Current Conditions
Temp0.9 C
RH78 %
WindE 14 mph
RoadClosed
Mauna Kea Observatories Forecast
5 PM HST Monday 19 August (0300 UTC Tuesday 20 August) 2019
Warning(s)
None
Cloud Cover and Fog/Precipitation Forecast
The summit will remain dry and stable, while there is a chance that isolated thin high clouds will drift in from the south toward the end of the night.
Summary of Key Meteorological Variables
Summit temperatures will be near 5 C this evening and 4 C tomorrow morning. Winds will start out from the ENE at 15-25 mph, easing to 10-20 through the night. Seeing will be near 0.6-0.7 arcseconds, while precipitable water is expected to be in the 2-3 mm range for the night.
Discussion
The tradewind inversion will continue to cap low-level moisture primarily near 8 thousand feet and ensure the summit steers free of fog and precipitation through the next 5 nights. However, there is a possibility that summit-level humidity will increase toward 60-70% as minor moisture passes through the area for tomorrow night and Friday night. Daytime clouds will be minimal and short-lived for today, Wednesday and Thursday, but could turn extensive for Tuesday, Friday and Saturday.

There is a chance that isolated thin high clouds will occasionally drift in from the south toward the end of tonight and more scattered cirrus may also fill the northern skies for Thursday night. Clear skies will prevail for the remainder of the forecast period.

Precipitable water is expected to linger in the 2-3 mm range for tonight, increase to 3-4 mm for tomorrow night, slip to 1.5-2 mm for Wednesday and Thursday night, then jump to 4 mm again for Friday night.

Although relatively calm skies will prevail in the free atmosphere throughout the forecast period, minor boundary layer turbulence will contribute to more average-like seeing for tonight and Wednesday night. There is a good chance that lighter summit-level winds will allow for better than average seeing for tomorrow night, while while stronger summit-level winds will increase boundary layer turbulence again, resulting in poorer than average seeing for Thursday and Friday night.

Little change since the morning forecast....A deep ridge will continue to sit to the north of the state before a tight mid/upper-level low drops in from the NE and undercuts the ridge later in the week. Nevertheless, the low will remain too far to the north to have an affect on the stability of the atmosphere. Furthermore, subsidence associated with (at a minimum) low-level ridge will help maintain a fairly well-defined inversion near 8 thousand feet and ensure the summit steers free of fog and precipitation over the next 5 nights. There is a chance that residual tropical moisture passing just south of the Big Island will push summit-level humidity toward 60-70% and increase the risk for daytime clouds and perhaps isolated afternoon convection on the slopes for tomorrow and maybe as the upper-level low passes by on Friday and and over the weekend. Regardless, the deep ridge will help maintain light/laminar flow and clear/calm skies in the free atmosphere through the week. As a result, seeing will be mainly governed by summit-level winds and thus boundary layer turbulence, which could be an issue for tonight, Wednesday night and especially as winds clear 20 mph on Thursday and Friday night.
WRF Astronomical Observing Quality Guidance
Cloud Cover and Precipitable Water Analyses
MK CN² Profiles
5 Day Forecast Summary (Graphical Trend)
HST Cloud Fog/Precip Temp Wind Seeing PW
Cover (%) Height (km) Probability (%) (Celcius) (Dir/MPH) (Arcseconds) (mm)
Mon Aug 19 - 8 PM0-10Clear0 / 05ENE/15-250.55-0.852-3
Tue Aug 20 - 2 AM0-209.5-100 / 04E/10-200.5-0.72-3
2 PM0-209.5-1040 / 109ESE/10-20NaN3-5
8 PM0-10Clear0 / 03.5ESE/5-150.45-0.653-4
Wed Aug 21 - 2 AM0-5Clear0 / 03E/5-150.4-0.63-4
2 PM0-20Clear0 / 09NE/5-15NaN3-5
8 PM0-5Clear0 / 04NE/10-200.5-0.72-3
Thu Aug 22 - 2 AM0-5Clear0 / 03.5NE/10-200.55-0.751.5-2
2 PM0-20Clear0 / 09ENE/10-20NaN1.5-2.5
Fri Aug 23 - 2 AM0-209-100 / 03SE/15-250.5-0.91.5-2
2 PM0-20Clear40 / 108SE/15-25NaN2-4
Sat Aug 24 - 2 AM0-5Clear0 / 02ESE/20-350.6-13-5
2 PM0-20Clear60 / 207E/15-25NaN4-8
Rise and Set times for the Sun and Moon
Night (HST) Sun Set Twilight End Twilight Beg Sun Rise Moon Rise Moon Set Illumination (%) RA DEC
Mon Aug 19 - Tue Aug 20 18:57 20:04 4:47 5:54 21:35 N/A 79 1 26.9 3 00
Tue Aug 20 - Wed Aug 21 18:56 20:03 4:47 5:55 22:11 N/A 71 2 12.2 7 29
Wed Aug 21 - Thu Aug 22 18:55 20:02 4:48 5:55 22:48 N/A 61 2 59.2 11 43
Thu Aug 22 - Fri Aug 23 18:54 20:01 4:48 5:55 23:28 N/A 51 3 48.6 15 30
Fri Aug 23 - Sat Aug 24 18:53 20:00 4:49 5:55 0:13 N/A 41 4 41.0 18 37
Forecast Issued by: Ryan Lyman
Next update at 10 AM HST (2000 UTC) Tuesday 20 August 2019.
Additional Information
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