Mark’s Nightmare Weather Pattern

May 30, 2006

TI think I mentioned earlier this spring that there is one weather pattern that I hate forecasting for…an upper level low sitting offshore with waves rotating out of it and into the Northwest.  2 reasons for that:  one is that models don’t handle the individual shortwaves well.  The other is that the periods of steady rain are usually quite short, followed by hours of sunshine if the onshore flow isn’t too strong.  So what starts out as a rainy day forecast could be wet until 8am, mostly sunny from 9am-4pm, then rain again after 5pm.  Viewers think we don’t know what we’re talking about and can’t forecast the weather…ugh!

What sticks out tonight is the good plume of moisture across the Eastern Pacific.  Models show precipitable water well above 1.20" the next 2 days as several waves move inland.  No big onshore push though until Friday, which leaves us increasingly warm & humid.  One wave moves into Wednesday evening, and another later Thursday/Friday AM.  With high freezing levels (10,000’+) and good subtropical moisture feed, we could get a good soaking.  Maybe .50"-1.00" in the lowlands.

As for the chances for thunder tomorrow & Thursday?  Tough one.  Our RPM (rapid update precision model) model here at the station seems to indicate some convection just ahead of the main line of rain tomorrow evening, and the same thing Thursday afternoon.  It’s tough because solid cloud cover (with surface cooling) ahead of both waves could cancel out the lifting effects of the approaching wave.  We’ll see.  Flow is southwest, which IS a similar setup to our convection about a week and a half ago.

Memorial Day Break

May 29, 2006

A break today since it’s a holiday, but I’ll be back on tomorrow night.  Looks like quite a bit of weather moving through in the next 7 days.  Enjoy the sun Tuesday.

Brightness in The Tunnel

May 26, 2006

A pleasant surprise in the maps today in the long term…but first tonight.

Cold upper trough is overhead now…er, actually part is slipping south along the Oregon Coast and the other part is in Southern British Columbia.  I was disappointed by the lack of strong convection today, but there’s always tomorrow right?  Snow levels right now are moving back down pretty close to the passes (Gov’t Camp, Santiam, Willamette).  Last visible camera pictures showed some snow on the side of Willamette Pass.   I love camping, but between crowds & cold this weekend, somehow I don’t mind that I work over the holiday.  I’m sure that "Memorial Day" taken in late July or August will be quite a bit more comfortable don’t you think?

Tomorrow the showers come in from the northwest or even north-northwest by late in the day as a chunk of that British Columbia low slides south over us.  Expect another cold & showery day.  Then northerly flow on Sunday keeps us cool with lighter showers.

So the change is Monday and beyond.  Yesterday’s GFS was trending towards more troughiness next week right over us, while the ECMWF had more troughing offshore, giving us a weak ridge.  Now the GFS & NAM are looking like the ECMWF with more ridging developing over the West again from Monday-Thursday next week.  Looks like early summer weather will be coming back.  75-80 in this pattern is most likely.

Cold Days Ahead

May 25, 2006

Sorry for the lack of info last night, I felt kind of well…crappy.  A rare late May cold, must be due to the weather.

Record "low" highs the next 2 days are 56 & 57 degrees at PDX, and I think it’ll be close.  Very cold airmass is moving onshore this evening, partially evidenced by the showers continuing well past sunset and more showers showing up on radar offshore.  Tomorrow should be a busy weather day, but not severe, as cold unstable air combines with sunbreaks to bring us lots of convection.  Freezing level bottoms out near 4,000′ the next 2 mornings for flurries in the passes, but no accumulation.

Beginning Sunday the airmass moderates to a bit more reasonable, but still cool, for this time of the year.  I also noticed tonight that we could easily see another .50-1.00" the next 3 days in the lowlands, which will push our May rainfall well above normal.  So much for the "early fire season" talk eh? 

Stay warm the next few days and keep putting out the slug bait!  Mark Nelsen

Short Post Tonight

May 24, 2006

Nothing has changed this evening, cold trough slow approaches tomorrow and moves overhead Friday-Sunday.  Then back to weak ridging or troughiness for the beginning of next week…Mark

Big Cold Trough

May 23, 2006

No changes in forecast "philosophy" tonight.  BIg trough sitting offshore the next two days, sending impluses inland from time to time.  This keeps showers moving in pretty regularly.  A more organized system moves in Thursday, which may give us steadier rain.
The trough, along with lower freezing levels, moves inland Friday-Sunday.  Thunderstorms a much better bet with cold atmosphere overhead combining with almost "Solstice strength" sunshine.
Models still show the low kicking out early next week, for a return to milder late May/early June weather with very little rain…Mark

Chilly Forecast

May 22, 2006

Looks like classic May weather is here for a few days.  Lots of showers with occasional steady rain periods.  But sunbreaks too.  Unlikely that we’ll see more than a 6 hour dry period, except maybe some nighttime periods.

Pattern changes very little in the next 6 days.  A cold trough remains offshore the next 3 days and then the entire thing moves inland Friday-Sunday.   That means a cooler airmass late week (better chance for cold thunderstorms), leading to Cascade snow down to at least 5,000′.  Cold (and crowded) camping ahead for the Memorial Day Weekend.

Beyond that, models seem to be a bit more reasonable for late May, with warming temps back to at least normal and not much rain after Sunday…Mark