Fort Smith
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Fort Smith clear sky chart from 2005-11-06 to 2025-10-04.

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% 9% 4 10% 6% 6% 6% 5% 7% 8% 33%	131166
	Night	8% 12% 5% 12% 7% 7% 7% 5% 6% 7% 25%	126854
Transparency	Day	29% 39% 8% 16% 6%	130820
	Night	36% 39% 8% 13% 4	126780
Seeing	Day	15% 9% 29% 29% 15% 4	18262
	Night	14% 8% 30% 31% 15% 2	26131

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	5% 12% 7% 18% 13% 10% 10% 6% 8% 3 8%	2259
	11th to 20th	Day	5% 9% 3 14% 8% 8% 11% 8% 9% 8% 17%	2360
	21st to end	Day	10% 19% 6% 12% 8% 7% 7% 5% 10% 6% 12%	3240
February	1st to 10th	Day	4 9% 6% 16% 10% 9% 9% 6% 8% 7% 16%	1410
	11th to 20th	Day	4 11% 4 13% 8% 6% 8% 6% 8% 9% 23%	1595
	21st to end	Day	3 11% 5% 14% 11% 10% 6% 7% 9% 6% 18%	1485
March	1st to 10th	Day	4 13% 6% 12% 7% 7% 6% 6% 9% 8% 22%	4289
	11th to 20th	Day	3 8% 5% 14% 9% 8% 7% 6% 7% 7% 26%	4988
	21st to end	Day	3 6% 4 12% 6% 6% 5% 4 7% 7% 40%	5595
April	1st to 10th	Day	8% 13% 4 9% 7% 5% 5% 4 5% 6% 34%	2600
	11th to 20th	Day	5% 10% 4 9% 6% 5% 5% 4 7% 6% 39%	2575
	21st to end	Day	9% 9% 3 10% 6% 5% 5% 4 7% 8% 35%	2935
May	1st to 10th	Day	7% 7% 3 8% 5% 6% 5% 5% 7% 9% 38%	6780
	11th to 20th	Day	8% 9% 3 9% 6% 5% 5% 4 6% 7% 37%	7175
	21st to end	Day	12% 5% 2 5% 5% 5% 5% 5% 7% 10% 41%	8409
June	1st to 10th	Day	13% 10% 3 9% 5% 5% 5% 4 6% 7% 32%	3400
	11th to 20th	Day	12% 6% 2 8% 6% 6% 5% 4 6% 7% 37%	3400
	21st to end	Day	7% 6% 2 7% 6% 6% 7% 5% 7% 8% 40%	3400
July	1st to 10th	Day	8% 5% 3 8% 6% 6% 6% 5% 8% 10% 34%	7700
	11th to 20th	Day	9% 5% 2 6% 4 5% 5% 4 6% 7% 47%	7700
	21st to end	Day	9% 5% 2 6% 4 5% 6% 4 7% 10% 42%	7984
August	1st to 10th	Day	7% 4 2 6% 5% 5% 5% 3 5% 7% 51%	4870
	11th to 20th	Day	13% 8% 3 8% 5% 5% 4 4 6% 6% 38%	4775
	21st to end	Day	15% 7% 3 8% 5% 6% 6% 5% 7% 9% 30%	4677
September	1st to 10th	Day	15% 8% 3 8% 5% 5% 5% 5% 7% 8% 32%	2600
	11th to 20th	Day	14% 10% 4 9% 5% 5% 4 4 5% 7% 32%	2285
	21st to end	Day	16% 12% 4 8% 5% 5% 5% 4 6% 7% 30%	2195
October	1st to 10th	Day	11% 19% 5% 7% 5% 5% 3 3 6% 7% 30%	3179
	11th to 20th	Day	14% 16% 5% 10% 5% 4 4 3 6% 7% 27%	2811
	21st to end	Day	8% 19% 10% 15% 6% 5% 5% 4 5% 6% 18%	2754
November	1st to 10th	Day	15% 19% 7% 15% 5% 6% 5% 3 4 4 18%	1412
	11th to 20th	Day	10% 19% 7% 20% 10% 10% 3 3 3 3 11%	1215
	21st to end	Day	9% 19% 7% 18% 9% 8% 6% 3 4 4 13%	1119
December	1st to 10th	Day	5% 18% 8% 19% 11% 11% 6% 5% 4 4 10%	1630
	11th to 20th	Day	7% 15% 6% 16% 10% 5% 8% 6% 6% 10% 11%	1879
	21st to end	Day	5% 14% 5% 17% 9% 7% 7% 4 6% 6% 20%	2486
January	1st to 10th	Night	4 14% 8% 19% 12% 10% 10% 6% 6% 4 9%	7686
	11th to 20th	Night	4 8% 4 13% 8% 7% 12% 7% 9% 6% 22%	7538
	21st to end	Night	8% 17% 7% 15% 8% 7% 6% 6% 7% 5% 14%	7716
February	1st to 10th	Night	3 8% 4 14% 10% 10% 10% 8% 7% 7% 19%	3000
