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 2024-11-02.

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	6% 9% 3 8% 6% 6% 6% 5% 7% 8% 36%	101589
	Night	6% 10% 4 9% 6% 6% 6% 5% 7% 8% 33%	97450
Transparency	Day	43% 10% 17% 19% 9% 2	101340
	Night	46% 12% 16% 17% 8% 2	97345
Seeing	Day	11% 15% 30% 27% 14% 3	15648
	Night	10% 8% 29% 33% 18% 2	23866

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	7% 13% 6% 18% 10% 8% 6% 5% 6% 7% 14%	2219
	11th to 20th	Day	10% 10% 6% 10% 8% 6% 5% 5% 7% 10% 24%	2203
	21st to end	Day	5% 20% 7% 13% 8% 7% 6% 5% 6% 7% 16%	2794
February	1st to 10th	Day	6% 14% 6% 10% 6% 7% 6% 6% 7% 8% 24%	1605
	11th to 20th	Day	5% 11% 5% 10% 6% 6% 6% 5% 8% 9% 31%	1665
	21st to end	Day	2 12% 4 11% 9% 10% 7% 5% 8% 8% 24%	1474
March	1st to 10th	Day	1 9% 4 9% 6% 7% 8% 7% 10% 10% 30%	3138
	11th to 20th	Day	2 6% 2 6% 6% 5% 7% 6% 9% 10% 41%	3447
	21st to end	Day	3 11% 4 10% 8% 7% 7% 6% 7% 10% 28%	4032
April	1st to 10th	Day	4 10% 5% 10% 9% 7% 8% 6% 8% 9% 25%	2280
	11th to 20th	Day	5% 10% 6% 10% 8% 6% 6% 5% 8% 8% 27%	2296
	21st to end	Day	6% 12% 4 10% 7% 6% 5% 5% 7% 9% 28%	2631
May	1st to 10th	Day	7% 9% 3 8% 6% 6% 5% 5% 6% 8% 37%	4420
	11th to 20th	Day	8% 9% 3 9% 7% 6% 6% 5% 7% 11% 30%	4377
	21st to end	Day	13% 14% 4 10% 7% 6% 7% 5% 6% 6% 21%	4899
June	1st to 10th	Day	12% 9% 3 9% 8% 6% 6% 4 7% 7% 29%	2973
	11th to 20th	Day	14% 9% 4 9% 9% 7% 6% 5% 7% 7% 23%	3040
	21st to end	Day	7% 6% 3 9% 7% 7% 6% 5% 7% 8% 37%	3010
July	1st to 10th	Day	4 3 1 4 4 4 4 4 5% 7% 59%	4740
	11th to 20th	Day	3 3 1 3 3 3 3 3 5% 8% 64%	4740
	21st to end	Day	5% 4 1 4 4 4 4 4 6% 8% 55%	4855
August	1st to 10th	Day	3 3 1 4 3 4 5% 4 7% 9% 57%	4401
	11th to 20th	Day	2 3 2 6% 5% 5% 7% 5% 9% 11% 47%	4214
	21st to end	Day	7% 5% 2 7% 4 5% 5% 5% 7% 9% 44%	4349
September	1st to 10th	Day	6% 5% 2 6% 4 5% 4 3 6% 8% 51%	2280
	11th to 20th	Day	9% 7% 3 8% 4 5% 5% 5% 6% 7% 42%	2280
	21st to end	Day	9% 7% 3 8% 5% 6% 5% 4 6% 8% 39%	2024
October	1st to 10th	Day	7% 8% 3 8% 5% 5% 4 4 7% 6% 42%	1900
	11th to 20th	Day	7% 6% 3 7% 5% 6% 6% 5% 8% 9% 37%	1894
	21st to end	Day	8% 12% 3 7% 7% 5% 6% 5% 8% 8% 32%	1880
November	1st to 10th	Day	7% 13% 5% 11% 7% 6% 6% 5% 6% 7% 28%	1496
	11th to 20th	Day	4 10% 3 8% 7% 6% 6% 6% 7% 8% 35%	1520
	21st to end	Day	5% 12% 5% 10% 8% 6% 7% 5% 8% 9% 25%	1479
December	1st to 10th	Day	4 14% 6% 12% 9% 6% 8% 6% 6% 9% 22%	1309
	11th to 20th	Day	5% 18% 10% 15% 9% 6% 5% 5% 5% 5% 18%	1442
	21st to end	Day	4 12% 5% 14% 8% 8% 8% 6% 8% 8% 20%	2283
January	1st to 10th	Night	7% 18% 7% 15% 7% 7% 7% 5% 7% 6% 14%	4726
	11th to 20th	Night	9% 14% 5% 13% 8% 6% 5% 4 9% 6% 21%	4694
	21st to end	Night	6% 15% 6% 14% 8% 8% 8% 5% 7% 7% 15%	4862
February	1st to 10th	Night	8% 13% 5% 13% 9% 7% 6% 4 6% 7% 22%	2571
	11th to 20th	Night	5% 13% 3 8% 7% 6% 6% 5% 7% 8% 33%	2402
	21st to end	Night	3 14% 5% 11% 8% 7% 7% 5% 7% 8% 27%	1979
