Mattawa
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Mattawa clear sky chart from 2005-11-06 to 2026-01-02.

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% 12% 4 9% 5% 4 4 3 5% 6% 29%	127975
	Night	16% 14% 5% 11% 5% 5% 4 3 4 5% 27%	123398
Transparency	Day	56% 3 10% 21% 8% 1	131520
	Night	60% 3 10% 18% 9% 1	127941
Seeing	Day	25% 15% 30% 20% 8% 2	16377
	Night	25% 12% 29% 24% 9% 1	25316

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% 20% 9% 17% 10% 6% 4 3 3 3 12%	3165
	11th to 20th	Day	10% 18% 7% 19% 8% 5% 5% 3 4 5% 16%	3552
	21st to end	Day	12% 21% 9% 15% 5% 4 4 3 4 6% 17%	4418
February	1st to 10th	Day	9% 20% 7% 15% 9% 6% 5% 3 4 4 17%	1800
	11th to 20th	Day	11% 20% 6% 12% 8% 5% 5% 3 4 5% 20%	1753
	21st to end	Day	16% 17% 5% 13% 8% 5% 4 3 4 5% 20%	1506
March	1st to 10th	Day	20% 15% 5% 12% 4 5% 4 3 4 5% 23%	4838
	11th to 20th	Day	13% 14% 6% 12% 6% 5% 4 4 5% 7% 24%	4980
	21st to end	Day	16% 15% 6% 9% 6% 5% 4 3 3 4 29%	5504
April	1st to 10th	Day	22% 15% 4 8% 5% 3 4 3 5% 6% 27%	2400
	11th to 20th	Day	21% 13% 4 6% 4 3 3 3 4 5% 33%	2463
	21st to end	Day	22% 13% 3 7% 4 4 3 2 4 4 34%	2600
May	1st to 10th	Day	21% 10% 3 7% 5% 5% 5% 4 4 6% 31%	6199
	11th to 20th	Day	16% 9% 3 7% 4 4 5% 4 5% 7% 37%	6318
	21st to end	Day	22% 10% 3 6% 4 4 4 3 4 6% 34%	6949
June	1st to 10th	Day	21% 10% 3 7% 5% 5% 5% 4 5% 6% 31%	2850
	11th to 20th	Day	16% 6% 3 6% 5% 5% 5% 5% 6% 7% 37%	3000
	21st to end	Day	20% 7% 3 6% 5% 5% 5% 4 7% 7% 31%	3000
July	1st to 10th	Day	19% 7% 2 6% 5% 5% 5% 4 6% 9% 32%	6819
	11th to 20th	Day	15% 6% 2 5% 4 5% 4 3 6% 8% 42%	6554
	21st to end	Day	11% 5% 2 5% 4 4 5% 4 6% 10% 44%	6926
August	1st to 10th	Day	14% 7% 3 8% 6% 6% 6% 4 6% 8% 33%	4241
	11th to 20th	Day	18% 8% 2 6% 5% 4 5% 4 6% 8% 35%	4174
	21st to end	Day	11% 6% 2 7% 5% 5% 5% 4 6% 8% 41%	4510
September	1st to 10th	Day	18% 7% 2 6% 4 4 4 4 5% 7% 38%	2400
	11th to 20th	Day	18% 6% 2 5% 4 4 4 3 5% 7% 42%	2350
	21st to end	Day	23% 9% 3 7% 5% 3 4 4 5% 6% 33%	2120
October	1st to 10th	Day	20% 11% 4 7% 4 3 3 4 5% 6% 34%	2000
	11th to 20th	Day	25% 15% 3 8% 6% 4 4 3 4 5% 23%	2000
	21st to end	Day	27% 17% 5% 8% 4 4 4 2 4 5% 19%	2161
November	1st to 10th	Day	21% 15% 5% 9% 3 4 3 3 4 6% 27%	1659
	11th to 20th	Day	17% 20% 6% 10% 6% 5% 4 3 4 5% 19%	1680
	21st to end	Day	23% 23% 6% 14% 5% 3 4 3 3 3 14%	1680
December	1st to 10th	Day	17% 24% 9% 15% 6% 4 4 3 4 4 10%	2680
	11th to 20th	Day	16% 20% 6% 15% 8% 5% 3 2 3 4 18%	3066
	21st to end	Day	18% 21% 8% 17% 5% 3 3 4 3 4 14%	3660
January	1st to 10th	Night	13% 20% 11% 18% 9% 6% 4 2 3 4 11%	6810
	11th to 20th	Night	11% 16% 7% 21% 9% 6% 5% 3 4 4 14%	6315
	21st to end	Night	9% 23% 10% 14% 6% 7% 5% 3 4 4 15%	6536
February	1st to 10th	Night	11% 15% 7% 14% 10% 6% 5% 4 5% 5% 18%	2600
	11th to 20th	Night	12% 17% 7% 14% 7% 6% 4 4 4 4 22%	2533
