Montague
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Montague clear sky chart from 2005-11-06 to 2025-02-25.

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	17% 8% 2 7% 5% 4 4 4 6% 7% 37%	108635
	Night	17% 7% 3 6% 4 4 4 3 5% 7% 39%	110018
Transparency	Day	46% 4 11% 23% 15% 2	112184
	Night	44% 3 11% 24% 15% 2	114633
Seeing	Day	25% 15% 28% 19% 9% 3	15188
	Night	23% 14% 28% 26% 9% 1	24515

By Month

Percentage Cloud Cover NE (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	12% 10% 3 8% 5% 4 4 4 6% 6% 37%	3597
	11th to 20th	Day	14% 11% 4 10% 6% 5% 4 3 5% 6% 33%	3570
	21st to end	Day	17% 10% 3 6% 5% 4 5% 3 5% 5% 38%	4374
February	1st to 10th	Day	16% 8% 3 8% 5% 5% 5% 4 6% 6% 34%	1800
	11th to 20th	Day	14% 9% 3 7% 5% 5% 4 3 5% 6% 39%	1898
	21st to end	Day	17% 10% 3 6% 5% 3 4 3 5% 7% 35%	1610
March	1st to 10th	Day	26% 10% 3 7% 4 4 3 2 4 5% 34%	3116
	11th to 20th	Day	10% 7% 3 8% 6% 6% 4 4 6% 8% 39%	3413
	21st to end	Day	21% 8% 2 5% 4 3 3 3 4 5% 41%	4088
April	1st to 10th	Day	17% 9% 2 6% 6% 5% 4 3 5% 6% 37%	2280
	11th to 20th	Day	18% 7% 2 5% 5% 4 4 4 4 7% 39%	2254
	21st to end	Day	18% 6% 2 7% 5% 5% 5% 4 6% 5% 37%	2280
May	1st to 10th	Day	27% 8% 2 5% 4 4 3 3 5% 7% 31%	4193
	11th to 20th	Day	22% 9% 3 8% 4 5% 5% 4 5% 6% 29%	4398
	21st to end	Day	13% 5% 2 5% 4 4 5% 4 7% 10% 42%	4837
June	1st to 10th	Day	15% 6% 2 6% 5% 5% 5% 5% 6% 9% 35%	2660
	11th to 20th	Day	16% 6% 2 6% 5% 5% 5% 5% 6% 9% 35%	2660
	21st to end	Day	13% 6% 2 8% 6% 5% 5% 4 6% 9% 38%	2660
July	1st to 10th	Day	10% 6% 3 8% 5% 6% 5% 5% 7% 10% 35%	4440
	11th to 20th	Day	10% 6% 2 6% 4 5% 6% 4 8% 10% 37%	4440
	21st to end	Day	14% 8% 3 8% 5% 5% 5% 4 6% 8% 33%	4814
August	1st to 10th	Day	22% 5% 2 7% 5% 5% 6% 5% 7% 7% 29%	4181
	11th to 20th	Day	14% 5% 2 7% 4 4 6% 5% 6% 8% 39%	3742
	21st to end	Day	14% 6% 2 5% 3 3 4 3 5% 10% 45%	4180
September	1st to 10th	Day	16% 6% 2 5% 4 4 4 3 6% 7% 42%	2280
	11th to 20th	Day	13% 5% 1 4 3 5% 4 3 5% 7% 49%	2233
	21st to end	Day	18% 7% 3 6% 4 4 4 4 5% 7% 39%	2090
October	1st to 10th	Day	21% 6% 2 6% 4 4 3 3 5% 7% 39%	1928
	11th to 20th	Day	14% 7% 2 6% 4 4 4 4 5% 8% 42%	1900
	21st to end	Day	22% 6% 2 5% 4 4 5% 3 6% 6% 37%	1969
November	1st to 10th	Day	13% 7% 2 5% 3 3 4 2 4 6% 51%	1761
	11th to 20th	Day	18% 7% 2 4 3 3 4 3 6% 7% 43%	1800
	21st to end	Day	17% 8% 2 5% 5% 4 5% 5% 5% 7% 38%	1643
December	1st to 10th	Day	16% 9% 2 7% 4 4 5% 4 5% 6% 37%	2600
	11th to 20th	Day	21% 9% 2 6% 3 3 3 3 5% 5% 39%	2986
	21st to end	Day	18% 10% 4 9% 5% 5% 4 4 5% 7% 30%	3960
January	1st to 10th	Night	13% 7% 3 9% 5% 5% 5% 4 6% 7% 37%	6349
	11th to 20th	Night	12% 8% 4 11% 5% 5% 5% 4 5% 7% 35%	6315
	21st to end	Night	17% 8% 3 7% 4 4 4 4 5% 6% 38%	6565
February	1st to 10th	Night	16% 9% 3 5% 5% 4 4 3 5% 6% 39%	2600
	11th to 20th	Night	16% 7% 2 6% 4 5% 5% 4 5% 7% 38%	2387
