Fisher Branch
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Fisher Branch clear sky chart from 2005-11-06 to 2024-02-05.

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	12% 9% 4 7% 7% 4 6% 6% 6% 7% 33%	77676
	Night	10% 10% 5% 8% 7% 4 6% 5% 6% 7% 32%	81179
Transparency	Day	48% 7% 14% 22% 8% 1	77378
	Night	49% 6% 14% 21% 9% 1	81058
Seeing	Day	15% 8% 30% 28% 15% 4	15165
	Night	15% 6% 29% 34% 14% 2	25293

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	6% 14% 7% 10% 8% 7% 8% 7% 9% 6% 18%	2219
	11th to 20th	Day	5% 8% 5% 19% 14% 8% 7% 8% 7% 8% 11%	2199
	21st to end	Day	7% 13% 9% 12% 9% 5% 6% 5% 7% 7% 19%	2733
February	1st to 10th	Day	8% 11% 5% 11% 10% 6% 8% 7% 7% 8% 20%	1517
	11th to 20th	Day	8% 10% 4 8% 6% 5% 9% 7% 6% 8% 28%	1574
	21st to end	Day	6% 11% 6% 8% 9% 4 6% 8% 6% 7% 28%	1403
March	1st to 10th	Day	12% 11% 4 9% 10% 4 7% 6% 5% 8% 24%	1818
	11th to 20th	Day	9% 9% 4 10% 9% 4 7% 6% 6% 6% 30%	1978
	21st to end	Day	10% 10% 4 8% 7% 4 6% 6% 5% 7% 34%	2178
April	1st to 10th	Day	10% 10% 3 8% 6% 4 6% 4 5% 7% 37%	2223
	11th to 20th	Day	12% 8% 4 7% 6% 4 5% 5% 6% 7% 35%	2312
	21st to end	Day	13% 8% 3 6% 6% 4 5% 5% 5% 8% 37%	2340
May	1st to 10th	Day	15% 9% 3 6% 5% 3 4 5% 5% 7% 38%	2454
	11th to 20th	Day	17% 8% 3 4 5% 3 4 5% 5% 7% 40%	2655
	21st to end	Day	19% 9% 3 6% 6% 3 4 5% 5% 6% 35%	2918
June	1st to 10th	Day	17% 7% 3 6% 5% 3 4 6% 5% 8% 35%	2700
	11th to 20th	Day	16% 6% 3 6% 7% 3 6% 5% 6% 7% 35%	2700
	21st to end	Day	13% 6% 3 5% 6% 3 6% 6% 7% 8% 36%	2700
July	1st to 10th	Day	9% 4 2 4 5% 3 5% 7% 7% 8% 47%	2700
	11th to 20th	Day	10% 6% 3 5% 5% 4 5% 5% 6% 9% 43%	2700
	21st to end	Day	8% 5% 2 5% 4 3 5% 5% 6% 9% 48%	2939
August	1st to 10th	Day	8% 5% 2 4 6% 4 7% 5% 6% 9% 44%	2490
	11th to 20th	Day	13% 4 2 4 5% 3 5% 6% 5% 9% 44%	2301
	21st to end	Day	14% 5% 2 5% 4 3 5% 5% 7% 7% 43%	2574
September	1st to 10th	Day	11% 6% 2 5% 5% 3 5% 4 6% 7% 46%	2253
	11th to 20th	Day	15% 6% 4 7% 6% 4 5% 4 6% 8% 36%	1980
	21st to end	Day	13% 7% 4 6% 6% 3 4 5% 6% 8% 37%	1980
October	1st to 10th	Day	18% 9% 4 8% 6% 3 4 5% 6% 7% 31%	1843
	11th to 20th	Day	13% 12% 4 8% 8% 4 4 5% 6% 7% 27%	1724
	21st to end	Day	15% 14% 6% 9% 8% 3 6% 5% 6% 5% 23%	1782
November	1st to 10th	Day	17% 13% 7% 10% 9% 3 4 3 5% 6% 24%	1497
	11th to 20th	Day	9% 14% 6% 11% 8% 5% 6% 5% 5% 6% 24%	1511
	21st to end	Day	12% 15% 5% 9% 9% 4 5% 5% 5% 6% 24%	1330
December	1st to 10th	Day	8% 13% 6% 12% 11% 6% 9% 6% 5% 7% 17%	1330
	11th to 20th	Day	8% 13% 7% 13% 8% 4 5% 6% 6% 7% 21%	1679
	21st to end	Day	8% 9% 5% 8% 9% 4 5% 6% 6% 7% 33%	2442
January	1st to 10th	Night	6% 12% 6% 11% 9% 6% 9% 7% 7% 8% 20%	4737
	11th to 20th	Night	5% 11% 7% 15% 13% 8% 9% 7% 6% 5% 14%	4709
	21st to end	Night	8% 14% 8% 12% 9% 4 6% 6% 6% 7% 19%	4933
February	1st to 10th	Night	7% 12% 5% 9% 9% 4 7% 7% 7% 7% 27%	2538
