Thursday, December 31, 2015

Weather It Is (Dangerous Storm Arrives)

Good Evening:

The storm is upon us and very heavy rain in on our door step.

In the next several hours there is a high probability of more than 10 mm per 3 hours in a broad area from the coastal plain to the central (and northern mountains).  There will be locally heavier rain, and thunder and lightning.

Total rain amounts will be between 50 to 100 mm in the lowlands, central mountains, and mountains of the north, with 25 to 50 mm in the immediate vicinity of the Kinneret.

Winds will become dangerously strong  (gale force) tonight in the heavy rain, and strong winds with higher gusts will persist tomorrow.

As temperatures cool tonight, and strong storms develop, expect rain mixed with ice pellets.  A coating of snow is possible in the higher elevations tomorrow afternoon, especially in Gush Etzion, Sefad, and other high elevations, with more significant snow amounts in the Golan.

Shabbat is shaping up as a big question mark.  An reinforcing push of cold air will arrive at upper levels.  It may arrive before the colder air at lower levels erodes away -- and hence there is another chance of snow, with rain elsewhere.

With all this cold air coming in, I would be tempted to predict more snow than the models suggest. But the models are predicting that temperatures will be above freezing except in the very highest elevations.  Model forecasts can be wrong, but it would be a surprise if snow accumulates in the central areas more than predicted.

Heavy dust in the south.

Barry Lynn

Weather It Is (Dangerous Winter Storm)

Good Afternoon:

A dangerous winter storm is upon us.

Here are the highlights.

Wind: Strong winds today - gale winds or possibly storm force winds Thursday night into Friday evening.

Rain: Heavy rain beginning from mid-evening (along the coast) to mid-night (Jerusalem).  Over about two days, 50 to 100 mm of rain will fall in the coastal plain eastward to the Jerusalem area and southward to Beer-Sheva. Rain rates tonight could be 10 to 25 mm per three hours, with locally higher amounts.

Visibility: The rain tonight will be especially strong and blowing rain in strong winds will make for very poor visibility.

Snow: Tonight in the Golan.  Snow tomorrow in Safed (several centimetres).  Snow and graupel will mix with the rain in the area of Gush Etzion tonight and become more likely Friday afternoon and evening.  Rain and ice pellets (graupel) in the Jerusalem area tonight and rain/snow becoming mostly wet snow late afternoon and evening.  There may be a light accumulation in Jerusalem on colder surfaces and a few centimeters of snow in Gush Etzion Friday afternoon and evening.


Dust: Dust storm in the south.

General Synopsis:

A strong winter storm will approach our area today, and last into Sunday morning. While temperatures are cold enough at 850 mb and 700 mb for snow late Thursday night (and especially Friday afternoon/evening), 500 mb temperatures are only marginal for strong convective storms during this period.  Moreover, while temperatures are below freezing at 850 mb, they are not as cold as in last February's storm (where they were about 1.5 degrees colder at 850/700 mb and temperatures at 500 mb were 7 degrees Celsius colder.   Hence, surface temperatures will most likely remain above freezing except at the highest elevations.

A reinforcing shot of cold air will arrive at upper levels Shabbat Afternoon/evening.  This will be a few degrees colder than in the first part of our storm, and will have to be watched closely.

Otherwise, we've entered a significantly wetter pattern.

Barry Lynn

Wednesday, December 30, 2015

Weather It Is (Winter Weather)

Good Afternoon:

I am bit worn out from following this storm.  Here are the highlights.

Through Saturday 2:00 A.M

Rain Amounts:  25 -- 50 mm across the hills east of the coastal plain; 10 to 25 mm in the coastal cities themselves.   Central Mountain: general 25 -- 50 mm, with > 50 mm in the area from Jerusalem south along the mountain spine.  Light rain in the Arava, but between 10 to 25 mm in the area of Beer-Sheva. Northern Mountains and Golan: 50 to 100 mm, with > 100 mm on the Golan.

Snow Amounts: 10 to 25 cm on the Golan and far northern mountains;  50 -- 100 cm on Har Hermon.

Winds:  Thursday > 50 km/h, and Friday > 60 km/h, with higher gusts.

