Scientific Forecaster Discussion
fxus66 kmfr 231131 aaa
Area forecast discussion
National Weather Service Medford or
310 am PDT Fri Aug 23 2019
Updated aviation discussion and first paragraph of public discussion.
Discussion...23/00z NAM/GFS/ec in.
Mostly clear skies prevail across the area this morning, except for
patches of low clouds and fog along the coast north of Cape Blanco,
in the Coquille Valley, and in the Umpqua basin.
An upper ridge is building over the area along with a thermal
trough offshore. A strong warming trend will affect all areas
through Friday. By that time highs will be 5-10 degrees above
Short waves moving over the top of the ridge will keep it from
building any further this weekend, and this will put the brakes
on the warming trend. Saturday and Sunday highs will be about the
same as the Friday highs. A dry cold front will move through
Saturday. It won't bring any cooling, but it will bring gusty
winds to the east side Saturday afternoon and evening.
The ridge will build in more strongly next week, and the thermal
trough will move inland. That's when it will get really hot over
the area. Another strong warming trend will occur Monday into
Tuesday, and the Tuesday highs will be 10-15 degrees above normal.
The Medford high will be near 100 degrees Monday and will exceed
it Tuesday. Wednesday will be similar to Tuesday with mostly clear
skies and hot temperatures.
At some point the ridge will break down and the possibility of
thunderstorms will enter the forecast with slightly cooler
temperatures. The latest GFS run continues to show that Lis will
remain positive Wednesday afternoon and evening with pws of around
0.66 inches, which is too stable and marginally dry. However, on
Thursday afternoon and evening there is a significant area of
negative Lis from around Crater Lake southeast through the east
side, and the pws rise to 0.75 to 1.0 inches. That is sufficient
for thunderstorm activity and thus will keep the current forecast
of a slight chance of thunder at that time and location.
Aviation...for the 23/12z tafs...along the coast, in the coastal
valleys, and over the coastal waters...isolated IFR cigs/vsbys in
low clouds and fog will clear to VFR by mid-morning Friday. VFR
conditions will then prevail into Friday evening, then areas of IFR
cigs/vsbys in low clouds and fog will develop Friday night,
persisting into Saturday morning. Over the remainder of the
area...VFR conditions will prevail into Saturday morning, except for
patchy IFR cigs over the Umpqua basin that will clear to VFR by late
Marine...updated 230 am PDT Friday 23 August 2019...the thermal
trough has returned and will persist into early next week, although
there will be a period of weakening later this evening into Saturday
morning then a re-strengthening Saturday afternoon into Monday
Winds reached a peak on Thursday evening but gusty north winds and
steep to very steep and hazardous seas are likely to continue south
of Cape Blanco through tonight. The weakening on Saturday will be
most noticeable north of Cape Blanco.
Small Craft Advisory conditions are expected south of Cape Blanco
Saturday into Saturday night. After that, winds will strengthen
again Sunday with an area of gales possible again south of Cape
Blanco from late Sunday morning through Monday evening. The thermal
trough is expected to push inland and weaken Tuesday, allowing
conditions to improve at least into Thursday. -Keene/dw
Fire weather...updated 300 am PDT Friday 23 August 2019...there
was little change made to the forecast, mainly fine tuning of the
relative humidity forecast. A strong warming and drying trend
will begin today. The warmest and driest conditions are likely on
Tuesday, but improvement during the remainder of next week will be
While the passage of a weak, dry cold front on Saturday will not
bring any cooling, it will bring gusty westerly winds east of the
Cascades with afternoon and evening speeds stronger than normal at
12 to 18 mph with gusts up to 25 mph.
Associated with the warming and drying trend will be night into
morning northeast winds of 5 to 15 mph over the Coast Range with
moderate mid slope and ridge humidity recoveries tonight through
The air mass will remain stable at least through Tuesday night, and
likely through Thursday morning. Model uncertainty increases beyond
day 5 with differences in the track of a closed low over the
Pacific coastal waters...Small Craft Advisory until 5 am PDT Sunday
Hazardous seas warning until 5 am PDT Saturday for pzz356-376.