Esther
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Esther clear sky chart from 2005-11-06 to 2024-09-29.

This page is a summary of past forecasts. Even though it's based only on forecasts, some people use these pages as clue to a site's climate. But climate data based on actual observation should be preferred (if you can find it!).

Cloud, Transparency and Seeing forecasts are summarized individually. But because good observing conditions require a combination of minimum cloud cover, transparency and seeing, the individual forecast summaries can be difficult to interpret. The observing conditions section counts the combinations of conditions needed for common types of astronomical observation.

Observing Conditions

The following tables count the occurrence of the combinations of forecast and darkness conditions needed for different observations. Conditions are rated by by what percentage of the hours the observation would likely be attempted are usable.

Observation Type	Minimum conditions for hour to be usable				Out of hours
	Clear of Clouds	Transparency	Seeing	Sky Brightness
Planetary:	50%	(no limit)	Average	(no limit)	Nighttime Hours
Deep Sky:	70%	Average	(no limit)	5.9	Nighttime Hours
CCD Imaging:	70%	Below Average	Poor	(no limit)	Nighttime Hours

Percentages are of nighttime hours per month, or per year, when a particular observing conditions was met. Deep Sky percentages never exceed 50% because the moon is up half the time. Deep sky percentages are much lower for charts at high latitudes because of fewer dark hours in the summer.

Overall

By Month

Individual Forecasts

The length of each colored bar in the "occurrence of each Forecast" column is proportional to the number of times the chart forecast that color. The percentages are of the total number of hours per month, or per year, with a particular forecast. The colors as the same as those used in clear sky charts.

Note: Transparency probabilities are only counted for those hours that have 30% or less cloud cover. Seeing probabilities are only counted for those hours that have 80% or less cloud cover. If that's too tricky, try Observing Conditions instead.

Overall

		Occurrence of each Forecast	Data Points
Cloud Cover	Day	9% 8% 3 8% 5% 5% 5% 4 6% 8% 38%	101569
	Night	7% 8% 3 9% 6% 6% 5% 5% 7% 8% 37%	96746
Transparency	Day	42% 7% 16% 24% 10% 1	101310
	Night	43% 7% 15% 23% 10% 1	96651
Seeing	Day	12% 8% 27% 30% 17% 5%	15494
	Night	11% 7% 30% 36% 15% 2	24569

