Weather It Is (Winter Weather Advisory)

Good Morning:

After a lot of talk, and even more than that, it comes down to a degree or two -- but for snow lovers a degree or two too warm.

Temperatures at 850 mb will fall until evening, but middle and upper level temperatures will warm.

Then, when the cold air and heavy precipitation arrives towards Thursday morning with an extremely cold upper level trough, temperatures will be steady or rise a bit in the middle and lower levels.

This is response to the arrival of a really moist layer (from the sea).  It has also been pointed out that the height of the 500 mb level is higher than usual in storms that bring snow.  This means that cold air descending in convective storms has more time to diabatically warm (with increasing pressure).  Hence, any snow/ice would just become wet snow or rain tomorrow morning as the cold air moves in.

The lower levels will start to cool down in the afternoon, but the upper trough will be moving through, reducing the air parcel ascent required for precipitation formation.

Yet, there is a middle atmospheric disturbance (at 700 mb) shown to arrive in the evening with the coldest air at lower levels, and our high resolution model shows some precipitation at this time.

For this reason, we'll issue a "Winter Weather Advisory" for the possibility of some snow/ice in the afternoon and evening on Thursday.

Very cold nighttime temperatures could lead to slippery conditions on Friday morning.

There are some lower level temperature differences between the different global models, but it is hard to see how the initial burst of very heavy precipitation tomorrow morning will be anything but rain.

If you like snow, then hope that your trusted weatherman will be wrong.

Barry Lynn

Weather It Is (Winter Weather Warning/Winter Storm Watch (5))

Good Afternoon:

There was a bit of excitement in the air this morning.

The reason?  The global forecast models are suggesting that it will be wetter and colder on Wednesday and Thursday than previously forecast.

The problem, it may not be cold enough to accumulate snow.

The cold air will arrive tonight in the lower and middle atmosphere (850/700 mb levels).  Our highest resolution model indicates that this will produce a very light snowfall in the area of Gush Etzion (and northern mountains), with some wet snow/rain possible in Jerusalem.

By mid-morning and afternoon, temperatures aloft will warm a bit, so any precipitation would just fall as rain.

Thursday, a very cold upper trough (500 mb) is expected to arrive in the morning and produce a period of much heavier precipitation than we've seen up to now into the evening hours.

The high resolution model indicates that snow is more likely during this period, but no accumulation is expected in Jerusalem, but perhaps on cars, while a light accumulation is expected in Gush Etzion (heavier amounts in the Golan).

The reason: surface temperatures are currently forecast to be too warm for a major accumulation.

Since one degree either way could make a big difference, we'll have to report back tomorrow with the latest high resolution forecast data.

Barry Lynn

Weather It Is (Quick Update)

The latest weather forecast indicates a greater likelihood of snow (accumulating) Wednesday and Thursday in the mountains of Jerusalem.

This means that the Winter Storm Watch will likely be changed to a Winter Storm Warning.

I hope to update the forecast with more specifics in a couple of hours.

Barry Lynn

Weather It Is (Winter Weather Warning/Winter Storm Watch (4))

Good Afternoon:

The global ensemble forecasts have backed off a bit from a prediction for heavy snow.

Basically, the storm that will bring the coldest air is forecast to move a bit east of its previously forecast position, reducing the time it spends over the eastern Mediterranean and our area.

There will be periods of rain and thunderstorm into Tuesday night, when the rain may mix with wet snow late Tuesday night and Wednesday morning in the central mountains, and peaks of the Galilee (snow in the Golan and Hermon).

Snow is likely sometime Thursday afternoon into early Friday morning.  It looks like the arrival of the upper level "energy" (cold) will bring a burst of snow, which will probably make for dangerous driving in the area of the central mountains, and mountains of the Galilee.

Several centimeters of snow is possible, but there is still a lot of variability in the temperature and precipitation forecasts (several days in advance), so this is speculation (pending forecast information from our highest resolution model the day before).

The snow should end on Friday, regardless, but Shabbat will remain chilly.

Barry Lynn

Weather It is (Winter Weather Warning/Winter Storm Watch (3))

Good Evening:

This has been a winter more notable for what it wasn't than for what it was.

It seemed that a number of potential winter storms passed us by, leaving winter storm enthusiasts frustrated.

I am sure that most folks have noticed the inclement weather, which has been punctuated by periods of rain or showers, as well as thunderstorms.

The chilly weather and rain will continue through Tuesday, with the heaviest rain from Netanya and then eastward to Jerusalem, and then south to Beer-Sheva.

We'll then be affected by two storms, from afternoon Wednesday until sometime Friday night.

Mixed rain and snow is likely Wednesday night becoming wet snow on Thursday in the area of the central mountains, transitioning to a drier snow Thursday night and continuing into Friday evening.

Winds should be breezy, reducing visibility in snow, but at the moment are forecast to be below blizzard levels.

The temperatures at 500 mb are forecast to be quite cold (possibly below -30 C).  However, the height of the 500 pressure level is higher than in past storms.  This suggests a moist middle to upper layer arriving with the cold air.  Indeed, the global ensemble shows a 2 to 3 times increase in precipitation amounts from Wednesday afternoon until Friday evening.

Our high resolution model will probably show even more precipitation than the global ensemble than it typically does because of this moist layer (during the time of heaviest snow), as air flows over the central mountains and precipitates out.

There is still uncertainty in the extent of the cold, so stay tuned.

Barry Lynn

Weather It Is (Winter Weather Warning/Winter Storm Watch (2))

Good Morning:

Thunderstorms have arrived as a week of winter weather is upon us.

The storm actually consists of three parts.

In Part 1, there is strong upper air support (with temperatures at 500 mb below -25 C), but with lower level temperatures moist, but not particularly cool. This means we will have periods of rain/thunderstorms with heaviest amounts from just north of Tel-Aviv, south to Beer-Sheva, and eastward to the Dead Sea area. Part 1 will persist from now until Tuesday night.

Part 2 is from early Wednesday into Thursday morning. At this time, there is some uncertainty about the strength of the upper level support, but lower levels (850 mb) and middle levels (700 mb) are cold enough for a wet snow in the central mountains and other high elevation areas.

Part 3 is from Thursday afternoon into Saturday morning.  There is greater certainty that there will be significantly cold temperatures at all levels of the atmosphere, leading to a prolonged period of accumulating snow.

Barry Lynn

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

Good Evening:

We've had several Erev Shabbat where the global forecast ensembles have hinted at an upcoming  mid-week snow. We've opened our computers Motzei Shabbat and (at least for some) been disappointed.  The system either moves too far west or remains to our north.

But sometimes -- and just sometimes (we live in the Mid-East) -- things are different and this Motzei Shabbat is the exception.

Our high resolution forecast model shows a fairly steady rain from Sunday into Tuesday, while the GEFS shows periods of precipitation continuing into Friday.

Moreover, the GEFS suggests that 850 mb temperatures will fall a couple of degrees below zero late Tuesday night, while 700 mb temperatures potentially fall below -12 C.  Wintry temperatures should be with us into Shabbat.

Five hundred millibar upper level support appears that it may arrive as early as Wednesday, but is more likely on Friday into Shabbat.  By this I mean that temperatures could fall well below -25 C, which will set up conditions more favorable for a heavier snowfall late in the week.

Because temperatures at 500 mb should be -25 C or below during the initial rain event, expect instability to increase and thunderstorms (with graupel and/or hail).

We'll take each forecast as it comes, and update you accordingly.

Barry Lynn