NWS Medford, OR wrote its last area forecast discussion before the first event at Jul 31, 7:52 PM PST, 4 hours 8 minutes earlier.
Area forecast discussion, Jul 31, 7:52 PM PST, 4 hours 8 minutes before
Area Forecast Discussion
National Weather Service Medford OR
852 PM PDT Tue Jul 31 2018
.SHORT TERM...The upper ridge is centered east of the area today
and will gradually shift further east on Wednesday while an upper
trough nears the Pacific Northwest coast. This trough is expected
to move inland late Thursday and Friday, centered to the north
over Washington and northern Oregon. This will bring lowered
temperatures to inland areas late this week.
On Wednesday, expect high temperatures across inland areas to be
a couple degrees cooler than today. Of note, winds will increase
some on Wednesday afternoon and evening. Gusty west to southwest
winds and expected for areas east of the Cascades Wednesday
afternoon and evening. In Modoc County, these gusty winds will
combine with very dry humidities and unstable conditions bringing
the potential for increased fire danger. A red flag warning
(RFWMFR) is in effect for portions of Modoc County on Wednesday.
West of the Cascades, expect northwest winds, which will be breezy
in the late afternoon into the evening. Smoke from area fires will
continue to affect areas across southwest Oregon, especially in
Josephine, Jackson, southeast Douglas, Klamath and Lake counties.
An air quality advisory (AQAMFR) remains in effect for these areas
in southwest Oregon due to smoke impacts on air quality. Air
quality levels will fluctuate with time of day and locations.
Models indicate smoke impacts may be greatest in the afternoon and
evening for many western valleys in Josephine and Jackson
counties. In the Klamath basin, smoke impacts may occur through
most the night and day due to smoke moving into the area from
western fires tonight then from fires to the southwest tomorrow
afternoon/evening. In Northern California, Siskiyou and Modoc
county will also continue to see some from fires in southwest
Oregon and to the south and southwest in California.
Along coastal areas, low marine clouds have spread inland again
this evening and will continue to spread into coastal valleys and
into potions of the lower Umpqua Basin tonight and tomorrow
morning, mainly northwest of Roseburg.
On Thursday, expect temperatures to cool around 5 to 8 degrees
across inland areas. Breezy northwest to west winds are expected
late in the afternoon and evening over inland areas. Also expect
marine push to bring low clouds to much of the Umpqua basin
Thursday morning, with the low cloud deck extending up to about
3000 ft MSL.
&&
.AVIATION...For the 01/00Z TAFs...Along the coast and over the
coastal waters...Areas of IFR cigs/vsbys will thicken and return to
the coast early this evening and spread into the coastal valleys
overnight. The lower conditions will be slower to burn back to the
coast on Wednesday than they were today. But, coastal valleys are
expected to see VFR by the afternoon.
Over the remainder of the area, mostly clear skies will prevail
through Wednesday, but areas of MVFR vsbys and local IFR vsbys
due to smoke from numerous wildfires will persist. The one inland
area that will be relatively free of smoke will be northern Douglas
county. -DW
&&
.MARINE...Updated 800 PM PDT Tuesday 31 July 2018...Light to
moderate northerly winds will persist into Wednesday with high
pressure offshore and a thermal trough inland. The thermal trough
will redevelop near the coast Thursday into Friday, and this will
bring stronger north winds and choppier seas to the area. Small
Craft Advisory conditions may develop south of Cape Blanco
Thursday afternoon through Saturday evening. A weak front will
move onshore Sunday night.
&&
.PREV DISCUSSION... /Issued 309 PM PDT Tue Jul 31 2018/
DISCUSSION...Visible imagery is showing some cirrus (mostly up
around 300 mb) moving across the area this afternoon, but moisture
isn't deep enough and instability isn't great enough to generate
thunderstorms. There still may be a few cumulus/buildups out there
this afternoon, but the closest activity will likely remain SE of
the area. Wildfire smoke continues to bring reduced visibility
(2-4 miles) and poor air quality to many areas south and east of
the Umpqua Divide this afternoon. This will likely remain the
case through the balance of the week, despite some fluctuations
up or down due to changes in wildfire smoke output, wind speeds
and wind directions.
