McDonald Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the McDonald Park clear sky chart from 2005-11-06 to 2024-04-03.

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	25% 10% 4 6% 5% 3 4 4 4 5% 29%	78467
	Night	29% 11% 3 6% 5% 3 4 4 4 5% 28%	81607
Transparency	Day	58% 4 13% 16% 7% 1	78180
	Night	60% 4 13% 14% 7% 2	81474
Seeing	Day	29% 11% 24% 23% 11% 3	14322
	Night	35% 6% 16% 24% 17% 3	22834

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	40% 16% 4 8% 5% 2 3 3 3 3 11%	2219
	11th to 20th	Day	28% 12% 5% 7% 5% 3 3 3 3 4 26%	2299
	21st to end	Day	44% 16% 4 6% 5% 2 2 2 3 3 12%	2794
February	1st to 10th	Day	35% 11% 5% 8% 5% 3 4 3 4 4 17%	1697
	11th to 20th	Day	30% 14% 4 7% 5% 3 4 4 3 4 22%	1665
	21st to end	Day	27% 17% 5% 7% 6% 5% 5% 3 3 3 20%	1462
March	1st to 10th	Day	27% 15% 5% 9% 7% 3 4 4 3 4 19%	1924
	11th to 20th	Day	31% 13% 4 7% 6% 3 5% 4 3 4 20%	2090
	21st to end	Day	29% 14% 4 8% 7% 3 6% 4 4 4 17%	2387
April	1st to 10th	Day	29% 12% 4 8% 6% 4 5% 5% 5% 5% 17%	2185
	11th to 20th	Day	26% 11% 4 9% 7% 4 6% 4 5% 5% 19%	2176
	21st to end	Day	27% 11% 5% 8% 7% 4 4 4 5% 5% 21%	2423
May	1st to 10th	Day	22% 9% 4 7% 7% 3 5% 5% 4 5% 29%	2520
	11th to 20th	Day	19% 9% 3 7% 6% 3 5% 5% 6% 7% 29%	2477
	21st to end	Day	26% 10% 4 7% 6% 3 4 4 4 5% 27%	2723
June	1st to 10th	Day	27% 9% 4 7% 6% 4 4 4 4 6% 25%	2682
	11th to 20th	Day	30% 11% 4 8% 7% 3 4 4 4 5% 20%	2700
	21st to end	Day	17% 8% 3 7% 6% 3 5% 5% 5% 6% 35%	2700
July	1st to 10th	Day	14% 6% 3 4 5% 3 4 4 5% 5% 47%	2700
	11th to 20th	Day	12% 7% 2 4 4 2 4 4 4 7% 49%	2688
	21st to end	Day	10% 4 2 3 3 2 3 3 4 5% 61%	2741
August	1st to 10th	Day	12% 5% 2 4 3 2 4 4 5% 6% 53%	2507
	11th to 20th	Day	9% 4 2 4 4 2 3 4 5% 8% 55%	2317
	21st to end	Day	15% 6% 3 5% 6% 3 4 4 4 7% 43%	2484
September	1st to 10th	Day	14% 7% 3 6% 5% 3 3 3 4 6% 47%	2160
	11th to 20th	Day	18% 7% 3 7% 6% 3 4 4 4 4 39%	2160
	21st to end	Day	25% 6% 3 6% 5% 3 3 4 4 5% 37%	1907
October	1st to 10th	Day	24% 9% 3 5% 5% 3 3 3 5% 5% 35%	1800
	11th to 20th	Day	30% 9% 3 6% 5% 3 4 4 4 6% 26%	1800
	21st to end	Day	36% 7% 2 5% 5% 3 4 3 4 6% 23%	1836
November	1st to 10th	Day	38% 10% 3 7% 6% 4 4 3 4 5% 17%	1495
	11th to 20th	Day	38% 13% 3 6% 5% 2 3 3 3 3 22%	1520
	21st to end	Day	38% 11% 4 6% 5% 3 4 3 4 3 19%	1520
December	1st to 10th	Day	31% 14% 4 7% 4 2 3 3 3 3 26%	1520
	11th to 20th	Day	34% 13% 4 8% 5% 3 4 3 3 3 19%	1747
	21st to end	Day	34% 16% 5% 9% 6% 3 4 4 3 4 12%	2442
January	1st to 10th	Night	40% 17% 5% 7% 6% 3 3 3 3 3 13%	4726
	11th to 20th	Night	32% 11% 3 4 3 2 3 3 4 6% 29%	4596
	21st to end	Night	42% 15% 4 7% 4 2 3 2 2 3 14%	4862
February	1st to 10th	Night	36% 12% 4 7% 6% 3 4 4 3 4 19%	2480
	11th to 20th	Night	30% 15% 3 6% 6% 3 4 3 3 4 21%	2402
	21st to end	Night	30% 13% 4 6% 6% 3 3 3 3 5% 24%	1991