	11th to 20th	Night	4 10% 5% 13% 8% 7% 6% 7% 7% 8% 26%	2697
	21st to end	Night	3 11% 5% 14% 9% 8% 8% 4 8% 6% 24%	2145
March	1st to 10th	Night	3 11% 7% 16% 7% 8% 6% 6% 8% 6% 24%	5592
	11th to 20th	Night	4 7% 3 12% 8% 7% 8% 5% 7% 8% 31%	5011
	21st to end	Night	2 6% 4 9% 7% 6% 5% 4 6% 7% 45%	5377
April	1st to 10th	Night	8% 13% 4 9% 4 4 5% 4 5% 7% 36%	1800
	11th to 20th	Night	5% 9% 4 7% 6% 4 4 4 6% 10% 41%	1776
	21st to end	Night	7% 9% 3 8% 6% 6% 5% 5% 8% 9% 35%	1462
May	1st to 10th	Night	8% 7% 4 8% 6% 6% 5% 5% 7% 8% 35%	3180
	11th to 20th	Night	8% 9% 3 9% 6% 6% 7% 5% 6% 8% 34%	2718
	21st to end	Night	12% 6% 3 8% 6% 5% 4 3 7% 9% 37%	2466
June	1st to 10th	Night	16% 8% 3 8% 6% 5% 5% 5% 6% 8% 30%	1000
	11th to 20th	Night	11% 6% 3 8% 4 5% 6% 5% 7% 7% 40%	1000
	21st to end	Night	5% 4 2 7% 5% 6% 6% 6% 10% 7% 42%	1000
July	1st to 10th	Night	12% 6% 2 7% 5% 5% 5% 6% 7% 9% 35%	2260
	11th to 20th	Night	8% 4 2 4 4 5% 5% 4 6% 10% 49%	2260
	21st to end	Night	8% 5% 2 5% 4 5% 5% 4 9% 10% 43%	2844
August	1st to 10th	Night	9% 6% 2 6% 3 4 4 3 5% 6% 52%	2280
	11th to 20th	Night	12% 5% 2 7% 5% 6% 5% 4 6% 8% 40%	2270
	21st to end	Night	16% 7% 3 8% 6% 5% 5% 4 6% 7% 33%	3232
September	1st to 10th	Night	14% 8% 3 7% 5% 5% 5% 3 7% 8% 33%	1800
	11th to 20th	Night	17% 8% 2 7% 5% 4 4 3 6% 7% 36%	2113
	21st to end	Night	13% 11% 3 7% 4 5% 5% 4 6% 8% 32%	2205
October	1st to 10th	Night	11% 17% 4 9% 5% 5% 5% 4 6% 7% 28%	3856
	11th to 20th	Night	13% 16% 6% 9% 5% 5% 5% 4 5% 7% 25%	4086
	21st to end	Night	12% 21% 8% 15% 7% 6% 5% 3 4 5% 14%	4804
November	1st to 10th	Night	12% 18% 7% 17% 8% 5% 4 3 4 5% 16%	2882
	11th to 20th	Night	11% 17% 8% 18% 11% 8% 5% 4 4 4 12%	3185
	21st to end	Night	8% 18% 7% 17% 11% 9% 6% 5% 4 4 10%	3280
December	1st to 10th	Night	8% 18% 8% 19% 9% 7% 8% 6% 5% 3 7%	5550
	11th to 20th	Night	5% 13% 6% 16% 8% 9% 9% 6% 7% 8% 12%	6313
	21st to end	Night	5% 15% 5% 14% 8% 7% 6% 5% 5% 5% 25%	8470

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	57% 28% 7% 7% 1	2259
	11th to 20th	Day	42% 30% 7% 17% 4	2375
	21st to end	Day	50% 30% 8% 10% 2	3240
February	1st to 10th	Day	26% 63% 3 5% 3	1410
	11th to 20th	Day	22% 63% 5% 8% 1	1603
	21st to end	Day	25% 62% 2 7% 4	1485
March	1st to 10th	Day	43% 30% 8% 12% 7%	4289
	11th to 20th	Day	38% 30% 5% 15% 11%	4989
	21st to end	Day	28% 29% 7% 16% 20%	5595
April	1st to 10th	Day	18% 62% 5% 9% 7%	2600
	11th to 20th	Day	16% 63% 5% 9% 7%	2575
	21st to end	Day	17% 63% 4 13% 3	2935
May	1st to 10th	Day	27% 31% 10% 16% 15% 1	6780
	11th to 20th	Day	31% 30% 8% 20% 11%	7179
	21st to end	Day	26% 31% 10% 22% 10% 1	8410
June	1st to 10th	Day	22% 63% 4 8% 3	3400
	11th to 20th	Day	17% 63% 3 11% 6%	3400
	21st to end	Day	16% 63% 6% 10% 5%	3400
July	1st to 10th	Day	32% 29% 16% 18% 5%	7616
	11th to 20th	Day	24% 27% 7% 34% 7% 1	7607
	21st to end	Day	26% 28% 13% 32% 2	7759
