Latest Forecast for Mauna Kea Observatories
8 AM HST (1800 UTC) Wednesday 11 July 2018

Warnings
None

Cloud Cover and Precipitation Forecast
The summit will remain dry and stable, but there is a chance that stray patches of thin cirrus will pass through/over the area through the night.

Summary of Key Meteorological Variables
Summit temperatures will be near 9 C this afternoon, 4 C this evening and 3.5 C tomorrow morning. Winds will be from the ENE 5-15 mph, with seeing near 0.4-0.5 arcseconds. Precipitable water is expected to exceed 4 mm through the night.

Graphical Summary

Discussion
The tradewind inversion will continue to cap low-level moisutre near 7-8 thousand feet and ensure the summit remains dry and stable through at least Friday night. There is a possibility that patches of mid/low-level moisture may weaken/lift the inversion and increase the risk for fog and light rain at the summit for Saturday and Sunday night. Daytime clouds will be minimal and short-lived through Friday, but could pick up over the weekend and early part of next week.

Stray patches of thin cirrus may fill in from the west and pass through/over the area during the night. A band of high clouds will likely set up along the western skies tomorrow, with dissipating cirrus occasionally exiting that area and drifting over/near the summit for tomorrow night. While this band will likely turn more compact on Friday, it could slip further eastward, increasing cloud cover for that night. This band will then begin to shift northward and break up a bit through Saturday, but there is a chance thicker mid/low-level clouds may develop and/or move in from the east for the remainder of the weekend.

Precipitable water is expected to linger near or exceed 4 mm through the next 5 nights.

Relatively weak winds and calm stable skies will prevail, likely allowing for better than average seeing over the next 3 nights (and possibly excellent seeing mainly for tonight). However, there is a chance for variability in seeing if/when winds cease for prolong periods particularly for tonight and again Thursday and Friday night. A possible increase in moisture could degrade seeing for Saturday night.

Subsidence associated with a mid/low-level and upper-level ridge to the north and south, respectively, will help maintain a well-defined inversion near 7-8 thousand feet and ensure a dry/stable summit-level air mass until the latter deteriorates and the mid-level portion retreats further northward on Saturday. In addition, the presence of the upper-level ridge will contribute to calm skies in the free atmosphere, which should allow for good/excellent seeing over the next 3 nights. However, there is a possibility for variability in seeing should winds cease for prolong periods, particularly for Thursday and Friday night. The erosion of the upper-level ridge will begin to occur as the tropical upper-tropospheric trough develops to the NW of the state early in the weekend. While instability associated with the TUTT will be fairly weak and/or focused further off toward the west, deeper mid/low-level moisture riding in with the trades are expected to weaken/lift the inversion early Saturday evening. This may allow the atmosphere to turn fairly saturated, increasing the risk for fog, high humidity and light rain at the summit for that night and Sunday night.

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


5-day Forecast
Summary

Graphical Trend
02 pm HST
Wed 11 Jul
08 pm HST
Wed 11 Jul
02 am HST
Thu 12 Jul
02 pm HST
Thu 12 Jul
08 pm HST
Thu 12 Jul
02 am HST
Fri 13 Jul
02 pm HST
Fri 13 Jul
08 pm HST
Fri 13 Jul
02 am HST
Sat 14 Jul
02 pm HST
Sat 14 Jul
02 am HST
Sun 15 Jul
02 pm HST
Sun 15 Jul
02 am HST
Mon 16 Jul
00 UTC
Thu 12 Jul
06 UTC
Thu 12 Jul
12 UTC
Thu 12 Jul
00 UTC
Fri 13 Jul
06 UTC
Fri 13 Jul
12 UTC
Fri 13 Jul
00 UTC
Sat 14 Jul
06 UTC
Sat 14 Jul
12 UTC
Sat 14 Jul
00 UTC
Sun 15 Jul
12 UTC
Sun 15 Jul
00 UTC
Mon 16 Jul
12 UTC
Mon 16 Jul
Cloud Cover (%) 10 to 30 0 to 20 0 to 20 0 to 20 0 to 20 10 to 30 20 to 40 40 to 60 40 to 60 60 to 80 70 to 90 70 to 90 60 to 80
Cloud Height (km) above sea level 9.5-10 9.5-10 9.5-10 9.5-10 9.5-10 9-10 9-10 9-10 6-9 4-8 4-8 4-8 5-8
Chance for Fog/Precip (%) 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 25/5 75/40 80/50 70/30
PW (mm, summit upward) 4 to 6 4 to 6 4 to 6 4 to 6 4 to 6 4 to 6 4 to 6 4 to 6 4 to 6 4 to 8 8 to 12 8 to 12 8 to 12
Mean Seeing (arcsecs) N/A 0.45 ± 0.1 0.45 ± 0.1 N/A 0.55 ± 0.15 0.55 ± 0.15 N/A 0.5 ± 0.15 0.55 ± 0.15 N/A 1.0 ± 0.3 N/A 0.9 ± 0.3
Summit Temp (°C) 9 4 3.5 9 4 3.5 9 3.5 3 6 1 5 1
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)

E/5 to 15

ENE/5 to 15

ENE/5 to 15

ESE/0 to 10

E/0 to 10

ENE/0 to 10

NW/0 to 10

N/0 to 10

NNE/0 to 10

WNW/0 to 10

N/0 to 10

N/0 to 10

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
Wed.Jul.11/Thu.Jul.12
19:15
20:27
4:28
5:41
5:17
18:09
1
6 43.4
20 06
Thu.Jul.12/Fri.Jul.13
19:14
20:27
4:28
5:41
6:23
19:12
0
7 47.3
19 29
Fri.Jul.13/Sat.Jul.14
19:14
20:27
4:29
5:41
N/A
20:12
3
8 50.1
17 27
Sat.Jul.14/Sun.Jul.15
19:14
20:27
4:29
5:42
N/A
21:06
8
9 50.5
14 13
Sun.Jul.15/Mon.Jul.16
19:14
20:26
4:30
5:42
N/A
21:56
15
10 47.8
10 07


Forecast issued by: Ryan Lyman
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Next update at 5 PM HST Wednesday 11 July (0300 UTC Thursday 12 July) 2018.
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