The climate in Israel is characterized by hot and sunny summers, and by a long period of sunshine, with clear skies from May to September. The rains (where they occur) are concentrated from November to March.
Along the west coast (see Tel Aviv, Haifa, Netanya), the climate is Mediterranean, with very mild and rainy winters, and hot and sunny summers, during which the air is humid but tempered the breeze. In Tel Aviv, the average temperature in January is 14 °C (57 °F), while in July and August it's about 26 °C (79 °F). Heat waves can occur especially in the period from April to June, when the wind from the Egyptian desert can raise the temperature to around 40 °C (104 °F) even on the coast.
Here are the average temperatures in Tel Aviv.
Average temperatures - Tel Aviv

Tel Aviv	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
Tel Aviv	J	F	M	A	M	J	J	A	S	O	N	D
Min (°C)	10	10	12	14	17	20	23	23	22	19	15	12
Max (°C)	18	18	20	23	25	27	29	30	29	27	24	20
Min (°F)	50	50	54	57	63	68	73	73	72	66	59	54
Max (°F)	64	64	68	73	77	81	84	86	84	81	75	68

Rainfall, concentrated in the winter months, amounts to around 580 millimetres (23 inches) per annum, and from December to February it is quite abundant. Here is the average precipitation.
Average precipitation - Tel Aviv

Tel Aviv	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec	Year
Tel Aviv	J	F	M	A	M	J	J	A	S	O	N	D	Y
Prec. (mm)	145	110	60	15	4	0	0	0	1	35	80	125	585
Prec.(in)	5.7	4.3	2.4	0.6	0.2	0	0	0	0	1.4	3.1	4.9	23
Days	13	11	8	2	1	0	0	0	0	4	7	10	56

The sun in Tel Aviv often shines even in winter, except for the periods of bad weather, while in the long dry season the sky is normally clear.
Sunshine - Tel Aviv

Tel Aviv	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
Tel Aviv	J	F	M	A	M	J	J	A	S	O	N	D
Sun (hours)	6	7	8	9	11	12	12	12	10	9	8	6

On the Mediterranean coast, the sea is warm enough for swimming from June to November.
Sea temperature - Tel Aviv

Tel Aviv	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
Tel Aviv	J	F	M	A	M	J	J	A	S	O	N	D
Sea (°C)	18	17	17	18	21	24	26	28	27	26	23	20
Sea (°F)	64	63	63	64	70	75	79	82	81	79	73	68

In the interior (see Jerusalem), the climate becomes more arid, but also more continental, due both to the greater distance from the sea and the elevation: Jerusalem is located at 700 metres (2,300 feet) above sea level, Bethlehem, in the West Bank, at almost 800 metres (2,600 feet), while Nazareth is located at a lower altitude, around 300/500 metres (1,000/1,600 feet). In these inland areas, winter is still fairly mild, but intrusion of cold air masses from Russia can bring even snow in January and February (and sometimes also in early March), usually above 600 metres (2,000 feet). During summer, the air in this area is dry and the heat is usually tolerable, but the sun hits hard, moreover, hot air masses from the Egyptian desert can sometimes bring some days with scorching heat even here. In Jerusalem, the average temperature in January is 9 °C (48 °F), while in August it's 24.5 °C (76 °F). Here are the average temperatures in Jerusalem.
Average temperatures - Jerusalem

Jerusalem	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
Jerusalem	J	F	M	A	M	J	J	A	S	O	N	D
Min (°C)	6	6	8	13	16	18	19	20	19	17	12	8
Max (°C)	12	13	15	22	25	28	29	29	28	25	19	14
Min (°F)	43	43	46	55	61	64	66	68	66	63	54	46
Max (°F)	54	55	59	72	77	82	84	84	82	77	66	57

Annual precipitation is around 550 mm (21.5 in), concentrated in the cold half of the year, while from May to mid-October it almost never rains. Here is the average precipitation.
Average precipitation - Jerusalem

Jerusalem	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec	Year
Jerusalem	J	F	M	A	M	J	J	A	S	O	N	D	Y
Prec. (mm)	135	120	95	25	3	0	0	0	0	15	60	105	555
Prec.(in)	5.3	4.7	3.7	1	0.1	0	0	0	0	0.6	2.4	4.1	21.9
Days	12	12	9	4	1	0	0	0	0	3	7	11	59

In Jerusalem too, the amount of sunshine is good in winter, while it's excellent from May to September.
Sunshine - Jerusalem

Jerusalem	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
Jerusalem	J	F	M	A	M	J	J	A	S	O	N	D
Sun (hours)	6	7	7	9	11	13	12	12	10	9	8	6

