Sawyer Lake
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Sawyer Lake clear sky chart from 2005-11-06 to 2024-11-08.

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	13% 9% 3 8% 5% 5% 5% 4 6% 7% 36%	101561
	Night	13% 10% 4 8% 5% 4 4 3 5% 7% 37%	97642
Transparency	Day	46% 5% 12% 24% 12% 1	105070
	Night	46% 4 12% 25% 12% 1	102273
Seeing	Day	19% 10% 31% 25% 12% 4	16032
	Night	18% 8% 30% 32% 11% 1	25897

By Month

Percentage Cloud Cover SE (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	12% 14% 4 11% 7% 6% 5% 3 5% 6% 27%	2527
	11th to 20th	Day	10% 13% 5% 12% 7% 7% 6% 5% 7% 7% 20%	2530
	21st to end	Day	13% 17% 7% 13% 6% 4 4 4 4 5% 23%	2783
February	1st to 10th	Day	9% 12% 3 10% 6% 5% 5% 4 5% 7% 36%	1679
	11th to 20th	Day	9% 12% 3 9% 5% 5% 5% 4 6% 6% 36%	1767
	21st to end	Day	11% 13% 3 9% 6% 5% 3 4 6% 7% 32%	1570
March	1st to 10th	Day	12% 11% 3 6% 4 4 3 2 4 6% 45%	3120
	11th to 20th	Day	7% 10% 3 10% 7% 6% 5% 4 6% 8% 34%	3283
	21st to end	Day	19% 13% 4 12% 5% 5% 4 3 4 5% 27%	4161
April	1st to 10th	Day	15% 12% 3 8% 6% 6% 5% 4 5% 5% 31%	2280
	11th to 20th	Day	20% 10% 3 7% 5% 5% 5% 4 5% 6% 31%	2254
	21st to end	Day	17% 11% 3 7% 5% 4 6% 5% 5% 6% 32%	2427
May	1st to 10th	Day	15% 7% 3 8% 5% 4 5% 4 5% 6% 39%	4295
	11th to 20th	Day	13% 7% 2 6% 4 4 4 3 5% 7% 43%	4399
	21st to end	Day	12% 9% 3 8% 5% 5% 5% 4 6% 7% 37%	4824
June	1st to 10th	Day	11% 6% 3 7% 5% 6% 5% 5% 6% 7% 40%	2660
	11th to 20th	Day	13% 7% 3 6% 5% 5% 5% 4 6% 7% 38%	2660
	21st to end	Day	11% 6% 2 6% 5% 4 5% 4 7% 10% 38%	2660
July	1st to 10th	Day	13% 5% 2 5% 5% 6% 6% 5% 7% 9% 38%	4440
	11th to 20th	Day	5% 4 2 4 4 5% 6% 5% 7% 10% 49%	4440
	21st to end	Day	7% 6% 2 6% 5% 5% 5% 4 7% 8% 46%	4813
August	1st to 10th	Day	10% 6% 2 7% 5% 6% 6% 4 7% 8% 38%	4423
	11th to 20th	Day	12% 5% 2 6% 4 5% 5% 4 6% 8% 45%	3991
	21st to end	Day	13% 7% 3 8% 5% 5% 5% 4 5% 8% 39%	4180
September	1st to 10th	Day	13% 6% 2 7% 4 4 5% 3 6% 7% 44%	2280
	11th to 20th	Day	11% 6% 2 6% 4 5% 4 5% 6% 8% 43%	2199
	21st to end	Day	12% 8% 3 7% 5% 5% 4 4 8% 7% 37%	2090
October	1st to 10th	Day	15% 8% 3 5% 4 4 3 4 5% 8% 40%	1962
	11th to 20th	Day	18% 10% 4 8% 5% 4 5% 3 5% 6% 31%	1863
	21st to end	Day	19% 11% 4 10% 4 4 3 4 5% 6% 30%	1881
November	1st to 10th	Day	13% 9% 3 7% 5% 4 4 4 6% 7% 37%	1735
	11th to 20th	Day	13% 12% 5% 11% 7% 5% 5% 5% 5% 7% 26%	1644
	21st to end	Day	14% 11% 3 8% 7% 5% 4 5% 6% 6% 31%	1520
December	1st to 10th	Day	12% 13% 4 10% 5% 5% 5% 4 6% 8% 29%	1520
	11th to 20th	Day	15% 15% 4 9% 6% 6% 6% 5% 6% 6% 23%	1918
	21st to end	Day	19% 24% 5% 9% 5% 4 3 3 3 5% 19%	2783
January	1st to 10th	Night	12% 15% 6% 11% 5% 4 4 4 4 6% 30%	4428
	11th to 20th	Night	9% 14% 6% 12% 7% 6% 5% 4 6% 8% 24%	4440
	21st to end	Night	11% 16% 9% 12% 6% 4 4 4 5% 5% 24%	4884
February	1st to 10th	Night	8% 12% 5% 11% 5% 5% 4 3 4 6% 36%	2499
