Mauna Kea Weather Center Forecast

Maunakea Observatories Forecast
10 AM HST (2000 UTC) Wednesday 18 May 2022

Warning(s)
Fog/ice and flurries

Cloud Cover and Fog/Precipitation Forecast
There is a high risk for fog, ice and flurries at the summit, especially as the night progresses. Broken thick clouds are expected to build in from the west and will likely blanket skies for much of the night.

Summary of Key Meteorological Variables
Summit temperatures will be near 4 C this afternoon, -1 C this evening and -1.5 C tomorrow morning. Winds will be from the south at 15-30 mph, with seeing near 0.9-1 arcsecond. Precipitable water is expected to exceed 4 mm for the night.

Discussion
Although the inversion will remain somewhat intact near 7-8 thousand feet probably throughout the forecast period, deep mid-level moisture building into the area is set to saturate the air mass between 12-20 thousand feet, likely contributing to extensive fog, ice and/or flurries at the summit over the next 3 nights. The risk for fog/precipitation is expected to gradually decrease as this moisture disperses in the area over the weekend. Extensive daytime clouds are expected through Saturday, and there is an outside chance for isolated convection along the western Big Island slopes mainly through Friday; daytime clouds will taper for Sunday and especially early next week.

Thick band clouds will continue to build in from the west over the next 24 hours, then stall over the Big Island likely contributing to mostly overcast skies for the next 2 nights. These clouds will begin to slowly disperse in the area late Friday, opening up skies as the weekend progresses.

Precipitable water is expected to linger near or exceed 4 mm throughout most of the forecast period; there is a chance that it will trend back toward 2 mm around sunrise Monday.

A mixture of boundary layer turbulence and/or deep moisture will contribute to poor/bad seeing probably into Saturday night. There is a good chance that seeing will improve as the air mass dries out and deep easterly flow builds in over the summit for Sunday night.

A very late-season low will continue to intensify to the NNW and shift eastward through late this evening, then will begin to take off toward north and dissipate thereafter. While a fairy distinct mid-level ridge to the NE will continue to promote subsidence in the area throughout the forecast period, the frontal band associated with the low is set to build in overhead through the night. This band will remain quite organized as its stall out over the Big Island, then will very gradually disperse in the area over the weekend. Widespread thick clouds and deep moisture will contribute to overcast skies, extensive fog, ice and flurries at the summit particularly between late this evening and midnight Friday. There is an outside chance for isolated convection mainly along the western skies at night and along the western slopes during the afternoon over the next 3 days. While summit-level humidity could remain near 60-80% through the weekend, skies will begin to open up and the risk for fog/flurries will subside during that time. More normal conditions and clear skies will return to the summit once this moisture fully destrains into the surrounding air mass for the early part of next week.

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)
Wed May 18 - 2 PM	60-80	4-8	40 / 10	4	S/15-30	NaN	4-8
8 PM	80-100	4-9	75 / 30	-1	S/15-30	0.7-1.1	6-10
Thu May 19 - 2 AM	80-100	4-10	95 / 65	-1.5	S/15-30	0.7-1.3	8-12
2 PM	80-100	4-9	100 / 95	3	W/10-20	NaN	10-15
8 PM	80-100	4-8	100 / 95	-1	SW/5-15	0.7-1.5	10-15
Fri May 20 - 2 AM	80-100	4-8	100 / 90	-1	NNW/5-15	0.7-1.5	10-15
2 PM	70-90	4-7	95 / 75	4	NNW/0-10	NaN	8-12
8 PM	50-70	4-6	90 / 60	-0.5	NNE/5-15	0.7-1.3	8-12
Sat May 21 - 2 AM	40-60	4.5-6	75 / 40	-0.5	NE/5-15	0.7-1.1	8-12
2 PM	60-80	4-6	90 / 50	5	NE/5-15	NaN	6-10
Sun May 22 - 2 AM	20-40	4.5-5	60 / 15	0	NE/15-30	0.6-1	4-8
2 PM	20-40	4-5	25 / 5	6	NE/10-20	NaN	2-4
Mon May 23 - 2 AM	0-20	Clear	10 / 0	1	NE/5-15	0.5-0.8	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
Wed May 18 - Thu May 19	19:01	20:13	4:24	5:35	22:02	N/A	85	19 04.4	-27 24
Thu May 19 - Fri May 20	19:02	20:13	4:23	5:35	23:03	N/A	75	20 09.7	-25 40
Fri May 20 - Sat May 21	19:02	20:14	4:23	5:35	23:57	N/A	64	21 10.7	-22 21
Sat May 21 - Sun May 22	19:03	20:14	4:23	5:34	0:44	N/A	53	22 06.9	-17 51
Sun May 22 - Mon May 23	19:03	20:15	4:22	5:34	1:25	N/A	42	22 58.6	-12 36

Forecast Issued by: Ryan Lyman
Next update at 5 PM HST Wednesday 18 May (0300 UTC Thursday 19 May) 2022.

Additional Information
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NWS Hawaiian Islands Synoptic Discussion and Guidance
Honolulu National Weather Service Data and Products

Current Conditions
Temp		6.1 C
RH		33 %
Wind		ENE 9 mph
Road		Open (4x4)