Further to the east, in the Jordan valley, where the altitude goes even below sea level (from Lake Tiberias to the Dead Sea), winter is mild, but summer becomes definitely hot. Here are the average temperatures in Tiberias, on the shores of the lake of the same name (or Sea of Galilee).
Average temperatures - Tiberias

Tiberias	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
Tiberias	J	F	M	A	M	J	J	A	S	O	N	D
Min (°C)	10	10	12	15	19	22	25	25	23	21	16	12
Max (°C)	18	19	23	28	33	36	38	38	36	32	26	20
Min (°F)	50	50	54	59	66	72	77	77	73	70	61	54
Max (°F)	64	66	73	82	91	97	100	100	97	90	79	68

In Tiberias, an average of 435 millimetres (17 inches) of rain fall each year, concentrated as usual in the winter months.
Average precipitation - Tiberias

Tiberias	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec	Year
Tiberias	J	F	M	A	M	J	J	A	S	O	N	D	Y
Prec. (mm)	105	90	55	20	5	0	0	0	1	15	50	95	437
Prec.(in)	4.1	3.5	2.2	0.8	0.2	0	0	0	0	0.6	2	3.7	17.2
Days	12	10	8	3	1	0	0	0	0	3	6	10	53

Continuing south and heading towards the Dead Sea, precipitation becomes scarcer, and the landscape, apart from the areas where the river's waters are used to irrigate fields, becomes semi-desert.
Further to the south, in the areas bordering the Sinai Peninsula and the Red Sea, we find the Negev Desert, which has mild winters and hot summers. Unlike the Mediterranean coast, summer is not the best time for a beach holiday at the Red Sea: in Eilat, the average maximum temperature in July and August is 40 °C (104 °F), but sometimes it can exceed 45 °C (113 °F). In return, in April and October, the maximum temperature is around 31/33 °C (88/92 °F), and sunshine is still guaranteed.
Average temperatures - Eilat

Eilat	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
Eilat	J	F	M	A	M	J	J	A	S	O	N	D
Min (°C)	10	12	15	18	22	25	27	27	25	22	16	12
Max (°C)	21	23	26	31	36	39	40	40	37	33	28	23
Min (°F)	50	54	59	64	72	77	81	81	77	72	61	54
Max (°F)	70	73	79	88	97	102	104	104	99	91	82	73

In Eilat, the rainfall is very poor, since it doesn't even reach 50 millimetres (2 inches) per year.
Average precipitation - Eilat

Eilat	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec	Year
Eilat	J	F	M	A	M	J	J	A	S	O	N	D	Y
Prec. (mm)	4	3	3	2	1	0	0	0	0	4	2	5	22
Prec.(in)	0.2	0.1	0.1	0.1	0	0	0	0	0	0.2	0.1	0.2	0.9
Days	2	2	1	1	1	0	0	0	0	1	1	2	9

In Eilat the sun shines regularly throughout the year, but occasionally some cloud banks can pass, even in summer.
Sunshine - Eilat

Eilat	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
Eilat	J	F	M	A	M	J	J	A	S	O	N	D
Sun (hours)	7	8	8	9	10	11	11	11	10	9	8	7

At Eilat, the Red Sea is a bit cool for swimming in winter, while it is pleasantly warm in the summer months.
Sea temperature - Eilat

Eilat	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
Eilat	J	F	M	A	M	J	J	A	S	O	N	D
Sea (°C)	22	21	21	23	25	26	28	28	28	27	25	23
Sea (°F)	72	70	70	73	77	79	82	82	82	81	77	73

The best times to visit Israel are spring and autumn, and in particular the months of April, May and October. Easter is therefore usually a good time to visit the sites of historical and religious interest in the country.
For a beach holiday, on the Mediterranean coast the warm and sunny season is long and runs from mid-May to mid-October, although as we have seen in May the sea is still a bit cool.
The Red Sea is warmer, but as mentioned in summer the heat is too intense for sunbathing, especially from June to September, while in winter, from December to February, pleasant days alternate with others which can be bit cold: so here the best periods for a beach holiday are the month of April, and from mid-October to mid-November.


In winter: in Jerusalem and inland hills: warm clothes, jacket, hat, raincoat or umbrella, scarf for the wind, hiking shoes; in the Jordan Valley and Eilat: spring/autumn clothes, shirt for the day, jacket and sweater, umbrella for the area north of the Dead Sea. In Tel Aviv and the Mediterranean coast: spring/autumn clothes, sweater and jacket, raincoat or umbrella.

In summer: in Jerusalem and inland hills: light clothes, sun hat, sweatshirt for the evening, scarf for the wind-borne sand and dust, hiking shoes. In the Jordan valley and Eilat: lightweight clothing of natural fibres, desert turban; in Tel Aviv and the Mediterranean coast, light clothing, a light sweatshirt for the evening.
For the reef, snorkeling equipment, water shoes or rubber soled shoes.