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 2024-02-05.

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% 4 7% 6% 4 5% 5% 6% 8% 37%	77609
	Night	7% 8% 4 8% 7% 4 6% 6% 6% 8% 36%	81206
Transparency	Day	44% 7% 16% 23% 9% 1	77311
	Night	43% 7% 15% 22% 10% 1	81084
Seeing	Day	12% 8% 27% 30% 17% 5%	14471
	Night	11% 7% 30% 36% 15% 2	23869

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% 11% 9% 5% 5% 6% 6% 7% 30%	2219
	11th to 20th	Day	4 8% 4 10% 9% 5% 6% 12% 7% 9% 26%	2199
	21st to end	Day	4 12% 5% 9% 7% 4 5% 6% 6% 7% 35%	2516
February	1st to 10th	Day	8% 11% 6% 11% 8% 5% 5% 5% 6% 7% 27%	1599
	11th to 20th	Day	8% 13% 5% 9% 8% 5% 6% 6% 7% 8% 26%	1575
	21st to end	Day	7% 10% 6% 10% 8% 5% 6% 8% 7% 8% 25%	1332
March	1st to 10th	Day	7% 10% 6% 11% 11% 5% 6% 5% 6% 9% 25%	1840
	11th to 20th	Day	7% 10% 6% 9% 7% 3 5% 4 5% 9% 33%	1979
	21st to end	Day	10% 11% 5% 11% 8% 4 5% 5% 6% 8% 29%	2178
April	1st to 10th	Day	8% 9% 5% 8% 8% 5% 7% 5% 6% 7% 33%	2210
	11th to 20th	Day	10% 11% 5% 8% 7% 3 5% 6% 7% 7% 31%	2310
	21st to end	Day	14% 10% 4 6% 5% 4 5% 4 7% 9% 33%	2366
May	1st to 10th	Day	13% 8% 3 8% 7% 4 6% 5% 6% 7% 32%	2520
	11th to 20th	Day	8% 6% 3 6% 7% 4 6% 5% 7% 8% 40%	2590
	21st to end	Day	18% 8% 3 6% 5% 4 5% 6% 6% 8% 32%	2917
June	1st to 10th	Day	16% 6% 4 6% 5% 3 5% 5% 7% 9% 34%	2700
	11th to 20th	Day	19% 8% 3 6% 6% 4 6% 5% 6% 8% 29%	2700
	21st to end	Day	10% 4 3 5% 6% 4 6% 6% 8% 8% 40%	2700
July	1st to 10th	Day	6% 5% 2 5% 5% 3 6% 7% 7% 10% 44%	2700
	11th to 20th	Day	9% 4 2 4 5% 3 6% 6% 7% 9% 45%	2700
	21st to end	Day	5% 3 1 3 4 3 5% 6% 7% 9% 54%	2938
August	1st to 10th	Day	8% 5% 3 4 6% 3 5% 5% 7% 9% 45%	2549
	11th to 20th	Day	9% 5% 2 4 4 2 4 5% 6% 9% 49%	2299
	21st to end	Day	8% 4 2 4 4 3 5% 6% 6% 9% 49%	2574
September	1st to 10th	Day	11% 6% 2 5% 5% 3 4 5% 4 8% 47%	2214
	11th to 20th	Day	15% 6% 3 5% 6% 3 4 4 4 6% 44%	2062
	21st to end	Day	10% 5% 2 5% 4 2 3 4 6% 7% 51%	1962
October	1st to 10th	Day	11% 9% 3 6% 4 2 4 3 5% 7% 45%	1800
	11th to 20th	Day	8% 7% 4 7% 6% 3 4 6% 4 7% 44%	1800
	21st to end	Day	7% 10% 3 8% 7% 4 5% 6% 6% 8% 35%	1697
November	1st to 10th	Day	11% 14% 5% 8% 8% 4 6% 5% 6% 8% 26%	1488
	11th to 20th	Day	6% 10% 5% 12% 8% 4 5% 5% 6% 7% 32%	1520
	21st to end	Day	6% 10% 6% 11% 6% 4 6% 5% 7% 8% 30%	1402
