Diamond Trailhead
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Diamond Trailhead clear sky chart from 2005-11-06 to 2024-01-14.

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	25% 15% 4 6% 5% 3 3 3 4 5% 27%	74736
	Night	26% 17% 4 6% 4 2 3 3 4 5% 26%	75037
Transparency	Day	61% 6% 10% 14% 7% 1	74423
	Night	63% 6% 10% 13% 7% 2	74868
Seeing	Day	32% 13% 25% 20% 8% 1	14260
	Night	35% 8% 23% 22% 11% 1	22568

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	36% 23% 4 5% 3 2 2 3 3 4 15%	1329
	11th to 20th	Day	31% 18% 5% 6% 5% 3 2 3 3 6% 19%	1281
	21st to end	Day	26% 23% 4 7% 4 2 2 3 4 3 20%	1535
February	1st to 10th	Day	26% 23% 6% 6% 4 2 3 4 3 5% 18%	1620
	11th to 20th	Day	21% 25% 4 7% 4 2 3 3 4 5% 23%	1575
	21st to end	Day	16% 26% 7% 8% 6% 3 4 3 4 3 19%	1336
March	1st to 10th	Day	25% 21% 5% 8% 5% 2 3 4 3 4 19%	1858
	11th to 20th	Day	27% 30% 5% 6% 5% 2 3 2 3 3 15%	1980
	21st to end	Day	26% 25% 6% 8% 6% 3 3 3 3 3 15%	2232
April	1st to 10th	Day	24% 25% 5% 8% 6% 2 4 4 3 4 13%	2160
	11th to 20th	Day	26% 23% 5% 7% 6% 3 4 3 3 3 17%	2234
	21st to end	Day	26% 21% 5% 9% 5% 3 4 3 3 3 17%	2402
May	1st to 10th	Day	20% 16% 5% 9% 7% 3 4 4 4 4 23%	2520
	11th to 20th	Day	21% 13% 5% 7% 6% 4 5% 5% 6% 6% 22%	2477
	21st to end	Day	28% 12% 4 6% 5% 3 4 4 4 6% 23%	2814
June	1st to 10th	Day	33% 12% 4 7% 4 3 4 4 4 5% 20%	2700
	11th to 20th	Day	32% 14% 5% 8% 6% 3 4 4 4 5% 14%	2700
	21st to end	Day	25% 10% 3 7% 5% 3 3 3 4 6% 31%	2700
July	1st to 10th	Day	17% 9% 3 6% 5% 3 4 4 4 6% 41%	2700
	11th to 20th	Day	15% 6% 3 5% 5% 2 4 5% 5% 7% 44%	2700
	21st to end	Day	13% 5% 2 4 4 2 3 5% 5% 6% 52%	2826
August	1st to 10th	Day	15% 6% 2 4 4 2 3 3 4 6% 50%	2503
	11th to 20th	Day	11% 5% 2 5% 4 3 3 4 5% 6% 53%	2298
	21st to end	Day	18% 7% 2 6% 5% 3 4 4 6% 7% 38%	2529
September	1st to 10th	Day	17% 6% 3 5% 4 2 4 4 5% 6% 43%	2160
	11th to 20th	Day	23% 9% 3 5% 4 2 3 3 4 4 38%	2156
	21st to end	Day	28% 9% 4 4 4 2 3 3 4 5% 34%	1895
October	1st to 10th	Day	27% 10% 3 4 4 2 3 3 4 4 35%	1800
	11th to 20th	Day	35% 10% 3 5% 4 2 3 4 4 6% 24%	1800
	21st to end	Day	37% 14% 3 5% 4 2 2 3 2 5% 23%	1807
November	1st to 10th	Day	38% 14% 4 6% 4 2 3 4 3 3 18%	1488
	11th to 20th	Day	36% 22% 3 5% 3 1 2 2 2 3 21%	1520
	21st to end	Day	34% 18% 4 4 4 3 3 3 3 4 20%	1520
December	1st to 10th	Day	27% 19% 5% 7% 3 1 3 2 2 3 28%	1454
	11th to 20th	Day	34% 21% 5% 8% 5% 2 2 2 2 3 16%	1685
	21st to end	Day	32% 23% 6% 8% 5% 3 3 3 2 3 13%	2442
January	1st to 10th	Night	34% 23% 3 6% 4 2 3 3 3 3 15%	2836
	11th to 20th	Night	33% 17% 4 6% 3 3 3 3 4 6% 17%	2757
	21st to end	Night	25% 22% 4 7% 4 3 2 3 3 5% 21%	2815
February	1st to 10th	Night	26% 21% 6% 6% 5% 2 3 4 4 6% 18%	2340
	11th to 20th	Night	21% 25% 6% 7% 4 2 3 3 4 4 22%	2272
	21st to end	Night	18% 25% 5% 8% 5% 3 3 4 3 4 23%	1919
