Weather Service Report


392 
FXAK67 PAJK 231525
AFDAJK

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
625 AM AKST Sun Feb 23 2020

.SHORT TERM...Remember the uncertainties of yesterday? Some of our
concerns were realized overnight. For starters the baroclinic low
that developed offshore became stronger than forecast. Cross Sound
and Skull Island both reported small craft winds from the east
during large periods. Widespread mixing was not confined to marine
areas but spread into many communities in the advised areas of
winter weather. Gustavus, Juneau, Hoonah, and Sitka all reported 
temperature rises between 35 to 40 degrees overnight. These new 
warm temperatures had to be considered in the new equations. But 
as noted by colleagues earlier, the stronger low also spawned 
stronger offshore easterlies in the low levels. And this helped 
dry the atmosphere. Thus, forecasted precipitation has been late 
with a few exceptions. To account for this, we curtailed model QPF
this morning and curtailed less through time until mid-morning. 
All of these factors caused us to cancel the Sitka advisory as the
window for our forecasted snow amounts had decreased by half as 
it rained much of the night. We also did away with the 
Hoonah/Tenakee advisory, as both temperatures and late 
precipitation arrival demanded it. 

One other observation was that the low may have set up a little
farther west than originally thought. Likewise, the heaviest
precipitation overnight likely occurred offshore. Pelican could
have been in these bands. Temperatures in the Pelican area have
remained cooler than Sitka all night, below freezing at times.
Thus we felt good enough to leave the Pelican winter weather
advisory. Juneau, on the other hand was another case. Greatly
affected by the drying offshore easterlies, snowfall amounts had
to be lowered early. Yet bands could still develop later this 
morning and could prove intense at times. However, dry slotting 
on satellite allows doubt to creep in, and thus far amounts have 
been disappointing. But warming was not as rampant in the Juneau 
area overnight, and thus temperatures would do little to dampen 
accumulations. 

Two spots where snow appears greater than forecast were Haines 
and Yakutat. The visibility in Haines dropped below 2 miles late 
yesterday evening and has consistently been low all night. Webcams
also reveal snow squalls. With light winds, we felt confident 
enough to upgrade the advisory to a winter storm warning for total
of 5 to 8 inches of snow. Yakutat was always thought to be on the
storm's edge, thus our forecasts more than anything hedged on 
snow chances. Its dive in visibility early this morning gives 
evidence that the low to the south took a slightly more westerly 
track than forecast. Yakutat is one to watch for a possibly new 
advisory this morning. 

Small craft westerly winds across the gulf will begin to weaken
but seas demand small craft advisory extensions into Sunday
night. Winds are largely southerly in the central Inner Channels
(affected by the low offshore), light northerly in Upper Lynn 
Canal, and light northwesterly in the southern Inner Channels. 
Easterlies increase through the gulf ahead of a new front lifting 
north late Monday. Temperatures were warmed ahead of the system, 
but we feel confident that for most areas of the Panhandle, the 
precipitation will begin as snow. How much is still too early to 
say for sure. There could also be some wind issues in the far 
south, especially from Ketchikan to Prince of Wales Island. 

Most edits were made to adjust storm totals with new trends
overnight. Forecast confidence is moderate. 

.LONG TERM.../Tuesday through Sunday as of 10 pm Saturday/Very 
active long term period as at least two or possibly three storms
take aim at the gulf. This is all made possible by the main 
Pacific storm track terminating in the Gulf of Alaska throughout 
next week. This only starts to change late week into next weekend 
as the mostly zonal flow gets disrupted by a deeper trough/ridge 
pattern developing in the gulf.

Overall changes to the forecast were rather minor with most
guidance falling in line with each other through Thu night. In 
fact the main deviation from consensus in this period was from 
the ECMWF which was favoring a farther west storm track then most 
other models. Forecast still trending toward a somewhat mild and
damp forecast as SW flow persists across the panhandle. Several
troughs/front will move through the area bringing more precip. 850
mb temps will generally be in the -4 to -7C range which will mean
mostly rain for the southern half of the panhandle and possibly
some switching between rain and snow for the north through the
period. Snow accumulations may vary but should be below advisory
criteria.

The late week into the weekend period is the most uncertain part
of the forecast as the developing trough/ridge pattern aloft is
not very well represented by guidance yet. Surface features either
have another strong low taking aim at the panhandle, or are much
farther south with the same storm. However, the general trend
retains the rather mild and damp weather that we have been dealing
with earlier in the week. Favored WPC and NBM for updates where
needed.

&&

.AJK Watches/Warnings/Advisories...
PUBLIC...Winter Weather Advisory until 3 PM AKST this afternoon for 
     AKZ025.
     Winter Weather Advisory until noon AKST today for AKZ022.
     Winter Storm Warning until 3 PM AKST this afternoon for AKZ019.
MARINE...Small Craft Advisory for PKZ021-022-041>043-051-052. 

&&

$$

JWA/EAL

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