Convective Outlook Valid for Today, Tonight and Tomorrow

Regional Impacts

NS/NB … Disorganized thundershowers possible along enhanced terrain this afternoon, rainfall rates of 10 to 15 mm/h are possible.

NL … A few thunderstorms are possible in western and central Labrador this afternoon along a cold front, rainfall rates of 15 to 20 mm/h are possible.

PEI … None

 

Convective Discussion …

A few pop up thundershowers are possible over portions of Nova Scotia, New Brunswick, and central Newfoundland this afternoon. Any cells that develop today will likely be restricted to areas of enhanced topographic forcing, as limited triggers are available across the region. Weak wind shear (15 to 25 kts) in addition to warm air advection in the mid and upper levels increasing throughout the day should inhibit any organized thunderstorm activity. Some more organized thunderstorm activity is expected in central Labrador this afternoon and into this evening with an incoming cold front over northern Quebec.

 

Tomorrow looks to be more interesting in terms of severe weather. The remnants of a trough that brought tornadoes to southern Manitoba on Wednesday, and has prompted tornado watches in central Ontario and southern Quebec today, moves into the region. Models have been struggling to get a handle on this system once it crosses the St. Lawrence River tonight. Model runs have also consistently been backing off on CAPE values tomorrow afternoon across New Brunswick, with current guidance indicating 1000 J/kg in western New Brunswick tomorrow afternoon, down from over 1500 J/kg in previous runs. Much of this model inconsistency seems to be due to the slowing down of the trough as it approaches New Brunswick tonight. Timing of the thermal trough moving in tomorrow afternoon will also be crucial for organized thunderstorms to develop, thus the highest risk for severe weather is likely to be restricted to western New Brunswick where the thermal trough will erode the capping inversion. Any strong cells that do develop, are likely to produce strong wind gusts up to 90 km/h, hail of 1 to 2 cm, and rainfall rates of 25 to 40 mm/h.

 

Thunderstorm Outlook for Today

 

Thunderstorm Outlook for Tonight

 

Thunderstorm Outlook for Tomorrow

 

Copp

Convective Outlook Valid for Today, Tonight and Tomorrow

REGIONAL IMPACTS

 

Today: Thunderstorms possible across NB that may bring up to 25mm of rain locally. Similar non-severe convection as yesterday across spine of NS, and in western Labrador.

Tonight: No overnight convection is expected in the Maritimes. Embedded thundershowers are likely along frontal boundary that will bring rain to eastern Newfoundland tonight.

Thursday: Similar NB locations will be impacted by similar threats as occurred on Wednesday in NB. NS will see more non-severe inland convection spreading a bit further east than on Wednesday (through Musq. Valley)

Friday: Stronger and more organized severe thunderstorms are likely with the passage of an aggressive frontal feature coming out of Quebec and Maine. Multiple hazards are possible late day.

 

CONVECTIVE DISCUSSION

 

On the large scale, an upper level low is creating instability over the AOR, and will continue to do so over the next 36hrs. MLCAPE values aided by sfc heating could support small hail and moderate showers developing along the remote terrain in NB. A frontal feature with sub-tropical characteristics is forecast to affect eastern Nfld tonight – main hazards being lightning and heavy rain. And way back to the west, a sharp trof is digging from James Bay down to the Great Lakes - trundling towards the Maritimes - the potential story for Friday. 0-6k shear for today is nothing to write home about. 10-15kts over NB will equate to very slow moving cells. A small yellow area was denoted to simply show that the cells over NS will be less moisture rich that those in central NB. Based on this, it's never black and white.

 

Thunderstorm Outlook for TODAY

 

Thunderstorm Outlook for TONIGHT

 

Thunderstorm Outlook for TOMORROW

 

Thunderstorm Outlook for FRIDAY

 

Forecaster: Tirone.

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