March	1st to 10th	Night	2 13% 5% 9% 5% 6% 7% 5% 8% 10% 32%	3736
	11th to 20th	Night	1 6% 2 5% 4 4 5% 5% 8% 10% 50%	3530
	21st to end	Night	6% 10% 3 9% 6% 6% 6% 5% 6% 8% 35%	3621
April	1st to 10th	Night	3 9% 3 10% 6% 6% 7% 5% 7% 8% 36%	1900
	11th to 20th	Night	2 8% 4 8% 8% 6% 6% 6% 8% 9% 35%	1833
	21st to end	Night	5% 9% 4 9% 6% 4 5% 5% 7% 10% 35%	1549
May	1st to 10th	Night	6% 10% 4 10% 7% 5% 4 3 5% 6% 40%	2540
	11th to 20th	Night	7% 8% 4 9% 6% 5% 6% 5% 8% 9% 33%	2516
	21st to end	Night	10% 10% 4 9% 7% 7% 6% 5% 7% 9% 26%	2671
June	1st to 10th	Night	12% 6% 3 7% 6% 5% 5% 5% 8% 8% 35%	1202
	11th to 20th	Night	9% 8% 3 8% 7% 6% 6% 6% 6% 9% 31%	1140
	21st to end	Night	5% 6% 3 7% 5% 6% 6% 5% 7% 7% 44%	1165
July	1st to 10th	Night	5% 5% 2 5% 4 4 4 4 6% 7% 55%	2220
	11th to 20th	Night	3 3 2 3 3 3 5% 3 6% 7% 63%	2220
	21st to end	Night	4 4 1 4 4 4 5% 4 7% 8% 53%	2695
August	1st to 10th	Night	3 2 1 6% 3 4 4 4 7% 8% 57%	2529
	11th to 20th	Night	4 4 1 5% 5% 5% 6% 5% 8% 11% 45%	2615
	21st to end	Night	7% 5% 2 7% 4 5% 5% 5% 7% 7% 45%	3323
September	1st to 10th	Night	4 4 2 6% 4 4 5% 3 5% 7% 55%	1900
	11th to 20th	Night	8% 6% 2 5% 5% 4 5% 4 6% 8% 47%	1900
	21st to end	Night	7% 7% 3 6% 4 4 5% 4 6% 8% 45%	2154
October	1st to 10th	Night	6% 7% 2 7% 5% 6% 6% 5% 6% 8% 42%	2280
	11th to 20th	Night	8% 8% 3 8% 5% 4 6% 5% 7% 8% 39%	2285
	21st to end	Night	6% 10% 4 9% 7% 6% 5% 5% 6% 7% 35%	2717
November	1st to 10th	Night	9% 12% 4 10% 7% 6% 5% 5% 6% 8% 27%	2616
	11th to 20th	Night	4 10% 4 10% 7% 6% 6% 6% 8% 8% 32%	2660
	21st to end	Night	6% 15% 5% 11% 7% 7% 5% 5% 7% 9% 23%	2679
December	1st to 10th	Night	5% 14% 5% 12% 8% 6% 6% 5% 7% 8% 25%	2869
	11th to 20th	Night	10% 18% 7% 15% 7% 6% 5% 4 6% 7% 15%	3750
	21st to end	Night	6% 14% 5% 12% 8% 8% 8% 6% 7% 7% 19%	5401

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	63% 18% 10% 8% 1	2219
	11th to 20th	Day	53% 12% 18% 8% 2 6%	2224
	21st to end	Day	66% 12% 11% 9% 2	2794
February	1st to 10th	Day	57% 11% 13% 11% 6% 1	1605
	11th to 20th	Day	48% 11% 17% 16% 9%	1674
	21st to end	Day	56% 10% 14% 14% 5% 1	1474
March	1st to 10th	Day	44% 12% 20% 17% 6%	3138
	11th to 20th	Day	36% 10% 24% 25% 4	3447
	21st to end	Day	50% 10% 20% 12% 7%	4032
April	1st to 10th	Day	54% 12% 17% 13% 4	2280
	11th to 20th	Day	52% 10% 13% 15% 9% 1	2296
	21st to end	Day	52% 8% 16% 16% 8%	2631
May	1st to 10th	Day	39% 8% 16% 24% 11% 1	4420
	11th to 20th	Day	43% 9% 21% 19% 7%	4380
	21st to end	Day	57% 10% 16% 13% 3 1	4900
June	1st to 10th	Day	52% 8% 13% 14% 9% 3	2973
	11th to 20th	Day	58% 8% 15% 13% 6%	3040
	21st to end	Day	42% 7% 19% 18% 11% 2	3010
July	1st to 10th	Day	24% 5% 11% 23% 24% 13%	4666
	11th to 20th	Day	19% 5% 12% 29% 28% 7%	4659
	21st to end	Day	25% 5% 19% 26% 18% 7%	4701
August	1st to 10th	Day	22% 7% 13% 35% 21% 2	4384
	11th to 20th	Day	27% 12% 25% 24% 11% 1	4256
