Convective Outlook for the Maritimes valid for tomorrow July 12th

This is an update to the previous forecast for tomorrow July 12^th.

 

With a higher level of confidence I have updated the outlook for tomorrow to include a increased area of severe weather for northwestern New Brunswick. Most of the outlook remains the same with a chance of organised convection late in the afternoon, overall updrafts are not particularly strong but favourable dynamics may be enough to produce severe storms, with heavy rain and potentially strong wind gusts.

 

ML

 

 

Thunderstorm Outlook for Day 2

 

Convective Outlook Valid for Today and Tomorrow and Wednesday

Regional Impacts

For Today... Minimal impacts expected with only a slight chance of thunderstorms expected parts of New Brunswick and Labrador.

For Tomorrow... Organized convection possible late tomorrow afternoon and evening for northern New Brunswick, locally heavy downpours can be expected.

Convective Discussion

No significant convection is expected today with little potential energy and no significant forcings. Tomorrow the dynamics will begin to organize with an approaching upper trough and increasing mid level shear. There is still some uncertainty with the amount of CAPE with expected values around 500 J/kg, but with high Precipitable Water values approaching 50mm some locally heavy downpours could occur. In addition there is a slight risk that organized convection in the form of a squall line or QLCS (quasi linear convective system) may form further west and move over NB late in the afternoon. As the system develops we will have a better understanding of the potential, please look for the updated outlook tomorrow.

Mel Lemmon

Outlook for Today

Outlook For Tomorrow

Outlook for Wednesday

Convective Outlook Valid for Today and Tomorrow

Regional Impacts:

 

Today

Labrador: scattered lightning over southern and eastern areas with 0-1 cm hail, 20 mm rainfall, isolated lightning elsewhere.

Northern Newfoundland and Gulf waters: isolated lightning and locally heavy downpours.

 

Tonight

Labrador: isolated lightning over southeastern areas.

 

Sunday

Labrador: Isolated lightning over western area and southeastern areas.

Newfoundland: isolated lightning over northern and northeastern areas.

 

Convective Discussion:

A stacked centre of low pressure remains nearly stationary over southern Labrador today with an upper trough moving eastward through Newfoundland today with scattered showers. This low will continue to weaken then slowly drift southeastward on Sunday. Instability near the low centre and within the trough will allow the possibility of isolated to scattered convection today that is already gotten going over the lower North Shore Quebec. In the area near and east of the low centre, with bulk shears of 25-30 kts, MLCAPES of 500-750 J/kg, and precipitable water near 20 mm, storms are expected to remain sub-severe criteria. Small hail near 1cm is also possible given low freezing levels. There is also a risk of cold core funnels with low LCLs and weak vertical shear. Elsewhere across Labrador and northern Newfoundland, isolated lightning is possible.

 

For tonight, storms will weaken in the evening and become elevated as the low slowly moves eastward.

 

For Sunday, some lingering convection is possible over southeastern Labrador and northeastern Newfoundland as the low centre continues to drift southeastward. Meanwhile, another upper low will move into western Labrador from central Quebec in the afternoon,  providing some instability with isolated thunderstorms.

 

Thunderstorm outlook for today:

 

 

Thunderstorm outlook for tonight:

 

 

Thunderstorm outlook for tomorrow:

 

Convective Outlook Valid for Today and Tomorrow

Regional Impacts:

 

Today

NB: 15-25mm/hr, 70-90 km/h gusts, 1-2 cm hail.

Labrador: isolated lightning

Gulf waters: isolated lightning, possible squalls for western areas (70 km/h+ gusts).

PEI: western Prince County 15-25mm/hr, 70-90 km/h gusts, 1-2 cm hail. Elsewhere isolated lightning

NS: isolated lightning in the evening for northern areas.

 

Tonight

Labrador: isolated lightning in southern areas.