	21st to end	Night	14% 18% 6% 12% 6% 7% 4 3 4 5% 20%	2123
March	1st to 10th	Night	16% 19% 4 10% 4 3 4 4 4 5% 26%	4998
	11th to 20th	Night	14% 17% 5% 10% 5% 4 4 4 6% 7% 24%	4979
	21st to end	Night	17% 14% 5% 10% 5% 4 4 2 4 4 29%	5427
April	1st to 10th	Night	20% 16% 4 7% 5% 3 3 3 5% 4 29%	2000
	11th to 20th	Night	20% 11% 4 7% 4 4 4 3 4 5% 33%	1902
	21st to end	Night	22% 12% 3 7% 5% 4 4 4 4 5% 31%	1800
May	1st to 10th	Night	20% 10% 3 6% 4 4 3 3 5% 6% 35%	3742
	11th to 20th	Night	14% 7% 3 6% 4 4 4 4 5% 7% 43%	3575
	21st to end	Night	18% 10% 3 7% 4 4 4 3 4 6% 35%	3926
June	1st to 10th	Night	16% 9% 3 8% 6% 5% 5% 3 5% 5% 34%	1546
	11th to 20th	Night	18% 6% 3 5% 3 5% 5% 3 5% 8% 41%	1400
	21st to end	Night	16% 9% 2 7% 5% 4 6% 4 5% 7% 36%	1400
July	1st to 10th	Night	19% 7% 3 7% 4 5% 5% 3 5% 7% 34%	3160
	11th to 20th	Night	17% 6% 2 5% 4 4 4 3 5% 7% 44%	3410
	21st to end	Night	13% 5% 2 4 4 4 4 4 6% 7% 47%	3926
August	1st to 10th	Night	13% 6% 2 6% 4 4 4 4 7% 7% 43%	2905
	11th to 20th	Night	18% 6% 3 5% 4 4 5% 3 5% 6% 40%	2875
	21st to end	Night	17% 6% 2 5% 3 3 4 3 6% 8% 44%	3354
September	1st to 10th	Night	16% 5% 2 6% 4 4 4 3 5% 6% 46%	2000
	11th to 20th	Night	17% 7% 2 5% 3 3 3 3 5% 4 47%	2049
	21st to end	Night	20% 9% 2 6% 3 5% 3 3 4 6% 40%	2280
October	1st to 10th	Night	19% 9% 3 7% 4 4 4 3 5% 6% 36%	2400
	11th to 20th	Night	25% 14% 3 8% 5% 4 4 2 3 4 28%	2400
	21st to end	Night	26% 16% 4 8% 4 4 3 3 5% 5% 23%	2678
November	1st to 10th	Night	20% 17% 4 7% 4 4 4 3 4 5% 28%	2857
	11th to 20th	Night	19% 19% 5% 10% 6% 5% 4 3 4 5% 21%	2940
	21st to end	Night	23% 21% 6% 11% 6% 3 4 3 4 4 15%	2940
December	1st to 10th	Night	17% 24% 8% 15% 8% 6% 4 3 3 3 9%	4720
	11th to 20th	Night	17% 20% 6% 15% 7% 4 4 3 3 4 18%	5348
	21st to end	Night	20% 20% 6% 18% 6% 4 4 2 3 4 13%	7544

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	78% 2 7% 10% 3	3166
	11th to 20th	Day	73% 2 8% 10% 7%	3582
	21st to end	Day	70% 3 6% 13% 8% 1	4418
February	1st to 10th	Day	71% 2 7% 13% 6% 1	1800
	11th to 20th	Day	68% 2 8% 13% 9% 1	1762
	21st to end	Day	68% 2 5% 16% 8% 1	1506
March	1st to 10th	Day	65% 2 9% 12% 11% 2	4841
	11th to 20th	Day	61% 2 13% 15% 8% 1	4980
	21st to end	Day	61% 2 6% 20% 10% 2	5504
April	1st to 10th	Day	60% 2 7% 20% 9% 2	2400
	11th to 20th	Day	55% 2 5% 23% 12% 2	2463
	21st to end	Day	56% 2 6% 19% 14% 3	2600
May	1st to 10th	Day	56% 3 6% 21% 9% 5%	6209
	11th to 20th	Day	48% 3 9% 26% 13% 1	6322
	21st to end	Day	53% 2 10% 20% 13% 2	6949
June	1st to 10th	Day	55% 3 8% 22% 11% 1	2850
	11th to 20th	Day	46% 3 11% 26% 12% 2	3000
	21st to end	Day	51% 4 12% 22% 10% 1	3000
July	1st to 10th	Day	48% 5% 13% 26% 7%	6746
	11th to 20th	Day	39% 4 15% 34% 7%	6474
	21st to end	Day	35% 4 16% 33% 11%	6728
August	1st to 10th	Day	47% 5% 13% 28% 7%	4227