Marine layer stratus has retreated to near or just offshore this
afternoon, but it will return to the coast and into the lower
Umpqua Valley again tonight. RAWS observations from Long Prairie
and also Red Mound this morning indicated some drizzle that
managed to register a click or two on the rain gauges. So, expect
patchy drizzle where the stratus sets up again tonight into
tomorrow morning.
Wednesday will likely be the last day of above normal warmth/heat
for inland areas as an upper trough approaches the PacNW coast.
We still aren't expecting any thunderstorms due to dry southwest
flow aloft in advance of the trough. But, it will kick up west-
northwest breezes during the afternoon/evening. The trough should
also serve to deepen the marine layer Wednesday night into
Thursday morning. Have therefore shown marine stratus pushing
farther inland to about the Umpqua Divide by Thursday morning.
Models are still indicating some light QPF over the coastal waters
and along the coast north of Cape Blanco.
We should see about 5-10 degrees of cooling for inland areas
Thursday, compared to Wednesday. So, that will result in high
temperatures down closer to or even a bit below normal. Normal
high temperatures peak the first week of August. Medford's normal
high is 93, Klamath Falls' is 86 and Mount Shasta City's is 88.
Models are in good agreement through Friday and Saturday,
maintaining near normal temperatures. Both show a shortwave
arriving at the coast Saturday with some moisture and instability
near the Cascades and over the east side. Have added a slight
chance of thunder for the afternoon/evening period for those
areas.
Later in the weekend into early next week, we have preferred the
12z GEFS and 12z EC/EC ensemble mean, which show a continued break
down of the SW ridge and a deepening trough in the eastern
Pacific. This should lead to a further cooling trend beginning
Sunday and persisting into next week. The 12z GFS, while not
completely out of the realm of possibility, appears to be a SW
outlier with respect to the ensembles with a closed low position
out near 42 N and 138 W. We have therefore discounted its much
warmer solution at this time. Incidentally, the 12z ECMWF is about
10 degrees of longitude farther east in the closed low position
at 168 hours and would bring rain to the coast and even areas
inland to the Cascades during this time frame. While not
completely buying into the EC solutions, which would have us much
cooler/wetter, we have gone with an overall model blend with
temperatures about 5-10 below normal (low to mid 80s here in
Medford) along with rain chances up to about the Cascades, highest
along the coast. -Spilde
FIRE WEATHER...Updated 255 PM PDT Tuesday, 31 July 2018...
A weak shortwave is moving over the area in southwest flow aloft
this afternoon. This will continue to result in some mid-high
cloudiness through this evening, and even some light returns on
radar, but the moisture is too high to produce thunder. Meanwhile,
Haines 5 conditions west of the Cascades and Haines 6 conditions
over Lake and Modoc counties mean that it is very dry and unstable
above the boundary layer there, so any new fires have the potential
to spread rapidly. While winds will be breezy this afternoon and
evening, mainly east of the Cascades, and RHs will be low for all
areas inland from the coast, winds will be a bit stronger and RHs
and bit lower for areas east of the Cascades on Wednesday. The
combination of Haines 6 conditions and wind and RH reaching red flag
criteria have resulted in the issuance of a Red Flag Warning for
most of FWZ 285 for Wednesday from 2PM - 11PM PDT. While it will
also be breezy across Klamath and Lake counties, RHs are expected to
be higher.
As we head through late this week into this weekend the upper level
trough will move from west to east across the forecast area. A
somewhat vigorous shortwave in WSW flow on Saturday could bring some
showers and thunderstorms Saturday afternoon and evening for area
north to east of Crater Lake National Park if it maintains its
current forecast track.
While models are well agreed in the cooling trend to below normal
temperatures through Sunday, there is a significant amount of spread
in them early next week with the placement of the trough. While CPC
has stuck to a 5 out 5 level of confidence for increased chances of
cooler and wetter, some of the GFS model members have backed off on
how far the trough makes it inland next week. However, the majority
of the GEFS members do maintain the idea of the trough moving in.
These members, and the 12Z ECMWF indicate that it will probably rain
along and near the coast early next week, and maybe even
substantially so in some areas. Give the uncertainty/spread in the
models at this time, the general message is that there is a
possibility of rainfall across the forecast area from about the
Cascades westward early next week. -Lutz
&&
.MFR WATCHES/WARNINGS/ADVISORIES...
OR...None.
CA...Red Flag Warning from 2 PM to 11 PM PDT Wednesday for CAZ285.
Pacific Coastal Waters...None.
CC