March	1st to 10th	Night	29% 11% 4 7% 5% 3 4 4 3 6% 23%	2256
	11th to 20th	Night	30% 12% 4 7% 5% 3 4 3 5% 5% 22%	2089
	21st to end	Night	33% 13% 4 7% 6% 3 4 4 4 4 19%	2210
April	1st to 10th	Night	28% 12% 4 6% 6% 3 6% 5% 5% 5% 21%	1820
	11th to 20th	Night	24% 11% 3 8% 6% 4 5% 5% 4 5% 24%	1732
	21st to end	Night	31% 10% 3 7% 6% 3 3 5% 5% 5% 21%	1536
May	1st to 10th	Night	20% 7% 3 7% 5% 4 4 5% 4 5% 35%	1440
	11th to 20th	Night	17% 7% 3 6% 6% 3 6% 6% 7% 6% 33%	1416
	21st to end	Night	19% 9% 2 6% 6% 3 5% 4 5% 7% 34%	1552
June	1st to 10th	Night	19% 8% 4 8% 8% 4 6% 4 5% 5% 30%	1276
	11th to 20th	Night	23% 9% 4 7% 7% 4 5% 4 6% 6% 24%	1260
	21st to end	Night	15% 8% 1 4 5% 3 4 5% 6% 7% 43%	1260
July	1st to 10th	Night	13% 6% 2 5% 4 2 4 5% 4 5% 50%	1260
	11th to 20th	Night	9% 5% 2 4 3 2 3 3 4 6% 57%	1268
	21st to end	Night	7% 2 1 2 3 2 3 3 5% 6% 66%	1576
August	1st to 10th	Night	11% 4 2 3 3 1 3 3 5% 6% 60%	1432
	11th to 20th	Night	7% 3 1 4 2 2 2 4 5% 7% 63%	1580
	21st to end	Night	11% 5% 2 5% 5% 3 4 5% 5% 9% 45%	1871
September	1st to 10th	Night	12% 5% 1 4 4 3 3 4 5% 7% 52%	1800
	11th to 20th	Night	19% 5% 2 7% 5% 3 4 4 4 6% 42%	1800
	21st to end	Night	20% 8% 2 6% 5% 3 4 4 4 5% 39%	2049
October	1st to 10th	Night	23% 7% 3 5% 5% 2 5% 4 4 5% 36%	2160
	11th to 20th	Night	31% 9% 3 5% 4 2 3 4 3 6% 29%	2160
	21st to end	Night	33% 10% 3 6% 5% 2 3 3 3 5% 27%	2520
November	1st to 10th	Night	38% 12% 4 6% 5% 2 4 4 4 4 18%	2580
	11th to 20th	Night	39% 10% 3 6% 5% 3 3 3 3 4 21%	2660
	21st to end	Night	39% 10% 3 6% 5% 3 3 3 3 4 20%	2660
December	1st to 10th	Night	31% 11% 3 5% 5% 2 4 4 4 4 27%	2660
	11th to 20th	Night	39% 14% 3 7% 5% 3 4 3 3 3 15%	3453
	21st to end	Night	38% 15% 4 7% 6% 3 4 3 3 3 13%	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	78% 2 8% 9% 3	2219
	11th to 20th	Day	63% 3 12% 13% 4 5%	2320
	21st to end	Day	78% 3 8% 8% 3 1	2794
February	1st to 10th	Day	71% 4 9% 9% 7% 1	1697
	11th to 20th	Day	67% 4 9% 12% 7% 2	1674
	21st to end	Day	70% 3 9% 11% 5% 2	1462
March	1st to 10th	Day	68% 3 11% 12% 5% 1	1924
	11th to 20th	Day	69% 3 10% 13% 5% 1	2090
	21st to end	Day	71% 4 12% 12% 2	2387
April	1st to 10th	Day	69% 6% 12% 11% 2	2185
	11th to 20th	Day	66% 4 9% 11% 8% 1	2176
	21st to end	Day	66% 4 12% 10% 7% 1	2423
May	1st to 10th	Day	57% 5% 14% 17% 6% 1	2520
	11th to 20th	Day	53% 5% 19% 17% 6%	2480
	21st to end	Day	59% 6% 16% 16% 3	2724
June	1st to 10th	Day	61% 4 15% 14% 4 3	2682
	11th to 20th	Day	67% 4 15% 11% 3	2700
	21st to end	Day	50% 4 18% 19% 8% 1	2700
July	1st to 10th	Day	40% 6% 15% 25% 12% 2	2626
	11th to 20th	Day	35% 5% 17% 30% 10% 2	2607
	21st to end	Day	25% 3 16% 36% 15% 4	2589
August	1st to 10th	Day	32% 5% 19% 31% 12% 2	2490
	11th to 20th	Day	28% 5% 21% 28% 15% 3	2317
	21st to end	Day	41% 4 19% 27% 8% 1	2484
