Latest Forecast for Mauna Kea Observatories
10 AM HST (2000 UTC) Thursday 23 March 2017

Warnings
None

Cloud Cover and Precipitation Forecast
The summit will remain dry and stable, while scattered high clouds pass over and especially along the northern skies through this evening.

Summary of Key Meteorological Variables
Summit temperatures will be near 6 C this afternoon, 1 C this evening and 0 C tomorrow morning. Winds will be light and from the SW, with seeing near 0.5 arcseconds. Precipitable water is expected to be in the 1.5-2 mm range for the first half of the night and 1-1.5 mm range for the second half.

Graphical Summary

Discussion
The tradewind inversion will continue to cap low-level moisture at or below 8 thousand feet and ensure the summit steers free of fog and precipitation through the next 5 nights. Daytime clouds will be minimal and short-lived throughout the forecast period.

Scattered high clouds will continue to pass along the northern skies and occasionally drift over the summit area through this evening. These clouds will quickly shift eastward during the second half of the night, leaving predominately clear skies for at least tomorrow night. However, there is a possibility that scattered high clouds passing further along the northern skies will be visible from the summit for the following 2-3 nights.

Precipitable water is expected to briefly increase toward 2 mm for this evening, slip back toward 1 mm by the end of the night and for the following 2 nights. It could increase back toward 1.5 mm for Sunday night and 2 mm for Monday night.

Although there is a possibility for minor turbulence in the free atmosphere over the next 3 nights, better than average seeing should prevail for tonight (but there is a possibility for large variations). A increase in boundary layer turbulence could degrade seeing toward more average-like values for Friday and Saturday night. Calmer skies should allow seeing to improve once again for the following 2 nights.

While the mid-level ridge is set to weaken as a trough passes to the north over the next 24 hours, the low-level ridge will persist to the north well into next week, while a new ridge fills in from the west over the weekend. Nevertheless, strong large-scale subsidence will prevail in the area, which will easily maintain a well-defined inversion at or below 8 thousand feet and ensure a dry/stable summit-level air mass throughout the forecast period. The passing trough will send scattered high clouds along the northern skies through this evening, then will shift eastward, leaving predominately clear skies overhead for at least Friday night. There is a possibility that stray high clouds passing further to the north within a relatively zonal westerly jet could be visibile from the summit for the following 3 nights. The jet is expected to remain off toward the north, which should keep turbulence in the free atmosphere to a minimum. However, there is a chance that the new building mid-level ridge will increase summit-level winds and thus boundary layer turbulence, which could affect seeing for Friday and Saturday night.

Astronomical Observing Quality Guidance
05 pm HST Thursday 23 March (03 UTC Friday 24 March)CN2
08 pm HST Thursday 23 March (06 UTC Friday 24 March)CN2
11 pm HST Thursday 23 March (09 UTC Friday 24 March)CN2
02 am HST Friday 24 March (12 UTC Friday 24 March)CN2
05 am HST Friday 24 March (15 UTC Friday 24 March)CN2
08 am HST Friday 24 March (18 UTC Friday 24 March)CN2
Latest WRF CN2 Profiles Animation | Collage


5-day Forecast
Summary

Graphical Trend
02 pm HST
Thu 23 Mar
08 pm HST
Thu 23 Mar
02 am HST
Fri 24 Mar
02 pm HST
Fri 24 Mar
08 pm HST
Fri 24 Mar
02 am HST
Sat 25 Mar
02 pm HST
Sat 25 Mar
08 pm HST
Sat 25 Mar
02 am HST
Sun 26 Mar
02 pm HST
Sun 26 Mar
02 am HST
Mon 27 Mar
02 pm HST
Mon 27 Mar
02 am HST
Tue 28 Mar
00 UTC
Fri 24 Mar
06 UTC
Fri 24 Mar
12 UTC
Fri 24 Mar
00 UTC
Sat 25 Mar
06 UTC
Sat 25 Mar
12 UTC
Sat 25 Mar
00 UTC
Sun 26 Mar
06 UTC
Sun 26 Mar
12 UTC
Sun 26 Mar
00 UTC
Mon 27 Mar
12 UTC
Mon 27 Mar
00 UTC
Tue 28 Mar
12 UTC
Tue 28 Mar
Cloud Cover (%) 40 to 60 20 to 40 0 to 20 0 to 20 0 to 5 0 to 5 0 to 20 0 to 20 10 to 30 10 to 30 0 to 20 0 to 20 0 to 20
Cloud Height (km) above sea level 8-9 8-9 N/A N/A N/A N/A 8-9 8-9 8-9 8-9 8-9 8-9 8-9
Chance for Fog/Precip (%) 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0
PW (mm, summit upward) 1 to 2 1.5 to 2 1 to 1.5 0.8 to 1.2 0.9 to 1.1 0.9 to 1.1 1 to 1.5 0.9 to 1.1 0.9 to 1.1 1 to 2 1.25 to 1.75 1.5 to 2.5 2 to 3
Mean Seeing (arcsecs) N/A 0.5 ± 0.15 0.5 ± 0.15 N/A 0.6 ± 0.1 0.65 ± 0.15 N/A 0.65 ± 0.15 0.65 ± 0.15 N/A 0.55 ± 0.1 N/A 0.55 ± 0.1
Summit Temp (°C) 6 1 0 5 -0.5 -1 5 -1 -1 5 0 6 0.5
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)

SW/0 to 10

SW/0 to 10

SW/0 to 10

NNE/5 to 15

ENE/10 to 20

ENE/15 to 25

E/15 to 25

ENE/15 to 25

ENE/10 to 20

E/5 to 15

ENE/5 to 15

E/5 to 15

ENE/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
Thu.Mar.23/Fri.Mar.24
18:43
19:47
5:09
6:13
3:48
N/A
16
21 17.2
-14 32
Fri.Mar.24/Sat.Mar.25
18:43
19:48
5:08
6:12
4:34
N/A
9
22 09.3
-11 22
Sat.Mar.25/Sun.Mar.26
18:43
19:48
5:07
6:11
5:18
16:48
4
23 01.6
-7 33
Sun.Mar.26/Mon.Mar.27
18:44
19:48
5:06
6:11
6:03
17:45
1
23 54.4
-3 14
Mon.Mar.27/Tue.Mar.28
18:44
19:49
5:05
6:10
6:49
18:45
0
0 48.0
1 20


Forecast issued by: Ryan Lyman
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Next update at 5 PM HST Thursday 23 March (0300 UTC Friday 24 March) 2017.
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