Tuesday, January 31, 2017

Weather It Is (Rain, Possible Snow Showers, and Extreme Cold)

Good Evening:

As the first wave of upper air instability passes over of this evening, showers will continue to develop over the warm seas and move periodically inland over the coastal plain and mountains.  Rain will also head south tonight towards Beer-Sheva and Mitpe Ramon.

Tonight, temperatures will fall rapidly passing their inflection point around midnight, and continuing to fall into tomorrow evening.  Temperatures near freezing by morning and strong winds imply wind chill values below freezing in many hilly locations. By evening, the winds will die down and Thursday morning will probably be the coldest morning of the year throughout the country.

In fact, temperatures at 850 mb will fall to -3 or below by late tomorrow afternoon, meaning that temperatures may rise little if none at all tomorrow.

As the cold air arrives tonight, light snow may develop in the lingering moisture behind the cold front in the central mountain area. However, our models don't show very much precipitation.  Nevertheless, standing water on the roads will probably freeze at the higher elevations.

The GEFS and GFS both show another upper air disturbance approaching tomorrow evening. However, dry winds from the north suggest that it will pass by without any significant precipitation. But, because of the cold at the surface and aloft, we can't rule out some instability rain (inland) snow (mountain areas) showers.

The next week will turn a bit milder, but nothing that says spring is on the way.

For reference, we're noting another possible winter storm arriving late next week.

Barry Lynn

Monday, January 30, 2017

Weather It Is (Some Precipitation Than Extreme Cold)

Good Afternoon:

There comes a time in a persons life when he must admit that he (or she) has truly arrived at a milestone.  The milestone I am speaking about is the freezing mark, when water transforms to ice.  For those of you who are not aware, ice has a lower density than liquid water.  I do not know of any other liquid (some special elements may) that has this characteristic, and this special characteristic makes possible life in the seas and lakes, and most likely on land itself (since some claim that my great, great... grandfather was a fish).

Anyway, the forecast shows a significant change in our weather.  Unfortunately for snow lovers, the trajectory of the storm will be a bit too far north and east to tap into the Mediterranean moisture for any real length of time.  Still, there may be some rain changing to snow showers late Tuesday night and Wednesday (especially as there will be some low level moisture lingering behind the system).

There is a slight chance (about 15%) that a secondary trough will arrive Wednesday night and bring some heavier snow showers.

The intensely cold weather will last into Friday morning, with temperatures most likely below freezing on Wednesday in many higher elevations. Thursday night's low temperatures will probably burst the "Coltrim" on the solar panels unless the circulation to them is closed off until after the ice within melts the next morning.  

Thereafter, winter will seem just a distant memory.

Barry Lynn

Saturday, January 28, 2017

Weather It Is (Cold Advisory)

Good Evening:

Donald Trump can win the presidential election and it can snow when temperatures are warmer than -25 Celsius at 500 mb.  Last night there were periods of snow in Gush Etzion and snow showers in Jerusalem.  In Efrat, we had a late night inch of snow, while in Jerusalem a mix of graupel and snow in the middle of the night left a dusting.  The key was that it was quite cold at 700 mb (around -12 C), and at 850 mb (-2 C).  Temperatures dropped closed to zero in Gust Etzion during the snowfall.

Tonight the rain will come to an end, but very cold air is moving in at 850 mb.  This could cause freezing of some road surface late at night and early morning, making for dangerous driving conditions -- so care must be taken!

The weather will warm a bit ahead of our next system, which should arrive Monday night.  This may bring some showers, strong winds, and snow on the Hermon, with temperatures in the lower single digits. This will be followed by even colder air from Wednesday into Friday.

It appears to be a stormy time and a stormy week, but the global ensemble forecast does not show a lot of precipitation, so the total amounts of rain (or snow) will not (as of yet) be very large.

