Latest Forecast for Mauna Kea Observatories
10 AM HST (2000 UTC) Tuesday 13 February 2018

Warnings
Increasing humidity
Chance for fog/ice and flurries
Moderate winds

Cloud Cover and Precipitation Forecast
There is a possibility for periods of fog, ice, high humidity and light flurries particularly toward the end of the night. Broken to overcast mid-level clouds will continue to spread in from the west and pass over the summit area through the night.

Summary of Key Meteorological Variables
Summit temperatures will be near 5 C this afternoon, 0 C this evening and -2 C tomorrow morning. Winds will be from the SW at 15-30 mph for today, increasing to 20-35 mph for the night. Seeing will be near 0.9-1 arcsecond, while precipitable water is expected to exceed 4 mm through the night.

Graphical Summary

Discussion
Although the tradewind inversion will remain intact near 6-8 thousand feet for the next 24 hours, an influx of widespread mid-level moisture will likely result in an increase in humidity toward 60-80%, and will help raise the stakes on fog, ice and flurries at the summit, particularly as the night progresses. Building instability is expected to dismantle the inversion as more deep moisture fills into the area, which will further increase this risk and perhaps allow convection to develop near/over the Big Island during the following 4 nights (Saturday night in particular). There is also a possibility for brief periods of heavy snow at the summit at virtually anytime, especially over the weekend. Daytime clouds will be minimal and short-lived for today, but could pick up tomorrow and turn extensive for the remainder of the week.

Broken to overcast mid-level clouds will continue to spread in from the SW and pass over the summit area through the night. The bulk of these clouds will shift eastward by tomorrow evening, but there is a possibility for patches of thick clouds lingering the area and/or developing along the northern skies over the following 2 nights. Thicker more organized/widespread clouds may begin to develop all around the Big Island area late Friday night, likely contributing to overcast skies for the following night.

Precipitable water is expected to exceed 4 mm throughout the forecast period.

A mixture of moderate boundary layer turbulence, instability, moisture and/or mid/upper-level turbulence will contribute to poor/bad seeing throughout the forecast period.

Although the ridge to the SE will still remain close enough to the Big Island to promote large-scale subsidence and maintain the tradewind inversion near 7-8 thousand feet for another 24 hours, the low to the NW will continue to strengthen, slowly dig south-southeastward and help draw widespread mid-level moisture/clouds into the area during this time. This moisture/clouds will result in an increase in summit-level humidity (and likely cloud cover) toward 80% over the course of the night and raise the stakes on fog, ice and light flurries at the summit, particularly toward the end of the night. The bulk of this moisture will eventually shift eastward later tomorrow, only to get drawn back into the center of the low, eventually developing into a somewhat ragged frontal-like feature near the central part of the state later that night. Regardless, instability associated with the low will begin to influence the air mass near the Big Island, which will help erode the inversion by tomorrow evening. In addition, this aforementioned front is set to make its way toward the Big Island by late Thursday morning, then will stall out in the area and weaken as its parent low falls apart on Friday. Unfortunately, the front is expected to regenerate as a short-wave trough digs in from the NW and help revitalize the low to the northwest over the weekend. Consequently, this will likely allow mostly inoperable conditions to plague the summit, with the chance for convection in the area and periods of heavy snow at the summit beyond tonight. The risk for widespread convection and heavy snow will likely increase further as the second short-wave trough digs in around Saturday and Sunday.

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


5-day Forecast
Summary

Graphical Trend
02 pm HST
Tue 13 Feb
08 pm HST
Tue 13 Feb
02 am HST
Wed 14 Feb
02 pm HST
Wed 14 Feb
08 pm HST
Wed 14 Feb
02 am HST
Thu 15 Feb
02 pm HST
Thu 15 Feb
08 pm HST
Thu 15 Feb
02 am HST
Fri 16 Feb
02 pm HST
Fri 16 Feb
02 am HST
Sat 17 Feb
02 pm HST
Sat 17 Feb
02 am HST
Sun 18 Feb
00 UTC
Wed 14 Feb
06 UTC
Wed 14 Feb
12 UTC
Wed 14 Feb
00 UTC
Thu 15 Feb
06 UTC
Thu 15 Feb
12 UTC
Thu 15 Feb
00 UTC
Fri 16 Feb
06 UTC
Fri 16 Feb
12 UTC
Fri 16 Feb
00 UTC
Sat 17 Feb
12 UTC
Sat 17 Feb
00 UTC
Sun 18 Feb
12 UTC
Sun 18 Feb
Cloud Cover (%) 60 to 80 70 to 90 80 to 100 70 to 90 50 to 70 40 to 60 70 to 90 60 to 80 40 to 60 80 to 100 60 to 80 80 to 100 80 to 100
Cloud Height (km) above sea level 6-8 6-8 5-8 4-8 5-7 6-7 4-8 4-7 4-6 4-8 4-6 4-9 4-10
Chance for Fog/Precip (%) 0/0 30/10 60/30 75/25 80/30 75/25 90/50 75/40 75/40 90/60 90/60 95/80 95/90
PW (mm, summit upward) 4 to 8 4 to 8 4 to 8 6 to 10 4 to 8 4 to 8 6 to 10 4 to 8 4 to 8 6 to 10 4 to 8 8 to 12 6 to 10
Mean Seeing (arcsecs) N/A 0.9 ± 0.2 1.0 ± 0.2 N/A 1.0 ± 0.2 1.1 ± 0.3 N/A 1.1 ± 0.3 1.2 ± 0.4 N/A 1.0 ± 0.3 N/A 1.4 ± 0.5
Summit Temp (°C) 5 0 -2 1 -2.5 -3 1.5 -2 -2.5 1 -2.5 -1 -4.5
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)

SW/15 to 30

SW/20 to 35

SW/20 to 35

SW/20 to 35

WSW/20 to 35

SW/20 to 35

WSW/25 to 40

WSW/25 to 40

WSW/25 to 40

WSW/20 to 35

SW/20 to 35

SSW/20 to 35

SW/20 to 35


 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.Feb.13/Wed.Feb.14
18:30
19:35
5:37
6:42
5:59
17:00
2
20 47.2
-17 26
Wed.Feb.14/Thu.Feb.15
18:30
19:35
5:37
6:42
6:41
17:51
0
21 36.0
-14 59
Thu.Feb.15/Fri.Feb.16
18:31
19:36
5:36
6:41
7:22
18:42
0
22 24.2
-11 51
Fri.Feb.16/Sat.Feb.17
18:31
19:36
5:36
6:41
N/A
19:34
2
23 12.0
-8 10
Sat.Feb.17/Sun.Feb.18
18:31
19:36
5:35
6:40
N/A
20:26
6
23 59.7
-4 04


Forecast issued by: Ryan Lyman
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Next update at 5 PM HST Tuesday 13 February (0300 UTC Wednesday 14 February) 2018.
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