	11th to 20th	Day	46% 5% 14% 27% 7%	4213
	21st to end	Day	40% 4 13% 33% 9% 1	4510
September	1st to 10th	Day	46% 4 13% 26% 11%	2400
	11th to 20th	Day	43% 3 13% 30% 10%	2350
	21st to end	Day	53% 4 11% 25% 7%	2120
October	1st to 10th	Day	53% 4 10% 25% 7%	3260
	11th to 20th	Day	57% 4 12% 21% 6%	3240
	21st to end	Day	69% 3 12% 12% 4	3475
November	1st to 10th	Day	60% 2 13% 19% 5%	1659
	11th to 20th	Day	68% 3 10% 12% 7% 1	1680
	21st to end	Day	78% 3 9% 7% 3	1680
December	1st to 10th	Day	78% 3 8% 8% 2	2680
	11th to 20th	Day	74% 1 5% 15% 5%	3066
	21st to end	Day	75% 3 5% 14% 2	3660
January	1st to 10th	Night	80% 2 7% 7% 3	6810
	11th to 20th	Night	75% 2 7% 9% 6%	6360
	21st to end	Night	73% 3 5% 10% 9%	6536
February	1st to 10th	Night	68% 3 9% 14% 7%	2600
	11th to 20th	Night	66% 2 9% 16% 6% 1	2535
	21st to end	Night	67% 3 7% 16% 6% 1	2123
March	1st to 10th	Night	62% 2 9% 14% 10% 3	5008
	11th to 20th	Night	60% 3 13% 15% 8% 1	4980
	21st to end	Night	61% 2 6% 18% 12% 2	5427
April	1st to 10th	Night	59% 3 6% 19% 11% 2	2000
	11th to 20th	Night	54% 2 6% 23% 14% 1	1902
	21st to end	Night	56% 3 7% 16% 14% 3	1800
May	1st to 10th	Night	51% 2 7% 22% 14% 4	3748
	11th to 20th	Night	42% 3 13% 23% 16% 3	3576
	21st to end	Night	51% 3 10% 22% 13% 2	3927
June	1st to 10th	Night	51% 4 9% 22% 13% 1	1546
	11th to 20th	Night	43% 3 11% 26% 16% 1	1400
	21st to end	Night	47% 6% 13% 22% 12% 1	1400
July	1st to 10th	Night	48% 5% 12% 25% 9% 1	3125
	11th to 20th	Night	42% 4 16% 30% 9%	3367
	21st to end	Night	36% 4 12% 36% 13%	3809
August	1st to 10th	Night	37% 6% 16% 29% 11%	2895
	11th to 20th	Night	43% 6% 18% 26% 7% 1	2902
	21st to end	Night	38% 5% 15% 30% 10% 3	3354
September	1st to 10th	Night	39% 4 16% 29% 11% 1	2000
	11th to 20th	Night	40% 3 15% 33% 10%	2049
	21st to end	Night	46% 4 13% 29% 9%	2280
October	1st to 10th	Night	47% 4 11% 28% 9%	3920
	11th to 20th	Night	55% 3 13% 21% 7%	3899
	21st to end	Night	59% 5% 16% 14% 5%	4314
November	1st to 10th	Night	60% 3 13% 18% 7%	2857
	11th to 20th	Night	67% 4 10% 14% 5%	2940
	21st to end	Night	75% 3 9% 10% 3	2940
December	1st to 10th	Night	81% 3 7% 7% 2	4720
	11th to 20th	Night	72% 2 5% 11% 9%	5348
	21st to end	Night	77% 2 5% 12% 4	7544

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% 21% 37% 14% 4	202
	11th to 20th	Day	26% 16% 34% 19% 7%	200
	21st to end	Day	23% 19% 34% 16% 7% 1	320
February	1st to 10th	Day	30% 24% 32% 8% 5%	300
	11th to 20th	Day	26% 27% 38% 8% 1	300
	21st to end	Day	41% 16% 32% 10% 1	270
March	1st to 10th	Day	28% 17% 37% 15% 2 1	500
	11th to 20th	Day	26% 18% 37% 14% 4 1	500
	21st to end	Day	29% 19% 29% 17% 5% 1	550
April	1st to 10th	Day	32% 20% 28% 14% 5% 1	500
	11th to 20th	Day	35% 16% 23% 15% 8% 3	492
	21st to end	Day	33% 17% 29% 13% 7% 1	500
May	1st to 10th	Day	27% 16% 29% 18% 8% 2	503
