Ashcroft
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Ashcroft clear sky chart from 2005-11-06 to 2026-10-14.

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	5% 7% 3 8% 6% 6% 6% 5% 7% 9% 38%	153438
	Night	5% 9% 4 9% 6% 6% 6% 5% 7% 8% 35%	146984
Transparency	Day	41% 9% 17% 22% 10% 2	153148
	Night	43% 11% 16% 20% 9% 1	146856
Seeing	Day	11% 14% 30% 27% 15% 4	18214
	Night	10% 7% 28% 34% 18% 2	26344

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% 13% 5% 14% 8% 8% 8% 6% 8% 8% 17%	4125
	11th to 20th	Day	5% 7% 4 8% 5% 5% 5% 5% 10% 11% 33%	4137
	21st to end	Day	3 14% 6% 11% 7% 7% 6% 5% 8% 9% 24%	5186
February	1st to 10th	Day	6% 13% 5% 10% 6% 8% 7% 6% 7% 8% 23%	1775
	11th to 20th	Day	4 11% 4 9% 6% 6% 7% 5% 8% 9% 30%	1845
	21st to end	Day	2 12% 4 12% 9% 9% 7% 6% 8% 7% 23%	1624
March	1st to 10th	Day	1 8% 4 9% 6% 7% 7% 6% 9% 10% 32%	4618
	11th to 20th	Day	1 6% 3 8% 7% 7% 9% 7% 9% 10% 34%	5052
	21st to end	Day	3 10% 4 10% 8% 7% 8% 6% 8% 10% 26%	5912
April	1st to 10th	Day	4 10% 5% 9% 8% 6% 8% 6% 8% 9% 27%	2520
	11th to 20th	Day	5% 10% 5% 10% 8% 7% 6% 5% 8% 8% 29%	2541
	21st to end	Day	5% 11% 4 10% 7% 6% 5% 5% 7% 9% 31%	2908
May	1st to 10th	Day	5% 7% 3 7% 4 5% 5% 4 6% 8% 47%	8195
	11th to 20th	Day	7% 9% 3 11% 7% 7% 7% 5% 8% 9% 26%	8160
	21st to end	Day	8% 9% 3 9% 6% 6% 7% 5% 7% 9% 31%	9163
June	1st to 10th	Day	11% 9% 3 9% 7% 6% 6% 4 7% 7% 30%	3286
	11th to 20th	Day	13% 9% 3 9% 8% 7% 6% 5% 7% 7% 26%	3360
	21st to end	Day	6% 6% 3 9% 7% 7% 7% 5% 7% 8% 36%	3326
July	1st to 10th	Day	3 4 2 6% 5% 5% 5% 5% 6% 9% 51%	8820
	11th to 20th	Day	3 3 1 4 3 4 4 4 6% 8% 59%	8820
	21st to end	Day	3 3 1 4 4 4 5% 4 6% 8% 57%	9036
August	1st to 10th	Day	3 2 1 4 3 3 4 4 6% 9% 61%	6441
	11th to 20th	Day	2 2 1 5% 5% 5% 7% 6% 9% 11% 46%	6195
	21st to end	Day	6% 4 2 7% 5% 5% 5% 5% 8% 9% 43%	6327
September	1st to 10th	Day	6% 5% 2 6% 4 4 4 3 6% 8% 52%	2520
	11th to 20th	Day	8% 6% 3 7% 4 5% 5% 4 6% 7% 45%	2520
	21st to end	Day	8% 7% 2 8% 5% 6% 6% 4 6% 8% 39%	2237
October	1st to 10th	Day	5% 7% 3 8% 5% 6% 5% 4 7% 7% 43%	3380
	11th to 20th	Day	9% 8% 3 7% 4 6% 6% 5% 8% 8% 37%	3273
	21st to end	Day	5% 9% 3 7% 6% 6% 6% 5% 9% 9% 35%	3187
November	1st to 10th	Day	7% 12% 5% 10% 7% 6% 6% 5% 6% 7% 29%	1648
	11th to 20th	Day	4 10% 4 9% 7% 6% 6% 6% 7% 8% 33%	1680