December	1st to 10th	Day	7% 10% 5% 12% 9% 4 9% 6% 6% 7% 25%	1330
	11th to 20th	Day	5% 9% 5% 11% 9% 6% 7% 6% 6% 8% 28%	1682
	21st to end	Day	4 8% 4 8% 6% 3 5% 4 5% 7% 45%	2442
January	1st to 10th	Night	3 8% 5% 11% 9% 6% 7% 8% 8% 9% 26%	4726
	11th to 20th	Night	3 6% 4 11% 10% 7% 8% 10% 7% 7% 27%	4699
	21st to end	Night	5% 9% 4 7% 8% 4 6% 6% 7% 7% 35%	5168
February	1st to 10th	Night	5% 9% 6% 11% 9% 5% 6% 7% 7% 7% 29%	2455
	11th to 20th	Night	6% 10% 4 9% 9% 5% 8% 8% 8% 7% 26%	2272
	21st to end	Night	5% 8% 4 8% 9% 4 8% 7% 8% 8% 31%	1924
March	1st to 10th	Night	7% 9% 4 11% 8% 6% 6% 6% 7% 8% 29%	2118
	11th to 20th	Night	7% 9% 3 8% 6% 4 6% 7% 7% 9% 34%	1980
	21st to end	Night	9% 10% 4 9% 7% 5% 6% 6% 7% 8% 29%	2178
April	1st to 10th	Night	9% 8% 3 6% 6% 4 7% 6% 6% 8% 37%	1747
	11th to 20th	Night	8% 11% 4 9% 8% 3 6% 6% 6% 7% 31%	1601
	21st to end	Night	11% 8% 3 7% 6% 4 5% 5% 6% 9% 35%	1593
May	1st to 10th	Night	12% 7% 3 6% 6% 3 5% 5% 6% 7% 37%	1440
	11th to 20th	Night	6% 6% 2 5% 5% 4 5% 5% 6% 10% 46%	1302
	21st to end	Night	16% 6% 2 6% 4 3 6% 5% 5% 8% 39%	1358
June	1st to 10th	Night	14% 9% 4 6% 6% 4 6% 7% 7% 7% 32%	1260
	11th to 20th	Night	16% 7% 3 6% 4 3 5% 5% 7% 9% 34%	1260
	21st to end	Night	8% 4 2 4 5% 3 6% 6% 8% 9% 44%	1260
July	1st to 10th	Night	7% 5% 3 5% 5% 3 5% 5% 5% 8% 49%	1260
	11th to 20th	Night	8% 4 2 4 4 2 5% 6% 7% 11% 48%	1260
	21st to end	Night	3 2 1 3 5% 2 3 4 5% 9% 62%	1379
August	1st to 10th	Night	6% 3 2 5% 6% 3 5% 6% 8% 9% 48%	1385
	11th to 20th	Night	10% 5% 2 4 5% 3 4 4 6% 10% 47%	1602
	21st to end	Night	6% 4 1 5% 4 3 4 5% 7% 9% 51%	1782
September	1st to 10th	Night	9% 4 2 5% 4 3 4 5% 5% 7% 50%	1746
	11th to 20th	Night	12% 6% 2 5% 5% 3 3 3 5% 7% 49%	1894
	21st to end	Night	7% 6% 2 4 5% 3 6% 5% 6% 9% 48%	1998
October	1st to 10th	Night	10% 8% 4 6% 4 2 5% 4 6% 8% 43%	2160
	11th to 20th	Night	7% 6% 3 7% 6% 4 5% 5% 5% 6% 45%	2160
	21st to end	Night	7% 9% 3 8% 7% 4 6% 5% 6% 8% 35%	2638
November	1st to 10th	Night	11% 13% 5% 7% 8% 3 4 4 5% 7% 31%	2590
	11th to 20th	Night	6% 8% 4 10% 9% 5% 6% 5% 5% 7% 34%	2660
	21st to end	Night	5% 11% 6% 9% 8% 5% 5% 5% 6% 9% 31%	2777
December	1st to 10th	Night	7% 10% 5% 10% 10% 6% 6% 5% 5% 9% 26%	2850
	11th to 20th	Night	5% 10% 6% 11% 10% 5% 6% 5% 6% 9% 27%	3510
	21st to end	Night	4 6% 3 6% 7% 3 5% 6% 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	55% 6% 11% 20% 7% 1	1599