By Month

Percentage Cloud Cover NW (2006-)
Color Meanings: Overcast 90% covered 80% covered 70% covered 60% covered 50% covered 40% covered 30% covered 20% covered 10% covered Clear
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	6% 12% 5% 12% 7% 6% 5% 4 6% 7% 30%	2219
	11th to 20th	Day	3 9% 4 12% 8% 6% 6% 10% 7% 9% 25%	2199
	21st to end	Day	4 12% 4 10% 6% 6% 5% 5% 6% 7% 35%	2516
February	1st to 10th	Day	8% 14% 5% 12% 7% 6% 5% 4 6% 6% 26%	1653
	11th to 20th	Day	7% 13% 4 11% 6% 6% 6% 4 7% 7% 27%	1665
	21st to end	Day	6% 11% 4 11% 8% 7% 7% 5% 6% 8% 25%	1413
March	1st to 10th	Day	5% 11% 5% 10% 8% 7% 7% 5% 6% 8% 29%	3232
	11th to 20th	Day	4 11% 5% 9% 5% 4 4 3 6% 11% 38%	3489
	21st to end	Day	7% 12% 5% 15% 6% 5% 4 4 5% 7% 29%	3825
April	1st to 10th	Day	8% 10% 4 9% 7% 6% 6% 4 6% 7% 33%	2334
	11th to 20th	Day	9% 13% 4 10% 5% 4 6% 4 7% 6% 31%	2440
	21st to end	Day	13% 11% 4 7% 4 6% 4 4 7% 8% 32%	2498
May	1st to 10th	Day	17% 12% 4 9% 5% 5% 5% 4 5% 5% 29%	4430
	11th to 20th	Day	10% 8% 3 9% 7% 6% 7% 5% 7% 8% 31%	4591
	21st to end	Day	13% 8% 3 8% 5% 5% 6% 5% 7% 9% 30%	5161
June	1st to 10th	Day	16% 7% 3 7% 5% 5% 5% 4 7% 9% 34%	2850
	11th to 20th	Day	18% 9% 3 7% 6% 6% 5% 4 7% 7% 29%	2850
	21st to end	Day	9% 5% 2 6% 5% 5% 6% 5% 8% 9% 40%	2850
July	1st to 10th	Day	6% 4 2 6% 4 5% 6% 5% 7% 10% 45%	4740
	11th to 20th	Day	7% 4 2 6% 4 4 5% 4 7% 9% 48%	4740
	21st to end	Day	4 3 1 3 3 4 4 4 6% 9% 59%	5138
August	1st to 10th	Day	8% 6% 3 5% 4 4 5% 4 6% 7% 47%	4463
	11th to 20th	Day	6% 4 1 5% 4 4 4 5% 6% 10% 50%	4028
	21st to end	Day	8% 4 2 4 4 4 4 4 7% 9% 51%	4521
September	1st to 10th	Day	10% 6% 2 6% 4 4 4 4 4 7% 48%	2336
	11th to 20th	Day	15% 7% 3 6% 4 4 4 3 4 6% 44%	2176
	21st to end	Day	10% 5% 2 6% 3 3 3 3 6% 7% 52%	2051
October	1st to 10th	Day	11% 10% 3 6% 4 2 5% 2 5% 7% 45%	1800
	11th to 20th	Day	8% 7% 4 9% 5% 4 4 4 4 7% 44%	1800
	21st to end	Day	7% 11% 3 9% 6% 5% 6% 4 7% 8% 35%	1697
November	1st to 10th	Day	11% 15% 3 9% 7% 7% 5% 4 6% 7% 26%	1488
	11th to 20th	Day	5% 11% 4 13% 6% 6% 5% 4 6% 7% 32%	1520
	21st to end	Day	6% 11% 5% 12% 6% 5% 5% 4 7% 8% 30%	1402
December	1st to 10th	Day	7% 11% 5% 13% 8% 7% 7% 5% 6% 6% 25%	1330
	11th to 20th	Day	4 11% 4 13% 8% 7% 6% 5% 6% 8% 28%	1682
