Northern Alaska Forecast Discussion National Weather Service Fairbanks AK 114 PM AKDT Sun Apr 23 2017
.DISCUSSION... General model consistency with the upper level features through Thursday with the upper level low moving eastward across the Arctic with frontal feature moving northward across Interior Alaska and extending towards Yukon Delta. A shortwave rotating around the the upper level low near Adak will bring clouds and precipitation to the Yukon Delta tonight as it spreads northward toward Seward Peninsula by Tuesday.
Arctic Coast and Brooks Range: The main concern for the north will be the dense fog that redevelops this evening into Monday morning. Expect quarter mile visibility along the Arctic coast line with areas of fog pushing up against the Brooks Range. Light onshore flow will also continue across the Chukchi coast from Point Lay up through Barrow with quarter mile visibility due to the fog as well. However, fog should dissipate through the late morning. There is a a low pressure trough in Eastern Chukchi Sea that will move across the Chukchi Sea coast tonight and spread across the Eastern North Slope area before dissipating. Stratus along and west of this trough will spread east across the North Slope tonight into Monday.
West Coast and western Interior: A frontal boundary will bring isolated to scattered rain and snow showers tonight into Monday across the Yukon Delta and Lower Yukon Valley. By Tuesday the frontal boundary will move northward with scattered rain and snow showers along and south of Seward Peninsula as showers also push into the western Interior. Any precipitation accumulation will be relatively light. It looks like it will remain colder for St Lawrence Island for snow but will be rain along the west coast during the day and evening with transition or mixture of rain and snow overnight. Along the Northern Bering Sea and Bering Strait the winds will remain from northeast with small craft and brisk wind advisories extending from St Lawrence Island through Point Hope. Although winds are not reaching strength for small craft advisory in Norton Sound they are close. Expect the winds to diminish in Norton Sound by Tuesday.
Central and eastern Interior: Mostly sunny skies across much of the Interior with high clouds moving in from south. Continue to have the warming trend through Monday. For Fairbanks, expecting high temperatures in mid to upper 50s for Monday with overnight lows around 30 Monday morning. The warming temperatures will allow for the continued melt of area snowpack. Expect slightly cooler temperatures across the Interior on Tuesday and Wednesday as a weak front will bring increased cloud cover and at least a slight chance for some rain or snow showers.The GFS and NAM bring much more precipitation along the frontal boundary but likely a bit overdone in the precipitation. Thus expect isolated showers extending from Fort Yukon to Galena on Tuesday into Wednesday.
.FIRE WEATHER...No red flag concerns. Dry and sunny conditions will continue across the Interior today with only slight increase of moisture for Monday. There will be an increase in moisture resulting in increase in afternoon minimum RH values on Tuesday. However, the gradual increase in downslope winds with southerly flow and moisture will limit any precipitation in the Alaska Range on Monday night into Tuesday.
.AFG WATCHES/WARNINGS/ADVISORIES... Small Craft Advisory for PKZ210.
Brisk Wind Advisory for PKZ220-PKZ225. &&
000 FXAK68 PAFC 240013 AFDAFC
Southcentral and Southwest Alaska Forecast Discussion National Weather Service Anchorage AK 413 PM AKDT Sun Apr 23 2017
.ANALYSIS AND UPPER LEVELS...
An amplified ridge spreads from mainland Alaska southeastward along the British Columbia Coast. While the ridge continues to obstinately keep the Aleutian low from pushing too far east, an upper level wave and weakening front are helping to bring in clouds to much of the Southcentral mainland. However, there is just enough perpendicular flow associated with this front, and enough dry air in place at lower levels to limit precipitation. Downsloping is also keeping places such as Iliamna dry and while widespread mountain waves are evident across the Alaska Peninsula in the IR satellite imagery. Meanwhile the low south of the Central Aleutians continues to support unsettled weather across the Bering.
.MODEL DISCUSSION... Models are in generally good agreement synoptically in the short term, with some more evident divergence in the long term. In the short term a blend of models was favored due to the strong agreement, but the high resolution NAM was favored for local effects in Southcentral.
.AVIATION... PANC...VFR conditions and light winds will persist. Gusty southeasterly Turnagain Arm winds are expected through this evening and may develop again Monday afternoon.
.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
As high pressure continues to slide north this evening, a frontal boundary currently draped across Kodiak Island will begin to shift north and east into the northern Gulf of Alaska. This will bring a period of light to moderate rainfall to most coastal locations through Tuesday as rainfall upslopes along the coastal mountains. Inland locations will be hard-pressed to see any rainfall as the upper level pattern doesn`t seem conducive to drive the front inland and weak cross barrier flow should keep the lowest pretty dry. Some gusty winds will develop across Turnagain Arm, the Knik River Valley and the Copper River as the front nears the coast Monday and Tuesday but will likely remain below 30 mph. Temperatures will continue to be slightly above normal with overnight low temperatures ranging from the lower 30s to lower 40s and highs generally in the mid 40s to mid 50s.
