Current Conditions
Temp5.0 C
RH27 %
WindNW 22 mph
RoadOpen
Mauna Kea Observatories Forecast
10 AM HST (2000 UTC) Thursday 29 January 2015
Warning(s)
Moderate winds
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 5 this afternoon and -0.5 C this evening and -1 C tomorrow morning. Winds will be from the WSW at 15-30 mph, with seeing around 0.8 arcseconds. Precipitable water is expected to be in the 2-2.5 mm range for the night.
Discussion
The 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 Sunday night. However, there is a chance that the inversion will start to breakdown/lift as moisture and instability builds into the area early next week. This will increase the summit-level humidity toward 60-80% and may allow for fog for Monday night; precipitation is unlikely. Daytime clouds will be minimal and short-lived through Friday, but could pick up a tad over the weekend and especially the early part of next week.

Skies will remain clear through the next 5 nights.

Precipitable water will linger near 2-2.5 mm for tonight, increase to 3-4 mm for the remainder of the week and probably 4+ mm for Monday night.

Steady boundary layer turbulence is expected to contribute to poor seeing through the weekend. There is very good chance that the boundary layer turbulence will increase and further degrade seeing for the early part of next week.

The mid/low-level ridge will continue to sit over/near the Islands and promote steady/strong large-scale subsidence in the area through the week. This will help maintain a well-defined tradewind inversion at or below 9 thousand feet and ensure the summit remains dry and stable Sunday night. Skies are expected to remain predominately clear with a zonal westerly jet persisting to the north of the state through the weekend. However, the jet will remain close enough to the state to keep summit-level winds near 25-30 mph, which will stir up boundary layer turbulence and contribute to poor seeing during that time. In addition, a very large trough is expected build to the north of the state, gradually weakening the inversion and pulling moisture in from the south over the weekend. Although this should not affect the stability of the nighttime air mass, the slightly weakened inversion coupled with daytime heating will allow for afternoon clouds during that time. An embedded short-wave trough is expected to fill in from the northwest, which could further pull more moisture in from the south and destabilize the air mass early next week. This could raise summit-level humidity toward 60-80% and increase the risk for fog at the summit late Monday night (and especially for Tuesday night). Winds will also strengthen as the jet moves closer to the summit during that time. All in all, expect clear skies and dry/stable conditions, but less than marginal seeing/PW over the next 4 nights and perhaps poor/bad conditions, seeing and PW for the early part of 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 (%) (Celcius) (Dir/MPH) (Arcseconds) (mm)
Thu Jan 29 - 2 PM0-20Clear0 / 05SW/15-30NaN1-2
8 PM0-5Clear0 / 0-0.5WSW/15-300.6-12-2.5
Fri Jan 30 - 2 AM0-5Clear0 / 0-1WSW/15-300.6-12-2.5
2 PM0-20Clear0 / 04.5WSW/15-30NaN2-3
8 PM0-5Clear0 / 0-0.5SW/15-300.6-13-4
Sat Jan 31 - 2 AM0-5Clear0 / 0-1SW/15-300.6-13-4
2 PM20-404-4.525 / 03.5SW/15-30NaN3-5
8 PM0-5Clear0 / 0-1.5WSW/15-300.6-13-4
Sun Feb 01 - 2 AM0-5Clear0 / 0-2.5WSW/20-350.6-1.23-4
2 PM20-404-4.525 / 03W/25-40NaN3-5
Mon Feb 02 - 2 AM0-5Clear0 / 0-3WNW/25-400.8-1.63-4
2 PM40-604-640 / 53WNW/35-50NaN4-8
Tue Feb 03 - 2 AM0-5Clear50 / 10-3WNW/35-501-23-6
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
Thu Jan 29 - Fri Jan 30 18:22 19:28 5:42 6:48 N/A 3:42 81 5 10.8 18 14
Fri Jan 30 - Sat Jan 31 18:22 19:29 5:42 6:48 N/A 4:33 88 6 04.2 18 23
Sat Jan 31 - Sun Feb 01 18:23 19:29 5:42 6:48 N/A 5:20 94 6 56.7 17 38
Sun Feb 01 - Mon Feb 02 18:23 19:30 5:41 6:48 16:33 6:05 98 7 48.0 16 02
Mon Feb 02 - Tue Feb 03 18:24 19:30 5:41 6:47 17:24 6:47 100 8 37.8 13 44
Forecast Issued by: Ryan Lyman
Next update at 5 PM HST Thursday 29 January (0300 UTC Friday 30 January) 2015.
Additional Information
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This message is also available at the MKWC road conditions page.
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