Current Conditions
Temp6.1 C
RH54 %
WindWSW 6 mph
RoadOpen (4x4)
Mauna Kea Observatories Forecast
830 AM HST (1830 UTC) Wednesday 29 June 2016
Cloud Cover and Fog/Precipitation Forecast
Although humidity will linger in the 40-60% range, the summit will steer free of fog and precipitation through the night. Broken to overcast thick clouds are set to develop over the summit and/or drift in from the SW contributing to extensive cloud cover or even overcast skies for tonight.
Summary of Key Meteorological Variables
Summit temperatures will be near 5 C this afternoon and 1 C for the night. Winds will be from the south at 10-20 mph, with seeing near 0.65-0.7 arcseconds. Precipitable water is expected to exceed 4 mm through the night.
Although summit-level humidity will linger near 40-60% for tonight, a fairly well-defined inversion near 6-7 thousand will keep the atmosphere quite stable and ensure the summit steers free of fog and precipitation through Saturday night (humidity should slip back toward 20-30% after tonight). There is a possibility that an influx of unstable low-level clouds will lift the inversion toward 12-14 thousand feet, which could increase the risk for fog and light rain at the summit for Sunday night. Some afternoon clouds are possible through tomorrow, but will become minimal and short-lived for Friday and Saturday, then could turn extensive for Sunday and Monday.

Broken to overcast thick clouds are set to develop over the summit and/or drift in from the SW contributing to extensive cloud cover or even overcast skies through at least Friday night. There is a very good chance that these clouds will shift westward a bit and thin out on Saturday, opening at least part of the sky for that night. However, high clouds may continue to fill the northern skies and perhaps drift back over the summit area for Sunday night.

Precipitable water will likely linger near or exceed 4 mm through the next 5 nights.

A mixture of mid/upper-level turbulence and moisture will give way to boundary layer turbulence and eventually low-level turbulence, likely contributing to poor/bad seeing throughout the forecast period.

The mid/low-level ridge will continue to sit to the north of the state, while the tropical upper tropospheric trough (TUTT) persists to the west probably well into next week. Fortunately, the former will maintain relatively steady/strong large-scale subsidence in the area, which should help keep the air mass between 10-18 thousand feet quite dry and stable through at least Saturday night. However, the TUTT and especially its associate sub-tropical jet will continue to stream mid/upper-level moisture/clouds out of the tropics, which will contribute to broken/overcast skies and high PW through Friday night. There is a possibility that bulging ridge upper-level ridge to the SE will subtly shift the TUTT/STJ off toward the NW, which could help open up skies a bit for Saturday night. However, the upper-level ridge may also augment mid-level flow near the state, which could push summit-level winds toward 40 mph, mainly for Friday night. While winds should subside as the upper-level ridge retracts southward as the weekend progresses, it may also allow the southern fringe of STJ to return to the area by late in the weekend. The STJ should no longer have access to mid-level moisture, but will likely stream more high clouds over the summit area for Sunday night. Finally, global models still expect a tropical wave to pass to the south of the Big Island later in the weekend, but have backed off a bit on the amount of associated low-level moisture. Although I suspect this trend will either continue and/or the wave will pass further to the south, I have included a risk for fog/precip at the summit for Sunday 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)
Wed Jun 29 - 2 PM60-804-80 / 05SSW/10-20NaN4-8
8 PM60-805-80 / 01S/10-200.5-0.84-8
Thu Jun 30 - 2 AM80-1005.5-90 / 01SSE/10-200.5-0.94-8
2 PM80-1006-100 / 06.5SE/10-20NaN4-8
8 PM80-1006-100 / 01.5E/10-200.6-14-6
Fri Jul 01 - 2 AM80-1006-100 / 01.5E/10-200.6-14-6
2 PM80-1006-100 / 07E/15-30NaN4-8
8 PM80-1006-100 / 02ENE/25-400.7-1.34-6
Sat Jul 02 - 2 AM80-1006-100 / 02ENE/25-400.7-1.34-6
2 PM60-806-80 / 010E/15-30NaN4-8
Sun Jul 03 - 2 AM40-606-70 / 05E/15-300.5-0.84-6
2 PM60-804-860 / 159E/10-20NaN4-8
Mon Jul 04 - 2 AM60-808-1040 / 103.5ESE/10-200.4-0.84-6
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
Wed Jun 29 - Thu Jun 30 19:15 20:29 4:23 5:37 2:18 N/A 21 2 55.9 11 33
Thu Jun 30 - Fri Jul 01 19:15 20:29 4:23 5:37 3:09 N/A 12 3 53.6 14 39
Fri Jul 01 - Sat Jul 02 19:15 20:29 4:24 5:37 4:04 N/A 6 4 52.6 16 50
Sat Jul 02 - Sun Jul 03 19:15 20:29 4:24 5:38 5:01 17:48 2 5 52.2 17 54
Sun Jul 03 - Mon Jul 04 19:15 20:29 4:24 5:38 6:00 18:47 0 6 51.3 17 48
Forecast Issued by: Ryan Lyman
Next update at 5 PM HST Wednesday 29 June (0300 UTC Thursday 30 June) 2016.
Additional Information
For public road conditions and snow report message please call (808) 935-6268.
This message is also available at the MKWC road conditions page.
NWS Hawaiian Islands Synoptic Discussion and Guidance
Honolulu National Weather Service Data and Products