Area Forecast Discussion
Issued by NWS Medford, OR

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FXUS66 KMFR 270456
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
957 PM PDT Wed Jul 26 2017

.DISCUSSION...Isolated thunderstorms continues in northern Klamath
County and the Klamath Basin south into western Modoc County in a
north to northwest flow. There is a smaller area of thunderstorms
over Mount Eddy just west of Mount Shasta. We expect most of these
storms to dissipate in a few hours after the sun has gone down,
but the cluster near Chemult could hold itself longer as it moves
Into the area near Bly due to short wave support to this system.
A weak short wave ridge is expected to move into our forecast area
around daybreak and this will help to stabilize the atmosphere.
Temperature on Thursday could be around seasonal values with
mainly west to northwest wind behind the trough.

Things are on track for a rapid warm up next weekend which could
actually start as early as Friday. This warming period of 95-100
range for the Rogue Valley could last into the middle of next week
with the GFS suggesting lower 100`s possible. /FB

&&

.AVIATION...27/00Z TAF CYCLE...Along the coast...IFR cigs and
visibility will prevail north of Cape Blanco the rest of tonight
through about 20z Thursday, then scatter out thereafter with
gusty north winds developing again Thursday afternoon. South of
Cape Blanco, VFR this evening will become IFR again overnight
into Thursday before clearing out in the afternoon.

Models continue to indicate a deeper marine push into the Umpqua
Basin with some lower ceilings developing at KRBG toward
morning. Confidence here isn`t high, so have indicated just a
scattered deck around 3000 feet in the morning, but there is a
chance of MVFR ceilings for a couple of hours. Either way, VFR will
prevail there after 18z. VFR is expected across the remainder of the
inland west side.

Brief MVFR in isolated to scattered showers and thunderstorms east
of the Cascades this evening should gradually end late this evening
and overnight with VFR the predominant condition. -Spilde

&&

.MARINE...Updated 800 PM PDT Wednesday 26 July 2017...Seas will
subside below small craft advisory levels north of Cape Blanco
this evening. However, the thermal trough will remain in place
through the remainder of the week into this weekend, and small
craft advisory conditions will likely persist south of Cape
Blanco. The thermal trough strengthens some this weekend, and
gales will be possible south of Cape Blanco with small craft
advisory conditions possibly reaching north of Cape Blanco.
-Spilde

&&

.FIRE WEATHER...Updated 930 PM Wednesday 26 July, 2017...
Thunderstorm coverage is decreasing significantly this evening. The
Red Flag Warning for abundant lightning has now been cancelled.

After tonight, we will return to drier and hotter conditions. This
trend will promote the growth of any sleeper fires in the area.
Additionally, gusty winds and low humidities may be possible on
Friday which could create problems, especially for California fire
zone 285. East to northeast winds will accompany poor to moderate
overnight humidity recoveries Friday night, and temperatures
Saturday and Sunday will be about 10 degrees above normal for this
time of year. Recoveries through the weekend will continue to
decrease into the moderate to poor range for many areas. /FB

&&

.PREV DISCUSSION... /Issued 717 PM PDT Wed Jul 26 2017/

DISCUSSION...
125 cloud to ground lightning strikes have been observed by
lightning detection across our forecast area in the past 12 hours,
as of 315 PM PDT. Many of these have occured in the past hour,
especially across southern Lake and southeastern Modoc Counties.
We have also had some isolated strikes over and around the
Cascades. Those west of the crest occurred this morning.

This afternoon increasing northerly flow at and near storm top
level on the west side of the upper level trough that is
currently moving across northern California appears to be
disrupting thunderstorm formation west of the Cascades.
Additionally, morning cloudiness has also, likely, played some
role in the more limited convection along and west of the Cascades
and Siskiyous. For the remainder of the afternoon into the
evening confidence continues to be highest in thunderstorms being
scattered across Lake and Modoc Counties. Due to the subsident
northerly flow across the West Side, Cascades, Siskiyous, and
Klamath County, confidence is not as high for more than isolated
thunderstorms there. The further west one goes the lower the risk
of thunderstorms. That said, guidance does indicate some threat
remaining in these lower confidence areas, so have continued with
a mention of thunderstorm potential along and near the Cascades
and Siskiyous south and eastward.

After storms wind down from west to east this evening through
tonight we expect a couple of days of drier conditions with
temperatures the same or even a little cooler than today.
Guidance, collectively, now indicates that the heat wave expected
late this week into the weekend will probably take until Saturday
or Sunday to really get going, but then the latest guidance
increases the magnitude and duration of the heat early next week.
For now have trended toward this model trend, but am not sold on
the details, as recent heat waves in the day 3 to 7 time frame
have not been quite as hot as some of the hotter guidance has
indicated. Expect that, if the models continue as hot or hotter
than is currently forecast, that thunderstorm chances, especially
east of and along the Cascades, will trend upward. If the models
cool off, they`re likely to trend downward. That said, the one
day we have some thunder for parts of the East Side and Cascades
in the forecast now (after today) is Tuesday. BTL

AVIATION...27/00Z TAF CYCLE...Along the coast...IFR cigs and
visibility will prevail north of Cape Blanco the rest of tonight
through about 20z Thursday, then scatter out thereafter with
gusty north winds developing again Thursday afternoon. South of
Cape Blanco, VFR this evening will become IFR again overnight
into Thursday before clearing out in the afternoon.

Models continue to indicate a deeper marine push into the Umpqua
Basin with some lower ceilings developing at KRBG toward
morning. Confidence here isn`t high, so have indicated just a
scattered deck around 3000 feet in the morning, but there is a
chance of MVFR ceilings for a couple of hours. Either way, VFR will
prevail there after 18z. VFR is expected across the remainder of the
inland west side.

Brief MVFR in isolated to scattered showers and thunderstorms east
of the Cascades this evening should gradually end late this evening
and overnight with VFR the predominant condition. -Spilde

MARINE...Updated 230 PM PDT Wednesday 26 July 2017...Seas will
subside below small craft advisory levels north of Cape Blanco this
evening. However, the thermal trough will remain in place through
the remainder of the week into this weekend, and small craft
advisory conditions will likely persist south of Cape Blanco. The
thermal trough strengthens some this weekend, and gales will be
possible south of Cape Blanco with small craft advisory conditions
possibly reaching north of Cape Blanco. -Spilde

FIRE WEATHER...Updated 215 PM Wednesday 26 July, 2017...
Thunderstorms will continue through this evening, and we are still
looking at the possibility for erratic winds near thunderstorms
and anywhere an outflow boundary occurs from a collapsing
storm...which could continue for miles away from the thunderstorm
it came from. This could great gusty, erratic winds for ongoing
incidents as well as for new fires that crews are attacking. After
tonight, the storms will move eastward out of the area and things
will return to drier and hotter conditions. This trend will
promote the growth of any sleeper fires in the area. Additionally,
gusty winds and low humidities may be possible on Friday which
could create problems, especially for California fire zone 285.
East to northeast winds will accompany poor to moderate overnight
humidity recoveries Friday night, and temperatures Saturday and
Sunday will be about 10 degrees above normal for this time of
year. Recoveries through the weekend will continue to decrease
into the moderate to poor range for many areas. -Schaaf

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Red Flag Warning until 11 PM PDT this evening for ORZ624-625.
     Red Flag Warning until 11 PM PDT this evening for
     ORZ617-621-623.

CA...Red Flag Warning until 11 PM PDT this evening for
     CAZ280-281-284-285.

Pacific Coastal Waters...Small Craft Advisory until 11 PM PDT Friday
for PZZ356-376.

$$

FJB/BTL/MAS


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