March	1st to 10th	Night	25% 21% 5% 7% 5% 2 3 3 4 4 21%	2102
	11th to 20th	Night	26% 28% 4 6% 3 3 3 3 3 4 16%	1979
	21st to end	Night	28% 21% 5% 6% 5% 2 4 3 4 4 18%	2123
April	1st to 10th	Night	24% 22% 5% 7% 6% 4 4 4 4 4 17%	1800
	11th to 20th	Night	22% 21% 4 6% 5% 2 4 3 4 5% 23%	1673
	21st to end	Night	25% 17% 4 8% 4 3 3 3 4 6% 23%	1558
May	1st to 10th	Night	18% 13% 3 5% 5% 3 6% 4 4 6% 32%	1440
	11th to 20th	Night	19% 12% 4 6% 5% 3 5% 6% 6% 8% 26%	1416
	21st to end	Night	22% 12% 4 5% 5% 3 5% 4 4 6% 30%	1458
June	1st to 10th	Night	27% 11% 4 7% 6% 3 4 5% 4 4 25%	1260
	11th to 20th	Night	26% 14% 5% 7% 6% 3 3 5% 5% 5% 21%	1260
	21st to end	Night	21% 8% 2 6% 6% 3 4 4 5% 6% 35%	1260
July	1st to 10th	Night	14% 7% 3 5% 4 3 3 4 4 6% 48%	1260
	11th to 20th	Night	12% 7% 2 4 5% 3 3 3 5% 7% 50%	1260
	21st to end	Night	10% 5% 2 3 2 2 3 4 4 6% 60%	1490
August	1st to 10th	Night	13% 6% 1 3 2 1 3 4 4 5% 58%	1433
	11th to 20th	Night	9% 4 1 3 3 2 4 5% 4 7% 57%	1602
	21st to end	Night	14% 8% 2 5% 5% 4 4 5% 6% 8% 40%	1826
September	1st to 10th	Night	14% 7% 2 5% 3 2 4 4 5% 8% 47%	1800
	11th to 20th	Night	23% 8% 3 4 4 2 3 3 5% 5% 40%	1801
	21st to end	Night	26% 11% 3 4 4 2 3 4 3 6% 33%	2064
October	1st to 10th	Night	24% 11% 3 4 4 2 3 4 4 4 35%	2160
	11th to 20th	Night	33% 12% 3 5% 5% 2 3 3 4 4 27%	2160
	21st to end	Night	34% 14% 4 6% 4 2 3 3 4 4 23%	2545
November	1st to 10th	Night	40% 17% 4 5% 4 2 3 3 3 4 15%	2590
	11th to 20th	Night	35% 20% 4 4 4 2 3 3 2 3 19%	2660
	21st to end	Night	32% 19% 4 5% 4 2 3 3 3 3 21%	2660
December	1st to 10th	Night	26% 17% 4 6% 5% 3 4 3 4 4 25%	2724
	11th to 20th	Night	35% 22% 5% 7% 4 2 3 3 3 3 13%	3520
	21st to end	Night	34% 24% 5% 6% 5% 2 3 2 2 3 14%	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	76% 5% 5% 8% 4 2	1329
	11th to 20th	Day	70% 5% 8% 10% 4 3	1281
	21st to end	Day	71% 5% 7% 11% 4 2	1535
February	1st to 10th	Day	71% 4 8% 8% 7% 2	1620
	11th to 20th	Day	67% 5% 8% 13% 7% 1	1584
	21st to end	Day	71% 6% 8% 10% 5% 2	1336
March	1st to 10th	Day	71% 6% 8% 10% 5% 1	1858
	11th to 20th	Day	77% 3 6% 9% 4 1	1980
	21st to end	Day	76% 4 8% 9% 2	2232
April	1st to 10th	Day	75% 6% 10% 7% 1	2160
	11th to 20th	Day	74% 4 7% 8% 7%	2234
	21st to end	Day	75% 6% 6% 8% 5%	2402
May	1st to 10th	Day	65% 7% 11% 12% 5% 1	2520
	11th to 20th	Day	61% 9% 11% 14% 4 1	2480
	21st to end	Day	64% 7% 10% 14% 4	2815
June	1st to 10th	Day	68% 8% 10% 8% 4 2	2700
	11th to 20th	Day	73% 6% 11% 7% 2	2700
	21st to end	Day	57% 5% 13% 17% 7% 2	2700
July	1st to 10th	Day	47% 7% 13% 20% 11% 2	2626
	11th to 20th	Day	40% 8% 17% 25% 10%	2619
	21st to end	Day	32% 7% 14% 27% 17% 4	2669
August	1st to 10th	Day	35% 8% 15% 25% 14% 2	2486
	11th to 20th	Day	32% 8% 17% 24% 16% 3	2298
