Convective Outlook Valid for Today, Tonight and Tomorrow

Regional Impacts

NS/NB/PEI… Scattered thunderstorms possible across the central Maritimes this afternoon, main risks are heavy downpours, strong wind gusts, and small hail.

NLFD… Isolated thunderstorms possible in central Newfoundland this afternoon, main risks are strong wind gusts and heavy downpours.

 

Convective Discussion…

As very warm temperatures continue across the Maritimes today, a cold front will begin to move south across the region. Surface based CAPE values are forecast to soar upwards of 2000 J/kg in southern New Brunswick and mainland Nova Scotia ahead of the front in addition to decent bulk shear values of 30 to 35 kts. Due to the strength of the ridge south of Nova Scotia, the front is expected to slow down and weaken as it moves across New Brunswick, and stall over southern Nova Scotia tonight. This will cause some issues in the erosion of the thermal ridge, especially over southern Nova Scotia. In addition, the location of the 500 mb jet over central Quebec is not ideal. As such, the main focus for severe thunderstorms will be in southeastern New Brunswick and central Nova Scotia today. PWAT values on the Yarmouth tephigram this morning indicate 45 to 50 mm, which is consistent with what models have been forecasting ahead of the front. With these high PWAT values, heavy downpours of 25 to 50 mm/h are expected to be the main hazard with any thunderstorms that develop, in addition to strong wind gusts of 70 to 90 km/h and small hail up to dime size.

A second round of convection may move through southern Nova Scotia from the west overnight tonight, as a weak shortwave rides the thermal ridge across the region. Heavy downpours may company these storms if they persist over the Gulf of Maine.

In central Newfoundland, similar conditions to central Nova Scotia are expected, however bulk shear values are likely to be slightly lower here (20 to 25 kts), which may prevent more organized thunderstorm activity. Another limiting factor is a layer of warmer air evident in the mid levels persisting over central Newfoundland today. Any thunderstorms that do develop may struggle to get organized, but may produce strong wind gusts of 70 to 90 km/h and heavy downpours up to 25 mm/h, in addition to the small chance of some pea sized hail.

 

Thunderstorm Outlook for Today

Thunderstorm Outlook for Tonight

Thunderstorm Outlook for Tomorrow

Copp

Convective Outlook Valid for Today , Tonight and Tomorrow

Regional Impacts

NB

Today…Risk of severe thunderstorms late in the day - heavy rain and strong wind gusts (and some hail)

Thursday… Scattered thunderstorms - heavy rain, strong wind gusts (and some hail)

 

NS

Today…risk of a non-severe thunderstorm late this afternoon

Thursday… Scattered thunderstorms - heavy rain, strong wind gusts (and some hail)

 

PEI

Today…risk of non-severe thunderstorms, except for northern Prince county where strong wind gusts are possible late in the day

Thursday… Scattered thunderstorms - heavy rain, strong wind gusts (and some hail)

 

Labrador

Today…Numerous strong thunderstorms with strong wind gusts, heavy rain (and some hail)

Thursday…Isolated thunderstorms - heavy rain, strong wind gusts

 

NF

Today…isolated non-severe thunderstorms along portions of the west coast

Thursday…Scattered thunderstorms - heavy rain, strong wind gusts (and some hail)

 

Convective Discussion

 

The 500mm heights continue to rise over the region, the highest value reported this morning is Washington and Long Island with 598 dam. The moisture content is also slowly increasing at the surface dewpoint temperatures are ranging from 18 to 24 and derived precipitable water from this morning soundings are ranging from 40 to 50 mm.

Most of the convective action will be occurring over Labrador today and a Watch message has been issued. In terms of forcing the surface cold front extends from Ungava to James bay and is already triggering some thunderstorm activity. This feature will be advancing gradually throughout the day, as the airmass ahead it becomes more unstable with falling 500mb heights. Surface dewpoints of 20 deg., Surface CAPE values between 1000-1500 J/Kg, and deep-layer shears of 40 kt will contribute to the development of hefty thunderstorms capable of producing straight-line 50kt gusts, rain rates of 25-50 mm/h, and to a lesser extent 1-3 cm hail.

