Nice Day!

April 18, 2006

Today was the essence of Northwest spring weather if you were to ask me.  I spent the morning working outside.  Chilly at first and then warm/sunny by midday.  Of course I would order about 10 degrees of warming, but I only forecast it, I don’t create.

Nice again tomorrow, a bit warmer too.  No offshore flow, or else we’d be up into the lower 70’s.

The big change in the last 24 hours is with the late week system.  Now models bring it through quickly, with just light rain Thursday night and Friday morning.  By late Friday afternoon flow turns northerly at the surface, always a "clearing" wind in the spring, so mostly clear by Friday evening.  I notice 00z ETA now has strong offshore flow developing already by Saturday morning.  Longer range models had that over us Sunday and Monday too. 

That should give us our first warm east wind event of the spring, so 70’s will finally arrive, and maybe well INTO the 70’s too.  We have a beautiful sunny weekend coming!  So the forecast for the next 7 days really includes only 1 weak system Friday.  Things are really going to start drying out around here.

Warmer Temps

April 17, 2006

A short post tonight because it’s 11:38pm.

Nice end to our cold & wet weekend today, even though it didn’t really end until Monday evening.  A cluster of thunderstorms developed over the preferred Columbia River corridor, dropping lightning strikes into Parkrose, Fairview, Camas, Troutdale and Oxbow Park areas around 4:30 this afternoon.  Troutdale got soaked and hammered with hail.  Sound familiar?  Troutdale seemed to be a hotspot twice last season in the late afternoons too with this thunderstorm/downpours stuff.

Nice ridging the next few days just to our east warms us up, but it’s far enough east to keep the real warm weather in Idaho and Eastern Oregon.  It’s possible we still won’t hit 70 this week.  Either way, enjoy the nice dry spell…Mark

Rain Coming

April 12, 2006

Nicer day than expected today…at least temperature-wise.  Shows us how easily April sunshine can push temperatures up.

One last dry day tomorrow as westerly flow increases overhead.  We’ll be feeling the edges of an approaching upper-level trough by Thursday evening.   I’m impressed by the cold air with this.  ETA 00z cross-sections show freezing levels down to around 2000′ Saturday and Sunday.  I don’t think snow will fall much lower than that, but that cold of an airmass along with April sunbreaks should give us vigorous showers both days, after Friday’s steady cold front rain.

We may also see a frost outside of Portland Sunday or Monday night as skies begin to clear out.

Enjoy one last dry day!

Location Is Everything II

April 11, 2006

I mentioned a few weeks back how location is just everything.  Well my forecast went from "complete bust, I can’t do anything right" to "wow, what a forecasting machine I am!" in about 30 minutes.

Here’s a little story from today to go with that:

As you recall, last night I mentioned (and showed on the tube), that showers would develop over the higher terrain this afternoon and most of the metro area would probably stay dry.  So I get up this morning, do some work outside and then it starts raining with cloudy skies at my home between 12-1pm.  I drive through cloudy and very convective looking rainy skies into the middle of the metro area where it dries up.  Then by the time I get to downtown it’s warm and partly cloudy outside, where it never rained all day!  Just living at 1000′ on the west slopes of the Cascades puts you into rainier weather in some cases.  When I left home I was convinced the day was going to be a widespread washout and I’d have to write up a big forecast screwup for the blog tonight.  Instead the showers stayed where expected during the daylight hours.  The models did quite well.  It’s amazing how different the weather can be from mile-to-mile in this showery weather.

So tonight another wave is moving north through the Willamette Valley.  It should be the last from the low that’s heading into California.  Then our attention turns to the west for a strong cold front coming on Friday.  I do expect light convection to break out again tomorrow afternoon, mainly over the hills.  BUT, the flow will be westerly tomorrow, so we have a better chance of getting leftovers drifting out over the valleys.  As for that cold front Friday…easy call…solid cold rain.  Then several days of cold showers from the west.

Thicknesses and 850mb temps support snow down to 2000′ over the weekend, which is pretty low for mid-April.  Some of you may remember an Easter Sunday around 1980 where snow fell down to 500′ or less.  I forget which year, but it may have been in March, not April.  Anybody out there remember?  Either way it won’t be quite that cold this time.

Long range maps show no end to the seasonal wet/mild pattern.  No sign of warm 70-80 degree weather yet.  April temperatures HAVE been a bit above average, mainly due to warm nights

Another Nice Break

April 10, 2006

Not much to talk about tonight..but I’ll find something.

3 days of pretty calm weather ahead as a deep low heads into California again.  But this one doesn’t swing north towards us, it just continues east towards the Plains.  So the only good chance for rain or rain showers is from afternoon instability each day.  It’s most likely over higher terrain where there is more lifting.  Onshore flow does increase on Thursday, so we cool and see more cloud cover that day.

Friday-Sunday looks a bit…gruesome…a big trough of low pressure drops into the Northwest.  This time right at us, not into California.  Of course that cold of a trough overhead in April should produce a nice round of hail & thunderstorms too.

Rain on the Way (or Thunder?)

April 7, 2006

What an interesting month we’ve had with a repeating pattern.  Upper-level troughs drop south out of the Gulf of Alaska and move into California, then we get the leftovers.  Each time we get a period of southeasterly upper-level flow just as the low approaches the coastline.  That’s happening again this evening.  Radar is lighting up nicely with showers AFTER sunset, which is a pretty clear sign of good dynamic lifting, unrelated to daytime heating.  In summer we get excellent thunderstorm potential with this setup (as I’ve mentioned about 4 times in the last month), this time of the year we CAN get lightning, but it’s not quite as likely.  What does that mean?  Possibly a flash of lightning or rumble overnight.

00z ETA looks just like the earlier MM5 model which shows a nice deformation band developing right over NW Oregon and SW Washington by daybreak, then it sits right over us much of the day tomorrow.  Once again, as we’ve seen the last few times, this should lead to tonight’s showers becoming solid rain overhead.  Basically a pretty gray and wet day for most of us tomorrow.

Offshore flow continues this evening (3+ millibars at 8pm from PDX-DLS), but reverses by daybreak and we get a strong onshore push.  Combine that with the rain and it’ll be tough to get out of the mid 50’s tomorrow.  Quite a change from today.

Speaking of today…we only hit 67 at PDX, the warmest day of the year so far, but too much cloud cover to make it to 70.  Kelso & McMinnville did make it to that special little number though.  The average date for the first 70 degree temperature at PDX is April 2nd.

Tough Forecast Again

April 6, 2006

Lots of variables in tomorrow’s forecast.

First the temperature:  Staying with the 70 degree forecast.  If the clouds are too thick, we stay near 66, if the clouds thin out quickly and we turn mostly sunny, we could hit 73.  Offshore flow is beginning this evening, a very good sign.  The pressure gradient through the Gorge has just turned flat at 10pm after being westerly all day.

Then the rain:  00z models look slightly wetter by tomorrow evening.  Past experience tells me this is a possible thunderstorm pattern with the diffluent southeasterly flow and plenty of moisture.  BUT, no model shows a good chance for thunder and lifted indexes stay above zero.  Of course remember that yesterday’s thunder was with a lifted index around +3

Either way, enjoy the warm weather tomorrow since the trough and it’s cool showers are definitely back by daybreak Saturday.