Latest Forecast for Mauna Kea Observatories
5 PM HST Tuesday 13 March (0300 UTC Wednesday 14 March) 2018

Warnings
Winter weather, moderate winds, fog/ice/snow.

Cloud Cover and Precipitation Forecast
Extensive fog, ice, thick clouds and light/moderate stratiform snow will continue to plague the summit through the night.

Summary of Key Meteorological Variables
Summit temperatures will be near 0 this evening and -0.5C tonight. Winds will be from the SSW at 20-30 mph. Seeing and precipitable water are expected to exceed 1 arcsecond and 4 mm, respectively, through the night.

Graphical Summary

Discussion
The airmasses over and around the Big Island will continue to be saturated and unstable, resulting in extensive fog, ice and frozen rain/snow to plague the summit through at least Thursday night, perhaps even through Friday and the weekend nights. Short periods of heavy snow and convection are also possible at times through tomorrow. Moisture should decrease some Friday and Saturday but airmasses will be slow to dry, and more moisture could be advected over the area starting late on Sunday. Extensive afternoon clouds are expected through Friday, but may taper some over the weekend.

Broken to overcast thick clouds will continue to pass over/linger near the summit, blanketing skies probably through Wednesday night. Clouds are expected to start thinning on Thursday and through Friday shifting eastward allowing skies to start opening up for that night and and through Saturday night. More clouds are expected to approach the area from the NW on Sunday.

Precipitable water will continue to exceed 4 mm throughout the forecast period.

A mixture of abundant moisture (particularly in the low-levels), strong mid-level turblence, boundary layer turbulence and/or instability will contribute to poor/bad seeing probably through Thursday night. There is a small/moderate chance for some improvement as the atmosphere begins to stabilize on Friday and Saturday night.

Not much is changed since the morning forecast... The deep moisture over the State will continue to plague the summit while slowly moving east-northeastward, advected and organized by the short-wave trough to the NW. An upper level low to the SW of the State associated with the shortwave will dissipate over the area by tomorrow/Thursday, therefore the air mass near the Big Island will remain saturated and unstable, allowing inoperable conditions to plague the summit probably through Thursday night. Winter-like conditions, with moderate winds, extensive fog, heavy ice/rime and periods of moderate/heavy snow and convection along the eastern slopes and to the SW are also possible mainly as the low moves through the area by tomorrow afternoon. There is a possibility that the air mass will warm-up a bit and winds will taper as the low rapidly dissipates then. A weak ridge building in from the SE will eventually settle in over the southern half of the State and perhaps begin to stabilize the air mass a bit by Friday, but there is a good chance that moisture will get caught up in the ridge and persist (while slowly detraining into the surrounding atmosphere) in the area well into the weekend. Expect winter weather probably through tomorrow and part of Thursday, mostly fog and light rain into Friday night, with a slight overall improvement from Friday into Saturday.

Astronomical Observing Quality Guidance
05 pm HST Tuesday 13 March (03 UTC Wednesday 14 March)CN2
08 pm HST Tuesday 13 March (06 UTC Wednesday 14 March)CN2
11 pm HST Tuesday 13 March (09 UTC Wednesday 14 March)CN2
02 am HST Wednesday 14 March (12 UTC Wednesday 14 March)CN2
05 am HST Wednesday 14 March (15 UTC Wednesday 14 March)CN2
08 am HST Wednesday 14 March (18 UTC Wednesday 14 March)CN2
Latest WRF CN2 Profiles Animation | Collage


5-day Forecast
Summary

Graphical Trend
08 pm HST
Tue 13 Mar
02 am HST
Wed 14 Mar
02 pm HST
Wed 14 Mar
08 pm HST
Wed 14 Mar
02 am HST
Thu 15 Mar
02 pm HST
Thu 15 Mar
08 pm HST
Thu 15 Mar
02 am HST
Fri 16 Mar
02 pm HST
Fri 16 Mar
02 am HST
Sat 17 Mar
02 pm HST
Sat 17 Mar
02 am HST
Sun 18 Mar
02 pm HST
Sun 18 Mar
06 UTC
Wed 14 Mar
12 UTC
Wed 14 Mar
00 UTC
Thu 15 Mar
06 UTC
Thu 15 Mar
12 UTC
Thu 15 Mar
00 UTC
Fri 16 Mar
06 UTC
Fri 16 Mar
12 UTC
Fri 16 Mar
00 UTC
Sat 17 Mar
12 UTC
Sat 17 Mar
00 UTC
Sun 18 Mar
12 UTC
Sun 18 Mar
00 UTC
Mon 19 Mar
Cloud Cover (%) 80 to 100 80 to 100 80 to 100 80 to 100 80 to 100 80 to 100 60 to 80 60 to 80 60 to 80 50 to 70 50 to 70 40 to 60 50 to 70
Cloud Height (km) above sea level 4-10 4-10 4-10 4-10 4-10 4-10 4-9 4-8 4-8 4-6 4-6 4-5 4-6
Chance for Fog/Precip (%) 100/100 100/100 100/80 100/80 100/80 100/80 90/60 80/50 80/50 60/40 60/40 40/20 60/40
PW (mm, summit upward) 12 to 18 12 to 18 12 to 18 10 to 14 10 to 14 10 to 14 10 to 14 10 to 14 10 to 14 8 to 12 8 to 12 8 to 12 8 to 12
Mean Seeing (arcsecs) 1.5 ± 0.5 1.5 ± 0.5 N/A 0.8 ± 0.2 0.8 ± 0.2 N/A 0.8 ± 0.2 0.7 ± 0.2 N/A 0.6 ± 0.2 N/A 0.6 ± 0.2 N/A
Summit Temp (°C) 0 -0.5 2 -0.5 -1 2 0.5 0 2 -0.5 2 0 2
Wind Dir/Speed (mph)
    Summit (615 hPa)
    19,000 ft (500 hPa)
    24,500 ft (400 hPa)
    31,000 ft (300 hPa)
    35,000 ft (250 hPa)
    40,000 ft (200 hPa)
    46,000 ft (150 hPa)
    54,000 ft (100 hPa)

SSW/20 to 35

SSW/20 to 30

SSW/15 to 25

S/10 to 20

SSE/10 to 20

SSE/10 to 20

SE/10 to 20

SE/10 to 20

S/10 to 20

SE/5 to 15

E/5 to 15

SSW/5 to 15

NW/10 to 20


 Rise and Set times for the Sun and Moon
Night (HST)
Sun Set
Twilight End
Twilight Beg
Sun Rise
Moon Rise
Moon Set
Illum (%)
RA
Dec
Tue.Mar.13/Wed.Mar.14
18:40
19:44
5:18
6:22
4:37
N/A
9
21 22.3
-15 54
Wed.Mar.14/Thu.Mar.15
18:40
19:44
5:17
6:21
5:19
N/A
5
22 10.9
-12 55
Thu.Mar.15/Fri.Mar.16
18:40
19:45
5:16
6:20
5:59
17:26
1
22 59.1
-9 19
Fri.Mar.16/Sat.Mar.17
18:41
19:45
5:15
6:20
6:39
18:19
0
23 47.2
-5 15
Sat.Mar.17/Sun.Mar.18
18:41
19:45
5:14
6:19
N/A
19:12
1
0 35.6
-0 53


Forecast issued by: Tiziana Cherubini
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Next update at 10 AM HST (2000 UTC) Wednesday 14 March 2018.
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