	21st to end	Day	5% 12% 5% 11% 8% 7% 6% 5% 8% 10% 24%	1634
December	1st to 10th	Day	4 12% 5% 10% 7% 6% 10% 9% 10% 8% 20%	2310
	11th to 20th	Day	6% 16% 7% 13% 8% 7% 8% 6% 6% 5% 17%	2322
	21st to end	Day	3 11% 5% 13% 9% 9% 9% 6% 8% 7% 20%	3355
January	1st to 10th	Night	5% 16% 7% 15% 8% 8% 8% 6% 8% 7% 13%	8770
	11th to 20th	Night	5% 9% 3 10% 6% 5% 5% 5% 9% 9% 34%	8746
	21st to end	Night	4 11% 5% 11% 7% 7% 8% 5% 8% 8% 27%	8994
February	1st to 10th	Night	8% 12% 5% 12% 9% 7% 6% 5% 6% 7% 22%	2841
	11th to 20th	Night	5% 12% 3 8% 6% 6% 6% 5% 7% 8% 32%	2662
	21st to end	Night	3 13% 5% 12% 8% 7% 7% 5% 7% 8% 26%	2181
March	1st to 10th	Night	2 10% 4 9% 5% 6% 7% 6% 8% 10% 33%	5496
	11th to 20th	Night	1 6% 2 6% 5% 5% 6% 6% 9% 10% 43%	5165
	21st to end	Night	6% 10% 3 10% 7% 6% 7% 5% 8% 9% 30%	5305
April	1st to 10th	Night	3 9% 3 10% 7% 5% 7% 5% 7% 8% 35%	2100
	11th to 20th	Night	3 8% 4 8% 7% 6% 6% 6% 9% 9% 35%	2027
	21st to end	Night	5% 9% 4 8% 6% 4 6% 4 7% 10% 37%	1712
May	1st to 10th	Night	4 7% 3 8% 6% 5% 5% 3 5% 6% 48%	4724
	11th to 20th	Night	7% 8% 4 8% 6% 6% 6% 5% 8% 9% 32%	4700
	21st to end	Night	7% 8% 3 8% 6% 6% 6% 5% 8% 10% 34%	5003
June	1st to 10th	Night	11% 6% 3 8% 6% 5% 5% 5% 8% 8% 35%	1328
	11th to 20th	Night	9% 7% 3 7% 7% 6% 6% 6% 6% 9% 34%	1260
	21st to end	Night	5% 7% 2 7% 4 6% 6% 4 8% 8% 44%	1288
July	1st to 10th	Night	4 5% 2 6% 5% 5% 5% 4 6% 8% 49%	4140
	11th to 20th	Night	3 3 2 4 3 4 4 3 5% 6% 63%	4140
	21st to end	Night	3 3 1 5% 4 4 4 4 6% 9% 57%	5030
August	1st to 10th	Night	2 2 1 5% 3 3 4 4 6% 7% 64%	3709
	11th to 20th	Night	4 5% 2 7% 5% 6% 7% 5% 8% 10% 41%	3841
	21st to end	Night	6% 4 2 7% 4 5% 5% 5% 7% 8% 47%	4831
September	1st to 10th	Night	4 4 2 6% 4 4 5% 3 5% 8% 55%	2100
	11th to 20th	Night	7% 6% 2 5% 4 4 5% 4 6% 7% 49%	2100
	21st to end	Night	7% 7% 3 7% 4 4 5% 4 6% 8% 43%	2381
October	1st to 10th	Night	5% 7% 2 7% 5% 6% 6% 5% 7% 8% 42%	4040
	11th to 20th	Night	5% 7% 2 8% 5% 5% 6% 5% 8% 10% 38%	3950
	21st to end	Night	6% 8% 3 9% 7% 6% 6% 7% 9% 7% 32%	4600
November	1st to 10th	Night	8% 12% 4 10% 7% 6% 5% 5% 6% 8% 28%	2870
	11th to 20th	Night	5% 9% 4 10% 7% 6% 6% 6% 8% 8% 30%	2940
	21st to end	Night	6% 14% 5% 11% 7% 7% 6% 5% 8% 9% 22%	2961
December	1st to 10th	Night	4 11% 4 9% 7% 6% 9% 7% 9% 7% 26%	5074
