147 FXAK68 PAFC 172312 AFDAFC Southcentral and Southwest Alaska Forecast Discussion National Weather Service Anchorage AK 312 PM AKDT Tue Mar 17 2020 .ANALYSIS AND UPPER LEVELS... Two low pressure systems are our focus today. The first is a weak low pressure system moving northeast up Cook Inlet. Surface observations show the barrier jet and turnagain winds beginning to set up as expected with this system. RADAR also shows precipitation moving up the Cook Inlet. The backside of this low is moving through southwest AK, with RADAR and satellite showing precipitation coming to an end. This system is being supported in the upper levels by a 500MB shortwave trough currently over Southwest AK and diving southeast. It should be noted that this trough has a push of colder air behind it, depicted well at the 850MB level. The other system is a large low pressure system just moving into the western Bering Sea. Satellite shows it is a mature and has a well wrapped occlusion. Its front is currently pushing through the western Aleutians. && .MODEL DISCUSSION... Models are in good agreement through the short term forecast. As mentioned in the previous discussion, there was a change in driving cold air more southerly behind the passage of the low currently working its way up the Cook Inlet. However, models all agree on the change so we have adjusted the forecast. Since models are agreeing even when trending towards new solutions, we have high confidence in the forecast going forward. && .AVIATION... PANC...MVFR to IFR conditions in snow are expected into early Wednesday morning, then should improve to VFR by late morning. Light winds are expected. && .SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)... The upper level trough over southwest Alaska will continue to track east. This should bring a shot of precipitation to Southcentral Alaska as it moves east. The main upper low will drop southeast from the Iliamna area across the Barren Islands to the Gulf of Alaska overnight. The surface low forming in the base of this upper trough will be near the southern Kenai Peninsula this evening and track to the east and southeast overnight. Conditions are expected to remain cold enough from the Susitna Valley and Copper River Basin to support snow. South of these areas enough warm air should move over the Kenai Peninsula and Prince William Sound to result in a mix of rain and snow or all rain. Colder air will flow back across the region tonight as the upper trough moves southeast. An upper level ridge then builds over the Bering Sea coast by Wednesday morning. How fast conditions dry out is the concern. It is likely some snow showers will persist into the early morning for the Cook Inlet to Susitna Valley region. The Copper River Basin will be slower to dry, thus we will hold on to snow showers through the morning, though these should be scattered and have little accumulation. The outflow returns Wednesday and we should see outflow wind in the usual places of the Chugach Mountains, Whittier, Valdez/Thompson Pass and the Copper River Delta. The wind is not expected to be very strong, generally remaining below 30 mph. The Ridge will slowly move across the southern mainland Wednesday and be pushed east Thursday as another front moves into the Bering Sea coast. As this front moves through, moisture returns to the southern mainland along with snow or rain and snow likely. && .SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3)... A front is currently tracking across Southwest Alaska bringing rain and snow to the Bristol Bay region and all snow to the Kuskokwim Delta. As temperatures are near freezing, only minimal accumulations are expected through the remainder of the afternoon. A ridge will build in this evening in the wake of the front. Thus, skies will clear overnight and winds will diminish, leading to the potential of fog developing over much of the area into Wednesday morning. Another front will move over Wednesday night and light rain/snow is likely through Thursday. A series of upper level shortwaves Thursday afternoon through Friday morning will keep snow showers in the forecast for mainly the areas of Bethel to Hooper Bay to Kipnuk. Weak upper level ridging is expected to move into areas along the AKPEN and Bristol Bay area keeping the area dry with the normal upslope regions of the Alaska Range experiencing continued snowfall. .SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through 3)... A strong front is bringing gusty southwesterly winds and rain to the western Aleutians. This will track west to east through Wednesday, however as it will be relatively fast moving, impacts should remain minimal. An upper level shortwave will move across the Bering and Aleutian Chain Thursday afternoon through Friday afternoon bringing a mix of rain and snow. An upper level ridge will begin to move over the western Bering and western Aleutian Chain Friday afternoon. && .MARINE (Days 3 through 5 Fri through Sun)... Due to a triple point low in the northern Gulf Friday, expect gale force winds to occur through channels including Shelikof Strait, the Barren Islands and through gaps and passes on the Pacific side of the Alaska Peninsula through Saturday morning. Following this, there are indications that another triple point low will spin up. If this plays out, expect similar winds in the aforementioned channels through Sunday. A gale force front over the Bering will continue to push northeastward before it exits the Bering Friday. There is moderate confidence that another front will enter the western Bering Friday night. Forecast challenges include timing and strength. If the faster and stronger solution holds, gale force winds will be possible in the western Bering through Sunday. && .LONG TERM FORECAST (Days 3 through 7 Fri through Wed)... On Friday, an upper level ridge looks to move across the Bering and into southern Alaska. Similar to last week, warm temperatures and moist conditions will advect into the Aleutians and the Bering Sea following the backside of the ridge through Saturday. Behind this, an upper level trough splits this upper level ridge with another upstream. This looks to bring westerly flow to the Southwest which will propagate precipitation into the region through Sunday. This active weather pattern will continue through the middle of the week. && .AFC WATCHES/WARNINGS/ADVISORIES... PUBLIC...NONE. MARINE...Storm Warning 177. Gale Warning 130>132 170 173>176 178 179 185. FIRE WEATHER...NONE. && $$ SYNOPSIS AND MODEL DISCUSSION...BB SOUTHCENTRAL ALASKA...SA SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...AP/MV MARINE/LONG TERM...CK