Pense
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Pense clear sky chart from 2005-11-06 to 2025-05-26.

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	8% 8% 3 9% 6% 5% 5% 4 6% 8% 38%	117236
	Night	7% 9% 4 9% 6% 5% 5% 4 6% 7% 36%	120735
Transparency	Day	43% 7% 16% 24% 9% 1	116993
	Night	45% 6% 15% 23% 9% 1	120624
Seeing	Day	12% 9% 29% 30% 16% 4	16677
	Night	12% 7% 31% 35% 13% 1	26250

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% 14% 5% 13% 9% 9% 8% 5% 7% 6% 19%	3179
	11th to 20th	Day	3 8% 3 11% 9% 8% 9% 7% 10% 9% 23%	3497
	21st to end	Day	5% 10% 5% 14% 7% 6% 6% 4 5% 7% 32%	4004
February	1st to 10th	Day	8% 13% 6% 13% 9% 7% 7% 5% 6% 7% 21%	1661
	11th to 20th	Day	7% 14% 4 9% 7% 7% 8% 6% 7% 7% 25%	1755
	21st to end	Day	5% 11% 6% 13% 9% 7% 7% 6% 7% 6% 23%	1603
March	1st to 10th	Day	7% 11% 5% 14% 8% 4 5% 3 5% 7% 30%	4500
	11th to 20th	Day	5% 13% 6% 14% 6% 5% 5% 3 5% 7% 30%	4787
	21st to end	Day	8% 12% 5% 14% 7% 5% 5% 4 5% 7% 27%	5876
April	1st to 10th	Day	6% 9% 3 7% 6% 4 6% 5% 7% 8% 38%	2400
	11th to 20th	Day	13% 13% 4 10% 7% 5% 5% 4 7% 6% 28%	2389
	21st to end	Day	14% 11% 3 7% 5% 5% 4 3 5% 6% 36%	2775
May	1st to 10th	Day	17% 11% 3 6% 4 4 4 3 5% 7% 36%	4570
	11th to 20th	Day	9% 8% 3 7% 5% 6% 7% 5% 7% 8% 35%	4528
	21st to end	Day	13% 7% 2 8% 6% 6% 6% 5% 6% 8% 33%	4956
June	1st to 10th	Day	15% 7% 2 7% 4 4 4 4 6% 8% 38%	2969
	11th to 20th	Day	18% 7% 3 7% 5% 5% 5% 4 6% 8% 32%	3040
	21st to end	Day	9% 6% 2 6% 4 5% 5% 5% 7% 9% 42%	3040
July	1st to 10th	Day	5% 4 2 6% 5% 5% 6% 5% 8% 9% 45%	4850
	11th to 20th	Day	5% 3 1 4 3 4 5% 5% 7% 10% 53%	4622
	21st to end	Day	3 3 1 4 3 3 4 3 5% 8% 62%	4802
August	1st to 10th	Day	8% 5% 2 5% 3 4 4 4 6% 7% 52%	4412
	11th to 20th	Day	7% 4 2 5% 3 4 4 4 7% 10% 52%	4318
	21st to end	Day	9% 5% 2 5% 4 3 4 3 4 8% 55%	4273
September	1st to 10th	Day	11% 5% 2 6% 3 4 4 4 5% 9% 49%	2280
	11th to 20th	Day	13% 7% 2 6% 4 5% 5% 3 4 7% 44%	2275
	21st to end	Day	12% 5% 2 5% 3 3 3 3 6% 9% 48%	2050
October	1st to 10th	Day	9% 7% 2 6% 5% 4 5% 3 6% 7% 45%	3170
	11th to 20th	Day	6% 7% 2 6% 3 3 4 4 7% 11% 48%	3033
	21st to end	Day	7% 10% 4 9% 6% 4 5% 4 6% 8% 39%	3091
November	1st to 10th	Day	11% 15% 5% 9% 6% 5% 4 3 4 6% 32%	1635
	11th to 20th	Day	6% 12% 5% 14% 8% 6% 5% 4 5% 7% 29%	1600
	21st to end	Day	10% 12% 5% 10% 7% 7% 6% 5% 6% 6% 27%	1465
December	1st to 10th	Day	6% 13% 4 13% 8% 7% 6% 5% 6% 6% 26%	2290
	11th to 20th	Day	7% 16% 7% 14% 10% 6% 7% 4 5% 6% 18%	2475
	21st to end	Day	5% 8% 4 12% 8% 5% 5% 4 5% 6% 38%	3066
January	1st to 10th	Night	3 11% 5% 13% 10% 8% 7% 5% 7% 6% 25%	6766
	11th to 20th	Night	4 8% 4 12% 9% 9% 9% 6% 8% 6% 23%	6412
	21st to end	Night	5% 11% 5% 12% 7% 6% 6% 4 5% 7% 32%	6974
February	1st to 10th	Night	7% 12% 5% 12% 9% 7% 7% 5% 6% 7% 24%	2755
	11th to 20th	Night	6% 11% 4 10% 7% 5% 7% 6% 6% 7% 29%	2532
