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Area forecast discussion 
National Weather Service Medford or
814 PM PST Sat Nov 22 2014

Discussion...there are still some rain and snow showers out
there this evening, especially in the Cascades due to moist
onshore flow. Web cams are still showing some pretty good snow
showers around Diamond and Crater Lakes. A Winter Weather Advisory
(npwmfr) remains in effect until 10 PM PST. Showers will end
later this evening and overnight as heights begin to rise and
onshore flow lessens. Have adjusted tonight's minimum temperatures
a tad lower based on some clearing expected during the first part
of the overnight...especially east of the Cascades and in northern
California. Since the boundary layer will remain quite moist,
expect some low clouds and fog to develop in many locations toward
sunrise. Expect these conditions to improve by late Sunday morning
or early Sunday afternoon. A warm front will lift northward along
the coast later Sunday night and Monday. This may bring some light
warm advection precipitation to areas along and west of the
Cascades. Spilde

&&

Aviation...for the 23/00z taf cycle...isolated to scattered
showers will diminish this evening and clouds will thin out. As a
result, areas of LIFR low clouds and fog will likely develop
overnight, especially in the valleys west of the Cascades. Some
lower ceilings and visible are also possible over the east side and in
northern California, but confidence in these occurring is lower
than it is west of the Cascades. Spilde

&&

Marine...westerly swell will persist the remainder of this
weekend then slow diminish into next week. A warm front will lift
northward through the waters Sunday night into Monday with light
south winds and some light rain. Mainly light south to southwest
winds are expected through midweek. A frontal system will move in
Wednesday night into Thursday that may bring an increase in south
winds and seas. Unsettled weather is expected late this week into
the weekend. Spilde

&&

Previous discussion... /issued 222 PM PST Sat Nov 22 2014/

Discussion...moist onshore flow will continue through this evening
with showers moving in from the west. A few isolated storms
develop in the last couple of hours in Coos and western Douglas
County as a cool pool aloft combined with daytime heating has
created sufficient instability. Could not rule out a few more
isolated storms in the same areas early this evening. Meanwhile
snow showers will continue above 4000 feet with accumulating snow
likely around crater and Diamond Lake areas. Snow showers are
likely near the Lake of The Woods, but were not expecting any
accumulation. Weak ridging builds into the area tonight and
showers will be on the decrease with most ending after midnight.
With ample moisture on the ground, low clouds and fog are likely
to develop for the Westside valleys if there's enough clearing.

Weak upper ridging moves into the area Sunday. It's not a Sharp
Ridge, but rather flat, but it should be enough to shift the storm
track north of our area and we'll end up dry. The models show a warm
front moving into the area Monday. The NAM is now the most aggressive
with respect to quantitative precipitation forecast amounts. The ec and GFS show little or nothing.
Compared to yesterday the GFS has trended weaker and the ec continues
to remain dry. Gut feeling is the NAM may be overdone given 500 mb
heights are rising as the upper ridge starts to amplify. For now
kept in slight chance to chance probability of precipitation west of the Cascades. The upper
ridge axis builds into the area Tuesday with continued dry
conditions, although the ec hints at some warm frontal precipitation
riding over the ridge and possibly bringing light precipitation to
the northwest part of the area. There's a good chance we'll have low
clouds and fog for most of not all Westside valleys given that we
have sufficient moisture on the ground and a stable atmosphere
Tuesday morning and probably again Tuesday night. -Petrucelli

Long term...Wednesday through Saturday...deterministic and ensemble
model runs continue to show good consistency in an upper ridge
holding over our area Wednesday and Wednesday night. Precipitation
will be held at Bay to our west during the period, but inversions
are likely to be strong and thus valley fog is still a good bet.

There is a bit more consistency regarding the breakdown of the ridge
and the arrival of new precipitating systems late this week into
next weekend. Ensemble means support deterministic runs which
show a trough or series of troughs coming into our area during
this period. While spreads are still higher than I would like to
see, the spread appears to have more to do with the timing of the
troughs than their existence. That said, confidence is still not
high enough to go a lot higher than climatology for pops, but I did
raise pops, especially later Friday into Saturday. -Wright

&&

Mfr watches/warnings/advisories...
or...Winter Weather Advisory until 10 PM PST this evening for
orz027-028-617-623-624.

California...none.

Pacific coastal waters...Small Craft Advisory for hazardous seas
until 4 PM PST Monday for pzz350-356-370-376.

$$

Mas/map/trw

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