Scientific Forecaster Discussion
fxus66 kmfr 192144
Area forecast discussion
National Weather Service Medford or
244 PM PDT Thu Sep 19 2019
Discussion...2:30 PM satellite imagery is showing clouds all
across southern Oregon and northern California with a few clear
spots along the Oregon coast. The larger cumulonimbus clouds
circulating around the low continue to push eastward and southward
away from Modoc County. A few of the clouds in Klamath, lake and
Modoc counties have started to tower a bit, but no lightning
strikes have been recorded in our forecast area as of yet.
Although the thunderstorm threat will continue for the next few
hours, it will diminish as the low pushes away from the area and
things begin to stabilize. The real concern for tonight is any
clearing in regards to the clouds. With the amount of clouds in
the area right now, I have less confidence in significant
clearing. This has caused ME to raise temperature forecasts a few
degrees across the area. That being said, we are still expecting
patchy to somewhat abundant frost east of the Cascades tonight.
Many locations east of the Cascades are already at their normal
end of the growing season (i.E. Crescent, Alturas, lakeview).
Other areas, like Klamath Falls, despite being near the end of
their growing season haven't quite made it to the finish line yet.
Although it is normal to see frost at this time of year, the
aforementioned reasoning for low confidence is why we are going
with patchy frost in this area. This precludes ME from issuing a
frost advisory. Subsequent shifts, however, may decide to issue a
frost advisory; especially if the cloud cover diminishes in the
next few hours.
We then begin a slow warming trend on Friday and Saturday with no
precipitation expected either day. Then, another low comes
through the Pacific northwest--this one best classified as an
inside slider type of low. What this means is that on Sunday,
we'll receive some light to locally moderate rainfall before it
moves away from the area on Sunday night where we dry out by
Monday. Snow levels will be around 7000 to 8000 feet, so expect
the highest of the Cascades to see some snow, and possibly even
The Crater Lake Rim, but don't expect it to be that much.
Then, we start moving back to a slight warming trend with overall
dry weather through the remainder of the week. Confidence in the
forecast is relatively low as both the GFS and ec ensembles have
large swings in conditions (from areas of high pressure, to
general troughing). Most of the ensemble members show a troughing
scenario, so have capped the warming in the extended; and then
showed a trough coming in by next weekend which could produce some
rainfall for US. Keep an eye on this forecast because things will
change greatly in the next 8 to 10 days. -Schaaf
Aviation...for the 19/18z tafs...along the coast and just
offshore...VFR conditions are expected into early this evening.
Gusty north breezes are expected this afternoon into early this
evening at North Bend. Marine stratus will develop this evening
with ceilings lowering to MVFR to start, then to IFR later in the
evening and tonight. The timing of when lower conditions develop
in the North Bend taf is low to medium, so watch for updates.
A mix of MVFR/VFR conditions prevail with terrain obsurations for
inland Westside valleys into early this afternoon. Ceilings should
improve to VFR later this afternoon, but still could not rule out at
least partial mountain obscurations.
This evening and tonight. Plenty of low level moisture will be
present and if it clears out enough, then there will be an
opportunity for MVFR ceilings to develop late tonight into Friday
morning. Confidence was high enough to include the lower conditions
in the Medford and Roseburg taf's, but not Klamath Falls. However at
the same time could not rule lower conditions there late tonight, so
watch for updates. -Petrucelli
Marine...updated 115 PM PDT Thursday 19 September 2019...high
pressure offshore and a thermal trough along the coast will
persist through Saturday. Seas will become steep south of Port
Orford this afternoon then persist into Saturday evening. The
strongest winds will occur during the afternoon and evening hours.
Conditions will improve later Saturday night into Sunday morning as
the thermal trough pattern gets interrupted when the next front
moves through the waters. This front is likely to bring rain showers
and early indicators hint there may be enough instability to support
a thunderstorm in the early afternoon. A northwest swell of about
seven feet (ten seconds) will be present during this calm and
continue to persist. After, the thermal trough is likely to quickly
develop again early next week with strengthening northerly winds
into mid-week. This may include gales developing south of Cape
Blanco on Monday afternoon. /Dw/miles