Illustration (Image Credit: Wix)
Meteorologists -- and by extension you -- are faced with a complex weather system that should affect us during the next two to three days. This means that the forecast is actually a debate rather than a statement of what will be. The storm that should affect us is actually two storms. The first should arrive Thursday and bring heavy rain, thunder and lightning, and some hail to a large part of the country, with flooding possible from north to south. This storm is suppose to form east of Crete, and move across our area tomorrow afternoon. The next storm is also suppose to form west of Cyprus, drop southward, and then move across our area late Thursday night into Friday. This means that the coldest air associated with this system will be stuck over the sea before arriving towards morning. This also means that the winds blowing counterclockwise around the storm will have a southerly component, which should force a break in the precipitation even while the coldest air in the lower layer arrives. The lower layer (850 mb), middle layer (700 mb), and 500 mb temperatures will align for snow conditions from about 3 A.M until 2 P.M (1400), but the moisture will align only from about 9 A.M to 2 P.M.
Afterwards, the temperatures should be quite cold aloft, and precipitation will become even heavier. It will probably be a combination of rain and ice that continue until Saturday morning. In fact, our higher resolution forecast shows an accumulation of hail late afternoon and evening in Jerusalem and the central mountains. A secondary system may arrive on Saturday/Shabbat afternoon, bringing more rain and hail.
Image credit: The Jerusalem Herald
It all seems relatively simple, except that the passage of the first storm will "shake things up" a bit, and that bit may be enough to affect the position of the second storm. That is, it may move first east of Cyprus, which means that the coldest air associated with the storm will better align with the cold. This is indicated by several ensemble members that continue the "cold enough for snow" conditions until evening or even midnight. The probability is less than 50%, but it shouldn't be discounted. In regard to snow accumulation, this is more likely in the higher mountains around Jerusalem than in Jerusalem itself. The best chance for an accumulating snow both in Jerusalem and its environ is from early morning until afternoon on Friday. The strong winds may make for briefly blizzard conditions. How much will fall, we still don't know; the debate won't help, but the passage of time will.
Dr. Lynn is a lecturer at The Hebrew University of Jerusalem, Earth Sciences Department. He is also CEO of Weather It Is, LTD, a company that specializes in reducing weather risk.