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Blackfoot
Clear Sky Chart
History

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

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% 3 9% 6% 5% 5% 4 6% 8% 35%	105716
	Night	8% 9% 4 10% 6% 6% 5% 5% 6% 8% 34%	101910
Transparency	Day	45% 7% 17% 23% 8%	105459
	Night	46% 7% 17% 22% 9% 1	101813
Seeing	Day	12% 6% 25% 31% 19% 6%	15502
	Night	12% 6% 29% 36% 16% 2	24464

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	4 11% 5% 13% 9% 6% 6% 5% 6% 8% 26%	2219
	11th to 20th	Day	4 9% 3 9% 7% 7% 7% 7% 9% 10% 28%	2199
	21st to end	Day	6% 12% 4 10% 7% 6% 4 3 5% 7% 36%	2573
February	1st to 10th	Day	8% 14% 6% 11% 9% 7% 5% 4 6% 7% 24%	1520
	11th to 20th	Day	5% 13% 6% 12% 6% 5% 7% 5% 7% 7% 27%	1636
	21st to end	Day	4 12% 5% 11% 8% 6% 8% 5% 6% 8% 27%	1436
March	1st to 10th	Day	4 11% 6% 13% 8% 6% 6% 5% 6% 9% 26%	3138
	11th to 20th	Day	4 12% 5% 9% 5% 4 4 3 5% 11% 38%	3489
	21st to end	Day	8% 13% 6% 18% 7% 5% 4 3 5% 6% 25%	3825
April	1st to 10th	Day	9% 13% 4 8% 5% 6% 6% 5% 7% 7% 30%	2399
	11th to 20th	Day	12% 12% 4 8% 6% 5% 5% 4 6% 7% 31%	2440
	21st to end	Day	12% 11% 3 8% 5% 5% 5% 4 6% 8% 32%	2470
May	1st to 10th	Day	15% 10% 3 9% 6% 5% 5% 4 5% 6% 31%	4631
	11th to 20th	Day	12% 11% 3 8% 6% 5% 6% 5% 6% 7% 30%	4694
	21st to end	Day	12% 10% 4 9% 6% 6% 5% 4 7% 9% 29%	5161
June	1st to 10th	Day	14% 8% 4 9% 6% 5% 6% 5% 5% 8% 31%	2850
	11th to 20th	Day	17% 11% 3 10% 6% 6% 5% 5% 6% 8% 23%	2850
	21st to end	Day	11% 6% 2 7% 5% 5% 6% 4 8% 9% 36%	2850
July	1st to 10th	Day	7% 5% 2 6% 5% 5% 5% 4 6% 8% 47%	4740
	11th to 20th	Day	8% 5% 2 6% 5% 5% 4 4 7% 8% 46%	4740
	21st to end	Day	10% 6% 3 6% 4 4 4 4 6% 8% 44%	5138
August	1st to 10th	Day	11% 6% 2 6% 4 5% 5% 4 7% 9% 40%	4572
	11th to 20th	Day	8% 5% 2 6% 4 5% 5% 5% 8% 10% 43%	4115
	21st to end	Day	10% 5% 2 6% 4 4 4 4 7% 9% 44%	4521
September	1st to 10th	Day	11% 6% 1 6% 5% 5% 5% 4 6% 8% 42%	2426
	11th to 20th	Day	14% 7% 3 7% 4 4 5% 3 5% 8% 41%	2090
	21st to end	Day	8% 7% 2 7% 5% 5% 5% 4 6% 9% 43%	2090
October	1st to 10th	Day	10% 7% 4 10% 6% 5% 5% 3 6% 7% 39%	3248
	11th to 20th	Day	10% 9% 3 7% 5% 5% 4 3 6% 9% 38%	2936
	21st to end	Day	7% 11% 4 8% 5% 5% 5% 4 6% 7% 38%	3013
November	1st to 10th	Day	8% 14% 6% 10% 6% 6% 5% 4 6% 8% 27%	1528
	11th to 20th	Day	6% 11% 5% 15% 7% 6% 5% 4 5% 7% 29%	1395
	21st to end	Day	4 11% 5% 13% 8% 5% 4 4 6% 8% 32%	1330