	21st to end	Day	44% 9% 16% 23% 7% 2	2529
September	1st to 10th	Day	43% 8% 11% 25% 10% 4	2160
	11th to 20th	Day	51% 4 9% 17% 17% 3	2156
	21st to end	Day	55% 6% 11% 16% 10% 2	1895
October	1st to 10th	Day	54% 6% 12% 16% 12%	1800
	11th to 20th	Day	64% 5% 9% 15% 6% 1	1800
	21st to end	Day	67% 4 9% 12% 7% 1	1807
November	1st to 10th	Day	72% 7% 6% 8% 6% 1	1488
	11th to 20th	Day	73% 4 7% 7% 7% 3	1520
	21st to end	Day	71% 5% 5% 10% 8% 2	1520
December	1st to 10th	Day	65% 5% 8% 11% 10% 2	1454
	11th to 20th	Day	76% 4 6% 8% 3 2	1688
	21st to end	Day	78% 6% 4 8% 3 1	2442
January	1st to 10th	Night	76% 4 5% 9% 3 2	2836
	11th to 20th	Night	69% 6% 8% 8% 5% 3	2757
	21st to end	Night	67% 7% 7% 11% 7% 2	2815
February	1st to 10th	Night	70% 5% 8% 9% 7% 2	2340
	11th to 20th	Night	68% 5% 8% 10% 7% 2	2274
	21st to end	Night	67% 4 9% 11% 7% 2	1919
March	1st to 10th	Night	69% 5% 8% 12% 5% 1	2102
	11th to 20th	Night	74% 5% 8% 8% 5% 1	1980
	21st to end	Night	72% 7% 11% 8% 2	2123
April	1st to 10th	Night	70% 7% 10% 11% 1	1800
	11th to 20th	Night	64% 7% 9% 12% 7% 1	1673
	21st to end	Night	64% 6% 12% 11% 6%	1558
May	1st to 10th	Night	52% 10% 17% 17% 4 1	1440
	11th to 20th	Night	55% 9% 17% 14% 4	1416
	21st to end	Night	55% 8% 15% 17% 4	1458
June	1st to 10th	Night	62% 6% 17% 8% 3 3	1260
	11th to 20th	Night	65% 7% 14% 10% 4	1260
	21st to end	Night	51% 9% 14% 17% 6% 3	1260
July	1st to 10th	Night	39% 7% 18% 20% 14% 2	1225
	11th to 20th	Night	34% 8% 20% 26% 11%	1218
	21st to end	Night	25% 6% 15% 31% 17% 5%	1407
August	1st to 10th	Night	29% 6% 18% 26% 17% 3	1425
	11th to 20th	Night	28% 9% 21% 23% 15% 5%	1602
	21st to end	Night	42% 8% 17% 23% 7% 2	1826
September	1st to 10th	Night	36% 9% 16% 24% 13% 3	1800
	11th to 20th	Night	47% 6% 11% 16% 15% 5%	1801
	21st to end	Night	54% 5% 13% 17% 8% 3	2064
October	1st to 10th	Night	54% 7% 11% 16% 11% 1	2160
	11th to 20th	Night	63% 6% 9% 15% 8%	2160
	21st to end	Night	67% 5% 7% 12% 8% 1	2545
November	1st to 10th	Night	75% 4 7% 8% 5% 2	2590
	11th to 20th	Night	72% 5% 7% 7% 6% 3	2660
	21st to end	Night	70% 4 6% 8% 9% 2	2660
December	1st to 10th	Night	64% 6% 9% 11% 9% 2	2724
	11th to 20th	Night	78% 6% 5% 5% 4 2	3516
	21st to end	Night	79% 3 3 8% 5% 1	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	42% 15% 19% 14% 8% 2	180
	11th to 20th	Day	44% 7% 22% 20% 7%	166
	21st to end	Day	39% 7% 26% 20% 7%	181
February	1st to 10th	Day	41% 16% 29% 10% 4	340
	11th to 20th	Day	37% 15% 27% 18% 2 1	335
	21st to end	Day	29% 22% 27% 17% 4	282
March	1st to 10th	Day	35% 18% 25% 17% 5%	420
	11th to 20th	Day	37% 18% 19% 17% 8%	420
	21st to end	Day	42% 15% 23% 12% 7% 1	462
April	1st to 10th	Day	44% 16% 19% 14% 6% 1	420
	11th to 20th	Day	39% 18% 21% 14% 7% 1	412
	21st to end	Day	40% 17% 20% 16% 7%	420
May	1st to 10th	Day	29% 16% 26% 23% 6% 1	423