	11th to 20th	Night	7% 15% 6% 15% 8% 7% 7% 6% 7% 7% 16%	6090
	21st to end	Night	5% 12% 5% 12% 8% 7% 8% 7% 7% 7% 21%	7885

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	56% 16% 11% 13% 3	4125
	11th to 20th	Day	40% 12% 17% 23% 5% 3	4158
	21st to end	Day	53% 11% 13% 18% 5%	5187
February	1st to 10th	Day	56% 11% 13% 10% 8% 1	1775
	11th to 20th	Day	47% 10% 16% 18% 8%	1854
	21st to end	Day	56% 10% 14% 13% 5% 1	1624
March	1st to 10th	Day	43% 10% 20% 18% 8%	4618
	11th to 20th	Day	41% 10% 20% 22% 6%	5052
	21st to end	Day	50% 11% 17% 14% 8%	5912
April	1st to 10th	Day	51% 12% 18% 15% 4	2520
	11th to 20th	Day	50% 10% 14% 16% 9% 1	2541
	21st to end	Day	49% 7% 15% 18% 9% 1	2908
May	1st to 10th	Day	34% 6% 14% 33% 12% 1	8195
	11th to 20th	Day	49% 9% 17% 20% 5%	8163
	21st to end	Day	45% 10% 18% 22% 4 1	9164
June	1st to 10th	Day	50% 8% 14% 16% 9% 3	3286
	11th to 20th	Day	55% 8% 14% 15% 8%	3360
	21st to end	Day	42% 8% 18% 18% 11% 2	3326
July	1st to 10th	Day	30% 6% 14% 23% 19% 7%	8746
	11th to 20th	Day	23% 6% 13% 28% 24% 5%	8739
	21st to end	Day	24% 6% 18% 31% 16% 4	8840
August	1st to 10th	Day	20% 6% 13% 34% 24% 4	6424
	11th to 20th	Day	28% 11% 25% 27% 8% 1	6237
	21st to end	Day	35% 9% 23% 27% 5% 1	6326
September	1st to 10th	Day	30% 8% 18% 28% 13% 3	2520
	11th to 20th	Day	38% 7% 14% 26% 13% 2	2520
	21st to end	Day	43% 9% 20% 18% 8% 1	2237
October	1st to 10th	Day	40% 8% 19% 24% 7% 1	3380
	11th to 20th	Day	44% 10% 16% 24% 6%	3273
	21st to end	Day	42% 11% 22% 22% 3	3187
November	1st to 10th	Day	55% 10% 13% 18% 4 1	1648
	11th to 20th	Day	47% 15% 15% 17% 6%	1680
	21st to end	Day	51% 15% 17% 12% 4 1	1634
December	1st to 10th	Day	53% 13% 20% 12% 1	2310
	11th to 20th	Day	62% 12% 11% 9% 5%	2324
	21st to end	Day	56% 17% 13% 12% 2	3355
January	1st to 10th	Night	60% 14% 12% 10% 4	8770
	11th to 20th	Night	45% 10% 15% 21% 6% 3	8787
	21st to end	Night	52% 12% 12% 16% 7%	8994
February	1st to 10th	Night	57% 12% 11% 13% 6% 1	2841
	11th to 20th	Night	48% 9% 17% 17% 8% 1	2664
	21st to end	Night	53% 10% 17% 14% 6%	2181
March	1st to 10th	Night	39% 11% 21% 21% 7%	5496
	11th to 20th	Night	33% 10% 21% 23% 12%	5166
	21st to end	Night	48% 11% 16% 16% 10%	5305
April	1st to 10th	Night	44% 11% 20% 19% 6%	2100
	11th to 20th	Night	43% 12% 16% 19% 11%	2027
	21st to end	Night	40% 10% 17% 20% 13% 1	1712