Gulf waters: isolated lightning

 

Tuesday:

Labrador: scattered lightning over southern areas with 0-1 cm hail, 10-15 mm/hr, isolated lightning elsewhere.

Gulf waters: scattered lightning over northern sections.

 

Convective Discussion:

Today: Clearing is already evident behind our initial shortwave that was responsible for showers and thundershowers in southern NB and western PEI this morning. This clearing in northeastern to central NB will allow for surface instability to build into the afternoon hours ahead of broad upper trough that will move into northern NB later this afternoon. Strong zonal flow across the Maritimes will provide 35-50 kts of bulk shear, given the linear character and steep moist low level lapse rates a wind hazard later this afternoon into the evening hours is possible. MLCAPE between 750-1000 J/kg with this type of shear and a lowering HGZ does support hail, however marginal lapse rates of 6.5C/km between 500-700mb should act to limit upward velocities into HGZ, capping the hail sizes to 1 to 2cm. Storm motion should be from west to east with the mean wind at ~30-35 kts, with any supercells moving to the right in a southeasterly direction. The fast motion will limit rainfall in general, however PWATs into the mid 30s, with moist profiles from the surface to 650mb and high 0-3km CAPE could still support rainfall rates hitting 25mm/hr despite the quick movement giving a rainfall hazard to go with a primary wind hazard. Watches may be issued earlier this afternoon primarily for the wind/ rainfall rate hazards. Storms should weaken later in the evening before reaching southernmost NB, central PEI and northern NS as solar insolation wanes.  Across the gulf isolated lightning with our initial shortwave this morning will advect east-northeastward, however storms moving off eastern NB may provide a squall hazard. Meanwhile in Labrador isolated lightning is also likely with broad instability present ahead of the upper trough.

 

Tonight: Storms from the evening will weaken and become elevated moving northeastward across the gulf into southern Labrador as the base of the upper trough rounds the upper low analyzed at 12z over north-central Quebec.

 

Saturday: Scattered lightning with steep mid level lapse rates from the upper low is expected over southern Labrador. Storm motion will be variable and low with rainfall rates of 10-15mm/hr and small hail given the low freezing levels. Vertically stack vorticity, low LCLs and little vertical shear suggest that cold core funnel clouds are possible. Elsewhere across Labrador lightning should be more isolated in nature associated with general instability of the upper trough.

 

Thunderstorm outlook for today:

 

Thunderstorm outlook for tonight:

 

 

Thunderstorm outlook for Saturday:

 

Convective Outlook Valid for Today and Tomorrow

Thunderstorm Outlook for Today

Isolated non-severe thunderstorms

 

Regional Impacts

Clusters of thunderstorms will likely develop over western and central Labrador.. producing heavy showers and some wind gusts to around 70 km/h.

Risk of a thunderstorm over northeastern Newfoundland.

 

Convective Discussion

At the surface this morning is a low pressure area over the south coast of NF with extensive cloud and rain associated with it. The frontal boundary is supported by a southwesterly upper jet crossing the Avalon. The YJT sounding is saturated but Satellite imagery is showing some breaks in the clouds along the south coast. MUCAPE values are indicative of a potential for convection over parts of the island. Some limited surface heating may help the development of Cu/Tcu, and with the frontal boundary / upper jet / some pva at 500mb.. there is a risk that these convective clouds could evolve into CB’s.

Another area of focus today will be south of Ungava bay with a cold front southwestward. Surface CAPE values could reach 500 J/Kg ahead of this feature during the afternoon, modified LaGrande sounding indicates the potential for heavier showers and wind guts between 30-40kt.  

 

 

 

Thunderstorm Outlook for Friday

A new low pressure will emerge from the northern Quebec frontal boundary and become established over Labrador Friday. A cold frontal band will stretch southwestward from the low and swing across the Maritimes. There is a potential for mixed-layer CAPE values of more than 500J/Kg, Lifted indices of -4, and deep layer shear of 30+Kt, all of which could lead to some bowing lines over central and northern NB.