Area Forecast Discussion
Issued by NWS Medford, OR
FXUS66 KMFR 291658
Area Forecast Discussion
National Weather Service Medford OR
958 AM PDT MON AUG 29 2016
.DISCUSSION...The forecast was updated to reflect increased cloud
cover with cirrocumulus arriving from the southwest, and also
clouds that formed overnight at about 10K FT in Jackson County
with contribution from the smoke emanating from the Gap Fire in
the Seiad Valley. It was also updated to slightly expand the
coverage where there is a slight chance of thunderstorms on
Tuesday afternoon. It now extends from the southern Oregon
Cascades northeastward across northern Klamath County into northwest
Lake County. The Tuesday afternoon risk reflects the latest timing
of a shortwave trough that is presently still far offshore from
central California. The risk of thunderstorms is small. But, cells
could produce a few lightning strikes and the trough will be a
fast mover. Thus, any thunderstorms will not produce much
The other short term concern is gusty winds and low humidities.
Westerly winds will increase this afternoon and evening, with the
strongest winds east of the Cascades. A red flag warning remains
in effect for portions of Klamath, Lake, and Modoc Counties. It
will be dry and windy on the east side again tomorrow. A focus for
the afternoon package will be on the possible need for the
issuance of a new headline.
.AVIATION...29/12Z TAF cycle...Along the coast and over the coastal
waters...widespread IFR cigs will persist most of the morning.
There`s a chance CIGS could improve to MVFR in the afternoon, but
confidence of the timing is low. The onshore flow has increased
enough for low clouds to move further inland. Right now Roseburg is
clear, but the low clouds are slowly advancing towards it. Clouds
could sneak into to Roseburg briefly this morning but confidence is
low to medium on the timing and the event happening. For now went
with MVFR cigs at 15z, but this will need to be monitored closely, so
watch for updates on this. Elsewhere, VFR cigs will continue through
the TAF period. However, smoke and haze will impact airspace with
lower visibilities near the Gap Fire in northern Siskiyou County
this morning and could spread north into Jackson County this
.MARINE...Updated 830 AM PDT Monday 29 August 2016...A quiet pattern
is expected for most of the week. South winds will increase this
afternoon well ahead of a front which will move onshore Wedneday
morning. Conditions will remain below Small Craft Advisory criteria.
More weak fronts will follow Thursday through Friday, but none of
them are expected to bring small craft conditions. Small craft
conditions will return next Saturday at the earliest. -JRS
.PREV DISCUSSION... /Issued 455 AM PDT MON AUG 29 2016/
The mirage of the transition to a wet pattern for the later half
of the week into the weekend continues to dry up as we approach
it. However, a much welcomed cooling (at least for me) for the
next several days through the weekend.
Models and forecast continue on track with strong wind low
humidity event on the east side this afternoon into the evening
with pressure gradient tightening from west to east. This
increased surface pressure gradient flow will also be enhanced by
strong winds up to 700 mb on the east side in the afternoon into
the evening with good mixing. Up valley flow in the west side
valleys will also be stronger than the past several days with the
tighter gradient. The upper sheild of smoke from the fire near
Seiad Valley should push to the north as the winds up to 700 mb
increase in that area during the day, but there may still remain
low smoke t inhibit heating in that area.
the upper level trough moves closer to the coast tuesday, bringing
increased moisture feed as southerly flow increases. This
increased moisture into the region with weaker winds up to 700 mb
should keep the wind/humidity combination below red flag criteria.
Models are indicating elevated instablity straddling the Cascades
at 18z as a strong vort moves through, but we will be nowhere near
the convective temp with cloud cover over the region in that area.
Another strong factor inhibiting convection is very low 700-500
RH`s below 20 percent in Northern California. the most favorable
areas for convection is in the northern Cascades where the mid
level rH`s are above 60 percent, and even there steering winds are
from the SSE at 20-30 kt and very few bolts are likely to be put
down before those that do develop move out of the region.
Westerly surface flow to southwesterly 700 mb flow shifts moisture
east and with the left exit region to the north of the region
there will be very little precip with the next front, but a
cooler air mass will bring temperatures to near normal Wednesday
and Thursday and into the weekend. Sven
FIRE WEATHER...Updated 230 AM PDT Monday 28 August 2016...Dry
weather continues today with temperatures averaging 2-4 degrees
cooler compared to yesterday for interior locations. The main
concern over the next couple of days will be gusty winds, mainly
east of the Cascades with low relative humidities this afternoon and
again Tuesday afternoon and evening. A red flag warning remains in
effect from 12 pm until 8 pm pdt today for these conditions. See
PDXRFWMFR for more details. Models show 700 mb winds between 20-25
kts and with a shortwave trough moving into the area Tuesday and
there may be a better chance for these stronger winds to surface,
but Rh`s are expected to be higher, so not as confident red flag
conditions for winds and low relative humidities will be met. Later
shifts will need to take another look at this.
Speaking of the shortwave trough, the models are in good agreement
with timing of this feature. Pattern recognition suggest most of the
instability should be mainly north and northeast of our area and
this is being supported by the models. Additionally, most of the
moisture is around 500 mb and its` possible there may be sufficient
cloud cover to limit the amount of heating and thus keep most of the
instability in check. Therefore have kept the slight chance for
thunderstorms confined to the northern Cascades and northern fire
zone 624 and northwest 625. Keep in mind the coverage of
thunderstorms could vary depending on the timing of this shortwave
trough. If it comes in faster, then the best chance for
thunderstorms will be north and northeast of our area.
The models are in pretty good agreement in the overall pattern from
Wednesday into next weekend. Basically we`ll have an upper trough
over the PAC northwest with a ridge building in the south central
plains by mid week, then shifting into the southeast U.S. late in
the week into next weekend. This will result in cooler temperatures
and a slight chance of precipitation, mainly over the northwest part
of the region Wednesday, Thursday and Friday. -Petrucelli
OR...Red Flag Warning until 9 PM PDT this evening for ORZ624-625.
CA...Red Flag Warning until 9 PM PDT this evening for CAZ285.
Pacific Coastal Waters...None.