September	1st to 10th	Day	40% 4 16% 23% 13% 5%	2160
	11th to 20th	Day	49% 3 12% 17% 17% 3	2160
	21st to end	Day	51% 4 15% 18% 11% 2	1907
October	1st to 10th	Day	53% 3 14% 17% 12%	1800
	11th to 20th	Day	58% 5% 13% 16% 7% 1	1800
	21st to end	Day	63% 3 14% 12% 9% 1	1836
November	1st to 10th	Day	71% 3 11% 11% 3 1	1495
	11th to 20th	Day	71% 2 9% 10% 5% 2	1520
	21st to end	Day	70% 3 7% 11% 8% 2	1520
December	1st to 10th	Day	65% 5% 9% 10% 11% 1	1520
	11th to 20th	Day	70% 3 11% 12% 3 1	1750
	21st to end	Day	75% 2 12% 7% 3	2442
January	1st to 10th	Night	78% 2 7% 11% 2	4726
	11th to 20th	Night	58% 4 14% 13% 6% 5%	4637
	21st to end	Night	77% 2 8% 8% 3 1	4862
February	1st to 10th	Night	70% 4 10% 9% 5% 2	2480
	11th to 20th	Night	68% 3 8% 12% 7% 1	2404
	21st to end	Night	64% 3 9% 15% 7% 1	1991
March	1st to 10th	Night	63% 4 14% 13% 5% 1	2256
	11th to 20th	Night	64% 4 13% 13% 5%	2090
	21st to end	Night	69% 3 16% 10% 1	2210
April	1st to 10th	Night	65% 5% 15% 12% 2	1820
	11th to 20th	Night	62% 5% 11% 14% 7% 2	1732
	21st to end	Night	65% 4 12% 13% 6% 1	1536
May	1st to 10th	Night	53% 5% 18% 17% 6% 1	1440
	11th to 20th	Night	50% 6% 21% 17% 6%	1416
	21st to end	Night	50% 6% 21% 19% 4	1552
June	1st to 10th	Night	57% 4 18% 14% 4 3	1276
	11th to 20th	Night	61% 6% 19% 11% 3	1260
	21st to end	Night	41% 5% 25% 19% 6% 3	1260
July	1st to 10th	Night	37% 5% 17% 24% 15% 2	1225
	11th to 20th	Night	31% 5% 18% 32% 13% 1	1226
	21st to end	Night	20% 4 16% 34% 20% 5%	1488
August	1st to 10th	Night	26% 4 21% 29% 16% 3	1424
	11th to 20th	Night	22% 5% 25% 28% 14% 6%	1580
	21st to end	Night	37% 5% 20% 28% 9% 1	1871
September	1st to 10th	Night	35% 5% 18% 24% 14% 4	1800
	11th to 20th	Night	46% 3 15% 18% 15% 5%	1800
	21st to end	Night	49% 4 16% 18% 10% 2	2049
October	1st to 10th	Night	52% 4 15% 19% 9% 1	2160
	11th to 20th	Night	59% 3 14% 16% 8% 1	2160
	21st to end	Night	62% 4 11% 15% 8%	2520
November	1st to 10th	Night	71% 3 10% 11% 4 1	2580
	11th to 20th	Night	69% 4 9% 10% 6% 2	2660
	21st to end	Night	70% 4 8% 10% 8% 1	2660
December	1st to 10th	Night	60% 5% 12% 13% 8% 1	2660
	11th to 20th	Night	76% 3 10% 7% 4 1	3449
	21st to end	Night	77% 2 9% 8% 4	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	43% 16% 16% 13% 7% 4	180
	11th to 20th	Day	44% 13% 14% 16% 11% 1	180
	21st to end	Day	45% 9% 21% 16% 8% 1	198
February	1st to 10th	Day	47% 13% 19% 13% 6% 2	357
	11th to 20th	Day	42% 11% 24% 18% 4 1	365
	21st to end	Day	39% 13% 27% 14% 6% 1	332
March	1st to 10th	Day	37% 14% 24% 16% 8% 1	460
	11th to 20th	Day	36% 11% 22% 18% 12% 1	460
	21st to end	Day	38% 15% 20% 18% 8%	506
April	1st to 10th	Day	39% 12% 23% 18% 7% 1	429
	11th to 20th	Day	31% 15% 25% 17% 11% 1	412
	21st to end	Day	29% 17% 27% 16% 9% 2	420
May	1st to 10th	Day	22% 12% 31% 26% 8% 1	423
