Current Conditions
Temp4.9 C
RH44 %
WindESE 18 mph
RoadOpen (4x4)
Mauna Kea Observatories Forecast
10 AM HST (2000 UTC) Tuesday 26 July 2016
Moderate winds
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 5.5 C this afternoon, 0.5 C this evening and 0 C tomorrow morning. Winds will be from the east at 20-35 mph, with seeing around 0.9 arcseconds. Precipitable water is expected to be in the 3-4 mm range for the night.
The tradewind inversion will continue to cap low-level moisture primarily near 6-7 thousand feet and ensure the summit remains dry and stable through the next 5 nights. Daytime clouds will be minimal and short-lived throughout the forecast period.

Skies will remain predominately clear through the next 5 nights.

Precipitable water is expected to linger in the 3-4 mm range for the next 2 nights, drop toward 1 mm through Thursday night and likely bottom out near 0.8-0.9 mm for Friday night. There is a chance that it will trend back to 2+ mm again through Saturday night.

Boundary layer turbulence will contribute to poor seeing for the next 2 nights. Calmer skies should allow seeing to improve toward more average-like values (if not slightly better) for Thursday night, but there is a possibility that a patch of low-level turbulence will disrupt seeing for Friday and Saturday night.

The mid/low-level ridge to the north will continue to promote steady/strong large-scale subsidence in the area, which will help maintain a well-defined inversion near 6-7 thousand feet and ensure the summit remains dry and stable through the next 5 nights. And while skies will remain predominately clear during this period, lingering mid-level moisture and a relatively tight wind gradient will keep PW near 3-4 mm and winds near 25-30 mph, respectively, over the next 2 nights. The latter will stir up boundary layer turbulence and contribute to poor seeing during this time. Winds are set to weaken as the ridge axis lifts subtly to the north and broadens westward, which should allow calmer skies to prevail and seeing to improve toward 0.5-0.6 arcseconds for Thursday night. PW is also expected to drop toward 1 mm as a weak upper-level ridge augments the subsidence in the area for Thursday and Friday night. However, a mid/upper-level trough/low building in from the east could bring minor mid/low-level turbulence to the area, which could disrupt seeing a bit over the weekend. There is a chance that mid-level moisture associated with this trough/low will push PW back toward 2 mm through Saturday night and perhaps to 4+ mm for Sunday 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)
Tue Jul 26 - 2 PM0-20Clear0 / 05.5ENE/20-35NaN3-5
8 PM0-5Clear0 / 00.5ENE/20-350.7-1.13-4
Wed Jul 27 - 2 AM0-5Clear0 / 00E/20-350.7-1.13-4
2 PM0-20Clear0 / 04E/20-35NaN3-5
8 PM0-5Clear0 / 0-0.5E/20-350.6-13-4
Thu Jul 28 - 2 AM0-5Clear0 / 0-0.5E/15-300.6-0.93-4
2 PM0-20Clear0 / 06E/10-20NaN2-4
8 PM0-5Clear0 / 01NE/5-150.5-0.61.5-2.5
Fri Jul 29 - 2 AM0-5Clear0 / 01.5N/5-150.45-0.551-1.5
2 PM0-20Clear0 / 08N/5-15NaN0.8-1.2
Sat Jul 30 - 2 AM0-5Clear0 / 03SSE/0-100.5-0.80.7-1
2 PM0-20Clear0 / 07.5SW/5-15NaN0.8-1.2
Sun Jul 31 - 2 AM0-5Clear0 / 02SW/10-200.4-0.81-2
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
Tue Jul 26 - Wed Jul 27 19:10 20:21 4:36 5:47 0:15 N/A 44 2 43.1 10 34
Wed Jul 27 - Thu Jul 28 19:10 20:21 4:36 5:47 1:04 N/A 33 3 39.4 13 51
Thu Jul 28 - Fri Jul 29 19:10 20:20 4:37 5:47 1:56 N/A 23 4 36.9 16 15
Fri Jul 29 - Sat Jul 30 19:09 20:19 4:37 5:48 2:51 N/A 14 5 35.1 17 39
Sat Jul 30 - Sun Jul 31 19:09 20:19 4:38 5:48 3:48 N/A 7 6 33.2 17 56
Forecast Issued by: Ryan Lyman
Next update at 5 PM HST Tuesday 26 July (0300 UTC Wednesday 27 July) 2016.
Additional Information
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This message is also available at the MKWC road conditions page.
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