	11th to 20th	Night	5% 10% 4 9% 7% 4 7% 7% 8% 8% 32%	2273
	21st to end	Night	6% 10% 4 8% 8% 5% 6% 6% 6% 7% 34%	1870
March	1st to 10th	Night	11% 10% 5% 8% 7% 5% 6% 5% 5% 7% 32%	2142
	11th to 20th	Night	8% 9% 4 7% 5% 4 5% 4 6% 8% 41%	1980
	21st to end	Night	12% 11% 4 7% 6% 3 5% 4 5% 7% 36%	2178
April	1st to 10th	Night	10% 7% 3 5% 6% 4 6% 6% 7% 8% 40%	1734
	11th to 20th	Night	13% 9% 3 7% 6% 3 5% 5% 6% 6% 37%	1599
	21st to end	Night	11% 6% 4 6% 6% 4 5% 6% 6% 7% 39%	1620
May	1st to 10th	Night	18% 9% 3 7% 5% 3 5% 5% 5% 6% 35%	1502
	11th to 20th	Night	13% 8% 4 5% 5% 2 3 4 4 8% 43%	1241
	21st to end	Night	17% 6% 3 5% 5% 4 5% 4 6% 7% 37%	1358
June	1st to 10th	Night	15% 7% 2 6% 5% 3 4 5% 6% 8% 38%	1260
	11th to 20th	Night	15% 4 2 5% 5% 3 6% 5% 6% 8% 41%	1260
	21st to end	Night	11% 4 3 5% 5% 3 5% 6% 6% 11% 40%	1260
July	1st to 10th	Night	6% 2 1 3 3 2 4 5% 7% 9% 57%	1260
	11th to 20th	Night	9% 4 1 3 4 2 6% 4 6% 9% 52%	1260
	21st to end	Night	7% 4 2 4 4 2 4 4 8% 10% 52%	1379
August	1st to 10th	Night	7% 3 2 4 5% 3 4 6% 6% 8% 54%	1445
	11th to 20th	Night	8% 5% 2 4 3 3 4 4 6% 9% 53%	1600
	21st to end	Night	12% 6% 2 4 4 3 3 4 4 8% 49%	1782
September	1st to 10th	Night	9% 6% 2 4 5% 2 4 4 6% 8% 50%	1702
	11th to 20th	Night	13% 6% 3 5% 5% 3 3 4 5% 8% 44%	1980
	21st to end	Night	13% 6% 3 6% 6% 3 5% 5% 7% 8% 40%	1980
October	1st to 10th	Night	15% 9% 3 5% 5% 3 4 6% 5% 7% 37%	2098
	11th to 20th	Night	14% 11% 4 7% 5% 3 4 5% 6% 6% 33%	2235
	21st to end	Night	16% 13% 5% 7% 6% 2 4 4 5% 6% 31%	2574
November	1st to 10th	Night	14% 12% 5% 9% 8% 4 6% 5% 5% 7% 25%	2581
	11th to 20th	Night	10% 14% 7% 10% 8% 4 5% 5% 5% 6% 24%	2666
	21st to end	Night	11% 14% 7% 12% 10% 4 5% 4 5% 7% 21%	2850
December	1st to 10th	Night	6% 11% 6% 12% 12% 6% 8% 6% 6% 7% 22%	2850
	11th to 20th	Night	8% 13% 7% 11% 7% 4 5% 6% 6% 7% 25%	3518
	21st to end	Night	8% 9% 4 10% 9% 5% 5% 5% 6% 7% 31%	5225

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	62% 7% 14% 15% 2	2219
	11th to 20th	Day	69% 5% 10% 13% 3	2220
	21st to end	Day	63% 5% 12% 15% 5%	2733
February	1st to 10th	Day	59% 7% 12% 13% 8% 1	1517
	11th to 20th	Day	52% 6% 14% 19% 9%	1583
	21st to end	Day	52% 4 13% 23% 8%	1403
March	1st to 10th	Day	57% 7% 12% 16% 8%	1818
	11th to 20th	Day	53% 6% 14% 19% 7% 1	1980
	21st to end	Day	49% 7% 14% 20% 9% 1	2178
April	1st to 10th	Day	46% 6% 13% 22% 12% 1	2223
	11th to 20th	Day	48% 6% 9% 20% 16% 1	2312
	21st to end	Day	45% 6% 13% 26% 7% 2	2340
May	1st to 10th	Day	45% 6% 12% 22% 14% 1	2454
	11th to 20th	Day	44% 6% 9% 24% 15% 2	2659
	21st to end	Day	50% 6% 10% 20% 13% 1	2918
June	1st to 10th	Day	46% 7% 12% 23% 10% 1	2700
	11th to 20th	Day	47% 7% 12% 21% 12% 1	2700
	21st to end	Day	43% 9% 17% 24% 7%	2700
July	1st to 10th	Day	32% 8% 18% 30% 12% 1	2626
	11th to 20th	Day	35% 7% 18% 30% 9% 1	2619
	21st to end	Day	33% 8% 20% 31% 8%	2776
August	1st to 10th	Day	33% 9% 19% 32% 6%	2473
