Stargate Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Stargate Observatory clear sky chart from 2005-11-06 to 2024-04-03.

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	14% 9% 4 7% 6% 4 5% 5% 6% 7% 33%	78692
	Night	15% 10% 4 7% 6% 3 5% 5% 5% 7% 34%	81448
Transparency	Day	49% 6% 12% 21% 11% 1	78403
	Night	50% 5% 12% 21% 11% 1	81259
Seeing	Day	16% 9% 29% 25% 15% 6%	14444
	Night	18% 8% 29% 30% 12% 1	24242

By Month

Percentage Cloud Cover SE (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	16% 17% 6% 10% 8% 3 4 4 4 6% 23%	2527
	11th to 20th	Day	15% 18% 6% 11% 10% 5% 6% 5% 6% 5% 14%	2533
	21st to end	Day	27% 18% 7% 8% 7% 3 4 3 3 3 16%	3124
February	1st to 10th	Day	15% 14% 5% 11% 10% 4 5% 4 4 6% 22%	1710
	11th to 20th	Day	14% 12% 6% 11% 9% 3 5% 4 5% 6% 26%	1761
	21st to end	Day	13% 14% 6% 10% 7% 3 4 5% 6% 5% 26%	1570
March	1st to 10th	Day	15% 12% 5% 9% 6% 3 5% 4 5% 6% 29%	1962
	11th to 20th	Day	13% 12% 5% 7% 6% 3 5% 4 4 6% 33%	2090
	21st to end	Day	19% 13% 4 8% 6% 4 4 4 5% 5% 28%	2299
April	1st to 10th	Day	16% 11% 5% 7% 6% 3 4 5% 5% 7% 31%	2087
	11th to 20th	Day	16% 9% 3 7% 6% 4 4 4 6% 7% 34%	2302
	21st to end	Day	18% 8% 3 7% 6% 3 5% 5% 4 6% 34%	2340
May	1st to 10th	Day	16% 8% 3 8% 6% 3 5% 5% 6% 7% 33%	2340
	11th to 20th	Day	18% 8% 4 6% 5% 3 4 5% 5% 6% 36%	2301
	21st to end	Day	12% 5% 2 6% 6% 3 5% 6% 5% 9% 40%	2531
June	1st to 10th	Day	10% 5% 3 6% 6% 4 5% 5% 6% 8% 42%	2663
	11th to 20th	Day	10% 5% 2 6% 5% 4 5% 5% 6% 10% 42%	2700
	21st to end	Day	10% 6% 3 5% 5% 4 6% 6% 7% 10% 39%	2671
July	1st to 10th	Day	6% 4 2 5% 6% 3 5% 6% 6% 9% 46%	2520
	11th to 20th	Day	9% 4 3 5% 5% 4 5% 6% 7% 10% 43%	2520
	21st to end	Day	7% 4 3 6% 6% 4 6% 7% 8% 10% 40%	2565
August	1st to 10th	Day	8% 4 2 5% 6% 4 6% 7% 8% 9% 39%	2327
	11th to 20th	Day	9% 4 2 6% 7% 4 6% 6% 8% 9% 39%	2303
	21st to end	Day	11% 5% 3 6% 5% 4 5% 5% 5% 9% 42%	2574
September	1st to 10th	Day	10% 6% 3 6% 5% 4 4 5% 7% 9% 39%	2030
	11th to 20th	Day	10% 5% 2 5% 5% 3 6% 6% 6% 9% 45%	1980
	21st to end	Day	13% 7% 3 5% 5% 4 6% 6% 6% 9% 37%	1980
October	1st to 10th	Day	12% 7% 3 5% 7% 3 4 5% 6% 7% 41%	1908
	11th to 20th	Day	18% 8% 4 7% 6% 4 6% 4 4 7% 33%	1800
	21st to end	Day	19% 10% 4 9% 5% 3 5% 5% 4 6% 30%	1856
November	1st to 10th	Day	11% 9% 3 8% 5% 3 5% 5% 6% 8% 37%	1672
	11th to 20th	Day	14% 10% 4 8% 6% 4 4 6% 6% 6% 33%	1710
	21st to end	Day	18% 11% 5% 8% 6% 3 5% 4 4 6% 29%	1533
December	1st to 10th	Day	13% 13% 7% 11% 7% 5% 5% 4 5% 7% 22%	1520
	11th to 20th	Day	16% 15% 5% 9% 5% 4 4 5% 7% 6% 25%	1788
	21st to end	Day	27% 19% 7% 9% 6% 3 4 4 4 5% 13%	2595
January	1st to 10th	Night	17% 15% 5% 9% 7% 4 4 4 5% 6% 26%	4428
	11th to 20th	Night	14% 17% 6% 12% 8% 5% 6% 6% 4 5% 18%	4435
	21st to end	Night	23% 17% 8% 9% 5% 3 4 4 3 4 20%	4532
February	1st to 10th	Night	15% 14% 5% 11% 9% 4 6% 5% 5% 5% 23%	2470
