ECCC Convective Outlook Valid for Today, and Tomorrow

Thunderstorm Outlook for SATURDAY:

 

Regional Impacts

Isolated non-severe thunderstorms possible this afternoon in many different areas of the Atlantic provinces, due to various weak forcing features. An approaching trof in northern Quebec may produce a marginally severe thunderstorm this afternoon in extreme western Labrador – greatest hazards being heavy rain and lightning.

 

Convective Discussion

Various features will create weak and short-lived thunderstorms today. A decaying trof over northern Nfld, a weakening low centre with associated occluded fronts near James Bay, and a weak sea breeze convergence zone over interior NS are the easiest to pick out from this morning’s air mass analysis. The ongoing heat wave across the Maritimes is keeping mid levels quite dry. Surface dew points are over 19 already, bringing Humidex values near 40 in Cape Breton this morning. Across NS/NB/PEI the expected weak thermal trof-ing at 850 to 500 is also occurring. Hence a shower that struggles to build will do just that, struggle.

 

Thunderstorm Outlook for Day 1 - JULY 23, 2022

 

Thunderstorm Outlook for SUNDAY:

 

Regional Impacts

Scattered non-severe thunderstorms possible tomorrow afternoon in parts of New Brunswick and Labrador. Isolated severe thunderstorms are possible in central Newfoundland including Gander and vicinity. Main hazards will be gusty winds, small hail, and frequent lightning. Rainfall rates could exceed 30mm/h in local pockets of heaviest downpours.

 

Convective Discussion

The focus of this discussion will be central Newfoundland. A strong short wave setup will destabilize a very hot and humid air mass currently established over the interior mid-day Sunday. As such, MU CAPE values are very high at over 2000J/kg, and ML CAPE is near 1300. ML CAPE is the most important here as we need the dew points to remain over 16 to have heights climb to severe levels. 0-6k shear is at 40kts. Storm type will be Supercell in this environment, and storm motion will be Bunkers RM. This has the potential to become a complex weather situation if the ingredients all line up at the right time of day. A funnel cloud or short lived tornado cannot be completely ruled out, however the probability of that remains very low at this time. Hail and strong winds have been included on the Day2 graphic in Area B to express the severe weather risk to the public. This weather threat may be upgraded to HIGH in future forecast issues. Storms will weaken in the evening as they head out over much cooler ocean waters and become de-coupled from the surface. Elevated lightning (from 700mb and above) could continue along the coast late into the evening.

 

Thunderstorm Outlook for Day 2 - JULY 24, 2022

 

Forecaster: TIRONE.

Convective Outlook Valid for Today and Tomorrow

Regional Impacts

 

Today

Southern LAB/western NL: scattered elevated thunderstorms possible.

NS: slight risk of an isolated thunderstorm for eastern mainland.

 

Tonight

Southeastern LAB/NL: isolated thunderstorms possible

 

Saturday

Western LAB/northern NB/northeastern NL: isolated thunderstorms possible.

 

Convective Discussion

A much quieter day compared to the severe weather in NW NB yesterday. Some ongoing elevated thunderstorms associated with the upper trough moving over the GLFSTLAWR will likely be on and off this afternoon and into tonight as it slopwly progresses eastward over southern LAB and NL. Only some locally heavy downpours are expected but could be some gusty winds as well in some of the stronger cells. That same trough will likely give some isolated stuff overnight and into Saturday morning for parts of Newfoundland. And a slight risk of a thunderstorm this afternoon for eastern mainland NS close to that 500mb trough.

 

On Saturday a new 500 mb trough/short wave will approach from Quebec increasing the chance for thunderstorms across western LAB and far northwestern NB. Also a slight chance for an isolated cell for northeastern NL close to that first departing trough.

 

Thunderstorm Outlook for Day 1 afternoon/evening

 

Thunderstorm Outlook for Day 1 night/Day 2 morning

 

Thunderstorm Outlook for Day 2 afternoon/evening

 

Jeremy

Convective Outlook Valid for Today and Tomorrow

Regional Impacts

 

Today

NB: scattered strong to severe thunderstorms expected this afternoon and into the evening across NW portions of the province.

 

Tonight/Friday morning

NB/Western NS/PEI: isolated thunderstorms possible.

Central LAB: isolated thundershowers possible.

 

Friday afternoon/evening

MRTMS/central LAB/western NL: isolated to scattered thunderstorms possible. Some of the cells could be strong.

