Current Conditions
Temp-3.6 C
RH94 %
WindWSW 62 mph
RoadClosed
Mauna Kea Observatories Forecast
5 PM HST Tuesday 20 February (0300 UTC Wednesday 21 February) 2018
Warning(s)
Fog, ice and high humidity
Chance for afternoon convection and snow
Moderate/strong winds
Cloud Cover and Fog/Precipitation Forecast
There is a moderate/high risk for fog, ice and high humidity throughout the night; isolated convection and more snow are also possible, mainly for this afternoon/evening. Patches of mid-level clouds will also continue to linger in the area, especially to the south, throughout the night.
Summary of Key Meteorological Variables
Summit temperatures will be near -5 C this evening, -6 C tomorrow morning. Winds will be from the WSW at 35-50 mph for the start of the night, easing to 25-40 mph by the end. Seeing and precipitable water are expected to exceed 1 arcsecond and 4 mm, respectively throughout the night.
Discussion
The tradewind inversion will remain weak/elevated near 14 thousand feet, before falling apart completely as the air mass becomes saturated again starting late tomorrow evening and probably for the remainder of the week. Consequently, there is a high risk for fog, ice, high humidity and light flurries at the summit throughout the forecast period. There is a possibility for another round of isolated afternoon convection and periods of heavy snow at the summit over the next 2 afternoons/evenings. Convection could become more widespread beginning early Thursday morning, which may allow for more/prolong periods of moderate to heavy snow at the summit for the remainder of the forecast period. Extensive daytime clouds are possible throughout the forecast period.

There is a possibility for lingering patches of mid-level clouds (particularly to the south) and/or residual cirrus exhaust in the area for tonight. The former is set to become more organized and spread northward, signficantly increasing cloud cover through tomorrow night and probably will blanket summit skies for the following 3 nights.

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

Strong boundary layer turbulence and lingering instability/mositure will contribute to bad seeing for tonight. Although the turbulence is set to subside through tomorrow, the air mass is expected to grow more unstable and saturated, which will not help to improve seeing for the remainder of the forecast period.

No change since the morning forecast...Although the low to the north will continue to dissipate, lingering instability associated with a large/quasi-stationary trough to the NW, combined with residual moisture in the area will keep the inversion from rebuilding over the next 24-30 hours. This will likely allow for more periods of fog, ice and high humidity at the summit for tonight and even another round of afternoon/evening convection and flurries. Winds, on the other hand, are set to gradually receed as the low falls apart overnight. Unfortunately, a new short-wave trough digging in from the NW is expected to help redevelop a new broader low to the NW, bringing fresh more widespread instability to the area beginning late tomorrow evening. Moreover, this low/trough will veer mid/low-level winds toward the south, which will advect deep widespread tropical moisture back into the area probably for the remainder of the week. This will likely allow inoperable summit conditions to plague the summit during this period. Eventually, this moisture and instability will erode what's left of the inversion, allowing the entire atmosphere to turn saturated between at least early Thursday morning and Sunday morning. That will significantly increase the risk for widespread convection in the area and periods of heavy snow at the summit, especially between Thursday afternoon and early Saturday morning. There is a chance that the bulk of this moisture will begin to slide westward as a ridge tries to build to the NE very late in the weekend and into the early part of next week. Still, it is doubtful that dry/stable conditions will return to the summit until the trades strengthen and usher all of the moisture out of the area until around Tuesday/Wednesday.
HST CC (%) CLD HGT (km) Fog Prob (%) Prcp Prob (%) Temp (C) Wind (dir/mph) Seeing (asec) PW (mm)
---------------------------------------------------------------------------------------------------------------------------------------
02/20/2018 2000 20-40 4.5-6 90 30 -5 240/35-50 1-2 4-6
02/21/2018 0200 10-30 4.5-5.5 90 15 -6 240/25-40 0.7-1.7 4-6
02/21/2018 1400 80-100 4-7 95 60 -1 270/15-30 NaN 6-10
02/21/2018 2000 60-80 4-7 90 40 -3 240/5-15 0.7-1.3 6-10
02/22/2018 0200 60-80 4-8 95 60 -3 225/5-15 0.7-1.5 8-12
02/22/2018 1400 80-100 4-9 95 75 -1 135/5-15 NaN 8-12
02/22/2018 2000 80-100 4-10 95 90 -4 90/15-30 0.8-1.6 8-12
02/23/2018 0200 80-100 4-10 95 90 -4 120/10-20 0.9-1.7 8-12
02/23/2018 1400 80-100 4-10 95 90 -1 150/15-30 NaN 8-12
02/24/2018 0200 80-100 4-10 95 90 -3.5 240/15-30 0.9-1.9 8-12
02/24/2018 1400 80-100 4-10 95 90 -1 270/10-20 NaN 8-12
02/25/2018 0200 80-100 4-10 90 80 -3 330/5-15 0.8-1.6 8-12
02/25/2018 1400 80-100 4-10 95 85 -1 45/5-15 NaN 8-12
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
Cover (%) Height (km) Probability (%) (Celcius) (Dir/MPH) (Arcseconds) (mm)
Tue Feb 20 - 8 PM20-404.5-690 / 30-5WSW/35-501-24-6
Wed Feb 21 - 2 AM10-304.5-5.590 / 15-6WSW/25-400.7-1.74-6
2 PM80-1004-795 / 60-1W/15-30NaN6-10
8 PM60-804-790 / 40-3WSW/5-150.7-1.36-10
Thu Feb 22 - 2 AM60-804-895 / 60-3SW/5-150.7-1.58-12
2 PM80-1004-995 / 75-1SE/5-15NaN8-12
8 PM80-1004-1095 / 90-4E/15-300.8-1.68-12
Fri Feb 23 - 2 AM80-1004-1095 / 90-4ESE/10-200.9-1.78-12
2 PM80-1004-1095 / 90-1SSE/15-30NaN8-12
Sat Feb 24 - 2 AM80-1004-1095 / 90-3.5WSW/15-300.9-1.98-12
2 PM80-1004-1095 / 90-1W/10-20NaN8-12
Sun Feb 25 - 2 AM80-1004-1090 / 80-3NNW/5-150.8-1.68-12
2 PM80-1004-1095 / 85-1NE/5-15NaN8-12
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 Feb 20 - Wed Feb 21 18:33 19:37 5:33 6:38 N/A 23:07 29 2 27.0 8 56
Wed Feb 21 - Thu Feb 22 18:33 19:38 5:33 6:37 N/A 0:04 39 3 19.7 12 50
Thu Feb 22 - Fri Feb 23 18:33 19:38 5:32 6:37 N/A 1:03 50 4 15.1 16 08
Fri Feb 23 - Sat Feb 24 18:34 19:38 5:32 6:36 N/A 2:04 61 5 13.4 18 32
Sat Feb 24 - Sun Feb 25 18:34 19:39 5:31 6:35 N/A 3:05 72 6 14.3 19 48
Forecast Issued by: Ryan Lyman
Next update at 10 AM HST (2000 UTC) Wednesday 21 February 2018.
Additional Information
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This message is also available at the MKWC road conditions page.
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