	21st to end	Night	17% 8% 2 7% 4 4 4 3 5% 6% 39%	1939
March	1st to 10th	Night	23% 11% 3 6% 3 3 3 3 4 5% 35%	3724
	11th to 20th	Night	12% 8% 2 6% 4 4 5% 4 6% 8% 42%	3543
	21st to end	Night	16% 9% 3 7% 4 3 3 3 5% 5% 41%	3544
April	1st to 10th	Night	17% 9% 3 8% 5% 4 5% 4 5% 7% 35%	1900
	11th to 20th	Night	19% 6% 2 5% 5% 5% 4 4 4 7% 38%	1875
	21st to end	Night	19% 6% 2 6% 4 3 4 2 6% 6% 40%	1900
May	1st to 10th	Night	27% 8% 3 6% 4 4 4 3 5% 7% 31%	2760
	11th to 20th	Night	23% 10% 3 6% 5% 4 4 3 5% 5% 32%	2495
	21st to end	Night	13% 7% 2 6% 5% 4 4 4 7% 9% 40%	2738
June	1st to 10th	Night	17% 5% 2 5% 5% 4 4 3 5% 8% 43%	1520
	11th to 20th	Night	13% 6% 3 4 5% 4 5% 4 6% 8% 43%	1520
	21st to end	Night	12% 4 2 6% 3 3 4 4 6% 10% 45%	1520
July	1st to 10th	Night	10% 5% 2 6% 5% 6% 5% 4 7% 9% 40%	2520
	11th to 20th	Night	12% 6% 1 6% 4 5% 6% 4 7% 10% 40%	2520
	21st to end	Night	18% 6% 2 5% 4 4 5% 4 6% 7% 38%	2739
August	1st to 10th	Night	22% 6% 2 7% 4 4 5% 4 5% 8% 34%	2745
	11th to 20th	Night	15% 7% 3 6% 4 4 5% 3 5% 6% 42%	3054
	21st to end	Night	12% 5% 2 5% 3 4 4 3 5% 8% 50%	3476
September	1st to 10th	Night	16% 5% 2 5% 4 4 3 3 5% 7% 46%	1900
	11th to 20th	Night	14% 5% 2 4 3 3 3 2 5% 6% 52%	1947
	21st to end	Night	17% 6% 3 5% 4 4 3 3 5% 6% 43%	2090
October	1st to 10th	Night	21% 7% 2 5% 4 3 4 3 4 6% 42%	2250
	11th to 20th	Night	17% 5% 2 5% 4 3 3 3 4 6% 47%	2280
	21st to end	Night	22% 6% 2 5% 4 2 3 3 5% 6% 42%	2627
November	1st to 10th	Night	13% 6% 2 5% 3 3 4 3 5% 6% 49%	2537
	11th to 20th	Night	19% 7% 2 5% 3 3 3 3 5% 6% 45%	2600
	21st to end	Night	14% 8% 2 6% 4 4 4 4 5% 6% 43%	2755
December	1st to 10th	Night	14% 8% 3 7% 4 4 4 3 5% 7% 41%	4580
	11th to 20th	Night	24% 8% 2 5% 4 4 4 3 4 5% 38%	5208
	21st to end	Night	20% 11% 4 7% 5% 4 4 3 4 6% 32%	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	47% 3 8% 28% 12% 2	3598
	11th to 20th	Day	53% 3 9% 20% 11% 4	3600
	21st to end	Day	48% 3 9% 24% 15% 1	4374
February	1st to 10th	Day	51% 4 11% 20% 14% 1	1800
	11th to 20th	Day	48% 3 8% 22% 17% 2	1907
	21st to end	Day	50% 2 9% 23% 13% 3	1610
March	1st to 10th	Day	56% 1 8% 23% 10% 2	3119
	11th to 20th	Day	44% 2 11% 30% 12% 2	3413
	21st to end	Day	48% 2 7% 15% 24% 5%	4088
April	1st to 10th	Day	49% 3 8% 21% 15% 4	2280
	11th to 20th	Day	46% 2 10% 21% 17% 3	2254
	21st to end	Day	47% 3 8% 22% 15% 4	2280
May	1st to 10th	Day	55% 2 11% 18% 12% 2	4207
	11th to 20th	Day	57% 2 10% 20% 9% 1	4402
	21st to end	Day	39% 3 11% 27% 17% 3	4837
June	1st to 10th	Day	46% 5% 11% 23% 15% 1	2660
	11th to 20th	Day	45% 5% 12% 25% 11% 2	2660
	21st to end	Day	43% 4 12% 26% 14%	2660
July	1st to 10th	Day	43% 7% 12% 23% 14% 1	4370
	11th to 20th	Day	39% 6% 17% 24% 13% 1	4365
	21st to end	Day	49% 5% 11% 19% 15% 2	4661
August	1st to 10th	Day	51% 5% 13% 20% 10%	4167
	11th to 20th	Day	41% 5% 14% 28% 11% 1	3778
