Mauna Kea Weather Center Forecast

Mauna Kea Observatories Forecast
5 PM HST Thursday 03 December (0300 UTC Friday 4 December) 2020

Warning(s)
None

Cloud Cover and Fog/Precipitation Forecast
There is a small risk for periods of fog and high humidity mainly for early this evening; precipitation is not expected. There is a chance for patches of high clouds and mid-level clouds along the northern and southern skies, respectively, through the night.

Summary of Key Meteorological Variables
Summit temperatures will be near 1 C this evening and 0.5 C tomorrow morning. Winds will be from the SE at 15-25 mph, with seeing near 0.7-0.75 arcseconds. Precipitable water is expected to exceed 4 mm for the night.

Discussion
The tradewind inversion will remain a bit weak/elevated, which could allow for periods of fog and high humidity mainly for early this evening. The inversion is set to quickly restrengthen as the night progresses, becoming well-established near 7 thousand feet and will ensure a dry/stable summit-level air mass for the following 4 nights. There is a possibility for a some limited afternoon clouds at the summit through the weekend, then will become minimal and short-lived for the early part of next week.

There is a chance for residual patches of high clouds along the northern skiesfor much of tonight. In addition, mid-level clouds begin to fill in from the SE as the night progresses, then will linger along the southern skies through the weekend. Cloud cover should not exceed 25% for any prolong period and clear skies are expected for Monday night.

Precipitable water is expected to linger near or exceed 4 mm through the weekend, then could trend toward 2 mm through Monday night.

A mixture of light boundary layer turbulence as well as mid-level turbulence will contribute to poor seeing through the next 5 nights.

No change since the morning forecast...Mid/low-level winds are set to switch to a more SE direction as a relatively flat ridge to the north continues to split and shift off toward the east and west. While the ridge will still promote large-scale subsidence in the area well into next week the SE winds will advect mid/low-level moisture, which could negate this subsidence over the next 12-18 hours. This may result in a minor erosion of the inversion, which could lead to fog/high humidity at the summit mainly for early this evening. The bulk of the low-level moisture will slide westward as the night progresses, but patches of mid-level clouds associated with an inverted trough to the south will move from the SE during that time. The trough is set to weaken thereafter, but the mid-level clouds may persist in the area well into the weekend. In addition, a tight wind gradient between the ridge to the NE and dissipating trough will likely keep summit-level winds around 20 mph, enough to stir up boundary layer turbulence probably throughout the forecast period. There is also a possibility that mid-level turbulence/instability along the northern fringe of the trough will also contribute to some degradation in seeing, mainly over 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
HST	Cover (%)	Height (km)	Probability (%)	(Celcius)	(Dir/MPH)	(Arcseconds)	(mm)
Thu Dec 03 - 8 PM	10-30	6-9	30 / 0	1	SE/15-25	0.55-0.95	4-6
Fri Dec 04 - 2 AM	0-20	5-9	10 / 0	0.5	SE/15-25	0.5-0.9	4-6
2 PM	10-30	5-7	0 / 0	5	ESE/10-20	NaN	4-8
8 PM	10-30	5-6	0 / 0	0.5	ESE/15-25	0.5-0.9	4-6
Sat Dec 05 - 2 AM	10-30	5-6	0 / 0	0.5	ESE/15-25	0.6-1	4-6
2 PM	10-30	5-6	0 / 0	5	SE/10-20	NaN	4-8
8 PM	0-20	5-6	0 / 0	0.5	ESE/15-25	0.6-1	4-6
Sun Dec 06 - 2 AM	0-20	5-6	0 / 0	0	ESE/15-25	0.7-1.1	4-6
2 PM	0-20	5-6	0 / 0	5	E/10-20	NaN	4-8
Mon Dec 07 - 2 AM	0-20	5-6	0 / 0	-0.5	ENE/15-25	0.7-1.1	4-6
2 PM	0-20	Clear	0 / 0	4	ENE/10-20	NaN	3-5
Tue Dec 08 - 2 AM	0-10	Clear	0 / 0	-1.5	ENE/10-20	0.5-0.9	2-4
2 PM	0-20	Clear	0 / 0	4	E/10-20	NaN	1-2

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 Dec 03 - Fri Dec 04	17:52	19:00	5:25	6:33	20:39	N/A	84	8 08.4	23 37
Fri Dec 04 - Sat Dec 05	17:52	19:00	5:25	6:34	21:36	N/A	76	9 03.8	21 10
Sat Dec 05 - Sun Dec 06	17:52	19:01	5:26	6:34	22:35	N/A	66	9 57.8	17 35
Sun Dec 06 - Mon Dec 07	17:52	19:01	5:26	6:35	23:33	N/A	56	10 50.4	13 02
Mon Dec 07 - Tue Dec 08	17:53	19:01	5:27	6:35	0:31	N/A	45	11 41.9	7 45

Forecast Issued by: Ryan Lyman
Next update at 10 AM HST (2000 UTC) Friday 4 December 2020.

Additional Information
For public road conditions and snow report message please call (808) 935-6268.
This message is also available at the MKWC road conditions page.
NWS Hawaiian Islands Synoptic Discussion and Guidance
Honolulu National Weather Service Data and Products

Current Conditions
Temp		1.9 C
RH		26 %
Wind		ESE 8 mph
Road		Open (4x4)