	11th to 20th	Night	9% 11% 4 9% 5% 5% 5% 3 5% 8% 37%	2299
	21st to end	Night	13% 12% 5% 8% 6% 4 3 3 6% 6% 34%	1884
March	1st to 10th	Night	10% 8% 3 6% 4 4 4 3 5% 8% 46%	3733
	11th to 20th	Night	9% 9% 4 8% 5% 4 5% 4 6% 7% 38%	3707
	21st to end	Night	17% 11% 4 11% 6% 4 4 3 5% 7% 29%	3468
April	1st to 10th	Night	19% 11% 3 7% 5% 4 4 3 5% 6% 32%	1900
	11th to 20th	Night	20% 9% 3 5% 4 4 5% 3 4 6% 37%	1875
	21st to end	Night	16% 9% 3 7% 5% 5% 4 4 5% 7% 35%	1753
May	1st to 10th	Night	16% 7% 3 7% 4 5% 4 4 5% 7% 37%	2602
	11th to 20th	Night	11% 6% 2 6% 5% 4 4 5% 5% 6% 44%	2506
	21st to end	Night	16% 7% 3 8% 4 4 5% 3 5% 8% 37%	2743
June	1st to 10th	Night	10% 6% 3 6% 4 4 5% 4 5% 8% 47%	1520
	11th to 20th	Night	11% 7% 3 8% 6% 5% 5% 4 6% 7% 38%	1520
	21st to end	Night	10% 5% 2 6% 4 4 4 4 7% 9% 45%	1520
July	1st to 10th	Night	14% 5% 2 5% 4 4 4 4 5% 9% 45%	2530
	11th to 20th	Night	5% 4 1 3 3 3 4 4 6% 10% 57%	2530
	21st to end	Night	10% 6% 2 6% 4 3 3 3 4 7% 52%	2750
August	1st to 10th	Night	11% 5% 3 6% 4 5% 5% 4 5% 8% 44%	2517
	11th to 20th	Night	11% 4 2 5% 4 3 5% 4 6% 8% 48%	2838
	21st to end	Night	12% 9% 3 6% 3 4 3 3 4 6% 47%	3476
September	1st to 10th	Night	9% 6% 2 5% 4 3 4 3 5% 7% 53%	1900
	11th to 20th	Night	11% 4 2 5% 4 3 4 3 5% 8% 51%	1962
	21st to end	Night	13% 8% 2 5% 4 3 4 4 5% 8% 44%	2090
October	1st to 10th	Night	14% 6% 2 5% 3 4 4 3 5% 7% 46%	2215
	11th to 20th	Night	15% 9% 3 7% 4 3 4 4 5% 7% 37%	2316
	21st to end	Night	18% 10% 3 8% 5% 4 4 4 5% 7% 32%	2717
November	1st to 10th	Night	14% 11% 3 5% 5% 3 4 3 5% 8% 38%	2504
	11th to 20th	Night	13% 11% 5% 9% 5% 5% 4 4 5% 6% 32%	2533
	21st to end	Night	13% 11% 3 9% 6% 4 4 3 6% 7% 32%	2660
December	1st to 10th	Night	12% 14% 4 8% 6% 5% 4 4 5% 7% 31%	2660
	11th to 20th	Night	11% 15% 5% 10% 6% 4 4 4 5% 5% 30%	3279
	21st to end	Night	22% 21% 6% 8% 4 3 3 2 3 4 23%	4884

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	58% 4 10% 21% 7% 1	2528
	11th to 20th	Day	62% 4 11% 16% 6% 1	2530
	21st to end	Day	64% 3 12% 16% 5% 1	2783
February	1st to 10th	Day	48% 5% 11% 21% 14% 1	1679
	11th to 20th	Day	46% 6% 11% 25% 10% 2	1776
	21st to end	Day	51% 3 11% 22% 11% 2	1570
March	1st to 10th	Day	42% 3 12% 20% 21% 2	3120
	11th to 20th	Day	45% 6% 13% 22% 12% 1	3283
	21st to end	Day	60% 4 8% 18% 9% 1	4161
April	1st to 10th	Day	54% 5% 10% 18% 12% 1	2280
	11th to 20th	Day	54% 4 7% 22% 11% 2	2254
	21st to end	Day	53% 5% 9% 19% 13% 2	2427
May	1st to 10th	Day	45% 5% 9% 25% 15% 1	4334
	11th to 20th	Day	40% 5% 11% 30% 13% 1	4403
	21st to end	Day	47% 5% 9% 22% 16% 1	4837
June	1st to 10th	Day	40% 5% 12% 28% 13% 1	2660
	11th to 20th	Day	44% 5% 14% 22% 14% 1	2660
	21st to end	Day	39% 6% 16% 26% 12% 1	2660
July	1st to 10th	Day	40% 6% 15% 27% 11% 1	4371
	11th to 20th	Day	27% 6% 14% 36% 15% 2	4365
	21st to end	Day	34% 5% 11% 30% 18% 1	4662
