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Area Forecast Discussion (AFD)

Issued by Juneau, AK (AJK)

                            
103 
FXAK67 PAJK 212251
AFDAJK

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
251 PM AKDT Sat Apr 21 2018

.SHORT TERM...Some dense areas of fog arose this early morning in
Peril Strait, Gustavus, and Hoonah, before burning off mid-
morning. Residual showers persisted throughout the afternoon (and
even some ice pellets), as yesterday's frontal system exits and
drags the precip with it. Our next system we're looking at will
make its entrance late Sunday into Monday, followed by another
quick band of frontal precip late Monday night into early Tuesday. 

Temperatures at the 500 mb level are still in the mid -20C range,
which are below normal for this time of year. Temperatures Sunday
into early Monday morning won't be following a diurnal curve, as
some warmer, borderline-unstable air sneaks in. Maximum 
temperatures were lowered into Monday, following rain soaked 
cooling and some pockets of CAA that slip in behind the front. 
Minimum temperatures were raised for tonight especially, as cloud 
cover prevails for most of the short term. Temperature edits were 
done through a GFS blend and some local edits using MOS Guidance.

Rain showers will become more widespread throughout the panhandle
into tonight with some snow showers mixing in over the northern 
panhandle. QPF will be 2-3 standard deviations above normal during
this timeframe. POP was blended with some SREF, AKHIRESWarw, and
GFS and QPF the AKHIRESWarw and GFS, respectively. 

Pressure adjustments were made using a NAM/ECMWF blend to better
capture the "waves" associated with the second front. The biggest
change to the short term was increasing winds locally late sunday
night into Monday and increasing to gales along the outer coast.
Model agreement has been doing relatively well, however, the exact
timing and details of these next waves may need further fine 
tuning.

.LONG TERM.../Monday through Saturday as of 10 pm Friday/ Upper
trof will move NE across the area Mon-Tue. Another trof will 
amplify over the N-central PAC into the E Bering Sea. Ridging will
build downstream over western Canada. Models have trended toward 
a stronger ridge, and this will likely have an effect on a system 
moving toward the area for late Tue into early Thu. Still some 
important model differences to work out for this system and any 
following systems later in the week. Ended up basically staying 
with current forecast in long range, waiting to see if we get 
better agreement especially on Tue-Wed system.

Occluded front will be moving slowly E across the area Mon and Mon
night. Looking like most precip with this front will fall over the
NW half of the area. May have some gale force winds over the NE 
gulf early Mon but front will be weakening. Weak trof should move
in behind the front Tue.

Following occluded front appears to be weaker and holding up 
further W in latest model runs, but models have been inconsistent 
with it. Big problem seems to be how strong ridging builds over 
and E of the area. If the current models maintain the stronger 
ridge idea, later shifts may need to keep the front further W 
along with the stronger winds and precip. After Wed night,
forecast confidence drops off even more as the model differences
only increase. Overall, looking more like the southern panhandle
will not get as much rain as previously thought, which may not 
alleviate the abnormally dry conditions there.

&&

.AJK Watches/Warnings/Advisories...
PUBLIC...None.
MARINE...Gale Warning for PKZ041>043-051-052. 
     Small Craft Advisory for PKZ022-033-035-036-053. 

&&

$$

SS/RWT

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