	21st to end	Day	4 9% 4 8% 5% 4 5% 3 6% 7% 45%	2442
January	1st to 10th	Night	3 9% 5% 12% 8% 8% 7% 6% 8% 8% 26%	4726
	11th to 20th	Night	3 7% 4 13% 9% 8% 9% 8% 7% 7% 26%	4699
	21st to end	Night	5% 10% 4 9% 7% 5% 6% 5% 7% 7% 35%	5168
February	1st to 10th	Night	6% 11% 5% 12% 8% 6% 6% 5% 6% 7% 28%	2527
	11th to 20th	Night	5% 10% 4 10% 7% 7% 7% 6% 7% 7% 28%	2402
	21st to end	Night	4 10% 3 9% 8% 6% 7% 6% 8% 8% 30%	2041
March	1st to 10th	Night	5% 10% 4 13% 9% 8% 6% 4 7% 8% 28%	3638
	11th to 20th	Night	4 7% 4 8% 5% 5% 6% 6% 7% 10% 38%	3490
	21st to end	Night	6% 11% 5% 16% 7% 7% 6% 4 6% 6% 25%	3828
April	1st to 10th	Night	9% 10% 2 8% 5% 6% 5% 5% 6% 8% 36%	1843
	11th to 20th	Night	8% 12% 4 10% 7% 4 6% 5% 6% 7% 31%	1691
	21st to end	Night	11% 9% 3 8% 6% 5% 6% 4 6% 9% 35%	1681
May	1st to 10th	Night	22% 11% 4 7% 4 4 4 3 5% 6% 29%	2540
	11th to 20th	Night	8% 7% 2 7% 5% 6% 6% 5% 8% 10% 35%	2304
	21st to end	Night	12% 7% 3 9% 5% 6% 6% 5% 7% 8% 33%	2414
June	1st to 10th	Night	13% 9% 3 7% 5% 5% 6% 5% 7% 7% 33%	1330
	11th to 20th	Night	16% 7% 3 6% 3 4 6% 5% 7% 8% 34%	1330
	21st to end	Night	9% 4 2 5% 4 4 6% 5% 8% 9% 44%	1330
July	1st to 10th	Night	5% 4 2 6% 5% 6% 5% 6% 7% 8% 46%	2220
	11th to 20th	Night	5% 3 2 4 3 3 5% 5% 7% 11% 52%	2220
	21st to end	Night	2 2 1 4 4 3 3 3 7% 9% 62%	2414
August	1st to 10th	Night	8% 5% 2 6% 4 4 5% 4 7% 7% 48%	2454
	11th to 20th	Night	6% 4 2 6% 4 4 5% 4 6% 10% 50%	2811
	21st to end	Night	10% 4 1 5% 3 3 4 4 6% 10% 49%	3146
September	1st to 10th	Night	9% 4 2 6% 4 4 5% 3 5% 7% 51%	1843
	11th to 20th	Night	12% 7% 2 6% 5% 4 3 3 5% 7% 48%	2000
	21st to end	Night	6% 6% 2 5% 4 4 5% 4 7% 8% 48%	2097
October	1st to 10th	Night	10% 9% 3 7% 4 3 4 4 6% 8% 43%	2160
	11th to 20th	Night	7% 7% 3 8% 5% 5% 4 4 5% 6% 45%	2160
	21st to end	Night	7% 10% 3 10% 5% 6% 6% 4 6% 8% 35%	2638
November	1st to 10th	Night	11% 14% 4 9% 7% 5% 3 3 6% 7% 31%	2590
	11th to 20th	Night	5% 9% 3 12% 7% 7% 5% 5% 5% 8% 34%	2660
	21st to end	Night	4 13% 5% 11% 7% 6% 5% 4 6% 8% 30%	2777
December	1st to 10th	Night	7% 12% 4 11% 9% 8% 6% 4 6% 8% 26%	2850
	11th to 20th	Night	5% 11% 5% 12% 8% 6% 6% 4 6% 9% 27%	3510
	21st to end	Night	4 7% 3 7% 6% 5% 5% 4 5% 7% 48%	5214

