Sunday, March 27, 2016

Weather It Is (Winter Holds On, But...)

Good Afternoon:

Thursday night's late update suggested that heavy rain would fall in the center of the country, as well as south.  Yet, later updates trended the position of the low and heavy rain further south, until the forecast model correctly predicted that the rain system would mostly affect the south (as well as a good part of Jordan).

The Thursday night forecast for Shabbat's heavy rain was a forecast made 36 to 48 hours in advance.  We had mentioned that storms approaching from the south (with a tropical moisture source) are the most difficult to predict -- one reason being that there are fewer radiosondes (and other data sources) over Africa.

Still, there always seems to be a limit of useful predictability for our little country and I would say that beyond 30 hours is it (at least in terms of predicting the area of heaviest rain or snowfall).  There is not much we can do about this, except to possibly run more forecast ensemble members, but the cost of producing these forecasts is proportional to the number of forecasts made.

Even so, we predicted correctly that our temperatures today are more similar to those of winter and that such cold temperatures should persist until Wednesday.  With the cold temperatures will come a chance of rain at night and Monday morning, with the highest chances in the north. Forecast amounts are  likely to be between 10 and 25 mm, with rain possible as far south as Beer-Sheva.  The area of Jerusalem may also see > 10 mm over the storm's lifetime, but the probability is lower than in the north.

Another wave of low pressure should occur on Wednesday, but then temperatures should begin to climb, and they may climb all the way into the second week of April.

Spring may have finally sprung, with the exception of Yom HaAtmahut, which always seem to be rainy and/or chilly, no matter when it comes on the Calendar.

Barry Lynn

Friday, March 25, 2016

Weather It Is (Correction! Tropical Rain)

Good Morning:

The tropical rain is expected to begin tonight and become heavy at times throughout the south and eastern sections, including the Dead Sea Area (and possibly the Jordan Valley).

Expect heavy flooding of rivers, streams. and creeks.

Showers of rain are expected Sunday and rain is possible on Monday.

Purim Samaech and Shabbat Shalom,

Barry Lynn

Thursday, March 24, 2016

Weather It Is (A Tropical Rain)

Good Evening:

Purim (in most of the land) turned out to be a fine day weather wise, although there were some clouds  from time to time.

There will also be some dust ahead of our next system, which should arrive Saturday night.

The Motzei Shabbat storm should bring plenty of tropical moisture coupled with cooling temperatures aloft.  The combination should create both a steady, light rain, but occasional thunderstorms as well  At the moment, there looks to be enough rain to cause flooding in the Arava, as well as the Dead Sea Area.

Cold air should continue to pour southward on Monday, and Tuesday may bring a more winter like storm, with even some ice pellets thrown in for good measure.

The cold weather will last into Wednesday, and the temperatures should moderate a bit as we head towards the end of the week.


Barry Lynn

Tuesday, March 22, 2016

Weather It Is (Some Nice Weather, Some Rain)

Good Afternoon:

The weather pattern is full of changes.  The next couple of days will be quite warm, with Thursday the warmest of the two.  Friday will turn a tad cooler, but Shabbat will warm up ahead of an approaching front.

A few days ago, we mentioned a 60% chance that the atmosphere would develop a pronounced longwave pattern, with a strong storm developing over the eastern Mediterranean.  However, it now looks like a series of weak storms will affect us next week, instead.

This means that rain chances will grow, but that heavy rain is not likely.

It's almost April, and it is unusual to have a heavy, prolonged rain at this time of the year.

Yet, the weather can turn chilly, and it will do this on Sunday and Monday of next week.

Purim Samaech!

Barry Lynn


Saturday, March 19, 2016

Weather It Is (Some Rain, Some Nice Weather, and A Storm to End the Month)

Good Evening:

A weak storm will approach tonight and bring a period of rain in the morning, with between 5 to 10 mm from north to south (of the Dead Sea).  Scattered rain showers will persist in the afternoon and evening.

The weather will stay cool on Monday, but Tuesday will see a significant warm up that should last through Purim Day.

