Harvey Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Harvey Observatory clear sky chart from 2005-11-06 to 2025-01-22.

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	13% 9% 3 7% 5% 4 4 4 6% 7% 37%	104991
	Night	14% 10% 3 7% 4 4 4 3 5% 6% 38%	104450
Transparency	Day	45% 6% 12% 22% 14% 2	108597
	Night	45% 5% 11% 22% 15% 2	108985
Seeing	Day	16% 9% 28% 25% 16% 6%	15929
	Night	18% 9% 30% 30% 13% 1	25871

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	14% 14% 8% 15% 6% 5% 4 3 5% 6% 20%	2607
	11th to 20th	Day	14% 12% 7% 13% 6% 6% 6% 7% 7% 5% 17%	2610
	21st to end	Day	24% 22% 6% 10% 4 3 3 2 4 5% 18%	2915
February	1st to 10th	Day	17% 12% 4 10% 6% 5% 4 3 5% 6% 27%	1829
	11th to 20th	Day	15% 12% 4 9% 6% 5% 5% 3 4 7% 31%	1848
	21st to end	Day	17% 15% 5% 8% 5% 3 3 3 6% 6% 31%	1570
March	1st to 10th	Day	18% 18% 4 8% 4 4 3 2 3 4 30%	3120
	11th to 20th	Day	11% 8% 3 6% 4 5% 4 4 6% 8% 40%	3245
	21st to end	Day	15% 12% 5% 9% 6% 5% 5% 3 6% 7% 27%	4165
April	1st to 10th	Day	15% 11% 3 7% 5% 3 4 3 6% 7% 35%	2280
	11th to 20th	Day	17% 8% 4 6% 4 5% 4 4 5% 7% 38%	2254
	21st to end	Day	19% 9% 3 8% 5% 4 4 3 5% 6% 34%	2372
May	1st to 10th	Day	17% 8% 3 7% 5% 5% 6% 5% 7% 9% 29%	4082
	11th to 20th	Day	17% 7% 2 7% 4 5% 5% 4 6% 7% 36%	4108
	21st to end	Day	8% 5% 2 7% 4 5% 5% 4 6% 9% 45%	4824
June	1st to 10th	Day	9% 6% 2 7% 4 4 5% 5% 6% 9% 43%	2660
	11th to 20th	Day	8% 5% 2 6% 5% 4 4 5% 7% 8% 47%	2660
	21st to end	Day	9% 7% 3 7% 6% 5% 5% 5% 7% 9% 39%	2660
July	1st to 10th	Day	13% 6% 3 6% 5% 5% 5% 5% 7% 10% 35%	4440
	11th to 20th	Day	7% 5% 1 5% 4 4 5% 5% 8% 12% 44%	4440
	21st to end	Day	9% 6% 2 6% 5% 5% 5% 5% 7% 9% 41%	4813
August	1st to 10th	Day	7% 4 2 5% 4 4 4 4 6% 9% 50%	4177
	11th to 20th	Day	8% 6% 2 5% 4 5% 5% 4 8% 11% 42%	3729
	21st to end	Day	6% 4 2 5% 4 4 4 4 6% 10% 51%	4180
September	1st to 10th	Day	10% 6% 3 5% 4 4 4 4 5% 8% 46%	2280
	11th to 20th	Day	10% 5% 2 4 4 4 5% 4 5% 7% 51%	2131
	21st to end	Day	12% 6% 3 5% 4 4 4 4 6% 7% 45%	2090
October	1st to 10th	Day	10% 5% 2 7% 5% 4 5% 3 5% 7% 48%	2090
	11th to 20th	Day	16% 6% 2 8% 3 4 4 4 5% 6% 42%	1893
	21st to end	Day	19% 9% 3 7% 4 4 4 4 5% 6% 35%	1881
November	1st to 10th	Day	12% 6% 2 5% 3 4 4 3 5% 7% 49%	1762
	11th to 20th	Day	17% 11% 3 8% 4 3 4 3 4 5% 39%	1800
	21st to end	Day	17% 10% 3 10% 5% 5% 4 3 4 5% 35%	1800
December	1st to 10th	Day	12% 12% 4 7% 4 3 3 3 4 6% 41%	2686
	11th to 20th	Day	14% 15% 6% 12% 5% 6% 5% 4 5% 5% 23%	3008
	21st to end	Day	28% 17% 7% 12% 4 4 4 3 3 4 12%	3982
January	1st to 10th	Night	15% 16% 7% 11% 5% 4 4 3 4 5% 26%	4568
	11th to 20th	Night	13% 19% 6% 13% 6% 6% 5% 4 4 4 20%	4580
	21st to end	Night	25% 16% 6% 9% 4 3 4 2 3 4 22%	4771
February	1st to 10th	Night	18% 12% 4 10% 5% 5% 4 3 4 5% 28%	2349
	11th to 20th	Night	13% 11% 4 9% 5% 5% 4 3 5% 6% 35%	2218
