Convective Outlook Valid for Today, Tonight and Tomorrow

REGIONAL IMPACTS

 

Today: Chance of non-severe thunderstorms over portions of western NB, as well as along the spine of NS. Embedded thundershowers also possible across parts of Nfld.

Tonight: No overnight convection is expected.

Wednesday: Similar NB locations will be impacted by similar threats as occurred on Tuesday in NB. Western Labrador may hear some thunder.

Thursday: Non-severe thundershowers confined to northern half of Maritimes, Gulf waters, and parts of Labrador. A frontal feature will bring embedded convection to eastern Nfld - heavy rain is the possible hazard as this airmass has tropical characteristics.

*Outlook for Friday: Stronger and more organized thunderstorms are possible with the passage of a strong frontal feature coming out of Quebec and Maine.

 

CONVECTIVE DISCUSSION

 

Dynamics at play today remain fairly weak and disorganized. Many impulses are riding a long wave trof that is to the west of the AOR. This will help to destabilize areas across western NB later in the day (similar to yesterday). Very small pea-sized hail is possible with 700-500mb differences of 17 in the most favourable pockets. Moisture is decent up until 700mb, then it is quite dry. Pwats 22-27 today. Morning soundings suggest no wind threat, and effective shear is struggling to reach 15kts. MLCAPE in NB is 500-750J per kg. Much less across NS where inland development is highly conditional upon sea breeze development. The TS risk in Nfld is ahead of the sfc low(shortwave trof) located near Deer Lake this morning.

 

Thunderstorm Outlook for Today

 

Thunderstorm Outlook for Tonight

 

Thunderstorm Outlook for Tomorrow

 

Thunderstorm Outlook for Thursday

 

Forecaster: Tirone.

Convective Outlook Valid for Today , Tonight and Tomorrow

Regional Impacts:

 

Today

NB/NS/PEI/Labrador: Chance of a thundershower.

NL: None

 

Tonight

NS/NB/PEI/NL/Labrador: None.

 

Tuesday

NB/NL: Chance of a thundershower.

NS/PEI/Labrador: None

 

Convective Discussion:

A broad and weakening surface low over the region (with supportive upper low) will allow skinny CAPE thundershowers to develop where surface heating is expected. With CAPE values under 400 J/kg, just scattered/non-severe thundershowers are expected.

 

Thunderstorm Outlook for Today

 

Thunderstorm Outlook for Tonight

 

Thunderstorm Outlook for Tomorrow

Convective Outlook Valid for Today , Tonight and Tomorrow

Regional Impacts

Newfoundland and Labrador… Embedded thunderstorms giving 5 to 10mm with a possibility of showery ice pellets today

Maritimes… none today

 

Convective Discussion

An upper cold low currently sits over western NF and soundings are indicating temperatures below -20 at the 500mb level. Surface reports are showing a weak cyclonic circulation over the Island with a few rain bands rotating around it. Forecast guidance is suggesting the possibility of isolated weak/low-top CB’s within the cold pool. The main indicator is surface-based CAPE values in excess of 200 J/kg and LI between 0 to -2 over central regions. Brief moderate showers (with showery ice pellets) can be expected

A frontal trough currently over the Scotian Slope will intensify into a closed low pressure system as it moves towards the Grand Banks tonight. This very dynamic feature will be supported by a 50kt southerly low-level jet which will provide a good supply of moisture (precipitable water of 30+mm) and instability (MUCAPE of 500 J/kg and Showalter Index of -2 or less). Moderate to heavy rain (rainfall rates of 10-20mm) are expected offshore / Grand Banks but isolated thundershowers could brush the Avalon.

 

Thunderstorm Outlook for Today

 

 

Thunderstorm Outlook for Tonight

 

 

Thunderstorm Outlook for Tomorrow

 

Convective Outlook Valid for Today , Tonight and Tomorrow

Regional Impacts

Newfoundland and Labrador… Airmass thunderstorms giving 15-20mm.

Nova Scotia and New Brunswick… Airmass thunderstorms giving 20 to 25mm with small hail possible.

 

Convective Discussion

 

With relatively low moisture and minimal wind shear available organised convection will be fairly limited. The is potential for some airmass thunderstorm with mixed layer CAPE values around 500 J/kg and most unstable CAPE values over 1000 J/kg for western NB, less so in other areas. Most probable areas for convection to initiate will be over southwest NS and Western NB. Down draft potential is high enough to provide some gusty winds near thunderstorms but it is not expected to reach near warning level, however the situation will be monitored through the day for changes. There is a slight possibility that training or back building thunderstorms could develop increasing the rainfall potential.

 

Over the next few days the potential for thunderstorms will slowly but gradually diminish

 

Thunderstorm Outlook for Today

 

 

Thunderstorm Outlook for Tonight

 

 

 

Thunderstorm Outlook for Tomorrow

 

 

Mel Lemmon

Convective Outlook Valid for Today , Tonight and Tomorrow

Regional Impacts

 

Labrador… Isolated thunderstorms giving 15-20mm of rain today and tomorrow.

New Brunswick.. Isolated thunderstorms giving 15-20mm of rain today and tomorrow.

Nova Scotia… A chance of thunderstorms over western areas this tonight and tomorrow, possibly giving 30mm/hr rainfall rates.

 

Convective Discussion

 

A slow moving area of low pressure will move eastward very slowly over the next few days, while a tough of low pressure develops southwest of the Maritimes. With the upper low(s) over Ontario and Newfoundland remaining virtually stationary as well no significant dynamics will come into play for the Atlantic Region. Moisture is modest at best with precipatable water values generally around 20mm with some pockets of higher amounts. However there is some decent instability and airmass thunderstorms could develop for a lot of areas, it is possible that significant downdrafts near 70 km/hr could occur with some thunderstorms .

Overnight and early tomorrow there is a slight chance that an organised area of convection will set up over southwest Nova Scotia giving potentially heavier rainfall mounts possibly up to 30mm, however this band could also remain just offshore. We will revaluate during the remainder of the day as new guidance becomes available.

 

Thunderstorm Outlook for Today

 

Thunderstorm Outlook for Tonight

 

 

Thunderstorm Outlook for Tomorrow

 

 

Mel Lemmon