Current Conditions
Temp0.5 C
RH6 %
WindSE 27 mph
Mauna Kea Observatories Forecast
5 PM HST Monday 27 April (0300 UTC Tuesday 28 April) 2015
High humidity
Chance for fog
Cloud Cover and Fog/Precipitation Forecast
There is a risk for periods of fog and high humidity at the summit and isolated patches of mid/low-level clouds in the area (mainly to the north) through the night; precipitation is unlikely. High clouds will also start to litter the southern skies by the end of the night.
Summary of Key Meteorological Variables
Summit temperatures will be near 1 C this evening and 1.5 C tomorrow morning. Winds will be from the NW at 10-20 mph for today, switching to a more NE direction through the night. Seeing will be near 0.75-0.8 arcseconds, while precipitable water is expected to start out near 2 mm, but slip toward 1 mm by the end of the night.
The tradewind inversion will remain rather weak/indistinct near 11-12 thousand feet, perhaps allowing for short-lived fog and/or periods of high humidity through tonight. The risk for fog and high humidity will subside (but not to zero) as the inversion restrengthens near 9-10 thousand feet for the following 2 nights, then increase again as the inversion lifts back to 11-12 thousand feet for Thursday and Friday night. Precipitation is highly unlikely through the next 5 nights. Some afternoon clouds are likely throughout the forecast period, particularly for Thursday and Friday.

There is a possibility for isolated mid/low-level clouds in the area for much of tonight, and banding high clouds may start to litter the southern skies near sunrise tomorrow. The former will dissipate for subsequent nights, but the latter is expected to make a move northward and drift over the summit between late tomorrow evening and early Wednesday evening. These clouds will shift eastward thereafter, leaving clear skies for the remainder of the week.

Precipitable water will start out near 2 mm for this evening, but quickly slip toward 1 mm by the end of the night and likely settle in near 0.8-0.9 mm for the remainder of the week. There is a slight possibility it will briefly dip toward 0.7 mm mainly for Thursday night.

Low-level and boundary layer turbulence will likely contribute to poor seeing for tonight and tomorrow night, respectively (perhaps even early Wednesday evening). Calmer skies at and above the summit should allow seeing to improve toward 0.5-0.55 arcseconds for most of Wednesday and Thursday night, but there is a possibility for some degradation due to an influx of upper-level turbulence for Friday night.

Little change synoptically, but there have been subtle (mostly unfavorable) changes for almost all variables....The decaying front approaching from the NW will temporarily push the ridge off toward the SE over the next 12 hours, then will gradually fall apart over/near the Big Island as a new ridge fills in from the west over the following few days. Nonetheless, the moisture associated with the front will lift the inversion toward 12 thousand feet and perhaps allow for periods of fog and high humidity at the summit throughout the night. The building ridge will help restrengthen the inversion near 9-10 thousand feet for subsequent nights, but the relatively moisture-rich low-level cloud field coupled with deep easterly winds may be able to periodically overcome the inversion and bring more short-lived fog/high humidity to the summit during that time (though the odds are quite low). Turbulence associated with the front as well as a brief increase in summit-level winds (and thus boundary layer turbulence) will likely contribute to poor seeing over the next 2 nights. Both sources of turbulence are slated to subside once the ridge fills into the north of the summit by around late Wednesday morning. This should allow for clear/calm skies and average/good seeing for at least Wednesday and Thursday night, but there is a possibility that a patch of upper-level turbulence associated with left jet entrance region will degrade seeing a tad for Friday night. There is also a chance that a weak upper-level trough passing through the area will destabilize the air mass and perhaps weaken the inversion a bit for Thursday and Friday.
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 27 - 8 PM10-309-1030 / 51N/5-150.6-0.91.5-2.5
Tue Apr 28 - 2 AM10-308-925 / 51.5NE/10-200.65-0.951-1.5
2 PM40-604-940 / 56ENE/15-25NaN1-2
8 PM60-808-910 / 01.5E/20-300.7-1.10.9-1.1
Wed Apr 29 - 2 AM80-1008-910 / 00.5E/20-300.6-10.8-1
2 PM60-804-930 / 55E/20-30NaN1-2
8 PM40-608-910 / 01E/15-250.5-0.70.8-1
Thu Apr 30 - 2 AM0-20Clear10 / 00E/10-200.45-0.550.8-1
2 PM20-404-560 / 154E/10-20NaN2-4
Fri May 01 - 2 AM0-10Clear25 / 50ENE/5-150.45-0.650.7-0.9
2 PM20-404-560 / 154NNE/5-15NaN2-4
Sat May 02 - 2 AM0-10Clear20 / 5-0.5NW/5-150.5-0.80.8-1
2 PM20-404-4.540 / 55NW/5-15NaN2-4
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 27 - Tue Apr 28 18:53 20:01 4:38 5:46 N/A 2:41 72 10 17.7 6 49
Tue Apr 28 - Wed Apr 29 18:53 20:02 4:37 5:45 N/A 3:18 80 11 03.4 3 15
Wed Apr 29 - Thu Apr 30 18:54 20:02 4:36 5:44 N/A 3:55 87 11 49.0 -0 30
Thu Apr 30 - Fri May 01 18:54 20:03 4:35 5:44 N/A 4:32 93 12 35.0 -4 17
Fri May 01 - Sat May 02 18:54 20:03 4:34 5:43 N/A 5:11 97 13 22.1 -7 57
Forecast Issued by: Ryan Lyman
Next update at 10 AM HST (2000 UTC) Tuesday 28 April 2015.
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