Ashcroft
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Ashcroft clear sky chart from 2005-11-05 to 2018-02-22.

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% 8% 4 7% 7% 4 6% 6% 6% 8% 31%	49369
	Night	6% 9% 4 8% 7% 4 6% 6% 7% 8% 31%	49060
Transparency	Day	49% 9% 16% 17% 7%	49027
	Night	48% 11% 16% 17% 6%	48907
Seeing	Day	12% 14% 29% 27% 12% 2	6707
	Night	10% 7% 26% 34% 18% 2	15410

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 15th	Day	5% 10% 7% 12% 12% 6% 7% 7% 7% 7% 13%	1358
	16th to end	Day	5% 12% 6% 11% 9% 4 7% 7% 8% 8% 18%	1602
February	1st to 15th	Day	8% 11% 6% 9% 7% 4 7% 6% 6% 8% 23%	1640
	16th to end	Day	3 9% 4 7% 9% 5% 7% 7% 7% 9% 27%	1514
March	1st to 15th	Day	2 7% 4 9% 8% 5% 7% 7% 8% 9% 27%	1841
	16th to end	Day	2 8% 4 7% 9% 5% 8% 7% 8% 9% 26%	2190
April	1st to 15th	Day	5% 9% 6% 10% 9% 5% 7% 6% 7% 8% 23%	2149
	16th to end	Day	6% 9% 6% 8% 9% 4 6% 6% 7% 8% 24%	2412
May	1st to 15th	Day	6% 9% 4 8% 7% 4 7% 5% 6% 7% 30%	2511
	16th to end	Day	11% 9% 4 8% 8% 5% 8% 5% 6% 7% 23%	2645
June	1st to 15th	Day	14% 7% 5% 7% 8% 5% 6% 5% 6% 6% 25%	2838
	16th to end	Day	8% 7% 3 8% 9% 4 7% 6% 6% 7% 28%	2861
July	1st to 15th	Day	5% 4 2 4 5% 3 6% 5% 6% 9% 45%	2700
	16th to end	Day	5% 3 2 4 5% 3 6% 5% 6% 8% 47%	2739
August	1st to 15th	Day	4 4 2 5% 4 3 5% 5% 7% 9% 48%	2520
	16th to end	Day	4 4 2 6% 6% 4 5% 6% 7% 7% 43%	2436
September	1st to 15th	Day	6% 4 1 5% 5% 3 4 4 5% 7% 51%	2160
	16th to end	Day	9% 6% 2 6% 5% 3 6% 5% 6% 9% 38%	1998
October	1st to 15th	Day	6% 6% 3 6% 5% 4 5% 5% 7% 8% 39%	1800
	16th to end	Day	8% 9% 3 6% 7% 4 6% 6% 8% 9% 29%	1783
November	1st to 15th	Day	7% 10% 3 8% 8% 4 7% 6% 5% 10% 28%	1528
	16th to end	Day	3 10% 7% 9% 8% 5% 6% 6% 7% 9% 24%	1532
December	1st to 15th	Day	4 11% 8% 10% 9% 4 6% 6% 5% 7% 24%	1286
	16th to end	Day	5% 12% 6% 12% 10% 5% 6% 6% 5% 7% 20%	1326
January	1st to 15th	Night	6% 16% 6% 10% 10% 5% 9% 7% 7% 6% 12%	2911
	16th to end	Night	6% 13% 6% 12% 10% 5% 8% 7% 6% 6% 16%	2974
February	1st to 15th	Night	10% 12% 4 9% 9% 4 5% 5% 5% 6% 23%	2540
	16th to end	Night	3 9% 4 8% 6% 4 7% 5% 7% 9% 31%	2105
March	1st to 15th	Night	3 9% 3 8% 6% 4 7% 6% 8% 10% 32%	2118
	16th to end	Night	2 7% 3 6% 5% 4 7% 8% 9% 10% 33%	2029
April	1st to 15th	Night	3 7% 2 7% 7% 4 6% 6% 8% 9% 35%	1799
	16th to end	Night	3 9% 4 7% 7% 4 6% 6% 7% 10% 32%	1548
May	1st to 15th	Night	6% 7% 3 8% 6% 3 5% 5% 7% 8% 37%	1439
	16th to end	Night	12% 7% 3 6% 6% 3 6% 6% 8% 9% 28%	1463
June	1st to 15th	Night	11% 5% 2 6% 7% 3 6% 7% 6% 9% 33%	1119
	16th to end	Night	6% 6% 3 6% 7% 5% 6% 5% 6% 8% 37%	1096
July	1st to 15th	Night	4 4 2 2 4 2 6% 5% 7% 8% 50%	1260
	16th to end	Night	5% 3 1 3 4 2 5% 5% 6% 10% 51%	1427
August	1st to 15th	Night	3 3 5% 3 3 4 4 7% 9% 54%	1440
	16th to end	Night	4 4 1 5% 5% 3 5% 6% 7% 7% 48%	1765
September	1st to 15th	Night	5% 3 2 4 4 2 4 4 4 6% 55%	1800
	16th to end	Night	7% 5% 2 4 4 3 5% 5% 5% 8% 47%	1961
October	1st to 15th	Night	6% 7% 3 7% 6% 3 5% 5% 5% 6% 41%	2160
	16th to end	Night	6% 7% 3 8% 7% 4 6% 6% 6% 8% 33%	2440
November	1st to 15th	Night	8% 10% 4 8% 8% 4 6% 6% 6% 9% 27%	2660
	16th to end	Night	6% 11% 6% 10% 7% 5% 6% 5% 8% 8% 22%	2743
December	1st to 15th	Night	5% 12% 7% 11% 9% 4 6% 5% 7% 8% 22%	3003
	16th to end	Night	5% 15% 6% 11% 9% 5% 6% 6% 7% 8% 18%	3260

