Latest Forecast for Mauna Kea Observatories
830 AM HST (1830 UTC) Thursday 30 July 2020

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 11 C this afternoon and 6 C for the night. Winds will be from the east at 5-15 mph, switching to a more NE direction through the night. Seeing will be near 0.35-0.4 arcseconds, while precipitable water is expected to be in the 0.55-0.7 mm for the night.

Graphical Summary

Discussion
A distinct inversion will continue to cap low-level moisture near 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 or organized clouds throughout the forecast period, though there is a chance for isolated patches of high clouds moving in from the south on Saturday and Sunday night.

Precipitable water is expected to linger 0.6-0.7 mm for tonight and early tomorrow evening, but will trend toward 1 mm by the end of the latter night and probably 2 mm for early Saturday night. It will likely subside thereafter and settle in below 1 mm again for Sunday and Monday night.

A very stable air mass, combined with calm skies and relatively deep/light easterly flow at and above the summit should allow seeing to settle in near 0.4-0.45 arcseconds throughout most of the forecast period. There is a chance that seeing will dip below 0.4 arcseconds mainly for tonight and again on Sunday night.

A fairly deep ridge will continue to sit to the NNW of the state and promote steady/strong large-scale subsidence in the area and likely prohibit the tropical upper-tropospheric trough from rebuilding in the area until late next week. Nevertheless, the subsidence will easily maintain a very distinct tradewind inversion near 7-8 thousand feet and ensure a dry/stable summit-level air mass throughout the forecast period. This stability, combined with the absence of the TUTT and its southern counterpart, aka the sub-tropical part, will allow calm predominately clear skies to prevail overhead, which should translate to good/excellent seeing over the next 5 nights. Precipitable water will also benefit from the enhanced subsidence associated with the deep ridge and linger at or below 0.8 mm through tomorrow evening. There is a chance that a patch of mid/upper-level moisture passing to the south will briefly increase PW toward 2 mm for Saturday night, but PW is expected to quickly settle back in below 1 mm as this patch slips westward for the following 2 nights.

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
02 pm HST
Thu 30 Jul
08 pm HST
Thu 30 Jul
02 am HST
Fri 31 Jul
02 pm HST
Fri 31 Jul
08 pm HST
Fri 31 Jul
02 am HST
Sat 01 Aug
02 pm HST
Sat 01 Aug
08 pm HST
Sat 01 Aug
02 am HST
Sun 02 Aug
02 pm HST
Sun 02 Aug
02 am HST
Mon 03 Aug
02 pm HST
Mon 03 Aug
02 am HST
Tue 04 Aug
00 UTC
Fri 31 Jul
06 UTC
Fri 31 Jul
12 UTC
Fri 31 Jul
00 UTC
Sat 01 Aug
06 UTC
Sat 01 Aug
12 UTC
Sat 01 Aug
00 UTC
Sun 02 Aug
06 UTC
Sun 02 Aug
12 UTC
Sun 02 Aug
00 UTC
Mon 03 Aug
12 UTC
Mon 03 Aug
00 UTC
Tue 04 Aug
12 UTC
Tue 04 Aug
Cloud Cover (%) 0 to 20 0 to 5 0 to 5 0 to 20 0 to 5 0 to 5 0 to 20 0 to 20 0 to 20 0 to 20 0 to 20 0 to 20 0 to 5
Cloud Height (km) above sea level N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A
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) 0.8 to 1.2 0.55 to 0.7 0.55 to 0.7 0.8 to 1.2 0.6 to 0.8 0.8 to 1 1 to 2 1.5 to 2 1 to 1.5 0.8 to 1.2 0.6 to 1 0.8 to 1.2 0.6 to 1
Mean Seeing (arcsecs) N/A 0.35 ± 0.1 0.4 ± 0.1 N/A 0.4 ± 0.1 0.45 ± 0.1 N/A 0.45 ± 0.1 0.4 ± 0.1 N/A 0.35 ± 0.1 N/A 0.4 ± 0.1
Summit Temp (°C) 11 6 6 12 6 5 10 5.5 5 10.5 5 9.5 4
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

NE/5 to 15

E/5 to 15

E/10 to 20

E/10 to 20

E/10 to 20

E/10 to 20

E/10 to 20

E/10 to 20

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.Jul.30/Fri.Jul.31
19:09
20:19
4:38
5:48
N/A
3:20
88
17 52.9
-24 03
Fri.Jul.31/Sat.Aug.01
19:08
20:18
4:38
5:48
N/A
4:16
94
18 52.6
-24 44
Sat.Aug.01/Sun.Aug.02
19:08
20:17
4:39
5:49
17:41
5:13
98
19 51.4
-23 59
Sun.Aug.02/Mon.Aug.03
19:07
20:17
4:39
5:49
18:32
6:11
100
20 48.0
-21 56
Mon.Aug.03/Tue.Aug.04
19:07
20:16
4:40
5:50
19:19
N/A
99
21 41.6
-18 50


Forecast issued by: Ryan Lyman
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Next update at 5 PM HST Thursday 30 July (0300 UTC Friday 31 July) 2020.
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