Current Conditions
Temp3.4 C
RH59 %
WindNW 22 mph
RoadOpen
Mauna Kea Observatories Forecast
10 AM HST (2000 UTC) Tuesday 31 March 2015
Warning(s)
None
Cloud Cover and Fog/Precipitation Forecast
The summit will remain dry and stable, but there is a possibility for light cirrus in the area for early this evening and building more widespread high clouds filling in from the west near sunrise.
Summary of Key Meteorological Variables
Summit temperatures will be near 3.5 C this evening and -1 C for the night. Winds will be from the WSW at 5-15 mph for today, switching to a more NW toward the end of the night. Seeing will be near 0.55-0.6 arcseconds, while precipitable water will start out near 2 mm, but slip toward 1 mm through the night.
Discussion
The tradewind inversion will continue to cap low-level moisture near 8 thousand feet and ensure the summit will remain dry and stable through at least Thursday afternoon. There is a possibility that the inversion will begin to breakdown as moisture and instability accumulates in the area later that night. This will increase the risk for fog, ice, high humidity and short periods of light flurries particularly for the following 2 nights. Daytime clouds will be minimal and short-lived through Thursday, then turn extensive for Friday and over the weekend.

There is a possibility for residual light cirrus in the area for this evening and building more widespread high clouds are expected to fill in from the west around sunrise tomorrow. The latter set will likely blanket summit skies by late that evening and especially for the following 3 nights. In addition, there is a good chance that these clouds will thicken for Thursday and especially the following 2 nights.

Precipitable water will start out near 2 mm for this evening, but briefly slip toward 1 mm by the end of the night. It is then expected to increase back toward 2 mm for tomorrow night and likely exceed 4 mm for the following 3 nights.

Light/moderate turbulence in the free atmosphere will likely contribute to slightly poorer than average seeing over most of the next 2 nights. A combination of building upper-level turbulence and boundary layer turbulence will likely further degrade seeing for the following 3 nights.

Although the mid/low-level ridge will continue to gradually weaken over the next 48 hours, it will still promote steady large-scale subsidence in the area during this time. This will help maintain the tradewind inversion near 8 thousand feet and ensure the summit remains dry and stable over the next 2 nights. Unfortunately, the westerly jet is slated to sag southward and over the Islands during this same period, eventually re-estabilishing the sub-tropical jet in the area for the remainder of the week. This will allow relatively flow to persist aloft, which will not only contribute to free atmospheric turbulence, but also transport broken to overcast high clouds over the summit, mainly after tonight. The decay of the ridge will also permit mid/low-level ridge to accumulate in the area starting early Thursday afternoon. This moisture, combined with pockets of turbulence associated with the sub-tropical jet may help erode the inversion thereafter, which could allow for periods of fog, ice and light flurries at the summit mainly after Thursday night. Upper-level instability and dynamics neccessary for widespread thunderstorms will be fairly insignificant, which will help minimize the risk for heavy snow during that time. Nonetheless, expect mostly cloudy skies after tonight and perhaps wet conditions over much of Easter weekend.

Please Note: It should be noted that over the last 5 days or so the GFS feed has been subject to slow connection, large lags and/or missing data, particularly in the forecast beyond 2 nights. Thus, the forecast beyond that period is subject to large errors than normal as I constantly piece together the missing data from older data sets.
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)
Tue Mar 31 - 2 PM10-309-100 / 03.5WSW/5-15NaN2-3
8 PM0-20Clear0 / 0-1W/5-150.55-0.651.5-2
Wed Apr 01 - 2 AM0-20Clear0 / 0-1NW/5-150.5-0.61-1.5
2 PM40-609-100 / 04SW/5-15NaN1-2
8 PM60-808.5-100 / 00.5WNW/5-150.5-0.71.5-2
Thu Apr 02 - 2 AM80-1008.5-100 / 0-0.5WSW/5-150.5-0.72-2.5
2 PM80-1008-100 / 03.5SW/10-20NaN2-3
8 PM80-1007-1025 / 5-1WSW/15-300.6-1.23-4
Fri Apr 03 - 2 AM80-1006-1040 / 10-2WSW/20-350.7-1.33.5-4.5
2 PM80-1004-1060 / 152WNW/20-35NaN4-8
Sat Apr 04 - 2 AM80-1006-1060 / 20-3NW/20-350.7-1.34-6
2 PM80-1004-1075 / 251SW/15-30NaN4-8
Sun Apr 05 - 2 AM80-1006-1060 / 20-4NNW/20-350.7-1.34-6
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
Tue Mar 31 - Wed Apr 01 18:45 19:50 5:02 6:07 N/A 4:42 91 10 32.0 5 48
Wed Apr 01 - Thu Apr 02 18:45 19:50 5:01 6:06 N/A 5:19 96 11 17.9 2 09
Thu Apr 02 - Fri Apr 03 18:45 19:50 5:00 6:05 17:21 5:56 99 12 03.7 -1 37
Fri Apr 03 - Sat Apr 04 18:46 19:51 4:59 6:04 18:09 6:33 100 12 50.0 -5 22
Sat Apr 04 - Sun Apr 05 18:46 19:51 4:58 6:03 18:58 N/A 99 13 37.3 -8 57
Forecast Issued by: Ryan Lyman
Next update at 5 PM HST Tuesday 31 March (0300 UTC Wednesday 1 April) 2015.
Additional Information
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