Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Medford or
1257 am PDT sun may 3 2015
Discussion...03/00z NAM/GFS in.
Mostly clear skies prevail across the Medford County Warning Area this
morning...except for some marine stratus around Cape Blanco...
Brookings...the Coquille Valley...and the outer marine waters.
There is also bits of convective debris east of the Cascades.
Upper level flow will remain roughly zonal over the area through
Sunday with embedded short waves moving onshore well to the north
of the County Warning Area...and a weak baggy trough off to the southwest.
Mostly dry and warm weather will persist through Sunday. Sunday
highs will be similar to the Saturday highs...around 10 degrees
above normal in the Umpqua basin and 10 to 15 degrees above
normal over the rest of the County Warning Area.
Some showers developed over Modoc County Saturday afternoon and
evening...indicating that sufficient moisture has filtered into
the area. Upper level support for showers remains marginal...but
it will be slightly better Sunday with a weak elongated short wave
over the area.
The 03/00z model solutions are forecasting increased lifted
indices as compared to what occurred Saturday afternoon. Overall
the thunderstorm forecast for Sunday matches up well with all the
inputs...so will let that forecast ride for the most part.
The pattern starts to change Monday as a digging offshore long
wave trough will bring increasing southwest flow to the area.
Monday highs will be several degrees cooler over the west side and
near east side as the marine influence and cloud cover increases
over the area. Over Lake County and Modoc County...Monday highs
will be similar to the Sunday highs. East of the Cascades and over
northern California...there will be another round of isolated
thunderstorms in roughly the same area as the Sunday activity.
The transition to a cooler and showery pattern will occur Monday
night into Tuesday as an upper level long wave trough edges
onshore. This will push a cold front onshore Monday night into
Tuesday. Associated precipitation will be light and mostly limited
to the west side. Tuesday will be quite a bit cooler everywhere
with highs dropping to near normal values over most of the
area...and ranging to near five degrees above normal over Lake
County and northern California.
The trough will move through the area slowly as short waves
diving down the back side of the trough will impede its progress.
All that cool air aloft and the short waves will support rounds of
showers Tuesday night into Wednesday...but timing those rounds is
a difficult forecast this far out. Temperatures will be cooler
still with many areas dropping slightly below normal.
Long term discussion from the Saturday afternoon afd...Wednesday may
6th through sun may 10th. A trough of low pressure with an
associated -25c to -30c 500mb cold pool is expected to elongate
and wobble southward from Washington to California, inland from
the coast, Wednesday through Thursday. The exact location of this
trough and how it is stacked vertically when it moves through will
all influence precipitation potential and resultant sensible
weather from this weather system. In short, it will be cooler with
highs mostly in the 50s and 60s. Lows will be near freezing across
the east side and in the 30s and 40s on the west side with some
frost potential in the usually colder western valley spots. We do
expect showers and a slight chance of afternoon and evening
thunderstorms during this time period, with the greatest chance of
precipitation being along and near the Cascade crest. Snow levels
will be mostly between 5000 and 7000 feet. While precipitation
amounts will be generally light, a quick shot of wetting
precipitation is possible during this time period in isolated to
Friday through Sunday the initial trough is expected to move into
the Great Basin while another trough slips onto the West Coast south
of a strong ridge over southeastern Alaska. While details are very
much in question as to how and when this pattern transition will
occur, it appears the net result is likely to be a bit of a warm-up
followed by another opportunity for showers and isolated
thunderstorms across the area.
Altogether, we expect the cooler conditions and showers to slow
drying across the area. However, periods of windy conditions and
lower dewpoints are likely to counteract moisture saving effects in
many areas. The lower dewpoints also raise concern for some
seasonable frost and freeze possibilities during this time period in
some west side areas. Btl
Aviation...for the 03/06z taf cycle...areas of MVFR ceilings will
impact the coast north of Cape Blanco, including koth, overnight
into early Sunday morning. These will spread into extreme
northern Curry and southern Coos County through the Camas Valley and
into portions of southern Douglas County south of Roseburg
overnight. These ceilings may impact krbg for a few hours Sunday
morning, otherwise, VFR will prevail. Some IFR fog/ceilings may develop
near Brookings overnight into Sunday morning. Gusty north winds
will redevelop at koth with gusts of 25-30 knots. The rest of the area
will be VFR, but expect some buildups from northern California to
southern Klamath and lake counties with a slight chance of
Marine...updated 1030 PM PDT Saturday, 2 may, 2015...a thermal
trough along the Curry County and northern California coasts will
bring gusty north winds and steep to very steep seas into Sunday.
The gales south of Cape Blanco will ease back to Small Craft
Advisory winds on Sunday, but seas will remain quite hazardous.
Winds and seas both will diminish Sunday night into Monday. A cold
front will bring some showers and building west swell on Tuesday.
Seas will gradually lower on Wednesday. Then the thermal trough and
north winds are forecast to return late next week. Cirrocumulus/spilde
Fire weather...conditions along a line extending from around
Mount Shasta northeast into Southern Lake County for Sunday
afternoon and evening look slightly more moist than Saturday with
precipitable waters around 0.60" and instability a bit more significant. Thus,
we probably will see at least a few storms Sunday afternoon and
evening. Storms motion will be east at about 10 knots. With
current fuel conditions resulting in moderate fire danger,
concerns for fire starts are there, but not major. This is mainly
due to the current significant live fuel component.
Pacific coastal waters...Small Craft Advisory for winds until 11 PM
PDT Sunday for pzz350-356-370-376.
Small Craft Advisory for hazardous seas until 8 am PDT Monday
Gale Warning until 2 am PDT Sunday for pzz356-376.
Hazardous seas warning until 11 PM PDT Sunday for pzz356-376.
Small Craft Advisory for hazardous seas from 5 am to 11 PM PDT
Sunday for pzz370.
Hazardous seas warning until 11 am PDT Sunday for pzz370.
Small Craft Advisory for hazardous seas from 5 am Sunday to 8 am
PDT Monday for pzz376.
Small Craft Advisory for hazardous seas until 11 PM PDT Sunday
Hazardous seas warning until 5 am PDT Sunday for pzz350.