August	1st to 10th	Day	18% 37% 10% 24% 9% 1	4852
	11th to 20th	Day	26% 38% 7% 16% 12%	4820
	21st to end	Day	31% 39% 15% 13% 1	4676
September	1st to 10th	Day	22% 59% 10% 9% 1	2600
	11th to 20th	Day	21% 58% 9% 11% 2	2285
	21st to end	Day	22% 58% 7% 9% 4 1	2195
October	1st to 10th	Day	35% 38% 12% 14% 2	3179
	11th to 20th	Day	37% 38% 8% 15% 2	2811
	21st to end	Day	41% 39% 11% 9%	2754
November	1st to 10th	Day	32% 58% 6% 4 1	1412
	11th to 20th	Day	33% 58% 4 4 1	1215
	21st to end	Day	32% 58% 5% 4 1	1119
December	1st to 10th	Day	53% 36% 4 5% 1	1630
	11th to 20th	Day	47% 33% 5% 12% 4	1880
	21st to end	Day	46% 28% 9% 13% 3	2486
January	1st to 10th	Night	58% 28% 6% 7% 1	7686
	11th to 20th	Night	38% 28% 8% 21% 5%	7585
	21st to end	Night	51% 31% 7% 9% 2	7716
February	1st to 10th	Night	25% 63% 5% 6% 2	3000
	11th to 20th	Night	21% 62% 6% 9% 1	2699
	21st to end	Night	22% 62% 4 6% 4 1	2145
March	1st to 10th	Night	44% 30% 11% 11% 4	5592
	11th to 20th	Night	34% 31% 7% 15% 13%	5011
	21st to end	Night	24% 29% 6% 22% 19%	5377
April	1st to 10th	Night	16% 62% 4 11% 7%	1800
	11th to 20th	Night	16% 62% 4 10% 8%	1776
	21st to end	Night	16% 63% 4 14% 4	1462
May	1st to 10th	Night	34% 31% 8% 16% 10% 1	3180
	11th to 20th	Night	31% 32% 9% 19% 8% 1	2718
	21st to end	Night	34% 30% 6% 21% 8% 1	2466
June	1st to 10th	Night	23% 63% 4 8% 2	1000
	11th to 20th	Night	15% 62% 5% 12% 7%	1000
	21st to end	Night	16% 64% 6% 8% 7%	1000
July	1st to 10th	Night	33% 28% 14% 21% 4	2235
	11th to 20th	Night	21% 27% 11% 32% 9%	2230
	21st to end	Night	25% 28% 15% 31% 1	2764
August	1st to 10th	Night	19% 37% 8% 24% 12%	2273
	11th to 20th	Night	23% 38% 8% 17% 13% 1	2291
	21st to end	Night	33% 38% 15% 12% 2	3232
September	1st to 10th	Night	22% 59% 8% 9% 2	1800
	11th to 20th	Night	17% 58% 9% 14% 2	2113
	21st to end	Night	19% 59% 10% 8% 4	2205
October	1st to 10th	Night	39% 38% 9% 14%	3856
	11th to 20th	Night	40% 39% 10% 10% 1	4086
	21st to end	Night	48% 39% 6% 6% 1	4804
November	1st to 10th	Night	32% 56% 5% 6%	2882
	11th to 20th	Night	34% 58% 4 4 1	3185
	21st to end	Night	33% 59% 4 4 1	3280
December	1st to 10th	Night	55% 36% 4 4 1	5550
	11th to 20th	Night	47% 33% 5% 13% 2	6311
	21st to end	Night	42% 29% 16% 10% 3	8470

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	8% 13% 35% 30% 14% 2	200
	11th to 20th	Day	14% 11% 30% 30% 14% 3	200
	21st to end	Day	17% 13% 36% 21% 9% 4	220
February	1st to 10th	Day	10% 8% 39% 26% 13% 6%	200
	11th to 20th	Day	6% 9% 40% 27% 16% 3	217
	21st to end	Day	5% 10% 29% 35% 16% 4	249
March	1st to 10th	Day	8% 10% 37% 28% 13% 5%	395
	11th to 20th	Day	10% 12% 36% 31% 9% 2	500
	21st to end	Day	9% 12% 36% 26% 12% 5%	550
April	1st to 10th	Day	16% 14% 36% 20% 11% 2	500
	11th to 20th	Day	11% 11% 35% 28% 10% 5%	497
	21st to end	Day	14% 10% 30% 30% 14% 2	700
