Myrtle Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Myrtle Park clear sky chart from 2005-11-06 to 2026-03-03.

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	26% 9% 3 6% 4 4 4 3 5% 6% 31%	134700
	Night	30% 10% 3 6% 3 3 3 3 4 5% 30%	135193
Transparency	Day	56% 6% 14% 16% 7% 1	134408
	Night	58% 5% 13% 15% 8% 1	135064
Seeing	Day	32% 8% 21% 24% 12% 3	16951
	Night	37% 5% 14% 25% 17% 2	25299

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	45% 14% 3 7% 5% 4 3 3 4 4 9%	4125
	11th to 20th	Day	23% 11% 3 5% 3 3 3 2 5% 7% 35%	4119
	21st to end	Day	45% 7% 2 4 3 3 3 2 3 4 24%	5183
February	1st to 10th	Day	35% 13% 4 8% 4 5% 3 3 5% 6% 15%	1890
	11th to 20th	Day	32% 14% 3 7% 4 3 4 2 4 5% 22%	1845
	21st to end	Day	30% 15% 3 7% 7% 5% 4 3 4 4 19%	1574
March	1st to 10th	Day	30% 19% 4 8% 5% 4 4 3 4 4 14%	4686
	11th to 20th	Day	29% 15% 3 7% 4 4 3 3 4 4 23%	5000
	21st to end	Day	36% 14% 3 8% 5% 4 4 3 5% 5% 14%	5633
April	1st to 10th	Day	31% 13% 3 8% 5% 6% 4 4 5% 6% 15%	2400
	11th to 20th	Day	25% 12% 3 9% 5% 4 4 4 5% 5% 24%	2471
	21st to end	Day	28% 12% 3 7% 4 4 5% 4 5% 6% 23%	2663
May	1st to 10th	Day	16% 10% 3 7% 4 4 4 3 5% 6% 40%	6320
	11th to 20th	Day	22% 9% 3 7% 4 5% 4 5% 6% 8% 26%	6277
	21st to end	Day	26% 8% 2 6% 4 4 5% 4 7% 8% 24%	7055
June	1st to 10th	Day	25% 10% 3 7% 4 4 4 3 5% 7% 28%	3000
	11th to 20th	Day	25% 11% 3 9% 6% 5% 5% 4 5% 6% 22%	3000
	21st to end	Day	18% 9% 2 7% 5% 4 5% 3 6% 6% 34%	3000
July	1st to 10th	Day	10% 4 2 4 3 3 4 3 4 5% 58%	6780
	11th to 20th	Day	6% 3 1 3 2 2 2 2 3 6% 68%	6780
	21st to end	Day	11% 4 2 4 2 3 3 2 5% 9% 56%	7011
August	1st to 10th	Day	7% 4 2 3 2 2 2 2 4 5% 66%	4515
	11th to 20th	Day	18% 6% 3 7% 4 4 4 3 4 7% 41%	4156
	21st to end	Day	20% 6% 2 6% 4 3 4 3 5% 7% 41%	4553
September	1st to 10th	Day	15% 7% 2 6% 4 3 3 3 5% 7% 43%	2400
	11th to 20th	Day	22% 8% 3 6% 4 4 4 2 4 5% 38%	2400
	21st to end	Day	29% 6% 2 5% 3 4 4 3 6% 6% 33%	2102
October	1st to 10th	Day	29% 8% 2 7% 5% 4 4 3 5% 6% 27%	3280
	11th to 20th	Day	39% 7% 2 5% 3 4 4 3 6% 6% 21%	3261
	21st to end	Day	38% 13% 3 7% 3 4 4 4 6% 5% 14%	3276
November	1st to 10th	Day	44% 10% 2 7% 4 4 4 2 4 4 15%	1648
	11th to 20th	Day	43% 12% 2 8% 3 2 3 3 3 3 17%	1680
	21st to end	Day	43% 11% 3 5% 3 3 3 3 3 4 18%	1680
December	1st to 10th	Day	29% 11% 2 7% 4 4 5% 4 5% 8% 22%	2647
	11th to 20th	Day	49% 15% 3 6% 3 3 3 2 3 3 10%	2715
	21st to end	Day	50% 14% 3 7% 4 4 3 2 3 3 7%	3575
January	1st to 10th	Night	43% 14% 3 7% 4 4 3 2 3 3 13%	8770
	11th to 20th	Night	26% 7% 2 5% 2 3 3 2 5% 7% 37%	8779
	21st to end	Night	41% 7% 2 4 2 2 2 2 3 4 30%	8997
February	1st to 10th	Night	35% 13% 4 7% 4 4 3 3 4 4 19%	2730
	11th to 20th	Night	29% 14% 4 7% 4 3 4 2 4 4 25%	2662
	21st to end	Night	33% 14% 3 6% 4 3 4 2 4 5% 23%	2231