	11th to 20th	Day	23% 15% 29% 21% 9% 3	527
	21st to end	Day	23% 14% 32% 19% 8% 3	573
June	1st to 10th	Day	26% 11% 33% 23% 6% 1	580
	11th to 20th	Day	21% 14% 29% 24% 10% 2	730
	21st to end	Day	21% 15% 32% 22% 8% 2	730
July	1st to 10th	Day	15% 12% 31% 32% 10% 1	721
	11th to 20th	Day	17% 12% 30% 28% 11% 2	609
	21st to end	Day	13% 10% 32% 30% 12% 3	576
August	1st to 10th	Day	19% 6% 30% 27% 13% 5%	526
	11th to 20th	Day	17% 6% 25% 30% 14% 7%	519
	21st to end	Day	17% 13% 29% 23% 12% 5%	583
September	1st to 10th	Day	23% 9% 31% 19% 12% 6%	530
	11th to 20th	Day	19% 8% 23% 26% 15% 9%	530
	21st to end	Day	26% 12% 24% 23% 12% 3	530
October	1st to 10th	Day	26% 13% 26% 20% 12% 3	530
	11th to 20th	Day	29% 19% 31% 16% 3 1	530
	21st to end	Day	35% 14% 30% 17% 4	561
November	1st to 10th	Day	34% 18% 35% 11% 2	233
	11th to 20th	Day	28% 21% 32% 15% 5%	220
	21st to end	Day	36% 21% 32% 8% 1 1	220
December	1st to 10th	Day	34% 13% 35% 15% 4	220
	11th to 20th	Day	32% 21% 34% 9% 3 1	220
	21st to end	Day	33% 20% 31% 12% 5%	242
January	1st to 10th	Night	28% 15% 34% 18% 5%	1005
	11th to 20th	Night	28% 14% 31% 21% 5%	800
	21st to end	Night	17% 12% 35% 25% 9% 1	880
February	1st to 10th	Night	21% 19% 36% 20% 5%	800
	11th to 20th	Night	23% 15% 37% 19% 6%	783
	21st to end	Night	24% 18% 33% 22% 3	660
March	1st to 10th	Night	24% 19% 32% 22% 3	800
	11th to 20th	Night	24% 19% 33% 18% 5% 1	800
	21st to end	Night	25% 12% 32% 24% 6% 1	880
April	1st to 10th	Night	30% 14% 29% 24% 4	800
	11th to 20th	Night	28% 15% 25% 24% 8%	718
	21st to end	Night	28% 11% 28% 25% 8% 1	600
May	1st to 10th	Night	24% 9% 26% 32% 8%	470
	11th to 20th	Night	22% 8% 34% 26% 10%	394
	21st to end	Night	21% 8% 30% 32% 9%	433
June	1st to 10th	Night	22% 7% 31% 32% 8%	400
	11th to 20th	Night	20% 7% 27% 36% 10%	400
	21st to end	Night	20% 8% 27% 33% 11% 1	400
July	1st to 10th	Night	13% 5% 32% 35% 14% 1	390
	11th to 20th	Night	13% 6% 28% 36% 16% 1	388
	21st to end	Night	12% 5% 29% 38% 14% 1	438
August	1st to 10th	Night	16% 6% 20% 36% 20%	587
	11th to 20th	Night	13% 5% 20% 41% 20% 2	594
	21st to end	Night	20% 7% 25% 30% 16% 2	739
September	1st to 10th	Night	20% 6% 25% 30% 18% 1	800
	11th to 20th	Night	21% 6% 24% 25% 21% 4	800
	21st to end	Night	25% 6% 23% 29% 16% 1	800
October	1st to 10th	Night	24% 10% 28% 26% 11% 1	800
	11th to 20th	Night	31% 12% 29% 21% 7% 1	800
	21st to end	Night	36% 12% 25% 23% 4	880
November	1st to 10th	Night	32% 12% 28% 21% 7% 1	820
	11th to 20th	Night	28% 18% 31% 16% 7%	840
	21st to end	Night	36% 14% 25% 19% 6%	840
December	1st to 10th	Night	32% 14% 32% 16% 6% 1	840
	11th to 20th	Night	29% 17% 31% 18% 4 1	840
	21st to end	Night	34% 14% 31% 18% 4	1097

Page generated at 2025-12-30 01:14:05. Version ac07

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