Conditions will become more favorable for severe weather over NB-NS-NF on Thursday.

 

 

Thunderstorm Outlook for Today

 

 

Thunderstorm Outlook for Tonight

 

 

Thunderstorm Outlook for Tomorrow

Convective Outlook Valid for Today , Tonight and Tomorrow

Regional Impacts

NB

Today…slight chance of severe thunderstorms late this afternoon and evening with heavy rain and strong wind gusts

Tomorrow… Occasional thunderstorms bring heavy downpours and some strong winds

 

Labrador

Tomorrow… Thunderstorms wind strong winds and some small to moderate hail, heavy rain possible.

 

Convective Discussion

With the very high moisture making its way over the region and the slowly approaching low pressure system we are in for a multi-day event for convective weather, beginning late today in northwest NB and slowly spreading eastward tomorrow and finally into Thursday. Quebec is expected to see severe thunderstorms today with the edge of the severe thunderstorm risk just coming into NB later today. There is some indication that some thunderstorms could organise into supercell/bow echo cells but with a significant area on convective inhibition around 700 mb it may be a challenge to get thunderstorms going. However the potential for strong surface will be a concern as the day unfolds.

 

Tomorrow things shift a bit becoming more favourable for a multicell situation with the potential for heavy rain, should storms become organised (ie training thunderstorms) some areas of New Brunswick could receive more than the highlighted amounts in the forecast for day 2. For Labrador tomorrow the environment will move to a supercell/bow echo situation so strong wind gust to warning level a certainly possible. Paying close attention to overshooting tops and lightning will be helpful in the absence of radar data.

 

As we move into Thursday the dynamics will become more favourable for severe thunderstorms for the remaining areas of the Atlantic provinces please stay tuned as the situation develops over the next couple of days.

 

Thunderstorm Outlook for Today

 

Thunderstorm Outlook for Tonight

 

Thunderstorm Outlook for Tomorrow

 

Mel Lemmon

 

 

Convective Outlook Valid for Today, Tonight and Tomorrow

Regional Impacts

Slight risk of a thundershower this afternoon over southeastern Labrador.

Risk of a thunderstorm for NW New Brunswick Tuesday late afternoon and evening.

 

Convective Discussion

As an upper trough moves into western Labrador this afternoon, daytime heating (inland temperatures into the mid 20s) and convergence ahead of the trough could help trigger an isolated CB over southeastern Labrador this afternoon. Some strong convective gusts are possible, however, increasing shear above 50kt may shear off any developing TCUs. Moisture is also only low to moderate with precipitable water less than 20 mm.  

 

A ridge of high pressure dominates south of the Maritimes today while an upper warm front weakens as it tracks into the southwestern Maritimes this afternoon and tonight.

 

A trough approaches New Brunswick tomorrow and there is a risk of a thunderstorm reaching northwestern areas by the late afternoon or early evening. Although there is good thermodynamic potential with daytime highs reaching 30C, there is increasing warmth in the lower to mid layers may cap convection.

 

 

Thunderstorm Outlook for Today

 

Thunderstorm Outlook for Tonight

 

Thunderstorm Outlook for Tomorrow

 

 

Roberta McArthur

 

 

Convective Outlook Valid for Today , Tonight and Tomorrow

Regional Impacts

Slight risk of a thunderstorm this afternoon across central NL.

Slight risk of a afternoon thunderstorm for SE LAB Monday afternoon.

 

Convective Discussion

An upper trough will cross NL today giving the chance for an isolated thunderstorm. The 12Z tephi out of YJT has a pretty good warm nose at 700 mb, but steep lapse rates below that layer so, if there is ample surface heating, the cap could be breached and an isolated CB could develop this afternoon. There is a fairly strong jet of 30-35 knots in the lower levels so gusty surface winds are possible (even in areas of TCU). PWATs are low so rainfall is not a concern.

 

There will be a slight chance of an afternoon thunderstorm in SE LAB on Monday in association with a short wave trough.

 

OTWZ nil sig wx is xpctd.

 

Thunderstorm Outlook for Today

 

Thunderstorm Outlook for Tonight

 

Thunderstorm Outlook for Tomorrow

 

Jeremy