Current Conditions
Temp5.1 C
RH34 %
WindSW 0 mph
RoadOpen (4x4 only)
Mauna Kea Observatories Forecast
5 PM HST Friday 02 October (0300 UTC Saturday 3 October) 2015
Chance for fog/high humidity
Possibility for convection/rain
Cloud Cover and Fog/Precipitation Forecast
There is a moderate/high risk for fog, high humidity and rain at the summit, particularly as the night progresses. Banding high clouds flowing along the southern skies are expected to drift northward and thicken mainly during the second half of the night.
Summary of Key Meteorological Variables
Summit temperatures will be near 5 C this evening and 4.5 C tomorrow morning. Winds will be from the SW at 5-15 mph for today, switching to a more southerly direction through the night. Seeing will start out near 0.6 arcseconds, but trend toward 1 arcsecond as the night progresses. Precipitable water is expected to be in the 1.5-2 mm range for the first half of the night and 2-4 mm range for the second half.
The tradewind inversion is slated rapidly breakdown as deep tropical moisture fills in fron the south and instability builds to the north through the night. This will likely lead to a completely saturated air mass between late tomorrow afternoon and early Sunday afternoon. While there is a chance that the inversion will restrengthen a tad for Sunday night, the air mass above 15 thousand feet will remain quite moist during that time. In addition, more deep moisture is slated to drift in from the south and breakdown the inversion for the early part of next week. Consequently, there is a high risk for fog, high humidity and precipitation at the summit throughout most of the forecast period. Convection is also possible in the area, particularly for Saturday night and again for the early part of next week. Daytime clouds will likely very extensive for the following 5-7 days.

Banding high clouds flowing along the southern skies are expected to drift northward over the next 24 hours, while thicker mid/low-level clouds fill in from the SE during the night. These clouds are expected to congregate over the Big Island, blanketing skies for at least Saturday night. There is a possibility for a partial clearing as these clouds shift subtly off toward the NW and break up a bit for Sunday night. However, more deep clouds are slated to fill in from the south by Monday morning, and will likely contribute to overcast skies for the early part of next week.

Precipitable water is expected to start out near 1.5 mm for this evening, but will likely drift toward 4 mm by the end of the night and execeed 8 mm probably for the remainder of the forecast period.

Increasing turbulence and instability in the atmosphere will likely degrade seeing through tonight, and contribute to bad seeing for the following 4 nights.

Little change since the morning forecast, though there is small possibility that the moisture won't arrive until the last 1/4 of the night...A low developing to the north of the state is still slated to draw deep tropical moisture over the Big Island and help develop a frontal band-like feature in the area over the next 24 hours. This band/moisture coupled with instability associated with the low will erode the inversion during this time and likely completely saturate the air mass between as early as the tomorrow morning and early Sunday afternoon. This will likely deteriorate summit-level conditions/skies during the second half of tonight and probably result in inoperable conditions/skies for tomorrow night. In addition, there is a possibility for widespread convection in the area and rain at the summit mainly between tomorrow afternoon and sunrise Sunday. The bulk of the low-level moisture is slated to shift subtly to the NW as the low begins to take off toward the north on Sunday. While this may help to stabilize/dry out the low-level air mass and perhaps rebuild a part of the inversion, the air mass above 15 thousand feet will remain fairly saturated and cloudy for that night. In addition, an upper-level trough will continue to linger in the area and global models suggests that a tropical system will develop within the frontal band to the SSW of the Big Island during the weekend and drift northward for the early part of next week. Lots of uncertainty surrounds this developing system, but current model run expects this low to bring a fresh supply of deep tropical moisture to the area as it meanders 200-400 KM south of the Big Island for the early part of next week. This moisture may breakdown the inversion, saturate the air mass and could bring another round of widespread convection to the area for Monday and Tuesday night. In the long term (for what it is worth) this tropical system is expected to strengthen a tad, take on a more horseshoe path and pass to the east of the Big Island over the middle/late part of next week. This would suggest that the summit will continue to see poor/bad conditions/skies through the next 7+ nights...
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)
Fri Oct 02 - 8 PM40-608-1040 / 105SW/5-150.5-0.71.5-2
Sat Oct 03 - 2 AM60-807-1060 / 304.5SSE/5-150.6-1.22-4
2 PM80-1004-10100 / 806.5SE/10-20NaN8-12
8 PM80-1004-10100 / 903SE/10-201-310-20
Sun Oct 04 - 2 AM80-1004-10100 / 953.5ESE/15-301-310-20
2 PM80-1004-1095 / 805.5SE/15-30NaN10-20
8 PM70-904.5-1080 / 502SE/10-201-210-20
Mon Oct 05 - 2 AM70-905-1070 / 402SSE/5-150.8-1.610-20
2 PM80-1004-1090 / 606.5SSE/10-20NaN10-20
Tue Oct 06 - 2 AM80-1004-1090 / 753S/10-201-210-20
2 PM80-1004-1090 / 757SSE/10-20NaN10-20
Wed Oct 07 - 2 AM80-1004-1085 / 603ESE/10-200.8-1.810-20
2 PM80-1004-1090 / 706E/20-35NaN10-20
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
Sun Oct 04 - Mon Oct 05 18:16 19:20 5:01 6:05 0:09 N/A 44 7 19.7 16 50
Mon Oct 05 - Tue Oct 06 18:15 19:20 5:01 6:05 1:01 N/A 34 8 11.1 15 06
Tue Oct 06 - Wed Oct 07 18:15 19:19 5:01 6:05 1:52 N/A 25 9 00.4 12 43
Wed Oct 07 - Thu Oct 08 18:14 19:18 5:01 6:06 2:42 N/A 17 9 47.7 9 49
Thu Oct 08 - Fri Oct 09 18:13 19:17 5:02 6:06 3:31 N/A 11 10 33.6 6 33
Forecast Issued by: Ryan Lyman
Next update at 10 AM HST (2000 UTC) Monday 5 October 2015.
Additional Information
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