Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service Medford or
845 PM PDT Sat Aug 27 2016

Discussion...low clouds and fog have moved back into the coastal
area this evening. Onshore pressure gradient is similar to
yesterday so we do not expect the low clouds to spread beyond the
coastal range. High temperatures today were down 2 to 5 degrees
from yesterday and we expect similar temperatures for Sunday
before we start to see a more drastic cool down on Tuesday into
the lower to middle 80s for the Rogue Valley. The current forecast
covers this trend and no update to the grids was issued this
evening. /Fb

&&

Aviation...28/00z taf cycle...along the coast and over the coastal
waters...IFR conditions will return late this afternoon and lower to
LIFR tonight in low clouds and fog. The lower conditions will make
some inland progress tonight...but should stay west of Roseburg.
Coastal IFR conditions should clear by late Sunday morning or early
afternoon. Over the remainder of the area...VFR conditions under
clear skies will persist through Sunday. /Nsk



&&

Marine...updated 830 PM PDT Saturday 26 August 2016...a weak
pressure pattern will make for light winds through early next
week. Northwest swell between 2 and 4 feet and a south swell
around 2 feet will result in seas of 4 to 6 feet at about 9
seconds through the evening. Combined seas will gradually subside
to around 4 feet on Sunday. Winds will turn southerly and increase
on Monday, and several fronts will move through the waters
starting late Monday, but small craft conditions are not expected
at this time. /Nsk

&&

Previous discussion... /issued 745 PM PDT Sat Aug 27 2016/

Updated aviation discussion.

Discussion...the 12z models are in very good agreement through
Monday and compared to yesterday they have trended toward better
agreement for the remainder of the week. The most consistent of
the medium term models is the European model (ecmwf). Conditions on Sunday are
expected to closely resemble those of today. Modest cooling of a
few degrees will follow on Monday as a broad trough approaches
from the west and kicks the thermal trough farther inland.

Thereafter, our streak of nearly 3 weeks of above normal inland
temperatures looks to come to an end. There is still very good
agreement on a general change to a cooler, more active weather
pattern on Tuesday that will persist through the remainder of the
week. That said, most of the energy from the series of systems
will be focused north of our area...continuing the long dry spell
in southern Oregon and northern California. The probability of
precipitation in our area will generally be highest in Coos and
Douglas counties and usually not more than a slight chance.

The GFS and European model (ecmwf) now both indicate inland high temperatures from
Tuesday through Saturday will range from around normal to about 5
degrees below normal...mainly in the lower 80s on the west side
and mid 70s on the east side. Meantime...onshore flow will also
keep the coast a bit cool to near normal in the 60s. The weaker
cooling and lower probability of precipitation indicated by the
GFS GOES in concert with a solution of the bulk of the colder and
moister air remaining from northern Oregon northward.

In the short term, a deep marine layer will persist at the coast
with the potential for early morning drizzle to accompany low
clouds and patchy fog. Meantime, the skies inland will remain
largely clear with just a few wisps of cirrus. This will change on
Tuesday as a shortwave rotates northeastward from northern
California across south central Oregon into north central and
northeast Oregon. There is better agreement that this disturbance
will rotate through our area during Tuesday morning, which will
lower the risk of showers and thunderstorms in comparison with a
passage during the heat of the afternoon. The risk of
thunderstorms will be highest in north central Oregon, but the 21z
sref model does show some 0 to -1 lifted indices extending into
far northern portions of Klamath and lake counties. So, a slight
chance of thunderstorms is (barely) Worth mentioning.

A cold front will follow to the coast Tuesday night into Wednesday
morning with a slight chance to chance of showers at the coast and
in Douglas County. With support from subsequent model runs, one
could see raising the probability of precipitation for the Coos
and Douglas County coast area. It is already likely that Washington
and northern Oregon will receive a wetting rain. The main effect
for the remainder of our area will be cooler temperatures
accompanied by substantial mid-level cloudiness and perhaps a bit
of virga.

A cool, onshore flow with only a couple of weak embedded
shortwaves is likely to follow on Wednesday. This will continue a
slight chance of light coastal showers with a few clouds to
partly cloudy skies for most of our area. Confidence in the
timing and strength of features Thursday into the Holiday weekend
is not as high. But, the probability of precipitation has been
lowered in Harmony with the weakening trend shown in the GFS and
European model (ecmwf).

Aviation...28/00z taf cycle...along the coast and over the coastal
waters...IFR conditions will return late this afternoon and lower to
LIFR tonight in low clouds and fog. The lower conditions will make
some inland progress tonight...but should stay west of Roseburg.
Coastal IFR conditions should clear by late Sunday morning or early
afternoon. Over the remainder of the area...VFR conditions under
clear skies will persist through Sunday. Sk

Marine...updated 230 PM PDT Saturday 26 August 2016...a weak
pressure pattern will make for light winds through early next week.
Northwest swell between 2 and 4 feet and a south swell around 2 feet
will result in seas of 4 to 6 feet at about 9 seconds through the
evening. Combined seas will gradually subside to around 4 feet on
Sunday. Winds will turn southerly and increase on Monday, and
several fronts will move through the waters starting late
Monday, but small craft conditions are not expected at this time.
-Sk

Fire weather...updated 245 PM PDT Saturday 26 August 2016...dry
and hot weather will persist through the rest of the weekend over
inland areas. Low clouds and fog will persist near the coast.
Winds will be gusty east of the Cascades Sunday afternoon and
again Monday afternoon. Relative humidities will be low both
days...but winds will be slightly stronger Monday. Therefore a
Fire Weather Watch has been issued for orz624/625 and caz085. The
first in a series of fronts will move onshore Tuesday night.
Isolated dry showers and thunderstorms may develop east of the
Cascades Tuesday afternoon. It will also be cooler. The cooling
and moistening trend will continue Wednesday into next weekend as
more fronts move onshore. -Jrs

&&

Mfr watches/warnings/advisories...
or...Fire Weather Watch from Monday afternoon through Monday evening
for orz624-625.

California...Fire Weather Watch from Monday afternoon through Monday evening
for caz285.

Pacific coastal waters...none.

$$

Fjb/jrs/nsk

National Weather Service Glossary of Abbreviations