Current Conditions
Temp4.8 C
RH14 %
WindNNE 14 mph
RoadOpen (4x4)
Maunakea Observatories Forecast
5 PM HST Friday 17 September (0300 UTC Saturday 18 September) 2021
Warning(s)
Increasing winds
Cloud Cover and Fog/Precipitation Forecast
The summit will remain dry and stable, while scattered high clouds continue to dissipate in the area and/or shift off toward the west through the night.
Summary of Key Meteorological Variables
Summit temperaturs will be near 5 C this evening and 4.5 C tomorrow morning. Winds will be from the NE at 15-30 mph, with seeing near 0.8-0.9 arcseconds for the night. Precipitable water is expected to be in the 2.5-3.5 mm range throughout the night.
Discussion
A very distinct inversion will continue to cap low-level moisture at or below 9 thousand feet and ensure a dry and stable summit-level air mass through the next 5 nights. Daytime clouds will be minimal and short-lived through Tuesday, but could pick up on Wednesday.

Scattered high clouds will continue to dissipate in the area, while also shifting off toward the west, opening up skies as the night progresses. Skies will start out mostly clear for tomorrow night, but strands of high clouds may begin to move in from the east early Sunday morning and perhaps persist in the area for that night. More strands of cirrus could fill in from the NW and dissipate overhead for Monday night. There is chance that patches of high clouds will develop in the area and/or fill in from the osuth for Tuesday night.

Precipitable water is expected to linger near 3 mm for tonight, then settle in near 1.5-2 mm, probably for the remainder of the forecast period.

A bout of boundary layer turbulence will likely contribute to poor seeing for tonight. Winds are set to taper through tomorrow, allowing seeing to settle back in near 0.5-0.6 arcseconds as relatively calm/stable skies with deep NE flow prevails above the summit, probably for the weekend. There is a chance further improvement in seeing as lighter flow builds in at and above the summit for the early part of next week.

Little change since the morning forecast...The mid/low-level ridge will continue to sit to the north of the state and promote steady/strong large-scale subsidence in the area well into next week. This subsidence will easily maintain a well-defined inversion primarily near 8-9 thousand feet and ensure a dry/stable summit-level air mass throughout the forecast period. An upper-level ridge passing over and just south of the Big Island will help clear the high clouds out of the area, opening up most of the sky for the night. However, a brief rounding of the mid-level ridge is expected to tighten the wind gradient, which will result in an increase in summit-level winds over the next 24 hours. This will increase boundary layer turbulence and contribute to poor seeing for tonight. Seeing is set to improve and settle in near 0.5-0.55 arcseconds as winds subside in response to a zonal flattening of the ridge for Saturday and Sunday night. There is a chance that upper-level winds will weaken significantly as a very subtle upper-level trough axis slowly passes through, which may actually help to further improve seeing (toward 0.4-0.5 arcseconds) for the early part next week.
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)
Fri Sep 17 - 8 PM10-308-90 / 05NE/15-300.7-1.12.5-3.5
Sat Sep 18 - 2 AM0-208-90 / 04.5NE/15-300.6-12.5-3.5
2 PM0-20Clear0 / 011NE/10-20NaN2-4
8 PM0-5Clear0 / 06ENE/10-200.45-0.651.5-2
Sun Sep 19 - 2 AM0-209-100 / 05ENE/10-200.4-0.61.5-2
2 PM0-209-100 / 010ENE/10-20NaN2-3
8 PM0-209-100 / 04.5ENE/10-200.475-0.7251.5-2
Mon Sep 20 - 2 AM0-209-100 / 03.5E/10-200.4-0.61.5-2
2 PM20-409-100 / 08E/5-15NaN1.5-2.5
Tue Sep 21 - 2 AM0-209-100 / 03ENE/5-150.325-0.5751.5-2
2 PM20-409-100 / 08ESE/5-15NaN2-3
Wed Sep 22 - 2 AM10-309-100 / 03ENE/5-150.325-0.5751-2
2 PM60-804-1065 / 207SE/5-15NaN4-8
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
Fri Sep 17 - Sat Sep 18 18:31 19:35 4:57 6:01 N/A 4:16 92 21 51.4 -18 42
Sat Sep 18 - Sun Sep 19 18:30 19:35 4:57 6:01 17:12 5:13 97 22 44.0 -13 55
Sun Sep 19 - Mon Sep 20 18:29 19:34 4:57 6:02 17:51 6:07 99 23 33.5 -8 34
Mon Sep 20 - Tue Sep 21 18:28 19:33 4:57 6:02 18:28 6:59 100 0 20.9 -2 57
Tue Sep 21 - Wed Sep 22 18:27 19:32 4:58 6:02 19:02 N/A 98 1 06.9 2 41
Forecast Issued by: Ryan Lyman
Next update at 10 AM HST (2000 UTC) Monday 20 September 2021.
Additional Information
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