Area Forecast Discussion
Issued by NWS Medford, OR

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FXUS66 KMFR 191605

Area Forecast Discussion
National Weather Service Medford OR
905 AM PDT Thu Sep 19 2019

.DISCUSSION...Current observations are showing a some clouds over
our area with some taller clouds occurring southeast of Lake and
Modoc Counties. These clouds are circulating counter-clockwise
around a low pressure system. This low will continue to move away
from southern Oregon and northern California, but before it does
so, another round of showers and thunderstorms will be possible
today for areas east of the Cascades. The thunderstorms will
generally occur in the early afternoon with things beginning to
stabilize after 6 pm. Have not made any changes at this point
since what is in there seems appropriate. -Schaaf


.PREV DISCUSSION... /Issued 346 AM PDT Thu Sep 19 2019/

DISCUSSION...Cold air aloft and energy associated with an upper
trough brought some thunderstorms to the forecast area yesterday.
80 cloud to ground lightning strikes were observed over the past
24 hours. There were seven strikes in Jackson County yesterday
evening when a strong storm resulted in some tree damage and some
accumulation of small hail. According to lightning climatology, at
least one strike has occurred during the week of Sep 17-23 about
5 of the past 30 years. This shows that lightning`s not uncommon
this time of year, and this continues to be the case through
late September before an abrupt decrease in thunderstorm chances
when October arrives. In terms of rainfall over the past 24
hours, at least a quarter inch of rain was observed over most of
the forecast area. Given the showery nature of the precipitation,
there were spots with much more rainfall and less.

Rain chances today will be less, and coverage of showers will be
less too. After a few showers this morning west of the Cascades,
showers this afternoon will be confined mostly to areas from the
Cascades eastward. Lightning chances this afternoon will be confined
to Modoc, Lake, and Eastern Klamath Counties. Latest high-resolution
model data supports this idea. On Friday, the air mass dries some
for most of the area, but we`ll still be under the influence of
upper troughing. A bit of energy will travel along the back side
of the upper trough and bring a chance for rain to the northern
portion of the forecast area. So, even though temperatures will
trend warmer on Friday, some clouds will remain over the region,
and temperatures will still be 5 to 10 degrees below normal for
this time of year. A drier, sunny day is expected Saturday, and
temperatures will bump up to near normal for this time of year.
Meanwhile, overnight low temperatures will dip to near freezing
for some areas east of the Cascades. Frost conditions (33-36) can
be expected in Lakeview, Alturas, and Klamath Falls tonight and
Friday night. These low temperatures are not very different for
normal conditions this time of year, so we haven`t issued any
Frost/Freeze hazards for this.

The next upper trough and cold front will arrive Sunday from the
northwest and spread showers across the forecast area. The cold air
aloft is forecast to be slightly warmer than the system that moved
through yesterday, but there should still be enough instability to
generate some thunderstorms at the coast Sunday morning and then
inland Sunday afternoon. A return to a warming/drying trend is
expected Monday into Wednesday. Latest ensemble data suggests an
upper trough developing over the Pacific Northwest late next week,
introducing cooler conditions and a chance for rain. Both the EC and
GEFS mean data show this.

AVIATION...For the 19/12Z TAFs...Shower coverage will continue to
diminish this morning, except for a continued slight chance of
showers and thunderstorms over Lake and Modoc counties through this
afternoon. A mix of MVFR/VFR conditions prevail with widespread
terrain obsurations and areas of IFR cigs in westside valleys.
Conditions overall will gradually improve late this morning into the
afternoon. Areas of coastal and westside valley MVFR will expand
again this evening into Friday morning. /DW

MARINE...Updated 300 AM 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. A 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




Pacific Coastal Waters...Small Craft Advisory from noon today to 8 PM PDT Saturday for

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