Weather Service Report


848 
FXAK67 PAJK 221340
AFDAJK

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
540 AM AKDT Thu Jun 22 2017

.SYNOPSIS...Low pressure in the eastern gulf will dissipate this
afternoon allowing a ridge of high pressure to extend across the
northern and eastern gulf. A weather front advancing into the 
central gulf Friday morning will push the ridge into the
Panhandle. Meanwhile low pressure persists across Canada.

&&

.SHORT TERM...Thursday through Friday night...The low responsible
for the convective air mass that has affected Southeast Alaska 
for days still churns but in an aged, decrepit state. Hence we 
keep scattered showers going through the day in the hopes that 
they finally end this evening for all areas. There have been some 
breaks overnight between showers, but these have resulted in some 
very low cloud decks occasionally forming and not any 
quintessential fog. As the low ceases to exist tonight, a ridge of
high pressure assumes control, and conditions will be much more 
conducive to patchy fog development Friday morning. 

A front entering the central gulf Friday will shove high pressure
over the Panhandle. This will prima facie pump a warmer, more 
stable air mass into the region. While we are currently 
forecasting high temperatures of 5 to 10 degrees warmer on Friday,
it is concerning that models are seeming to slow the warming at 
850 mb. With synoptic wind components very light, we should expect
mainly channel breezes to develop Friday, and this can limit
heating along immediate shorelines where the majority of our
communities are situated. Significant downsloping winds appear to
be absent as well. Nevertheless, MOS numbers are still buoyant. 
Thus, we keep the numbers high at this time.

A chance of rain is reintroduced Friday night as the front nears
the coast. But because of the front's negative tilt, the chance of
rain will remain generally confined to the outer coast at least
initially Friday night. We bring the chance of rain farther 
inland on Saturday. 

NAM was the primary model of choice, although elements of the GFS
and ECMWF came in handy. Confidence is good to average for the
period. 

.LONG TERM...Saturday through Thursday...As of 9 PM 
Wednesday...Period begins with low pressure system in the S 
central gulf and ridge axis over the panhandle. Models in decent 
agreement with the low moving towards the central panhandle Sat 
night into Sun before moving slowly inland Mon. Surface ridge is 
progged to develop over the gulf early next week and push eastward
through mid next week. Model solutions diverge by mid next week 
with high pressure pushing E as low pressure moves into the gulf. 

This will result in increased PoPs Sat into early next week before
a drying and warming trend through mid next week. Inherited
forecast represents this well, but did increase E winds in Cross
Sound to advisory levels for about 6 hours as high pressure moving
E interacts with the low moving into the gulf. 

&&

.AVIATION...Scattered showers will cause some MVMC conditions
today from Haines south. These conditions should improve markedly
by this evening with shower activity ceasing and clearing taking 
hold. Saturated conditions in Ketchikan, Petersburg, and Gustavus 
have necessitated some morning IFR tempos for ceilings. Confidence
in impactful patchy fog early Friday morning at central/southern 
TAF Sites is low enough to omit at this time.


&&

.MARINE...With a low filling in the gulf and high pressure
ready to expand across the region, we expect light winds through
Friday. Thermally driven low pressure across Canada may at times
enhance southerly winds through northern Lynn Canal. A front
entering the gulf Friday will increase easterlies across the gulf.
Cross Sound will increase to small craft by Saturday. 

&&

.AJK Watches/Warnings/Advisories...
PUBLIC...None.
MARINE...None.

&&

$$

JWA/BC

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