Regarding the possibility of snow in Jerusalem. The first chance will be with the onset of the heaviest precipitation after midnight, Thursday night.  Temperatures at 850 mb will be falling below 0 and below minus 10 Celsius at 700 mb.  They will be close to minus 25 Celsius at 500 mb.  The next chance will be in the late afternoon and evening as temperatures at 850 mb and 700 mb drop to close to minus 3 C and minus 13 Celsius at 700 mb.

However, because the 500 mb temperatures will not be exceptionally cold, the precipitation will be mostly stratiform or orographic-convective, meaning that precipitation rates will not be overly high (except, perhaps, Thursday night when the cold air makes its entrance).  This means that snow amounts will not accumulate very quickly, and are more likely in areas higher than Jerusalem (like Gush Etzion). In fact, a first look at high resolution forecast surface temperatures in Jerusalem suggests that snow will not accumulate in Jerusalem, until possibly Erev Shabbat.

Lastly, we don't usually see a storm that is so cold at the 850 mb and 700 mb, but not at 500 mb.  Perhaps we're seeing the result of a lack of winter elsewhere, where the cold air has built up at the poles and is now able to head far south without strong upper level support (and an even stronger and prolonged ridge over Europe).

Looking further ahead: Motzei Shabbat appears to bring another 500 mb cold trough, but temperatures will start warming at middle and lower levels, so rain is more likely than wet snow (or with a possible mix).  The chances for snow are higher in the north.

There is still plenty of cold air to our north, and this will help to create a stormy weather pattern for the following week, if not more.

Barry Lynn
P.S. A more exact snowfall forecast will be made on Thursday, when our highest resolution forecast will extend until mid-day Friday.




Tuesday, December 29, 2015

Weather It Is (Getting Closer)

Good Afternoon:

Those of us who are optimists might be hoping that the probability of snow will increase to near 100% by Thursday night/Friday.  However, there are probably those (also optimists) hoping the opposite.

What we see is that a ridge of high pressure will ride up into northern Europe; conversely, a sharp trough will develop on its eastern flank, and this means that the gates of winter will open as far south as the eastern Mediterranean.

Concurrently, a storm moving across the southern jet stream along the Mediterranean sea will couple link up with the source of cold air creating the necessary dynamical and isentropic lifting needed to produce a bout of rain and possibly snow.

The coldest temperatures should arrive late Friday and Friday night, when temperatures at 850 mb will fall a degree or so below freezing.  We expect the cold lower level temperatures to persist until Saturday (Shabbat afternoon).  There is a 15% chance that temperatures will return to below freezing levels very early in the week.

At 700 and 500 mb, some of the ensemble members show that temperatures are forecast to be just barely cold enough for good snow development, while a large number of ensemble members do not. This is a bit of an unusual situation. Again, there is 15% chance of strong forcing arriving early next week.

Looking at the forecast precipitation amounts, we see a lot of variability.  This means that we're still not settled on the amount of cold aloft.  Without it, there will be rain, but much less likelihood of heavy rain/accumulating snow (now, about 30%).

Strong, possibly damaging, winds are forecast from Thursday afternoon into Friday night.

Today a Red Sea Trough will pass by to our southeast, bringing some rain to the southern Arava. Tonight our cold weather system will approach and bring a broad area of rain from Netanya south to Ashkelon and east through Efrat to the Dead Sea Basin. Five to 10 mm of rain are expected.

The rain should return towards evening and through Thursday night we expect 25 to 50 mm in an area focused from Ashkelon eastward through Jerusalem/Hebron into the Dead Sea Basin.

The forecast for Friday's possible snow event remains unclear.  We'll be wise to wait until we see actual snow/rain amounts from our high resolution forecasts.

Otherwise, snow is expected in the Hermon, beginning tomorrow (Wednesday). Moreover, we look to be entering a wet pattern next week.  The very cold air is forecast to be lurking just to our north and  there is an active southern jet stream. We e still have the possibility of a cold-storm to follow this week's storm arly next.

Barry Lynn


Monday, December 28, 2015

Weather It Is (Wind/Cold/Rain/Snow?)

Good Afternoon:

We've been talking about the weather for the last week or so, hinting at what might be, and now the hint has become more than a hint.  It's 12 Celsius, 41% humidity, and the winds are gusting to 35 km/h.  It feels like winter and strangely the weather map agrees.

