textproduct: Anchorage

SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3)

The forecast remains largely on track. The main low is beginning to stall near southern Kenai Peninsula. Meanwhile, a secondary surface low is spinning up over the northeastern Gulf this morning and is expected to interact, nearly merging with the currently low near the Kenai Peninsula. Together, these lows track northwestward and an additional surge of winds and precipitation will push through Prince William Sound and across the Chugach Mountains for Friday morning.

This is complex pattern, with a plethora of subtle meso-scale features, including weak vorticity lobes embedded in the upper- level flow lifting over the coastal mountains at various times through Friday. Given the influx of moisture and easterly wind flow of varying magnitude, there will be times over the next day or two when the shower activity spills over the coastal mountains into the western Kenai Peninsula, Anchorage Bowl, and Copper River Basin. The stronger northerly flow over the Mat-Su Valleys, however, will likely keep near surface conditions dry, leading to only a few sprinkles at best.

The airmass in place is also rather stagnant in terms of cold or warm air advection. As such, snow levels will not change much from where it sits currently, leading to mostly rain for the Seward Highway corridor through Friday morning. An additional 2 to 3 inches is expected for Thompson Pass.

The entire upper-level trough lifts north across Southcentral later Friday with the potential for precipitation to set up again around Cook Inlet. Colder air will arrive in the wake of the trough passage leading to lower snow levels. A persistent weak flow across the coastal mountains through the latter half of the week will allow for periods of light precipitation at inland locations with continued rainfall along the coast as low pressure lingers in the northwestern Gulf. Each feature embedded in the upper level pattern will play a key role in the enhancement of the precipitation and wind outcome for the rest of the week. Over the weekend, cooler temperatures are expected with showers decreasing.

TM/Rux

LONG TERM FORECAST (Days 4 through 7: Sunday - Wednesday)

The global models are in reasonable agreement that there will be a broad (or even complex) vertically stacked low somewhere in the central Gulf Sunday afternoon. The 500 mb pattern shows a closed upper low opening into a trough across Southcentral and the Gulf for this time, and the positioning of the surface low will be directed in part by how much amplification there will be of an upper ridge downstream over parts of Canada. For the western domain, the general consensus shows a deep, closed upper low and positively tilted trough envelope drifting southeastward over the Bering Sunday to Monday, which will help to usher in an unseasonably cold airmass over the region. Heading out to Day 7 or so, there is a strong enough signal in the guidance that an upper low in some form centers itself over the southern Bering, which increases forecaster confidence that the Aleutians and Alaska Peninsula may become quite windy by the end of the long term period. 850 mb temperature anomalies show marginally below average temperatures for Southcentral, with more significant cold temperature anomalies for the Bering, Aleutians, Alaska Peninsula, and Southwest Alaska through the end of the long term.

-AM

AVIATION

PANC...VFR expected with surface winds persisting out of the north. As a push of winds increase across the Chugach mountains Friday morning, LLWS is possible Friday around 18Z. Confidence with timing showers remains low today, though the most likely timeframe would be later this morning and early afternoon.