Convective Outlook Valid for Today, Tonight, and Tomorrow

Regional Impacts

NS and NB: Embedded thundershowers today with locally heavy rain, 20 to 40 mm along Atlantic shores of NS and south-central NB.

NL: Isolated embedded thundershowers possible over central Labrador this afternoon, local rainfall amounts 15 to 25 mm.

PEI: Isolated thundershowers possible this afternoon, locally heavy rain of 10 to 15 mm.

 

Convective Discussion…

As an area of high pressure sits east of Newfoundland, a quasi-stationary trough extends from the US east coast through the St. Lawrence river valley, and into northern Labrador. This pattern in combination with a 40 kt low level jet is supplying ample moisture over the next few days across Atlantic Canada. MUCAPE values of 500 to 750 J/kg and 40 kts of 0-6 km shear will allow for some sustained embedded convection today along Atlantic shores of NS, as well as in south-central NB. The main threat with these storms will be locally heavy rainfall, with 20 to 40 mm possible in areas of convection. This threat will persist overnight along the south shore of NS.

 

A weak shortwave will move into southern Labrador this afternoon, providing ample lift for some organized convection between Labrador City and Goose Bay with 40 kts of 0-6 km shear. The main threat with these thundershowers will be locally heavy rain, with 15 to 25 mm possible.

 

Tomorrow, a shortwave will approach northern NB from the west. This, in combination with 20-30 kts of 0-6 km shear and surface-based CAPE values of 1000-1250 J/kg will allow for a line of organized convection to form over northern Maine. Main threats with these thunderstorms will be 0 to 1 cm hail, and locally heavy rain of 20 to 40 mm. There is still some model disagreement on the speed at which this shortwave will approach NB, so the risk area may need to be extended to the southeast as models gain a better handle on the system.

 

Thunderstorm Outlook for Today

 

Thunderstorm Outlook for Tonight

 

Thunderstorm Outlook for Tomorrow

 

Copp

Convective Outlook Valid for Today and Tomorrow

Regional Impacts

NB and NS: Risk of an embedded thunderstorm, bands of heavier showers giving 10 to 20 mm today

Lab: occasional rain spreading over western Lab, amounts less than 10mm today

Rest of NF and PEI: none

 

Convective Discussion

Surface low over south-central Ontario with inverted trough extending towards northern Quebec. Surface warm front extends from the Low to southern Quebec-southern Maine-South shore of NS. A high pressure area now sits east of NF. The biggest change in the past 24 hours is the northward and eastward propagation of the increasingly moist air mass that has been sitting over the Maritimes. A strong southerly low-level-jet 30kt will maintain the supply of moisture with calculated precip. water from the upper air soundings indicating values in the 35-45 mm range.. this trend is expected to spread into NF&Lab today and tonight. The cloud deck mostly consists of overcast layers from near or at the surface extending up above 9-10km. While the extensive cloud cover will make it difficult to get enough surface heating to initiate convection, in their current state, soundings from YQI and YAW show plenty of instability (MUCAPE of 300 or 400 J/Kg) for embedded CB’s with tops up to 7-9 km. Deep layer shear values are a solid 35kt which might help sustain the convection over the Gulf of Maine until the clusters reaches the Fundy region later today. A few public forecast regions have been identified with the greatest potential for high rainfall rates/amounts during the next 48H, some of the forecast guidance is indicating amounts as high as ~100 mm.. but an average of the main deterministic models indicates a medium probability of 40 to 60. Regardless of the numbers, the maximum amounts will be driven by convective bands and it would be fairly difficult to identify which location/county will receive the most.

 

 

 

Thunderstorm Outlook for Today

 

 

Thunderstorm Outlook for Tonight

 

 

Thunderstorm Outlook for Wednesday

 

Convective Outlook Valid for Today and Tomorrow

Regional Impacts

 

NB and NS: Risk of an embedded thunderstorm.

NL: None.

 

Convective Discussion

A warm front extends from a surface/upper low over the Great Lakes to the Gulf of Maine-Lurcher-Lahave Bank. The front will push northward slightly tonight and Tuesday. Few clusters of thunderstorms are detected by CLDN along the front. The instability over the Maritimes will remain quite weak and therefore the risk of thunderstorms over the area depicted is minimal 30% or less. Rainfall rates over the region are not expected exceed 5mm, however closer to the front (Maine) the rates will likely be in the 10-20mm range.