 

Convective Discussion

It appears prime for possible strong to severe thunderstorms across northwestern NB this afternoon and evening. From top down: an approaching 250 jet maxima (right quadrant) and associated divergence by mid to late afternoon approaching northern ME and NW NB; an approaching 500mb trough currently over QC and a strong 50-50 knot jet just ahead of it; good dry air in the mid levels as is currently evident in conventional SAT PIX; Very moist air from 850mb to the surface and a strong LLJ of around 30 knots (~925mb) which was seen upstream in the 12Z Albany sounding. The really interesting area that would have been nice to have a sample from was missed, but adjusting the Grey and Albany soundings produces 1000-2000 j/kg SBCAPE, with 0-6 km effective westerly shear up around 50 knots and decent 0-3 km srh helicty of just shy of 200. That area will be advecting northeastward coinciding with the approaching trough (both at the surface and 500 mb), which in most circumstances spells trouble. Given the observed data and higher resolution model support we expect winds to be the main issue, however owning to the strong updrafts in the deeper cells hail is also a potential. PWAT is around 40, but storms should be moving fast enough to not produce a significant amount of rain (unless there is slight back-building or training of storms). In line with the Storm Prediction Center there is also a slight risk of seeing a tornadic supercell.

 

In summary: Strong to severe storms producing wind gusts of 60-100 km/h and hail up to 2 cm for northwestern counties in NB possible this afternoon and evening.

 

Thunderstorm Outlook for Day 1

 

Thunderstorm Outlook for tonight and Friday morning

 

Thunderstorm Outlook for Day 2 afternoon and evening

 

Jeremy

Convective Outlook Valid for Today and Tomorrow

Regional Impacts

 

Today

NL: isolated thundershowers giving locally heavy downpours.

 

Tonight

No thunderstorms forecast.

 

Thursday

NB: scattered thundershowers with risk of lightning, heavy rain and strong winds.

 

Convective Discussion

An upper trough with a cut-off surface low pressure system will slowly weaken as it tracks northeastward over Newfoundland today. Any remaining convection today will be near the low centre where cooling aloft along with surface based heating will help provide instability for isolated thundershowers. With low CAPE values of 200-400 J/kg and not much bulk shear, the main threat will be enhancement to rainfall where precipitable water remains in the low 30s, however, low level winds will maintain quick movement of anything that develops.  

 

An approaching hot and humid air mass moves into the Maritimes on Thursday. Ahead of an upper trough that will be moving through southern Quebec/New England during the day will trigger organized convection that will likely move into extreme northwestern New Brunswick later in the day. There looks to be ample energy with forecasted CAPE values of over 1000 J/kg with sufficient 0-6km shear as well as low level shear to support organized bowlines and possible supercells ahead of the trough. The uncertainty at the moment is the timing of this feature as it progresses into New Brunswick as instability will diminish into the evening/overnight period.

 

Thunderstorm Outlook for Day 1

 

Thunderstorm Outlook for Day 1 night/Day 2 morning

 

Thunderstorm Outlook for Day 2

 

 

Convective Outlook Valid for Today and Tomorrow

Regional Impacts

 

Today

NL/NS/PEI: isolated thundershowers giving locally heavy downpours.

Labrador: isolated to scattered thunderstorms possibly giving strong winds and small hail in the west.

NB: scattered thunderstorms possibly giving strong winds, hail and heavy rainfall.

 

Tonight

NL: isolated thundershowers giving locally heavy downpours

 

Wednesday

NL: isolated thundershowers.

 

Convective Discussion

None of the upstream TEPHIs are going to give the air mass moving into western NB any justice since the prime location is east of Maniwaki and north of Grey ME. But a fairly sharp and digging upper trough (and associated surface front) is evident in WV imagery this morning over Quebec and is already initiating some storms. The 12Z KCAR profile shows about 40 knots of westerly shear but is moist given the precipitation at the time of the launch. Things dry rapidly in the mid-levels not far upstream and, combined with MLCAPE up around 1000 J/Kg will generate some strong to possibly severe cells this afternoon and into the evening. Freezing levels are pretty high but will be lowering and since the CAPE is fairly “fat” some of the stronger updrafts could support some 1-2 cm hail. PWATs are high with ample low level moisture and TDs around 20 will give a threat to torrential rainfall as well. A thickness ridge currently moving across the MRTMS will enter NL this afternoon with perhaps an isolated embedded thundershower associated with it. There could be an isolated strong to possibly severe cell that may impact the Churchill Falls and Lab West/Wabush areas this afternoon giving strong winds and small hail. There is already convection upstream over Quebec so will also have to keep an eye on things up in the Big Land.

 

Thunderstorm Outlook for Day 1

 

Thunderstorm Outlook for Day 1 night/Day 2 morning

 

Thunderstorm Outlook for Day 2 afternoon

 

Jeremy