Current Conditions
Temp4.5 C
RH13 %
WindNNE 1 mph
RoadOpen (4x4)
Maunakea Observatories Forecast
5 PM HST Monday 26 September (0300 UTC Tuesday 27 September) 2022
Cloud Cover and Fog/Precipitation Forecast
The summit will remain dry and stable, but there is a possibility for patches of dissipating cirrus moving in from the north through the night.
Summary of Key Meteorological Variables
Summit temperatures will be near 9 C this afternoon, 4 C this evening and 3 C tomorrow morning. Winds will be from the ENE at 5-15 mph, with seeing near 0.4-0.5 arcseconds. Precipitable water is expected to be in the 3-4 mm range for the night.
A well-defined tradewind inversion will continue to cap low-level moisture at or below 8 thousand feet and ensure a dry/stable summit-level air mass through the next 5 nights. Some minor daytime clouds are possible through Wednesday, then will turn minimal and short-lived for the remainder of the forecast period.

While there is a possibility that patches of cirrus will move in from the north and dissipate in the area over the next 2 nights, cloud cover should not exceed 20% for any prolong period. Clear skies will for the following 3 nights.

Precipitable water is expected to linger near 3.5-4 mm for the next 3 nights, then slip toward 1-1.5 mm for Thursday and Friday night.

Calm/stable skies will mostly light/laminar NE flow at and above the summit should allow seeing to settle in near 0.4-0.5 arcsecond for another night. There is possibility for a brief injection in low-level turbulence, which may degrade seeing for Tuesday night. This turbulence will subside through Wednesday, as upper-level flow turns to light westerlies, allowing seeing to drift back to 0.4-0.5 arcseconds again for the remainder of the forecast period.

No change since the morning forecast...The mid/surface ridge will continue to sit to the north of the state and span across the eastern Pacific, promoting strong/steady large-scale subsidence in the area probably through 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. The tropical upper-tropospheric trough will also continue to slowly decay as the atmosphere quietly transitions more toward a winter-time pattern with the strengthening/broadening of the westerly jet. Fortunately, the westerly jet will remain far off to the north, which could help with development of weak upper-level ridges in the area and/or allow light flow to prevail in the free atmosphere through the week. This, combined with a stable air mass and summit-level winds near 5-10 mph, should allow seeing to settle in near 0.4-0.5 arcseconds throughout most of the forecast period. The only exception could be as a patch of colder air between 15-18 thousand feet passes through, creating a secondary inversion for Tuesday night. This could generate weak low-level turbulence and perhaps contribute to slight degradation in seeing during that time.
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)
Mon Sep 26 - 8 PM0-209-100 / 04ENE/5-150.35-0.553-4
Tue Sep 27 - 2 AM0-209-100 / 03.5ENE/5-150.35-0.553.5-4.5
2 PM20-404-4.50 / 08E/5-15NaN4-6
8 PM0-209-100 / 03ENE/0-100.5-0.83.5-4.5
Wed Sep 28 - 2 AM0-209-100 / 03ENE/0-100.475-0.7253.5-4.5
2 PM20-404-4.50 / 08NE/5-15NaN4-6
8 PM0-10Clear0 / 03ENE/5-150.35-0.553-4
Thu Sep 29 - 2 AM0-10Clear0 / 02.5ENE/5-150.4-0.63-4
2 PM0-20Clear0 / 08NE/5-15NaN2-4
Fri Sep 30 - 2 AM0-5Clear0 / 03NNE/5-150.35-0.551-1.5
2 PM0-20Clear0 / 07.5N/5-15NaN1-2
Sat Oct 01 - 2 AM0-10Clear0 / 02NNE/0-100.35-0.551-1.5
2 PM0-20Clear0 / 07.5NNE/5-15NaN1.5-2.5
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 Sep 26 - Tue Sep 27 18:23 19:27 4:59 6:03 N/A 19:15 2 13 25.2 -7 16
Tue Sep 27 - Wed Sep 28 18:22 19:26 4:59 6:03 N/A 19:52 7 14 13.9 -13 01
Wed Sep 28 - Thu Sep 29 18:21 19:25 4:59 6:03 N/A 20:33 13 15 05.6 -18 16
Thu Sep 29 - Fri Sep 30 18:20 19:25 5:00 6:04 N/A 21:19 22 16 00.9 -22 40
Fri Sep 30 - Sat Oct 01 18:19 19:24 5:00 6:04 N/A 22:10 32 16 59.9 -25 52
Forecast Issued by: Ryan Lyman
Next update at 10 AM HST (2000 UTC) Tuesday 27 September 2022.
Additional Information
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This message is also available at the MKWC road conditions page.
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