March	1st to 10th	Night	29% 18% 3 6% 4 3 3 3 4 5% 22%	5251
	11th to 20th	Night	32% 13% 2 6% 3 4 3 3 4 5% 26%	4999
	21st to end	Night	43% 12% 3 7% 3 3 3 2 3 4 16%	5341
April	1st to 10th	Night	31% 13% 3 7% 5% 4 4 3 4 5% 21%	2000
	11th to 20th	Night	22% 13% 3 7% 4 4 4 4 4 6% 28%	1876
	21st to end	Night	26% 11% 3 7% 5% 5% 4 3 4 7% 26%	1735
May	1st to 10th	Night	18% 9% 2 4 3 3 3 2 4 4 47%	3640
	11th to 20th	Night	17% 7% 3 8% 4 4 4 4 7% 9% 35%	3616
	21st to end	Night	21% 10% 3 9% 5% 4 5% 3 5% 7% 28%	3816
June	1st to 10th	Night	24% 7% 2 7% 5% 4 5% 4 5% 5% 33%	1400
	11th to 20th	Night	19% 11% 4 6% 5% 4 5% 3 6% 7% 29%	1400
	21st to end	Night	16% 6% 2 7% 5% 4 3 4 5% 6% 41%	1400
July	1st to 10th	Night	10% 4 1 4 2 3 3 2 4 5% 62%	3180
	11th to 20th	Night	4 2 2 2 1 2 2 3 5% 77%	3180
	21st to end	Night	9% 4 1 4 2 3 3 3 5% 6% 61%	3829
August	1st to 10th	Night	6% 2 1 2 2 2 2 2 4 6% 72%	2633
	11th to 20th	Night	12% 6% 2 5% 3 4 4 3 6% 7% 48%	2902
	21st to end	Night	17% 5% 3 6% 4 3 4 3 5% 6% 44%	3359
September	1st to 10th	Night	10% 4 2 6% 3 3 4 2 5% 7% 54%	2000
	11th to 20th	Night	22% 7% 2 5% 3 3 3 4 4 5% 42%	2000
	21st to end	Night	26% 8% 2 6% 4 3 3 2 4 5% 37%	2293
October	1st to 10th	Night	26% 8% 3 7% 4 4 4 3 5% 5% 29%	3920
	11th to 20th	Night	37% 8% 2 5% 3 3 3 3 4 5% 27%	3897
	21st to end	Night	39% 12% 2 5% 3 3 3 2 4 5% 22%	4523
November	1st to 10th	Night	43% 11% 3 6% 4 4 3 2 4 4 17%	2870
	11th to 20th	Night	41% 11% 3 6% 3 3 3 2 3 3 21%	2940
	21st to end	Night	40% 11% 3 7% 4 3 3 2 4 4 20%	2940
December	1st to 10th	Night	31% 10% 3 5% 3 3 4 3 4 6% 28%	4751
	11th to 20th	Night	48% 13% 3 6% 4 3 3 2 3 3 11%	5710
	21st to end	Night	50% 16% 3 6% 3 3 2 2 3 3 11%	7623

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	78% 5% 7% 7% 1	4125
	11th to 20th	Day	49% 5% 11% 19% 13% 2	4140
	21st to end	Day	67% 3 6% 16% 8%	5184
February	1st to 10th	Day	71% 5% 9% 8% 4 3	1890
	11th to 20th	Day	66% 5% 8% 13% 6% 1	1854
	21st to end	Day	71% 3 10% 10% 4 2	1574
March	1st to 10th	Day	72% 6% 9% 10% 3	4686
	11th to 20th	Day	66% 5% 9% 17% 2 1	5000
	21st to end	Day	74% 5% 11% 8% 2	5633
April	1st to 10th	Day	71% 6% 13% 8% 2	2400
	11th to 20th	Day	64% 4 12% 11% 7% 2	2471
	21st to end	Day	65% 6% 12% 12% 5%	2663
May	1st to 10th	Day	46% 5% 19% 20% 9%	6320
	11th to 20th	Day	55% 8% 19% 15% 3	6280
	21st to end	Day	57% 8% 18% 15% 2	7056
June	1st to 10th	Day	59% 4 18% 12% 4 2	3000
	11th to 20th	Day	65% 5% 16% 11% 3	3000
	21st to end	Day	53% 7% 16% 16% 7% 1	3000
July	1st to 10th	Day	30% 6% 18% 23% 18% 5%	6706
	11th to 20th	Day	20% 6% 20% 33% 19% 1	6699
	21st to end	Day	28% 7% 29% 23% 12% 1	6815
August	1st to 10th	Day	23% 4 11% 45% 15% 1	4498
	11th to 20th	Day	46% 7% 19% 17% 9% 1	4195
	21st to end	Day	45% 6% 18% 18% 11% 1	4552
September	1st to 10th	Day	42% 6% 14% 23% 11% 4	2400