	11th to 20th	Night	13% 12% 6% 8% 8% 4 5% 5% 5% 5% 28%	2300
	21st to end	Night	18% 11% 4 8% 6% 4 5% 4 5% 5% 29%	1884
March	1st to 10th	Night	15% 10% 5% 8% 6% 3 4 4 4 6% 34%	2218
	11th to 20th	Night	13% 7% 4 5% 5% 3 5% 6% 5% 8% 38%	2090
	21st to end	Night	19% 9% 3 6% 6% 3 5% 5% 5% 5% 34%	2299
April	1st to 10th	Night	17% 9% 4 6% 5% 3 4 5% 5% 7% 35%	1932
	11th to 20th	Night	18% 7% 3 6% 4 3 4 5% 5% 8% 38%	1606
	21st to end	Night	16% 8% 3 5% 5% 2 5% 5% 5% 7% 39%	1620
May	1st to 10th	Night	15% 8% 3 7% 7% 4 4 5% 6% 8% 34%	1620
	11th to 20th	Night	17% 6% 3 5% 5% 3 4 5% 5% 7% 41%	1592
	21st to end	Night	9% 5% 2 5% 6% 2 4 5% 6% 9% 47%	1740
June	1st to 10th	Night	9% 4 3 5% 5% 3 3 5% 6% 9% 46%	1293
	11th to 20th	Night	10% 5% 3 5% 4 3 4 6% 6% 9% 46%	1260
	21st to end	Night	8% 4 3 5% 6% 3 4 4 6% 9% 49%	1283
July	1st to 10th	Night	7% 4 2 3 4 3 6% 4 5% 8% 54%	1440
	11th to 20th	Night	8% 3 2 4 5% 3 4 4 6% 10% 51%	1440
	21st to end	Night	5% 4 2 4 4 3 5% 6% 8% 10% 49%	1748
August	1st to 10th	Night	7% 4 2 4 5% 3 6% 4 8% 9% 49%	1611
	11th to 20th	Night	6% 4 2 4 5% 4 5% 5% 6% 9% 49%	1598
	21st to end	Night	8% 4 2 4 5% 2 5% 5% 5% 7% 53%	1782
September	1st to 10th	Night	9% 5% 3 6% 6% 3 5% 4 5% 7% 47%	1906
	11th to 20th	Night	9% 5% 2 5% 4 2 4 4 5% 8% 53%	1980
	21st to end	Night	14% 5% 2 5% 5% 3 4 5% 5% 7% 45%	1980
October	1st to 10th	Night	14% 6% 2 5% 4 2 4 4 6% 7% 45%	2052
	11th to 20th	Night	17% 8% 3 6% 6% 4 4 5% 5% 6% 35%	2160
	21st to end	Night	21% 9% 3 6% 5% 4 5% 5% 5% 6% 31%	2497
November	1st to 10th	Night	13% 8% 2 5% 5% 3 4 5% 5% 7% 43%	2406
	11th to 20th	Night	15% 9% 4 7% 6% 4 5% 5% 6% 7% 31%	2470
	21st to end	Night	18% 12% 4 7% 5% 3 5% 4 5% 6% 29%	2645
December	1st to 10th	Night	17% 12% 6% 10% 7% 4 5% 5% 5% 6% 23%	2660
	11th to 20th	Night	14% 13% 5% 9% 7% 4 5% 4 6% 6% 26%	3404
	21st to end	Night	27% 20% 7% 9% 6% 3 4 3 4 4 14%	5067

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	63% 4 14% 13% 5% 1	2528
	11th to 20th	Day	71% 6% 11% 9% 3	2533
	21st to end	Day	73% 4 12% 7% 3 1	3124
February	1st to 10th	Day	64% 5% 9% 15% 7%	1710
	11th to 20th	Day	58% 4 10% 18% 8% 2	1770
	21st to end	Day	59% 3 12% 18% 6% 2	1570
March	1st to 10th	Day	56% 5% 13% 17% 8% 1	1962
	11th to 20th	Day	51% 5% 10% 20% 11% 3	2090
	21st to end	Day	58% 5% 9% 18% 8% 1	2299
April	1st to 10th	Day	52% 5% 11% 20% 11% 1	2087
	11th to 20th	Day	49% 5% 11% 19% 14% 2	2302
	21st to end	Day	49% 6% 13% 17% 12% 2	2340
May	1st to 10th	Day	48% 6% 11% 22% 11% 2	2340
	11th to 20th	Day	48% 5% 11% 20% 14% 2	2305
	21st to end	Day	41% 6% 14% 22% 15% 2	2531
June	1st to 10th	Day	39% 6% 13% 26% 14% 2	2663
	11th to 20th	Day	37% 7% 14% 24% 16% 3	2700
	21st to end	Day	37% 8% 12% 25% 16% 2	2671
July	1st to 10th	Day	33% 7% 10% 27% 19% 3	2451
	11th to 20th	Day	33% 7% 14% 27% 17% 2	2445
	21st to end	Day	35% 8% 15% 22% 17% 3	2423
