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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




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