Current Conditions
Temp8.4 C
RH50 %
WindESE 9 mph
RoadOpen (4x4)
Mauna Kea Observatories Forecast
10 AM HST (2000 UTC) Monday 24 July 2017
Warning(s)
None
Cloud Cover and Fog/Precipitation Forecast
The summit will remain clear, dry and stable through the night.
Summary of Key Meteorological Variables
Summit temperatures will be near 8 C this afternoon, 3 C this evening and 2 C tomorrow morning. Winds will be from the ESE at 5-15 mph for today and 10-20 mph for the night. Seeing is expected to linger near 0.45 arcseconds, while precipitable water is expected to be in the 2-2.5 mm range for the night.
Discussion
The tradewind inversion will continue to cap low-level moisture at or below 9 thousand feet and ensure a dry/stable summit-level air mass through the next 5 nights. Daytime clouds will be minimal and short-lived through Thursday, but could pick up a bit on Friday.

Skies will remain predominately clear through Tuesday night. Bands of high clouds are expected to build in from the south beginning late Wednesday morning and become thicker and more widespread, likely contributing to periods of extensive cloud cover for the following 2 nights. There is a chance that these bands will thin out on Friday, which could help open up skies for that night.

Precipitable water is expected to linger near 2 mm for the next 3 nights, then increase to 3-4 mm for Thursday and Friday night.

Relatively calm skies at and above the summit should allow seeing to settle in near 0.4-0.5 arcseconds through at least early tomorrow evening. An increase in shear/turbulence in the free atmosphere is expected to degrade seeing toward 0.6-0.65 arcseconds for Wednesday and Thursday night. There is a chance that this turbulence will shift out of the area, allowing seeing to improve again through Friday night.

The persistent mid/low-level ridge to the NE of the state will continue to promote steady/strong large-scale subsidence in the area through the week. This subsidence will easily maintain a well-defined inversion at or below 9 thousand feet and ensure a dry/stable summit-level air mass through the next 5 nights. The ridge will also help push the remnants of Fernanda off toward the NW, allowing clear/calm skies to build in overhead for the next 2 nights. The sub-tropical jet is set to rebuild in from the south on Wednesday, which could increase shear/turbulence in the free atmosphere and degrade seeing for that night as well as Thursday night. The jet is also expected to bring strands of mid/upper-level clouds in from the south, which could contribute to periods of extensive cloud cover and high PW for much of Thursday. The STJ is expected to weaken and shift northward on Friday, which should help reduce shear/turbulence in the free atmosphere and allow seeing to improve again for that night. This may also help cut the jet's access to tropical high clouds, which will help open up skies for that 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 Jul 24 - 2 PM0-20Clear0 / 08ESE/5-15NaN1-2
8 PM0-5Clear0 / 03ESE/10-200.35-0.552-2.5
Tue Jul 25 - 2 AM0-5Clear0 / 02ESE/10-200.3-0.52-2.5
2 PM0-20Clear0 / 07.5E/10-20NaN2-3
8 PM0-5Clear0 / 02.5E/10-200.35-0.551.75-2.25
Wed Jul 26 - 2 AM0-5Clear0 / 02.5E/10-200.45-0.651.75-2.25
2 PM20-409-100 / 08ENE/10-20NaN2-3
8 PM40-608-100 / 03.5ENE/10-200.5-0.71.75-2.25
Thu Jul 27 - 2 AM60-806-100 / 03.5ENE/10-200.5-0.81.75-2.25
2 PM60-806-100 / 09E/5-15NaN2-4
Fri Jul 28 - 2 AM60-806-100 / 03.5ESE/10-200.45-0.753-4
2 PM60-804-925 / 57ENE/5-15NaN4-8
Sat Jul 29 - 2 AM20-407-90 / 03ENE/5-150.4-0.73-4
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 Jul 24 - Tue Jul 25 19:11 20:22 4:35 5:46 N/A 20:36 5 10 05.8 11 34
Tue Jul 25 - Wed Jul 26 19:11 20:22 4:35 5:46 N/A 21:22 11 10 59.3 7 41
Wed Jul 26 - Thu Jul 27 19:10 20:21 4:36 5:47 N/A 22:05 19 11 50.2 3 29
Thu Jul 27 - Fri Jul 28 19:10 20:21 4:36 5:47 N/A 22:45 28 12 39.1 -0 47
Fri Jul 28 - Sat Jul 29 19:10 20:20 4:37 5:47 N/A 23:24 37 13 26.7 -4 55
Forecast Issued by: Ryan Lyman
Next update at 5 PM HST Monday 24 July (0300 UTC Tuesday 25 July) 2017.
Additional Information
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