	21st to end	Day	36% 4 11% 33% 15% 2	4180
September	1st to 10th	Day	41% 5% 11% 24% 18% 2	2280
	11th to 20th	Day	36% 2 9% 25% 25% 3	2233
	21st to end	Day	46% 3 9% 20% 20% 2	2090
October	1st to 10th	Day	42% 4 7% 20% 23% 4	3201
	11th to 20th	Day	33% 3 8% 29% 23% 3	3140
	21st to end	Day	31% 3 16% 27% 21% 3	3220
November	1st to 10th	Day	37% 2 12% 26% 20% 3	1761
	11th to 20th	Day	41% 2 10% 26% 18% 3	1800
	21st to end	Day	45% 5% 13% 26% 10% 2	1643
December	1st to 10th	Day	46% 4 15% 25% 9% 1	2600
	11th to 20th	Day	48% 2 14% 22% 12% 2	2986
	21st to end	Day	55% 3 9% 19% 14% 1	3960
January	1st to 10th	Night	46% 3 9% 25% 15% 2	6349
	11th to 20th	Night	48% 4 13% 19% 12% 4	6360
	21st to end	Night	47% 2 10% 20% 17% 4	6565
February	1st to 10th	Night	46% 3 14% 24% 12% 1	2600
	11th to 20th	Night	46% 3 9% 22% 17% 4	2389
	21st to end	Night	47% 2 7% 25% 15% 3	1939
March	1st to 10th	Night	53% 1 9% 23% 12% 2	3734
	11th to 20th	Night	41% 2 14% 27% 15% 2	3544
	21st to end	Night	47% 2 6% 18% 21% 5%	3544
April	1st to 10th	Night	50% 3 9% 20% 15% 3	1900
	11th to 20th	Night	47% 3 10% 20% 19% 1	1875
	21st to end	Night	45% 3 9% 23% 17% 4	1900
May	1st to 10th	Night	55% 2 10% 21% 10% 1	2766
	11th to 20th	Night	55% 2 14% 18% 10% 1	2496
	21st to end	Night	41% 4 14% 25% 14% 2	2739
June	1st to 10th	Night	42% 4 11% 25% 19% 1	1520
	11th to 20th	Night	39% 4 16% 28% 11% 1	1520
	21st to end	Night	35% 4 16% 30% 14% 1	1520
July	1st to 10th	Night	39% 7% 16% 20% 16% 2	2480
	11th to 20th	Night	39% 7% 14% 26% 13% 1	2472
	21st to end	Night	43% 6% 14% 18% 18% 1	2651
August	1st to 10th	Night	49% 6% 16% 20% 9% 1	2735
	11th to 20th	Night	43% 4 14% 28% 10%	3084
	21st to end	Night	33% 4 11% 34% 17% 1	3476
September	1st to 10th	Night	38% 4 12% 27% 19% 1	1900
	11th to 20th	Night	34% 3 9% 26% 25% 2	1947
	21st to end	Night	42% 3 8% 24% 22% 1	2090
October	1st to 10th	Night	42% 4 10% 24% 19% 1	3757
	11th to 20th	Night	31% 2 10% 28% 26% 3	3779
	21st to end	Night	32% 3 15% 30% 18% 1	4326
November	1st to 10th	Night	36% 3 12% 24% 22% 2	2537
	11th to 20th	Night	42% 2 10% 23% 20% 3	2600
	21st to end	Night	41% 2 14% 29% 12% 1	2755
December	1st to 10th	Night	43% 3 12% 32% 8% 1	4580
	11th to 20th	Night	50% 2 12% 20% 14% 2	5208
	21st to end	Night	54% 3 10% 19% 12% 2	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	38% 22% 24% 13% 4	200
	11th to 20th	Day	43% 23% 27% 7% 2	200
	21st to end	Day	31% 28% 30% 6% 3 2	310
February	1st to 10th	Day	34% 27% 27% 10% 2	300
	11th to 20th	Day	40% 24% 27% 8% 1	446
	21st to end	Day	34% 24% 27% 12% 3	398
March	1st to 10th	Day	32% 21% 29% 15% 3	460
	11th to 20th	Day	31% 24% 28% 13% 4 1	460
	21st to end	Day	32% 22% 30% 10% 4 1	506
April	1st to 10th	Day	33% 20% 27% 14% 4 1	460
	11th to 20th	Day	29% 21% 27% 14% 8% 2	452
	21st to end	Day	29% 18% 33% 14% 5% 2	460
