Latest Forecast for Mauna Kea Observatories
10 AM HST (2000 UTC) Friday 14 September 2018

Warnings
None

Cloud Cover and Precipitation Forecast
There is a small risk for short-lived fog/high humidity, mainly for early this evening and during the second half of the night; precipitation is not expected. High clouds may also creep in from the west and pass primarily along the northern skies throughout the night.

Summary of Key Meteorological Variables
Summit temperatures will be near 6.5 C this afternoon, 2.5 C this evening and 2 C tomorrow morning. Winds will be from the NE at 5-15 mph, with seeing near 0.6-0.65 arcseconds. Precipitable water is expected to linger near 4-5 mm for the night.

Graphical Summary

Discussion
There is a chance that lingering patces of instability and moisture will periodically lift the inversion toward 10-12 thousand feet and increase the risk for fog/high humidity mainly for early this evening and again during the second half of the night; precipitation is not expected. The inversion is expected more firmly established near 6-7 thousand feet through tomorrow, ensuring the summit remains dry and stable for that night, Sunday and probably Monday night. However, increasing instability may deepen the low-level cloud field and increase the risk for moisture at the summit around Tuesday/Wednesday. Some afternoon clouds and isolated convection are possible for today and perhaps tomorrow, then will become minimal and short-lived for Sunday and Monday, only to pick up again on Tuesday.

Scattered high clouds are expected to creep in from the west and pass mainly along the northern skies for tonight. More widespread clouds may fill in from the west and pass directly over the summit, contributing to periods of extensive cloud cover for Saturday, Sunday and probably Monday night. There is a chance that these clouds will shift to the southeast skies on Tuesday, but patches of thick clouds may spread in from the east during that night.

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

Relatively calm skies will prevail at and above the summit, and together with a drier more stable air mass should allow for better than average seeing probably through most of the next 4 nights. There is a possibility for some variability mainly if moisture briefly becomes an issue for early this evening and again near sunrise tomorrow. There is also a chance that pockets of minor turbulence will pass through the area and contribute to some fluctuations for Sunday and Monday night. A potential increase in upper-level turbulence/instability and summit-level moisture may degrade seeing for Tuesday night.

Although the ridge to the NNE is expected to reinstill large-scale subsidence in the area over the next several days, residual pockets of tropical moisture associated with Olivia combined with weak instability from the tropical upper-tropospheric trough (TUTT) lingering overhead may allow for the development of isolated convection along the slopes mainly for today. This could bring periods of fog/high humidity to the summit, which may persist into early this evening. There is also a chance that a small pocket of unstable low-level clouds will drift in from the NE and lift the inversion, increasing this risk toward the end night, but the odds are slim. Drier more stable conditions are expected to return to the summit as the TUTT and the remainder of Olivia shift off toward the west through tomorrow. However, the interaction between the two will continue to fire off deep convection way south of the state, and the TUTT's southern counterpart, the sub-tropical jet, is expected to stream the cirrus exhaust over the area, contributing to extensive cloud cover probably for Saturday, Sunday and Monday night. Eventually, a short-wave trough is set to dig in from the NNW and shift the TUTT back over the state, bringing more widespread instability to the area, which could deep the low-level cloud flow and increase the risk for moisture at the summit and perhaps convection in the area late Tuesday night. On the other hand, this incoming trough could help push the STJ off toward the SE, opening up skies a bit for that night.

Astronomical Observing Quality Guidance
05 pm HST Friday 14 September (03 UTC Saturday 15 September)CN2
08 pm HST Friday 14 September (06 UTC Saturday 15 September)CN2
11 pm HST Friday 14 September (09 UTC Saturday 15 September)CN2
02 am HST Saturday 15 September (12 UTC Saturday 15 September)CN2
05 am HST Saturday 15 September (15 UTC Saturday 15 September)CN2
08 am HST Saturday 15 September (18 UTC Saturday 15 September)CN2
Latest WRF CN2 Profiles Animation | Collage


5-day Forecast
Summary

Graphical Trend
02 pm HST
Fri 14 Sep
08 pm HST
Fri 14 Sep
02 am HST
Sat 15 Sep
02 pm HST
Sat 15 Sep
08 pm HST
Sat 15 Sep
02 am HST
Sun 16 Sep
02 pm HST
Sun 16 Sep
08 pm HST
Sun 16 Sep
02 am HST
Mon 17 Sep
02 pm HST
Mon 17 Sep
02 am HST
Tue 18 Sep
02 pm HST
Tue 18 Sep
02 am HST
Wed 19 Sep
00 UTC
Sat 15 Sep
06 UTC
Sat 15 Sep
12 UTC
Sat 15 Sep
00 UTC
Sun 16 Sep
06 UTC
Sun 16 Sep
12 UTC
Sun 16 Sep
00 UTC
Mon 17 Sep
06 UTC
Mon 17 Sep
12 UTC
Mon 17 Sep
00 UTC
Tue 18 Sep
12 UTC
Tue 18 Sep
00 UTC
Wed 19 Sep
12 UTC
Wed 19 Sep
Cloud Cover (%) 60 to 80 10 to 30 20 to 40 40 to 60 50 to 70 60 to 80 60 to 80 60 to 80 60 to 80 50 to 70 60 to 80 60 to 80 20 to 40
Cloud Height (km) above sea level 4-10 9-10 9-10 4-10 9-10 8.5-10 8-10 8-10 8-9.5 8-10 9-10 4-10 6-8
Chance for Fog/Precip (%) 60/20 30/0 25/0 20/5 0/0 0/0 0/0 0/0 0/0 0/0 10/0 40/10 60/20
PW (mm, summit upward) 4 to 8 4 to 6 4 to 6 4 to 8 3.5 to 4.5 3.5 to 4.5 3 to 5 3 to 4 3 to 4 3 to 5 3.5 to 4.5 4 to 8 4 to 6
Mean Seeing (arcsecs) N/A 0.65 ± 0.15 0.6 ± 0.15 N/A 0.55 ± 0.1 0.55 ± 0.1 N/A 0.55 ± 0.1 0.6 ± 0.15 N/A 0.6 ± 0.15 N/A 0.9 ± 0.2
Summit Temp (°C) 6.5 2.5 2 7 2.5 2.5 7.5 3 2.5 8 3 7.5 2.5
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)

NE/5 to 15

NE/5 to 15

NE/5 to 15

NNE/5 to 15

NNE/5 to 15

N/5 to 15

N/5 to 15

N/5 to 15

NW/0 to 10

WNW/0 to 10

S/0 to 10

SSW/5 to 15

SSW/10 to 20


 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.Sep.14/Sat.Sep.15
18:34
19:39
4:56
6:00
N/A
22:41
34
16 11.6
-16 57
Sat.Sep.15/Sun.Sep.16
18:33
19:38
4:56
6:01
N/A
23:26
44
17 02.7
-19 19
Sun.Sep.16/Mon.Sep.17
18:32
19:37
4:56
6:01
N/A
0:13
54
17 54.0
-20 47
Mon.Sep.17/Tue.Sep.18
18:31
19:36
4:57
6:01
N/A
1:01
63
18 45.3
-21 18
Tue.Sep.18/Wed.Sep.19
18:30
19:35
4:57
6:01
N/A
1:50
72
19 36.3
-20 52


Forecast issued by: Ryan Lyman
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Next update at 5 PM HST Friday 14 September (0300 UTC Saturday 15 September) 2018.
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