Weather It Is (One Storm Arrives, And Then Snow?)

Good Evening:

Right on schedule, our lightning detection network has identified a long line of thunderstorms arriving at our coast line.  The map shows a radar depiction of the storms ("PulseRad") derived from the lightning data.

The storms are occurring along a frontal zone ahead of a low pressure area moving into Turkey. Very cold temperatures aloft will mean that hail should occur with these thunderstorms, while cold temperatures near the surface mean that ice ("cubes") could coat the ground tonight into tomorrow.

It will be followed by a brief warm-up, and then by a stronger storm developing just west of Cyprus.  Just where this storm develops (just east of Cyprus is better) will determine the elevation at which snow falls on Sunday into Monday.  The further east it develops, the colder the temperatures at the surface will be (as cold air moving over the sea absorbs heat from the Mediterranean Sea).

Right now, temperatures at upper levels should be cold enough for convective precipitation, which when combined with temperatures at middle levels just cold enough for good snow growth, means that this storm will give it a good try to bring snow to Jerusalem.

The problem is that any snowflake making the plunge towards earth will encounter temperatures near the surface that will probably be above freezing (with 850 mb temperatures possibly from just above freezing to a degree or so below).  Basically, this is not a good situation to be in if you're a snowflake, and many of them may simply choose to stay aloft in the clouds, instead of taking the risk of melting on the way down.

Hence, we'll have to wait and see our high resolution forecasts in order to be able to know at what elevations snow might accumulate on the ground (if any, in our area).

Until then, we can't say if there will just be rain and mixed snow, or wet snow that might coat the highest elevations.

It might also be of interest to note that about 30% of our forecasts are predicting that the mid-week period will bring even colder weather.  This could occur as cold air wraps behind our early next week's storm and possibly moves directly south into our area, with minimal moderation from warm sea-surface temperatures.

Barry Lynn

Weather It Is (The Tension Builds)

Good Evening:

Last week we spoke about the things we know, the things we know are not known, and the things that we don't know we don't know.

There are still plenty of things we don't know we don't know, but the things we know (or don't know) are becoming better known.

For instance, we see that our next storm -- to arrive immediately after the relatively weak (but still) wet) storm affecting us now will bring cold temperatures aloft, but nothing too chilly at lower levels. This means periods of rain mixed with graupel/hail.  This storm will be arriving from our west, as higher heights (NAO) build over Greenland - meaning that initially the ridge trough couplet (west to east, respectively) will be located at first too far to the west -- so the lower levels in the next storm will be moderated by the warm sea.

In contrast, we now have indications that the storm that should follow Shabbat or early next week will arrive from the north (as Siberian air makes its way southward).  Our current forecasts show a 60/40 in split in favor of extremely cold temperatures aloft.  This means that the forecasts are clustering around either a cold, snowy "solution" to the equations that describe our future weather or a warmer solution, with a lean toward the colder forecasts. However, there is less certainty about lower level temperatures. Still, many ensemble members show temperatures below freezing at least at some point during the storm.

So, we know that we can be more positive about the possibility of our first snow (in the Jerusalem area) early next week, but there are still a lot of unknowns (just how directly the storm arrives from the north) and even unknowns we don't know -- besides model errors, how many people want snow or don't want snow, which can sometimes tip the balance.

Barry Lynn

Weather It Is (Things We Know: Or will it Snow?)

Good Afternoon:

I am sure that many readers appreciate the heavy rainfall, but more it must be satisfying to know that winter in Israel can still feel like winter's past!

To understand what may be in store for us next week, we need to review a bit of history.

After the attack of "9/11," former United States Secretary of Defense Donald Rumsfeld stated:

"Reports that say that something hasn't happened are always interesting to me, because as we know, there are known knowns; there are things we know we know. We also know there are known unknowns; that is to say we know there are some things we do not know. But there are also unknown unknowns—the ones we don't know we don't know."

Mr. Rumsfeld was far more prescient than he possibly knew.  He might just have been speaking about the weather, if not the weather we "expect' next week.

Here are the things we know:  We know that the global weather forecasts are showing the possibility of the coldest weather in many years to arrive next week.  We also know that there will be prolonged and heavy precipitation over several days. Lastly, we know that there is no "flip-side" to the forecasts. We're not seeing an equal number of equally unusually warm vs unusually cold forecasts within the global ensemble.   It's either winter as usual or winter as we've not known it for many years (perhaps going back to the time when snow fell in Tel-Aviv in 1950 (see: https://en.wikipedia.org/wiki/Snow_in_Israel).  

However, there are many known unknowns.  For example, there is something referred to as the North Atlantic Oscillation.  It has no significance by itself, but a negative NAO index indicates a weather pattern that can produce strong storms, but storms that drop down west of Cyprus, and then move across the sea. This means that these storms warm up in their lower levels too much for any heavy snow in the Jerusalem area.  While half our forecasts are indicating abnormally cold air towards the end of next week,  the other half are not. . We just don't know how strong a "Ridge" of warm air will build over Greenland (a negative NAO) -- which will determine not only how much cold air arrives earlier versus later in the week, but just how much of our precipitation falls as snow.

We also have unknown, unknowns: we often assume that when the forecast synoptic pattern of the global forecast indicates certainty (> 90%) then we can confidently use a higher resolution forecast model to forecast the details of the upcoming weather event.  However, there are unknown errors and non-linear interactions that can grow to even create variability in an otherwise "certain" synoptic forecast pattern.  This can turn what looks like a sure snow event into a missed forecast, and even our higher resolution forecasts can't correct for that (as they depend on the information they receive from the global model).

