The description of our convective forecasts
A convective forecast is issued on our webpage when atmospheric deep moist convection can be expected over Hungary AND this convection may involve one of the following events:
Severe weather events:
wind speed >= 90 km/h
hail diameter >= 2 cm
Significantly severe weather events:
wind speed >= 120 km/h
hail diameter >= 5 cm
tornado >= EF2
A convective forecast (similarly to an outlook) consists of a detailed, technical analysis of the expected convective situation which means the followings:
- description of synoptic and mesoscale processes which can create favourable conditions for severe convective events over Hungary
- the synopsis of the ingredients (instability, moisture, lifting and wind shear) necessary for severe convection
- the expected temporal and spatial coverage of the predicted severe weather events within Hungary
- a list of the impending hazards related to convection (large hails/tornados/damaging windgusts/flash floods)
The convective forecasts are published preferably before the formation of severe events (maximum 24h before the first appearance of severe convective cells) and cover the following 24h +/- 6h from the time of its publication. We produce the forecast until 10 a.m. if we expect the development of severe convective events before 10 p.m. (i. e. the late evening) on that day. If the occurence of events is predicted after 10 p.m. (i. e. after the late evening, during the night) then the forecast is issued until 2 p.m. (in the early afternoon). If the severe convective events may occur in the morning or before noon (between 6 and 12 p.m.) then we publish the forecast until 10 p.m. in the previous day evening. These times are meant to be local times. As our forecaster experts make the outlooks in their free time we cannot guarantee a 24/7 coverage of convective forecasts. Additionaly, if we do not expect weather events falling in the listed criteria we do not issue forecast.
The predictions and possibilities described in our forecast cannot be regarded as statements of facts, nor can be qualified as public threats, but we merely present our comments and expectations on the impending weather situation. Everybody has an individual responsibility to what extent takes this forecast into account.
The convective forecasts are classified into four numbered categories based on the intensity and spatial coverage of the expected convective events (please note that these categories are not consistent with the warning scale applied by the Hungarian Meteorological Service and levels produced by the ESTOFEX). To decide the category of an actual convective forecast we consider the followings:
There is a modest possibility of severe events in several places but the uncertainty is very high, therefore choosing Category 1 is inadequate. In addition, Category 0 is issued if we expect the occurence of non-mesocyclonic funnel cloud/tornado.
- instability and wind shear is sufficient for supercell development but the marginal moisture conditions make their actual formation highly questionable
- outputs of various models predict largely distinct weather scenarios
- quasi-stationary, permanent convergence with large horizontal wind shear along an occlusion which creates widely favourable conditions for non-mesocyclonic funnel clouds, possibly tornados, too
A weather situation recieves Category 1 if we expect severe events only in few places or there is a chance of flash floods (mostly related to multicellular thunderstorms with precipitation above 50 mm/3h embedded in mesoscale convective systems or forming continuously over the same area, in the case of adequate terrain conditions). In Category 1 we don't expect siginificant severe events.
- there is insufficient wind shear for supercell development but large instability may result in monocellular/multicellular thunderstorms which are capable of producing large hail
- if the propagation of cells in a multicellular cluster compensates their slow motion (driven by the mean wind) in such a way that they reach their own mature stage above the very same area exposing it to flash-flood hazard
- supercells are probable, but the conditions are not so favouring
If there is a chance of significant severe weather events we issue Category 2.
- probable supercells in extremely supportive (significant instability and wind shear) conditions accompanying large wind gusts and damaging downbursts
- highly organized multicell lines (squall lines) whith embedding hazardous bow echo segments
- in isolated supercells, due to the largely increased helicity and low lifting condensation level, there is a raised chance of tornado with EF2 strength
We issue the highest level, Category 3 when we expect severe convective events over a significant part of Hungary or the expected weather situation is mainly characterized by extremely hazardous convective storms.
- over a large portion of Hungary a squall line passage is probable which mainly consists of supercells producing significantly severe events over extended areas
- numerous supercells all over the country are expected with related severe and significantly severe weather events
- tornado outbreaks: over several places with tornados of EF2 or higher