Current Conditions
Temp5.5 C
RH47 %
WindNNE 8 mph
RoadOpen
Mauna Kea Observatories Forecast
10 AM HST (2000 UTC) Tuesday 30 September 2014
Warning(s)
Chance for fog/high humidity
Cloud Cover and Fog/Precipitation Forecast
There is a slight risk for fog and high humidity throughout the night; precipitation is not expected. High clouds are expected to stream along the southern skies, occasionally passing overhead mainly during the first half of the night.
Summary of Key Meteorological Variables
Summit temperatures will be near 5 C this afternoon, 1 C this evening and 0.5 C tomorrow morning. Winds will be light and variable, with seeing around 0.6-0.7 arcseconds. Precipitable water is expected to exceed 4 mm for the night.
Discussion
Although the tradewind inverison is slated to strengthen a bit near 6-7 thousand feet for the next 2 nights, moisture will continue to linger in the area which may allow for periods of short-lived fog and high humidity probably throughout the forecast period. In addition, there is also a possibility that building weak upper-level instability will erode the inversion and further increase this risk for moisture at the summit and perhaps isolated convection in the area between late Thursday evening and early Sunday morning. Precipitation is unlikely throughout the forecast period. Extensive afternoon clouds are possible throughout the forecast period.

A band of high clouds will stream along the southern skies, occasionally scraping the summit for the next 12-18 hours. There is a possibility that this band will retract further off to the SE during the second half of the night, but is expected to become more organized and return closer to the Big Island for Wednesday night and especially for the following 3 nights. This could push cloud cover to 50% or more, particularly during those night.

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

Moderate turbulence will persist in the free atmosphere, likely contributing to poorer than average seeing throughout the forecast period. There is also a possibility that mid-level turbulence will build into the area, which may further degrade seeing mainly for Friday night.

The low-level ridge will continue to sit just the north of the state, while the mid-level ridge remains rather weak and indistinct through the week. Although the low-level ridge will still maintain some level of subsidence in the area, a weak but persistent upper-level trough to the west will try to negate this and destabilize the air mass as it slowly shifts eastward over the next several days. In addition, weak mid-level flow will allow moisture to linger in the area, which could provide fuel for this instability. Initially, the bulk of the instability associated with the trough should linger to the west of the Big Island and likely spare the summit of convection and prolong periods of fog, high humidity and certainly precipitation. But that could change as the trough axis shifts over/near the Big Island between late Thursday night and early Sunday morning. Latest model runs suggested that the trough will weaken/erode the inversion toward summit-level, which will further increase the risk for fog, high humidity and perhaps afternoon convection during that time. Turbulence associated with the trough will also remain an issue throughout the forecast period, and could further strengthen around Friday night. The southeastern half of the trough, aka the sub-tropical jet, is also expected to have an ample supply of high clouds to stream along the southern skies through the next 5 nights. There is a very good chance that this stream of clouds will contribute to periods of extensive cloud cover mainly over 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)
Tue Sep 30 - 2 PM40-604-1060 / 155E/0-10NaN4-8
8 PM30-509-1030 / 01E/0-100.5-0.84-6
Wed Oct 01 - 2 AM10-309.5-1025 / 00.5E/0-100.5-0.84-6
2 PM40-604-1060 / 155.5W/0-10NaN4-8
8 PM10-309-1025 / 01.5W/0-100.5-0.74-6
Thu Oct 02 - 2 AM20-409-1025 / 01W/0-100.5-0.74-6
2 PM40-604-1070 / 206W/0-10NaN4-8
8 PM40-609-1030 / 01NW/0-100.5-0.84-6
Fri Oct 03 - 2 AM40-608.5-1040 / 51WSW/0-100.5-0.94-6
2 PM60-804-1075 / 255.5W/0-10NaN4-8
Sat Oct 04 - 2 AM60-808-1060 / 101W/0-100.5-1.14-6
2 PM60-804-1075 / 256W/0-10NaN6-10
Sun Oct 05 - 2 AM60-808-1060 / 101.5WSW/0-100.5-14-6
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 Sep 30 - Wed Oct 01 18:20 19:24 5:00 6:04 N/A 23:35 45 18 08.9 -18 38
Wed Oct 01 - Thu Oct 02 18:19 19:23 5:00 6:04 N/A 0:33 56 19 07.0 -17 30
Thu Oct 02 - Fri Oct 03 18:18 19:22 5:00 6:04 N/A 1:33 67 20 05.5 -15 16
Fri Oct 03 - Sat Oct 04 18:17 19:21 5:00 6:05 N/A 2:34 78 21 03.8 -12 04
Sat Oct 04 - Sun Oct 05 18:16 19:20 5:01 6:05 N/A 3:36 87 22 01.7 -8 03
Forecast Issued by: Ryan Lyman
Next update at 5 PM HST Tuesday 30 September (0300 UTC Wednesday 1 October) 2014.
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