So, we left with uncertainty, but "hope" too (if you like snow). In any case, I can state with near certainty that a lot of people will be following the weather over the next several days and hoping for Jerusalem snow.

Barry Lynn

Weather It Is (Rainy with Some Ice)

Good Evening:

As we head into the end of the month, we've arrived at an almost: an almost (Jerusalem) snow storm.

Tomorrow, the winds will switch to the southwest at all levels of the atmosphere, bringing with them dry and warmer air, as well as dust.  However,  by Wednesday, the winds are forecast to switch back to the west by northwest, and temperatures will plummet.  With the plummeting temperatures will come plenty of moisture, such that rain should return from the north to the northern Negev, and last into Friday, if not Shabbat.

On Thursday, forecast mean ensemble temperatures with this storm will be close to zero at 850 mb, and close to -10 C at 700 mb.  This will combine with average temperatures at 500 mb close to -25 degrees.  For snow to fall in Jerusalem, though, we need temperatures two to three degrees colder than the mean values just mentioned.  It seems unlikely that we will reach these values, even if the coldest forecasts among the set of 20 forecasts actually occurs.  Hence, while there is a chance of wet snow/rain on Thursday, it will more likely be rain mixed with ice pellets.

One might think that after our weather active November and December that January might take a few days off to bring us a bit more sun and warmth.  However, the long range forecast shows cold (Israeli winter) weather continuing the first two weeks of January with periods of precipitation within.

We'll keep you posted.

Barry Lynn

Weather It Is (Stormy Times)

Good Afternoon:

While the weather outside is pretty tranquil, there is a cool breeze and a definite chill in the air. You know things are serious when my Wife asks if it is going to snow.

Unlike me, she is a native Israel and very "in-tune" with the weather -- so long as she doesn't get confused by anything I might tell her.

There will be a series of storms in the next couple of weeks as storms move in from our northwest, before exiting to our east.  There is even a hint of potentially a more significant storm as we move into the last week of December, with cold air arriving directly from the north.  We've been seeing various members of the GEFS show temperatures below freezing at 850 mb the last week of December, which is necessary for snow to fall in the central mountains.  In fact, you can see exactly that on the enclosed graph that shows the 850 mb temperatures over the next couple of weeks.  Note that all members of the ensemble (each member is a line) indicate that the temperatures will be falling through the first half of the two week period (this coming week).  Then, about half the members remain pretty much the same, but a quarter warm up and a quarter of them get even colder with some forecasts going below freezing. (Actually, the first week of January also looks to be cold, based on the CFS (the Climate Forecast Systems Model)).

So, are you an optimist or a pessimist, and how shall we define that?  Perspective and historical background is everything.  "Some like it cold, some like it hot, and some like it in the pot, 9 days old."

In any case, it is interesting to note the perspective of Saeb Erekat, the so-called foreign minister of the "State of Palestine." Responding to Australia recognizing "West Jerusalem" as Israel's capital he said:  "“All of Jerusalem remains a final status issue for negotiations, while East Jerusalem, under international law, is an integral part of the occupied Palestinian territory"  (italics added) see: https://www.timesofisrael.com/erekat-slams-australian-recognition-of-west-jerusalem-as-israels-capital/).  What he says might be construed as a contradiction, or he simply means "what is mine is mine and what is yours is mine" (https://torah.org/learning/pirkei-avos-chapter5-13/). It's amazing how well Mr. Erekat knows Jewish religious texts, for someone who denies that Jerusalem was ever part of Jewish history or that the Jewish Temples ever existed. Or perhaps he is just a wicked man, as so aptly described in Pirkei Avot (Ethics of our Fathers).

Barry Lynn

Weather It Is (Rainy Weather Continues)

Good Evening:

It's not often that I get to bask in the accolades of my admirers -- there aren't many and they don't all live in the same place.  Still, it was nice to know that I've done a good job this year both forecasting the weather and arranging for quite a number of stormy days (we've got to sell an interesting product).

Fortunately, like a hitter on a hot streak, the rainy and wintry weather is forecast to continue through this coming week.  The next substantial rain will result from a large amplified ridge (over western Europe) combining with a deep trough over the Mediterranean.  It should arrive by Tuesday/Wednesday, and may be followed by another storm early the following week (but there is also the possibility that warmer and drier air could end our rainy streak).

It's raining while I write this blog, and it has generally been raining over a large portion of the country from about Jerusalem northward for a couple of days.  You probably heard that over 150 mm of rain fell in places closer to the coast, flooding streets and even buildings.  What was interesting about this storm was just how long it basically stayed in one location, with persistent heavy rain areas just north of areas with lighter amounts of rain (we had "just" 25 mm).

One can see below a forecast from our ensemble, which showed heavy rain falling within a 3 hour period Thursday night from Ashdod north to Netanya.  The forecast correctly depicted the sharp north to south gradient of the area of heavy rain, and it did so throughout the storm.

This is reassuring, and points out the usefulness of ensemble (multi-forecasts) that can correctly predict small scale, but very important differences in rainfall.

Have a good week, and Happy Chanukah.

Barry Lynn

Weather It Is (Special Weather Statement)

Good afternoon:

A strong and very moist storm will bring extremely heavy rains to central Israel, with heavy (but lighter rains both over northern and southern areas).

Forecasts show greater than 100 mm of rain over central Israel, including Jerusalem, from Thursday morning into Friday, which will most likely cause flooding of streets and streams.

Barry Lynn