Weather It Is (Winter Comes Back)

 Good Evening:

Winter is returning after a short recess.

Very strong high pressure exists off the coast of Alaska, which is modifying the atmospheric circulation downstream, even as far as our area.

Due in part to uncertainty concerning the strength of the high pressure area, the global forecast models are not able to pin down what type of weather we're to expect next week.  What we do know, though, is that next few days should be rather chilly, and a period of rain is expected on Friday into Shabbat.  After a quick early week warm up, temperatures should fall off again, and an extended period of rain (or snow in the higher elevations) is likely.

Sincerely,

Barry Lynn

Weather It Is (Winter Refuses To Give Up)

 Good afternoon:

The weather pattern remains progressive and very amplified.  Hence, as we move into Shabbat and next week, rain chances will increase, but so will the unusually chilly weather for this time of year.  Rain chances should be highest during Shabbat, and then from about Thursday next week until early March.

The ensemble forecast from the European center shows greater amplification than the ensemble from the American forecasting center.  Both forecast ensembles show a chance of snow late next week and then at the end of the month (February) and early March.  These are just chances, though, and will most likely just be a cold rain.

Be well,

Barry Lynn

Weather It Is (Stormy Weather)

Good Afternoon:

Rainy and cold temperatures are on tap for us Friday and Shabbat.

Because of unusually cold temperatures aloft, there is the potential for thunderstorms, as well as hail.  

Our forecast shows ice pellets in the Jerusalem mountain area (but no snow).  Snow is expected in the Golan above about 1000 m.

Strong winds should accompany the trough (~50 km/h), and generally 25 to 50 mm of rain will fall from the center to the north.  Lighter rains in the northern Negev could lead to flooding in these areas.  Flooding is also expected in the Jordan Valley rivers and Dead Sea Basin.

Next, there is a hint of an even colder storm during the coming mid-week period.   There is a 60% chance that temperatures will be near freezing in the higher elevations, but only a 20% chance of substantial precipitation.  

Chilly, if not cold temperatures are forecast for the week beginning Sunday February 13th (the third week in February).

This prolonged period of more winter-like weather is associated with a persistent ridge of warmer air over western Europe or the far Eastern Atlantic Ocean.  This encourages storminess associated with a trough of low pressure in the eastern Mediterranean. As mentioned in a previous blog, this ridge is associated with an unusually strong and persistent sub-surface Pacific El-Nino superimposed on a La-Nina. The resulting wave pattern favors stormy weather in our area, especially since El-Nino has "supercharged" the subtropical Jet Stream that passes over the Mediterranean.  When that combines with the European polar jet, heavy rain storms occur.  When arctic (Siberian) air interacts with the subtropical (or even both jet streams)  snow occurs (as we experienced).

As to why this happens, here is one reference, and here is another.

Be well,

Barry Lynn

Weather It Is (Winter Storm Warning for Wednesday/Thursday)

 Good Afternoon:

Major Winter Storm to Affect the Country on Wednesday and Thursday.

Our high resolution forecast model shows that rain should transition to snow in the higher elevations of the central and northern mountains, including Jerusalem, Wednesday late afternoon.  Our forecast maps show that snow should accumulate through the night into Thursday morning.  Snow could be heavy at times and strong winds and snow will likely greatly reduce visibility. Many roads will probably be closed.

At the moment, we're forecasting several centimeters of snow generally in the Jerusalem area and between 10 and 20 cm in higher areas within and the mountains just to the north and to the south (Gush Etzion).

The cold weather should persist into Shabbat.

Winds will be very strong, probably greater than 60 km/h during the afternoon and nighttime hours.  These winds could cause damage, so be sure to secure loose objects.

Overall, precipitation amounts Wednesday into Thursday should range from 50 to 75 mm generally from the center of the country to the north, where amounts will approach 100 mm again. Hence, urban flooding is possible, and river and stream flooding is likely from northern Israel to areas south of Mitzpe Ramon, and in the Jordan Valley.

Earlier, there were still some important differences in the positioning of the upper level trough between forecast centers. The NCEP GEFS brings the coldest air into our area, while the ECMWF's forecast model kept the trough a bit further to the north (as it phases with a Black Sea trough).  The latest forecast from the European Center has shifted towards the colder forecasts of the GEFS. How much snow will fall will depend on where we end up in the probability distribution of atmospheric temperatures that make up these global ensemble forecasts, as there is still some variability within them. Still, overall,  they indicate a significant snow event.  Our  high resolution WRF forecast is based on the NCEP GFS, which remains steadfast in bringing a major winter (snowy) storm into our area on Wednesday.

Barry Lynn

Weather It Is (Big Week of Weather)

Shavua Tov:

This weeks looks like our biggest chance for a real snow -- on Thursday and now it turns out Shabbat.

But, first a rainy and possibly mixed rain and snow event on Tuesday, and then the big event to follow.

https://blogs.timesofisrael.com/making-decisions-sometimes-the-right-one/

Weather It Is (Snow Advisory/Extreme Cold)

Good afternoon:

Extremely cold weather is on the way for the next couple of days.  Moreover, next week should see continued unusually cold weather with a good chance of accumulating snow.

Global forecasts show temperatures will soon drop below freezing at 850 mb.  Temperatures will also be unusually cold tonight at 700 mb.  However, relatively warm 500 mb temperatures precludes cooling of the surface layer in the mountain areas through mixing and evaporative cooling, which is usually the mechanism for how temperatures reach freezing or below during snow events.  Hence, during this possible snow event,  any change over to snow will occur simply because the lower atmosphere is chilling to unusually cold levels.

Our latest high resolution WRF ensemble forecasts show that precipitation amounts should be highest over the mountain areas of Jerusalem during the late afternoon and nighttime hour.  This is due to overrunning of moist sea air over cold lower atmospheric air.  This should produce good snowflake growth.  Total amounts of precipitation at the ground are  likely exceeding 25 centimeters.  Some of this precipitation is forecast to (not melt and)  fall as snow, but how much is hard to tell.

These WRF forecasts are based on the Global Ensemble Forecast System, and these are actually running a bit warmer than the European forecast model.  Hence, our forecasts may be underplaying the potential for an accumulating snow tonight.

Based on precipitation amounts, one might expect 10 cm generally to accumulate.  However, surface cooling is the key and this depends on which of the global forecasts verifies. A degree warmer, and just mixed rain and snow.  A degree or so colder, and several centimeters of accumulation in the higher elevations in and around Jerusalem. 

The probability for precipitation is high and the probability for extreme cold is very high.  Will they come together to produce accumulating snow?  Like many things in life, no one really knows, not even your weatherman.

Be well,

Barry Lynn

Weather It Is (Winter Storm Update)

The evening forecast is very similar to the previous forecast. 

The main event will be a period of snow in the Jerusalem area followed by even more extreme cold on Thursday and Friday morning than we just experienced.

Otherwise, periods of rain in the morning into the night over other areas.  Some areas could see 30 to 40 mm during the morning hours, especially in northern areas.

At this time, it's not clear whether there will be a few centimeters or several or even 10.   It will probably depend strongly on elevation.  In any case, the roads will freeze over in the late afternoon and/or evening, so people will be headed home by then.

Have a good night.