December	1st to 10th	Day	5% 13% 5% 9% 10% 8% 6% 5% 6% 8% 26%	1330
	11th to 20th	Day	6% 10% 4 12% 7% 7% 6% 4 8% 9% 26%	1682
	21st to end	Day	3 8% 3 9% 6% 5% 5% 4 5% 8% 43%	2442
January	1st to 10th	Night	4 10% 5% 15% 9% 7% 7% 5% 7% 8% 24%	4726
	11th to 20th	Night	3 7% 3 10% 9% 7% 6% 6% 7% 7% 34%	4699
	21st to end	Night	5% 13% 4 11% 6% 5% 5% 4 6% 7% 32%	5114
February	1st to 10th	Night	6% 10% 4 14% 8% 9% 6% 4 6% 7% 26%	2660
	11th to 20th	Night	5% 12% 4 10% 7% 6% 7% 5% 7% 8% 30%	2431
	21st to end	Night	4 10% 5% 12% 7% 6% 6% 5% 7% 8% 30%	2017
March	1st to 10th	Night	4 12% 6% 12% 7% 5% 5% 5% 8% 10% 27%	3736
	11th to 20th	Night	5% 8% 3 12% 6% 4 5% 4 6% 10% 37%	3490
	21st to end	Night	6% 12% 6% 16% 7% 6% 5% 5% 6% 8% 22%	3813
April	1st to 10th	Night	7% 11% 3 8% 6% 7% 6% 5% 7% 7% 34%	1781
	11th to 20th	Night	10% 11% 5% 10% 7% 6% 6% 5% 6% 6% 29%	1691
	21st to end	Night	13% 10% 3 8% 5% 5% 4 5% 6% 7% 35%	1710
May	1st to 10th	Night	23% 9% 3 8% 6% 5% 5% 4 5% 4 29%	2327
	11th to 20th	Night	12% 11% 3 9% 7% 6% 5% 5% 6% 7% 30%	2199
	21st to end	Night	13% 10% 3 7% 6% 7% 6% 4 7% 9% 28%	2414
June	1st to 10th	Night	15% 8% 4 8% 6% 5% 6% 5% 7% 7% 30%	1330
	11th to 20th	Night	16% 9% 3 9% 7% 7% 6% 5% 6% 8% 24%	1330
	21st to end	Night	10% 6% 3 7% 4 6% 5% 5% 7% 10% 38%	1330
July	1st to 10th	Night	8% 5% 3 8% 5% 5% 6% 5% 7% 7% 43%	2220
	11th to 20th	Night	8% 6% 2 6% 5% 5% 5% 5% 7% 10% 42%	2220
	21st to end	Night	12% 6% 2 5% 3 4 4 4 6% 10% 44%	2414
August	1st to 10th	Night	13% 6% 2 5% 5% 4 5% 4 6% 7% 43%	2355
	11th to 20th	Night	10% 8% 2 6% 5% 4 5% 4 6% 8% 41%	2720
	21st to end	Night	10% 6% 2 5% 5% 4 4 4 6% 9% 44%	3146
September	1st to 10th	Night	11% 5% 3 7% 4 4 4 3 5% 8% 46%	1752
	11th to 20th	Night	12% 7% 2 6% 3 3 4 4 5% 8% 46%	2090
	21st to end	Night	8% 6% 2 7% 5% 4 4 4 6% 9% 44%	2090
October	1st to 10th	Night	7% 7% 3 8% 5% 5% 5% 4 6% 9% 41%	3723
	11th to 20th	Night	9% 7% 3 7% 4 5% 5% 5% 7% 9% 40%	3988
	21st to end	Night	6% 9% 3 10% 5% 6% 5% 4 7% 9% 38%	4514
November	1st to 10th	Night	11% 16% 5% 9% 7% 5% 5% 4 5% 7% 27%	2673
	11th to 20th	Night	7% 14% 6% 11% 8% 7% 5% 4 5% 7% 28%	2783
	21st to end	Night	5% 11% 5% 12% 8% 5% 6% 5% 6% 7% 29%	2850
December	1st to 10th	Night	7% 13% 4 12% 9% 6% 5% 5% 6% 7% 27%	2850
	11th to 20th	Night	5% 12% 5% 14% 7% 7% 6% 5% 7% 8% 25%	3510
	21st to end	Night	3 7% 3 8% 6% 6% 6% 4 6% 8% 43%	5214

