Convective Outlook Valid for Today and Tomorrow

Thunderstorm Outlook for Day 1

 

 

 

Regional Impacts

 

Scattered showers and embedded thundershowers for today and this evening over western New Brunswick. Heavy rain and brief strong wind gusts are possible.

 

Convective Discussion

 

A near stationary low pressure system resides over James Bay with a long cold frontal boundary extending south over southern Quebec and along the eastern United States this morning. Most of the dynamics remains further west over southern Quebec into New England. Ahead of the front over New Brunswick today, there is warm advection in the mid to upper levels, limiting the energy possible in embedded thundershowers. It is also expected to remain cloudy today, prohibiting any surface based convection. There is however increasing 0-6km shear, and a low level jet will help destabilize the environmental flow this afternoon. Linear lines of convection may form but will be quite fast moving. There is also ample precipitable water available of 40 to 50 mm which could prompt some localized heavy downpours.

 

Meanwhile over Labrador, a warm front will push northward into central Labrador today. There is a very slight risk of elevated convection overnight in the warm sector over southwestern parts of Labrador.

 

Thunderstorm Outlook for Day 2

 

 

The weakening trough will continue to push into Nova Scotia overnight and stall on Friday. A short wave trough will move from Quebec into northwestern New Brunswick late afternoon. At this time, TCUs are expected. With very high shear but weak CAPE, CBs are not expected at this time.

 

Roberta McArthur

 

 

 

Convective Outlook Valid for Today and Tomorrow

Thunderstorm Outlook for Day 1

 

Regional Impacts

Brief showers with risk of a thundershower for Terra Nova, Clarenville and Bonavista Peninsula.

 

Convective Discussion

Surface High pressure system continues to build over the Maritimes. High cloudiness ahead of a warm front extending ahead of extratropical cyclone Cristobal will continue to push eastward during the next day reaching Maine by Thursday. A 50kt southwesterly low-level jet will advect some low cloud and moisture, and forecast guidance is suggesting some elevated CAPE and a slight risk of thundershower early Thursday morning.

 

Over Newfoundland today, the air mass is fairly unstable but lacking moisture and diurnal heating. Towering-cumulus giving brief showers are in store for the afternoon, however with the help of a convergence line over east-central portions of the island, one or two of these TCU’s could build high enough to have glaciated tops. A slight risk of a thundershower is indicated on the western edge of a deck of strato-cumulus covering southeastern regions of the Island

 

Thunderstorm Outlook for Day 2

 

Convective Outlook Valid for Today and Tomorrow

Thunderstorm Outlook for Day 1

 

Convective Discussion

There is a slight risk of thundershowers this afternoon and evening across SE NB, NRN/ERN NS, Cape Breton and PEI. There not a lot of support, but a fairly potent short wave trough will be moving through later today. An approaching 250 mb jet will place this areas near the left exit region which may support some development. CAPE values will be low, but there will be increasing shear as the day progresses (upwards of 40 knots). Freezing levels are quite low (6-7,000 feet) as well. Expect numerous TCUs to form (15,000-20,000 feet) with ISOL thundershowers as well. Given the low freezing levels, small hail/ice pellets is a possibility in some of the stronger echoes. Also gusty winds can be expected in some TCU/CBs. OTWZ nil sig weather is expected.

 

Regional Impacts

MRTMS: ISOL thundershowers possible this afternoon and evening.

 

Thunderstorm Outlook for Day 2

Convective Outlook Valid for Today and Tomorrow

Thunderstorm Outlook for Day 1

Convective Discussion

There is a slight chance of a thundershower across parts of the Maritimes today. The only issue will be the lack of sunshine as there is a lot of cloud cover. CAPE values will be low (in the 200-300 range) and the shear is relatively weak (roughly 30 knots). There does appear to be some vorticity advection which could aid in the formation of TCU and an isolated thundershower or 2. Cloud tops will be relatively low as well.

There is also a risk of a thundershower over western Newfoundland this afternoon and evening. An upper level trough, currently over the eastern Maritimes and Gulf of St. Lawrence area will gradually approach the island today. There has been history with some isolated thundershowers just ahead of it where there is some slight divergence aloft and associated PVA. Some locally heavy downpours are possible if the odd cell forms this afternoon.

Regional Impacts

Maritimes: slight chance of a thundershower this afternoon and into early this evening.

Newfoundland: slight chance of a thundershower this afternoon and evening.

Thunderstorm Outlook for Day 2

Convective Outlook Valid for Today and Tomorrow

Thunderstorm outlook for Day 1.

 

Convective Discussion

A slight chance of embedded convection today and tonight as a low currently south of Nova Scotia tracks towards NFLD tonight.  If any convection does get initiated, it would have to go through a significant warm nose before reaching a level of positive buoyancy at which 200 to 300 J/Kg is possible which is not significant.  However, a few cells passed over Sable island early this morning bringing near 60 mm over the island in a span of 3 hours (34 mm was reported in 1 hour).  There was no lightning detected on these cells but due to the amount of rainfall over a short period of time, this does indicate that there could be some convective activity.  This area of convection is expected to reach eastern Newfoundland later today so if the cells maintain their strength, it could result in some significant rainfall over a small period of time for parts of eastern NFLD.

 

Regional Impacts

Maritimes…

A slight chance of embedded convection over eastern NS.  No impacts expected.

 

Newfoundland…

A chance of embedded convection this afternoon and tonight over NFLD. Locally heavy downpours possible.

 

 

Thunderstorm outlook for Day 2.

 

 

Convective Discussion

Some instability expected over southeastern NB Monday afternoon but a capping inversion at around 11,000 ft could limit the vertical extent and thus hamper convective activity.  If this capping inversion is less significant than currently expected then non-severe thunderstorms are possible.

 

Regional Impacts

Maritimes…

None at this time.

 

Newfoundland…

None.

 

Barrie MacKinnon

Program Supervisor – Operations Support

Atlantic Storm Prediction Centre

Meteorological Service of Canada

45 Alderney Drive, Dartmouth

Nova Scotia, B2Y 2N6

Weather - Environment Canada

(902) 497-9317

 

Surveillant de Programme - Soutien aux Opérations

Centre de prévision des intempéries de la région de l'atlantique

Service météorologique du Canada

45 promenade Alderney, Dartmouth

Nouvelle-Écosse, B2Y 2N6

(902) 497-9317