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 15th	Day	66% 11% 11% 8% 1	1358
	16th to end	Day	57% 13% 15% 11% 2	1602
February	1st to 15th	Day	58% 11% 13% 12% 3	1640
	16th to end	Day	50% 10% 16% 16% 6%	1514
March	1st to 15th	Day	51% 11% 19% 12% 3	1841
	16th to end	Day	54% 9% 20% 13% 2	2190
April	1st to 15th	Day	58% 9% 14% 13% 3	2149
	16th to end	Day	56% 9% 15% 13% 4	2412
May	1st to 15th	Day	50% 7% 16% 15% 9%	2511
	16th to end	Day	59% 8% 15% 13% 3	2649
June	1st to 15th	Day	58% 7% 13% 13% 6% 1	2838
	16th to end	Day	50% 7% 16% 15% 8%	2861
July	1st to 15th	Day	34% 6% 15% 23% 16% 3	2541
	16th to end	Day	31% 7% 17% 29% 12% 1	2569
August	1st to 15th	Day	31% 8% 17% 27% 13% 1	2503
	16th to end	Day	36% 7% 19% 24% 10% 1	2436
September	1st to 15th	Day	32% 7% 15% 27% 14% 1	2160
	16th to end	Day	43% 9% 18% 17% 8% 2	1998
October	1st to 15th	Day	42% 10% 18% 22% 7%	1800
	16th to end	Day	51% 12% 16% 16% 3	1783
November	1st to 15th	Day	54% 13% 10% 16% 5%	1528
	16th to end	Day	52% 13% 15% 13% 3	1532
December	1st to 15th	Day	57% 12% 14% 13% 1	1286
	16th to end	Day	60% 12% 11% 12% 3	1326
January	1st to 15th	Night	65% 13% 11% 7% 1	2911
	16th to end	Night	61% 13% 12% 8% 2	2974
February	1st to 15th	Night	58% 10% 12% 14% 3	2552
	16th to end	Night	47% 8% 20% 17% 5%	2105
March	1st to 15th	Night	44% 11% 20% 16% 5%	2118
	16th to end	Night	43% 13% 21% 17% 3	2033
April	1st to 15th	Night	45% 9% 19% 19% 6%	1799
	16th to end	Night	45% 12% 17% 18% 6%	1548
May	1st to 15th	Night	44% 10% 13% 20% 10%	1440
	16th to end	Night	47% 11% 20% 15% 4	1463
June	1st to 15th	Night	45% 9% 15% 19% 8% 1	1119
	16th to end	Night	42% 7% 19% 20% 8% 1	1096
July	1st to 15th	Night	30% 8% 15% 24% 17% 3	1190
	16th to end	Night	28% 8% 18% 28% 14% 2	1335
August	1st to 15th	Night	24% 7% 19% 28% 16% 3	1432
	16th to end	Night	31% 7% 19% 26% 11% 3	1765
September	1st to 15th	Night	28% 6% 15% 30% 17% 1	1800
	16th to end	Night	35% 8% 19% 22% 11% 3	1961
October	1st to 15th	Night	43% 8% 17% 22% 8%	2160
	16th to end	Night	46% 9% 21% 18% 3	2440
November	1st to 15th	Night	53% 12% 14% 13% 5%	2660
	16th to end	Night	56% 14% 13% 10% 3	2743
December	1st to 15th	Night	56% 14% 14% 12% 3	3003
	16th to end	Night	61% 11% 10% 11% 4	3260

