FXUS66 KMFR 201602

Area Forecast Discussion
National Weather Service Medford OR
902 AM PDT Wed Jun 20 2018

.UPDATE...The latest models have trended a bit quicker with the
expected trough today, and has pushed the main areas of
convection to the north from previous runs. This has resulted in
a change to the thunderstorm forecast today, reducing the
thunderstorm chances south of Crater Lake, including Siskiyou and
Jackson counties. While not all models show this trend, several
have, and this has reduced confidence in the overall forecast, and
warranted the update.

Overall, thunderstorms are still expected today, mainly along and
east of the western Cascade foothills, into northern Klamath and
Lake counties. Some of these storms could produce gusty winds and
small hail, and plenty of lightning is likely. Take the proper
precautions and plan for the chance of strong thunderstorms this

For more on this and the rest of the forecast, see the previous
discussion below. -BPN


.AVIATION...For the 20/12Z TAFs...Marine layer will continue to
bring a mix of IFR/LIFR cigs along the coast, over the coastal
waters, and the Coquille Basin. Onshore flow will continue to push
the marine layer inland, but not confident it will make it to KRBG
and have removed the scattered MVFR mention from the KRBG TAF. It is
possible, however, to see some scattered cigs in the vicinity of
KRBG. Expect the marine layer to burn back to the coast this
afternoon where IFR cigs are likely to continue through the TAF

Elsewhere, VFR conditions prevail and will do so throughout the TAF
period. Thunderstorms are expected across many parts of SW Oregon
and northern California this afternoon. Confidence is high that LMT
will see thunderstorms at some point this afternoon, however, was
not confident enough to forecast it for a specific hour. Opted for a
tempo group to cover the time frame most favorable for thunderstorms
on station. Confidence remains that Jackson County will see
scattered thunderstorms this afternoon and a few could drift within
10 nm of the airport. Thunderstorms should be most numerous along
and east of the Cascades. Any thunderstorms that develop will be
capable of producing very strong gusty outflow winds. BR-y/-FB


.MARINE...Updated 130 AM PDT Wednesday 19 June 2018...Relatively
calm conditions will continue through Thursday. The thermal trough
redevelops Friday. Small craft conditions with steep wind driven
seas are expected to return by Friday night and continue into the
weekend. Gales are possible during the weekend, but confidence is
still low since it`s still a few days out. -FB/BR-y


.PREV DISCUSSION... /Issued 240 AM PDT Wed Jun 20 2018/

DISCUSSION...The left exit region of a strong mid-upper level jet
max will move across the forecast area this afternoon. Moisture
and instability will increase today in advance of a potent short
wave disturbance associated with an upper level trough off the
NorCal coast. Mid-level cooling forecast to arrive with the
shortwave at max surface heating this afternoon will lead to steep
lapse rates and MUCAPE ~1000J/Kg. The result will be scattered
strong to isolated severe thunderstorms over portions of the
forecast area this afternoon and evening. The main threat area
will be from the Cascades near Lake of the Woods north and
northeastward across far eastern Douglas County, northern Klamath
and northern Lake Counties. But, some isolated thunderstorms will
extend southward into northern California as well.

Convective initiation is expected from 19-21z (Noon-2pm PDT) with
the most robust convection expected from 21-06z (2-11pm PDT).
Storms are likely to initiate over the mountains in the Southern
Oregon Cascades, Siskiyous and western Siskiyou County early this
afternoon, and then spread north and northeast late this afternoon
and evening across Klamath and northern Lake Counties. Recent
runs of the convection allowing models show a threat period of 3-7
pm PDT for the Rogue Valley (especially south and east sections),
which falls in line with climatology. The main threats with
storms today will be frequent cloud to ground lightning, locally
heavy rainfall, and the possibility of damaging wind gusts and
hail. Most of the convection should stay east of a line from
Roseburg to Grants Pass.

Make sure to keep an eye to the sky and have a plan if
thunderstorms threaten. Seek shelter until the storms pass
completely. Please view the weather story on our home page at
weather.gov/mfr for more details on where the highest threat for
strong to severe thunderstorms exists today. Also refer to the
point and click map for forecasts specific to your location.

There may be some drizzle along the coast with a deepening marine
layer tonight. This will also mean more clouds farther inland into
the Umpqua Basin. Cooling behind today`s system will be minor,
perhaps not even noticeable in most places, but with more clouds
due to the marine layer, places like Roseburg will likely feel the
most change from today to tomorrow (Thursday).

Overall, Thursday to Saturday will be warm and probably dry for
inland areas with temperatures about 5-8 degrees above normal.
Another shortwave disturbance will move through Thursday
afternoon. Right now, moisture doesn`t look robust enough to
include a slight chance of thunderstorms, but there could be some
buildups over the East Side. Something to keep an eye on for
future shifts.

Models continue to show a spike in heat Sunday with forecast 850mb
temps in the 23-25C range. This would put highs in the upper 90s
here in Medford and near 90 in the Klamath Basin. 100F is in the
range of solutions for Medford, but is a high outlier at this
point. We are currently forecasting a high of 97 degrees.

This bout of heat will be short-lived, however, as the next
Pacific trough is expected to move in early next week. This will
bring a period of gusty afternoon west-northwest winds as the
trough moves onshore Monday. Without significant moisture,
however, we are not expecting any precipitation. While we`ll take
the edge off the heat Monday and Tuesday, we`ll still be about 5-8
degrees above normal. -Spilde




Pacific Coastal Waters...None.


NWS MFR Office Area Forecast Discussion