	11th to 20th	Day	53% 7% 13% 16% 10%	1584
	21st to end	Day	53% 8% 13% 17% 9%	1332
March	1st to 10th	Day	55% 8% 17% 15% 5%	1840
	11th to 20th	Day	48% 7% 15% 20% 9% 1	1980
	21st to end	Day	54% 8% 17% 16% 5% 1	2178
April	1st to 10th	Day	48% 7% 14% 21% 9% 1	2210
	11th to 20th	Day	49% 6% 13% 22% 8% 1	2310
	21st to end	Day	47% 8% 13% 23% 8% 2	2366
May	1st to 10th	Day	49% 7% 14% 21% 9%	2520
	11th to 20th	Day	39% 7% 13% 27% 13% 1	2594
	21st to end	Day	48% 8% 13% 21% 10% 1	2918
June	1st to 10th	Day	45% 7% 16% 23% 9% 1	2700
	11th to 20th	Day	52% 8% 13% 19% 7% 1	2700
	21st to end	Day	38% 10% 21% 22% 8% 1	2700
July	1st to 10th	Day	31% 10% 22% 29% 7% 1	2626
	11th to 20th	Day	34% 8% 20% 29% 9% 1	2619
	21st to end	Day	24% 8% 21% 33% 12% 1	2775
August	1st to 10th	Day	34% 8% 21% 25% 11% 1	2531
	11th to 20th	Day	31% 8% 22% 27% 11% 1	2299
	21st to end	Day	30% 8% 16% 32% 14% 1	2574
September	1st to 10th	Day	36% 6% 15% 25% 12% 6%	2214
	11th to 20th	Day	42% 5% 14% 29% 9% 2	2062
	21st to end	Day	31% 6% 16% 34% 11% 2	1962
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	51% 7% 13% 18% 10%	2455
	11th to 20th	Night	52% 8% 14% 17% 8%	2273
	21st to end	Night	47% 8% 14% 22% 9% 1	1924
March	1st to 10th	Night	50% 8% 17% 17% 8%	2118
	11th to 20th	Night	43% 8% 15% 24% 9% 1	1980
	21st to end	Night	50% 8% 17% 18% 7% 1	2178
April	1st to 10th	Night	42% 7% 14% 22% 14% 1	1747
	11th to 20th	Night	50% 6% 12% 20% 11% 1	1601
	21st to end	Night	45% 8% 11% 23% 12% 2	1593
May	1st to 10th	Night	43% 7% 10% 25% 14%	1440
	11th to 20th	Night	32% 7% 11% 31% 17% 1	1302
	21st to end	Night	43% 8% 13% 22% 13% 1	1358
June	1st to 10th	Night	46% 10% 15% 20% 8% 1	1260
	11th to 20th	Night	44% 8% 15% 20% 11% 1	1260
	21st to end	Night	30% 11% 22% 27% 9% 1	1260
July	1st to 10th	Night	30% 7% 22% 29% 10% 1	1225
	11th to 20th	Night	29% 9% 24% 25% 12% 1	1218
	21st to end	Night	19% 7% 20% 37% 15% 2	1302
August	1st to 10th	Night	29% 9% 23% 27% 11% 1	1378
	11th to 20th	Night	32% 7% 19% 29% 10% 2	1602
	21st to end	Night	27% 7% 15% 31% 17% 2	1782
September	1st to 10th	Night	32% 7% 16% 23% 15% 7%	1746
	11th to 20th	Night	36% 6% 13% 28% 15% 2	1894
	21st to end	Night	32% 7% 16% 27% 17% 2	1998
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% 10% 36% 25% 12% 1	225