	11th to 20th	Day	32% 8% 25% 23% 11% 1	448
	21st to end	Day	30% 12% 29% 19% 9% 2	576
June	1st to 10th	Day	38% 14% 24% 18% 4 1	630
	11th to 20th	Day	37% 17% 25% 16% 4 1	630
	21st to end	Day	26% 14% 26% 27% 6% 1	630
July	1st to 10th	Day	22% 11% 30% 27% 8% 2	621
	11th to 20th	Day	17% 14% 33% 27% 8% 1	618
	21st to end	Day	12% 9% 31% 32% 13% 3	572
August	1st to 10th	Day	15% 11% 26% 30% 13% 5%	447
	11th to 20th	Day	12% 8% 30% 34% 14% 3	437
	21st to end	Day	20% 14% 30% 25% 10% 2	495
September	1st to 10th	Day	23% 17% 31% 22% 5% 1	450
	11th to 20th	Day	32% 11% 26% 23% 8% 1	450
	21st to end	Day	30% 14% 26% 20% 9% 2	450
October	1st to 10th	Day	34% 13% 22% 19% 10% 2	450
	11th to 20th	Day	43% 9% 20% 18% 9% 2	450
	21st to end	Day	44% 12% 23% 14% 6% 1	347
November	1st to 10th	Day	39% 14% 23% 18% 6%	180
	11th to 20th	Day	46% 10% 14% 16% 13% 2	180
	21st to end	Day	45% 12% 19% 9% 10% 4	180
December	1st to 10th	Day	43% 9% 18% 15% 13% 2	180
	11th to 20th	Day	42% 12% 23% 16% 6% 1	180
	21st to end	Day	35% 11% 33% 16% 4	198
January	1st to 10th	Night	47% 10% 22% 16% 4 1	850
	11th to 20th	Night	42% 9% 24% 20% 5%	819
	21st to end	Night	37% 12% 27% 19% 5%	814
February	1st to 10th	Night	38% 9% 32% 18% 3	720
	11th to 20th	Night	33% 11% 31% 21% 4	704
	21st to end	Night	32% 12% 28% 19% 8%	592
March	1st to 10th	Night	37% 11% 23% 19% 9% 1	720
	11th to 20th	Night	42% 10% 22% 18% 7%	720
	21st to end	Night	40% 9% 24% 17% 9% 1	792
April	1st to 10th	Night	36% 8% 23% 23% 9% 1	720
	11th to 20th	Night	33% 8% 25% 25% 8% 1	605
	21st to end	Night	35% 5% 28% 20% 11%	478
May	1st to 10th	Night	24% 6% 23% 31% 17% 1	360
	11th to 20th	Night	28% 4 18% 32% 18% 1	354
	21st to end	Night	30% 4 23% 30% 13%	389
June	1st to 10th	Night	32% 5% 27% 21% 14% 1	360
	11th to 20th	Night	33% 8% 23% 24% 12% 1	360
	21st to end	Night	26% 5% 20% 30% 18% 1	360
July	1st to 10th	Night	15% 4 17% 35% 27% 1	350
	11th to 20th	Night	16% 3 14% 37% 28% 2	348
	21st to end	Night	10% 3 12% 36% 35% 4	394
August	1st to 10th	Night	16% 11% 33% 36% 4	359
	11th to 20th	Night	12% 1 10% 39% 35% 3	534
	21st to end	Night	21% 3 18% 32% 25% 2	638
September	1st to 10th	Night	18% 4 24% 34% 19% 1	720
	11th to 20th	Night	27% 4 19% 24% 22% 4	720
	21st to end	Night	32% 6% 20% 27% 14% 1	720
October	1st to 10th	Night	30% 7% 22% 26% 15% 1	720
	11th to 20th	Night	39% 6% 20% 23% 11% 1	720
	21st to end	Night	44% 8% 26% 17% 5% 1	792
November	1st to 10th	Night	52% 9% 21% 16% 2	740
	11th to 20th	Night	47% 9% 24% 15% 4 1	760
	21st to end	Night	41% 13% 22% 18% 5% 1	760
December	1st to 10th	Night	35% 9% 31% 18% 6% 1	791
	11th to 20th	Night	47% 10% 29% 12% 2	850
	21st to end	Night	45% 12% 28% 14% 1	935

Page generated at 2024-01-11 10:32:01. Version ac07

Copyright 2024 Attilla Danko