We've been discussing a number of global atmospheric indices that have a possible influence on our weather.  Here's another (The East Pacific Oscillation -- thank you to Jonathan Hoffman for pointing this one out).

http://www.theweathernetwork.com/news/articles/epo-what-you-need-to-know/43796

This index is forecast to go negative about the same time our next storm should arrive.  This index is associated with greater waviness in the atmospheric circulation pattern, and indeed it seems to be having an effect (perhaps with other global indices like the North Atlantic Oscillation which is suppose to return to positive in a few days as well) The interesting thing about our next storm -- or rather the forecasts concerning our next storm -- is that the latest 00 GMT Global Forecast Ensemble now shows much more variability (on the cold side) than before.  Along with the cold come several very cold ensemble members that drop down to close to -30 Celcius at 500 mb.  Combined with a 60% chance that temperatures at 850 mb will fall below freezing (and several predicting -2 to -3 C), we're getting indications that Friday and Shabbat could be snowy in the  upper elevations.

To put a number on it: the probability is now 25%, with a near 100% chance of measurable rain (although the ensembles are not indicating more than 50 mm yet, on average).

Moreover, with the cold should come very strong winds, even damaging winds.

It's actually warming a bit at 850 mb until the end of the day, but temperatures will head down thereafter until early next week.

Barry Lynn

P.S: It is necessary to consider that our weather exists within the global circulation patterns and hence these indices may be in part a reflection of our weather, rather than the cause. On the other hand, it necessary to send a block (ridge) northward into Europe  to allow cold air to dive southward and for a coupling of a southern stream storm with the northern stream Jet and strong baroclinic zone.

P.P.S: From http://www-das.uwyo.edu/~geerts/cwx/notes/chap12/nao.html:  On days when the NAO Index is high, there are strong winds, bringing mild and wet conditions over western Europe. This is usually associated with colder weather here, as the block extends further north than usual.

P.P.P.S. Jonathan created composite maps of past snowstorms of the 500 mb height and height anomalies.




Saturday, December 26, 2015

Weather Is (Quite A Yarn)

Good Evening:

It's quite easy to spin a really good yarn (story) out of model uncertainty.  One of my correspondents has described one of forecasts he saw as a stark reminder of the December 2013 snow storm.  Another has pointed out that the global models are all showing a big (winter) change next week.

Yesterday's GFS brought a prolonged period of cold and snow several days out.  However, the GFS ensemble shows about a 20% chance of a big rain event, with between a 10 or 20% chance of snow in the higher elevations, depending on which ensemble run you look at.

So, it's potentially very big, but it's also (more) potentially just ho-hum.

In the meantime, it should be mild through Monday before temperatures drop off substantially on Tuesday into Wednesday.  Rain is possible on Friday and if we go by the 00 GMT GFS snow will also arrive on Friday.  However, I wouldn't take down the snow boots because the latest 6 GMT update shows nothing. Moreover, the GFS ensemble shows heavier rain early the following week, not this week.

What does it mean? It means that the winter signal is not at well resolved by the models.

One further note: remember the forecast change in the Atlantic Oscillation? It was suppose to turn negative in early January.  Well, it keeps flipping from forecast to forecast. This means that we really don't know what the weather is going to be beyond the next few days as the atmospheric circulations that "count" are not well resolved or predicted.  It may not be satisfying, but it is suspenseful.

Barry Lynn

Tuesday, December 22, 2015

Weather It Is (Important Changes A Foot)

Good Evening:

The weather continues to be cold -- although not the "bone-chilling" cold I grew up with.  Still, it's colder than where I grew up with and that is pretty amazing for December.

It's even more interesting because the Arctic Oscillation (AO)  has been in its positive phase, meaning middle latitudes are generally warmer than on average.

Please see here for a nice summary:
 https://nsidc.org/cryosphere/arctic-meteorology/weather_climate_patterns.html

The North Atlantic Oscillation (NAO) NAO has been in its negative phase.

Please see here for a nice summary.
http://www.metoffice.gov.uk/learn-about-the-weather/north-atlantic-oscillation

My supposition is that the strong El-Nino is helping to build a trough in our region, leading to the cooler than normal weather.