	11th to 20th	Day	36% 7% 23% 28% 6%	2301
	21st to end	Day	39% 7% 19% 29% 7%	2574
September	1st to 10th	Day	36% 7% 18% 30% 8% 1	2253
	11th to 20th	Day	47% 6% 17% 25% 4	1980
	21st to end	Day	44% 7% 16% 25% 7%	1980
October	1st to 10th	Day	52% 6% 16% 21% 5%	1843
	11th to 20th	Day	55% 8% 13% 20% 4 1	1724
	21st to end	Day	62% 6% 14% 15% 3	1782
November	1st to 10th	Day	62% 4 12% 17% 4 1	1497
	11th to 20th	Day	60% 7% 14% 15% 4	1511
	21st to end	Day	60% 6% 15% 15% 4	1330
December	1st to 10th	Day	65% 7% 13% 12% 4	1330
	11th to 20th	Day	60% 7% 15% 13% 4	1680
	21st to end	Day	49% 5% 14% 18% 13% 1	2442
January	1st to 10th	Night	58% 7% 12% 17% 5%	4737
	11th to 20th	Night	70% 6% 8% 13% 3	4750
	21st to end	Night	62% 5% 11% 16% 5%	4933
February	1st to 10th	Night	54% 6% 12% 18% 10% 1	2538
	11th to 20th	Night	44% 7% 16% 22% 11%	2274
	21st to end	Night	48% 5% 11% 27% 10%	1870
March	1st to 10th	Night	51% 5% 13% 20% 10% 1	2142
	11th to 20th	Night	41% 5% 14% 27% 12% 2	1980
	21st to end	Night	48% 6% 12% 20% 12% 2	2178
April	1st to 10th	Night	39% 5% 12% 23% 17% 3	1734
	11th to 20th	Night	46% 5% 10% 19% 18% 3	1599
	21st to end	Night	43% 6% 11% 26% 12% 3	1620
May	1st to 10th	Night	50% 6% 8% 23% 12%	1502
	11th to 20th	Night	41% 5% 9% 26% 15% 4	1241
	21st to end	Night	45% 6% 13% 17% 16% 2	1358
June	1st to 10th	Night	42% 7% 15% 25% 10% 1	1260
	11th to 20th	Night	40% 6% 17% 22% 12% 2	1260
	21st to end	Night	37% 10% 20% 25% 8% 1	1260
July	1st to 10th	Night	23% 8% 17% 38% 13% 1	1225
	11th to 20th	Night	28% 7% 20% 32% 12% 1	1218
	21st to end	Night	26% 10% 16% 36% 11% 1	1302
August	1st to 10th	Night	27% 7% 18% 37% 10%	1438
	11th to 20th	Night	29% 7% 20% 34% 10% 1	1600
	21st to end	Night	33% 5% 16% 34% 11% 1	1782
September	1st to 10th	Night	32% 5% 18% 32% 12% 1	1702
	11th to 20th	Night	39% 6% 17% 28% 9% 1	1980
	21st to end	Night	40% 6% 15% 29% 9%	1980
October	1st to 10th	Night	46% 6% 16% 22% 9%	2098
	11th to 20th	Night	49% 7% 13% 26% 5%	2235
	21st to end	Night	54% 6% 15% 21% 4	2574
November	1st to 10th	Night	58% 6% 15% 15% 5% 1	2581
	11th to 20th	Night	60% 7% 16% 12% 5%	2666
	21st to end	Night	62% 6% 15% 13% 4	2850
December	1st to 10th	Night	61% 7% 16% 12% 5%	2850
	11th to 20th	Night	56% 7% 14% 15% 8%	3516
	21st to end	Night	52% 5% 10% 18% 14% 1	5225

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	9% 8% 36% 31% 10% 6%	270
	11th to 20th	Day	9% 4 35% 34% 15% 3	270
	21st to end	Day	16% 8% 27% 28% 17% 4	297
February	1st to 10th	Day	14% 4 33% 38% 9% 2	252
	11th to 20th	Day	11% 10% 35% 27% 12% 5%	240
	21st to end	Day	7% 6% 36% 29% 20% 3	198
March	1st to 10th	Day	15% 6% 29% 33% 17% 1	240
	11th to 20th	Day	13% 9% 35% 28% 12% 3	240
	21st to end	Day	12% 6% 35% 27% 19% 1	264
April	1st to 10th	Day	13% 8% 33% 31% 12% 2	483
	11th to 20th	Day	17% 10% 27% 32% 13% 2	590