Barry Lynn

Friday, January 27, 2017

Weather It Is (Stormy Weather, Severe Winds, and Possible Snow)

Good Morning:

The wind will gust gale force or higher as the day nears its end.  The day will also be marked by periods of rain.

Below zero temperatures at 850 mb will arrive this evening, and precipitation should intensify as it does.  Our latest one kilometer high resolution run shows some light snow accumulation in Gush Etzion and the mountains north of Jerusalem, with moderate snow amounts in the area of Safed, and heavy snow on the Golan.

Yesterday, we ran our forecast using the coldest member of the ensemble, which produced a very light coating of snow in the Jerusalem area (including temperatures near freezing).  Today, we used the GFS forecast, which is about a 1/2 degree warmer than the GEFS mean.  So, there is still room for a light accumulation of snow in Jerusalem.

The cold weather will last into Sunday, which will be followed by a quick warm-up.

The latest GEFS shows a majority of 850 mb temperatures falling quite a bit below zero from the first of February to the 5th of February (or from about Wednesday to Sunday of next week and after).  Several members also show upper air temperatures falling to critical "snow-levels" as well.

We've heard the words "snow possible" so many times this year that we should be forgiven for showing a bit of skepticism.  Well, there are judges in Jerusalem, and they may just rule that this time it will snow (the possible becomes probable, and then actual).

Shabbat Shalom,

Barry Lynn

Thursday, January 26, 2017

Weather It Is (Winter Weather Warning/Snow/Cold Advisory)

Good Evening:

The storm is upon us and it will be fierce.

The winds will gust to 90 km an hour along the coast and 80 km in the central and northern mountains.  In the Golan, there will be gusts above 100 km/h.  The high winds are expected tonight into late Friday night.

The largest amounts of rain will fall in the far north (> 100 mm) and in the area of the central mountains (50 to 75 mm, or even higher in localized areas).

Temperatures will fall to about freezing Friday night and Shabbat, when a coating of snow will be possible in the central mountains, especially after candle-lightning.  Much more snow should fall in the Galilee peaks and Golan.

The cold will intensify Motzei Shabbat, and the roads may ice over, and remain icy into Sunday morning.

While Monday will see a warm up, the rest of the week should be chilly (and maybe even cold), and there is the possibility of another storm Tuesday or Wednesday.

Barry Lynn

Wednesday, January 25, 2017

Weather It Is (Winter Weather Warning/Winter Storm Watch)

Good Evening:

There is a winter weather warning for Thursday night into Saturday morning.  Heavy rain, cold, and gale force winds (with higher gusts).

There is a Winter Storm Watch for Friday evening into Saturday afternoon for the northern peaks of the Galilee and central Mountains, including Jerusalem.

As noted, the main upper (500 mb) support for this storm will arrive Thursday night into Friday, with the coldest air at 700 and 850 mb arriving Friday evening and Shabbat (Saturday). The global ensemble (GEFS) still shows a possible reinforcing shot of cold air at 500 mb late Friday into Saturday.

The cold air in the lowest levels will remain into Sunday, so any snow or ice that accumulates will be slow to melt.

Because of the unusual situation concerning upper air versus middle/lower atmospheric temperatures, it would be misleading to even try to estimate possible snow amounts.  Instead, we'll rely heavily on our high resolution forecast data to give us more information as we approach Friday.

Tuesday of next week may bring another storm, with another round of frozen precipitation possible.

Barry Lynn

Weather It Is (Cold, Rainy, Windy, With A Touch Of Uncertainty)

Good Late Night:

The latest forecast continues to show stormy and very cold weather ahead.

Right now, we have high confidence that it will be near or below freezing in the higher elevations of the central mountains and northern Galilee peaks (and of course on the Hermon, where it will be quite a bit below).

We still see a range of temperatures at 700 mb, but the mean is below -10 C Friday night/Shabbat, which is cold enough for snow.