Transparency (when cloud cover <= 30%)
Color Meanings: Too cloudy to forecast Poor Below Average Average Above average Transparent
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	53% 7% 14% 18% 8% 1	2219
	11th to 20th	Day	49% 8% 15% 16% 11% 1	2220
	21st to end	Day	45% 8% 22% 21% 4	2516
February	1st to 10th	Day	56% 6% 11% 19% 7% 1	1653
	11th to 20th	Day	53% 7% 13% 16% 11% 1	1674
	21st to end	Day	54% 7% 13% 16% 9%	1413
March	1st to 10th	Day	52% 7% 17% 17% 7%	3232
	11th to 20th	Day	42% 7% 21% 20% 9%	3490
	21st to end	Day	53% 7% 15% 19% 5%	3825
April	1st to 10th	Day	48% 7% 15% 21% 9% 1	2334
	11th to 20th	Day	49% 6% 13% 23% 8% 1	2440
	21st to end	Day	47% 8% 13% 22% 8% 1	2498
May	1st to 10th	Day	55% 8% 12% 20% 5%	4430
	11th to 20th	Day	45% 9% 12% 23% 11%	4595
	21st to end	Day	46% 10% 16% 21% 8%	5162
June	1st to 10th	Day	44% 7% 16% 23% 10% 1	2850
	11th to 20th	Day	51% 8% 13% 20% 8% 1	2850
	21st to end	Day	37% 10% 21% 22% 9% 1	2850
July	1st to 10th	Day	31% 9% 20% 26% 14% 1	4666
	11th to 20th	Day	31% 7% 16% 32% 13% 1	4659
	21st to end	Day	21% 5% 15% 33% 21% 4	4976
August	1st to 10th	Day	34% 7% 16% 33% 9% 1	4445
	11th to 20th	Day	28% 7% 20% 36% 9% 1	4067
	21st to end	Day	28% 6% 19% 35% 12%	4520
September	1st to 10th	Day	35% 6% 15% 25% 13% 7%	2336
	11th to 20th	Day	42% 5% 14% 29% 8% 2	2176
	21st to end	Day	31% 6% 16% 33% 12% 3	2051
October	1st to 10th	Day	39% 5% 18% 28% 10%	1800
	11th to 20th	Day	39% 7% 17% 26% 11%	1800
	21st to end	Day	45% 8% 16% 22% 9%	1697
November	1st to 10th	Day	56% 7% 13% 16% 7% 1	1488
	11th to 20th	Day	50% 8% 16% 20% 6%	1520
	21st to end	Day	50% 8% 17% 20% 5%	1402
December	1st to 10th	Day	57% 7% 13% 15% 7% 1	1330
	11th to 20th	Day	53% 7% 17% 18% 5%	1684
	21st to end	Day	38% 6% 11% 26% 17% 2	2442
January	1st to 10th	Night	50% 9% 17% 19% 4 1	4726
	11th to 20th	Night	53% 6% 14% 15% 11% 1	4740
	21st to end	Night	45% 8% 16% 25% 5%	5168
February	1st to 10th	Night	52% 6% 13% 18% 10%	2527
	11th to 20th	Night	51% 8% 14% 17% 10%	2403
	21st to end	Night	46% 8% 13% 23% 9% 1	2041
March	1st to 10th	Night	51% 7% 16% 18% 7%	3638
	11th to 20th	Night	37% 9% 22% 24% 7% 1	3490
	21st to end	Night	56% 8% 13% 16% 6% 1	3828
April	1st to 10th	Night	43% 7% 14% 22% 13% 1	1843
	11th to 20th	Night	50% 6% 11% 20% 11% 1	1691
	21st to end	Night	45% 7% 10% 22% 13% 1	1681
May	1st to 10th	Night	54% 7% 9% 22% 8%	2540
	11th to 20th	Night	36% 10% 14% 26% 12% 1	2304
	21st to end	Night	44% 10% 15% 21% 8% 1	2414
June	1st to 10th	Night	46% 10% 14% 20% 9% 1	1330
	11th to 20th	Night	44% 8% 15% 21% 12% 1	1330
	21st to end	Night	31% 10% 21% 27% 10% 1	1330
July	1st to 10th	Night	31% 8% 20% 24% 16% 1	2185
	11th to 20th	Night	24% 7% 19% 34% 15% 1	2178
	21st to end	Night	18% 5% 16% 36% 22% 3	2337
August	1st to 10th	Night	33% 6% 18% 33% 9% 1	2447
	11th to 20th	Night	29% 6% 17% 39% 8% 1	2838
	21st to end	Night	30% 6% 16% 33% 14% 1	3146
September	1st to 10th	Night	31% 7% 16% 23% 16% 8%	1843
	11th to 20th	Night	37% 6% 13% 28% 14% 2	2000
	21st to end	Night	31% 6% 16% 27% 17% 2	2097
October	1st to 10th	Night	39% 6% 15% 26% 12% 1	2160
	11th to 20th	Night	37% 7% 14% 29% 12%	2160
	21st to end	Night	45% 8% 15% 24% 7% 1	2638
November	1st to 10th	Night	53% 6% 13% 19% 9% 1	2590
	11th to 20th	Night	48% 8% 18% 19% 7%	2660
	21st to end	Night	49% 8% 18% 18% 7%	2777
December	1st to 10th	Night	55% 6% 12% 17% 8% 1	2850
	11th to 20th	Night	52% 8% 20% 14% 6%	3507
	21st to end	Night	35% 6% 15% 22% 19% 3	5214

