Southcentral and southwest Alaska forecast discussion
National Weather Service Anchorage Alaska
500 am akdt Sat may 18 2013
Analysis and upper levels...
negative tilted upper level trough continues to hang from from
northwest Alaska southeastward through the western Gulf of Alaska.
The first vorticity maximum in the trough is pushing inland over the
north Gulf Coast early this morning while the second is digging into
the Gulf. The edge of higher moisture values ahead of the first
disturbance is evident on water vapor imagery...which signals the
decline of dynamic lift from southwest to northeast over the
southcentral. The remaining snowfall west of the chugach will
primarily be driven by cold advection from the west/northwest. The
southwest Mainland is entrenched in the gusty northwesterly flow
behind the Arctic front with isolated showers and below normal
temperatures.
Model discussion...
guidance remaining in great agreement with this late season snow
event and cold outbreak. Very similar timing and progression of the
upper trough briefly closing off then shifting to the east as a ridge
builds over the southwest Mainland and southcentral. Some slight
differences concerning a weak surface low in the Gulf but should not
have any implications on the current forecast. The NAM was preferred
in the short term.
Short term forecast...
southcentral Alaska...light snowfall will continue from the Susitna
Valley southward to the Anchorage bowl through the morning
hours...gradually tapering off by afternoon. Snowfall will linger
longest at higher elevations of the chugach and Talkeetna Mountains.
Unseasonable cold temperature will persist today with brisk
northwesterly winds continuing throughout the day. The next forecast
concern is how low temperatures fall tonight into Sunday morning.
With decreasing clouds throughout the day and a very cold air mass
aloft low temperatures are expected to drop rapidly into the 20s
early Sunday morning...flirting with record lows. Ridging overhead
into early next week will keep dry conditions with moderate
temperatures back to more reasonable levels but still slightly below
normal.
Southwest Alaska...northwesterly flow will begin to slacken today
over the Kuskokwim Delta as ridging builds in from the Bering Sea
bringing southerly winds and moderating temperatures. The Bristol Bay
region will see continued gusty northwesterly flow slowly lightening
through the day with partly sunny skies. A Bering Sea front will
return rain and snow to the Kuskokwim Delta on Monday while dry
conditions will persist for the Bristol Bay area.
Bering Sea and Aleutians...high pressure over the eastern Bering will
keep partly sunny skies and dry conditions on hand with some
lingering snow showers along the Alaska Peninsula. A North Pacific
low will send a warm front over the western Aleutians along with
strong southeasterly winds and rain. The front will progress to the
eastern Bering by Monday returning warmer temperatures...rain and
strong southerly winds to most of the chain.
Long term forecast...
a strong North Pacific system moving into the Bering Sea will promote
ridging over the southern Mainland. Dry conditions will persist with
near normal temperatures east of the Alaska Range with wetter
conditions west of the Alaska Range.
Aer/alu...watch/warning summary
public...Winter Weather Advisory 111 145
marine...
fire weather...none
Mtl may 13