May	1st to 10th	Night	35% 9% 12% 32% 11% 1	4721
	11th to 20th	Night	42% 13% 15% 22% 8%	4700
	21st to end	Night	41% 12% 18% 22% 6%	5007
June	1st to 10th	Night	45% 8% 14% 19% 11% 3	1328
	11th to 20th	Night	45% 9% 15% 18% 12% 1	1260
	21st to end	Night	35% 8% 21% 21% 11% 3	1288
July	1st to 10th	Night	33% 8% 12% 22% 18% 7%	4105
	11th to 20th	Night	21% 6% 14% 27% 27% 5%	4098
	21st to end	Night	25% 8% 17% 27% 16% 7%	4921
August	1st to 10th	Night	19% 6% 11% 32% 27% 5%	3701
	11th to 20th	Night	34% 11% 21% 24% 9% 1	3865
	21st to end	Night	32% 7% 24% 28% 9% 1	4831
September	1st to 10th	Night	28% 7% 17% 29% 15% 3	2100
	11th to 20th	Night	34% 7% 17% 26% 14% 3	2100
	21st to end	Night	37% 10% 22% 19% 10% 2	2381
October	1st to 10th	Night	39% 8% 20% 25% 7%	4040
	11th to 20th	Night	43% 9% 16% 24% 8%	3950
	21st to end	Night	44% 9% 18% 25% 4	4600
November	1st to 10th	Night	53% 11% 16% 14% 5% 1	2870
	11th to 20th	Night	49% 16% 15% 14% 6% 1	2940
	21st to end	Night	55% 15% 15% 11% 4	2961
December	1st to 10th	Night	48% 12% 19% 18% 3	5074
	11th to 20th	Night	61% 13% 13% 9% 4	6087
	21st to end	Night	53% 14% 14% 15% 4	7885

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	7% 13% 35% 31% 9% 5%	220
	11th to 20th	Day	6% 11% 30% 35% 15% 3	220
	21st to end	Day	15% 8% 34% 28% 14% 1	242
February	1st to 10th	Day	8% 14% 44% 24% 7% 3	315
	11th to 20th	Day	10% 11% 36% 29% 13% 2	425
	21st to end	Day	9% 15% 40% 24% 10% 2	391
March	1st to 10th	Day	10% 18% 35% 24% 12% 1	540
	11th to 20th	Day	10% 19% 35% 21% 13% 2	540
	21st to end	Day	13% 22% 31% 23% 9% 2	594
April	1st to 10th	Day	13% 21% 29% 26% 9% 2	540
	11th to 20th	Day	15% 20% 29% 21% 13% 3	532
	21st to end	Day	13% 21% 28% 23% 12% 3	540
May	1st to 10th	Day	11% 19% 32% 25% 11% 2	543
	11th to 20th	Day	14% 11% 29% 28% 14% 4	568
	21st to end	Day	14% 16% 27% 29% 12% 3	670
June	1st to 10th	Day	14% 18% 31% 26% 10% 1	916
	11th to 20th	Day	16% 13% 27% 27% 14% 3	990
	21st to end	Day	10% 10% 27% 30% 20% 2	956
July	1st to 10th	Day	9% 11% 30% 31% 17% 2	771
	11th to 20th	Day	7% 13% 27% 30% 19% 5%	768
	21st to end	Day	5% 7% 24% 33% 25% 5%	662
August	1st to 10th	Day	7% 6% 20% 30% 29% 8%	567
	11th to 20th	Day	6% 9% 21% 31% 24% 9%	557
	21st to end	Day	7% 11% 25% 31% 17% 9%	627
September	1st to 10th	Day	8% 13% 26% 27% 18% 8%	570
