Port Franks
Clear Sky Chart
History

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

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	14% 11% 4 9% 5% 4 4 4 6% 7% 33%	101371
	Night	15% 13% 4 9% 5% 4 4 3 5% 6% 30%	97617
Transparency	Day	47% 8% 13% 19% 11% 1	104984
	Night	50% 8% 13% 18% 10% 1	102131
Seeing	Day	20% 10% 27% 24% 13% 5%	15183
	Night	22% 9% 27% 29% 12% 1	24524

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	17% 23% 8% 15% 7% 4 4 2 3 4 13%	2467
	11th to 20th	Day	13% 20% 10% 21% 8% 5% 4 2 5% 4 8%	2667
	21st to end	Day	23% 21% 7% 13% 7% 5% 4 3 3 4 10%	3124
February	1st to 10th	Day	15% 18% 5% 14% 8% 5% 5% 4 5% 5% 17%	1710
	11th to 20th	Day	14% 13% 7% 15% 9% 7% 5% 3 4 4 20%	1692
	21st to end	Day	15% 16% 5% 11% 6% 4 5% 4 4 5% 24%	1570
March	1st to 10th	Day	17% 16% 5% 10% 5% 4 3 3 4 5% 28%	3302
	11th to 20th	Day	11% 14% 5% 11% 6% 4 4 3 5% 7% 29%	3480
	21st to end	Day	17% 12% 4 11% 4 4 4 3 5% 6% 31%	3815
April	1st to 10th	Day	14% 14% 4 7% 4 3 4 4 6% 8% 31%	2161
	11th to 20th	Day	17% 10% 3 6% 4 3 5% 3 6% 7% 36%	2442
	21st to end	Day	18% 10% 3 7% 4 4 4 3 5% 7% 36%	2470
May	1st to 10th	Day	16% 7% 3 7% 5% 4 5% 4 5% 8% 37%	4082
	11th to 20th	Day	16% 9% 4 7% 5% 4 4 3 6% 9% 34%	4081
	21st to end	Day	11% 5% 3 6% 4 4 4 4 5% 8% 47%	4755
June	1st to 10th	Day	11% 6% 2 6% 5% 5% 5% 5% 6% 8% 42%	2743
	11th to 20th	Day	9% 5% 2 5% 5% 4 5% 4 7% 10% 43%	2850
	21st to end	Day	11% 6% 2 7% 4 4 4 4 6% 9% 43%	2850
July	1st to 10th	Day	10% 5% 2 6% 5% 5% 5% 5% 7% 10% 41%	4697
	11th to 20th	Day	10% 5% 2 5% 4 4 4 4 6% 10% 47%	4355
	21st to end	Day	7% 5% 2 6% 4 5% 5% 4 8% 9% 44%	4466
August	1st to 10th	Day	13% 6% 2 6% 4 5% 5% 4 7% 10% 40%	4104
	11th to 20th	Day	10% 6% 2 7% 4 4 5% 5% 7% 11% 38%	4044
	21st to end	Day	9% 6% 2 6% 5% 4 5% 4 7% 9% 43%	4518
September	1st to 10th	Day	10% 7% 2 6% 5% 5% 5% 4 6% 8% 42%	2185
	11th to 20th	Day	11% 5% 1 6% 4 4 5% 4 6% 8% 46%	2090
	21st to end	Day	16% 7% 3 7% 4 6% 5% 4 6% 8% 35%	2090
October	1st to 10th	Day	14% 8% 3 7% 5% 5% 5% 4 6% 7% 36%	1967
	11th to 20th	Day	22% 12% 3 8% 5% 4 5% 3 5% 6% 26%	1900
	21st to end	Day	25% 15% 4 8% 5% 4 4 3 5% 6% 22%	2009
November	1st to 10th	Day	16% 14% 3 10% 5% 4 4 3 5% 7% 28%	1708
	11th to 20th	Day	15% 17% 5% 11% 6% 5% 4 3 5% 6% 22%	1596
	21st to end	Day	18% 20% 8% 12% 5% 5% 4 3 4 5% 15%	1520
