Current Conditions
Temp5.5 C
RH49 %
WindSSE 6 mph
Mauna Kea Observatories Forecast
5 PM HST Thursday 02 July (0300 UTC Friday 3 July) 2015
Cloud Cover and Fog/Precipitation Forecast
There is a small risk for fog as summit-level humidity is expected to increase toward 60-80% for tonight. There is also a possibility that high clouds will scrape the southern half of the Big Island during the second half of the night.
Summary of Key Meteorological Variables
Summit temperatures will be near 2 C this evening and 1 C tomorrow morning. Winds will be light and from the WSW, with seeing around 0.45-0.5 arcseconds. Precipitable water is expected to exceed 4 mm for the night.
While the tradewind inversion will remain fairly well-defined near 6-8 thousand feet through Monday morning, a brief influx of mid-level moisture may push humidity toward 50-70% for tonight. Still, the odds on fog and precipitation will remain quite low and the summit will steer free of moisture for the following 3 nights. There is a possibility that tropical moisture will spread into the area and breakdown the inversion and increase the risk for fog/precipitation beginning late Monday night. Some afternoon clouds are possible through tomorrow, then become minimal and short-lived for the weekend and likely Monday, but may pick up again on Tuesday.

Skies overhead will remain predominately clear through the next 5 nights. However, there is a possibility for isolated/scattered high clouds passing along the southern skies over the next 2 nights (particularly for much of tomorrow - Friday) and perhaps patchy high clouds along the northern skies for Sunday and Monday night.

Precipitable water is expected to exceed 4 mm for tonight, then drop back to 2.5-3 mm for the remainder of the forecast period.

Minimal turbulence will persist in the atmosphere, which should allow for the better than average seeing likely through at least the next 2 nights. There is a possibility that a patch of upper-level turbulence will briefly degrade seeing toward more average-like values for Saturday night. Seeing is slated to recover again for the following night, but an influx of mid-level turbulence may further impact seeing for the early part of next week.

Subtle changes have been made to the CC forecast, mainly for tomorrow morning/evening...Although the mid/low-level ridge will continue to sit over or to the north of the Islands and promote steady large-scale subsidence in the area throughout most of the forecast period, two features may affect summit-level conditions for tonight and again early next week. The first feature is a weak trough currently lingering to the north, which is pulling mid/low-level moisture over or just east of the Big Island for the next 24-30 hours. This moisture may raise summit-level humidity toward 60-80% and increase the risk for fog at the summit for tonight. Fortunately, this trough is expected to fold up as the ridge shifts northward through tomorrow, allowing the mid-level air mass to dry out for the following 3 nights. The seconds feature, a tropical wave, is expected to pass over or to the south of the Big Island starting late Monday night. Global models continue to be inconsistent with this feature, particularly its arrival time (with the latest model run setting the ETA back until late Tuesday night), and I suspect that this wave will pass further to the south, hardly affecting summit-level conditions until maybe later in the week, if at all. Still, I kept a slight risk for fog and precipitation at the summit for Monday night. At any rate, a weak but persistent tropical upper-tropospheric trough (TUTT) will continue to extend out from the California Coast and over or just west of the state well into the next week. The TUTT will have little to no impact on the stability of the atmosphere, and will actually keep the jet supressed to the south of the state throughout most of the forecast period (the only exception could be for Saturday night). This will allow for minimal turbulence in the atmosphere and likely better than average seeing for at least the next 4 nights. The aformentioned tropical wave may, however, bring mid/low-level turbulence to the area, which could impact seeing for the early part of next week.

Please Note: There will be no forecasts tomorrow, Friday July 3, in observance of Independence Day. I will likely issue a brief update Saturday morning and the normal forecast schedule will resume on Monday, July 6.
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 Jul 02 - 8 PM0-20Clear20 / 02WSW/0-100.45-0.554-6
Fri Jul 03 - 2 AM10-309.5-1015 / 01WSW/0-100.4-0.54-6
2 PM20-409-1025 / 07NNW/5-15NaN3-6
8 PM0-209-100 / 03N/5-150.4-0.52.5-3.5
Sat Jul 04 - 2 AM0-10Clear0 / 02NNW/5-150.4-0.52.5-3.5
2 PM0-20Clear0 / 07.5N/5-15NaN2-4
8 PM0-5Clear0 / 02.5N/5-150.5-0.62-3
Sun Jul 05 - 2 AM0-5Clear0 / 02NNW/5-150.45-0.552-3
2 PM0-20Clear0 / 08NNE/5-15NaN2-4
Mon Jul 06 - 2 AM0-20Clear0 / 03NNE/10-200.35-0.552.5-3.5
2 PM0-20Clear0 / 08NE/5-15NaN2-4
Tue Jul 07 - 2 AM0-20Clear20 / 52ESE/5-150.5-0.82.5-3.5
2 PM40-604-540 / 108SSE/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
Fri Jul 03 - Sat Jul 04 19:15 20:29 4:24 5:38 20:34 N/A 93 20 59.5 -13 38
Sat Jul 04 - Sun Jul 05 19:15 20:29 4:24 5:38 21:24 N/A 85 21 57.0 -9 57
Sun Jul 05 - Mon Jul 06 19:15 20:28 4:25 5:38 22:11 N/A 76 22 53.1 -5 43
Mon Jul 06 - Tue Jul 07 19:15 20:28 4:25 5:39 22:57 N/A 66 23 48.1 -1 13
Tue Jul 07 - Wed Jul 08 19:15 20:28 4:26 5:39 23:42 N/A 54 0 42.2 3 15
Forecast Issued by: Ryan Lyman
Next update at 10 AM HST (2000 UTC) Friday 3 July 2015.
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