textproduct: Anchorage

SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3)

Key Messages:

* Showers and thunderstorms will continue through late this evening, primarily for the Copper River Basin. Coverage of thunderstorms is expected to be be less than what they were yesterday. If you hear thunder or see lightning, seek shelter.

* Convection chances decrease over the next few days. A low approaching Kodiak will bring rain today through Monday. There is low confidence with how far north the front will affect mainland Southcentral and when it would arrive.

Discussion:

With a marine layer residing over much of the Cook Inlet this morning and early afternoon, coastal locations along the western Kenai Peninsula and northward to Anchorage have struggled to warm up today. The fog from earlier has mostly lifted, though a narrow corridor of low stratus still remains in place from Tyonek to just north of Anchor Point. Although satellite imagery shows that this low stratus deck is shrinking and scattering out, these locations have less time for daytime heating - so today's high temperatures have been lowered quite a bit for this afternoon with this forecast package for these areas.

Elsewhere, where it has been able to warm as expected today, radar returns as of 3PM AKDT depict isolated showers and thunderstorms ongoing across the central/southern Copper River Basin from Chitina to Glennallen. 500 mb vorticity analysis depicts a shortwave moving over this region and rotating northeastward around the northern flank of a vertically stacked coastal ridge situated over the eastern Gulf. There are also a couple of isolated storms forming across the northern Susitna Valley, though there is medium to high (70-80%) confidence that this area will see less storm coverage this afternoon given much of the upper level support/steeper lapse rates are located over the Copper River Basin.

Meanwhile, a weak North Pacific low is lifting a front northward across the western Gulf, bringing rainfall to Kodiak Island this afternoon. The models show that Kodiak Island will see periods of rain showers lasting into early next week.

At the surface, models indicate that the coastal ridge currently in place continues to build through Sunday afternoon. This will set up an east to west oriented pressure gradient from Whittier to Anchorage and develop a relatively weak Turnagain Arm wind Sunday afternoon. This jet will likely take a slight bend to the north as the flow is redirected by lower pressure from daytime heating across the Matanuska and Susitna Valley. There is a chance that breezy conditions clip West Anchorage Sunday afternoon, but that as of now is of lower confidence (20-30%).

Model agreement has improved somewhat for Monday as a complex low appears to form as a low pressure system dipping southward across the eastern Bering Sea interacts with the North Pacific low. The global models are starting to converge on the idea that the complex low enters the Gulf of Alaska where broad troughing sets up. Rain showers are expected to lift northward across the Gulf this weekend through Monday. There is growing confidence that rain showers reach coastal areas of Southcentral (from Homer to Seward to Cordova) as early as Monday morning. By late Monday, model consensus degrades, but big picture wise, troughing across the Gulf will likely send waves of moisture towards coastal Southcentral, though there is low confidence on how much rainfall and the timing/duration. Stay tuned.

-AM/Rux

AVIATION

PANC...VFR conditions expected to persist through the period. Mid and upper level cloud cover should mitigate fog and stratus development over Cook Inlet overnight. Turnagain Arm winds will increase Sunday afternoon...periodically bending into the terminal with gusts up to 20 kts.