Current Conditions
Temp-0.2 C
RH13 %
WindSE 22 mph
Mauna Kea Observatories Forecast
5 PM HST Friday 24 October (0300 UTC Saturday 25 October) 2014
Chance for fog/high humidity
Cloud Cover and Fog/Precipitation Forecast
There is a small to moderate risk for light fog and high humidity through the night; precipitation is not expected and skies will remain predominately clear.
Summary of Key Meteorological Variables
Summit temperatures will be near 1.5 C, with winds from the ENE at 10-20 mph for the first half of the night and 15-25 mph for the second half. Precipitable water is expected to be in the 2-3 mm range, with seeing around 0.6-0.65 arcseconds.
The tradewind inversion is expected to briefly lift toward 11-12 thousand feet, which will increase the risk for light fog and high humidity for tonight; precipitation is not expected. The inversion will then recover near 9 thousand feet by tomorrow afternoon and ensure low-level moisture remains capped at or below that level and that the summit air mass remains dry and stable for the following 4 nights. Some afternoon clouds are possible for tomorrow, but will become minimal and short-lived thereafter.

While skies overhead will remain predominately clear through the weekend, high clouds gathering to the west could start to move over the summit area late Monday morning and perhaps push cloud cover toward 50% mainly for much of Tuesday.

Precipitable water is expected to increase to 2-3 mm for tonight, then slip toward 0.9-1 mm for the remainder of the weekend. It will likely increase back to 1-1.5 mm for the early part of next week.

Boundary layer and/or low-level turbulence will contribute to slightly poorer than average seeing probably through Sunday evening. These sources of turbulence is slated to subside through Sunday night, allowing seeing to improve toward 0.5-0.55 arcseconds for the early part of next week.

No change since the morning forecast...Although the mid-level ridge will continue to sit to the north of the state and maintain some degree of large-scale subsidence in the area throughout the forecast period, a relatively unstable/deep patch of low-level clouds/moisture is expected to move in from the NE, lift the inversion toward 11-12 thousand feet and increase the risk for fog and high humidity at the summit for tonight. There is also a possibility that this patch will bring minor low-level turbulence to the area, which could affect seeing during this time. This patch is slated to shift off toward the southwest as an upper-level ridge fills in from the northwest late tomorrow morning. Although this will augment the subsidence in the area and help rebuild the inversion well below summit-level, the ridge could increase summit-level winds, which will likely stir up boundary layer turbulence and contribute to poorer than average seeing through Sunday evening. The upper-level ridge is expected to dissipate as a weak trough develops over/near the Islands for the early part of next week. This trough is not expected to affect the stability of the atmosphere, but may actually help to diminish summit-level winds and improve seeing for Monday and Tuesday night. However, there is a possibility that the trough will bring patchy high clouds over the summit area 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 (%) (Celcius) (Dir/MPH) (Arcseconds) (mm)
Fri Oct 24 - 8 PM0-5Clear30 / 01.5NE/10-200.5-0.72-3
Sat Oct 25 - 2 AM0-5Clear40 / 01.5ENE/10-200.55-0.752-3
2 PM20-40Clear20 / 07E/15-25NaN2-4
8 PM0-5Clear0 / 03E/15-200.55-0.850.9-1.1
Sun Oct 26 - 2 AM0-5Clear0 / 02.5E/15-250.55-0.850.9-1.1
2 PM0-20Clear0 / 08ENE/15-25NaN0.8-1.2
8 PM0-5Clear0 / 03E/15-250.5-0.80.8-1
Mon Oct 27 - 2 AM0-20Clear0 / 03E/10-200.45-0.650.8-1
2 PM0-209.5-100 / 08E/5-15NaN0.8-1.2
Tue Oct 28 - 2 AM20-409-100 / 02.5E/5-150.4-0.61-1.5
2 PM40-608.5-100 / 08ESE/5-15NaN1-1.5
Wed Oct 29 - 2 AM20-409-100 / 02.5SE/5-150.4-0.61-1.5
2 PM0-20Clear0 / 08ESE/5-15NaN1-2
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
Fri Oct 24 - Sat Oct 25 18:01 19:06 5:06 6:11 N/A 18:56 2 15 11.0 -15 11
Sat Oct 25 - Sun Oct 26 18:00 19:05 5:06 6:12 N/A 19:44 7 16 04.6 -17 15
Sun Oct 26 - Mon Oct 27 18:00 19:05 5:07 6:12 N/A 20:36 13 16 59.9 -18 26
Mon Oct 27 - Tue Oct 28 17:59 19:04 5:07 6:12 N/A 21:31 21 17 56.6 -18 37
Tue Oct 28 - Wed Oct 29 17:59 19:04 5:07 6:13 N/A 22:28 31 18 53.9 -17 44
Forecast Issued by: Ryan Lyman
Next update at 10 AM HST (2000 UTC) Monday 27 October 2014.
Additional Information
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