December	1st to 10th	Day	15% 24% 8% 14% 7% 5% 4 3 4 4 12%	1520
	11th to 20th	Day	18% 20% 10% 13% 5% 5% 5% 3 5% 4 12%	1910
	21st to end	Day	26% 24% 7% 11% 5% 3 3 3 4 4 8%	2431
January	1st to 10th	Night	17% 20% 9% 16% 7% 6% 4 2 3 4 12%	4485
	11th to 20th	Night	14% 21% 9% 17% 9% 5% 5% 3 5% 4 8%	4281
	21st to end	Night	21% 19% 7% 14% 7% 5% 4 3 4 4 11%	4532
February	1st to 10th	Night	17% 17% 5% 14% 9% 6% 5% 4 4 4 17%	2470
	11th to 20th	Night	15% 16% 6% 11% 7% 5% 5% 5% 5% 5% 19%	2370
	21st to end	Night	16% 13% 6% 12% 7% 5% 5% 4 5% 5% 22%	1884
March	1st to 10th	Night	15% 15% 3 8% 5% 4 4 3 5% 5% 32%	3551
	11th to 20th	Night	11% 10% 5% 10% 5% 5% 4 3 6% 7% 34%	3480
	21st to end	Night	15% 11% 4 10% 6% 4 4 3 4 5% 35%	3817
April	1st to 10th	Night	18% 13% 4 7% 5% 4 3 3 6% 6% 31%	2032
	11th to 20th	Night	17% 9% 3 5% 4 5% 5% 4 5% 7% 37%	1687
	21st to end	Night	17% 11% 3 7% 5% 4 4 3 5% 7% 34%	1710
May	1st to 10th	Night	16% 8% 2 7% 5% 4 4 3 5% 8% 37%	2813
	11th to 20th	Night	13% 9% 3 8% 5% 5% 4 4 5% 7% 37%	2812
	21st to end	Night	11% 5% 2 4 3 4 5% 4 6% 8% 49%	2799
June	1st to 10th	Night	13% 7% 3 5% 4 4 4 3 6% 8% 42%	1433
	11th to 20th	Night	9% 5% 3 6% 5% 5% 4 5% 8% 8% 43%	1330
	21st to end	Night	10% 5% 2 5% 5% 4 5% 4 6% 7% 47%	1330
July	1st to 10th	Night	7% 5% 2 6% 4 5% 4 3 6% 9% 49%	2268
	11th to 20th	Night	11% 4 1 4 3 3 4 3 5% 9% 52%	2609
	21st to end	Night	5% 5% 2 5% 4 5% 6% 5% 8% 8% 47%	3087
August	1st to 10th	Night	10% 6% 3 6% 4 4 5% 4 6% 7% 45%	2825
	11th to 20th	Night	10% 7% 2 7% 4 4 3 4 6% 8% 45%	2785
	21st to end	Night	9% 7% 2 6% 5% 4 5% 3 5% 8% 47%	3124
September	1st to 10th	Night	11% 5% 2 6% 5% 4 5% 4 6% 6% 45%	1972
	11th to 20th	Night	11% 5% 1 5% 4 3 4 4 5% 6% 52%	2090
	21st to end	Night	16% 8% 3 8% 4 5% 4 4 5% 6% 38%	2090
October	1st to 10th	Night	14% 8% 3 7% 5% 4 3 3 5% 6% 40%	2213
	11th to 20th	Night	23% 11% 3 8% 4 4 4 3 5% 6% 30%	2280
	21st to end	Night	24% 12% 4 9% 5% 3 5% 4 5% 6% 23%	2584
November	1st to 10th	Night	16% 14% 3 8% 5% 4 3 3 5% 6% 33%	2470
	11th to 20th	Night	16% 18% 5% 10% 6% 4 5% 3 5% 6% 20%	2581
	21st to end	Night	20% 20% 6% 11% 5% 3 4 3 4 4 19%	2660
December	1st to 10th	Night	18% 24% 9% 12% 6% 4 5% 3 3 4 12%	2660
	11th to 20th	Night	15% 22% 8% 13% 6% 5% 4 3 4 5% 16%	3285
	21st to end	Night	25% 24% 7% 12% 6% 4 3 2 3 3 10%	5218

