It has been an active few days and is setting up to continue for portions of far western Europe. The general pattern has been and will continue to feature upper level troughs diving in from the west and northwest increasing moisture levels. These upper level features induce surface low pressure systems which linger around the region. The vorticity (measure of the spin in the atmosphere) and divergence aloft accompanied with surface convergence from low-pressure systems and associated fronts will result in rising motion in the atmosphere. The saturated air mass in place along with this vertical motion will produce periods of rain and heavier showers at times into Spain (mainly southeastern portions through the weekend) and Portugal (has already received showers mid-week; gets the brunt of a few weather fronts early next week as well). The reasoning for this type of active pattern resides in the upper portions of the atmosphere.
Expansive upper level ridging has built in across northern and central Europe. This forces a block in the flow, slowing down the system pushing into Portugal and Spain leading to times of rain and moderate showers (mainly in southeastern Spain) through the weekend (image above shows the first system delivering rains represented in the green colors to Spain and Portugal Friday) with the next of possibly a few systems on its heels diving into the region early next week (image below). The block looks to hold in place during this time as more rain breaks out across Spain, Portugal and France lingering into the middle portions of next week.
More details and the exact placement of the system for the middle part of next week may shift over the coming days, however agreement between the all of the major global models and ensembles at this time shows the potential for a long-lasting meridional pattern across Europe with the main impacts felt across western sections.
ECMWF model output valid Friday at 12Z, Monday at 00Z, and Wednesday at 00Z. Notice how the pattern overall does not change all that much. This is courtesy of the omega block in the upper portions of the atmosphere outlined in black. As a note, the system for Friday through the weekend kicks out of the region early next week. The image for 00Z Wednesday is the next system diving in from the northwest.
The upper level setup that will produce this active pattern for western regions of the European continent is known as an omega block. Omega blocking patterns like the one shown above in the slideshow can last for several days and sometimes more (as model guidance through next week is indicating for this region). The upper level ridge in central and northern Europe (orange coloring) forces troughs (blue coloring) on both sides of the high pressure. Because of this setup, the trough in western Europe remains stagnant as the high pressure “blocks” the system from moving all that much. All the while on the other side of the ridge across the Middle East a trough remains stagnant until mid to late week. The black outline in each image traces the upper level flow from west to east. The resulting image takes the shape of the Greek letter Omega hence the term Omega block.
There are other blocking patterns in the atmosphere that develop and potentially lead to instances of inclement or anomalously warm/cold weather across portions of the world and the US. Other examples include a Rex Block, along with various teleconnections including the North Atlantic Oscillation, Arctic Oscillation, Pacific North American oscillation, among others. All of these patterns have significant impacts on global regions in their own respect, which will be covered in another article.
Courtesy of the GFS, stormy weather and perhaps some snow in the higher elevations of the Zagros mountains in western Iran early next week.
To close out this discussion, portions of the eastern Mediterranean into the Middle East will feel the impacts of this omega block as troughs swing into the region. These troughs will produce times of showers and thunderstorms across the desert while perhaps a bit of snowfall across the higher elevations of the Zagros mountains through early next week.
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©2019 Meteorologist Joe DeLizio