Area Forecast Discussion
Issued by NWS Medford, OR

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000
FXUS66 KMFR 281022
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
322 AM PDT Fri Jul 28 2017

.SHORT TERM...Very hot conditions will develop across inland
areas late this weekend into early next week. Today, a weak
shortwave will lift northeast and the upper level ridge will
strengthen over the Western U.S tonight into early next week. High
temperatures are expected to reach 100 for some western valleys
on Sunday then increase further early next week with very hot
temperatures developing. Models also continue to show very weak
impulses moving into the area, which combined with some mid level
moisture and instability may bring a slight risk for thunderstorms
to eastern Modoc and southeast Lake counties Saturday and Sunday.
Overall, this risk is only slight due to limited moisture and
forcing.

The building ridge will bring a warmer airmass and hot
temperatures to inland valleys this weekend. Highs are expected to
warm into the 90s to near 100 for many western valleys by Sunday
with highs in the lower to mid 90s across eastern valleys.
Meanwhile along the coast, a surface thermal trough will
strengthen and result in stronger east to northeast winds. This
will bring warming conditions to the coast, especially in the
Brookigns area where a moderate Chetco effect is expected.

Looking into early next week, the main concern is with the
potential for excessive heat across several inland valleys,
including the Rogue, Illinois and Applegate valleys and the
Shasta, Scott and Klamath river valleys in Northern California.
Models currently support afternoon temperatures rising into the
lower to mid 100s across these western valleys. Additionally,
overnight low temperatures are expected to be warmer than normal
with lows near 70 Monday night and Tuesday night. This will result
in only a brief period of relatively cooler temperatures in the
overnight hours. High temperatures east of the Cascades will also
rise early next week, reaching the upper 90s by Tuesday. Very hot
temperatures are expected to continue into Wednesday, then
conditions will gradually become less hot late next week as an
upper trough approaches the Pacific Northwest coast.


&&

.AVIATION...28/06Z TAF CYCLE...At the coast and just offshore. IFR
and local LIFR CIGS will persist for most of the morning. The
exception will be from Cape Blanco to Gold Beach where VFR Cigs are
expected. However this will have to be watched closely. Some
improvement is possible this afternoon as the marine stratus peels
back just off the coast with VFR CIGS, but confidence on the timing
is low to medium. The TAF at North Bend shows improving conditions
around 19Z, but this could change, so watch for updates on this.
Marine stratus will likely return to the coast this evening with IFR
and local LIFR CIGS.

Inland. The latest fog image shows marine stratus in the Coquille
Basin and river valleys in Curry County. This should burn off by
late this morning with clear skies for the afternoon. The marine
stratus will get close to Roseburg, but it should remain VFR through
the TAF period.  Elsewhere... VFR will persist overnight into Friday
across all inland areas, with the exception of in the vicinity of
wildfires, where smoke may occasionally restrict visibility to less
than a mile at times. -Petrucelli

&&

.MARINE...Updated 230 AM PDT Friday 28 July 2017...A thermal
trough in northern California will remain in place into next week
with north winds and steep to very steep seas. Small craft advisory
conditions will persist south of Cape Blanco this morning. The
thermal trough will strengthen this afternoon through early next
week with gales beyond about 5 NM from shore and south of Gold
Beach. Meanwhile small craft conditions will affect areas from
Bandon south through Sunday evening. The models suggest gales and
small craft conditions could expand in coverage Sunday night through
Monday evening and decided to expand the coverage of gales and small
craft conditions. Please see MWWMFR for more details. -Petrucelli


&&

.FIRE WEATHER...Updated 300 AM Friday 28 July, 2017...Dry and hot
weather away from the immediate coast will prevail through most of
next week. A weak upper trough will approach the area from the
southwest this afternoon. Models show south winds near 700mb
increasing between 15-20 kts and is likely to mix down near the
surface. Relative humidities will be low, but right now we don`t
think winds will be strong enough to warrant Red Flag conditions for
Fire zones 624, 625, 284 and 285, but this will need to be watched
carefully.  Instability will be marginal at best this afternoon, but
mid level moisture is lacking, so were not expecting much more than
a few cumulus build ups along the Cascades and east side this
afternoon and evening. Also the thermal trough will remain along the
coast resulting in breezy east to northeast winds near and at the
ridges in portions of Fire zones 618, 619 and 280 tonight into
Saturday morning along with moderate recoveries. Latest data still
does not support conditions reaching critical criteria, so we`ll
continue to headline in the Fire Weather Forecast.

The overall pattern is not expected to change much for all of next
week. However the models differ with the position ofthe upper ridge.
For example the GFS has the ridge positioned over the four corners
and we`ll be on the outer fringe of the ridge. Typically in this
type of situation we could be dealing with isolated thunderstorms.
Taking the GFS at face value would put southeastern Lake at risk for
thunderstorms. Given the high fire danger in these areas, decided to
err on the side of caution and keep a slight chance of storms in
southeast fire zone 625 Saturday and Sunday afternoons.

In contrast, the ECMWF has the ridge positioned right over our area
which will keep thunderstorm chances pretty much next to zero with
even hotter temperatures.

Relative humidities will be low during the afternoons, but models
are not showing particularly strong winds near and at 700 and even
the 700-500 mb winds are not strong. Also the pressure gradients are
not strong, therefore surface winds will not be strong enough to
warrant red flag concerns. -Petrucelli


&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...None.

CA...None.

Pacific Coastal Waters...Small Craft Advisory until 11 PM PDT Monday for PZZ356-376.
     Gale Warning from 11 AM this morning to 11 PM PDT Monday for
     PZZ356-376.
     Small Craft Advisory from 11 AM this morning to 11 PM PDT Monday
     for PZZ350-370.

$$

CC


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