August	1st to 10th	Day	36% 8% 14% 27% 13% 1	2314
	11th to 20th	Day	38% 7% 14% 27% 12% 2	2303
	21st to end	Day	39% 6% 10% 27% 16% 2	2574
September	1st to 10th	Day	40% 6% 15% 24% 13% 2	2030
	11th to 20th	Day	34% 6% 12% 34% 13%	1980
	21st to end	Day	42% 6% 13% 26% 12% 1	1980
October	1st to 10th	Day	41% 6% 12% 27% 13% 2	1908
	11th to 20th	Day	51% 5% 13% 21% 10% 1	1800
	21st to end	Day	55% 6% 12% 18% 8%	1856
November	1st to 10th	Day	43% 6% 13% 25% 11% 1	1672
	11th to 20th	Day	50% 6% 14% 19% 10% 1	1710
	21st to end	Day	57% 5% 13% 19% 6% 1	1533
December	1st to 10th	Day	62% 5% 12% 17% 4	1520
	11th to 20th	Day	58% 5% 15% 16% 6%	1784
	21st to end	Day	75% 4 10% 8% 3	2595
January	1st to 10th	Night	60% 5% 13% 16% 5% 1	4428
	11th to 20th	Night	66% 6% 13% 11% 3	4435
	21st to end	Night	69% 3 10% 15% 3	4532
February	1st to 10th	Night	62% 6% 9% 15% 7% 1	2470
	11th to 20th	Night	56% 5% 10% 19% 9% 1	2302
	21st to end	Night	56% 3 12% 19% 8% 1	1884
March	1st to 10th	Night	52% 4 11% 23% 9% 1	2218
	11th to 20th	Night	43% 6% 11% 22% 15% 2	2090
	21st to end	Night	52% 4 9% 23% 11% 1	2299
April	1st to 10th	Night	48% 5% 11% 21% 13% 2	1932
	11th to 20th	Night	45% 5% 11% 19% 18% 2	1606
	21st to end	Night	43% 6% 11% 21% 16% 4	1620
May	1st to 10th	Night	48% 5% 12% 21% 12% 3	1620
	11th to 20th	Night	43% 5% 11% 20% 19% 3	1593
	21st to end	Night	33% 7% 14% 25% 18% 3	1741
June	1st to 10th	Night	34% 6% 11% 29% 17% 3	1293
	11th to 20th	Night	35% 6% 14% 25% 19% 2	1260
	21st to end	Night	33% 6% 12% 27% 21% 1	1283
July	1st to 10th	Night	29% 5% 11% 29% 22% 4	1400
	11th to 20th	Night	28% 6% 14% 34% 16% 2	1392
	21st to end	Night	26% 8% 18% 24% 20% 3	1651
August	1st to 10th	Night	29% 6% 18% 32% 15% 2	1600
	11th to 20th	Night	31% 6% 14% 33% 12% 3	1598
	21st to end	Night	31% 6% 13% 30% 19% 1	1782
September	1st to 10th	Night	36% 6% 14% 27% 15% 2	1906
	11th to 20th	Night	30% 5% 14% 31% 19% 1	1980
	21st to end	Night	38% 4 14% 30% 12% 1	1980
October	1st to 10th	Night	39% 5% 11% 26% 18% 1	2052
	11th to 20th	Night	48% 5% 14% 20% 12% 1	2160
	21st to end	Night	52% 5% 11% 21% 9% 1	2497
November	1st to 10th	Night	41% 5% 13% 26% 15% 1	2406
	11th to 20th	Night	50% 5% 15% 21% 9% 1	2470
	21st to end	Night	56% 4 15% 19% 6%	2645
December	1st to 10th	Night	61% 5% 13% 15% 5%	2660
	11th to 20th	Night	57% 5% 14% 16% 7% 1	3407
	21st to end	Night	74% 5% 11% 7% 3	5067

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	20% 18% 37% 17% 7% 1	270
	11th to 20th	Day	21% 14% 43% 17% 4 1	270
	21st to end	Day	25% 11% 38% 19% 5% 1	297
February	1st to 10th	Day	21% 17% 41% 15% 4 1	270
	11th to 20th	Day	21% 17% 40% 19% 3	270
	21st to end	Day	20% 20% 45% 12% 3	225
March	1st to 10th	Day	22% 17% 38% 18% 4 1	332
	11th to 20th	Day	20% 15% 32% 26% 7% 1	460
	21st to end	Day	27% 12% 31% 23% 6% 1	506
April	1st to 10th	Day	15% 14% 38% 22% 9% 1	428