The Arctic Oscillation should go negative while the North Atlantic Oscillation should go back positive for the next few weeks.

(See here: http://www.metoffice.gov.uk/learn-about-the-weather/north-atlantic-oscillation)

A positive NAO brings more storms across the Atlantic, while the negative AO tends to bring colder weather southward from the poles.  The two together may help us build a ridge over central Europe and a trough in the eastern Mediterranean.  It also presents the possibility for storms in the southern Jet Stream to couple with the northern Jet Stream, which we need for the real-cold and wet to arrive here.

The result should be colder weather as we approach the new year. Hence, there is a 50% chance of rain and a 20% of our first snow.

In the meantime,  Thursday will see a 20% chance of a weak storm transversing our area and then several days of slightly warmer weather before the cool down as we approach next  year.

Barry Lynn

Sunday, December 20, 2015

Weather It Is (Summary)

Good Evening:

Not much going on, and for a while there won't be much going on.

We see that the 25th of December may bring a small weather disturbance, but the probability is just 25%.

The end of the month is showing the potential for change. The rather zonal flow may amplify with a large ridge building into northern Europe.  This will help to direct colder air far south.

At the moment, though, we don't see any storm in the southern Jet Stream to couple with this developing system -- or more accurately: the probability is about 15%.

We're still a lot cooler than the folks in the eastern US.  They have southerly winds rotating around a ridge to their east, while we have generally northerly winds around a ridge/trough couplet that stretches west to east across the Mediterranean.

We'll have to wait and see how the chances for a significant storm develop over the next several days. However, an Accu-Weather meteorologist has noted that the CFS is indicating that the second week of January may bring a more significant change in the global circulation pattern, which would be more like we had last winter than up to now.

Barry Lynn

Wednesday, December 16, 2015

Weather It Is (Small Scale)

Good Morning:

The temperatures in Israel remain on the chilly side, and are actually colder than those in many cities of the eastern US.   In that part of the world, a ridge of warm temperatures maintains a more southwesterly flow of warm air that had led to almost "balmy" temperatures.  Flowers are blooming and dogs are shedding out of season -- not to mention other animals that don't know whether to burrow  away or continue feasting on the usual availability of nuts, etc.

Here, we're under the influence of a weak trough of low pressure.  This means that, periodically, areas of low pressure moving through the southern Jet Stream bring localised rain.  Occasionally, these weak storms tap some of the winter time cold over eastern Europe.   Actually, the next localised rain event is expected on Thursday and will be focused on the area between Ashkelon and Tel-Aviv, where around 10 mm of rain is expected. Lighter rain is expected to eventually reach the area of the center mountains.

Last year, there was a strong ridge of high pressure over western Europe.  The result was a periodic phasing of the northern and southern Jet Streams, and strong, unusually cold (and even snowy) storms.
This year, there is a very strong northern Jet that traverses a large area from the eastern Atlantic ocean all the way across Europe into Siberia.  This means that the really cold air remains "trapped" far to our north.  If not for the fact that the area of warmth (desert low) usually located over Saudia Arabia is shifted far to our east, we too would be more on the balmy side of temperatures.  So, ironically, in a season of missed opportunities and unprecedented warmth, we're in the midst of a persistently cold winter.

Still, there is a 15 chance that the end of the year will end on the very rainy side.

Barry Lynn

Thursday, December 10, 2015

Weather It Is (Winter Rains Arriving)

Good Afternoon:

A strong low pressure system will arrive on Shabbat and last into Monday.  Rain associated with this system will overspread the western coastal areas sometime Saturday morning and arrive in the mid to late afternoon in the central mountains and eastern Valleys.

This looks to be a fairly widespread rain event, and it will be cold enough for accumulating snow on the Hermon.

There will be some very strong convective cells just off-shore, so there is the potential that the coastal cities will get brushed with heavy rain (we'll try to look into this more on Erev Shabbat).

Rain Motzei Shabbat/Saturday night (> 10 mm/3-hr) will bring the potential for flooding in the eastern Valleys, as well as areas of the Arava and possibly even down to Eilat.