After Purim Day, the weather will change significantly.  It may be Shushan Purim, or it may be the day after, or even Sunday, but much colder weather will arrive, and so should the rain.

There is an interesting weather pattern forecast. After the low pressure tomorrow, a weak ridge will build ahead of another system moving across the Mediterranean.  Southerly winds ahead of the low will bring unseasonably warm weather, and as the low approaches it will drag a cool front through our area.

That might normally be the end of it. The low would move through and we would have some light showers.

However, an intense storm will move into the eastern Atlantic and move north of England.  A southeast to northeast ridge should then shoot up into the Baltic Sea.  On the southeastern side of this ridge, cold, Siberian air should flow southwestward and spin up a major winter storm over our area. Hence, there is a 60% chance of heavy rain next week, with unusually cold temperatures.

Purim Samaech,

Barry Lynn

Friday, March 18, 2016

Weather It Is (Winter Hangs On, but Purim turns nice)

Good Afternoon:

The weather has warmed up a bit, and it will warm up some more tomorrow.

But then a cool front will once again bring a chill to the air, as well as another period of light rain on Sunday.

The cool weather will last into Tuesday, and then the weather should turn nice for Purim (nice and possibly quite warm). 

While it is true that the warm weather will make us think that spring has sprung, more winter like weather should return the following week.  It may actually turn downright chilly as a ridge of high pressure splits Europe between an intense low pressure area off the coast of England and a deep trough in the eastern Mediterranean.

Shabbat Shalom,

Barry Lynn

Wednesday, March 16, 2016

Weather It Is (Soggy Weather)

Good Morning:

Today and tonight's weather will bring periods of rain to the center area, including the coastal areas, the central mountains, and down to Beer-Sheva.  Total rain amounts are expected to exceed 10 mm over the period. Showers may persist on Thursday.

In the north, heavier rain is expected with areas around the Kinneret receiving between 10 and 25 mm, with localized heavier amounts, especially over the mountains.

We're in quite an active weather pattern.  It will stay on the chilly side until Friday, before a quick warm up on Shabbat (relatively speaking), followed by cooler weather and a chance of showers early next week.

Beyond this period, the global ensemble shows that our active weather pattern should continue, with the possibility of a more significant rain towards the end of the month, as well as a return to chilly weather.

It's rather late in the season for chilly weather.  However, a strong and persistent ridge in western Europe is helping to build a trough of colder weather to its east.  At the same time, there is a fairly active southern Jet stream.  As storms move eastward under the ridge, they are able to draw on unseasonably cold air in the trough, adding a bit more than usual for this time of year (cold air related) energy (there is a good baroclinic zone), bringing us first a brief warming and dust, followed by strong winds, chilly temperatures, and periods of rain.

Barry Lynn

Sunday, March 13, 2016

Weather It Is (The Weather "Cabal.")

Good Morning:

Highlights: Wind, Dust, Chill, and Occasional Rain.

I received an interesting e-mail question.  "I'm sure you've explained this before, but when you talk about some GFS ensemble members that are showing the possibility of X or Y, does that mean an actual person/organization that is putting out an actual forecast, or is it simply one of several hypothetical possibilities that X or Y could happen?

"I mean, who is this 'member'? 

"(And are they sitting in some place putting out forecasts that are consistently wrong?  If so, wouldn't they get fired by now?)"

It is true that different government and private organizations do put out forecasts, and one could consolidate these forecasts into a group, and then discuss which "member" of the group says one thing or another. We might refer to these forecasts as the "Elders of Weathzion" (not to be confused with the "Elders of Zion" which is a construct of the ignorant and antisemites).

However, this is not the way we do things around here (although, I do listen in on other forecasts for comparison purposes, and an occasional tidbit of information). 

Rather, we're speaking here about a single forecast model (the Global Forecast Model (GFS) or our own Weather Research and Forecasting Model (WRF))  that is "tweaked" to produce multiple forecasts for the next two weeks (or 36 hours in case of the WRF).  How do they tweak it?  Keep in mind that we never exactly know the weather at any time.  For instance, my weather station, which is located in the Dekel area of Efrat, might measure a different temperature (wind, etc) than someone else's in the Rimon neighborhood.  Even more so, my observations themselves have a margin of error.