August	1st to 10th	Day	41% 6% 14% 25% 14% 1	4408
	11th to 20th	Day	37% 5% 13% 33% 12%	4033
	21st to end	Day	43% 6% 14% 24% 14% 1	4179
September	1st to 10th	Day	39% 5% 13% 29% 14% 1	2280
	11th to 20th	Day	37% 5% 18% 31% 8% 1	2199
	21st to end	Day	44% 5% 12% 29% 10%	2090
October	1st to 10th	Day	30% 4 12% 32% 22%	3261
	11th to 20th	Day	47% 3 10% 24% 16% 1	3079
	21st to end	Day	49% 4 16% 24% 7%	3081
November	1st to 10th	Day	46% 4 11% 25% 12% 1	1735
	11th to 20th	Day	57% 5% 11% 18% 9% 1	1644
	21st to end	Day	52% 7% 13% 21% 5% 1	1520
December	1st to 10th	Day	53% 4 11% 23% 8%	1520
	11th to 20th	Day	59% 7% 11% 14% 9% 1	1915
	21st to end	Day	69% 3 6% 14% 8%	2783
January	1st to 10th	Night	54% 4 9% 24% 8% 1	4428
	11th to 20th	Night	59% 4 11% 20% 6%	4440
	21st to end	Night	62% 4 9% 19% 6% 1	4884
February	1st to 10th	Night	50% 3 8% 23% 13% 3	2499
	11th to 20th	Night	46% 5% 10% 25% 12% 3	2300
	21st to end	Night	51% 4 11% 22% 11% 2	1884
March	1st to 10th	Night	38% 3 16% 26% 14% 2	3733
	11th to 20th	Night	44% 5% 11% 26% 14% 1	3707
	21st to end	Night	56% 4 8% 20% 10% 1	3468
April	1st to 10th	Night	52% 6% 7% 17% 17% 1	1900
	11th to 20th	Night	48% 4 9% 23% 13% 3	1875
	21st to end	Night	48% 4 9% 23% 14% 1	1753
May	1st to 10th	Night	47% 5% 14% 21% 12% 1	2628
	11th to 20th	Night	38% 6% 11% 29% 13% 2	2507
	21st to end	Night	45% 5% 15% 18% 16% 2	2751
June	1st to 10th	Night	36% 6% 15% 26% 16% 1	1520
	11th to 20th	Night	43% 5% 13% 20% 17% 1	1520
	21st to end	Night	35% 6% 15% 31% 11% 2	1520
July	1st to 10th	Night	37% 5% 18% 25% 13% 3	2490
	11th to 20th	Night	22% 5% 17% 38% 15% 2	2482
	21st to end	Night	33% 4 13% 29% 20% 1	2662
August	1st to 10th	Night	38% 5% 14% 23% 18% 2	2508
	11th to 20th	Night	34% 6% 15% 29% 14% 2	2862
	21st to end	Night	39% 5% 13% 25% 17% 1	3476
September	1st to 10th	Night	31% 5% 12% 34% 16% 1	1900
	11th to 20th	Night	33% 4 15% 35% 12%	1962
	21st to end	Night	38% 5% 14% 30% 12% 1	2090
October	1st to 10th	Night	30% 3 9% 37% 19% 2	3696
	11th to 20th	Night	37% 4 11% 31% 16%	3839
	21st to end	Night	50% 4 10% 23% 12%	4467
November	1st to 10th	Night	44% 5% 11% 26% 14% 1	2504
	11th to 20th	Night	51% 5% 13% 18% 13% 1	2533
	21st to end	Night	51% 5% 13% 24% 6% 1	2660
December	1st to 10th	Night	53% 4 12% 22% 7% 1	2660
	11th to 20th	Night	55% 4 12% 19% 9% 1	3281
	21st to end	Night	66% 3 6% 18% 6%	4884

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	21% 10% 32% 24% 10% 2	270
	11th to 20th	Day	24% 10% 34% 25% 5% 1	270
	21st to end	Day	21% 9% 38% 25% 6% 1	297
February	1st to 10th	Day	17% 15% 39% 20% 7% 2	270
	11th to 20th	Day	20% 21% 39% 14% 6%	270
	21st to end	Day	20% 17% 45% 15% 2	225
March	1st to 10th	Day	18% 16% 46% 16% 4	270
	11th to 20th	Day	21% 12% 35% 22% 8% 2	270
	21st to end	Day	26% 10% 30% 23% 9% 1	502
April	1st to 10th	Day	25% 12% 33% 23% 7% 1	460
	11th to 20th	Day	33% 12% 25% 20% 8% 2	452
