Current Conditions
Temp1.3 C
RH7 %
WindSSE 7 mph
Mauna Kea Observatories Forecast
5 PM HST Thursday 30 October (0300 UTC Friday 31 October) 2014
Cloud Cover and Fog/Precipitation Forecast
There is a slight risk for fog particularly as the night progresses; precipitation is not expected. High clouds approaching from the north are expected to dissipate over/near the summit area through the night.
Summary of Key Meteorological Variables
Summit temperatures will be near 1.5 C this evening and 1 C tomorrow morning. Winds will be light and from the east, while seeing will start out near 0.55 arcseconds, but deteriorate toward 0.7-0.8 arcseconds for the morning hours. Precipitable water is expected to be in the 1.5-2 mm range for the night.
There is a slight risk for fog as the tradewind inversion weakens/lift toward 11-12 thousand feet for tonight. The odds on fog and perhaps light rain will increase as the inversion erodes further (toward 12-13 thousand feet) with large-scale instability and mid-level moisture building to the area over the weekend. There is also an outside chance for isolated convection in the area, but should be limited to the west of the Big Island and/or along the slopes during this period, primarily around 4 AM/PM. The inversion is expected to restrengthen near 7-8 thousand feet early Monday morning, but mid-level moisture may still persist, which could allow for more short-lived fog during that night. Daytime clouds could pick up tomorrow and turn extensive over the weekend, then begin to taper again for the early part of next week.

High clouds approaching from the north are expected to dissipate over/near the summit area through tonight. Banding high clouds are also slated to set up to the southeast and move closer to the Big Island through tomorrow night. These clouds will likely drift over the summit area, blanketing skies between Saturday evening and early Monday morning. There is a good chance that these clouds will actually thicken through Sunday night, then shift subtly eastward still contributing to extensive cloud cover for the following night.

Precipitable water is expected to linger in the 1.5-2 mm range for tonight, increase to 2-3 mm for tomorrow night and probably 4+ mm for the remainder of the forecast period (particularly Sunday and Monday night).

Increasing low-level turbulence will likely degrade seeing from near 0.5-0.6 arcseconds for this evening toward 0.7-0.8 arcseconds for tomorrow morning. Boundary layer turbulence is also slated to pick up, which won't help to improve seeing for Friday and Saturday night. While the boundary layer turbulence is expected to subside thereafter, there is a good chance that seeing won't improve much as upper-level turbulence builds into the area for Sunday and Monday night.

Little change since the morning forecast...A rapidly decaying front approaching from the north is expected to fall just short of the Big Island, but may still come close enough to the summit to allow for short-lived fog, some cloud cover and contribute to poor seeing for tonight. Another remnant patch moisture from the front is also expected to get caught up in the low-level trades, move through the Big Island and lift the inversion toward 12-13 thousand feet, further increasing the risk for fog at the summit for tomorrow night. In addition, a persistent upper-level trough is expected to spawn a low to the southwest of the Islands, which could allow large-scale (but relatively weak) instability to prevail in the area until the low collapses early Monday morning. This instability may keep the inversion elevated, while the low tries to drag mid/upper-level moisture/clouds over the summit area primarily between late Saturday afternoon and early Monday morning. This may allow for periods of extensive fog and probably overcast skies during that time. There is also a chance that this mixture of instability and abundant supply of moisture will help spark isolated convection along the slopes and/or on the Big Island plume to the west, primarily around 4ish AM/PM. The inversion is slated to rebuild near 6-8 thousand feet as the ridge reclaims control of the air mass around Monday afternoon. However, linger mid-level moisture may still remain an issue (allowing for high humidity/PW and perhaps short-lived fog/rain) through that 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 Oct 30 - 8 PM20-409-1010 / 01.5ENE/5-150.5-0.61.5-2
Fri Oct 31 - 2 AM10-309.5-1020 / 01E/5-150.6-0.91.5-2
2 PM20-404-540 / 106ESE/5-15NaN2-4
8 PM0-20Clear50 / 01E/10-200.6-12-3
Sat Nov 01 - 2 AM20-409.5-1060 / 00E/15-300.7-1.12-3
2 PM60-804-1075 / 255ESE/15-30NaN3-6
8 PM60-808.5-1060 / 100.5ESE/15-300.7-1.13-5
Sun Nov 02 - 2 AM80-1008-1060 / 100.5ESE/15-300.6-13-5
2 PM80-1004-1075 / 257SE/15-30NaN4-8
Mon Nov 03 - 2 AM80-1006-1050 / 102ESE/5-150.7-1.14-8
2 PM80-1004-860 / 156.5SSE/5-15NaN4-8
Tue Nov 04 - 2 AM60-805-825 / 51.5WSW/5-150.6-14-8
2 PM60-804-640 / 107E/5-15NaN4-8
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 Oct 30 - Fri Oct 31 17:58 19:03 5:08 6:14 N/A 0:26 53 20 47.9 -12 55
Fri Oct 31 - Sat Nov 01 17:57 19:03 5:09 6:14 N/A 1:26 64 21 44.0 -9 15
Sat Nov 01 - Sun Nov 02 17:57 19:02 5:09 6:15 N/A 2:25 75 22 39.4 -5 00
Sun Nov 02 - Mon Nov 03 17:56 19:02 5:09 6:15 N/A 3:25 84 23 34.5 -0 26
Mon Nov 03 - Tue Nov 04 17:56 19:01 5:10 6:16 N/A 4:24 92 0 29.7 4 09
Forecast Issued by: Ryan Lyman
Next update at 10 AM HST (2000 UTC) Friday 31 October 2014.
Additional Information
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