Latest Forecast for Mauna Kea Observatories
5 PM HST Friday 23 June (0300 UTC Saturday 24 June) 2017

Warnings
None

Cloud Cover and Precipitation Forecast
The summit will remain clear, dry and stable through the night.

Summary of Key Meteorological Variables
Summit temperatures will be near 5 C this evening and 4 C tomorrow morning. Winds will be light and from the NW, with seeing near 0.45-0.5 arcseconds. Precipitable water is expected to be in the 2-3 mm range for the night.

Graphical Summary

Discussion
The tradewind inversion will continue to cap low-level moisture primarily near 7-8 thousand feet and ensure a dry/stable summit-level air mass through the next 5 nights. Daytime clouds will be minimal and short-lived throughout the forecast period.

Skies overhead will remain predominately clear through tomorrow evening. Bands of scattered high clouds is set to build in from the WSW late Saturday evening, with more patchy high clouds filling in from the NW on Sunday. The latter is expected to fall apart later that night, while the former becomes more organized and widespread over the following day or two. This will likely lead to extensive cloud cover for Sunday night and perhaps overcast skies for the following 2 nights.

Precipitable water is expected to linger primarily in the 2-3 mm range throughout the forecast period.

Relatively calm skies and deep/uniform WNW flow at and above the summit should allow seeing to linger near 0.45-0.5 arcseconds for the next 2 nights. An increase in upper-level shear is expected to degrade seeing back toward 0.6-0.65 arcseconds for the following 3 nights.

Minor changes have been made to the PW forecast...A ridge in the lower half of the atmosphere will remain quasi-stationary/steady to the NE of the state and continue to promote steady/strong large-scale subsidence in the area well into next week. This subsidence will help maintain a well-defined inversion near 6-8 thousand feet, easily overcome instability associated with a building tropical upper-tropospheric trough (TUTT) to the west and ensure a dry/stable summit-level air mass throughout the forecast period. The TUTT and its associated southern counterpart, the sub-tropical jet (STJ), will remain relatively weak, minimizing shear/turbulence and allowing seeing to linger near 0.45-0.5 arcseconds for the next 2 nights. However, the STJ will gain access to high clouds drifting out of the tropics and stream it over the summit area beginning tomorrow night. The TUTT is expected to dig southward, allowing the STJ to strengthen and pull in more widespread banding high clouds up from the SW on Sunday. The former is expected to increase shear in the free atmosphere and degrade seeing toward more average-like values, while the latter will probably contribute to extensive cloud cover to overcast skies for Sunday night and early part of next week.

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


5-day Forecast
Summary

Graphical Trend
08 pm HST
Fri 23 Jun
02 am HST
Sat 24 Jun
02 pm HST
Sat 24 Jun
08 pm HST
Sat 24 Jun
02 am HST
Sun 25 Jun
02 pm HST
Sun 25 Jun
08 pm HST
Sun 25 Jun
02 am HST
Mon 26 Jun
02 pm HST
Mon 26 Jun
02 am HST
Tue 27 Jun
02 pm HST
Tue 27 Jun
02 am HST
Wed 28 Jun
02 pm HST
Wed 28 Jun
06 UTC
Sat 24 Jun
12 UTC
Sat 24 Jun
00 UTC
Sun 25 Jun
06 UTC
Sun 25 Jun
12 UTC
Sun 25 Jun
00 UTC
Mon 26 Jun
06 UTC
Mon 26 Jun
12 UTC
Mon 26 Jun
00 UTC
Tue 27 Jun
12 UTC
Tue 27 Jun
00 UTC
Wed 28 Jun
12 UTC
Wed 28 Jun
00 UTC
Thu 29 Jun
Cloud Cover (%) 0 to 5 0 to 5 0 to 20 20 to 40 40 to 60 40 to 60 60 to 80 70 to 90 80 to 100 80 to 100 80 to 100 80 to 100 70 to 90
Cloud Height (km) above sea level N/A N/A N/A 9.5-10 9-10 9-10 9-10 9-10 8-10 8-10 8-10 7-10 7-9
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) 2 to 3 2 to 3 2 to 4 2.5 to 3.5 2.5 to 3.5 2 to 3 2 to 3 2 to 3 2 to 3 1.5 to 2.5 2 to 3 2 to 3 2 to 3
Mean Seeing (arcsecs) 0.5 ± 0.1 0.45 ± 0.1 N/A 0.45 ± 0.1 0.5 ± 0.1 N/A 0.6 ± 0.1 0.65 ± 0.15 N/A 0.65 ± 0.15 N/A 0.6 ± 0.2 N/A
Summit Temp (°C) 5 4 9 4 3.5 8 3 2 7 2 7 2 7.5
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)

NW/0 to 10

NNW/0 to 10

ENE/0 to 10

SSE/0 to 10

S/0 to 10

S/0 to 10

SE/0 to 10

ESE/0 to 10

ESE/5 to 15

E/5 to 15

ENE/5 to 15

NE/5 to 15

NE/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
Fri.Jun.23/Sat.Jun.24
19:14
20:28
4:21
5:35
6:21
19:08
0
6 31.1
18 48
Sat.Jun.24/Sun.Jun.25
19:14
20:28
4:21
5:35
N/A
20:10
3
7 33.7
18 13
Sun.Jun.25/Mon.Jun.26
19:14
20:28
4:21
5:35
N/A
21:07
8
8 34.4
16 24
Mon.Jun.26/Tue.Jun.27
19:14
20:28
4:22
5:36
N/A
21:59
15
9 32.0
13 34
Tue.Jun.27/Wed.Jun.28
19:15
20:29
4:22
5:36
N/A
22:46
23
10 26.5
10 01


Forecast issued by: Ryan Lyman
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Next update at 10 AM HST (2000 UTC) Monday 26 June 2017.
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