.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)... Conditions will remain largely unchanged through the beginning of the week as moist southeasterly flow persists over the southwest mainland on the eastern periphery of the Bering Sea trough. This will yield continued cloudy and showery conditions as temperatures run above seasonal normal values. Showers will continue to favor western portions of Bristol Bay including upslope areas along the Kilbuck Mountains, while remaining lower in coverage through the typical downslope areas in the lee of the Alaska/Aleutian ranges.
.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)... The Bering region will remain locked in a benign showery regime for the next several days under the influence of broad cyclonic flow as a sprawling, vertically stacked low remains quasi- stationary in the vicinity of the Central Aleutians. Winds will mainly be southeasterly over the eastern Bering and northeasterly over the western Bering, while generally remaining below Small Craft Advisory criteria. Widespread marine stratus and patchy fog will also persist over much of the region as warmer air moves over the relatively cold waters of the Bering.
.LONG TERM FORECAST (Days 3 through 7)...
The long range forecast continues with a drier pattern inland as low pressure centers spin across waters of the Gulf and Bering. However...at the end of next week the synoptic pattern slowly shifts as the Bering low lifts northeast. Next Friday and Saturday the closed Bering low becomes an open wave over the southwest with a trough axis swinging over Southcentral which will bring increased chances for rain across the southern mainland.
The biggest challenge in the extended range surrounds the next storm system for the western Bering as a low organizes in the North Pacific. Model agreement is good with the initial timing of the front, pushing into the western Aleutians late Thursday, but they differ in the track and strength of the low as it progresses east through Saturday. Overall, the main impacts of gale force winds and rain are expected to remain over the Bering and Aleutians.
.AFC WATCHES/WARNINGS/ADVISORIES... PUBLIC...NONE. MARINE...NONE. FIRE WEATHER...NONE.
SYNOPSIS AND MODEL DISCUSSION...EN SOUTHCENTRAL ALASKA...MC SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...CB LONG TERM...KH
000 FXAK67 PAJK 232255 AFDAJK
Southeast Alaska Forecast Discussion National Weather Service Juneau AK 255 PM AKDT Sun Apr 23 2017
.SYNOPSIS...Broad area of low pressure centered along the central Aleutians impacts the Gulf of Alaska with a trough extending over gulf to the British Columbia coast. Higher pressure over northern Canada will weaken as the center moves east towards Hudson Bay.
.SHORT TERM.../ Sunday night to Tuesday night / An old trough extending over the gulf and Haida Gwaii has clouds and light rain/showers moving north and west across the southern panhandle Sunday afternoon. Expect to see the light rain to continue to work its way northward through the panhandle tonight. It isn`t until during the early day Monday when the trough has moved north to the northern gulf that PoP get more than low chance levels. Winds over the northern coastal marine zones also increase up to 20 kt, as the through approaches.
Another short wave/surface will be developing and increasing in strength as the feature moves east northeast of the Pacific towards the Haida Gwaii region later Monday with a closed surface low pattern go be about 200 nm southwest of the island midday Tuesday. The operational models are generally agreeing on the feature although have presently favored the more eastern/weaker solution pair of the NAM/EC. The low should be curving north into the southeast gulf west of Prince of Wales Island by early Wednesday morning. This track and strength seems to be a new path for the solutions from previous thinking, so blended into the Wednesday forecast periods.
The new low will spread a new front north into the southern panhandle and help to dry out the precipitation from the northern areas Tuesday, and then that front will start to spread the rain northward.
.LONG TERM.../Tuesday morning through Saturday/ Issued 5 am Sunday - There is not much change in the overall synoptic pattern through next week. The polar jet will remain over the central Pacific and this will keep the storm track south of the forecast area through mid week. There will be a stronger low pressure system that will lift north out of the north Pacific on Wednesday and move into the eastern gulf. There are some differences with the track of this low but the latest few model runs seem to be picking up on this feature. As the low slowly lifts northeast through Thursday the threat of precip will increase for the southern half of the forecast area. The northern areas right now will see a chance of rain. For late week into the early next weekend there is increased onshore flow from the southwest and with that a chance of rain with cloudy skies seems likely.
Wind wise...the inner channels will see relatively light winds from the north through Wednesday night with weak northernly pressure gradient. As the low moves into the eastern gulf winds will increase to 20 kt over marine waters with 15 mph over land from Fredrick Sound south. The winds will come around to the south late in the week as a ridge builds over the northern panhandle as the low moves into Canada on Friday.
Overall there is average forecaster confidence for Tuesday and Wednesday but lower confidence after that due to the differences with the low moving out of the north Pacific and spread in the ensembles. Changes in the long term were modified using the 00z nam and 12z ec through day 4 then WPC for late in the week into the weekend.
.AVIATION...We began the periods with vcsh in the southern zones, and only added change groups where ceilings fluctuated through the night and into Monday. The northern sites we added evening change groups as channel breezes fall and then even though vcsh may occur late tonight, we delayed adding until mvmc conditions arrived later Monday. No IMC conditions are forecast through the next 24 hours.
.MARINE...Winds primarily 20 kt or lest through the part of next week though will need to watch the low development Tuesday for the southeast gulf. Seas and swells for the coastal areas 5 to 7 feet tonight and into Monday. A localized buoy is reporting 8 feet, however I suspect those will subside through the evening.