We also see a prolonged period of precipitation from late Thursday into Sunday morning.  However, we also see that the coldest temperatures at 500 mb will occur Thursday night into Friday morning.  Yet, we still see the potential for colder upper air temperatures on Shabbat, which would make it more likely for snow to accumulate on Shabbat into Sunday morning.

Lastly, we're pretty sure that it will be quite windy Thursday night into Friday.

All in all, there is still more than a touch of uncertainty whether this coming storm will bring an accumulating snow or not.

Adding the to the uncertainty is possibly another upper air, very cold system to arrive at the start of next month.

Next update is planned, God willing, for Wednesday evening.

Barry Lynn

Tuesday, January 24, 2017

Weather It Is (Rain, Wind, and Possible Snow)

Good Morning:

Today will see the last of the warm winter days, and Wednesday will see a chance of tropical showers across the south.   Then, temperatures will fall steadily into Shabbat. Temperatures at 850 mb will pass through freezing sometime Friday night and this will set the stage for possible mixed precipitation or wet snow in the central mountains and on the northern peaks of the Galilee.

Like yesterday, we see the coldest temperatures aloft (500 mb) on Thursday night into Friday morning, while coldest temperatures at 700 mb  -- middle atmosphere (and at 850 mb  -- lower atmosphere) should occur Friday night into Sunday night (Sunday morning).

This forecast is quite tricky because there is still a lot of variability in the range of possible temperatures, especially at 700 and 500 mb.  The latest (00 GMT) global ensemble forecast continues to hint at secondary upper trough development Friday night into Shabbat.  The Euro suggests that the main upper level support will pass through at this time.  To create good mixing and good snow formation, the atmosphere should be below -25 C at 500 mb (preferably closer to -30 C).  Right now, several forecasts indicate 500 mb around or below -25 C, but the majority do not.

In summary: a soaking rain with thunderstorms, hail and graupel likely Thursday night into Friday with gale force winds lasting into Friday night. Periods of precipitation into Sunday morning, with mixed precipitation or snow possible, depending on what side of "uncertainty" we end up.

Barry Lynn

Monday, January 23, 2017

Weather It Is (Uncertainty)

Good Afternoon:

There is a lot of uncertainty regarding the outcome of our next storm.

What we do know is that the warm weather will break Tuesday night and temperatures will fall rapidly into Thursday.  Rain should also develop Thursday or Friday morning.

Friday morning into about Monday morning will be unusually cold and windy with periods of precipitation.

The uncertainty is in just how much precipitation will fall, although at least moderate amounts are expected.  Within the set of global ensemble forecasts there are wetter and colder forecast "solutions," which bring with them the possibility of snow.

Arguing against a large snowfall, however, is the positioning of the upper trough a bit too far to the east.  We can see quite clearly that the upper level trough will approach Thursday night and then pass through on Friday.  There are some indications that it may restrengthen Friday into Sunday, but for now the most likely scenario is that it won't.

Still, cold air in the lower (850 mb) and middle (700 mb) atmosphere may bring enough cold to allow for a period of wet snow and/or snow showers in the central mountain areas and northern peaks of the Galilee.

That's where we stand now -- for those who love snow, they should hope for a restrengthening of the upper trough beyond Friday morning.

Barry Lynn

Sunday, January 22, 2017

Weather It Is (A Storm Cooks)

Good Morning:

Last night the Knicks missed a chance to win on a 3-point end of the game buzzer shot. In and out, and the crowd groaned.

On the hand, it was an exciting game and part of the excitement is the tee-shirt give-away where tee-shirts are shot into the crowd.  Towards the end of the game one such tee-shirt headed over my way, to bounce off the hands of a young lady to my left right into my lap.  My son, being a gentlemen, tried to give it away to his cousin (whose father took us to the game).  Fortunately, his cousin is even more of a gentlemen.

Sometimes things do just fall into your lap, and an end of the month snowstorm may be just such a phenomena.

