Synopsis
A low near the southwest coast of Norway moves northeast along the Norwegian coast. Along with NO-ZW heat front above the southeast of the country moves southeast tonight. The cold front is initially still above the far northwest of the country moving southeast tonight. This front goes waves and this wave draws in the second half of the evening and in the night to Wednesday over the southeastern half of the country. After passage of the cold front, the upper air gradually cools down with a sinking altitude trench above the North Sea on Wednesday. This high trench passes through our country in the night to Thursday. Thursday during the day and in the evening an occlusion follows.

Model assessment
The timing of the fronts is unique in the models. In the hot sector and in the cold front, both models calculate ST. This is currently also happening in the warm sector and is therefore realistic. EC has this to a lesser extent, but this model is often too positive, so we follow UWC. This calculates northwest of the cold front also locally some turbulence stratus coming night and night to Thursday. On Thursday, UWC will also calculate local ST. This does not have EC, but is possible. Furthermore, based on the radar simulation of UWC and a look at the progtemps, there seems to be a chance of aligned convection on the cold front (LEWP). However, the risk of heavy wind blows (75+ km/h) is still limited to above the warm seawater, where the profiles are most unstable. The cooling upper air of Wednesday provides an increasing instability depth and CAPE. Chance of heavier showers with thunderstorms and hail increases north of the jetas at 300 hPa, approximately corresponding to the -25°C isotherm at 500 hPa. Convective gusts can also come out locally around 75 km/h during the day on Wednesday. Code yellow for thunderstorms issued. In Limburg it seems to be not so bad with the showers, also because of the late timing of the colder upper air. In the night to Thursday, passing the upper air trench causes the showers to rise further into the country than the models indicate. UWC seems to calculate too much wind on the coast and above the sea due to thunderstorm Thursday. The wind blows in UWC also seem too high above the west coast on Thursday. In the profiles there is not much wind, unless the wind blows are caused by water loading, but then UWC still seems too high.Issues

Wind
The signal for 7 Bft is withdrawn and occasionally 6 Bft remains. The wind blows seem to be in particular UWC on the high side. Deeper in the polar air convective outliers to approx. 75 km/h, possibly a little more at sea. Especially Thursday UWC overestimates the average wind at the coast, see model comparison.

Visibility
Good visibility, in precipitation moderate to poor visibility. Possibly locally inland in the nights nebula.

Temperature
Wednesday pretty cool with in the north during the day not more than 13°C. In the night to Thursday in the north locally below 5°C.

Cloud
In the warm sector a thick package of layered clouds. On the cold front some embedded CBs (top FL180) and inland also ST, see model comparison. CB-tops Wednesday and Thursday FL250-FL300. At the occlusion Thursday there is also a layered package and possibly local ST.

Precipitation
In the hot rain sector. On the cold front itself there is a chance of aligned convection in a regime of marginal CAPE 200-400 J/kg (above sea 400-700 J/Kg), but with quite a lot of shear in the lower 3 km, ca. 30 kn. Because the front goes above the south waves there are accumulations in the order of 20-40 mm possible until Wednesday morning. Wednesday from the north out of increasing showers. In the showers thunderstorm and locally also hail of 1-2 cm (FZL around FL050). Hours in Harmony are located in coastal areas above 20 mm. Based on UWEPS, the largest 24-hour sums are expected first at the wave (especially in Zeeland, the rivers area and Gelderland). On Thursday also showers and then most precipitation seems to fall in the far west, but these locations differ slightly per run.

Synoptic development
A steering low pressure area over the northern North Sea slowly moves north and gradually fills up. From the altitude trench above Western Europe, a cold low pressure zone is formed above south-eastern Europe, which, after the weekend, may be retreating westward over the Baltic Sea region. At the weekend from the west passes from a foothill of the Azores high, after which the current becomes western or northwest. In the course of the next week, part of the members form a high above the North Sea region, Scandinavia or Russia (omega blockade).

Model assessment and uncertainties
The probability of wind blows of more than 75 km/h in showers is on Thursday in EC Eps output zero, this is not realistic, in UWCeps Exports this probability on the coast is initially still 20-50%. The uncertainty after the weekend has increased. In an increasing proportion of members, low pressure comes from the east, which often coincides with the passage of an occlusion from the west. The probability of precipitation increased to about 50% on Monday. The chance of normal to slightly above normal temperatures from the beginning of the week has increased. The number of members with a blocking high above Northwest Europe has also increased.

Multi-day Summary
Gradually decreasing mood and less cool. During the weekend dry with occasional sunshine. Early next week, increasing chance of rain.

EPS Period Summary
Decreasing probability of precipitation, periods with sun and temperatures gradually slightly above the long-term average.

Valid from Thursday 12 September to Tuesday 24 September