	11th to 20th	Day	24% 9% 24% 26% 13% 4	448
	21st to end	Day	28% 11% 24% 23% 11% 4	485
June	1st to 10th	Day	26% 11% 30% 22% 9% 2	612
	11th to 20th	Day	30% 12% 28% 23% 6% 1	630
	21st to end	Day	20% 11% 26% 28% 14% 2	630
July	1st to 10th	Day	17% 7% 28% 35% 10% 2	621
	11th to 20th	Day	13% 10% 26% 35% 14% 3	606
	21st to end	Day	9% 6% 24% 38% 16% 7%	487
August	1st to 10th	Day	14% 6% 24% 31% 17% 9%	447
	11th to 20th	Day	10% 5% 24% 32% 22% 7%	437
	21st to end	Day	18% 11% 24% 28% 14% 5%	495
September	1st to 10th	Day	20% 11% 24% 29% 13% 3	450
	11th to 20th	Day	24% 8% 21% 28% 16% 4	450
	21st to end	Day	27% 9% 22% 25% 13% 4	450
October	1st to 10th	Day	30% 8% 20% 21% 17% 3	450
	11th to 20th	Day	36% 8% 17% 21% 14% 3	450
	21st to end	Day	38% 12% 21% 17% 10% 3	351
November	1st to 10th	Day	40% 13% 22% 19% 5% 1	183
	11th to 20th	Day	49% 7% 15% 13% 12% 3	180
	21st to end	Day	47% 8% 21% 9% 11% 3	180
December	1st to 10th	Day	46% 8% 19% 11% 9% 6%	180
	11th to 20th	Day	50% 7% 21% 15% 5% 2	180
	21st to end	Day	48% 12% 19% 16% 5% 1	198
January	1st to 10th	Night	50% 10% 16% 15% 8% 1	850
	11th to 20th	Night	45% 7% 16% 21% 11% 1	819
	21st to end	Night	43% 8% 18% 21% 9% 1	836
February	1st to 10th	Night	43% 9% 21% 21% 6% 1	760
	11th to 20th	Night	43% 7% 20% 22% 8%	744
	21st to end	Night	38% 10% 20% 22% 9% 1	628
March	1st to 10th	Night	34% 10% 18% 22% 15% 1	760
	11th to 20th	Night	40% 6% 19% 22% 13% 1	760
	21st to end	Night	40% 7% 18% 24% 9% 2	836
April	1st to 10th	Night	38% 6% 16% 27% 12% 2	728
	11th to 20th	Night	31% 7% 20% 25% 15% 1	664
	21st to end	Night	38% 4 16% 29% 12% 2	456
May	1st to 10th	Night	23% 7% 15% 29% 24% 1	360
	11th to 20th	Night	23% 2 10% 29% 32% 5%	354
	21st to end	Night	26% 2 10% 31% 28% 3	389
June	1st to 10th	Night	23% 3 16% 32% 21% 4	360
	11th to 20th	Night	26% 6% 14% 27% 22% 5%	360
	21st to end	Night	19% 2 11% 31% 32% 5%	360
July	1st to 10th	Night	15% 2 9% 28% 41% 4	350
	11th to 20th	Night	11% 5% 9% 29% 39% 7%	348
	21st to end	Night	9% 2 2 29% 50% 8%	394
August	1st to 10th	Night	14% 1 4 22% 47% 12%	358
	11th to 20th	Night	9% 1 6% 25% 47% 12%	512
	21st to end	Night	15% 3 8% 31% 38% 5%	683
September	1st to 10th	Night	17% 2 11% 38% 28% 5%	720
	11th to 20th	Night	22% 3 15% 22% 33% 7%	720
	21st to end	Night	27% 5% 13% 28% 25% 3	720
October	1st to 10th	Night	28% 4 15% 26% 25% 3	720
	11th to 20th	Night	37% 5% 14% 24% 17% 3	720
	21st to end	Night	41% 7% 17% 23% 10% 2	792
November	1st to 10th	Night	47% 7% 19% 21% 6%	740
	11th to 20th	Night	50% 7% 17% 16% 9% 1	760
	21st to end	Night	47% 9% 17% 15% 10% 2	760
December	1st to 10th	Night	37% 7% 22% 23% 11% 1	760
	11th to 20th	Night	51% 6% 21% 17% 4 1	818
	21st to end	Night	52% 7% 21% 16% 4	935

Page generated at 2024-03-31 03:08:56. Version ac07

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