	21st to end	Night	4 8% 3 13% 7% 6% 7% 4 7% 9% 33%	2026
March	1st to 10th	Night	6% 10% 6% 13% 6% 5% 6% 5% 7% 8% 29%	5374
	11th to 20th	Night	7% 11% 4 11% 7% 6% 5% 4 6% 8% 31%	5186
	21st to end	Night	8% 12% 5% 15% 7% 5% 6% 4 6% 7% 26%	5080
April	1st to 10th	Night	6% 9% 3 6% 4 5% 5% 4 7% 9% 43%	2000
	11th to 20th	Night	12% 12% 4 8% 4 5% 5% 4 6% 8% 33%	1962
	21st to end	Night	13% 9% 4 7% 5% 5% 6% 5% 5% 7% 34%	1622
May	1st to 10th	Night	19% 14% 3 6% 4 4 4 3 5% 6% 33%	2620
	11th to 20th	Night	13% 7% 2 6% 4 4 4 4 6% 8% 40%	2598
	21st to end	Night	14% 6% 2 6% 5% 5% 5% 4 7% 8% 39%	2743
June	1st to 10th	Night	12% 5% 2 5% 4 4 4 4 7% 9% 44%	1208
	11th to 20th	Night	14% 7% 2 5% 4 5% 4 3 6% 9% 41%	1140
	21st to end	Night	8% 5% 2 4 4 4 6% 5% 7% 9% 47%	1140
July	1st to 10th	Night	6% 4 1 4 4 4 5% 4 7% 10% 52%	2106
	11th to 20th	Night	5% 3 1 4 3 3 4 3 6% 8% 59%	2338
	21st to end	Night	3 3 1 4 2 3 3 3 5% 8% 64%	2762
August	1st to 10th	Night	7% 4 1 4 4 4 3 3 5% 8% 56%	2528
	11th to 20th	Night	4 3 2 5% 4 4 5% 5% 8% 9% 53%	2518
	21st to end	Night	7% 4 2 4 3 4 5% 4 6% 9% 53%	3393
September	1st to 10th	Night	9% 4 2 4 3 4 4 4 5% 7% 54%	1900
	11th to 20th	Night	10% 5% 2 5% 4 4 4 4 5% 8% 48%	1905
	21st to end	Night	10% 6% 2 5% 4 4 3 4 6% 7% 50%	2128
October	1st to 10th	Night	11% 7% 2 5% 4 3 4 3 5% 8% 48%	3800
	11th to 20th	Night	5% 6% 2 5% 3 3 4 4 6% 10% 51%	3863
	21st to end	Night	7% 8% 3 7% 5% 4 4 4 5% 7% 44%	4467
November	1st to 10th	Night	14% 13% 5% 8% 5% 4 4 4 4 6% 32%	2663
	11th to 20th	Night	8% 12% 4 12% 7% 6% 6% 4 6% 7% 28%	2800
	21st to end	Night	8% 13% 5% 11% 6% 5% 5% 3 7% 7% 30%	2933
December	1st to 10th	Night	7% 15% 5% 15% 9% 8% 5% 4 4 7% 21%	4900
	11th to 20th	Night	7% 14% 6% 14% 8% 7% 7% 5% 5% 6% 20%	5720
	21st to end	Night	4 7% 3 11% 8% 5% 5% 4 5% 6% 41%	7873

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% 7% 12% 12% 5%	3179
	11th to 20th	Day	53% 6% 15% 16% 10%	3521
	21st to end	Day	52% 5% 21% 19% 3	4004
February	1st to 10th	Day	62% 4 12% 16% 6%	1661
	11th to 20th	Day	55% 8% 11% 15% 11% 1	1764
	21st to end	Day	56% 8% 13% 15% 8%	1603
March	1st to 10th	Day	53% 6% 18% 17% 6%	4500
	11th to 20th	Day	53% 7% 18% 18% 4	4788
	21st to end	Day	55% 7% 13% 17% 8% 1	5876
April	1st to 10th	Day	40% 8% 17% 23% 12% 1	2400
	11th to 20th	Day	54% 6% 13% 19% 6% 2	2389
	21st to end	Day	48% 5% 15% 23% 8% 1	2775
May	1st to 10th	Day	48% 5% 14% 24% 9% 1	4570
	11th to 20th	Day	41% 9% 12% 24% 13%	4532
	21st to end	Day	44% 8% 14% 25% 8%	4956
June	1st to 10th	Day	42% 7% 14% 27% 10% 1	2969
	11th to 20th	Day	49% 7% 14% 19% 10% 1	3040
	21st to end	Day	35% 9% 17% 29% 10% 1	3040
July	1st to 10th	Day	30% 10% 24% 28% 8% 1	4776
	11th to 20th	Day	25% 7% 18% 36% 14% 1	4541
	21st to end	Day	20% 6% 13% 40% 18% 3	4651
August	1st to 10th	Day	30% 7% 19% 26% 17% 1	4396
	11th to 20th	Day	27% 6% 18% 38% 10% 1	4360
