Scientific Forecaster Discussion
Southeast Alaska forecast discussion
National Weather Service Juneau Alaska
540 am akst Sat Mar 8 2014
Short term...a gale force low over the east-central Gulf will move
northwest to the north-central Gulf this afternoon. Second wrap of occluded
front is over the far eastern Gulf and will weaken and drift onshore
through this evening. A low pressure trough will move NE across the
area tonight. Preferred the 00z ec/Gem/GFS handling of these
features...and this was close to previous pressure field...so did
not change it.
Main forecast issues will be ptype/amounts and winds. Right now
the rain/snow line is just S of a pajn-paoh line. Warmer air will
continue to push northward and should change the snow to rain in the
pajn-pael corridor by late this morning. It will take much longer
for the warmer air to move into the pahn/pagy areas as low level
flow will remain northerly until late tonight. This will keep them as
snow until late tonight...when winds become S and temperatures rise into
the middle to upper 30s. The precipitation will become showery from the west
through tonight...reaching all but the far northern and southeastern Inner
Channels by late tonight.
The second wrap feature has fairly heavy precipitation with it...with
the highest precipitation rates along a pasi-pahn line. Think this will
continue today...then shift eastward but diminish tonight as trough
moves onshore. Given that much of this will be snow in the pahn
area...decided to extend the ws warning until midnight
tonight...along with the pagy ww advisory. Kept the ww advisories for the
pajn/paoh/pags/pael areas until 9 am this morning. Pahn could see
well over 1 feet of snow as flow at 850 mb is southeasterly...which is
upslope for them. Pagy will get a decent shot of snow as
well...and they could get close to warning levels. Decided to
keep snowfall there at high end advisory levels...generally
4-6 inches today and another 2-4 tonight. The pajn/pags/pael/paoh
areas could see up to 4 inches of new snow before changing to
rain later this morning. Allowed the ww advisory for Hyder to expire
at 5 am as the precipitation there has diminished somewhat...and any
precipitation should become rain by late this morning anyway.
As for winds...strongest winds are in a band just ahead of the
second wrap occluded front. Gale force S-southeast winds are occurring
over the far eastern Gulf and near coastal inner channel areas
including Clarence Strait. These winds will slowly decrease
through the day as the second wrap weakens slowly...with winds
below gale force by late this afternoon. Kept the strong wind
headline through noon for pasi area. Rest of the Gulf should have
Small Craft Advisory level winds...with most of the Inner Channels at Small Craft Advisory as well
outside the gale area. These winds should diminish below Small Craft Advisory
tonight once the trough moves by the area.
Long term...models remain in general agreement through early
next week with continued onshore flow and a slight warming trend.
The European model (ecmwf) and Gem were used to refresh the inherited forecast
package through Monday evening. Over the northernmost
Panhandle...temperatures will remain cold enough for snow. The
frontal passage will continue to weaken with decreasing quantitative precipitation forecast
values. As another developing frontal system approaches the
eastern Gulf Monday afternoon...models slightly divert for timing
and intensity for the incoming front.
The wpc ensemble approach continues hinting a warming trend with
the incoming front due to its subtropical origin. Ahead and along
the frontal boundary...winds will increase to meet gale force over
the outer waters and immediate central Panhandle coastline. The
front will move onshore over the Panhandle Monday night through
Tuesday...then stall over the central and southern areas through
early Wednesday morning. Rain may become heavy at times with ample
subtropical moisture and slowing down the frontal system. Model
differences become larger by middle week and the wpc ensemble
approach should work nicely for the remaining long term periods
with another frontal passage on Thursday and Friday.
public...Winter Weather Advisory until 9 am akst this morning for
Strong wind until noon akst today for akz023.
Winter Weather Advisory until 1 am akdt Sunday for akz018.
Winter Storm Warning until 1 am akdt Sunday for akz019.
Marine...Gale Warning for pkz022-033-036-041>043.
Small Craft Advisory for pkz012-021-031-032-034-035-051-052.