To snow or to rain, that's the question. This dump is on the maps for over a week, but as we're getting closer to the actual rain or snowfall, more and more details are getting clear.
All the expectations are caused by the low pressure area called Pia, that's somewhere around Iceland at the moment. Pia will move to England the next couple of days to head north over the Northsea from Tuesday. The jet stream will move along with Pia, or actually it's the other way around: Pia is moving along with the jet stream. And that jet stream is moving south. The jet stream is moving from the south to the east. West of the Alps at first, but later more to the east.The Jetstream
This jet stream will pus fronts towards the Alps from Monday. First in the (south)west and later on more towards the east. You can see on the image above that the jet stream is filled with lots of warm air from Africa. Hot air can contain more moisture, so this is definitely an advantage, but this hot air might also cause the snow to fall as heavy slush, or even worse: rain. The temperature will determine if this will be PowderAlert #2 or a soaking wet week.
The fronts will be pushed to the southern parts of the western Alps from Monday and will move to the western Alps central later on. This will cause lots of rain in Nice on Monday, and the precipitation will move north after that. The precipitation will intensify in the western Alps south in the night from Monday to Tuesday and will move to the east. The first Genua low of the season is in effect. The fronts are moving to the Alps from the Gulf of Genua, traveling over the flat Po Valley. The first resistance they meet are the peaks of the southern Alps west and central. The precipitation will intensify in the night from Monday to Tuesday. These are the areas where the most snow is expected. The fronts will also hit the southern Alps east a bit later. The amount of fresh snow will depend on the temperature, but it's quite clear that there'll be enough moisture in the air for 100-150 centimeters of snow, locally even 200 cm or more!
The main question: the temperature
It's hard to predict the right temperature. The ensemble below is for the Monte Rosa in the southern Alps central and that's a pretty good indication for the complete southern Alps. The temperature will rise the moment the precipitation starts to fall, caused by the warm air from the south. It will be around 6 degrees at 1400 meters altitude. Other calculations confirm this and the freezing level will be around 2000 - 2500 meters. You can expect light snow above 2500 meters.
Is there any good news? Yes, this will be the base for the glaciers, the higher alpine and the higher (northern) expositions. And don't forget the orographic effects. Humid air has to rise and needs energy, causing it to cool down and this will cause it to snow or rain. The more intense the precipitation, the bigger the chance of a lower temperature than the maps predict. But it's hard to forecast this and local differences exist. It's realistic that the freezing level will be lower than 2500 meters. Maybe around 1500 - 2000 meters. And that's more interesting.
It's quite to forecast very precise this time of the year, especially with the dropping and rising temperatures, but let's give it a try.
Western Alps Central
The western Alps central will be colder than the southern Alps, but will get less precipitation. You can expect around 20-30 centimeters. Nice, but obviously not enough for a good powder day.
Western Alps South, Southern Alps west and central
This is the area where the most precipitation will fall. 100-150 centimeters, locally even more than 200 centimeters. The freezing level will be around 2000 - 25000 meters. But it might drop because of orographic effects. The most snow will fall in the stau areas of the Mont Viso, the Mont Blacns and the Monte Rosa. More details about the temperatures the next couple of days. Unfortunately, the local weather stations are our best source. Consider these to options before more details are clear:
Lift assisted powder above 2500 meter in the real stau areas. The visibility will improve from Thursday and the base is thick enough to take care of all the sharks. The sun might come out above the treeline on Thursday as well. Resorts: Saas Fee and Zermatt.
Southern Alps East
Intense precipitation is expected, but not as much as in the southern Alps central.
Should we call it a powder alert?
Mwaaah, it might be for some locals, but if you have to drive for hours to get to the Alps, it might be to uncertain. Zermatt and Saas Fee are the only resorts that are open and they don't have that much accessible terrain above 2500 meters.