	21st to end	Day	34% 9% 24% 27% 5% 1	4348
September	1st to 10th	Day	31% 8% 17% 28% 13% 3	2280
	11th to 20th	Day	41% 8% 14% 23% 12% 2	2280
	21st to end	Day	44% 9% 20% 17% 8% 1	2024
October	1st to 10th	Day	42% 10% 17% 25% 7%	1900
	11th to 20th	Day	43% 12% 19% 20% 6%	1894
	21st to end	Day	48% 11% 17% 19% 4	1880
November	1st to 10th	Day	56% 10% 13% 17% 4 1	1496
	11th to 20th	Day	46% 16% 15% 17% 6%	1520
	21st to end	Day	51% 15% 17% 12% 4 1	1479
December	1st to 10th	Day	58% 13% 14% 12% 2	1309
	11th to 20th	Day	65% 13% 10% 9% 3	1444
	21st to end	Day	57% 16% 14% 10% 2	2283
January	1st to 10th	Night	63% 17% 12% 6% 2	4726
	11th to 20th	Night	58% 11% 14% 9% 3 5%	4735
	21st to end	Night	65% 15% 11% 7% 3	4862
February	1st to 10th	Night	58% 12% 11% 13% 5% 1	2571
	11th to 20th	Night	49% 9% 17% 17% 8% 1	2404
	21st to end	Night	53% 10% 17% 14% 5%	1979
March	1st to 10th	Night	40% 12% 20% 20% 8%	3736
	11th to 20th	Night	28% 11% 25% 28% 7%	3531
	21st to end	Night	46% 11% 18% 15% 11%	3621
April	1st to 10th	Night	44% 11% 20% 19% 6%	1900
	11th to 20th	Night	42% 12% 16% 18% 11%	1833
	21st to end	Night	42% 11% 16% 19% 11%	1549
May	1st to 10th	Night	40% 11% 13% 24% 10% 2	2540
	11th to 20th	Night	39% 16% 17% 20% 8% 1	2516
	21st to end	Night	47% 15% 17% 15% 5%	2671
June	1st to 10th	Night	46% 8% 14% 19% 10% 3	1202
	11th to 20th	Night	47% 9% 16% 17% 10%	1140
	21st to end	Night	35% 8% 21% 21% 11% 4	1165
July	1st to 10th	Night	28% 7% 11% 16% 27% 11%	2185
	11th to 20th	Night	18% 8% 12% 25% 33% 4	2178
	21st to end	Night	27% 7% 14% 25% 15% 12%	2610
August	1st to 10th	Night	22% 8% 12% 30% 26% 2	2521
	11th to 20th	Night	30% 10% 20% 25% 13% 2	2639
	21st to end	Night	34% 8% 24% 24% 8% 1	3323
September	1st to 10th	Night	28% 8% 16% 30% 15% 4	1900
	11th to 20th	Night	36% 7% 17% 24% 14% 3	1900
	21st to end	Night	36% 10% 22% 19% 11% 2	2154
October	1st to 10th	Night	41% 8% 17% 25% 8%	2280
	11th to 20th	Night	44% 9% 18% 21% 7%	2285
	21st to end	Night	46% 9% 19% 20% 6%	2717
November	1st to 10th	Night	54% 11% 15% 14% 5% 1	2616
	11th to 20th	Night	49% 16% 15% 13% 6% 1	2660
	21st to end	Night	55% 14% 15% 10% 4	2679
December	1st to 10th	Night	55% 13% 14% 13% 4	2869
	11th to 20th	Night	65% 15% 10% 7% 3	3747
	21st to end	Night	58% 15% 14% 10% 3	5401

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	6% 16% 38% 25% 9% 6%	180
	11th to 20th	Day	7% 14% 32% 30% 14% 3	180
	21st to end	Day	15% 10% 37% 25% 11% 1	198
February	1st to 10th	Day	10% 16% 48% 20% 5% 1	265
	11th to 20th	Day	10% 12% 39% 27% 10% 2	365
	21st to end	Day	8% 17% 39% 23% 10% 2	337
March	1st to 10th	Day	10% 20% 35% 21% 12% 1	460
	11th to 20th	Day	8% 21% 35% 19% 13% 3	460
	21st to end	Day	13% 24% 31% 22% 10% 1	506
April	1st to 10th	Day	15% 23% 29% 25% 7% 1	460
	11th to 20th	Day	16% 21% 29% 19% 11% 3	452
	21st to end	Day	13% 22% 30% 23% 10% 2	460
May	1st to 10th	Day	11% 20% 32% 24% 11% 2	463
