Latest Forecast for Mauna Kea Observatories
5 PM HST Monday 21 October (0300 UTC Tuesday 22 October) 2019

Warnings
None

Cloud Cover and Precipitation Forecast
Summit skies will be predominantly free of clouds. High clouds might be visible along the SW horizon.

Summary of Key Meteorological Variables
Summit temperatures will be near 3.5 C this evening and 3 C tonight. Winds will be from the ENE starting at 15-25mph and settling in the 10-20 mph range during the second half of the night. Seeing will be variable and less than average during the first observing hours, improving as the night goes by, toward more average values. Precipitable water is expected to range between 1.5 and 2 mm.

Graphical Summary

Discussion
Episodes of high relative humidity are still somewhat likely throught this evening as a weakening front sweep by to the North of the State causing the inversion to weaken and lift some. The inversion is not expected to vanish completely and will quickly restrenghten through the second part of tonight allowing for a mostly stable and dry environment from then through the following 2/3 days. A second bout of moisture is expected to reach the Big Island from the SSE later on Thursday and through Friday, destabilizing some the environment and increasing the odds for fog particularly on Friday night. Daytime clouds will be very likely on Friday.

Summit skies will be predominantly free of clouds tonight, but for some high cirri visible along the SW horizon im the early morning. These might near tomorrow and perhaps obscure a small portion of the summit skies during the night. Clear skies are expected on Wednesday, while more high clouds will start approaching the area from the SW on Thursday night thickening in time through Friday, when are likely to obscure a good portion of the summit sky.

Precipit1able water will range between 1.5 and 2 mm tonight and tomorrow night. It will increase to the 3 to 4 mm range on Wednesday night and increase further on Thursday when it will likely reach the 4 mm threshold and exceed it by Friday night.

Observing conditions will start off in the less than average range tonight as a combination of variable and moderate winds at the surface along with some spotty moisture is likely to degrade seeing. Conditions might improve as the night progresses as winds are expected to taper and the air masses to stabilize. Also the contribution from the free atsmosphere should decrease in time. More average conditions are expected for Tuesday and particularly Wednesday night. From Thursday observing conditions will degrade: moisture will build up in the airmasses and clouds will also interfere with observations, particularly on Friday night.

No much chance since the morning forecast... The current weather scenario is characterized by a high pressure system to the NE of the islands, and by a weakening front just North of the high pressure ridge. This latter is projected to weaken further while shifting eastward. As a result the tradewind inversion over the northern part of the State is somewhat destabilized (lifted and weakened) and to some extent this will also affect the Big Island's summit: in fact, some moisture might slip up the summit at times today and this evening resulting in short episodes of high relative humidity. Also the surface winds today will be a tad stronger, which is likely to negatively contribute to degraded and variable seeing during the first half of tonight. As the front shifts eastward the inversion will rebuild and the ridge lift nortward. Therefore, beside some residual high clouds approaching the island from the West tomorrow, a mostly dry, stable and clear environment is expected for Tuesday and Wednesday night. Conditions will start to slowly degrade from late Thursday when more clouds from the SW will be advected over by an upper tropospheric trough developing to the NW of the State and sweeping by through Friday and the weekend. This system will also cause some tropical moisture to be advected over from the SE from late Thursday and through Friday, increasing the chances for high relative humidity, fog and obscured skies on Friday and part of the coming weekend.

Astronomical Observing Quality Guidance
Seeing/CN2 Images are not available today. Sorry for the inconvenience.
Latest WRF CN2 Profiles Animation | Collage


5-day Forecast
Summary

Graphical Trend
08 pm HST
Mon 21 Oct
02 am HST
Tue 22 Oct
02 pm HST
Tue 22 Oct
08 pm HST
Tue 22 Oct
02 am HST
Wed 23 Oct
02 pm HST
Wed 23 Oct
08 pm HST
Wed 23 Oct
02 am HST
Thu 24 Oct
02 pm HST
Thu 24 Oct
02 am HST
Fri 25 Oct
02 pm HST
Fri 25 Oct
02 am HST
Sat 26 Oct
02 pm HST
Sat 26 Oct
06 UTC
Tue 22 Oct
12 UTC
Tue 22 Oct
00 UTC
Wed 23 Oct
06 UTC
Wed 23 Oct
12 UTC
Wed 23 Oct
00 UTC
Thu 24 Oct
06 UTC
Thu 24 Oct
12 UTC
Thu 24 Oct
00 UTC
Fri 25 Oct
12 UTC
Fri 25 Oct
00 UTC
Sat 26 Oct
12 UTC
Sat 26 Oct
00 UTC
Sun 27 Oct
Cloud Cover (%) 0 to 20 0 to 20 10 to 30 20 to 40 20 to 40 0 to 20 0 to 20 0 to 20 0 to 20 20 to 40 30 to 50 60 to 80 20 to 40
Cloud Height (km) above sea level N/A N/A 7-8 7-8 7-8 N/A N/A N/A N/A 7-8 6-7 3.5-6 7-8
Chance for Fog/Precip (%) 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 50/10 80/20 40/0
PW (mm, summit upward) 2 to 2.5 1.5 to 2 2 to 3 1.5 to 2 1.5 to 2 2 to 3 3 to 4 3 to 4 3.5 to 4.5 3.5 to 4.5 3.5 to 4.5 5 to 7 4 to 6
Mean Seeing (arcsecs) 0.8 ± 0.2 0.65 ± 0.15 N/A 0.65 ± 0.15 0.50 ± 0.15 N/A 0.55 ± 0.15 0.55 ± 0.15 N/A 0.7 ± 0.2; N/A 0.8 ± 0.2 N/A
Summit Temp (°C) 3.5 3 8.5 4 3.5 10 4.5 3.5 8 3.5 7 2.5 7
Wind Dir/Speed (mph)
    Summit (615 hPa)
    19,000 ft (500 hPa)
    24,500 ft (400 hPa)
    31,000 ft (300 hPa)
    35,000 ft (250 hPa)
    40,000 ft (200 hPa)
    46,000 ft (150 hPa)
    54,000 ft (100 hPa)

NE/15 to 25

ENE/10 to 20

ENE/10 to 20

ENE/10 to 20

ENE/5 to 15

NNE/5 to 15

NNE/5 to 15

N/5 to 15

W/5 to 15

NNW/5 to 15

SW/5 to 15

W/5 to 15

WNW/5 to 15


 Rise and Set times for the Sun and Moon
Night (HST)
Sun Set
Twilight End
Twilight Beg
Sun Rise
Moon Rise
Moon Set
Illum (%)
RA
Dec
Mon.Oct.21/Tue.Oct.22
18:03
19:08
5:05
6:10
0:35
N/A
39
8 56.8
19 38
Tue.Oct.22/Wed.Oct.23
18:02
19:07
5:05
6:10
1:38
N/A
29
9 54.5
16 12
Wed.Oct.23/Thu.Oct.24
18:02
19:07
5:06
6:11
2:40
N/A
19
10 50.9
11 45
Thu.Oct.24/Fri.Oct.25
18:01
19:06
5:06
6:11
3:43
N/A
10
11 46.1
6 32
Fri.Oct.25/Sat.Oct.26
18:01
19:06
5:06
6:11
4:45
16:40
4
12 40.5
0 53


Forecast issued by: Tiziana Cherubini
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Next update at 10 AM HST (2000 UTC) Tuesday 22 October 2019.
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