	11th to 20th	Day	12% 6% 35% 34% 11% 2	240
	21st to end	Day	6% 7% 31% 31% 19% 5%	198
March	1st to 10th	Day	9% 12% 37% 30% 10% 2	369
	11th to 20th	Day	11% 10% 35% 27% 11% 5%	420
	21st to end	Day	13% 9% 31% 33% 12% 3	462
April	1st to 10th	Day	10% 11% 37% 25% 13% 2	420
	11th to 20th	Day	12% 11% 34% 29% 11% 2	412
	21st to end	Day	16% 12% 26% 31% 13% 2	446
May	1st to 10th	Day	14% 9% 22% 33% 16% 6%	603
	11th to 20th	Day	10% 5% 25% 34% 19% 7%	625
	21st to end	Day	18% 7% 21% 27% 20% 8%	679
June	1st to 10th	Day	15% 8% 24% 31% 18% 4	630
	11th to 20th	Day	20% 10% 29% 24% 14% 3	630
	21st to end	Day	10% 6% 21% 30% 24% 8%	630
July	1st to 10th	Day	10% 3 20% 39% 22% 6%	621
	11th to 20th	Day	12% 5% 26% 30% 21% 7%	618
	21st to end	Day	5% 5% 22% 31% 27% 10%	684
August	1st to 10th	Day	10% 6% 17% 36% 22% 9%	588
	11th to 20th	Day	10% 6% 18% 32% 25% 8%	437
	21st to end	Day	7% 6% 23% 30% 26% 8%	495
September	1st to 10th	Day	14% 10% 27% 30% 15% 4	450
	11th to 20th	Day	16% 7% 25% 29% 19% 4	450
	21st to end	Day	15% 9% 33% 25% 14% 4	432
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	10% 9% 24% 38% 16% 2	738
	11th to 20th	Night	10% 7% 35% 36% 10% 2	704
	21st to end	Night	7% 4 23% 38% 23% 5%	592
March	1st to 10th	Night	10% 5% 33% 38% 13% 2	720
	11th to 20th	Night	11% 7% 33% 36% 12% 2	720
	21st to end	Night	13% 6% 28% 33% 16% 3	792
April	1st to 10th	Night	9% 8% 35% 32% 13% 2	545
	11th to 20th	Night	13% 7% 35% 34% 11% 1	533
	21st to end	Night	16% 7% 24% 39% 13% 1	540
May	1st to 10th	Night	14% 6% 23% 38% 18% 1	540
	11th to 20th	Night	8% 7% 23% 40% 22% 1	417
	21st to end	Night	18% 4 19% 34% 22% 3	389
June	1st to 10th	Night	16% 6% 26% 34% 16% 3	360
	11th to 20th	Night	19% 6% 24% 32% 18% 1	360
	21st to end	Night	10% 3 21% 39% 24% 2	360
July	1st to 10th	Night	9% 5% 21% 46% 20%	350
	11th to 20th	Night	9% 3 25% 40% 21% 1	348
	21st to end	Night	5% 4 23% 43% 23% 3	394
August	1st to 10th	Night	6% 3 20% 42% 25% 5%	455
	11th to 20th	Night	12% 4 19% 41% 22% 2	534
	21st to end	Night	7% 4 26% 39% 23% 1	594
September	1st to 10th	Night	12% 5% 23% 41% 17% 2	540
	11th to 20th	Night	14% 4 25% 38% 18% 1	634
	21st to end	Night	10% 4 34% 36% 15% 2	720
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 2024-02-02 03:20:33. Version ac07

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