the region today – a weak trough that’s currently stretching from the Cape Cod area into southwestern NB and an upstream short wave trough currently over southern Quebec. The aforementioned trough could be the catalyst for an isolated strong to severe thunderstorm this afternoon/evening for a portion of eastern NS. The 12Z tephi out of YQI looks decent and adjusting the surface temp and dewpoint results in a mixed CAPE close to 1000 J/KG. There is also decent shear of around 35 knots. Of course there is PLENTY of low level moisture as we continue to be plagued with very high humidity near the surface (PWAT just shy of 50 mm at YQI). The instability is modest as well so we just need some sunshine to fire off a storm or 2. Upstream SAT PIX does show some openings in the overcast ST/SC deck but also some fairly fast approaching mid-level cloud in the gulf of ME. Given the recent flooding in areas of NS there is somewhat heightened awareness today in the event we see cells develop. The one saving grace would be the forward motion of the convection as the mean flow would have it moving eastward at 60-70 km/h. Rainfall rates of up to 50 mm/h look possible. The issue would be if we see any training/back-building of cells. We shall see…

 

The second feature mentioned above is already producing some storms upstream. As the short wave approaches ME and western NB we expect to see some scattered thunderstorms this afternoon and into this evening. Locally torrential downpours seem to be the main concern.

 

There could be some isolated convection tonight and into Sunday morning for eastern NB, NS and PEI as that same short wave moves across the MRTMS. And given what we are seeing at this hour in southern QB there is a chance that Cape Breton sees a isolated cells Sunday afternoon as the short wave just exits the region.

 

Thunderstorm Outlook for Today

 

Thunderstorm Outlook for Tonight

 

Thunderstorm Outlook for Tomorrow

 

Jeremy

Convective Outlook Valid for Today, Tonight and Tomorrow

Regional Impacts

Scattered thunderstorms are forecast over extreme SW-ern NS late today, as well as the potential for isolated marginally severe thunderstorms from Windsor through to Collegeville area today. More organized thunderstorms are forecast over western NB where partial clearing is forecast to occur. The main hazard for the day is heavy rain.

 

Convective Discussion

Complex “tropical-like” dynamics at play today for 3 main forcings for convection each with individual hazards associated. A front in Labrador may spark a few lightning strikes as it transits through over the next 24-hrs.

1. Western NB: MUCAPE values near 1000 could (with a strong enough forcing) even overcome the cap that exists at 500mb, leading to gusty winds and heavy rain. PWATS in this area with actual dew points near 20 at 45mm today.

2. An area of potential instability exists from Kings county through to Guysborough county late this afternoon. The forcing here would be a sea breeze type front. If this materializes, dew points are near 22 and PWATS close to 50 so rain is the main hazard.

3. A frontal feature streaming up from the U.S. eastern seaboard is feeding in moisture and buoyancy causing non-severe thundershowers – Shelburne area likely to be in this moisture feed this evening. Saturday morning the rain hazard exists again in central NS marked in yellow on the overnight graphic. Models are not in perfect agreement on placement, but there is a consistent signal again for decent rain rates (greater than 30mm/hr). These local areas have a high vulnerability/sensitivity based on rainfall that has fallen in the last week.

The rest of Saturday sees generally improving conditions for NS, with pop-up showers across much of NB, PEI and in eastern areas of Nfld. Sunday’s dynamics as humidity builds back into the Maritimes is not a clear picture at this point.

 

Thunderstorm Outlook for Today

 

Thunderstorm Outlook for Tonight

 

Thunderstorm Outlook for Tomorrow

 

Thunderstorm Outlook for Sunday

 

Forecaster: TIRONE

Convective Outlook Valid for Today, Tonight and Tomorrow

Regional Impacts

NS/NB… Scattered thunderstorms possible today. Main hazard is torrential downpours of 25 to 50 mm/h.

PEI… Isolated embedded thunderstorms possible this afternoon. Main hazard is locally heavy downpours of 15 to 25 mm/h.

NL… None

 

Convective Discussion…

A strong moisture plume from the remnants of Hurricane Beryl will move across the Maritimes today, bringing the risk for some scattered thunderstorms to parts of Nova Scotia and New Brunswick. A few thunderstorms have already developed in Maine this morning and have moved across the international border into New Brunswick. Watches have been issued for southern New Brunswick, and will likely be expanded into Nova Scotia this afternoon. This risk for severe storms will continue into this afternoon, especially along the Bay of Fundy, where good low level moisture flow will help fuel storms that fire along the 500 mb jet as it slowly moves east. One of the big challenges today however will be achieving sufficient instability. Models have backed off on MLCAPE values, likely due to increased cloud cover over the southern Maritimes, as well as the stalling of the thermal trough over New England. This should keep the risk for severe weather over and around the Bay of Fundy, though given sufficient clearing, there is a slight risk that some severe storms could fire in southwestern Nova Scotia. Dynamics will not be an issue today, with bulk shear values of 45 to 50+ kts. PWAT values have been observed to be between 50 to 60 mm based on the 12Z Yarmouth and Gray soundings. As such, the main hazard with any storms today are torrential downpours of 25 to 50 mm.

 

Thunderstorm Outlook for Today

Thunderstorm Outlook for Tonight

Thunderstorm Outlook for Tomorrow

Copp