Weather Outlook for April 27th to April 29th, 2019

Southern Nevada Outlook

SYNOPSIS: Isolated showers and thunderstorms possible over Lincoln County this afternoon. Warm, dry conditions expected elsewhere until an unsettled pattern begins late this weekend bringing periods of rain chances and breezy winds to the area through Tuesday.

DISCUSSION Saturday through Friday

Another shortwave will sweep across the PacNW today which will further suppress the weak ridge overhead. This will allow temperatures to be slightly cooler than yesterdays, but are still expected to remain above seasonal normals. Some breezy southwesterly winds will develop this afternoon and evening, with gusty winds possible across the western Mojave Desert. Similar to the last few days, some isolated high-based showers and thunderstorms are possible this afternoon. With meager moisture and instability, storms should be mainly confined to eastern Lincoln County. An approaching warm, closed low off the SoCal coast will begin to effect the region Sunday increasing cloud cover and bringing more breezy to gusty west-southwest winds across the region. As the low slides across CA/NV/AZ through Monday, it will bring mostly cloudy skies and widespread chances for showers and thunderstorms across the region. With added cloud cover, temperatures will decrease to slightly below normals Monday and Tuesday. QPF plumes have been trending downward for the Las Vegas Valley with mean values of 0.1-0.2", current forecast is quite a bit drier with only 0.03" for storm total at McCarran. Better moisture plumes (PW`s of 0.75"-1") will set up across Mohave County, where storm total amounts of 0.3"-0.4" with isolated higher amounts to 0.5" along higher terrain will be possible. As the low begins to lift off to the northeast sometime late Monday, another trough will begin to dig into the Intermountain West/Great Basin region mainly bringing gusty southwest winds Tuesday afternoon and more rain chances for eastern Nevada and northwest Arizona. Models have been trending downward with the magnitude of the winds across the region Tuesday afternoon, and still look to be sub-advisory level at the moment with the strongest winds setting up along the I-15 corridor. Behind the trough, expect dry zonal flow Wednesday with another possible weather system developing sometime late next week.

Hawaii Outlook

Synopsis

Daytime sea breezes and overnight land breezes will dominate through early next week, with showers favoring interior and mauka areas each afternoon and evening, and locations near the coast each night. An upper level trough passing over the state could bring some locally heavy showers and possibly a thunderstorm each afternoon and early evening through Monday. High pressure will then build north of the islands Tuesday through much of next week, bringing a return of more typical trade wind weather featuring windward and mauka showers.

Discussion

Currently at the surface, a 1033 mb high is centered around 2000 miles north-northeast of Honolulu, while a weakening cold front is located around 425 miles northwest of Kauai. Light trade winds continue to hold on across the eastern islands, while light and variable winds have taken hold over Oahu and Kauai. Infrared satellite imagery shows partly to mostly cloudy skies in place due to a combination of high and low clouds. Meanwhile, radar imagery shows lingering convective showers beginning to diminish across the state, with activity most prevalent over Oahu at the moment. Main short term concern revolves around the potential for locally heavy rainfall and thunderstorms over the weekend into early next week.

Model solutions are in good agreement showing a weakening cold front edging slowly eastward towards the island chain through the weekend, then stalling out and dissipating just to the north of Kauai on Monday. This will keep a light wind regime in place across the state, with overnight land breezes and daytime sea breezes expected in most areas. A new area of high pressure will build well to the northwest of the islands on Monday, then shift eastward well to the north of the area through the remainder of the work week. This will allow light to locally moderate trade winds to return Monday night, with moderate trades then expected Tuesday through Thursday. The trades may then ease again late next week as a front passes by to the north of the island chain.

The airmass will gradually de-stabilize through early next week, as upper level troughing becomes better established each day through Monday. The unstable airmass and light wind regime will result in afternoon/evening convective shower development each day, particularly over interior and mountain areas. Showers should fizzle out each evening, with some showers possible near the coast through the overnight hours. The best chance for thunderstorms appears to be on Monday when the coldest air aloft swings over the state, so will need to add thunder into the forecast. Thunder probabilities over the weekend don't appear too high, and if the latest model trends hold, we will likely be able to remove the mention of thunder at least through Saturday night, and possibly through Sunday night.

We should see more typical trade wind weather begin to fill in Monday night, with some evening convective showers diminishing over interior and leeward areas, before the focus returns to windward and mauka areas overnight. Trade showers should then continue to favor windward and mauka areas through the remainder of the work week, with a stray shower reaching leeward areas from time to time, but mainly in the overnight and early morning hours.