Current Conditions
Temp4.6 C
RH16 %
WindESE 8 mph
RoadOpen
Mauna Kea Observatories Forecast
730 AM HST (1730 UTC) Thursday 24 April 2014
Warning(s)
None
Cloud Cover and Fog/Precipitation Forecast
The summit will remain dry and stable, but thin high clouds will start to stream in from the southwest later today and thicken and become more widespread through the night.
Summary of Key Meteorological Variables
Summit temperatures will be near 7 C this afternoon and 1.5 C for the night. Winds will be from the ENE at 5-15 mph for today and 10-20 mph for the night. Precipitable water is expected to be in the 2.5-3.5 mm range, with seeing around 0.65 arcseconds.
Discussion
The tradewind inversion will continue to cap low-level moisture near 8 thousand feet and keep the mid/summit-level air mass dry and stable through the next 5 nights. Daytime clouds will be minimal and short-lived through Sunday, but could pick up a tad on Monday.

Thin high clouds are expected to stream in from the southwest through the day and thicken and become more widespread through the night. These clouds will likely blanket skies for Friday night and at least Saturday evening, then start to shift eastward through Sunday. This could help open up skies to the west during the latter night, but banding high clouds may still be visible along the southeastern skies through Monday evening.

Precipitable water will linger near 2.5-3 mm for the next 2 nights, increase toward 4 mm for Saturday and Sunday night, then return to 2 mm for the early part of next week.

Light/moderate turbulence in the free atmosphere will likely contribute to poorer than average seeing over the next 3 nights. This turbulence is slated to increase, which further degrade seeing for Sunday and Monday night.The mid/low-level ridge will continue to sit to the north of the state through Saturday evening, then will sag southward over the Islands as a developing trough passes to the north of the state late Sunday and into the early part of next week. Fortunately, the trough is not expected to deepen/intensify until it slips eastward, which will allow strong/steady large-scale subsidence to prevail in the area well into next week. The subsidence will help maintain the tradewind inversion at or below 8 thousand feet and ensure a dry and stable summit-level air mass through at least the next 5 nights. A fairly large sub-tropical jet is expected to settle in over the Islands, bringing lots of high clouds and light to moderate free atmospheric turbulence for the next 3 nights. These clouds are slated to thicken over the next 24 hours and will likely blanket summit skies between late tomorrow morning and most of Saturday night, while the turbulence will keep seeing near 0.7 arcseconds over the next 3 nights. The jet is slated to shift eastward as the trough approaches the area, which may help to clear out summit skies a bit thereafter. However, there is a possibility that the trough will bring minor mid-level moisture to the area, which could increase PW and perhaps summit-level humidity (toward 50%) for Saturday and Sunday night. Turbulence associated with this trough could also degrade seeing toward 0.9-1 arcseconds for Sunday and especially Monday night.
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 Apr 24 - 2 PM20-409.5-100 / 07ENE/5-15NaN2.5-3.5
8 PM40-609-100 / 01.5ENE/10-200.6-0.72.5-3.5
Fri Apr 25 - 2 AM60-808.5-100 / 01.5ENE/10-200.6-0.72.5-3.5
2 PM80-1008-100 / 07.5E/10-20NaN2.5-3.5
8 PM80-1008-100 / 02E/10-200.6-0.82-3
Sat Apr 26 - 2 AM80-1008-100 / 02E/10-200.6-0.82-3
2 PM80-1008-100 / 07ESE/5-15NaN2-3
8 PM80-1007.5-100 / 02.5ESE/5-150.6-0.83-4
Sun Apr 27 - 2 AM60-807.5-100 / 02SE/5-150.6-0.83.5-4.5
2 PM40-607.5-100 / 07W/5-15NaN4-6
Mon Apr 28 - 2 AM40-607-100 / 01W/5-150.7-1.12.5-3.5
2 PM40-608-100 / 06W/10-20NaN2-4
Tue Apr 29 - 2 AM0-20Clear0 / 01NW/10-200.7-1.31.5-2.5
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
Thu Apr 24 - Fri Apr 25 18:52 20:00 4:40 5:47 3:12 N/A 17 23 05.2 -2 33
Fri Apr 25 - Sat Apr 26 18:52 20:00 4:39 5:47 3:56 N/A 9 23 57.8 1 57
Sat Apr 26 - Sun Apr 27 18:53 20:01 4:38 5:46 4:40 N/A 4 0 50.0 6 16
Sun Apr 27 - Mon Apr 28 18:53 20:01 4:37 5:45 5:25 17:49 1 1 42.4 10 11
Mon Apr 28 - Tue Apr 29 18:53 20:02 4:37 5:45 6:11 18:46 0 2 35.1 13 30
Forecast Issued by: Ryan Lyman
Next update at 5 PM HST Thursday 24 April (0300 UTC Friday 25 April) 2014.
Additional Information
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