While today will be chilly, the week will quickly warm up ahead of a deepening trough that is forecast to plunge down over the eastern Mediterranean late in the week. Unlike previous storms that missed us to the west and north, this storm is suppose to arrive directly from the northwest. The majority of the  latest global ensemble forecasts show the preferred storm trajectory will bring us some unusually cold temperatures in both the lower and middle atmosphere. Moreover, their appears to be a west to east moisture stream that should bring plenty (but not extreme) precipitation amounts into the area of the central mountains as well.

The preferred "snow-dates" are the 28th and 29th of January, and the cold may linger into February.

There is, of course, a fly in the ointment: the upper level, 500 mb support for this storm is not yet firm. In fact, it may arrive before the coldest air in the middle and lower atmosphere.  For the best snow situation, we'd like the upper level trough to align with the middle (700 mb) and lower (850 mb) cold air. This brings the greatest threat of convective/thundersnow as the 500 mb trough encourages divergence aloft and rising air.

On the other hand, I only had to grab that shirt with a slight movement of my hands, so let's hope that our next storm system falls as easily into the forecasters lap.

Barry Lynn

Friday, January 20, 2017

Weather It Is (A Storm Brewing)

Good Motzei Shabbat:

Late Friday evening Israel time the latest weather maps show a potential storm brewing for the end of the month.  In fact, the forecasts have been signaling "storm" for the last week.

The forecasts correctly predicted that the warm weather would come to an end, and that temperatures would cool off quite a bit by Sunday morning.  The chilly weather will be followed by a warm up that should end in at least some rain by the end of the week.

The ensemble suggests that the initial burst of cold air will be followed by an even more intense storm affecting us early the following week.  At the moment, the probability is about 30%, but the fact that this feature remains as a possibility a week after it was first mentioned gives us a bit more hope that winter will return to the hills of Jerusalem and the Galilee.

Barry Lynn

Thursday, January 12, 2017

Weather It Is (Nice Weather)

Good Evening:

A ridge of high pressure is building over the eastern Mediterranean.

Contrast our beautiful weather with that in England (which some here would like,
and some like the gentlemen in front of me would not), where an arctic blast/trough
has barreled through with thunder snow.

http://www.telegraph.co.uk/news/2017/01/12/severe-snow-weather-warnings-across-uk-will-reach-london/

After a rainy, chilly December, it looks like January should be pretty much "bone-dry" and relatively mild.  This is because the ridge of high pressure looks to be a somewhat persistent feature for the next week or so.

Contrast this with the near misses we had when it came to possible big snows the past few weeks. However,  the storm track was just to our north, and that was enough to leave us out of the real cold and snowy weather.

So, if you like mild, sunny, Jerusalem winter weather, you should be happy for the next couple of weeks (with the exception of Sunday when it might shower).

As for February: nothing yet to report (but its 28 days should be enough to give us another chance or two for winter).

Barry Lynn

Sunday, January 8, 2017

Weather It Is (Winter Cold, Stormy Weather)

Good Afternoon:

A very strong storm is approaching from the northwest and it will bring the coldest weather of the year.  In fact, tomorrow morning should be the coldest weather of the year so far.

However, the storm will swing around back to the north, thus limiting the precipitation to the coastal and northern areas, where 25 to 50 mm should fall just to the north of Tel-Aviv and perhaps > 50 mm along the northern coast.  Snow in the Hermon will continue to add to their snowy winter totals.

The storm will bring strong, if not gale-force winds into Monday, and dust will be prevalent -- especially in southern areas.

I noted in the NWS forecast for New York City yesterday that their winter storm took an unexpected jog to the northwest, blanketing most of southeastern NY with half a foot of snow (and especially Long Island and southeastern Connecticut with even heavier snow). The forecast models picked up on this the Friday afternoon before the snow on Saturday (Shabbat).

Might a "jog" to the southeast happen here.  It could, but it isn't likely.  If it does, though, it would bring wet snow to the higher elevations of the central mountains.

