110 FXAK68 PAFC 181323 AFDAFC Southcentral and Southwest Alaska Forecast Discussion National Weather Service Anchorage AK 523 AM AKDT Thu Mar 18 2021 .ANALYSIS AND UPPER LEVELS... In the upper levels, a large upper level low and associated trough are centered right over the middle of the state this morning. An upper level low west of Attu is becoming vertically stacked with a nearby surface low. A small 105 knot jet streak is aligned northwest to southeast across Southwest Alaska and extending into the Gulf. A surface low is forming over the northern Gulf this morning in the left exit region of the aforementioned jet streak. Some limited moisture is trying to condense out as flurries or very light snow across portions of the Cook Inlet region, mainly along the Chugach and Kenai Mountains. Additional shower activity is developing over the open Gulf in response to the low forming. && .MODEL DISCUSSION... The models on the synoptic scale remain in excellent agreement through Friday night. Forecast confidence is high. Areas of uncertainty consist of peak wind speeds through some of the gaps today, and more significantly, the impacts from the upcoming low and front which will be moving into Kodiak late Friday night. Temperatures will be right near freezing with northeasterly winds throughout the atmosphere. Thus, there will be a very small space between 33 degrees and rain and 31 degrees and snow with this event. && .AVIATION... PANC...Flurries or very light snow may briefly cause MVFR conditions this morning, but VFR conditions will be predominant. VFR conditions are expected from this afternoon into this weekend. A period of winds with gusts to 20 mph are possible this afternoon, but will diminish by sunset. Light winds are then expected tonight through Friday morning. && .SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3/Today through Saturday night)... An upper level low and short-wave trough will dive southward across Southcentral today, brining a reinforcing shot of arctic air, which will prolong the ongoing stretch of below normal temperatures. A weak surface low will deepen along the north Gulf coast, out ahead of the short-wave. Expect snow to develop from Cordova northward into the Copper River Basin this morning, then exit quickly eastward this evening. Snow accumulation will be light. There will also be some areas of light snow (or flurries) from the western Kenai to Anchorage and the southern Mat-Su today, but this looks even less impressive. Any accumulation will likely be confined to the western slopes of mountains as cold advection and upslope flow kicks in this morning. Skies will clear behind the upper trough short-wave tonight, with temperatures across much of the region dropping to 5 below to 10 above zero - what can be considered "bitterly cold" for this time of year. Meanwhile, strong gap winds will develop along the coast today through tonight thanks to tightening pressure gradients, cold air advection, and strong subsidence from the upper level short-wave moving through. Winds will begin to diminish Friday, but that trend won't last long. A frontal system from the Bering Sea will enter the southwestern Gulf Friday night causing pressure gradients to tighten once again. Expect a triple point low to develop south of Kodiak on early Saturday, then continue eastward across the Gulf Saturday afternoon through Saturday night. As a result, this storm system will primarily impact Kodiak Island the Gulf waters. Based on this southerly low track, there won't be much in the way of warm air advection with this low. The south end of Kodiak Island may see a mix of rain and snow, or possibly even a changeover to rain. However, for Kodiak City and more northern communities, this looks to be an all snow event. There will also be quite a bit of wind accompanying the snow, primarily out of the northeast direction. This could lead to limited visibilities in blowing snow, but the onshore flow in Kodiak City tends to not be favorable for white-out conditions because the influence of above freezing water temperature tends to cause air temperatures to quickly rise to near freezing and limit the ability of the snow to effectively blow around. Of course, we are near the climatological minimum of sea surface temperatures, so the warming effect is not as significant. In any case, will need to consider issuing a Winter Weather Advisory for Kodiak as we get closer in time. As for Southcentral, expect to remain cold and mostly dry through Saturday night. There will be some moderation of temperatures Friday through Saturday, but still expect high temperatures to remain below freezing for all except perhaps a few locations right along the Gulf Coast. && .SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3: Today through Saturday)... Quiet conditions are seen this morning across the region, with mostly cloudy skies over the Kuskokwim Delta and clear skies elsewhere. Below zero temperatures are observed over many areas as well. Mostly sunny skies will continue today as a ridge builds between two upper lows. A front will move onshore early Saturday morning, bringing snow predominately to the Bristol Bay area. As the front will be weakening, snow totals do not look to be overly impressive with likely a few inches occurring along the coast. Brief periods of reduced visibility are likely as well in gusty southeasterly winds. Precipitation is likely to change to rain over the Alaska Peninsula. && .SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through 3: Today through Saturday)... A front tracking across the Bering will bring snow and blowing snow to the Pribilofs this evening into early Friday morning leading to periods of reduced visibility. Precipitation will change to rain thereafter. A strong ridge in the North Pacific combined a long southwesterly fetch will keep precipitation all rain over the central and eastern Aleutians. Colder air behind the aforementioned front along with a number of disorganized upper troughs and weak surface lows will allow for the persistence of snow showers into the weekend. && .MARINE (Days 3 through 5: Saturday through Monday)... Gulf: A low moves over the Northern Gulf through Mon. Its front extends across the Gulf through Mon. Model agreement is good. Widespread small craft winds and waves with gale force gap winds are expected through southern Cook Inlet and Shelikof Strait until early Sun. Waves to 14 feet are possible for Cook Inlet and Shelikof Strait. As the low moves east of Kodiak Island, a gale force barrier jet develops from the Barren Islands along the North Gulf Coast, diminishing Sun into widespread small craft winds through Mon. Seas to 18 feet across the Southern Gulf will subside Mon. Bering: A central Bering low complex moves into western Alaska through Monday. Weak high pressure moves across the Bering through Mon. Model agreement is good. Widespread small craft winds diminish Mon. Seas to 16 feet over the western Bering on Sat, subsiding. A well developed low and front passes south of the Aleutians through Mon. Widespread small craft winds south of the Aleutians becomes gale force winds into the southern Bering Sun and Mon. Seas to 12 feet south of the Aleutians through Mon. && .LONG TERM FORECAST (Days 4 through 7)... The long term forecast begins late Saturday with a ridge centered over the state surrounded by a trio of upper-level shortwaves. The biggest concern is the elongated shortwave situated over the Gulf of Alaska and extending west over the AKPEN. This feature will be associated with two surface lows. The first of these looks to be somewhere over the northern Gulf Saturday night, with snow likely for Kodiak Island and across the immediate Gulf coast. The second low is weakening system that looks to produce snow across coastal and interior Bristol Bay. By late Sunday, the first of these lows moves toward the Alaska Panhandle while the second dissipates. Given this, interior Southcentral and locations along the Kuskokwim Valley remain mainly clear, dry, and cold through Monday. By late Sunday, a shortwave over the central Bering will shift east, with its associated surface front moving over the Kuskokwim Delta. These features continue to work east, moving over Southcentral Alaska by Tuesday with another round of light snow through early Wednesday. Colder air advects back over the region in the wake of this system before another frontal system approaches the western coast with more snow for Southwest Alaska. && .AFC WATCHES/WARNINGS/ADVISORIES... PUBLIC...NONE. MARINE...Gale: 120 121 130 131 179-185 411 412 414. Heavy Freezing Spray: 121 129 130 139 160 180 185. && $$ SYNOPSIS AND MODEL DISCUSSION...JPW SOUTHCENTRAL ALASKA...SEB SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...AP MARINE/LONG TERM...MK/TM