Friday, February 20, 2015

Weather It Is (Friday Morning's Winter Storm Warning)

Good Morning:

Our latest 12 UTC and 18 UTC forecasts restored the heavier amounts of precipitation (somewhat "lost" in the 6 UTC run).

The forecast snow amounts remain fairly consistent from the previous values given.

The temperatures are zero or below in Jerusalem and the surrounding area, as well in the environs of Sefad.  They are expected to rise slightly in mid-to-late morning, which may hold down accumulations a bit (as previously noted) except in the highest parts of Jerusalem.

Our model shows that about about 50% of the precipitation forecast will convert to snow accumulation in Gush Etzion (and Sefad), while about 25% elsewhere.  These percentages are very temperature dependent and a small change in surface temperatures downward would bump up the total snow amounts in some neighbourhoods of Jerusalem (we just don't forecast this yet).

It is worth mentioning that our 12 UTC 4 km ensemble gives a burst of precipitation between 8 AM and 11 AM, which could bring 8 to 16 cm more of snow on top of what we'll have up to then.  The probabilities range from about 60% in Jerusalem to 100% in Gush Etzion (Efrat Southward).  If this strong surge occurs, it could also add several centimetres of snow to the amounts shown below.

In summary, our current forecasts have the snow transitioning to a "wetter" snow in the Jerusalem area around mid-morning, but not until noon/early-afternoon in Gush Etzion.  This accounts -- for the most part -- for differences in forecast snow amounts.

Here they are:

Snow accumulations are valid until 2 P.M tomorrow.

Hermon: 65 cm
Golan: 25-35 cm
Gush Etzion: 30-40 cm
Jerusalem: 20-25 cm, including about 15-20 cm in the Old City.
Bet-El/Har Bracha: 15-20 cm
Sefad: 10 to 20 cm.
Ramat Bet-Shemesh, Kefar Giladi: up to 5 cm.

Another round of precipitation is expected later in the afternoon into Shabbat morning. It will probably be mixed rain and snow, wet snow, and just snow, depending on elevation.

Barry Lynn

No comments:

Post a Comment

Note: Only a member of this blog may post a comment.