The weather has been cool in the mornings (about 5 Celsius here in Efrat) and we don't see a warm up in sight.  In fact, the end of next week or early next week may see a more significant winter storm, both in terms of cold and rain amounts.  One global ensemble member is also indicating very strong winds.

We'll see how that goes, but first this "weekend's" rains.

Chanukah Samaech,

Barry Lynn


Tuesday, December 8, 2015

Weather It Is (A Winter Rain)

Good Evening:

It certainly is a "Winter Rain" in a "Deep and Dark December."

A strong area of low pressure will make its approach on Wednesday.

While the heavy rain associated with this system will hold off until Friday night, the cold associated with it will not. Temperatures will be falling off into the low single digits at 850 mb, and to about -7 C at 700 mb.  Combined with a strong upper level trough, snow should fall on the Hermon and accumulate.

Elsewhere, expect some hail/graupel at times but no accumulation of snow outside of the Hermon.

The rain should last in Sunday and the cold will last into mid-next week.

When we look beyond mid-next week, we see some uncertainty. Most likely there will be a continued chill, but there are equal (20% chances) it will warm up a bit.

Barry Lynn

Saturday, December 5, 2015

Weather It Is (Close to Freezing or Below)

Good Evening:

Unusually cold weather for early December.

Tonight will see temperatures in Gush Etzion and other high elevations in the north reach the freezing mark.  Moreover, the winds will remain light to moderate, leading to wind chills below freezing.

Fog will also be possible tomorrow evening as well. Otherwise, it will be dry.

Looking forward: the mid-week will see a small warm up, but then temperatures will trend downwards until early next week.

The following week looks to continue to be dry, but the end of the week could turn sharply colder.  At least one or two of our ensemble members are indicating a heavy precipitation event.

Happy Chanukah.

Barry Lynn

Thursday, December 3, 2015

Weather It Is (Cold Weather Makes an Appearance)

Good Afternoon:

There is a 30% chance that temperatures will fall below freezing at the higher elevations on Shabbat/Motzei Shabbat.

However, there is only a very small chance of the cold air at 850 mb being in sync with colder air aloft, so we're not expecting anything dramatic, as we'll be on the western side of the trough.

Moreover, temperatures will be on an upward climb soon after until mid next week, when a cold front will arrive and drop us back to more seasonable cold.

The end of next week into the following week shows the potential for a heavier rain storm with unseasonable cold, but this is far from certain.

Barry Lynn

Tuesday, December 1, 2015

Weather It Is (A Dramatic Entrance)

Good Afternoon:

Today's rain is a fond reminder of the rains I remember growing up (in the eastern US).  We've had about 10 mm of rain (here in Efrat) since last night.  Last year, we also had a number of small rain events before January brought its unusual cold.

A weak storm will approach on Wednesday and then the bottom will fall out on the temperature scale.

We already mentioned that this El-Nino year is bringing instability to the global forecast pattern (as seen in some members of the global ensemble).  What do we mean by this? It means that the surface energy flux (associated with the warm Pacific waters) is creating strong convection that is feeding upscale into the global circulation pattern.  Because these convective systems are hard to predict, the ensemble forecast shows a lot of dispersion (as a realistic reflection of the "unknown" influences of this convection).

Well, one of those members has "decided" to "express" itself in a big way and right now it's dragging almost 60% of the global ensemble members with it -- to possibly the coldest weather this early in the winter season in years.

The chill should begin to move in after the storm on Thursday  (a light rain event) and then bone-chilling cold should arrive Erev Shabat and continue its grip into Sunday morning.

This is a rapidly evolving system and at the moment there is a greater than 50% chance that there will be snow showers (some of them briefly heavy) at the higher elevations.  However, at 700 mb and especially at 500 mb the upper level trough still remains ill-defined, so we wouldn't expect any more than a "wipe-away" accumulation (if that).

Yet, we expect this to change as "baroclinic" (temperature) feedbacks between the developing surface/lower atmospheric become better resolved by the ensemble.  When it does, we'll be able to tell whether this will be a showery or more significant rain/snow event.

We're just a few days away -- so there isn't much time for the circulation pattern to sort itself out -- but it will. You can count on it.

The unusually cold weather should be followed by normal winter cold next week.

Barry Lynn