Current Conditions
Temp4.1 C
RH9 %
WindE 18 mph
RoadOpen (4x4)
Mauna Kea Observatories Forecast
5 PM HST Monday 24 April (0300 UTC Tuesday 25 April) 2017
Cloud Cover and Fog/Precipitation Forecast
The summit will remain dry and stable, while the high clouds shift to the eastern skies through the night.
Summary of Key Meteorological Variables
Summit temperatures will be near 1.5 C this evening and 1 C tomorrow morning. Winds will be from the ESE at 10-20 mph, with seeing near 0.6 arcseconds. Precipitable water is expected to be in the 2-3 mm range for the night.
A fairly well-defined tradewind inversion will continue to cap low-level moisture at or below 9 thousand feet and ensure the summit remains dry and stable through at least Wednesday night. Building instability and moisture accumulating in the area could begin to erode the inversion and increase the risk for fog, high humidity, precipitation and ice at the summit over the following 2-3 nights. Daytime clouds will be minimal and short-lived through Thursday, but could pick up for Friday and especially over the weekend.

The bulk of the high clouds are set to shift east of the Big Island by this evening, leaving mostly residual patches of clouds along the eastern skies for much of tonight and the opening half of tomorrow night. Clear skies will prevail for the second half of Tuesday night and especially the following 2 nights, but more organized high clouds may begin to fill in from the NW and south and could merge over the summit area by early Saturday morning.

Precipitable water is expected to linger in the 2-3 mm range through Thursday night, then could increase toward 4 mm for Friday night.

Relatively calm skies (with very minor upper-level turbulence) should allow for for better than average seeing for tonight and probably the opening half of tomorrow night. However, building mid/upper-level turbulence may start to degrade seeing during the latter night and Wednesday night. This turbulence coupled with an eventual increase in shear could contribute to bad seeing for Thursday and Friday night.

Little change since the morning forecast...A rather broad mid/low-level ridge to the north of the state will continue to promote strong/steady large-scale subsidence in the area, which will help maintain a well-defined at or below 9 thousand feet and ensure a dry/stable summit-level air mass for at least the next 3 nights. A weak (but developing) upper-level low passing overhead is expected to shift the high clouds eastward, opening up skies through the night. However, there is a possibility for minor upper-level turbulence embedded in the low, that could periodically disrupt seeing through tomorrow evening (though better than average seeing should still prevail). Stronger turbulence along the western portion of this low will likely build in over the summit area, which could degrade seeing early Wednesday morning and especially for the following 2 nights. Models suggest that this low will shift further eastward as a large/deep late-season trough develops to the NW and digs southward around Thursday/Friday. There is a possibility that this trough will increase shear in the free atmosphere, which could further degrade seeing mainly for Thursday night. There is also a chance that this trough and its associated surface low will send a cold front toward the Islands, which could erode the inversion and increase the risk for moisture at the summit mainly for Friday night. In fact, long term projection suggest that the trough will cut off a low to the north of the state and drag deep moisture in from the south over the weekend. This could result in very/poor wet and potentially windy conditions as the weekend progresses.
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 Apr 24 - 8 PM40-608-90 / 01.5ESE/10-200.5-0.72-3
Tue Apr 25 - 2 AM20-408-90 / 01ESE/10-250.5-0.72-3
2 PM0-208-90 / 07ESE/10-20NaN2-4
8 PM0-208-8.50 / 02ESE/10-200.5-0.72.5-3.5
Wed Apr 26 - 2 AM0-5Clear0 / 01.5E/10-200.5-0.82.5-3.5
2 PM0-20Clear0 / 06.5E/10-20NaN2-4
8 PM0-5Clear0 / 01.5ENE/10-200.55-0.852.5-3.5
Thu Apr 27 - 2 AM0-5Clear0 / 01ENE/5-150.6-0.92-3
2 PM0-20Clear0 / 06E/5-15NaN2-4
Fri Apr 28 - 2 AM0-5Clear10 / 00.5SSE/5-150.8-1.22-3
2 PM40-604-520 / 54W/5-15NaN3-6
Sat Apr 29 - 2 AM60-807-1040 / 10-1.5WSW/5-150.7-1.13-5
2 PM60-804-1060 / 153.5W/15-30NaN4-8
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
Mon Apr 24 - Tue Apr 25 18:52 20:00 4:40 5:47 5:23 17:26 2 1 20.7 3 56
Tue Apr 25 - Wed Apr 26 18:53 20:00 4:39 5:47 6:12 18:28 0 2 16.8 8 27
Wed Apr 26 - Thu Apr 27 18:53 20:01 4:38 5:46 N/A 19:32 1 3 14.9 12 28
Thu Apr 27 - Fri Apr 28 18:53 20:01 4:37 5:45 N/A 20:36 5 4 14.9 15 41
Fri Apr 28 - Sat Apr 29 18:54 20:02 4:36 5:45 N/A 21:41 12 5 16.2 17 49
Forecast Issued by: Ryan Lyman
Next update at 10 AM HST (2000 UTC) Tuesday 25 April 2017.
Additional Information
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