With the Warm Moist NW creating quite favourable theta-e temps, combined with fairly cold upper level temps throughout tomorrow (-22 to -24*C) , shower activity will get going quite quickly.
Thing is, looking at the atmospheric profile tommorow, there is no limit to the free rise of convection, therefore showers will most likely muddy the environment for decent storms to develop. (I presume this is why the Metservice Convection Desk issued a Mod risk instead of High).
The frontal passage will be something to watch tomorrow evening on the West Coast. SFC Sea temps around Auckland/Waikato/BOP are at 15*C, Northland up to 16.7*C.
Those temps should be sufficient for thermal differentiation esp taking into consideration theta-e and potential latent heat release. A pitty that the main jucy shortwave passes through in the middle of the night Wednesday into Thursday.
Then we return to that oh-so-lovely SW flow with embedded scrappy showers Thursday.
Metservices Thunderstorm Outlook:
Metservice wrote: During the afternoon, temperatures continue cooling aloft over the North Island,allowing widespread shower activity to form in response to afternoon heating.
There is a moderate risk of afternoon thunderstorms developing from Bay of Plenty to the central high country and northwards to Northland. These thunderstorms could bring rainfall rates of 10-25mm/hr and hail of 5-15mm. This activity is expected to ease from the west from late afternoon, clearing eastern Bay of Plenty in the early evening.
During the evening, a front is expected to cross the northwest of the North Island supporting a band of heavy and possibly squally showers. Over western areas from Northland to Taranaki, there is a moderate risk of thunderstorms with brief heavy rain, squally wind gusts to 90km/hr, and the risk of one or two small tornadoes about the coast.
A larger low risk area extends from East Cape to Wairarapa, the Marlborough Sounds and onto Westland, as indicated on the chart.
Elsewhere, no thunderstorms or significant convection expected.