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	55% 8% 13% 20% 4 1	2219
	11th to 20th	Day	46% 6% 14% 17% 16% 1	2220
	21st to end	Day	47% 6% 18% 23% 5%	2573
February	1st to 10th	Day	58% 5% 15% 14% 8%	1520
	11th to 20th	Day	52% 8% 17% 16% 8%	1645
	21st to end	Day	52% 7% 12% 20% 8%	1436
March	1st to 10th	Day	52% 7% 15% 19% 7%	3138
	11th to 20th	Day	41% 8% 21% 21% 10%	3490
	21st to end	Day	57% 8% 12% 19% 4	3825
April	1st to 10th	Day	49% 8% 16% 18% 8% 1	2399
	11th to 20th	Day	49% 7% 14% 21% 9%	2440
	21st to end	Day	47% 7% 15% 22% 7% 1	2470
May	1st to 10th	Day	52% 7% 11% 25% 6%	4631
	11th to 20th	Day	47% 9% 11% 24% 9% 1	4698
	21st to end	Day	47% 8% 19% 18% 8%	5162
June	1st to 10th	Day	49% 7% 14% 21% 9% 1	2850
	11th to 20th	Day	55% 9% 15% 16% 4	2850
	21st to end	Day	40% 10% 20% 21% 8% 1	2850
July	1st to 10th	Day	34% 5% 18% 30% 11% 1	4666
	11th to 20th	Day	34% 7% 18% 29% 13%	4659
	21st to end	Day	37% 6% 22% 25% 10%	4976
August	1st to 10th	Day	40% 6% 19% 33% 2	4554
	11th to 20th	Day	35% 6% 24% 27% 8%	4156
	21st to end	Day	36% 5% 27% 27% 4 1	4520
September	1st to 10th	Day	37% 8% 20% 26% 7% 2	2426
	11th to 20th	Day	41% 5% 19% 28% 7%	2090
	21st to end	Day	37% 8% 18% 26% 8% 2	2090
October	1st to 10th	Day	45% 3 22% 24% 5%	3248
	11th to 20th	Day	44% 4 15% 28% 10%	2936
	21st to end	Day	45% 5% 18% 28% 4	3013
November	1st to 10th	Day	54% 8% 16% 16% 6% 1	1528
	11th to 20th	Day	54% 6% 17% 19% 4	1395
	21st to end	Day	49% 8% 18% 19% 5% 1	1330
December	1st to 10th	Day	55% 9% 11% 16% 8% 1	1330
	11th to 20th	Day	50% 7% 19% 17% 7%	1684
	21st to end	Day	39% 5% 11% 29% 14% 2	2442
January	1st to 10th	Night	55% 8% 14% 16% 6% 1	4726
	11th to 20th	Night	45% 8% 14% 18% 13% 1	4740
	21st to end	Night	49% 6% 18% 20% 7%	5114
February	1st to 10th	Night	55% 7% 14% 16% 8% 1	2660
	11th to 20th	Night	49% 7% 15% 17% 11% 1	2432
	21st to end	Night	48% 6% 14% 22% 9% 1	2017
March	1st to 10th	Night	49% 7% 16% 20% 8%	3736
	11th to 20th	Night	40% 6% 22% 20% 11% 1	3490
	21st to end	Night	55% 9% 13% 17% 5%	3813
April	1st to 10th	Night	44% 8% 15% 19% 12% 1	1781
	11th to 20th	Night	51% 7% 12% 18% 9% 2	1691
	21st to end	Night	45% 7% 13% 21% 12% 2	1710
May	1st to 10th	Night	55% 5% 9% 23% 7% 1	2327
	11th to 20th	Night	48% 9% 12% 21% 10% 1	2199
	21st to end	Night	49% 10% 17% 17% 8% 1	2414
June	1st to 10th	Night	49% 7% 14% 21% 9% 1	1330
	11th to 20th	Night	56% 8% 13% 17% 5%	1330
	21st to end	Night	39% 10% 23% 21% 6% 1	1330
July	1st to 10th	Night	39% 6% 17% 20% 17% 1	2185
	11th to 20th	Night	37% 5% 16% 31% 10% 1	2178
	21st to end	Night	35% 5% 23% 29% 8%	2337
August	1st to 10th	Night	39% 6% 21% 31% 2	2348
	11th to 20th	Night	40% 4 23% 24% 9%	2745
	21st to end	Night	35% 5% 24% 30% 6%	3146
September	1st to 10th	Night	35% 7% 19% 26% 11% 2	1752
	11th to 20th	Night	36% 6% 17% 29% 10% 2	2090
	21st to end	Night	35% 8% 15% 26% 13% 2	2090
October	1st to 10th	Night	40% 3 21% 29% 7%	3723
	11th to 20th	Night	39% 4 14% 35% 7%	3988
	21st to end	Night	42% 4 22% 25% 5% 1	4514
November	1st to 10th	Night	56% 7% 12% 19% 6%	2673
	11th to 20th	Night	55% 7% 13% 18% 6% 1	2783
	21st to end	Night	51% 8% 16% 18% 6% 1	2850
December	1st to 10th	Night	54% 6% 12% 17% 9% 1	2850
	11th to 20th	Night	55% 8% 16% 15% 6%	3507
	21st to end	Night	38% 5% 18% 19% 17% 3	5214