	21st to end	Night	18% 12% 3 9% 4 4 3 3 5% 5% 32%	1884
March	1st to 10th	Night	17% 15% 4 7% 4 3 3 3 4 6% 35%	3733
	11th to 20th	Night	11% 7% 3 7% 4 4 4 3 5% 6% 46%	3714
	21st to end	Night	19% 9% 3 8% 5% 5% 4 4 5% 6% 31%	3480
April	1st to 10th	Night	12% 9% 4 6% 5% 4 4 4 4 7% 41%	1900
	11th to 20th	Night	18% 9% 2 5% 4 3 4 3 4 6% 41%	1875
	21st to end	Night	18% 8% 3 6% 5% 5% 4 4 5% 6% 35%	1805
May	1st to 10th	Night	17% 9% 4 6% 5% 4 5% 3 6% 8% 33%	2813
	11th to 20th	Night	17% 8% 2 5% 4 4 4 4 6% 7% 39%	2782
	21st to end	Night	9% 6% 2 7% 5% 4 4 4 6% 9% 43%	2743
June	1st to 10th	Night	9% 5% 2 6% 4 5% 5% 3 5% 8% 50%	1520
	11th to 20th	Night	8% 5% 2 6% 4 3 5% 4 6% 8% 49%	1520
	21st to end	Night	8% 5% 2 6% 5% 4 5% 4 8% 9% 42%	1520
July	1st to 10th	Night	10% 5% 2 6% 5% 5% 4 3 7% 10% 43%	2530
	11th to 20th	Night	5% 3 2 5% 3 4 4 4 7% 10% 55%	2530
	21st to end	Night	6% 7% 2 7% 5% 5% 5% 4 6% 10% 43%	2750
August	1st to 10th	Night	7% 4 1 5% 4 3 4 4 6% 9% 53%	2751
	11th to 20th	Night	6% 4 2 5% 5% 5% 4 4 6% 9% 50%	3100
	21st to end	Night	7% 4 2 5% 3 4 4 4 5% 8% 55%	3476
September	1st to 10th	Night	11% 5% 2 5% 3 3 4 3 5% 7% 53%	1900
	11th to 20th	Night	7% 5% 1 4 4 4 4 4 6% 7% 55%	2028
	21st to end	Night	11% 6% 3 6% 3 3 4 4 6% 7% 47%	2090
October	1st to 10th	Night	10% 6% 2 6% 3 4 3 3 4 6% 54%	2090
	11th to 20th	Night	15% 6% 2 5% 3 3 3 3 4 6% 49%	2283
	21st to end	Night	18% 8% 2 7% 3 4 4 3 5% 5% 39%	2717
November	1st to 10th	Night	11% 7% 3 6% 3 4 4 3 4 7% 49%	2536
	11th to 20th	Night	14% 9% 3 7% 5% 4 4 4 4 6% 41%	2600
	21st to end	Night	18% 10% 4 9% 5% 4 3 3 5% 6% 34%	2600
December	1st to 10th	Night	12% 8% 3 8% 4 4 4 3 5% 6% 44%	4499
	11th to 20th	Night	17% 11% 5% 10% 4 5% 4 3 5% 5% 31%	5199
	21st to end	Night	27% 18% 6% 10% 4 4 4 3 4 5% 15%	6996

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% 5% 11% 14% 6%	2608
	11th to 20th	Day	66% 6% 10% 9% 8% 1	2610
	21st to end	Day	71% 4 8% 13% 4 1	2915
February	1st to 10th	Day	59% 5% 10% 16% 8% 2	1829
	11th to 20th	Day	54% 5% 11% 21% 9% 1	1858
	21st to end	Day	55% 5% 11% 20% 7% 2	1570
March	1st to 10th	Day	59% 4 7% 17% 11% 1	3120
	11th to 20th	Day	39% 7% 13% 27% 13% 1	3245
	21st to end	Day	53% 8% 16% 19% 4	4165
April	1st to 10th	Day	48% 7% 13% 19% 13%	2280
	11th to 20th	Day	45% 6% 11% 22% 12% 3	2254
	21st to end	Day	50% 5% 12% 19% 11% 2	2372
May	1st to 10th	Day	47% 10% 14% 22% 7%	4120
	11th to 20th	Day	44% 9% 13% 24% 9% 1	4112
	21st to end	Day	33% 8% 13% 19% 23% 3	4837
June	1st to 10th	Day	35% 9% 13% 23% 16% 3	2660
	11th to 20th	Day	33% 7% 12% 23% 21% 4	2660
	21st to end	Day	40% 8% 14% 20% 16% 3	2660
July	1st to 10th	Day	44% 6% 12% 24% 12% 2	4371
	11th to 20th	Day	32% 5% 16% 29% 16% 1	4365
	21st to end	Day	39% 5% 17% 20% 17% 2	4662
August	1st to 10th	Day	31% 5% 17% 31% 15% 1	4162
	11th to 20th	Day	34% 6% 14% 29% 16% 1	3765