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	71% 10% 12% 7% 1	2468
	11th to 20th	Day	77% 8% 9% 4 1	2667
	21st to end	Day	75% 9% 9% 5% 2	3124
February	1st to 10th	Day	66% 9% 10% 11% 4	1710
	11th to 20th	Day	64% 7% 10% 13% 5%	1701
	21st to end	Day	59% 9% 13% 12% 6% 1	1570
March	1st to 10th	Day	57% 8% 11% 19% 4	3302
	11th to 20th	Day	51% 9% 15% 18% 7% 1	3480
	21st to end	Day	51% 9% 13% 15% 10% 2	3815
April	1st to 10th	Day	49% 8% 14% 20% 9% 1	2161
	11th to 20th	Day	47% 7% 14% 17% 14% 2	2442
	21st to end	Day	48% 7% 14% 17% 12% 2	2470
May	1st to 10th	Day	43% 8% 13% 19% 14% 3	4120
	11th to 20th	Day	45% 11% 17% 18% 9% 1	4085
	21st to end	Day	34% 8% 12% 19% 21% 6%	4769
June	1st to 10th	Day	38% 9% 14% 26% 13% 1	2743
	11th to 20th	Day	35% 9% 13% 24% 17% 2	2850
	21st to end	Day	38% 8% 13% 24% 16% 1	2850
July	1st to 10th	Day	37% 7% 15% 23% 16% 2	4624
	11th to 20th	Day	31% 7% 14% 33% 14% 1	4280
	21st to end	Day	33% 9% 18% 19% 20% 1	4324
August	1st to 10th	Day	38% 9% 15% 22% 15% 1	4091
	11th to 20th	Day	37% 9% 16% 29% 8% 1	4083
	21st to end	Day	36% 7% 13% 30% 13% 1	4518
September	1st to 10th	Day	38% 9% 16% 24% 12% 1	2185
	11th to 20th	Day	33% 8% 15% 28% 15% 1	2090
	21st to end	Day	45% 9% 14% 23% 10% 1	2090
October	1st to 10th	Day	35% 8% 13% 27% 14% 2	3266
	11th to 20th	Day	46% 6% 11% 21% 16%	3140
	21st to end	Day	51% 7% 16% 19% 7%	3285
November	1st to 10th	Day	53% 7% 13% 19% 7% 1	1708
	11th to 20th	Day	57% 7% 16% 12% 7% 1	1596
	21st to end	Day	68% 8% 11% 11% 2	1520
December	1st to 10th	Day	69% 11% 10% 8% 2	1520
	11th to 20th	Day	70% 8% 12% 8% 1	1906
	21st to end	Day	80% 6% 9% 4 1	2431
January	1st to 10th	Night	69% 9% 12% 9% 1	4485
	11th to 20th	Night	72% 10% 10% 6% 2	4281
	21st to end	Night	72% 8% 11% 7% 2	4532
February	1st to 10th	Night	66% 8% 10% 12% 4	2470
	11th to 20th	Night	60% 7% 13% 14% 5%	2372
	21st to end	Night	61% 7% 12% 14% 6%	1884
March	1st to 10th	Night	52% 6% 12% 24% 5%	3551
	11th to 20th	Night	42% 9% 17% 20% 10% 1	3480
	21st to end	Night	47% 8% 13% 20% 11% 1	3817
April	1st to 10th	Night	51% 6% 11% 20% 11% 1	2032
	11th to 20th	Night	45% 7% 11% 18% 16% 2	1687
	21st to end	Night	48% 6% 11% 17% 14% 4	1710
May	1st to 10th	Night	43% 9% 11% 18% 15% 4	2840
	11th to 20th	Night	42% 10% 12% 23% 10% 2	2813
	21st to end	Night	31% 9% 12% 21% 22% 5%	2806
June	1st to 10th	Night	37% 7% 13% 25% 16% 2	1433
	11th to 20th	Night	34% 9% 14% 23% 19% 2	1330
	21st to end	Night	33% 7% 15% 25% 18% 1	1330
July	1st to 10th	Night	30% 6% 13% 28% 17% 6%	2232
	11th to 20th	Night	29% 6% 14% 32% 18% 1	2561
	21st to end	Night	30% 10% 16% 20% 21% 3	2988
August	1st to 10th	Night	36% 8% 14% 25% 16% 1	2814
	11th to 20th	Night	36% 7% 14% 29% 13% 1	2812
	21st to end	Night	34% 8% 13% 29% 15% 1	3124
September	1st to 10th	Night	36% 9% 14% 25% 14% 2	1972
	11th to 20th	Night	32% 6% 15% 28% 19% 1	2090
	21st to end	Night	44% 7% 13% 22% 12% 1	2090
October	1st to 10th	Night	30% 7% 11% 27% 24% 1	3694
	11th to 20th	Night	48% 5% 13% 19% 15%	3779
	21st to end	Night	48% 7% 14% 21% 10%	4245
November	1st to 10th	Night	48% 6% 13% 22% 10% 1	2470
	11th to 20th	Night	59% 8% 14% 13% 5% 1	2581
	21st to end	Night	65% 7% 14% 11% 2	2660
December	1st to 10th	Night	71% 8% 11% 8% 2	2660
	11th to 20th	Night	67% 8% 13% 10% 2	3288
	21st to end	Night	77% 7% 10% 5% 1	5218

