Current Conditions
Temp4.2 C
RH10 %
WindENE 0 mph
RoadOpen (4x4)
Mauna Kea Observatories Forecast
5 PM HST Monday 26 September (0300 UTC Tuesday 27 September) 2016
Cloud Cover and Fog/Precipitation Forecast
The summit will remain clear, dry and stable through the night.
Summary of Key Meteorological Variables
Summit temperatures will be near 4 C this evening and 3.5 C tomorrow morning. Winds will be light and from the East, with seeing near 0.45-0.5 arcseconds. Precipitable water is expected to be in the 0.8-1 mm range for the night.
The tradewind inversion will continue to cap low-level moisture at or below 9 thousand feet and ensure the summit remains dry and stable through at least Thursday night. There is a possibility that the inversion will breakdown/lift toward 15 thousand feet, increasing the risk for fog and rain at the summit for Friday night. Daytime clouds will be minimal and short-lived through Thursday, but could pick up on Friday and especially for the weekend.

Skies overhead will remain predominately clear through the next 4 nights, though there is a possibility for thin dissipating cirrus along the western skies mainly for Wednesday and Thursday night. There is a chance that these clouds to the west will become more widespread and perhaps drift closer to the summit area for Friday night. There is also a possibility for summit-level clouds during the second half of Friday night.

Precipitable water is expected to linger near or just below 1 mm for the next 2 nights, increase toward 1.5 mm for Wednesday night, drop back to 1 mm for Thursday night, then jump to 2-4 mm for Friday night.

Predominately calm skies and steady/deep subsidence will prevail in the free atmosphere, which should allow seeing to remain near 0.45-0.5 arcseconds over the next 4 nights. However, an influx of low-level turbulence may degrade seeing for Friday night.

Little change since the morning forecast...The mid/low-level ridge to the north combined with an upper-level ridge just south of the Big Island will continue to promote steady/strong large-scale subsidnece in the area through at least Friday morning. This subsidence will help maintain a well-defined inversion primarily near 7 thousand feet and ensure the summit remains dry and stable for the next 4 nights. The ridge to the south will keep the sub-tropical jet displaced further northward, which will minimize turbulence in the free atmosphere and likely allow seeing to linger near 0.5 arcseconds during this time. This ridge is set to fall apart as the tropical upper-tropspheric trough (TUTT) restrengthens over the state as we head into the weekend. This TUTT and an embedded mid/upper-level low (that is expected to develop to the NE), will begin to destabilize the atmosphere and could draw tropical moisture northward, where it can get caught up in the easterly low-level cloud flow. This moisture, combined with the building instability may lift the inversion toward 15 thousand feet and thus increase the risk for fog/rain at the summit for Friday night. There is a possibility that conditions will grow progressively worse as the upper-level low strengthens through 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)
Mon Sep 26 - 8 PM0-5Clear0 / 04E/0-100.45-0.550.8-1
Tue Sep 27 - 2 AM0-5Clear0 / 03.5E/0-100.4-0.50.8-1
2 PM0-20Clear0 / 08.5SE/0-10NaN1-2
8 PM0-10Clear0 / 03.5ESE/0-100.4-0.50.9-1.1
Wed Sep 28 - 2 AM0-10Clear0 / 03SE/0-100.45-0.551-1.5
2 PM0-20Clear0 / 08ESE/0-10NaN1-2
8 PM0-20Clear0 / 03ENE/0-100.4-0.61.25-1.75
Thu Sep 29 - 2 AM0-20Clear0 / 02.5N/0-100.4-0.61.25-1.75
2 PM0-20Clear0 / 08N/5-15NaN1-2
Fri Sep 30 - 2 AM0-20Clear0 / 03ENE/5-150.4-0.60.8-1.2
2 PM40-604-4.525 / 57NE/5-15NaN2-4
Sat Oct 01 - 2 AM30-509-1050 / 101.5NE/5-150.5-12-4
2 PM70-904-1075 / 254.5E/10-20NaN4-8
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
Mon Sep 26 - Tue Sep 27 18:23 19:27 4:59 6:03 3:19 N/A 12 9 44.3 11 31
Tue Sep 27 - Wed Sep 28 18:22 19:26 4:59 6:03 4:11 N/A 6 10 33.3 8 12
Wed Sep 28 - Thu Sep 29 18:21 19:25 4:59 6:04 5:02 17:12 2 11 20.6 4 33
Thu Sep 29 - Fri Sep 30 18:20 19:24 5:00 6:04 5:52 17:51 0 12 06.7 0 46
Fri Sep 30 - Sat Oct 01 18:19 19:23 5:00 6:04 6:41 18:28 0 12 52.2 -3 01
Forecast Issued by: Ryan Lyman
Next update at 10 AM HST (2000 UTC) Tuesday 27 September 2016.
Additional Information
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This message is also available at the MKWC road conditions page.
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