	21st to end	Day	26% 11% 30% 21% 10% 3	460
May	1st to 10th	Day	22% 14% 32% 21% 8% 3	586
	11th to 20th	Day	20% 9% 35% 24% 9% 3	675
	21st to end	Day	18% 9% 30% 26% 13% 4	734
June	1st to 10th	Day	14% 8% 30% 30% 15% 4	680
	11th to 20th	Day	18% 9% 29% 28% 13% 3	680
	21st to end	Day	13% 8% 29% 30% 15% 5%	680
July	1st to 10th	Day	10% 4 24% 34% 21% 6%	671
	11th to 20th	Day	10% 7% 29% 30% 17% 7%	668
	21st to end	Day	8% 6% 28% 32% 18% 8%	739
August	1st to 10th	Day	12% 5% 27% 29% 20% 6%	676
	11th to 20th	Day	16% 4 19% 28% 24% 8%	558
	21st to end	Day	16% 7% 22% 27% 21% 7%	539
September	1st to 10th	Day	17% 8% 23% 26% 18% 8%	490
	11th to 20th	Day	14% 7% 22% 35% 19% 4	490
	21st to end	Day	20% 9% 26% 26% 15% 4	490
October	1st to 10th	Day	23% 9% 27% 24% 13% 4	362
	11th to 20th	Day	25% 20% 35% 16% 4 1	300
	21st to end	Day	26% 15% 39% 16% 3	330
November	1st to 10th	Day	20% 12% 39% 21% 7% 2	291
	11th to 20th	Day	21% 16% 40% 16% 6% 1	270
	21st to end	Day	24% 17% 39% 14% 6% 1	270
December	1st to 10th	Day	20% 12% 43% 18% 5% 1	270
	11th to 20th	Day	26% 17% 34% 17% 5% 1	270
	21st to end	Day	31% 15% 34% 16% 4	297
January	1st to 10th	Night	17% 11% 38% 28% 6%	950
	11th to 20th	Night	20% 9% 37% 25% 7% 1	950
	21st to end	Night	18% 7% 37% 30% 8%	1045
February	1st to 10th	Night	15% 12% 37% 27% 8% 1	950
	11th to 20th	Night	16% 14% 34% 29% 7%	824
	21st to end	Night	21% 10% 36% 27% 5%	628
March	1st to 10th	Night	17% 10% 32% 32% 9%	760
	11th to 20th	Night	17% 10% 35% 30% 7% 1	706
	21st to end	Night	20% 7% 29% 33% 11% 1	627
April	1st to 10th	Night	25% 7% 33% 28% 6% 1	570
	11th to 20th	Night	25% 9% 28% 30% 9%	563
	21st to end	Night	22% 5% 30% 32% 10% 1	570
May	1st to 10th	Night	23% 5% 30% 34% 8% 1	570
	11th to 20th	Night	20% 5% 31% 35% 8% 1	561
	21st to end	Night	14% 5% 24% 40% 15% 1	617
June	1st to 10th	Night	12% 5% 26% 42% 15% 1	570
	11th to 20th	Night	18% 5% 25% 41% 11% 1	570
	21st to end	Night	12% 5% 21% 44% 17% 1	570
July	1st to 10th	Night	9% 2 20% 44% 23% 1	555
	11th to 20th	Night	11% 2 23% 41% 22% 1	552
	21st to end	Night	9% 3 21% 45% 21% 2	624
August	1st to 10th	Night	12% 2 20% 41% 23% 2	567
	11th to 20th	Night	11% 2 16% 39% 28% 4	564
	21st to end	Night	14% 4 19% 37% 25% 2	627
September	1st to 10th	Night	12% 4 23% 36% 20% 5%	570
	11th to 20th	Night	13% 4 25% 35% 20% 3	632
	21st to end	Night	16% 7% 24% 34% 17% 1	760
October	1st to 10th	Night	18% 8% 26% 28% 19% 1	760
	11th to 20th	Night	22% 11% 28% 32% 8%	760
	21st to end	Night	25% 8% 31% 26% 9% 1	836
November	1st to 10th	Night	20% 9% 37% 25% 8% 1	771
	11th to 20th	Night	20% 12% 36% 23% 7% 1	823
	21st to end	Night	20% 12% 33% 29% 6%	950
December	1st to 10th	Night	22% 11% 35% 23% 7% 1	950
	11th to 20th	Night	20% 11% 35% 26% 7% 1	950
	21st to end	Night	28% 10% 34% 24% 4	1045

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