Flood in Oregon, February 4, 2021

Area Forecast Discussion
National Weather Service Medford OR
355 AM PST Thu Feb 4 2021

.DISCUSSION...After long stretch of one winter storm after another
today's biggest concern is valley fog. A rex block pattern, an
upper low sitting north of a closed low, is sitting offshore this
morning with a thermal trough along the coast. This pattern has
cleared most of the clouds out of the region yesterday evening,
with fog and stratus forming in the valleys west of the cascades
this morning. The sounding showed the moistures to be somewhat
shallow, and east of the Cascades the moisture is most likely
being deposited as frost with the very low temperatures in clear
skies.

The upper high over low pattern begins to rotate clockwise into
Friday morning with a system sliding down the backside of the
broad upper ridge pattern into the Pacific Northwest, bringing
very light showers to the northern fringes of the forecast area,
mostly in northern Douglas and extreme northern Coos county
Friday. There will be increased cloud cover Friday night into
Saturday morning, with the most cover north of the Umpqua divide,
brining warmer overnight lows and decreased fog formation,
especially north of the Umpqua divide.

Into Saturday models show the Rex block breaking down and the
upper low beginning to flatten, but with the usually stubborn
nature of a Rex block, this solution may change as we move forward
in time.However, for now models are showing another weak system
moving down the back side of the ridge and bringing another round
of weak showers to the northern fringes of the forecast area
Saturday.

This pattern remain into Sunday with another system brining
similar results as the ones in the couple of days before, and
again into Monday. Sven

&&

.AVIATION...For the 04/12Z TAFs...The latest satellite image shows
stratus in portions of the Umpqua Basin, Illinois and Applegate
Valley and Grants Pass area. Recent images show the stratus
expanding into portions of the Rogue Valley. It has not quite got to
the Medford Airport, but expect low clouds to develop there around
daybreak although there's a chance the cloud layer could be shallow.
Low clouds will gradually burn off, but the timing indicated in the
TAF for Medford and Roseburg could vary. For example, in Roseburg
conditions may not improve until later than whats in the TAF. In
Medford, if the cloud layer remains shallow, then conditions could
improve earlier. Once the low clouds burn off, VFR conditions will
prevail through this evening, then low clouds are possible again
later tonight for many of the same areas as this morning, although
it will be a close call for Medford.

East of the cascades, VFR conditions will continue through the TAF
period. -Petrucelli

&&

.MARINE...Updated 200 AM PST Wednesday 3 Feb 2021...Relatively
calmer conditions are expected today. However a the combination of
offshore high pressure and a thermal trough along the south coast
will result in moderate north winds that will result in small craft
conditions from about Port Orford south that will continue through
Friday afternoon. Wind driven seas will likely be around 9 to 10
feet this afternoon and again on Friday afternoon. The thermal
trough is expected to weaken Saturday into Sunday. -Petrucelli

&&

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

CA...None.

Pacific Coastal Waters...Small Craft Advisory until 10 PM PST Friday for PZZ356-376.

SBN/SBN/SBN