May	1st to 10th	Day	17% 11% 29% 28% 13% 1	703
	11th to 20th	Day	13% 11% 26% 30% 16% 4	758
	21st to end	Day	12% 10% 30% 32% 13% 2	1006
June	1st to 10th	Day	22% 10% 28% 28% 9% 2	930
	11th to 20th	Day	16% 9% 28% 27% 16% 3	930
	21st to end	Day	8% 7% 23% 36% 21% 5%	930
July	1st to 10th	Day	15% 8% 23% 35% 14% 5%	916
	11th to 20th	Day	12% 6% 19% 36% 22% 5%	912
	21st to end	Day	12% 6% 21% 31% 25% 6%	968
August	1st to 10th	Day	12% 6% 20% 29% 25% 8%	726
	11th to 20th	Day	21% 8% 24% 31% 14% 2	708
	21st to end	Day	18% 8% 22% 32% 17% 3	583
September	1st to 10th	Day	22% 12% 30% 21% 11% 4	530
	11th to 20th	Day	18% 10% 28% 27% 15% 3	530
	21st to end	Day	20% 13% 32% 27% 6% 1	525
October	1st to 10th	Day	27% 9% 29% 21% 9% 5%	309
	11th to 20th	Day	23% 13% 35% 20% 7% 2	300
	21st to end	Day	19% 13% 36% 22% 8% 2	330
November	1st to 10th	Day	19% 12% 38% 17% 13% 2	220
	11th to 20th	Day	21% 10% 40% 20% 8% 3	200
	21st to end	Day	17% 8% 36% 23% 14% 2	200
December	1st to 10th	Day	14% 5% 32% 34% 13% 3	200
	11th to 20th	Day	14% 8% 32% 30% 13% 5%	200
	21st to end	Day	5% 7% 31% 32% 14% 10%	220
January	1st to 10th	Night	12% 9% 31% 32% 14% 3	1100
	11th to 20th	Night	13% 9% 33% 32% 12% 1	1100
	21st to end	Night	16% 12% 32% 27% 10% 2	1157
February	1st to 10th	Night	7% 9% 36% 31% 14% 5%	1000
	11th to 20th	Night	8% 8% 35% 34% 13% 2	790
	21st to end	Night	7% 8% 33% 33% 16% 1	660
March	1st to 10th	Night	7% 8% 28% 34% 18% 4	800
	11th to 20th	Night	12% 9% 32% 35% 12% 1	800
	21st to end	Night	6% 7% 33% 35% 18% 2	870
April	1st to 10th	Night	14% 10% 33% 29% 12% 2	600
	11th to 20th	Night	9% 7% 34% 33% 16% 1	593
	21st to end	Night	11% 7% 32% 34% 14% 2	462
May	1st to 10th	Night	11% 9% 33% 34% 13% 1	400
	11th to 20th	Night	12% 7% 35% 31% 14% 1	394
	21st to end	Night	13% 6% 32% 34% 14% 2	433
June	1st to 10th	Night	19% 10% 28% 28% 13% 3	400
	11th to 20th	Night	13% 4 24% 39% 21% 1	400
	21st to end	Night	6% 3 24% 38% 27% 2	400
July	1st to 10th	Night	11% 7% 19% 36% 22% 4	390
	11th to 20th	Night	11% 2 18% 41% 25% 3	388
	21st to end	Night	8% 3 17% 37% 30% 5%	438
August	1st to 10th	Night	13% 4 16% 40% 22% 6%	398
	11th to 20th	Night	17% 5% 23% 36% 18% 2	396
	21st to end	Night	17% 4 26% 34% 16% 3	647
September	1st to 10th	Night	18% 8% 25% 31% 17% 3	600
	11th to 20th	Night	22% 5% 23% 34% 13% 3	713
	21st to end	Night	19% 8% 32% 29% 11% 1	800
October	1st to 10th	Night	22% 10% 28% 27% 10% 3	772
	11th to 20th	Night	22% 7% 31% 27% 11% 2	760
	21st to end	Night	22% 12% 26% 26% 12% 2	1045
November	1st to 10th	Night	17% 9% 30% 27% 15% 2	975
	11th to 20th	Night	19% 10% 32% 26% 11% 3	1000
	21st to end	Night	17% 11% 32% 25% 13% 2	1040
December	1st to 10th	Night	15% 8% 31% 33% 11% 2	1100
	11th to 20th	Night	12% 10% 35% 28% 12% 3	1100
	21st to end	Night	12% 8% 30% 26% 19% 5%	1210

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