	21st to end	Day	29% 5% 14% 38% 12% 1	4272
September	1st to 10th	Day	32% 7% 14% 28% 16% 2	2280
	11th to 20th	Day	39% 5% 14% 28% 11% 2	2275
	21st to end	Day	33% 5% 14% 32% 14% 2	2050
October	1st to 10th	Day	38% 5% 15% 30% 11% 2	3170
	11th to 20th	Day	30% 4 16% 37% 11% 2	3033
	21st to end	Day	43% 5% 17% 28% 7%	3091
November	1st to 10th	Day	55% 5% 13% 18% 7%	1635
	11th to 20th	Day	55% 6% 14% 18% 6% 1	1600
	21st to end	Day	55% 8% 17% 16% 4	1465
December	1st to 10th	Day	57% 7% 18% 13% 4	2290
	11th to 20th	Day	66% 5% 19% 7% 3	2475
	21st to end	Day	47% 4 11% 22% 11% 5%	3066
January	1st to 10th	Night	57% 6% 14% 18% 5%	6766
	11th to 20th	Night	57% 6% 15% 13% 8%	6450
	21st to end	Night	50% 6% 23% 18% 3	6974
February	1st to 10th	Night	57% 6% 12% 17% 7%	2755
	11th to 20th	Night	51% 6% 13% 19% 11% 1	2533
	21st to end	Night	47% 5% 17% 23% 9%	2026
March	1st to 10th	Night	51% 7% 21% 18% 4	5374
	11th to 20th	Night	49% 7% 19% 20% 5%	5186
	21st to end	Night	56% 6% 12% 19% 7%	5080
April	1st to 10th	Night	37% 5% 16% 25% 16% 1	2000
	11th to 20th	Night	48% 6% 10% 22% 10% 3	1962
	21st to end	Night	46% 7% 11% 24% 11% 1	1622
May	1st to 10th	Night	50% 6% 10% 21% 12% 1	2620
	11th to 20th	Night	39% 7% 12% 23% 16% 3	2598
	21st to end	Night	39% 9% 13% 29% 9% 1	2743
June	1st to 10th	Night	34% 6% 15% 29% 14% 2	1208
	11th to 20th	Night	39% 8% 16% 23% 13% 1	1140
	21st to end	Night	31% 9% 17% 31% 11% 1	1140
July	1st to 10th	Night	25% 9% 29% 29% 7%	2071
	11th to 20th	Night	21% 6% 14% 39% 17% 2	2296
	21st to end	Night	18% 5% 14% 40% 18% 6%	2674
August	1st to 10th	Night	26% 7% 19% 31% 17% 1	2520
	11th to 20th	Night	24% 7% 17% 37% 13% 1	2542
	21st to end	Night	27% 6% 14% 37% 14% 2	3393
September	1st to 10th	Night	29% 6% 11% 30% 22% 3	1900
	11th to 20th	Night	33% 6% 15% 28% 16% 2	1905
	21st to end	Night	34% 5% 13% 31% 16% 2	2128
October	1st to 10th	Night	35% 4 16% 31% 11% 2	3800
	11th to 20th	Night	28% 4 15% 39% 13% 1	3863
	21st to end	Night	39% 4 12% 33% 11%	4467
November	1st to 10th	Night	54% 6% 13% 19% 7% 2	2663
	11th to 20th	Night	54% 7% 17% 16% 6%	2800
	21st to end	Night	52% 6% 19% 18% 4	2933
December	1st to 10th	Night	64% 7% 16% 10% 3	4900
	11th to 20th	Night	63% 7% 16% 11% 3	5719
	21st to end	Night	43% 4 11% 25% 13% 4	7873

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	13% 11% 28% 30% 15% 5%	200
	11th to 20th	Day	9% 11% 32% 30% 16% 2	274
	21st to end	Day	12% 9% 34% 33% 10% 1	330
February	1st to 10th	Day	14% 9% 37% 29% 11% 1	300
	11th to 20th	Day	13% 6% 37% 26% 15% 3	300
	21st to end	Day	6% 7% 32% 37% 15% 3	249
March	1st to 10th	Day	12% 8% 36% 28% 13% 3	300
	11th to 20th	Day	11% 11% 37% 26% 10% 4	405
	21st to end	Day	13% 11% 31% 29% 14% 2	550
April	1st to 10th	Day	10% 15% 36% 28% 10% 2	500
	11th to 20th	Day	16% 15% 33% 25% 10% 1	507
	21st to end	Day	16% 10% 29% 28% 16% 1	700
