Current Conditions
Temp8.7 C
RH20 %
WindW 17 mph
RoadOpen (4x4)
Maunakea Observatories Forecast
7 AM HST (1700 UTC) Tuesday 19 October 2021
Warning(s)
None
Cloud Cover and Fog/Precipitation Forecast
The summit will remain dry and stable, but there is a chance that isolated to scattered high clouds will occasionally pass mainly along the southern skies through the night.
Summary of Key Meteorological Variables
Summit temperatures will be near 8 C this afternoon and 3 C for the night. Winds will be from the NW at 15-30 mph for today and 10-20 mph through the night. Seeing will be around 0.5-0.55 arcseconds, but there is a possibility for some variability (particularly just after midnight). Precipitable water is expected to exceed 4 mm for the night.
Discussion
A well-defined tradewind inversion will continue to cap low-level moisture near 5-6 thousand feet and ensure the summit steers free of fog and precipitation through the next 5 nights. Daytime clouds will be minimal and short-lived throughout the forecast period.

Skies overhead will remain predominately clear through Thursday night, but there is a chance that isolated high clouds will pass mainly along the southern skies for tonight. Banding high clouds may approach along the SE skies just after sunrise on Friday and may contribute to periods of extensive cloud cover for that night. The bulk of these clouds will quickly pass to the western skies through Saturday, but there is still a chance that scattered high clouds will still persist in the area for that night.

Precipitable water is expected to exceed 4 mm for tonight, slip into the 3-4 mm range for most of the next 2 nights, then increase back to 4+ mm for Friday and Saturday night.

While relatively calm skies with deep/laminar NW flow will prevail in the free atmosphere, which should allow for better than average seeing, there is a possibility for bouts of light boundary layer turbulence that could occasionally disrupt seeing for tonight. Lighter summit-level winds will help seeing to stabilize and settle around 0.4-0.5 arcseconds for tomorrow night and most of Thursday night. However, an increase in mid-level turbulence may start to degrade seeing through the latter night and perhaps push seeing toward more average-like values for Friday and Saturday night.

Although the mid/surface ridge will remain displaced to the NW of the state, before spreading eastward later in the week, it will continue to promote rather steady large-scale subsidence in the area well into the weekend. This subsidence will easily maintain a relatively well-defined inversion near 6 thousand feet and ensure a dry and stable summit-level air mass throughout the forecast period. The westerly jet is expected to become more energetic and pick up steam well to the north, but upper-level flow in the area is set to weaken as ridge builds to the SE over the next 24 hours. While this could allow relatively weak/laminar flow to prevail in the free atmosphere, mid-level flow may in response to the upper ridge, and may contribute periods of light boundary layer turbulence for tonight. The upper ridge is projected to fall apart as weak upper-level trough redevelops overhead for the second half of this week, which should help winds to subside through tomorrow. The trough will not affect the stability of the atmosphere and the weaker summit-level winds, combined with a dry/stable air mas may allow seeing to settle back in around 0.4-0.5 arcseconds for Wednesday and Thursday night. However, there is a possibility that the trough will help deposit an upper-level low to the west of the state and re-establish the sub-tropical jet over/near the Big Island thereafter. This may bring mid/upper-level turbulence and clouds to the area, perhaps contributing to more average-like seeing and periods of extensive cloud cover, respectively, for Friday and Saturday 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 (%) (Celsius) (Dir/MPH) (Arcseconds) (mm)
Tue Oct 19 - 2 PM0-209-100 / 08NW/15-30NaN4-6
8 PM0-209-100 / 03NW/10-200.425-0.6754-6
Wed Oct 20 - 2 AM0-209-100 / 03NW/10-200.375-0.6254-6
2 PM0-20Clear0 / 08NW/10-20NaN4-6
8 PM0-10Clear0 / 03NW/5-150.35-0.553.5-4.5
Thu Oct 21 - 2 AM0-5Clear0 / 02NNW/5-150.3-0.53-4
2 PM0-20Clear0 / 07NE/5-15NaN3-5
8 PM0-5Clear0 / 01.5E/5-150.35-0.553-4
Fri Oct 22 - 2 AM0-20Clear0 / 01.5ESE/5-150.375-0.6253-4
2 PM40-608-90 / 07.5SSE/5-15NaN3-5
Sat Oct 23 - 2 AM60-806-90 / 02.5ESE/5-150.425-0.6754-6
2 PM40-606-90 / 08.5ESE/5-15NaN4-6
Sun Oct 24 - 2 AM20-406-80 / 03.5NNE/5-150.475-0.7254-6
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 Oct 19 - Wed Oct 20 18:04 19:09 5:05 6:09 17:35 6:34 100 1 37.0 6 31
Wed Oct 20 - Thu Oct 21 18:03 19:08 5:05 6:10 18:09 7:25 99 2 22.6 11 41
Thu Oct 21 - Fri Oct 22 18:03 19:08 5:05 6:10 18:45 N/A 97 3 09.3 16 19
Fri Oct 22 - Sat Oct 23 18:02 19:07 5:06 6:11 19:22 N/A 93 3 57.6 20 15
Sat Oct 23 - Sun Oct 24 18:01 19:06 5:06 6:11 20:03 N/A 87 4 47.6 23 17
Forecast Issued by: Ryan Lyman
Next update at 5 PM HST Tuesday 19 October (0300 UTC Wednesday 20 October) 2021.
Additional Information
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