	11th to 20th	Day	50% 6% 10% 18% 14% 2	2400
	21st to end	Day	55% 6% 14% 15% 9% 1	2102
October	1st to 10th	Day	60% 6% 15% 14% 5%	3280
	11th to 20th	Day	66% 6% 10% 11% 7%	3261
	21st to end	Day	72% 7% 8% 9% 4 1	3276
November	1st to 10th	Day	75% 4 8% 8% 4 1	1648
	11th to 20th	Day	74% 3 8% 8% 5% 2	1680
	21st to end	Day	72% 3 8% 9% 7% 1	1680
December	1st to 10th	Day	59% 5% 10% 16% 9% 1	2647
	11th to 20th	Day	82% 4 6% 5% 2 1	2718
	21st to end	Day	83% 5% 4 5% 2	3575
January	1st to 10th	Night	77% 4 6% 9% 3	8770
	11th to 20th	Night	46% 6% 13% 19% 14% 2	8820
	21st to end	Night	62% 3 8% 19% 9%	8997
February	1st to 10th	Night	70% 4 10% 8% 5% 3	2730
	11th to 20th	Night	64% 7% 9% 11% 8% 2	2664
	21st to end	Night	66% 3 11% 12% 6% 2	2231
March	1st to 10th	Night	66% 6% 9% 11% 7%	5251
	11th to 20th	Night	64% 4 11% 17% 4	5000
	21st to end	Night	74% 5% 12% 8% 2	5341
April	1st to 10th	Night	67% 5% 15% 12% 2	2000
	11th to 20th	Night	58% 6% 13% 14% 7% 2	1876
	21st to end	Night	61% 4 13% 15% 7%	1735
May	1st to 10th	Night	42% 5% 16% 25% 12%	3637
	11th to 20th	Night	46% 9% 22% 19% 4	3616
	21st to end	Night	57% 6% 20% 15% 2	3816
June	1st to 10th	Night	55% 5% 19% 13% 6% 3	1400
	11th to 20th	Night	56% 7% 18% 14% 4	1400
	21st to end	Night	45% 8% 21% 16% 7% 3	1400
July	1st to 10th	Night	25% 6% 21% 28% 16% 6%	3145
	11th to 20th	Night	13% 6% 22% 35% 23% 2	3138
	21st to end	Night	24% 6% 27% 27% 14% 2	3721
August	1st to 10th	Night	17% 3 16% 38% 25% 2	2625
	11th to 20th	Night	37% 8% 28% 16% 8% 3	2929
	21st to end	Night	42% 5% 20% 22% 9% 1	3359
September	1st to 10th	Night	33% 6% 19% 25% 14% 4	2000
	11th to 20th	Night	46% 7% 11% 17% 15% 4	2000
	21st to end	Night	52% 6% 15% 18% 8% 2	2293
October	1st to 10th	Night	58% 6% 16% 13% 6%	3920
	11th to 20th	Night	62% 4 9% 16% 8%	3897
	21st to end	Night	69% 5% 8% 13% 5%	4523
November	1st to 10th	Night	74% 4 8% 9% 4 1	2870
	11th to 20th	Night	71% 4 8% 9% 6% 2	2940
	21st to end	Night	71% 4 8% 8% 8% 1	2940
December	1st to 10th	Night	58% 6% 12% 17% 6% 1	4751
	11th to 20th	Night	81% 4 7% 6% 2 1	5706
	21st to end	Night	82% 3 5% 6% 3 1	7623

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	49% 7% 13% 18% 7% 6%	220
	11th to 20th	Day	45% 9% 14% 16% 15% 2	220
	21st to end	Day	50% 5% 15% 15% 14% 2	262
February	1st to 10th	Day	43% 8% 21% 18% 9% 1	430
	11th to 20th	Day	39% 8% 21% 21% 9% 1	425
	21st to end	Day	39% 12% 22% 18% 7% 1	365
March	1st to 10th	Day	37% 11% 21% 20% 10% 2	509
	11th to 20th	Day	41% 9% 15% 19% 15% 2	500
	21st to end	Day	43% 11% 22% 15% 7% 2	550
April	1st to 10th	Day	39% 13% 18% 19% 10% 1	500
	11th to 20th	Day	32% 12% 22% 20% 10% 3	492
	21st to end	Day	35% 11% 24% 19% 8% 3	500
May	1st to 10th	Day	26% 10% 24% 27% 12% 2	503
	11th to 20th	Day	30% 8% 20% 24% 13% 4	528
