Current Conditions
Temp7.2 C
RH59 %
WindENE 7 mph
RoadOpen (4x4)
Mauna Kea Observatories Forecast
5 PM HST Monday 01 June (0300 UTC Tuesday 2 June) 2020
Warning(s)
None
Cloud Cover and Fog/Precipitation Forecast
While humidity is expected to linger near 60%, the summit will remain clear, dry and stable through the night.
Summary of Key Meteorological Variables
Summit temperatures will be near 4 C this evening and 3 C tomorrow morning. Winds will be from the ENE at 10-20 mph for much of today, decreasing to 5-15 mph for the morning hours. Seeing will be near 0.6-0.65 arcseconds, while precipitable water is expected to exceed 4 mm for the night.
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. However, humidity is expected to linger near 50-60% for tonight and perhaps tomorrow night. Minor afternoon clouds are possible over the next 2 days, then will become minimal and short-lived for the remainder of the week.

Skies will remain predominately clear throughout the forecast period.

Precipitable water is expected to exceed 4 mm for the next 2 nights, slip toward 2-3 mm Wednesday and Thursday night and probably 1 mm for Friday night.

Despite relatively uniform/laminar easterly flow in the free atmosphere, turbulence in the lowest 1 km will likely contribute to poorer than average seeing probably throughout most of the forecast period. There is a possibility that boundary layer turbulence will increase, which could further degrade seeing for Wednesday and Thursday night.

No change since the morning forecast...A deep ridge will continue to sit to the NE of the state and promote steady/strong large-scale subsidence in the area throughout the week. This subsidence will easily maintain a well-defined inversion near 7-8 thousand feet and ensure a dry/stable summit-level air mass throughout the forecast period. However, widespread mid-level moisture filling in with the deep easterly trades will keep humidity and PW around 50-60% and 4+ mm, respectively for tonight and perhaps tomorrow night; both are set to subside as this moisture shifts off toward the west by late Wednesday morning. The upper-level porition of the ridge will help suppress the tropical upper-tropospheric trough and especially the sub-tropical jet off to the south, which will keep high clouds from passing overhead probably throughout the forecast period. It will also minimize free atmospheric turbulence (above 5 KM from SLP) as predominately uniform/laminar flow prevails aloft during this time. Unfortunately, there is a good chance that winds in the lowest 0.5-1 KM (above the summit) will stir up low-level turbulence or even boundary layer turbulence and contribute to average/poor seeing over the next 5 nights.
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 Jun 01 - 8 PM0-5Clear0 / 04ENE/10-200.5-0.84-8
Tue Jun 02 - 2 AM0-5Clear0 / 03ENE/5-150.5-0.74-8
2 PM0-20Clear0 / 09ESE/5-15NaN4-8
8 PM0-5Clear0 / 04E/10-200.5-0.84-6
Wed Jun 03 - 2 AM0-5Clear0 / 03.5E/10-200.5-0.94-6
2 PM0-20Clear0 / 09.5E/15-25NaN3-5
8 PM0-5Clear0 / 04.5E/15-250.5-0.92-3
Thu Jun 04 - 2 AM0-5Clear0 / 03.5E/15-250.6-12-3
2 PM0-20Clear0 / 08E/15-25NaN2-4
Fri Jun 05 - 2 AM0-5Clear0 / 02E/15-250.6-11.5-2.5
2 PM0-20Clear0 / 07.5E/15-25NaN1-2
Sat Jun 06 - 2 AM0-5Clear0 / 02.5E/10-200.45-0.750.8-1.2
2 PM0-20Clear0 / 08SSE/5-15NaN1-2
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 Jun 01 - Tue Jun 02 19:07 20:21 4:19 5:32 N/A 3:27 84 13 41.9 -6 12
Tue Jun 02 - Wed Jun 03 19:08 20:21 4:19 5:32 N/A 4:11 92 14 37.3 -11 53
Wed Jun 03 - Thu Jun 04 19:08 20:22 4:19 5:32 N/A 4:59 97 15 35.0 -16 55
Thu Jun 04 - Fri Jun 05 19:09 20:22 4:19 5:32 18:06 5:50 100 16 34.8 -20 54
Fri Jun 05 - Sat Jun 06 19:09 20:22 4:19 5:32 19:10 N/A 99 17 36.3 -23 32
Forecast Issued by: Ryan Lyman
Next update at 10 AM HST (2000 UTC) Tuesday 2 June 2020.
Additional Information
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