	11th to 20th	Day	12% 11% 30% 28% 14% 5%	488
	21st to end	Day	14% 14% 28% 29% 12% 3	576
June	1st to 10th	Day	15% 19% 30% 26% 9% 1	803
	11th to 20th	Day	17% 13% 27% 27% 14% 2	870
	21st to end	Day	10% 10% 28% 30% 19% 2	840
July	1st to 10th	Day	8% 11% 31% 31% 18% 2	671
	11th to 20th	Day	6% 13% 27% 30% 19% 5%	668
	21st to end	Day	5% 7% 24% 33% 26% 4	570
August	1st to 10th	Day	6% 7% 22% 30% 28% 7%	487
	11th to 20th	Day	5% 10% 21% 34% 22% 8%	477
	21st to end	Day	8% 12% 27% 32% 16% 6%	539
September	1st to 10th	Day	8% 14% 28% 29% 16% 4	490
	11th to 20th	Day	14% 12% 26% 26% 17% 5%	490
	21st to end	Day	15% 18% 32% 23% 10% 2	490
October	1st to 10th	Day	14% 14% 31% 24% 13% 4	490
	11th to 20th	Day	14% 20% 28% 23% 14% 1	484
	21st to end	Day	16% 12% 33% 27% 12% 1	329
November	1st to 10th	Day	14% 19% 35% 18% 13% 1	182
	11th to 20th	Day	11% 10% 42% 22% 12% 4	180
	21st to end	Day	11% 12% 36% 28% 8% 7%	180
December	1st to 10th	Day	9% 7% 32% 27% 20% 5%	180
	11th to 20th	Day	8% 11% 33% 28% 13% 7%	180
	21st to end	Day	11% 10% 35% 33% 10% 2	198
January	1st to 10th	Night	15% 10% 36% 28% 10% 2	850
	11th to 20th	Night	13% 7% 35% 32% 12% 1	847
	21st to end	Night	10% 6% 36% 31% 14% 2	836
February	1st to 10th	Night	14% 7% 34% 32% 12% 1	760
	11th to 20th	Night	10% 6% 32% 36% 14% 1	744
	21st to end	Night	8% 10% 35% 29% 17% 2	628
March	1st to 10th	Night	10% 9% 33% 31% 16% 1	760
	11th to 20th	Night	4 13% 34% 31% 16% 2	760
	21st to end	Night	8% 9% 32% 32% 17% 2	836
April	1st to 10th	Night	9% 10% 26% 33% 20% 2	760
	11th to 20th	Night	5% 9% 35% 34% 16% 1	705
	21st to end	Night	7% 9% 34% 32% 17% 1	409
May	1st to 10th	Night	8% 8% 30% 32% 20% 2	380
	11th to 20th	Night	9% 6% 22% 39% 22% 2	374
	21st to end	Night	15% 4 23% 34% 22% 2	411
June	1st to 10th	Night	13% 8% 26% 34% 18% 1	380
	11th to 20th	Night	13% 6% 23% 38% 18% 2	380
	21st to end	Night	6% 6% 25% 36% 26% 2	380
July	1st to 10th	Night	7% 4 22% 41% 24% 2	370
	11th to 20th	Night	7% 5% 18% 38% 29% 3	368
	21st to end	Night	6% 3 13% 42% 34% 3	416
August	1st to 10th	Night	5% 2 13% 34% 40% 6%	378
	11th to 20th	Night	5% 4 15% 35% 36% 6%	442
	21st to end	Night	8% 5% 19% 37% 30% 2	726
September	1st to 10th	Night	7% 5% 19% 40% 26% 4	760
	11th to 20th	Night	11% 5% 16% 29% 31% 7%	760
	21st to end	Night	13% 9% 24% 31% 19% 4	760
October	1st to 10th	Night	10% 9% 23% 34% 22% 2	760
	11th to 20th	Night	13% 9% 27% 31% 17% 3	760
	21st to end	Night	14% 9% 31% 32% 12% 2	836
November	1st to 10th	Night	16% 9% 33% 31% 10% 1	748
	11th to 20th	Night	12% 10% 34% 31% 12% 2	760
	21st to end	Night	14% 11% 31% 31% 10% 3	779
December	1st to 10th	Night	10% 7% 31% 36% 14% 2	959
	11th to 20th	Night	14% 9% 35% 32% 9% 1	1040
	21st to end	Night	13% 10% 36% 31% 10% 1	1044

Page generated at 2024-10-30 10:19:21. Version ac07

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