Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service Medford or
850 am PDT Tuesday Oct 13 2015 update to the forecast is not necessary. The 12z
GFS data is beginning to stream in and will be examined with a
focus on potential change to a cooler and wetter pattern at the
end of the week...beginning late Friday. In the mean time...coastal
temperatures will be very warm today then above normal through
Thursday despite night and morning low clouds. Inland highs will
continue at 15 to 25 degrees above normal through Friday.


Aviation...for the 13/12z taf cycle...along the coast north of Cape
Blanco...areas of IFR ceilings/visibilities will develop around sunrise then
clear to VFR by mid-morning. The lower conditions will return late
Tuesday night. Over the remainder of the Medford County Warning Area...VFR
conditions will prevail through Tuesday. /Fb


Marine...updated 230 am PDT Tuesday 13 Oct 2015...high pressure
over the eastern Pacific will gradually strengthen and move
northeastward through Wednesday. This will cause a thermal trough to
develop near the coast that will peak in strength this afternoon and
evening. Westerly swell is now peaking and will begin to subside
tonight. North winds will become gusty and seas will steepen
today...lingering into Wednesday. The thermal trough will drift
northward later this week before the next front arrives this
weekend. /Fb


Previous discussion... /issued 300 am PDT Tuesday Oct 13 2015/

Discussion...the forecast area will remain under the influence of
an upper level high pressure system today and Wednesday...while
an upper level low positioned near 28n and 123w off the coast of
Baja California California meanders northward toward Southern California. At
the surface, a thermal trough is nosing northward off the
southwest Oregon coast. This pattern means mainly sunny weather
will persist across the County Warning Area along with abnormal warmth through
midweek. The only exception will be some low cloudiness and fog at
times along the coast/lower Umpqua valley during the nights/early
mornings. High temperatures over many inland areas will be about
15-20 degrees above normal, which is near record territory.
Medford's record high for today is 88 set in 2004. Since the
thermal trough will be offshore along the south Oregon coast this
afternoon, we expect a Chetco effect to occur in Brookings with
highs in the middle to upper 80s. From about Gold Beach northward, it
won't be as warm, but highs will still be about 5-10 degrees above
average (upper 60s to middle 70s). On Wednesday, offshore flow will
prevail through about noon, then the thermal trough will shift
inland. With onshore winds developing Wednesday afternoon in
Brookings, a full-fledged Chetco effect is not expected. Even so,
it should reach the low to middle 70s before the onshore winds
return. It will remain quite warm inland with many areas once
again challenging record highs.

Wednesday night through Thursday night, a trough will deepen in
the northeast Pacific and this will force the upper low off
Southern California to move onshore very near Los Angeles by
Thursday night. Thursday could be the warmest day over inland
areas with model 850 temperatures prognosticated around 20-21c. However, the
flow aloft to the north of this system will become south to
southeasterly across the cwa, so there will be an increase in middle
and high level moisture. The nam12 is more bullish with moisture
and clouds, but the model consensus is to keep the deepest
moisture and any convection to the south and east over the Sierra
near Tahoe. We have left the forecast dry, but we'll continue to
monitor this for convective potential. It should be noted that
there will also be a stratus surge up the coast during this time
frame, which will bring an end to the unusual warmth there.

By Friday, the trough over the northeast Pacific will send a
pretty potent cold front toward the pacnw coast and the upper low
over Southern California will open up into a trough and move into
the Great Basin. The flow aloft over our County Warning Area will remain south to
southeast initially, but there should be plenty of middle and high
cloud over the area by then, so it probably won't be quite as warm
as it will be at midweek. Again, still expect most of the deep
moisture to remain south and east of the County Warning Area.

Some pre-frontal showers may develop over the mountains from the
Cascades westward Friday night, but expect the main rain band with
the front to arrive at the coast around daybreak Saturday. A
sharp change to cooler weather is expected on Saturday as the
front moves through (10-20 degrees lower than on Friday inland).
Have increased probability of precipitation to chance/likely for most areas with
categorical probability of precipitation over the Coast Ranges during the day. Have
also included a slight chance of thunder east of the Cascades
Saturday afternoon with weak instability present there. The front
moves through quickly and showers gradually diminish from west to
east Saturday evening/night.

There'll be a break Sunday (with temperatures closer to normal),
but another fast-moving shortwave will move into the area Sunday
night into Monday. The gfs40 is stronger and farther south than
the European model (ecmwf) with this system. Having lower confidence in the details
with this system, have opted to maintain the going forecast with
slight chance to chance pops, with the best chances in the north
Cascades and north of the Umpqua Divide.

The ridge is indicated to rebuild at least briefly on Tuesday of
next week. Spilde


Mfr watches/warnings/advisories...


Pacific coastal waters...Small Craft Advisory until 5 am PDT
Wednesday for pzz356-376.
Small Craft Advisory for hazardous seas until 11 am PDT this
morning for pzz356-376.



National Weather Service Glossary of Abbreviations