So, the folks who run NCEP (The National Center for Environmental Prediction) in their wisdom systematically perturb their measurements and then see what impact this has on the forecast.  As time goes on (several days), the impact can be quite substantial (and even over a single day if the weather is "mesoscale" (small) rather than "synoptic" (large)  scale).  However, when all members of the ensemble predict nearly the same weather, even several days down the road, it means that the "signal" (or (significant or strong) wave development) is such to imply that the initial condition "error" is less  important than whatever weather system is on its way. Such was the case before the large winter snow storm of December 2013. Hence, we have greater confidence in the forecast when many or even all members of the ensemble agree that an event will happen.

So, perhaps some of the error that our writer mentions is a result of initial condition uncertainty, and not a systematic error in the forecasts.

Speaking of which, we've been speaking about rain and cold weather this week for quite a while. After a warm day today, we indeed expect much cooler (chilly) temperatures and a chance of rain.  However, the chance for significant rain event is quite small.

Still, the water vapor loop shows a moisture stream from off eastern Atlantic, off the African coast.

http://tropic.ssec.wisc.edu/real-time/europe/movies/m7wvbbm/m7wvbbmjava.html

In fact, the first batch of heavier rain showers will likely occur late tonight and tomorrow morning (extending southward to Beer-Sheva).  Moisture from the Atlantic stream will combine with mositure from the Mediterranean to produce these showers.  The cold air will follow, and produce a second batch that will be mostly confined to the north central areas, and will occur on Tuesday.  Intermittent shower will occur in the cold air until the end of the week.

The main highlight here is the wind and chill, with strong or even gale force winds on Monday and Tuesday. Ahead of the today's storm, there will be dust overspreading the country. Heavier dust concentrations in the south will also make for difficult breathing for sensitive people.

We should start to warm up on Shabbat, but there is a 25% chance of significant rain late next week, with showers and colder temperatures again likely -- just in time for Purim.

Shavua Tov,

Barry Lynn

Thursday, March 10, 2016

Weather It Is (Warm then Cold)

Good Afternoon:

We're in for some changes in the weather.

Temperatures should warm substantially into Sunday as warm air is drawn northward ahead of an approaching low pressure area.   As the low pressure air moves in from the west, it will draw some tropical moisture northward, leading to the possibility of some tropical showers (laced with dust).

From Sunday night onwards, the weather will turn increasingly chilly, if not cold, and stay this way into the following week.  Showers are possible, and then rain is likely from mid-week onwards.

In our last blog, we spoke about a possible strong coupling between the northern and southern branches, possibly leading to an extended chill, with temperatures near freezing. 

The latest GFS forecast has the ridge a bit further east, and more closed off, which will likely bottle up some of that cold air to our north.  Even so, enough cold air should drain southward to spin up a strong area of low pressure, with a significant fetch across the Medterranean sea.  This means plenty of moisture for an extended period of rain and showers.

The GFS ensemble still shows a few members with even colder air than predicted with the deterministic GFS   model..  However, the chance of a late winter snow is probably close to zero.

Shabbat Shalom,

Barry Lynn

Wednesday, March 9, 2016

Weather It Is (A Roller Coaster)

Good Afternoon:

As noted, the weather has a spring, if not summer feeling to it.

I've noticed the plants greening up in Gush Etzion in anticipation of continued warm weather.

The first indication that someone forgot to tell "Mother Nature" will be tonight, when a cool front will drop temperatures by 5 to 10 C from today's highs. 

Temperatures will then rebound into Sunday night -- but then the bottom will drop out and temperatures (and the weather) will head downwards towards more winter like temperatures.

If one takes a look here: http://www.meteociel.fr/modeles/gfse_cartes.php?&ech=234&mode=0&carte=1

one notes a mass of very cold air situated to our north. It appears as if the coldest weather in the northern hemisphere has congregated in our longitude sector.