	21st to end	Day	29% 5% 15% 30% 16% 4	4179
September	1st to 10th	Day	35% 8% 12% 23% 18% 4	2280
	11th to 20th	Day	32% 7% 11% 24% 22% 5%	2131
	21st to end	Day	37% 5% 10% 24% 21% 2	2090
October	1st to 10th	Day	26% 3 7% 28% 33% 2	3480
	11th to 20th	Day	32% 3 10% 24% 29% 2	3121
	21st to end	Day	45% 3 8% 22% 20% 2	3081
November	1st to 10th	Day	36% 6% 15% 24% 17% 4	1762
	11th to 20th	Day	49% 3 11% 21% 13% 3	1800
	21st to end	Day	53% 5% 10% 21% 11% 1	1800
December	1st to 10th	Day	47% 3 11% 29% 10%	2686
	11th to 20th	Day	63% 5% 10% 17% 5%	3005
	21st to end	Day	77% 4 8% 8% 3	3982
January	1st to 10th	Night	59% 6% 12% 15% 7%	4568
	11th to 20th	Night	69% 4 9% 12% 7% 1	4580
	21st to end	Night	67% 4 9% 13% 7% 1	4771
February	1st to 10th	Night	57% 5% 12% 15% 9% 2	2349
	11th to 20th	Night	50% 5% 12% 20% 12% 2	2219
	21st to end	Night	53% 6% 10% 19% 10% 2	1884
March	1st to 10th	Night	50% 6% 10% 22% 10% 2	3733
	11th to 20th	Night	37% 6% 11% 26% 18% 2	3714
	21st to end	Night	51% 8% 13% 21% 6% 1	3480
April	1st to 10th	Night	42% 7% 11% 24% 14% 2	1900
	11th to 20th	Night	45% 6% 9% 21% 15% 4	1875
	21st to end	Night	48% 7% 10% 19% 12% 4	1805
May	1st to 10th	Night	47% 8% 12% 23% 10%	2840
	11th to 20th	Night	42% 9% 14% 25% 10% 1	2783
	21st to end	Night	35% 9% 12% 19% 19% 5%	2751
June	1st to 10th	Night	33% 6% 10% 27% 20% 3	1520
	11th to 20th	Night	31% 7% 12% 26% 21% 4	1520
	21st to end	Night	35% 8% 16% 21% 16% 4	1520
July	1st to 10th	Night	37% 5% 15% 26% 12% 5%	2490
	11th to 20th	Night	26% 4 15% 31% 23% 1	2482
	21st to end	Night	37% 4 17% 20% 17% 5%	2662
August	1st to 10th	Night	29% 5% 19% 31% 16% 2	2742
	11th to 20th	Night	32% 5% 14% 28% 19% 1	3130
	21st to end	Night	28% 5% 11% 33% 18% 4	3476
September	1st to 10th	Night	31% 6% 12% 25% 19% 7%	1900
	11th to 20th	Night	27% 6% 11% 25% 27% 5%	2028
	21st to end	Night	35% 6% 10% 23% 22% 4	2090
October	1st to 10th	Night	21% 3 6% 31% 36% 2	3480
	11th to 20th	Night	29% 3 8% 26% 32% 2	3794
	21st to end	Night	38% 3 8% 24% 23% 4	4467
November	1st to 10th	Night	36% 4 11% 27% 19% 4	2536
	11th to 20th	Night	44% 5% 11% 23% 15% 3	2600
	21st to end	Night	52% 4 10% 22% 12% 1	2600
December	1st to 10th	Night	43% 3 12% 29% 12% 1	4499
	11th to 20th	Night	56% 4 12% 16% 11% 1	5201
	21st to end	Night	72% 4 9% 10% 4	6996

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	22% 16% 34% 22% 5% 1	300
	11th to 20th	Day	23% 18% 39% 15% 4 1	300
	21st to end	Day	26% 13% 35% 21% 4	300
February	1st to 10th	Day	26% 15% 37% 18% 4	270
	11th to 20th	Day	26% 14% 37% 17% 5% 1	270
	21st to end	Day	28% 15% 43% 13% 2	225
March	1st to 10th	Day	21% 20% 40% 16% 3	270
	11th to 20th	Day	28% 15% 37% 16% 4	316
	21st to end	Day	29% 13% 33% 16% 8% 1	506
April	1st to 10th	Day	23% 14% 32% 23% 7% 2	460
	11th to 20th	Day	19% 18% 29% 19% 11% 3	452