May	1st to 10th	Day	13% 7% 28% 30% 18% 4	703
	11th to 20th	Day	14% 6% 27% 30% 17% 7%	725
	21st to end	Day	16% 8% 24% 28% 18% 6%	760
June	1st to 10th	Day	16% 11% 28% 24% 17% 4	680
	11th to 20th	Day	19% 13% 29% 25% 12% 3	680
	21st to end	Day	10% 8% 24% 32% 20% 5%	680
July	1st to 10th	Day	7% 5% 22% 35% 24% 7%	671
	11th to 20th	Day	7% 6% 28% 31% 21% 6%	668
	21st to end	Day	6% 6% 26% 31% 22% 9%	739
August	1st to 10th	Day	8% 6% 20% 38% 21% 6%	676
	11th to 20th	Day	8% 4 21% 35% 24% 8%	653
	21st to end	Day	10% 7% 24% 32% 21% 6%	539
September	1st to 10th	Day	11% 12% 29% 30% 13% 4	490
	11th to 20th	Day	16% 9% 28% 29% 16% 1	485
	21st to end	Day	14% 9% 30% 30% 14% 2	300
October	1st to 10th	Day	17% 8% 28% 26% 19% 2	300
	11th to 20th	Day	10% 12% 35% 25% 16% 1	300
	21st to end	Day	13% 11% 37% 28% 9% 2	330
November	1st to 10th	Day	20% 10% 29% 28% 10% 3	300
	11th to 20th	Day	14% 10% 38% 28% 10%	300
	21st to end	Day	13% 10% 37% 27% 11% 1	300
December	1st to 10th	Day	12% 8% 38% 30% 9% 3	300
	11th to 20th	Day	11% 9% 50% 24% 5% 1	263
	21st to end	Day	11% 5% 33% 34% 14% 3	220
January	1st to 10th	Night	7% 11% 36% 32% 12% 2	1000
	11th to 20th	Night	12% 11% 35% 33% 8% 1	1000
	21st to end	Night	12% 11% 38% 28% 10% 1	1100
February	1st to 10th	Night	11% 9% 33% 33% 13% 1	955
	11th to 20th	Night	10% 7% 35% 36% 10% 2	784
	21st to end	Night	5% 6% 26% 40% 19% 4	660
March	1st to 10th	Night	10% 8% 34% 34% 13% 2	800
	11th to 20th	Night	11% 7% 35% 32% 13% 1	800
	21st to end	Night	14% 7% 29% 35% 14% 1	704
April	1st to 10th	Night	9% 7% 36% 37% 11% 1	600
	11th to 20th	Night	17% 10% 32% 34% 6% 1	593
	21st to end	Night	18% 8% 30% 37% 7% 1	600
May	1st to 10th	Night	15% 5% 27% 36% 16% 1	600
	11th to 20th	Night	15% 7% 29% 34% 14% 1	591
	21st to end	Night	19% 5% 26% 32% 16% 2	634
June	1st to 10th	Night	13% 6% 29% 35% 16% 1	448
	11th to 20th	Night	17% 7% 28% 36% 12% 1	380
	21st to end	Night	10% 7% 25% 41% 16% 1	380
July	1st to 10th	Night	8% 4 19% 47% 19% 1	370
	11th to 20th	Night	7% 3 26% 45% 18% 1	434
	21st to end	Night	5% 3 25% 43% 22% 2	624
August	1st to 10th	Night	7% 3 24% 42% 21% 2	567
	11th to 20th	Night	6% 4 21% 42% 24% 3	564
	21st to end	Night	8% 4 27% 40% 19% 1	627
September	1st to 10th	Night	9% 6% 26% 39% 17% 3	570
	11th to 20th	Night	11% 6% 25% 42% 16% 1	570
	21st to end	Night	13% 5% 31% 39% 11% 1	608
October	1st to 10th	Night	18% 6% 27% 33% 15% 1	760
	11th to 20th	Night	12% 6% 30% 37% 14% 1	807
	21st to end	Night	16% 9% 32% 32% 9% 1	1045
November	1st to 10th	Night	20% 7% 33% 32% 8%	975
	11th to 20th	Night	14% 10% 34% 31% 9% 2	1000
	21st to end	Night	13% 10% 37% 34% 6% 1	1000
December	1st to 10th	Night	13% 7% 35% 30% 12% 3	1000
	11th to 20th	Night	13% 11% 34% 29% 12% 1	1000
	21st to end	Night	13% 5% 32% 35% 14% 2	1100

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