	11th to 20th	Day	25% 12% 29% 17% 11% 6%	412
	21st to end	Day	23% 11% 29% 23% 11% 3	420
May	1st to 10th	Day	22% 9% 29% 24% 12% 3	423
	11th to 20th	Day	20% 9% 25% 26% 14% 7%	447
	21st to end	Day	14% 5% 20% 30% 21% 9%	485
June	1st to 10th	Day	11% 5% 31% 33% 15% 4	593
	11th to 20th	Day	11% 5% 29% 32% 19% 4	630
	21st to end	Day	11% 6% 25% 33% 20% 5%	630
July	1st to 10th	Day	8% 4 19% 31% 24% 15%	621
	11th to 20th	Day	9% 5% 22% 35% 20% 9%	618
	21st to end	Day	7% 4 23% 30% 26% 11%	506
August	1st to 10th	Day	8% 4 18% 27% 28% 16%	446
	11th to 20th	Day	12% 3 14% 32% 23% 16%	439
	21st to end	Day	12% 5% 18% 30% 22% 13%	495
September	1st to 10th	Day	12% 5% 22% 23% 25% 12%	450
	11th to 20th	Day	10% 4 19% 22% 30% 15%	450
	21st to end	Day	15% 8% 23% 23% 21% 9%	450
October	1st to 10th	Day	14% 10% 26% 21% 18% 10%	450
	11th to 20th	Day	20% 15% 32% 24% 7% 2	450
	21st to end	Day	25% 11% 39% 18% 6% 1	371
November	1st to 10th	Day	17% 16% 35% 21% 9% 2	270
	11th to 20th	Day	19% 19% 35% 17% 8% 1	270
	21st to end	Day	24% 15% 37% 20% 4	185
December	1st to 10th	Day	20% 17% 42% 13% 8% 1	180
	11th to 20th	Day	29% 14% 38% 13% 4 1	180
	21st to end	Day	26% 18% 34% 18% 4	245
January	1st to 10th	Night	23% 12% 37% 22% 5% 1	950
	11th to 20th	Night	25% 12% 34% 25% 4 1	945
	21st to end	Night	20% 9% 35% 28% 7%	836
February	1st to 10th	Night	20% 11% 42% 24% 3	760
	11th to 20th	Night	20% 13% 36% 26% 5%	743
	21st to end	Night	23% 14% 39% 21% 2	628
March	1st to 10th	Night	20% 10% 36% 28% 6%	760
	11th to 20th	Night	16% 13% 38% 26% 6% 1	760
	21st to end	Night	22% 8% 33% 28% 8%	836
April	1st to 10th	Night	21% 12% 33% 29% 4	658
	11th to 20th	Night	21% 8% 33% 27% 9% 2	533
	21st to end	Night	19% 7% 31% 33% 10%	540
May	1st to 10th	Night	17% 6% 29% 36% 11% 1	540
	11th to 20th	Night	20% 4 26% 33% 16% 1	531
	21st to end	Night	10% 2 22% 41% 23% 2	580
June	1st to 10th	Night	11% 3 26% 46% 15%	360
	11th to 20th	Night	11% 3 24% 46% 16% 1	360
	21st to end	Night	11% 3 20% 45% 21% 1	383
July	1st to 10th	Night	8% 2 15% 40% 29% 6%	525
	11th to 20th	Night	10% 3 16% 42% 26% 3	522
	21st to end	Night	6% 3 18% 46% 25% 3	591
August	1st to 10th	Night	9% 2 13% 39% 34% 3	537
	11th to 20th	Night	7% 2 17% 38% 33% 4	534
	21st to end	Night	11% 2 17% 35% 33% 3	594
September	1st to 10th	Night	11% 6% 18% 35% 26% 5%	664
	11th to 20th	Night	11% 3 18% 35% 28% 5%	720
	21st to end	Night	16% 5% 20% 33% 22% 5%	720
October	1st to 10th	Night	16% 7% 25% 31% 18% 3	720
	11th to 20th	Night	23% 10% 29% 27% 9% 2	720
	21st to end	Night	26% 9% 32% 28% 4	792
November	1st to 10th	Night	18% 9% 30% 29% 14% 1	740
	11th to 20th	Night	20% 14% 33% 24% 8% 1	760
	21st to end	Night	26% 11% 34% 23% 6%	760
December	1st to 10th	Night	26% 11% 38% 20% 6%	760
	11th to 20th	Night	23% 11% 38% 24% 4	835
	21st to end	Night	29% 11% 33% 24% 3	1045

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