NWS Medford, OR wrote its last area forecast discussion before the first event at Aug 2, 8:47 AM PST, 4 hours 13 minutes earlier.
Area forecast discussion, Aug 2, 8:47 AM PST, 4 hours 13 minutes before
Area Forecast Discussion
National Weather Service Medford OR
947 AM PDT Fri Aug 2 2019
.DISCUSSION...After coordination with the Oregon Department of
Environmental Quality, the forecast was updated to extend an Air
Quality Alert for South Central Douglas County through Sunday
afternoon. Due to continuing effects of the Milepost 97 wildfire,
this includes Riddle, Canyonville, Azalea, and Glendale. The fire
activity has diminished somewhat. Northerly afternoon winds will
continue to send some smoke into Josephine and Jackson Counties
with at least a small amount of late day diminishment of air
quality. But, there is reason for optimism in those areas given
the good to moderate air quality readings from yesterday evening.
A dissipating cold front at the coast today will bring a few low
clouds to the Douglas and northern Coos County coastlines, while
the air mass will be stable with temperatures near normal across
the area. There is high confidence in hot weather Saturday through
Monday with valley highs in the upper 80s to lower 90s across the
east side and in the mid 90s to lower 100s on the west side. Also,
there is a growing probability of a noticeable cooling trend
Tuesday into the end of the week.
A focus for the afternoon forecast package will be on introducing
or adjusting the forecast probability of late day thunderstorms
from the weekend into next week. Based upon the 06Z model suite,
instability looks to be minimal during the weekend but perhaps
sufficient for cumulus buildups and a few isolated thunderstorms
over the higher terrain from western Siskiyou County to the
Cascades and northeastward. We will examine the new suite of 12z
data and coordinate with neighboring offices before making any
adjustments.
&&
.AVIATION...For the 02/12Z TAFs...Along and west of the coastal
ranges, clouds have developed ahead of a weak cold front that is
expected to push onshore this morning. MVFR/IFR conditions and light
showers are possible by daybreak as onshore flow increases and the
front passes, but inland extent of these clouds and any
precipitation will be limited. Prevailing VFR is expected for all
areas by midday, but IFR conditions are likely to return this
evening and tonight as the marine layer surges inland.
Elsewhere, smoke from the Milepost 97 Fire has been greatly reduced
due to firefighting efforts. Therefore, MVFR due to smoke is only
expected to affect areas within about 20 miles of the fire, at most,
through the next 24 hours. -BPN/BTL
&&
.MARINE...Updated 800 AM PDT Friday 02 August 2019... A weak cold
front will move onshore today, but will dissipate quickly as it
does. Expect breezy south to southwest winds and periods of light
rain through this morning, then winds will weaken through the
afternoon before shifting to the north this evening. Wind speeds
will remain below small craft conditions, but steep wind driven
seas of around 6 feet will continue through midday. Conditions
should improve through the afternoon and remain relatively calm
through Saturday morning.
By Saturday afternoon, expect a return of gusty north winds as the
thermal trough redevelops. Gusty north winds and steep seas will
likely persist through Monday, mainly south of Cape Blanco. The
thermal trough will likely weaken midweek, and conditions should
improve for the latter half of next week. -BPN
&&
.PREV DISCUSSION... /Issued 422 AM PDT Fri Aug 2 2019/
DISCUSSION...This morning's IR imagery shows low pressure moving
across Vancouver Island with a cold front extending south-
southwestward offshore of the Pacific Northwest. The front will
push into Washington and NW Oregon today, but will largely fall
apart as the upper support moves through British Columbia well to
our north. While there's a chance of a little light rain at some
coastal communities north of Cape Blanco this morning, most of the
precipitation will occur offshore and to the north. Meanwhile,
water vapor imagery is showing an upper level vorticity maximum
moving through northern California. This will move into south-
central Oregon this morning, then exit off to the NE of the area
by late this afternoon. The timing of this disturbance isn't quite
right for our area and instability is fairly weak. So, while
there can be some cumulus east of the Cascades and in northern
California today, we don't think they'll be able to grow into
thunderstorms. We expect fairly typical afternoon north-northwest
breezes, probably about 5 mph less than yesterday. Temperatures
for most areas today will be a couple of degrees lower than they
were yesterday.
Smoke output from the Milepost 97 fire was much less the last
couple of days compared to earlier in the week. As a result, air
quality has been much better. We'll continue to see localized
smoke impacts, especially right in the vicinity of the fire, but
the widespread poor air quality experienced at the start of the
week appears to be behind us for now. We are expecting a bit
deeper of a marine push tonight into Saturday morning. Model
guidance is showing clouds pushing into Coos County this evening,
then through the gap at Camas Valley overnight, and eventually
filling into portions of the Umpqua Basin by Saturday morning.
There should be some clouds again near the Milepost 97 fire by
Saturday morning.
This weekend into early next week, the persistent ridge over the
southern Rockies/Four Corners region will begin to build slightly
westward. As a result, we'll see a warming of the air mass aloft.
Model guidance is showing 850 temps jumping up to around 22-24C.
This translates to highs in the mid to upper 90s (F) in Medford.
It's not out of the question we'll get close to 100 degrees
Sun/Mon. We'll continue to be in a south-southwest flow aloft
during this time frame with daily build-ups in northern
California, and near and east of the Cascades. There is a slight
chance of a thunderstorm near the Cascades/Chemult area Monday
afternoon/evening.
We'll be on the lookout for a surge in moisture from the south as
an upper level low gathers offshore Tuesday into Wednesday of next
week. Right now, it's too early to say with much confidence
whether or not the ingredients will all come together for a
lightning outbreak across the area. Current guidance is showing
fairly low probabilities of thunder, so we are only carrying
slight chances for thunderstorms, mainly near the Cascades and
northward (both side of the Cascades) late Tuesday, then mostly
northern portions of the area from the Cascades eastward on
Wednesday. We still have a few days to monitor this, so stay
tuned.
Beyond that, models and ensembles show the closed low moving
onshore late next week with decided downturn in temperatures back
closer to or even below normal levels. -Spilde
FIRE WEATHER...Overall, fire weather conditions won't be as
significant across the area today, compared to yesterday. It'll
still be dry in many areas, but winds should be down by at least 5
mph area wide. Haines won't be an issue today, but should new
fires get going east of the Cascades, Haines 6 conditions are
expected to develop this weekend into early next week east of the
Cascades (mainly from the Fremont National Forest eastward).
Lightning risk remains fairly low as well, though we'll continue
to see daily cumulus build-ups in northern California and from the
Cascades eastward. There is a slight chance of a thunderstorm over
the northern Cascades Monday afternoon/evening.
We are monitoring the potential for more significant lightning
Tuesday/Wednesday of next week. It's still too early to say if
everything will come together. The position of the upper low
offshore and energy ejecting northward ahead of it are still up in
the air at this point. We'll have southerly flow, which should
allow moisture and instability to increase during this time
period, but model thunder probabilities are still pretty low.
We'll continue to adjust the forecast as needed, but right now we
have a slight chance of thunderstorms either side of the Cascades
late Tuesday, then across northern sections east of the Cascades
on Wednesday. -Spilde
&&
.MFR WATCHES/WARNINGS/ADVISORIES...
OR...None.
CA...None.
Pacific Coastal Waters...Small Craft Advisory until 11 AM PDT this
morning for PZZ370-376.
DW/MAP