Strong high pressure over the Lower Quebec north shore will dominate with some moist early morning boundary layer conditions over NF giving way to sunshine. The LG4 and Goose upper air soundings from this morning continue to show extremely dry conditions.

 

 

Thunderstorm Outlook for today

 

 

Thunderstorm Outlook for tonight

 

Thunderstorm Outlook for tonight

Convective Outlook Valid for Today and Tomorrow

Regional Impacts

 

NB: Isolated thunderstorms possible this afternoon and evening.

NL: Isolated embedded thundershowers possible today.

 

Convective Discussion

 

Not a whole lot of forcing to talk about today. There has been an isolated embedded lightning strike or 2 across central NL associated with the weak short wave trough crossing the region this morning. So there could be another flash or 2 but that’s about it. Oddly enough there was organized convection late last night and early this morning up over the Great Northern Peninsula and near the Blanc-Sablon area that was not expected with the workup yesterday…and quite frankly I am still a little miffed on why it happened. That area of activity has since died off.

 

There is a slight destabilization of the atmosphere today across NB so, as skies clear there should be some isolated CBs develop. The 12Z tephi from YZV supports this notion, and that air mass will be descending southward. However, there remains a lot of smoke aloft so it’s quite difficult to figure out just how that will impact the convection. In any event there is no severe weather expected at today…just some locally heavy downpours and perhaps small hail since FZLVLs will be on the low side.

 

NS should see some TCU and associated heavy downpours this afternoon. The 12Z soundings out of YQI and YAW really don’t support CBs…but an isolated flash or 2 is not out of the question.

 

Lastly, towards the end of D2, there could be some isolated cells south of NS that could move over the western mainland but that is solely based on computer guidance and is not to be trusted for the time being.

 

Thunderstorm Outlook for today

 

Thunderstorm Outlook for Monday

 

Jeremy

Convective Outlook Valid for Today and Tomorrow

Regional Impacts

 

Southern LAB: Scattered to frequent thunderstorms are expected this afternoon and evening giving strong wind gusts, small hail and heavy downpours.

Southern NB: Scattered thunderstorms possible later today, tonight and early Sunday morning giving heavy downpours. Isolated thunderstorms possible again Sunday afternoon/evening.

PEI: Scattered thunderstorms possible overnight tonight or early Sunday morning giving heavy downpours.

SWRN NL: Isolated thunderstorms possible Sunday morning giving heavy downpours.

NS: A very slight chance of a thunderstorm this afternoon/evening for some central locales giving heavy downpours.

 

Convective Discussion

 

The interesting area to watch today will be up in the Big Land, where a frontal trough (acting as the trigger) will give way to scattered to frequent thunderstorms this afternoon. Moisture is nothing to write home about, however the shear and instability is good. 12Z YYR sounding shows about 50 knots of westerly shear, as well as some fairly steep lapse rates in the mid-levels. That could lead to good vertical velocities and support small hail growth. Strong wind gusts of 70-80 km/h are possible. Pretty much all the activity will be confined to areas where there are no public forecasts. However, there is a possibility of a strong storm or 2 advecting towards southeastern communities later this afternoon and into this evening. The only caveat would be the enormous amount of smoke evident on visible SAT imagery. The current ongoing thunderstorm activity in the southeast will soon diminish.

 

A pre-frontal trough/short wave over the New England states will move into southwestern NB later today crossing the MRTMS tonight before weakening over southwestern NL Sunday morning. Although there is not much history of lightning, there are indications of development as the sun sets this evening leading to a nocturnal event for some areas. Locally heavy downpours are the threat if they form.

 

Lastly  a slight chance of an afternoon/evening thunderstorm Sunday for a portion of southwestern NB. Again, heavy downpours seems to be the main threat at the moment.

 

Thunderstorm Outlook for today

 

Thunderstorm Outlook for tonight/Sunday morning

 

Thunderstorm Outlook for Sunday

 

Jeremy