Current Conditions
Temp2.6 C
RH38 %
WindNW 8 mph
RoadOpen
Mauna Kea Observatories Forecast
5 PM HST Friday 29 May (0300 UTC Saturday 30 May) 2015
Warning(s)
Moderate (tapering) 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 2 C this evening and 1.5 C tomorrow morning. Winds will be from the west at 20-35 mph for the first half of the night, easing to 15-30 mph by the end of the night. Seeing will be near 0.8 arcseconds, while precipitable water is expected to be in the 3-4 mm range for the night.
Discussion
The tradewind inversion is expected to restrengthen near 7-8 thousand feet and ensure a dry and stable air mass for tonight. However, the inversion is slated to gradually erode over the next 2 nights, eventually becoming rather weak and elevated near 12-13 thousand feet for the early part of next week. This will increase the risk for fog and high humidity at the summit as the weekend progresses and particularly for Monday and Tuesday night. Daytime clouds will be minimal and short-lived for tomorrow, but could pick up on Sunday and the early part of next week.

Skies will remain predominately clear of organized clouds throughout the forecast period, though there is a possibility for summit/low-level clouds along the northern skies beginning late Sunday night.

Precipitable water is expected to linger near or exceed 3.5-4 mm through the next 5 nights.

Lingering boundary layer turbulence and/or low/mid-level turbulence will likely contribute to poor seeing through at least the weekend (particularly tonight). There is a chance that seeing will return toward more normal-like values as both sources of turbulence subside for the early part of next week.

Little change since the morning forecast, though I did decrease the risk for fog/precip at the summit a tad....Although the low to the NE is expected to depart eastward over the next 48 hours, it will leave its parent trough in the area until a sharper upper-level westerly trough builds in from the west late in the weekend and especially for the early part of next week. In addition, the mid-level ridge will remain weak and indistinct, leaving just the low-level ridge to help stabilize the atmosphere probably well into next week. While the latter should be enough to rebuild the inversion and ensure a dry/stable through tomorrow afternoon, residual moisture from the departing low is slated to return to the area (mainly to the north of the Big Island) via the building low-level easterly trades beginning early Saturday evening. This influx of moisture will start to erode the inversion over the next 24 hours, which could lead to short-lived fog and high humidity at the summit over the weekend. The aforementioned building westerly trough is expected to destabilize the upper-half of the air mass, which could further weaken the inversion (to 12-13 thousand feet) and up the ante of fog/high humidity and even light rain at the summit for the early part of next week. On the plus side, the departure of the low will allow winds to weaken significantly over the next 24 hours, with winds eventually settling in near 10-15 mph by the end of the weekend and for the early part of next week. While this should help reduce boundary layer turbulence after tonight, low-level turbulence may continue to be an issue and contribute to poor seeing through 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)
Fri May 29 - 8 PM0-5Clear0 / 02W/20-350.7-1.13-4
Sat May 30 - 2 AM0-5Clear0 / 01.5W/15-300.6-13-4
2 PM0-20Clear0 / 07WSW/10-20NaN3-5
8 PM0-10Clear10 / 02.5WSW/10-200.5-0.93.5-4.5
Sun May 31 - 2 AM0-10Clear20 / 02WSW/10-200.5-0.93.5-4.5
2 PM40-604-4.540 / 07WSW/10-20NaN4-8
8 PM0-10Clear30 / 53W/10-200.5-0.93.5-4.5
Mon Jun 01 - 2 AM0-20Clear40 / 102.5W/10-200.5-0.93.5-4.5
2 PM60-804-560 / 157W/5-15NaN4-8
Tue Jun 02 - 2 AM0-20Clear50 / 102.5W/5-150.45-0.654-6
2 PM60-804-560 / 156.5W/5-15NaN4-8
Wed Jun 03 - 2 AM0-20Clear50 / 101WNW/0-100.45-0.654-6
2 PM40-604-560 / 106NE/5-15NaN4-8
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
Fri May 29 - Sat May 30 19:06 20:19 4:20 5:33 N/A 3:47 89 13 53.3 -10 12
Sat May 30 - Sun May 31 19:06 20:19 4:20 5:33 N/A 4:30 94 14 43.0 -13 23
Sun May 31 - Mon Jun 01 19:07 20:20 4:20 5:33 17:19 5:15 98 15 35.1 -16 01
Mon Jun 01 - Tue Jun 02 19:07 20:20 4:19 5:32 18:13 6:04 100 16 29.5 -17 56
Tue Jun 02 - Wed Jun 03 19:08 20:21 4:19 5:32 19:08 N/A 99 17 25.9 -18 55
Forecast Issued by: Ryan Lyman
Next update at 10 AM HST (2000 UTC) Monday 1 June 2015.
Additional Information
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