	21st to end	Day	25% 9% 25% 25% 11% 4	634
June	1st to 10th	Day	29% 9% 25% 26% 9% 2	730
	11th to 20th	Day	31% 11% 25% 24% 7% 2	730
	21st to end	Day	26% 7% 23% 27% 14% 3	730
July	1st to 10th	Day	19% 7% 22% 35% 14% 3	721
	11th to 20th	Day	13% 8% 29% 34% 13% 3	718
	21st to end	Day	13% 5% 20% 39% 17% 6%	634
August	1st to 10th	Day	18% 5% 20% 30% 19% 8%	527
	11th to 20th	Day	15% 6% 19% 33% 21% 6%	517
	21st to end	Day	19% 8% 22% 30% 16% 6%	583
September	1st to 10th	Day	20% 7% 25% 27% 15% 5%	530
	11th to 20th	Day	29% 7% 18% 27% 17% 3	530
	21st to end	Day	34% 7% 19% 22% 14% 5%	530
October	1st to 10th	Day	35% 6% 19% 19% 18% 4	530
	11th to 20th	Day	42% 8% 15% 16% 14% 5%	530
	21st to end	Day	48% 9% 15% 16% 8% 4	431
November	1st to 10th	Day	44% 12% 18% 15% 10% 1	220
	11th to 20th	Day	52% 5% 11% 12% 11% 8%	220
	21st to end	Day	50% 9% 14% 14% 6% 8%	220
December	1st to 10th	Day	48% 8% 12% 9% 16% 7%	220
	11th to 20th	Day	55% 7% 9% 16% 10% 3	220
	21st to end	Day	49% 7% 14% 21% 7% 2	242
January	1st to 10th	Night	54% 7% 12% 18% 8% 1	950
	11th to 20th	Night	43% 6% 16% 24% 11% 1	950
	21st to end	Night	45% 5% 15% 23% 11% 1	935
February	1st to 10th	Night	41% 7% 17% 26% 8% 1	840
	11th to 20th	Night	37% 8% 18% 26% 11%	824
	21st to end	Night	40% 8% 18% 22% 11% 1	692
March	1st to 10th	Night	40% 7% 16% 21% 14% 1	808
	11th to 20th	Night	46% 7% 14% 21% 13% 1	800
	21st to end	Night	45% 5% 13% 22% 12% 2	880
April	1st to 10th	Night	40% 5% 13% 28% 12% 2	800
	11th to 20th	Night	33% 5% 18% 29% 13% 2	688
	21st to end	Night	36% 4 15% 30% 14% 2	535
May	1st to 10th	Night	21% 4 16% 36% 23% 2	400
	11th to 20th	Night	25% 4 10% 30% 27% 4	394
	21st to end	Night	24% 3 12% 35% 24% 1	433
June	1st to 10th	Night	28% 3 13% 33% 22% 1	400
	11th to 20th	Night	25% 5% 19% 31% 19% 2	400
	21st to end	Night	21% 3 14% 31% 28% 4	400
July	1st to 10th	Night	13% 2 11% 34% 38% 2	390
	11th to 20th	Night	11% 2 8% 33% 41% 5%	388
	21st to end	Night	8% 2 7% 31% 45% 7%	438
August	1st to 10th	Night	15% 1 4 27% 43% 10%	409
	11th to 20th	Night	12% 2 4 28% 44% 10%	594
	21st to end	Night	17% 3 11% 31% 34% 4	722
September	1st to 10th	Night	15% 2 12% 35% 32% 4	800
	11th to 20th	Night	26% 3 10% 24% 31% 7%	800
	21st to end	Night	34% 3 14% 27% 20% 2	800
October	1st to 10th	Night	31% 4 15% 26% 22% 4	800
	11th to 20th	Night	42% 3 14% 24% 14% 3	800
	21st to end	Night	45% 3 17% 24% 9% 3	880
November	1st to 10th	Night	51% 5% 16% 21% 6%	820
	11th to 20th	Night	51% 4 16% 18% 10% 1	840
	21st to end	Night	47% 6% 16% 18% 10% 3	840
December	1st to 10th	Night	39% 5% 16% 26% 12% 2	854
	11th to 20th	Night	55% 9% 13% 18% 5% 1	950
	21st to end	Night	52% 8% 17% 17% 5%	1045

Page generated at 2026-02-27 22:40:23. Version ac07

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