Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service Medford or
814 am PDT Friday Mar 27 2015

Discussion...no update is necessary this morning. Visible imagery
is showing a layer of low stratus along the coast with patchy low
clouds and fog in the Umpqua basin southward to the Illinois and
lower Klamath River valleys. A cold front currently offshore will
move onshore this afternoon. So sunshine in many other areas this
morning will give way to clouds and showers this afternoon and
evening. Some instability will develop in advance of the front,
mainly from the Cascades to portions of the east side, so there
is a slight chance of thunder in these areas this afternoon and
evening. The front will move well inland later tonight and
showers will gradually diminish...ending last in areas near the
Cascades Saturday morning. Overall, it will be a bit cooler than
yesterday, but temperatures still may flirt with records in
northern California and over the east side. Spilde

&&

Aviation...for the 27/12z taf cycle...along the coast and the
deeper valleys just inland (umpqua/Illinois/lower klamath)
..LIFR/IFR ceilings/visibilities will persist this morning...Then lift to
VFR with areas of MVFR ceilings by this afternoon. Widespread MVFR
ceilings will return to the area this evening after a front moves
onshore. The lower conditions will persist tonight. The rest of
the west side to the Cascades...VFR will prevail initially...then
areas of MVFR ceilings will develop late this afternoon with the
front...and higher terrain will become obscured. Thunderstorms may
develop near the Cascades this evening...then diminish tonight.
The lower conditions will persist through tonight. East of the
Cascades...VFR conditions will persist through tonight...but
areas of higher terrain will becoming obscured this afternoon and
evening with some gusty winds. Isolated evening thunderstorms are
possible. Jrs/spilde

&&

Marine...updated 2 am PDT Friday 27 Mar 2015...a weak cold front
will move through the area today. High pressure will build in
behind the front later tonight and persist through the
weekend...winds will become northerly. Moderate west swell will
build Sunday afternoon and subside late Sunday night...bringing
Small Craft Advisory seas to the area. High pressure will weaken
Monday and a stronger cold front will move onshore Monday evening.
This will bring a round of Small Craft Advisory south winds and
seas to the area. Yet another front will move in Tuesday night.
Jrs

&&

Previous discussion... /issued 414 am PDT Friday Mar 27 2015/

Climate...
calender day record high temperatures were set Thursday afternoon at
3 of our 7 primary ASOS locations and 2 were tied. Records were
broken in Roseburg, Klamath Falls, and Mount Shasta city at 78f,
71f, and 77f, respectively. The Mount Shasta city record was the
most notable, in that it broke the old record of 73f by 4f, last set
in 1966. Record highs of 80f and 75f were tied at Medford and
Montague, respectively. The tied record in Medford was actually
last set in 1923, or 92 years ago.

For today, we expect records will be at risk of being tied or
broken from the California Cascade crest and upper Klamath basin
eastward. We're forecasting 70f in Klamath Falls and 75f in
Alturas. Today's record in Klamath Falls is 70f, set in 1966. For
Alturas, the record is 78f, also set in 1966. Btl

Discussion...
fog along the immediate coast has lifted only a couple of hundred
feet overnight and has, thus far, been slow to develop inland.
Despite the lack of high clouds and higher dewpoints, the current
temperature and dewpoint spread at Roseburg is the same as it was
this time 24 hours ago, and it's 1 degree greater at both Medford
and Klamath Falls. Thus, while we expect fog to form this morning
similar to yesterday morning, i've reduced coverage some inland of
about Grants Pass south and east of the Umpqua Divide.

A cold front approaching today will yield another mild day,
though guidance indicates 850mb temperatures over Medford to be
about 4c cooler today versus yesterday and 0c to 2c cooler east of
the Cascade crest. Expect it to be cooler at most locations,
though portions of Klamath, eastern Siskiyou, Lake, and Modoc
counties could be the same of slightly warmer due to appreciable
southwest winds and localized downslope warming. In short, a middle-
level cold front or pre-frontal trough is expected to develop
along or near the Trinity Alps north to the Siskiyou and Cascade
crests this afternoon through the evening with a secondary cold
front pushing inland from the coast this evening through tonight.
While precipitation amounts will be below a quarter of an inch for
all areas and a tenth of an inch or less for most locations, there
is a sharp enough front to yield some convective instability this
afternoon and evening. Thus, have continued with shower and slight
chance of thunder wording along and near the Trinity Alps to
Cascades areas.

Winds will become breezy today- enough to be of concern for anyone
conducting pile or other prescribed Burns. Expect them to pick up
from late morning through late afternoon and then gradually settle
down evening through overnight.

After today and tonight's front we expect a couple of weak upper
level shortwave troughs to breeze over the area this weekend. This
will result in intervals of cloudiness, somewhat cooler
temperatures, and some build-ups and possibly a sprinkle, at
times, over some of the higher peaks and ridges.

The next appreciable front is expected to arrive early next week.
Models overnight show a 500mb cold pool of note associated with
this system at a chilly approximate -30c. This bears watching, as
a system of this nature would surely result in gusty winds with it
and in its wake, as well as the possibility of a brief period of
wetting precipitation and some mountain snow. It still appears
we'll be on the southern edge of this storm system, so it's not
likely to be a direct hit for US. I did boost probability of precipitation some for this
system due to increasing model agreement and confidence.

As the day shift pointed out, the pattern looks to remain at
least somewhat active next week with no major weather system
currently in site through day 8. We will need to keep an eye out
for some cool and possibly frosty nights for some of the
agricultural areas since plant growth is so far ahead of normal
due to the record warm general conditions of the last 6+ months.
Btl

Aviation...for the 27/12z taf cycle...along the coast...LIFR/IFR
ceilings/visibilities will persist into Friday morning...then lift to VFR with
areas of MVFR ceilings by Friday afternoon. Widespread MVFR ceilings will
return to the area Friday evening after a front moves onshore. The
lower conditions will persist through Friday night. From the
Cascades west...VFR conditions will prevail initially...then areas
of MVFR ceilings will develop late Friday afternoon with the front...and
higher terrain will become obscured. Thunderstorms may develop Friday
evening...diminishing tonight. The lower conditions will persist
through Friday night. East of the Cascades...VFR conditions will
persist through Friday night...but areas of higher terrain will
becoming obscured Friday afternoon and evening and winds will
becoming gusty. Isolated evening thunderstorms are possible.

Marine...updated 2 am PDT Friday 27 Mar 2015...high pressure will
weaken today and a weak cold front will move through the area this
afternoon. High pressure will build in behind the front and persist
through the weekend...and winds will become northerly. Moderate west
swell will build Sunday afternoon and subside late Sunday
night...bringing Small Craft Advisory seas to the area. High
pressure will weaken Monday and a stronger cold front will move
onshore Monday evening. This will bring a round of Small Craft
Advisory south winds and seas to the area. Yet another front will
move in Tuesday night.

&&

Mfr watches/warnings/advisories...
or...none.

California...none.

Pacific coastal waters...none.

$$

Mas/jrs/btl

National Weather Service Glossary of Abbreviations