	11th to 20th	Day	13% 11% 24% 27% 19% 7%	570
	21st to end	Day	14% 18% 32% 25% 10% 2	570
October	1st to 10th	Day	14% 13% 30% 26% 13% 4	570
	11th to 20th	Day	13% 18% 28% 24% 15% 1	536
	21st to end	Day	16% 11% 35% 27% 11% 1	362
November	1st to 10th	Day	15% 16% 37% 20% 11% 1	220
	11th to 20th	Day	11% 9% 40% 25% 12% 3	220
	21st to end	Day	10% 10% 35% 30% 9% 6%	220
December	1st to 10th	Day	10% 6% 31% 29% 20% 5%	220
	11th to 20th	Day	9% 10% 34% 29% 12% 5%	220
	21st to end	Day	12% 8% 34% 33% 10% 2	242
January	1st to 10th	Night	15% 9% 34% 31% 10% 2	950
	11th to 20th	Night	12% 7% 33% 35% 12% 1	945
	21st to end	Night	10% 6% 35% 34% 14% 2	924
February	1st to 10th	Night	13% 7% 33% 32% 13% 2	840
	11th to 20th	Night	11% 6% 30% 38% 15% 1	824
	21st to end	Night	8% 9% 36% 29% 17% 1	692
March	1st to 10th	Night	10% 9% 32% 32% 16% 1	840
	11th to 20th	Night	5% 12% 35% 31% 15% 2	840
	21st to end	Night	8% 9% 31% 33% 16% 2	924
April	1st to 10th	Night	9% 10% 25% 34% 20% 2	840
	11th to 20th	Night	6% 9% 34% 34% 16% 1	779
	21st to end	Night	7% 9% 32% 34% 18% 1	452
May	1st to 10th	Night	8% 7% 29% 35% 20% 2	420
	11th to 20th	Night	9% 5% 22% 39% 22% 2	414
	21st to end	Night	14% 4 24% 35% 22% 2	455
June	1st to 10th	Night	13% 8% 25% 36% 18% 1	420
	11th to 20th	Night	12% 5% 23% 39% 18% 3	420
	21st to end	Night	7% 5% 24% 36% 26% 2	420
July	1st to 10th	Night	6% 4 22% 42% 24% 2	410
	11th to 20th	Night	6% 5% 19% 39% 28% 3	408
	21st to end	Night	5% 2 13% 42% 35% 3	460
August	1st to 10th	Night	5% 2 12% 34% 40% 6%	418
	11th to 20th	Night	5% 4 14% 35% 36% 6%	489
	21st to end	Night	8% 4 17% 36% 31% 3	802
September	1st to 10th	Night	7% 4 18% 40% 26% 4	840
	11th to 20th	Night	11% 4 15% 30% 32% 8%	840
	21st to end	Night	13% 9% 23% 33% 18% 3	840
October	1st to 10th	Night	10% 8% 22% 36% 21% 2	840
	11th to 20th	Night	13% 8% 27% 32% 17% 2	812
	21st to end	Night	14% 9% 31% 31% 12% 2	880
November	1st to 10th	Night	15% 9% 33% 33% 10% 1	820
	11th to 20th	Night	12% 9% 33% 31% 13% 2	840
	21st to end	Night	14% 10% 30% 33% 10% 3	861
December	1st to 10th	Night	10% 6% 30% 37% 14% 2	1061
	11th to 20th	Night	14% 8% 36% 32% 9% 1	1160
	21st to end	Night	12% 9% 36% 32% 10% 1	1164

Page generated at 2026-10-11 02:06:30. Version ac07

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