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	25% 22% 26% 20% 6% 1	254
	11th to 20th	Day	26% 16% 40% 14% 3 1	270
	21st to end	Day	29% 13% 33% 21% 3 1	297
February	1st to 10th	Day	26% 20% 41% 11% 3	270
	11th to 20th	Day	25% 20% 39% 16%	270
	21st to end	Day	24% 30% 34% 12% 1	225
March	1st to 10th	Day	28% 14% 34% 17% 6%	374
	11th to 20th	Day	25% 13% 29% 26% 5% 1	460
	21st to end	Day	31% 13% 27% 22% 6% 1	506
April	1st to 10th	Day	24% 14% 33% 22% 7% 1	460
	11th to 20th	Day	28% 11% 29% 19% 10% 3	452
	21st to end	Day	25% 11% 31% 24% 7% 2	460
May	1st to 10th	Day	23% 10% 28% 25% 11% 3	463
	11th to 20th	Day	18% 9% 24% 28% 16% 6%	487
	21st to end	Day	16% 5% 23% 28% 20% 8%	529
June	1st to 10th	Day	14% 6% 31% 30% 13% 6%	573
	11th to 20th	Day	13% 8% 29% 31% 14% 5%	680
	21st to end	Day	15% 6% 26% 34% 15% 4	680
July	1st to 10th	Day	12% 4 25% 28% 23% 9%	671
	11th to 20th	Day	14% 4 27% 28% 18% 8%	622
	21st to end	Day	9% 3 21% 33% 24% 10%	532
August	1st to 10th	Day	12% 3 17% 29% 26% 13%	486
	11th to 20th	Day	13% 4 19% 28% 22% 15%	479
	21st to end	Day	15% 4 16% 31% 24% 9%	539
September	1st to 10th	Day	13% 6% 22% 26% 21% 12%	490
	11th to 20th	Day	10% 4 17% 25% 29% 14%	490
	21st to end	Day	18% 8% 24% 23% 18% 8%	490
October	1st to 10th	Day	19% 9% 24% 25% 18% 6%	490
	11th to 20th	Day	26% 13% 30% 21% 10% 1	490
	21st to end	Day	32% 12% 33% 18% 4 1	458
November	1st to 10th	Day	22% 16% 32% 20% 9% 2	282
	11th to 20th	Day	28% 15% 33% 17% 5% 2	216
	21st to end	Day	28% 18% 38% 12% 3	180
December	1st to 10th	Day	30% 17% 32% 14% 5% 1	180
	11th to 20th	Day	28% 22% 32% 15% 3	180
	21st to end	Day	33% 19% 34% 12% 2	198
January	1st to 10th	Night	27% 15% 35% 17% 5% 1	950
	11th to 20th	Night	30% 14% 30% 20% 5%	856
	21st to end	Night	23% 10% 34% 26% 6%	836
February	1st to 10th	Night	25% 13% 37% 23% 2 1	760
	11th to 20th	Night	24% 14% 30% 26% 5%	743
	21st to end	Night	25% 15% 36% 20% 4	628
March	1st to 10th	Night	21% 12% 33% 27% 7%	760
	11th to 20th	Night	20% 12% 36% 25% 7% 1	760
	21st to end	Night	24% 9% 28% 29% 9% 1	836
April	1st to 10th	Night	26% 12% 30% 27% 5%	746
	11th to 20th	Night	24% 9% 29% 26% 11% 1	563
	21st to end	Night	22% 7% 27% 34% 8% 1	570
May	1st to 10th	Night	20% 5% 29% 34% 11% 2	570
	11th to 20th	Night	16% 5% 25% 40% 13% 2	561
	21st to end	Night	13% 4 24% 40% 18% 1	453
June	1st to 10th	Night	15% 3 26% 39% 16% 1	380
	11th to 20th	Night	11% 4 23% 47% 15%	380
	21st to end	Night	12% 3 22% 43% 20% 1	380
July	1st to 10th	Night	8% 1 16% 49% 23% 2	401
	11th to 20th	Night	12% 2 18% 40% 25% 4	552
	21st to end	Night	9% 2 15% 47% 24% 2	624
August	1st to 10th	Night	10% 2 12% 41% 32% 3	567
	11th to 20th	Night	12% 2 12% 38% 31% 4	564
	21st to end	Night	14% 2 15% 38% 29% 2	627
September	1st to 10th	Night	12% 5% 18% 34% 25% 5%	741
	11th to 20th	Night	13% 4 15% 36% 27% 5%	760
	21st to end	Night	19% 6% 20% 34% 17% 4	760
October	1st to 10th	Night	19% 6% 26% 30% 17% 2	760
	11th to 20th	Night	31% 9% 23% 26% 10% 1	760
	21st to end	Night	33% 11% 27% 25% 4	836
November	1st to 10th	Night	26% 11% 26% 27% 9% 1	760
	11th to 20th	Night	28% 14% 31% 19% 6% 1	760
	21st to end	Night	33% 10% 29% 22% 5%	760
December	1st to 10th	Night	33% 16% 30% 17% 4	760
	11th to 20th	Night	26% 19% 33% 19% 3	760
	21st to end	Night	34% 13% 31% 20% 2	1040

Page generated at 2024-11-03 02:11:22. Version ac07

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