Current Conditions
Temp1.4 C
RH13 %
WindE 20 mph
RoadOpen
Mauna Kea Observatories Forecast
5 PM HST Wednesday 11 December (0300 UTC Thursday 12 December) 2013
Warning(s)
None
Cloud Cover and Fog/Precipitation Forecast
The summit will remain clear, dry and stable through the night.
Summary of Key Meteorological Variables
Summit temperatures will be near 0.5 C, with winds from the ENE at 15-25 mph for this evening, easing to 10-20 mph as the night progresses. Precipitable water is expected to be in the 2-3 mm range, while seeing will likely be around 0.7-0.8 arcseconds.
Discussion
The tradewind inversion will continue to cap low-level moisture near 6-8 thousand feet and the mid/summit-level air mass dry and stable through the next 5 nights. Daytime clouds will be minimal and short-lived throughout the forecast period.

Skies will remain predominately clear for tonight, but thin high clouds are expected to drift in from the west through early tomorrow afternoon and could thicken and become more widespread through that night and into Friday. The bulk of these clouds will slide off toward the northern skies for much of the weekend, but could still contribute to periods of extensive cloud cover mainly for Friday and Saturday night.

Precipitable water is expected to linger in the 2-3 mm range for tonight, slip toward 1.5 mm for Thursday and Friday night, then increase back to 2-3 mm for Saturday night and probably 3-4 mm for Sunday night.

While minor boundary layer turbulence will likely contribute to poor seeing for tonight, this turbulence is slated to subside, allowing seeing to improve back toward 0.5-0.55 arcseconds for tomorrow night. However, building turbulence in the mid/upper atmosphere will likely degrade seeing again for the remainder of the forecast period.

No change since the morning forecast....The mid/low-level ridge will continue to sit just north of the state for another 48-60 hours, then will shift off toward the east as a trough fills in from the northwest over the weekend. Still, the ridge will remain close enough to the Big Island to promote steady/strong large-scale subsidence in the area, maintain a fairly well-defined tradewind inversion at or below 8 thousand feet and ensure a dry and stable summit-level air mass through the next 5 nights. In fact, this trough is not expected to affect summit-level conditions much as it will slide off to the NE, taking its associated mid/low-level moisture/front with it well before reaching the Big Island area late in the weekend or the early part of next week. However, it will start to push high clouds over the summit starting late tomorrow afternoon, with these clouds slated to thicken and become more widespread over the following 24-48 hours. The bulk of the clouds will likely shift toward the northern skies late Friday, but could still contribute to periods of extensive cloud cover throughout most of the weekend. There is also a strong possibility that the trough will send pockets of mid/upper-level turbulence, which could negatively impact seeing throughout the weekend.
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)
Wed Dec 11 - 8 PM0-10Clear0 / 00.5E/15-250.6-12-3
Thu Dec 12 - 2 AM0-10Clear0 / 00.5E/10-200.6-0.82-3
2 PM20-409.5-100 / 06.5ESE/10-20NaN1.5-2
8 PM40-609-100 / 01.5SE/10-200.5-0.61.25-1.75
Fri Dec 13 - 2 AM60-808.5-100 / 01SSE/10-200.45-0.551.25-1.75
2 PM80-1008-100 / 05.5SSE/5-15NaN1.25-1.75
8 PM60-808-9.50 / 00.5S/0-100.45-0.851.25-1.75
Sat Dec 14 - 2 AM40-608-90 / 00ESE/0-100.6-0.91.25-1.75
2 PM60-807.5-90 / 05SW/0-10NaN1.5-2.5
Sun Dec 15 - 2 AM60-807.5-90 / 0-0.5W/0-100.6-12-3
2 PM40-607-8.50 / 04WSW/5-15NaN3-5
Mon Dec 16 - 2 AM20-407-8.50 / 0-2W/5-150.6-13-5
2 PM40-605-80 / 03.5NW/5-15NaN3-5
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
Wed Dec 11 - Thu Dec 12 17:54 19:02 5:29 6:38 N/A 2:56 77 1 25.6 10 17
Thu Dec 12 - Fri Dec 13 17:54 19:03 5:29 6:38 N/A 3:49 85 2 16.1 13 42
Fri Dec 13 - Sat Dec 14 17:54 19:03 5:30 6:39 N/A 4:41 92 3 07.3 16 26
Sat Dec 14 - Sun Dec 15 17:55 19:04 5:30 6:39 N/A 5:33 96 3 59.0 18 21
Sun Dec 15 - Mon Dec 16 17:55 19:04 5:31 6:40 16:40 6:24 99 4 51.0 19 23
Forecast Issued by: Ryan Lyman
Next update at 10 AM HST (2000 UTC) Thursday 12 December 2013.
Additional Information
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This message is also available at the MKWC road conditions page.
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