	21st to end	Day	16% 9% 33% 28% 12% 1	600
May	1st to 10th	Day	16% 11% 31% 26% 14% 2	603
	11th to 20th	Day	19% 9% 28% 25% 15% 4	625
	21st to end	Day	21% 9% 24% 26% 18% 2	679
June	1st to 10th	Day	19% 10% 27% 23% 14% 7%	630
	11th to 20th	Day	14% 11% 33% 24% 13% 5%	630
	21st to end	Day	14% 8% 22% 30% 19% 7%	630
July	1st to 10th	Day	9% 8% 29% 31% 17% 6%	621
	11th to 20th	Day	12% 8% 29% 29% 16% 6%	618
	21st to end	Day	7% 8% 26% 29% 22% 9%	684
August	1st to 10th	Day	9% 6% 28% 29% 22% 7%	626
	11th to 20th	Day	13% 5% 25% 27% 21% 10%	615
	21st to end	Day	15% 7% 25% 29% 20% 4	693
September	1st to 10th	Day	14% 9% 29% 30% 16% 2	543
	11th to 20th	Day	17% 7% 36% 25% 13% 2	270
	21st to end	Day	17% 9% 36% 27% 9% 2	270
October	1st to 10th	Day	27% 10% 23% 22% 14% 4	270
	11th to 20th	Day	16% 12% 31% 29% 9% 3	270
	21st to end	Day	25% 8% 29% 24% 11% 2	297
November	1st to 10th	Day	24% 11% 26% 25% 13% 1	270
	11th to 20th	Day	13% 11% 37% 26% 10% 2	270
	21st to end	Day	19% 14% 34% 27% 6%	270
December	1st to 10th	Day	14% 7% 34% 27% 14% 4	270
	11th to 20th	Day	13% 9% 41% 26% 8% 2	270
	21st to end	Day	12% 5% 30% 29% 19% 4	297
January	1st to 10th	Night	13% 6% 34% 32% 14% 2	950
	11th to 20th	Night	14% 7% 30% 37% 10% 2	950
	21st to end	Night	15% 6% 31% 35% 13% 1	1045
February	1st to 10th	Night	12% 6% 29% 38% 15% 1	923
	11th to 20th	Night	10% 6% 30% 34% 17% 3	879
	21st to end	Night	10% 6% 31% 35% 17% 1	686
March	1st to 10th	Night	14% 5% 29% 32% 17% 3	702
	11th to 20th	Night	12% 7% 37% 31% 13% 1	540
	21st to end	Night	20% 5% 28% 30% 14% 3	594
April	1st to 10th	Night	12% 8% 31% 35% 12% 3	540
	11th to 20th	Night	17% 5% 27% 36% 15% 1	533
	21st to end	Night	15% 6% 32% 36% 10% 1	540
May	1st to 10th	Night	22% 4 29% 34% 8% 2	540
	11th to 20th	Night	17% 7% 29% 31% 16% 1	531
	21st to end	Night	19% 5% 27% 34% 14%	584
June	1st to 10th	Night	18% 6% 26% 34% 16% 1	540
	11th to 20th	Night	16% 6% 26% 37% 15% 1	540
	21st to end	Night	13% 5% 20% 42% 19% 1	540
July	1st to 10th	Night	7% 3 24% 45% 20% 1	525
	11th to 20th	Night	10% 5% 25% 39% 19% 2	522
	21st to end	Night	8% 3 24% 36% 26% 3	591
August	1st to 10th	Night	10% 4 19% 44% 21% 1	537
	11th to 20th	Night	9% 3 22% 41% 22% 4	534
	21st to end	Night	14% 4 21% 39% 21% 2	594
September	1st to 10th	Night	13% 4 28% 34% 19% 2	540
	11th to 20th	Night	14% 6% 24% 41% 14% 1	540
	21st to end	Night	16% 4 31% 37% 11% 1	540
October	1st to 10th	Night	20% 6% 31% 34% 9%	658
	11th to 20th	Night	21% 6% 29% 29% 13% 1	795
	21st to end	Night	22% 9% 30% 29% 8% 1	990
November	1st to 10th	Night	20% 7% 32% 27% 11% 2	925
	11th to 20th	Night	18% 8% 34% 27% 9% 3	950
	21st to end	Night	17% 9% 39% 27% 7% 1	950
December	1st to 10th	Night	11% 7% 31% 33% 16% 3	950
	11th to 20th	Night	16% 8% 34% 31% 10% 2	950
	21st to end	Night	17% 6% 31% 29% 15% 2	1045

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