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.

 

Convective Outlook Valid for Today and Tomorrow

Thunderstorm Outlook for Today

Isolated thunderstorms with locally heavy rainfall

 

Regional Impacts

Eastern Maritimes and western NF: isolated thunderstorms embedded in a very moist airmass. Rainfall amounts 30 to 60 mm and locally exceeding 75 mm.

 

Convective Discussion

 

Surface low pressure over southeastern Maine will continue to advance towards NF today. Large area of continuous rain extends from near the centre of the low to southwestern NF. A warm front extending from the low to SW NF, this frontal boundary is the focus for isolated CB/ACB’s as depicted by the YJT upper air sounding.   

Dry air is entering region from the NW in advance of a surface ridge over northern Ontario / Quebec. Open cellular Cu/Tcu’s will develop ahead of the ridge, but surface temperatures would have to jump to the mid-20’s for this surface-based convection to reach the next level. Considering the origin of the air mass behind the low and the presence of a subsidence inversion, CB’s are ruled out behind the area of rain.

 

 

Thunderstorm Outlook for Tonight

 

 

 

Thunderstorm Outlook for Thursday

 

 

Convective Outlook Valid for Today and Tomorrow

Thunderstorm Outlook for Today

 

Regional Impacts

Southern sections of NF.. Slight risk of a thunderstorm with gusts to 70 km/h and a brief shower

Elsewhere, no thunderstorms expected.

 

Convective Discussion

The 500mb  upper low and its associated cold pool are located just off the coast of Labrador this morning and has an extensive area of cloud attached to it. Over NF, the latest soundings indicate fairly unstable conditions in the low levels, and since 12z satellite imagery is showing the development of cumulus clouds throughout the interior. Should the surface temperature reach 22 or 23 degrees it would probably be enough to produce enough surface-based CAPE to build towering cumulus, and even a small cumulonimbus. The window is short since the air mass will begin to warm in the mid-levels later today and become detrimental to deeper vertical development.

 

 

 

 

Thunderstorm Outlook for Day 2

A very moist air mass originating from the Great Lakes region will produce widespread rain, and some embedded thunderstorms.

 

A low pressure system will emerge from southern Quebec tonight, and move across Maine/NB on Wednesday, reaching NF late Wednesday. Rainfall amounts of 25 to 50 mm should be widespread, and there is a possibility of more than 50 mm in a swath extending from central NB to the south coast of NF. Isolated embedded thunderstorms are possible in the path of this system.

 

 

Convective Outlook Valid for Today and Tomorrow

Regional Impacts:

 

Today

NL: Wind gusts 70-90 km/h, hail 2-3 cm, rainfall 15-25mm, scattered to frequent lightning.

 

Tonight

None.

 

Tuesday

None.

 

Convective Discussion

An anomalous cold upper low located over central Labrador (more common in early spring rather than summer) is giving rise to a strong upper jet of ~ 130 kts east of the Avalon this morning. Here the Newfoundland is in a favourable region of synoptic lift given its proximity to the left exit of the this quick upper jet. On water vapour this morning a potent vorticity centre was located to the west of Stephenville, this feature is expected to round the southern periphery of the upper low (located over Labrador)  and move eastward towards Terra Nova providing ample PVA as it does so. Aloft lapse rates are also expected to steepen, with 500-700mb temperature differentials anticipated to increase from 14-15 C to 18-19 C later this afternoon. The biggest question mark remains the amount of instability later this afternoon, Canadian guidance seems to be the most bullish in supporting a T/Td spread of 22/14 yielding 1500 J/kg of SBCAPE. This level of instability given the high shear environment (35-50 kts of bulk shear), and 0-3km SRH values of 100, would support supercell development between Gander and Clarenville. However foreign guidance is consistently drier, supporting SBCAPEs under 1000 J/Kg (maxing out at 800 J/kg) giving some uncertainty. Nevertheless a small area of dew points in the low teens did exist on the 12z analysis this morning SE of Gander, so one cannot discount the RDPS/GDPS solution all together. Storm motion is expected to be ENE at 30-40 kts, with any supercells moving to the right in an easterly motion. The primary threat with storms today is expected to be hail given the unseasonably low HGZ with the cold upper trough, linear hodographs, and steep mid level lapse rates. A wind hazard also exists, especially with any supercell RFD adding to the quick storm motion. Rainfall over any given location will be limited by the progression of storms today, and the lower PWATs of ~20-23mm associated with the unseasonable cool upper air mass in place. A tornado threat was ruled improbable given little directional shear in the 0-1 km layer (not much in the way of low level backing), despite LCLs being under 1 km.

 

Thunderstorm outlook for today

 

 

Thunderstorm outlook for tonight

 

 

Thunderstorm outlook for Tuesday

 

Convective Outlook Valid for Today and Tomorrow

Regional Impacts

 

Today

NB: Scattered strong thunderstorms.

NS/PEI/NL/Labrador: isolated thundershowers.

 

Tonight

None.

 

Monday

NL/Labrador: isolated thundershowers

NB/NS/PEI: None.

 

Convective Discussion

A cold front is basically stalled over southern NB but will drift across NS tonight. There is a lot of shear (40 to 60 knots and linear) and the cape is 500 J/kg or less. The shear is likely too strong for the cape but for areas near the front today (southern NB) some enhanced activity is possible. PWAT values of 25 mm will give downpours. Guidance is suggesting hail near 1 cm and low freezing levels near 9000 feet. Dry mid levels support the model guidance of wind gusts to 40 kts.

 

Garden variety pop-up thundershowers are possible on Monday for Nfld/Lab.

 

 

Thunderstorm Outlook for today

 

 

 

 

 

Thunderstorm Outlook for tonight

 

 

Thunderstorm Outlook for Monday