Regional Impacts:
Today
NB/NS/PEI/NL/Labrador: None.
Tonight
NS/NB/PEI/NL/Labrador: None.
Tuesday
NB/NS/PEI/NL/Labrador: None.
Convective Discussion:
A trough moving across the region will usher in a cooler and drier airmass today. No thundershowers are expected today or tomorrow over land although according to the ECMWF, there is a very slight risk over interior Newfoundland on Sunday.
Thunderstorm Outlook for Today
Thunderstorm Outlook for Tonight
Thunderstorm Outlook for Tomorrow
Regional Impacts
NB … Strong thunderstorms possible this afternoon and into this evening with 70 to 90 km/h wind gusts, rainfall rates of 20 to 40 mm/h, and pea sized hail.
NL … Risk of some scattered thunderstorms this afternoon in western Labrador with rainfall rates of 20 to 30 mm/h and wind gusts of 60 to 80 km/h.
NS/PEI … Risk of an isolated thundershower later this evening with rainfall rates of up to 15 mm/h.
Convective Discussion …
An upper trough moving into the Maritimes brings the threat for strong thunderstorms across New Brunswick this afternoon. Good moisture advection at the surface will increase dewpoints to near 20 degrees in western New Brunswick, as such MUCAPE values are expected to climb to 1000 to 1500 J/kg this afternoon in this region. Remnant cloud from yesterdays convection over Ontario and Quebec moving through New Brunswick this morning will keep surface temperatures in the low to mid twenties, nonetheless an approaching cold front should provide ample surface lift to break any capping inversion that remains this afternoon. High shear values upwards of 50 knots will allow these storms to remain fairly organized throughout their lifespan, with a few supercells even possible. The main hazards with these storms will be strong wind gusts of up to 90 km/h, and heavy downpours of 20 to 40 mm/h. There is also a chance for some pea sized hail in some of the stronger cells. These storms are expected to die off as they approach the cooler waters of the Bay of Fundy and the Gulf of St. Lawrence later this evening, though a few lightning strikes are possible over southern Nova Scotia overnight.
In Labrador, some scattered thunderstorms are possible from Labrador City to Churchill Falls as the aforementioned upper trough approaches from the west. Thunderstorms may become organized this afternoon, as bulk shear values of 40 to 50 knots move through the region. Cape values are expected to reach 1000 J/kg this afternoon, however cloudy skies this morning may inhibit CAPE from getting this high. Thus the threat for any strong thunderstorms remains low. Any storms that do become organized may bring locally heavy rainfall of 20 to 30 mm/h and strong wind gusts of 60 to 80 km/h.
Thunderstorm Outlook for Today
Thunderstorm Outlook for Tonight
Thunderstorm Outlook for Tomorrow
Copp
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
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.
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.
