Frost and Freeze in Oregon, May 8, 2021

Area Forecast Discussion
National Weather Service Medford OR
800 PM PDT Fri May 7 2021

.DISCUSSION...08/00Z NAM in.

Mostly clear skies prevail over most of the WFO Medford forecast
area this evening.  The exceptions are stratocumulus clouds
along the south and east flanks of the Rogue, Umpqua, and
Coquille Basins. There are some clouds elsewhere, mostly over the
coastal waters and northern Klamath and Lake counties, but the
coverage there is minimal.

Mostly clear skies with a dry air mass will make for a cold
morning Saturday. A Freeze Warning is in effect for some of the
valleys of Jackson and Josephine counties.

A long wave ridge off the west coast will move slowly east through
the weekend. It will build in fits and starts due to weak short
waves moving over the top of it. These short waves will temper the
warming and drying trend that usually occurs with ridging, but
Saturday and Sunday will still be warm and dry. There may also be
a light shower or two over the Cascades around Diamond Lake
Saturday afternoon and evening, but the latest short term model
runs have lower POPs. With the exception of the possible showers,
Saturday and Sunday will look a lot alike.

However, the ridge will strengthen early next week as it
approaches the coast. A thermal trough will develop near the
coast, and inland high temperatures will be 5 to 10 degrees warmer
than the Sunday highs. Humidities will lower significantly as
well.

Long term discussion from the Friday afternoon AFD...Tuesday 11
May through Friday 14 May 2021. Upper level ridging will dominate
the weather in the region through the week, with mostly clear
skies and no precipitation chances to speak of, at least until
perhaps Friday when some form of trough may attempt to push
onshore. Until then, temperatures will see a steady warming trend
Tuesday and Wednesday, followed by slightly cooler conditions
towards the end of the week.

There may be some instances of the marine layer making a push, and
this could result in periods of fog or low clouds west of the
coastal ranges north of Cape Blanco, and some fog or low clouds
could also intrude to Brookings if sufficiently strong southerly
eddies form between the coast and north winds offshore. Otherwise,
clouds will be scarce.

As mentioned above, a weak trough is possible late in the week, but
there is some spread amongst the ensemble members about how much
moisture would accompany it. Chances are, this would be a mostly dry
system, but there are some indications a stronger trough could
arrive next weekend with more widespread precipitation, but
confidence is too low to pin it down in the forecast just yet. -BPN

The 8 to 14 day outlook, valid May 15-21 2021, calls for higher
chances of below normal temperatures and near normal
precipitation.

&&

.AVIATION...For the 08/00Z TAF Cycle...VFR is expected to persist
through Saturday afternoon, with the exception of patches of late
night into early morning MVFR both from around Cape Arago northward
including the Coquille and lower Umpqua valleys, and at the north
facing slopes near Canyonville and Ashland. DW

&&

.MARINE...Updated 800 PM PDT Friday 07 May 2021...A thermal trough
will persist near the coast with gusty north winds and steep to very
steep seas for areas south of Cape Blanco continuing through most of
next week. Steep seas are expected to expand north of Cape Blanco
Sunday night through at least Monday. The combination of winds and
seas could also result in hazardous seas warning conditions starting
Sunday night. Petrucelli/DW

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Freeze Warning from 2 AM to 10 AM PDT Saturday for ORZ024-026.

CA...None.

Pacific Coastal Waters...Small Craft Advisory until 5 PM PDT Sunday
        for PZZ356-376.
     Hazardous Seas Warning until 10 PM PDT this evening for PZZ356.
     Small Craft Advisory until 5 AM PDT Saturday for PZZ350-370.

15/15/16