Jacob's weather forecasts

 There's some interesting convective potential on Monday in the southeast, and more widespread potential on Tuesday Given that these are a couple day out, bear in mind that the situation is highly volatile. On both days, we will be seeing a low MUCAPE (<750 J/kg), but high shear (30kn+) setup associated with a cold front. This makes it tricky to forecast, as it's perfectly plausible that we don't see much stormy weather at all (particularly on Monday), or that severe weather quickly evolves into a rainy mess. The main hazards on both days are flash flooding and strong winds, as storms have the potential to organize, possibly into supercells. There's also a more marginal risk of hail on Tuesday. The risk of tornadoes and funnel clouds is low, as the atmosphere is only marginally favorable of storm rotation.

I remember last summer and late spring, where dreaded breakdowns of warm weather patterns to persistently cool, wet weather in weather models kept being downgraded to what was closer to average conditions. It relates to how weather models often incorrectly predict or underestimate the impact of SSTs on atmospheric circulation at 3+ days out and correct themselves closer to the time. An implication for this is that the longevity of "heat domes" can be underestimated by weather models in the context of global warming. The first reason for SSTs causing warm, dry weather is that a weaker AMOC, freshwater in the North Atlantic and cold blob are linked to a stronger Icelandic Low, causing southerly, anticyclonic conditions to dominate in late spring and early summer, when the cold SSTs in the North Atlantic are more pronounced from melting retreating ice in summer. Last spring, we saw some very stark, cold SST anomalies, which lead to a heatwave in April and May. These southerly wi...

I've had much time to forecast lately, but I just noticed that there seems to be a risk of thunderstorms tomorrow afternoon, south of the M4, particularly further inland The ingredients that come together for this are moderate CAPE, low CIN, low LFC, 7C/km lapse rates, and wind convergence. It means that in theory, there could be plenty of convective energy to create thunderstorms. Wind convergence may allow thunderstorms to stall over one area and strengthen, creating flooding and a risk of hail, though the risk of severe weather in any one area is low

In the shorter term, a more imminent potential tipping point could be an SPG convection collapse:   Abrupt Climate Change in the Subpolar North Atlantic: Drivers and Impacts In this study, climate models show that this tipping point is not a matter of if it happens, but when it happens. It may suggest that the tipping point may have already been reached, and the SPG convection is already in terminal decline, or it may be as a result of climate model biases, not including Greenland freshwater runoff, and resolution, which isn't high enough to properly represent eddies, though the model used (CESM2-LENS) is still fairly skillful. The timing of the collapse is uncertain, but the risk raises significantly in the 2030s, and into mid-century. The collapse would cause a significant drop in SSTs in the subpolar gyre, so it essentially strengthens the NAWH/cold blob, and is a more minor, abrupt version of an AMOC collapse, that would occur before it. The ensemble mean for the timing of this...

The impacts of an AMOC collapse on Europe Introduction As the Earth has warmed, one section of the Atlantic Ocean has been cooling. This has been attributed to an ocean current, known as the Atlantic Meridional Overturning Circulation (AMOC) weakening. This ocean current regulates the climate worldwide by transporting waters at different temperatures, but this is expected to continue to weaken with climate change, bringing worrying consequences on the climate. However, a more extreme, but still a very plausible scenario of the current collapsing may occur as early as mid-century, where the climate may rapidly change within a few decades. In this summary, I'll focus on Europe. Source: High-resolution ‘fingerprint’ images reveal a weakening Atlantic Ocean circulation (AMOC) The AMOC brings warmer water from the Gulf of Mexico to Europe, contributing to keeping its climate mild in comparison to areas such as Canada. Under a collapse, a lot of the warmer water is shut off, shown by the...

First, let's look at the main factors at play. Current situation Lack of a clear tropospheric polar vortex Higher pressure over Greenland, but not strong enough to have a big influence aside from weakening the Atlantic storm track High pressure over Scandinavian snow cover, trapping cold air that forces the Atlantic storm track to weaken and shift south as it moves west, into the UK Active Atlantic storm track, albeit weaker on the eastern side as it passes over the UK As a result, you have a weak zonal flow dominating the UK, causing rain, as well as more settled weather between low pressure systems. The lack of jet stream amplification keeps temperatures close to average. Mid-range model output On Monday to Wednesday, pressure over Scandinavia is reduced, strengthening the storm track. It creates wetter and slightly milder conditions On the rest of the week, cold air in Scandinavia and Siberia mixes with the Atlantic storm track. In the north of the UK, there's more influence...