Mauna Kea Weather Center Forecast

Maunakea Observatories Forecast
830 AM HST (1830 UTC) Friday 09 December 2022

Warning(s)
Moderate/strong winds

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 2 C this evening, -1 C this evening and -3 C tomorrow morning. Winds will be from the ENE at 35-50 mph, while seeing will exceed 1 arcsecond for the night. Precipitable water is expected to start out near 0.6 mm, but will trend toward 1 mm as the night progresses.

Discussion
A well-defined tradewind inversion will continue to cap low-level moisture near 7-8 thousand feet and ensure a dry/stable summit-level air mass through Saturday night. There is a chance that the inversion will weaken/lift toward 12-13 thousand feet and (initially) combined with deep/steady easterly winds, will allow allow for periods of fog, ice and high humidity at the summit for Sunday, Monday and Tuesday night; precipitation is unlikely. Daytime clouds will be minimal and short-lived through Saturday, but could turn extensive for Sunday and early part of next week.

Skies overhead will remain predominately clear of organized clouds throughout the forecast period. However, there is an outside chance for patches of low-level clouds building along the eastern skies for Sunday, Monday and Tuesday night.

Precipitable water is expected to start out near 0.6 mm for this evening, but will trend toward 1 mm as the night progresses, and to 2 mm for Saturday night. There is a good chance that PW will increase further to 3-4 mm and/or become more variable for the following 3 nights.

Strong/steady boundary layer turbulence will contribute to bad seeing through at least the weekend. While there is a chance that winds will slip below 20 mph for Monday night, residual boundary layer turbulence and/or an elevated inversion will limit much improvement during that night and probably Tuesday night.

A strong/deep surface ridge to the north will continue to promote steady subsidence in the area probably throughout the forecast period. Initially, this subsidence will help maintain a very well-defined inversion near 7-8 thousand feet and ensure a dry/stable summit-level air mass through at least Saturday night. Unfortunately, deep upper-level low to the ESE will also help maintain a tight the mid/surface wind gradient along the southern flank of the ridge, which will continue to spread across the state through the weekend. This will keep summit-level winds near 30-40 mph, before gradually tapering off as the ridge flattens out for the early part of next week. However, the upper-level low is expected to enhance the incoming low-level cloud field as it slowly progresses eastward over the weekend. This cloud field will begin to make a push through the area around early Sunday afternoon, and will help elevate/weaken the inversion toward 12-13 thousand feet thereafter. This, combined with the deep relatively strong easterly flow, will significantly increase the risk for fog, ice and high humidity at the summit for that night and probably the early part of next week (despite a drop in winds). There is also an outside chance for the development of shallow convection mainly along the eastern slopes and within the Big Island wake. Afternoon convection may also begin to develop along the Big Island slopes as the easterly winds taper for Tuesday and Wednesday.

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
HST	Cover (%)	Height (km)	Probability (%)	(Celsius)	(Dir/MPH)	(Arcseconds)	(mm)
Fri Dec 09 - 2 PM	0-20	Clear	0 / 0	2	ENE/35-50	NaN	0.8-1.2
8 PM	0-5	Clear	0 / 0	-1	ENE/35-50	1-3	0.6-0.8
Sat Dec 10 - 2 AM	0-5	Clear	0 / 0	-3	ENE/35-50	1-3	0.8-1
2 PM	0-20	9-10	0 / 0	2	ENE/25-40	NaN	1-1.5
8 PM	0-5	Clear	0 / 0	-2	ENE/25-40	1-2	1.5-2
Sun Dec 11 - 2 AM	0-5	Clear	0 / 0	-3	ENE/30-45	1-2	1.75-2.25
2 PM	20-40	4-4.5	40 / 10	1.5	NE/30-45	NaN	2-4
8 PM	0-20	Clear	75 / 20	-4	NE/30-45	1-2	3-5
Mon Dec 12 - 2 AM	0-20	Clear	75 / 25	-5	NE/20-35	0.8-1.6	3-5
2 PM	60-80	4-6	95 / 50	-1	NE/15-30	NaN	4-8
Tue Dec 13 - 2 AM	0-20	Clear	75 / 20	-3	NE/10-20	0.7-1.3	3-5
2 PM	60-80	4-5	90 / 40	0	NNE/10-20	NaN	4-8
Wed Dec 14 - 2 AM	0-20	Clear	65 / 15	-2	N/5-15	0.6-1.2	3-5

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 Dec 09 - Sat Dec 10	17:53	19:02	5:28	6:36	19:01	N/A	95	7 00.8	27 19
Sat Dec 10 - Sun Dec 11	17:53	19:02	5:28	6:37	19:54	N/A	90	7 54.3	25 58
Sun Dec 11 - Mon Dec 12	17:54	19:02	5:29	6:37	20:48	N/A	84	8 45.6	23 26
Mon Dec 12 - Tue Dec 13	17:54	19:03	5:29	6:38	21:40	N/A	76	9 34.6	19 55
Tue Dec 13 - Wed Dec 14	17:54	19:03	5:30	6:39	22:32	N/A	68	10 21.4	15 36

Forecast Issued by: Ryan Lyman
Next update at 5 PM HST Friday 09 December (0300 UTC Saturday 10 December) 2022.

Additional Information
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Current Conditions
Temp		1.8 C
RH		16 %
Wind		NNE 45 mph
Road		Open (4x4)