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	10% 3 28% 35% 20% 3	180
	11th to 20th	Day	9% 8% 28% 34% 16% 4	180
	21st to end	Day	9% 8% 33% 31% 15% 5%	198
February	1st to 10th	Day	7% 12% 28% 38% 12% 3	180
	11th to 20th	Day	9% 6% 29% 35% 18% 3	256
	21st to end	Day	7% 4 32% 31% 17% 8%	248
March	1st to 10th	Day	8% 8% 28% 34% 18% 3	460
	11th to 20th	Day	9% 5% 31% 33% 16% 7%	460
	21st to end	Day	12% 5% 26% 34% 17% 5%	506
April	1st to 10th	Day	10% 8% 31% 32% 15% 3	460
	11th to 20th	Day	15% 8% 19% 34% 18% 7%	452
	21st to end	Day	17% 7% 24% 31% 16% 5%	460
May	1st to 10th	Day	14% 9% 23% 31% 19% 5%	641
	11th to 20th	Day	11% 5% 25% 32% 21% 6%	675
	21st to end	Day	15% 6% 21% 29% 21% 8%	734
June	1st to 10th	Day	16% 8% 25% 30% 17% 4	680
	11th to 20th	Day	20% 8% 21% 26% 16% 9%	680
	21st to end	Day	12% 5% 19% 30% 23% 11%	680
July	1st to 10th	Day	10% 3 17% 32% 28% 10%	671
	11th to 20th	Day	10% 4 21% 30% 26% 9%	668
	21st to end	Day	9% 4 18% 32% 25% 11%	739
August	1st to 10th	Day	11% 3 19% 29% 25% 13%	593
	11th to 20th	Day	8% 4 24% 32% 24% 7%	477
	21st to end	Day	12% 7% 20% 29% 23% 9%	539
September	1st to 10th	Day	12% 7% 28% 27% 19% 6%	490
	11th to 20th	Day	18% 7% 23% 30% 18% 4	490
	21st to end	Day	11% 14% 32% 26% 15% 3	490
October	1st to 10th	Day	14% 7% 33% 25% 16% 5%	352
	11th to 20th	Day	15% 7% 29% 32% 15% 2	300
	21st to end	Day	14% 10% 38% 24% 12% 3	330
November	1st to 10th	Day	16% 4 32% 34% 12% 2	285
	11th to 20th	Day	11% 6% 38% 31% 12% 1	210
	21st to end	Day	4 7% 43% 29% 12% 4	180
December	1st to 10th	Day	11% 6% 33% 31% 13% 6%	180
	11th to 20th	Day	7% 9% 31% 33% 18% 1	180
	21st to end	Day	7% 5% 25% 40% 18% 5%	198
January	1st to 10th	Night	9% 6% 35% 35% 13% 2	950
	11th to 20th	Night	9% 8% 36% 33% 13% 1	950
	21st to end	Night	12% 9% 35% 31% 11% 2	984
February	1st to 10th	Night	9% 8% 28% 35% 18% 3	760
	11th to 20th	Night	9% 5% 34% 36% 15% 1	744
	21st to end	Night	6% 5% 29% 36% 18% 6%	628
March	1st to 10th	Night	9% 6% 28% 40% 15% 3	760
	11th to 20th	Night	11% 4 30% 37% 14% 3	760
	21st to end	Night	12% 6% 26% 36% 16% 3	836
April	1st to 10th	Night	10% 6% 27% 35% 19% 3	641
	11th to 20th	Night	13% 6% 29% 34% 17% 1	563
	21st to end	Night	15% 7% 24% 37% 16% 1	570
May	1st to 10th	Night	16% 7% 21% 35% 18% 3	437
	11th to 20th	Night	11% 5% 24% 39% 19% 3	374
	21st to end	Night	20% 6% 18% 34% 19% 2	411
June	1st to 10th	Night	17% 7% 22% 38% 14% 2	380
	11th to 20th	Night	22% 6% 19% 32% 21% 1	380
	21st to end	Night	11% 5% 17% 37% 26% 4	380
July	1st to 10th	Night	12% 2 16% 42% 26% 1	370
	11th to 20th	Night	10% 3 19% 44% 22% 2	368
	21st to end	Night	10% 2 19% 39% 27% 3	416
August	1st to 10th	Night	11% 3 16% 33% 31% 5%	378
	11th to 20th	Night	11% 4 17% 40% 25% 3	509
	21st to end	Night	12% 3 21% 39% 24% 1	627
September	1st to 10th	Night	12% 4 21% 36% 26% 2	579
	11th to 20th	Night	14% 4 22% 41% 18% 1	760
	21st to end	Night	11% 6% 29% 39% 14% 2	760
October	1st to 10th	Night	14% 5% 28% 38% 14% 1	760
	11th to 20th	Night	14% 5% 31% 36% 12% 1	760
	21st to end	Night	12% 8% 34% 34% 11%	869
November	1st to 10th	Night	18% 7% 33% 32% 9% 2	955
	11th to 20th	Night	12% 8% 35% 31% 11% 3	950
	21st to end	Night	8% 7% 39% 33% 11% 1	950
December	1st to 10th	Night	12% 9% 33% 30% 13% 3	950
	11th to 20th	Night	10% 8% 33% 35% 12% 2	950
	21st to end	Night	9% 5% 31% 35% 16% 3	1045

Page generated at 2024-11-03 11:18:59. Version ac07

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