Mauna Kea Weather Center Forecast

Mauna Kea Observatories Forecast
10 AM HST (2000 UTC) Tuesday 31 March 2020

Warning(s)
Fog, ice and high humidity
Chance for flurries

Cloud Cover and Fog/Precipitation Forecast
Extensive fog, thick clouds, high humidity, ice and/or light flurries will continue to plague the summit through the night.

Summary of Key Meteorological Variables
Summit temperatures will be near -1 C this afternoon, -4 C this evening and -4.5 C tomorrow morning. Winds will be from the SW at 15-30 mph for today, easing a bit to 10-20 mph through the night. Seeing and precipitable water are expected to exceed 1 arcsecond and 4 mm, respectively, through the night.

Discussion
An influx of widespread/deep mid-level moisture combined with an indistinct inversion will allow extensive fog, ice, high humidity and light flurries to plague the summit for tonight. THere is a chance that the air mass will dry out a bit by tomorrow evening, but the inversion will remain weak/indistinct through the weekend and there is a chance that more moisture will fill into the area mainly for Friday and Saturday night. Consequently, there is a moderate/high risk for more periods of fog, ice, high humidity and flurries at the summit even after tonight. Extensive daytime clouds are expected throughout the forecast period and there is a chance for isolated afternoon convection particularly for tomorrow.

Thick mid/upper-level clouds passing overhead will contribute to mostly overcast skies for tonight. There is good chance that skies will open up as only residual patches of mid-level clouds linger in the area for tomorrow night. However, banding high/mid-level clouds are set to spread in from the south early Thursday evening, blanketing skies for much of Friday and into Saturday. While there is a good chance that the high clouds will shift off toward the east on Saturday, patches of mid-level clouds may linger overhead through that night.

Precipitable water is expected to linger near or exceed 4 mm throughout most of the forecast period.

A mixture of moisture, instability, an elevated/indistinct inversion and turbulence mainly in the free atmosphere will contribute to poor/bad seeing throughout the forecast period.

The mid-level ridge will remain rather weak as a rather deep tropical upper-tropospheric trough prevails to the NW, which will eventually be quickly replaced by a large low later in the week and into the weekend. This will allow widespread instability to persist in the area probably through the week, which will keep the inversion rather weak/indistinct throughout the forecast period. In addition, a strong/deep sub-tropical jet along the southern fringe of the TUTT will continue to advect widespread mid/upper-level moisture into the area, contributing to overcast skies and extensive fog, ice, high humidity and flurries at the summit probably into tomorrow evening. There is also an outside chance for afternoon convection along the Big Island slope as a short-wave trough passes through later tomorrow. Latest model run suggest that the bulk of the moisture and clouds will shift off toward the east and NE through that night, which may help to improve conditions/skies. However, more banding high clouds are expected to spread in from the south as the low develops to the NW through Thursday night. mid-level moisture may also build into the area and there is a chance that instability associated with the low will help deepen the low-level cloud flow beginning Friday. Nevertheless, this will increase the risk for more rounds of moisture and extensive cloud cover at the summit for Friday and Saturday night.

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)
Tue Mar 31 - 2 PM	80-100	4-8	100 / 90	-1	SW/15-30	NaN	8-12
8 PM	80-100	4-8	100 / 95	-4	SW/15-30	1-2	8-12
Wed Apr 01 - 2 AM	80-100	4-7	100 / 95	-4.5	WSW/10-20	1-2	8-12
2 PM	60-80	4-6	95 / 65	-1	NNW/5-15	NaN	6-10
8 PM	20-40	5-6	75 / 30	-3	NW/5-15	0.7-1.3	4-6
Thu Apr 02 - 2 AM	20-40	5-6	65 / 20	-3	WNW/5-15	0.6-1	3-5
2 PM	60-80	4-6	90 / 50	0.5	WSW/5-15	NaN	4-8
8 PM	40-60	9-10	60 / 15	-2.5	WSW/5-15	0.6-0.9	3-5
Fri Apr 03 - 2 AM	60-80	8-10	65 / 20	-2.5	SSW/10-20	0.6-1	3-5
2 PM	80-100	4-10	90 / 50	0.5	SSW/10-20	NaN	4-8
Sat Apr 04 - 2 AM	80-100	5-9	75 / 30	-2.5	W/10-20	0.7-1.3	6-10
2 PM	80-100	4-8	90 / 50	0	NW/10-20	NaN	6-10
Sun Apr 05 - 2 AM	60-80	5-8	75 / 30	-2	W/10-20	0.7-1.3	4-8

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
Tue Mar 31 - Wed Apr 01	18:45	19:50	5:01	6:06	N/A	1:22	49	6 48.5	23 28
Wed Apr 01 - Thu Apr 02	18:45	19:50	5:00	6:05	N/A	2:17	60	7 46.6	22 49
Thu Apr 02 - Fri Apr 03	18:46	19:51	4:59	6:04	N/A	3:09	70	8 45.7	20 46
Fri Apr 03 - Sat Apr 04	18:46	19:51	4:58	6:03	N/A	3:59	80	9 44.7	17 21
Sat Apr 04 - Sun Apr 05	18:46	19:51	4:57	6:03	N/A	4:46	89	10 43.1	12 43

Forecast Issued by: Ryan Lyman
Next update at 5 PM HST Tuesday 31 March (0300 UTC Wednesday 1 April) 2020.

Additional Information
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Honolulu National Weather Service Data and Products

Current Conditions
Temp		-2.1 C
RH		100 %
Wind		SW 31 mph
Road		Open (4x4)