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 15th	Day	3 2 21% 31% 26% 15%	90
	16th to end	Day	13% 11% 37% 25% 10% 2	96
February	1st to 15th	Day	15% 11% 34% 30% 7% 1	210
	16th to end	Day	9% 13% 33% 30% 10% 2	237
March	1st to 15th	Day	15% 26% 33% 21% 3	270
	16th to end	Day	13% 28% 38% 14% 4	288
April	1st to 15th	Day	18% 16% 31% 24% 9%	269
	16th to end	Day	16% 27% 28% 21% 5% 1	270
May	1st to 15th	Day	13% 17% 33% 25% 7% 2	288
	16th to end	Day	18% 11% 24% 25% 16% 3	360
June	1st to 15th	Day	18% 13% 24% 27% 13% 1	633
	16th to end	Day	13% 13% 28% 28% 15% 1	656
July	1st to 15th	Day	9% 15% 27% 32% 13% 2	475
	16th to end	Day	6% 11% 29% 35% 14% 2	408
August	1st to 15th	Day	5% 8% 23% 32% 23% 5%	315
	16th to end	Day	7% 12% 32% 30% 14% 3	332
September	1st to 15th	Day	9% 16% 28% 27% 14% 3	315
	16th to end	Day	16% 11% 31% 26% 9% 4	315
October	1st to 15th	Day	14% 20% 31% 20% 9% 3	315
	16th to end	Day	14% 10% 29% 31% 14%	199
November	1st to 15th	Day	13% 20% 36% 15% 12% 2	90
	16th to end	Day	13% 7% 34% 25% 10% 8%	90
December	1st to 15th	Day	2 7% 24% 28% 24% 12%	90
	16th to end	Day	10% 2 30% 38% 16% 2	96
January	1st to 15th	Night	13% 9% 32% 27% 15% 2	825
	16th to end	Night	11% 6% 34% 32% 13% 2	846
February	1st to 15th	Night	15% 7% 25% 35% 13% 1	764
	16th to end	Night	6% 5% 28% 37% 19% 1	660
March	1st to 15th	Night	9% 13% 32% 32% 9% 2	720
	16th to end	Night	5% 12% 32% 32% 15% 2	768
April	1st to 15th	Night	8% 9% 23% 34% 21% 2	719
	16th to end	Night	8% 5% 31% 37% 15% 1	468
May	1st to 15th	Night	10% 6% 23% 38% 19% 2	360
	16th to end	Night	17% 3 15% 35% 25% 2	375
June	1st to 15th	Night	12% 6% 20% 36% 20% 2	360
	16th to end	Night	9% 5% 25% 39% 19% 1	360
July	1st to 15th	Night	6% 4 17% 39% 30% 2	340
	16th to end	Night	7% 4 14% 39% 32% 2	376
August	1st to 15th	Night	5% 11% 32% 43% 7%	360
	16th to end	Night	8% 3 15% 36% 33% 2	619
September	1st to 15th	Night	8% 4 12% 35% 31% 6%	720
	16th to end	Night	11% 6% 19% 32% 26% 4	716
October	1st to 15th	Night	12% 5% 23% 34% 20% 2	720
	16th to end	Night	12% 7% 28% 32% 15% 2	768
November	1st to 15th	Night	13% 10% 34% 30% 9% 1	760
	16th to end	Night	13% 10% 30% 31% 10% 3	793
December	1st to 15th	Night	12% 6% 26% 37% 13% 2	993
	16th to end	Night	10% 6% 36% 35% 9%	1020

Page generated at 2018-02-23 08:21:33. Version ac04

Copyright 2018 A. Danko