Looking further ahead: we still see lots of instability in the circulation pattern: heavier rain may fall generally across the country early next week, but this mid-week could first bring another bout of cold and showers.

Barry Lynn

Friday, January 6, 2017

Weather It Is (Very Cold, Dust, Some Precipitation)

Good Afternoon:

Highlights:

i) Much Colder

ii) Snow in the north, rain along the central and northern coasts.

iii) Lots of dust arriving until the storm brings cleansing rains Sunday night.

It may not feel much like winter today, but winter doesn't care.

Temperatures will fall tonight into Monday morning as a very strong storm approaches from the Northwest.

Right now, it appears that the heaviest precipitation will be from Tel-Aviv northward into the Hermon (where heavy snow will fall) from Sunday night into Monday.

The storm will bring strong to gale force winds.

The central mountainous area may get by with light precipitation as the storm is forecast to swing out just before causing a severe impact to the central areas.  Still, there may be a period of wet snow or snow Sunday night into Monday. If the storm swings away as forecast, though, it won't accumulate or make much of an impact.

Looking at the global forecast, we don't see much variability among forecasts so the likelihood that the storm will indeed move further south is not high.

The instability in the weather pattern should persist for the next couple of weeks.

For a more in depth look at the coming storm pattern, go here:

https://www.facebook.com/JerusalemWF/posts/1802855426634883

Wednesday, January 4, 2017

Weather It Is (Winter Storm Watch Cancelled)

Good Morning:

Last week both the European and American global forecast models suggested that a storm would arrive from the west, and then receive a reinforcing blast of cold air from the north.

A couple of days ago, the GEFS (American model) suggested that the storm arriving from the west would only give us a glancing blow, while the European model held on for a more snowy situation.

Now, both models forecast that the storm will miss us (to the north), bringing us only light rain along with chilly winter temperatures from the beginning to the middle of next week.

Temperatures will rise to mild winter levels from today to Friday, but will fall through Shabbat to quite chilly levels by Sunday morning, and remain there until Wednesday.

The GEFS is still showing the possibility of a period of snow within this period, but it might also just be light rain.

Until the forecasts from the ensemble converge, there isn't much more to add -- except that winds could be quite strong through the period, even gale force.

Barry Lynn

Monday, January 2, 2017

Weather It Is (Winter Storm Watch)

Good Evening:

Ynet is reporting that December was one of the coldest and wettest in many years.

http://www.ynetnews.com/articles/0,7340,L-4901825,00.html

This is good news.

We've been writing for the last few weeks about the waviness in the atmospheric circulation, and how changes to the very large scale from November to December provide an extra reason to "expect" snow this year.

The problem with expecting snow is that snowstorm happen in Israel once or twice a year even when global circulation patterns or not on average favorable, and sometimes not at all.  Folks report that the winter of 1991/92 actually brought an unusually high number of snow storms, but this was followed by a period of time in which the general knowledge was that it rarely snowed in Jerusalem.

Yet, anyone born since 2011 would have a different opinion, and remember snow in more years than less, and even snow twice a year in some.

Theoretically, if the global ensemble shows a snow storm 30% of the time (where time here is the period of one week), it should snow at least one of those times during a month.  Up to now, I have been wondering if the ensemble is a bit progressive (over-predicting the possibility of extreme cold/snow).  We've seen the possibility of snow appear on the week plus forecast and then disappear as the future blends into the present.

However, the storm on the horizon (for early next week) may just restore our faith in the GEFS (if not your weather forecaster). Perhaps, even more encouraging is the agreement between the EURO and GFS deterministic models, and their ensemble for a negatively tilted trough to move in (early next week).  When troughs are oriented NW to SE, it means that the circulation around the trough will encourage divergence aloft and the spin up of a surface low pressure (bringing strong vertical motion and plenty of moisture).

In the meantime, we'll continue to have chilly weather and light rain from time to time through Wednesday. before a bit of a warm up before the next storm.

Stay tuned.

Barry Lynn