Moreover, at least some of the GFS ensemble members bring in more than unseasonably cold air 8 or 9 days out:

http://www.meteociel.fr/modeles/gefs_cartes.php?code=6&ech=192&mode=0&carte=1

Getting back to practical weather: we're looking for at least a whole week's worth of unusually chilly weather. While there is 10% chance of snow, the most likely outcome will be periods of rain from Sunday onwards, with the greatest likelihood of more significant rain from the 15th to the 19th of the month (of March).

In the meantime, hot and cold, and there will be dust from south to north that will  reduce air quality. One would be excused if one felt like he was stuck on a rollercoaster with just too many drops.

Barry Lynn

Monday, March 7, 2016

Weather It Is (The Calm)

Good Afternoon:

The weather is certainly nice. In fact, it is a mild 19 C with 33 percent humidity, and 10 km/h winds.

The weather will certainly stay nice through Wednesday, slide down a bit on Thursday, poke up about Shabbat, and then slide down again next week. The warm, springlike weather is a result of a weak ridge of high pressure over our area ahead of a developing low pressure system over western Europe.

The latest forecast from the Global Forecast Systems model (GFS) shows a strong ridge eventually building up into western Europe, with its center moving just north of England.  The combined northerly growing ridge and the low pressure will help to build an eastern Mediterranean very elongated, north to south trough.

One might say coincidentally, but one should be careful when using this word -- that the development of the trough will facilitate the flow of cold air southward.   Yet, he severity of the cold air streaming southward is something more reminiscent of January or February, but rarely of March.

The GFS shows a rather large and menacing storm impacting our area about 10 days out.

Yet, the GFS ensemble suggests far less certainty in the forecast.

Even so -- as promised in the last blog -- we have a very high probability of sliding back into a wet and cold pattern mid-month and the week afterwards, while one might peg the probability of a late March snow at about 15%.

Of course, if the GFS were THE model (of record), this might be an open and shut case -- or the calm before the storm.

Barry Lynn

Friday, March 4, 2016

Weather It Is (10 Days)

Good Afternoon:

The window opens, the window closes.  It seems like a never ending battle between those who think spring has sprung, and those who think who think not.

Those who think yes will surely be in the ascendance during the next 10 days (even with Sunday's chill).  They will breeze through the week on warm southerly breezes, basking in the beautiful March sunshine.

However, like a wave crashing on shore, a ridge will shoot up over western Europe, which will help drive a trough down over the eastern Mediterranean.  In a rare confluence of signals, we can see out 10 days into the future, and watch this wave of cold winter air cast spring dreams away.  There is an 85% chance of winter's return, and a similar chance of significant rain.

The ensemble suggests that the near zero degree temperatures should persist for several days.  In fact, one doesn't see a return to warm weather before the end of the 16 day period shown in the forecasts.

As for storm intensity, there is still a lot of variation shown at 500 mb.  As for snow, most likely on the Hermon.

Until then, those who say spring has sprung will have won.

Barry Lynn

Thursday, March 3, 2016

Weather It Is (Rain Chances: moisture streams)

Good Late Night:

A cold front will pass through this morning.

In the meantime, moisture from the Atlantic will affect us, leading to the possibility (of about 60%) chance of rain from Jerusalem southward to Beer-Sheva, and in localised areas in the north.

http://tropic.ssec.wisc.edu/real-time/europe/movies/m7wvbbm/m7wvbbmjava.html

Barry

Tuesday, March 1, 2016

Weather It Is (Some Big Changes)

Good Afternoon:

The weather's been pretty nice (and warm as well).  Tomorrow, though, will bring even warmer temperatures and dust ahead of a weak low pressure system.

At the moment, the passage of this weather system will bring a return to chillier temperatures, which will last through Shabbat, and into Sunday.  Light rain is shown off-shore and along the coast Thursday, with a chance of light showers inland later on Thursday.

On Sunday, there is a 20% chance of more showers.

Looking further ahead: next week seems like it will bring a return to warm before a possible return to chiller weather mid-month.

Barry Lynn