Seeing (when cloud cover <= 80%)
Color Meanings: Too cloudy to forecast Bad 1/5 Poor 2/5 Average 3/5 Good 4/5 Excellent 5/5
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	10% 7% 27% 32% 18% 6%	180
	11th to 20th	Day	9% 7% 29% 31% 22% 2	180
	21st to end	Day	10% 9% 34% 32% 10% 5%	198
February	1st to 10th	Day	15% 11% 35% 26% 12% 1	243
	11th to 20th	Day	10% 5% 33% 35% 12% 4	270
	21st to end	Day	7% 8% 31% 31% 19% 4	225
March	1st to 10th	Day	9% 12% 36% 30% 11% 2	407
	11th to 20th	Day	10% 11% 35% 27% 11% 5%	460
	21st to end	Day	13% 10% 30% 33% 12% 3	506
April	1st to 10th	Day	11% 13% 37% 25% 12% 2	460
	11th to 20th	Day	13% 12% 34% 28% 11% 2	452
	21st to end	Day	15% 12% 27% 30% 14% 2	488
May	1st to 10th	Day	15% 9% 23% 32% 16% 6%	653
	11th to 20th	Day	11% 5% 25% 33% 19% 6%	675
	21st to end	Day	17% 7% 21% 26% 20% 8%	734
June	1st to 10th	Day	15% 10% 23% 31% 17% 4	680
	11th to 20th	Day	20% 10% 29% 24% 14% 3	680
	21st to end	Day	10% 6% 23% 29% 24% 7%	680
July	1st to 10th	Day	9% 3 19% 38% 23% 7%	671
	11th to 20th	Day	11% 5% 24% 30% 22% 8%	668
	21st to end	Day	5% 6% 22% 31% 27% 10%	739
August	1st to 10th	Day	10% 6% 18% 35% 22% 9%	635
	11th to 20th	Day	9% 6% 19% 32% 25% 8%	477
	21st to end	Day	7% 7% 24% 30% 25% 7%	539
September	1st to 10th	Day	13% 10% 26% 29% 18% 5%	490
	11th to 20th	Day	17% 7% 25% 29% 19% 3	490
	21st to end	Day	14% 10% 33% 25% 14% 4	465
October	1st to 10th	Day	19% 5% 26% 31% 14% 6%	270
	11th to 20th	Day	9% 11% 33% 29% 15% 3	270
	21st to end	Day	10% 9% 39% 27% 13% 1	297
November	1st to 10th	Day	20% 8% 30% 27% 13% 1	270
	11th to 20th	Day	11% 9% 41% 26% 12% 1	270
	21st to end	Day	6% 12% 36% 29% 12% 6%	214
December	1st to 10th	Day	9% 8% 35% 33% 12% 3	180
	11th to 20th	Day	9% 14% 35% 31% 11%	180
	21st to end	Day	13% 7% 27% 33% 17% 5%	198
January	1st to 10th	Night	7% 10% 33% 36% 13% 1	950
	11th to 20th	Night	9% 8% 37% 34% 10% 2	950
	21st to end	Night	10% 12% 35% 31% 11% 1	1012
February	1st to 10th	Night	11% 9% 24% 37% 16% 2	760
	11th to 20th	Night	10% 6% 34% 36% 11% 2	744
	21st to end	Night	7% 4 24% 37% 23% 4	628
March	1st to 10th	Night	9% 6% 32% 38% 12% 2	760
	11th to 20th	Night	10% 7% 34% 36% 12% 2	760
	21st to end	Night	13% 6% 29% 33% 16% 3	836
April	1st to 10th	Night	10% 9% 36% 32% 12% 2	575
	11th to 20th	Night	13% 8% 34% 34% 11% 1	563
	21st to end	Night	16% 7% 24% 39% 14% 1	570
May	1st to 10th	Night	15% 8% 22% 37% 17% 1	570
	11th to 20th	Night	8% 7% 23% 40% 21% 1	440
	21st to end	Night	17% 5% 19% 34% 23% 3	411
June	1st to 10th	Night	16% 7% 27% 33% 15% 2	380
	11th to 20th	Night	18% 6% 25% 32% 17% 1	380
	21st to end	Night	10% 4 21% 39% 23% 2	380
July	1st to 10th	Night	9% 5% 19% 46% 21%	370
	11th to 20th	Night	9% 3 24% 40% 23% 1	368
	21st to end	Night	5% 4 23% 42% 23% 4	416
August	1st to 10th	Night	6% 3 20% 41% 25% 5%	481
	11th to 20th	Night	12% 4 19% 41% 22% 2	564
	21st to end	Night	7% 4 26% 38% 22% 1	627
September	1st to 10th	Night	11% 5% 23% 41% 18% 2	570
	11th to 20th	Night	15% 4 25% 37% 18% 1	670
	21st to end	Night	9% 4 35% 36% 14% 2	756
October	1st to 10th	Night	14% 5% 31% 33% 17% 1	720
	11th to 20th	Night	10% 5% 32% 38% 13% 2	720
	21st to end	Night	12% 9% 35% 33% 11% 1	868
November	1st to 10th	Night	17% 8% 33% 33% 8% 1	925
	11th to 20th	Night	10% 8% 35% 33% 11% 3	950
	21st to end	Night	9% 8% 38% 34% 9% 2	950
December	1st to 10th	Night	12% 7% 32% 33% 13% 3	950
	11th to 20th	Night	10% 9% 36% 33% 11% 1	950
	21st to end	Night	10% 5% 35% 33% 15% 3	1045

Page generated at 2024-09-26 07:52:21. Version ac07

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