	21st to end	Day	23% 15% 34% 18% 8% 2	460
May	1st to 10th	Day	18% 12% 34% 25% 8% 3	463
	11th to 20th	Day	21% 8% 26% 27% 13% 5%	501
	21st to end	Day	12% 7% 31% 26% 16% 9%	734
June	1st to 10th	Day	10% 8% 26% 31% 19% 6%	680
	11th to 20th	Day	11% 5% 26% 32% 21% 5%	680
	21st to end	Day	12% 6% 31% 26% 19% 6%	680
July	1st to 10th	Day	11% 3 16% 29% 25% 16%	671
	11th to 20th	Day	7% 4 20% 31% 25% 12%	668
	21st to end	Day	10% 2 17% 33% 29% 9%	739
August	1st to 10th	Day	7% 2 14% 31% 31% 15%	543
	11th to 20th	Day	9% 3 17% 29% 31% 10%	479
	21st to end	Day	6% 2 16% 29% 34% 14%	539
September	1st to 10th	Day	12% 4 17% 28% 29% 10%	490
	11th to 20th	Day	9% 3 14% 27% 31% 17%	490
	21st to end	Day	14% 7% 25% 22% 22% 10%	490
October	1st to 10th	Day	11% 5% 27% 31% 19% 8%	490
	11th to 20th	Day	13% 19% 31% 26% 9% 2	303
	21st to end	Day	28% 14% 34% 18% 5% 2	330
November	1st to 10th	Day	14% 12% 34% 25% 12% 3	300
	11th to 20th	Day	24% 16% 31% 19% 8% 1	300
	21st to end	Day	23% 13% 37% 24% 4	300
December	1st to 10th	Day	18% 18% 42% 15% 7% 1	300
	11th to 20th	Day	18% 19% 38% 20% 5% 1	300
	21st to end	Day	28% 18% 32% 18% 3	330
January	1st to 10th	Night	21% 15% 37% 24% 3	1000
	11th to 20th	Night	22% 16% 37% 20% 5%	1000
	21st to end	Night	23% 12% 36% 25% 3	1051
February	1st to 10th	Night	25% 12% 37% 23% 3	829
	11th to 20th	Night	20% 14% 38% 24% 4	743
	21st to end	Night	27% 13% 36% 21% 3	628
March	1st to 10th	Night	21% 15% 35% 25% 4	760
	11th to 20th	Night	18% 13% 37% 26% 6% 1	760
	21st to end	Night	24% 9% 38% 24% 6%	641
April	1st to 10th	Night	17% 14% 37% 26% 6%	570
	11th to 20th	Night	21% 11% 32% 27% 9%	563
	21st to end	Night	22% 9% 35% 25% 8% 1	570
May	1st to 10th	Night	19% 7% 34% 32% 8%	570
	11th to 20th	Night	20% 4 28% 33% 14% 1	561
	21st to end	Night	11% 5% 25% 37% 19% 2	617
June	1st to 10th	Night	11% 4 24% 42% 18%	570
	11th to 20th	Night	12% 3 24% 42% 18% 1	570
	21st to end	Night	10% 3 25% 41% 21% 1	570
July	1st to 10th	Night	11% 1 15% 38% 30% 5%	555
	11th to 20th	Night	6% 2 18% 41% 29% 4	552
	21st to end	Night	6% 2 13% 44% 32% 2	624
August	1st to 10th	Night	7% 1 11% 45% 32% 4	567
	11th to 20th	Night	7% 1 13% 45% 30% 4	564
	21st to end	Night	8% 1 15% 32% 40% 3	627
September	1st to 10th	Night	14% 3 15% 38% 28% 3	570
	11th to 20th	Night	8% 4 14% 39% 32% 3	698
	21st to end	Night	13% 6% 23% 29% 26% 3	760
October	1st to 10th	Night	13% 5% 22% 37% 21% 3	760
	11th to 20th	Night	18% 11% 29% 28% 13%	760
	21st to end	Night	21% 14% 35% 24% 6%	836
November	1st to 10th	Night	13% 11% 40% 25% 10% 1	780
	11th to 20th	Night	19% 13% 33% 27% 7% 1	800
	21st to end	Night	24% 13% 33% 24% 7%	800
December	1st to 10th	Night	22% 12% 37% 24% 5%	945
	11th to 20th	Night	24% 11% 33% 26% 5%	1000
	21st to end	Night	31% 13% 31% 22% 3	1100

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