May	1st to 10th	Day	36% 16% 25% 13% 7% 2	463
	11th to 20th	Day	23% 18% 30% 18% 9% 2	487
	21st to end	Day	19% 9% 29% 26% 13% 3	529
June	1st to 10th	Day	20% 13% 31% 22% 12% 3	490
	11th to 20th	Day	21% 11% 25% 28% 13% 2	490
	21st to end	Day	18% 11% 33% 25% 11% 1	490
July	1st to 10th	Day	18% 5% 29% 26% 16% 6%	485
	11th to 20th	Day	13% 6% 26% 33% 19% 4	484
	21st to end	Day	16% 7% 36% 26% 13% 3	532
August	1st to 10th	Day	15% 6% 28% 31% 14% 6%	486
	11th to 20th	Day	14% 7% 24% 32% 18% 6%	479
	21st to end	Day	15% 10% 28% 24% 15% 8%	539
September	1st to 10th	Day	23% 10% 24% 23% 13% 7%	490
	11th to 20th	Day	15% 9% 27% 22% 16% 12%	490
	21st to end	Day	25% 9% 28% 22% 11% 5%	490
October	1st to 10th	Day	28% 11% 22% 20% 14% 5%	490
	11th to 20th	Day	21% 17% 29% 21% 10% 2	490
	21st to end	Day	30% 14% 29% 18% 8% 1	474
November	1st to 10th	Day	21% 19% 26% 22% 11% 2	395
	11th to 20th	Day	28% 18% 27% 21% 6% 1	400
	21st to end	Day	35% 19% 29% 14% 3 1	243
December	1st to 10th	Day	35% 22% 29% 11% 5%	200
	11th to 20th	Day	41% 20% 27% 10% 3	200
	21st to end	Day	30% 18% 35% 13% 5%	220
January	1st to 10th	Night	26% 22% 32% 18% 3	800
	11th to 20th	Night	28% 19% 28% 22% 3	800
	21st to end	Night	23% 22% 34% 19% 2	880
February	1st to 10th	Night	26% 19% 33% 21% 1	800
	11th to 20th	Night	29% 22% 34% 14% 1	783
	21st to end	Night	31% 20% 28% 18% 3	647
March	1st to 10th	Night	28% 19% 32% 18% 3	760
	11th to 20th	Night	26% 21% 29% 19% 4	760
	21st to end	Night	25% 20% 33% 15% 5%	836
April	1st to 10th	Night	26% 18% 32% 20% 4	760
	11th to 20th	Night	25% 16% 33% 20% 7%	751
	21st to end	Night	26% 13% 30% 24% 6%	760
May	1st to 10th	Night	27% 11% 29% 24% 7% 1	535
	11th to 20th	Night	22% 10% 31% 28% 7% 1	374
	21st to end	Night	17% 7% 23% 40% 13%	411
June	1st to 10th	Night	18% 6% 21% 38% 16% 1	380
	11th to 20th	Night	16% 5% 29% 37% 13%	380
	21st to end	Night	13% 5% 25% 43% 13% 1	380
July	1st to 10th	Night	12% 5% 20% 42% 19% 1	370
	11th to 20th	Night	13% 3 22% 43% 18% 1	368
	21st to end	Night	12% 6% 19% 43% 18% 2	416
August	1st to 10th	Night	12% 3 21% 40% 23% 2	513
	11th to 20th	Night	15% 4 16% 39% 24% 2	719
	21st to end	Night	16% 5% 20% 35% 22% 2	836
September	1st to 10th	Night	17% 6% 24% 33% 18% 3	760
	11th to 20th	Night	16% 6% 23% 29% 22% 5%	760
	21st to end	Night	21% 6% 23% 29% 18% 2	760
October	1st to 10th	Night	25% 11% 21% 26% 16% 1	760
	11th to 20th	Night	21% 11% 29% 30% 9%	760
	21st to end	Night	27% 13% 29% 23% 9%	836
November	1st to 10th	Night	18% 16% 29% 27% 9% 1	780
	11th to 20th	Night	26% 15% 27% 24% 7% 1	800
	21st to end	Night	21% 20% 29% 23% 6% 1	800
December	1st to 10th	Night	26% 17% 29% 22% 5%	800
	11th to 20th	Night	26% 19% 29% 22% 4	800
	21st to end	Night	28% 17% 30% 22% 3	880

Page generated at 2025-02-22 06:51:39. Version ac07

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