April 17, 2008
Wayne Garcia shouted at me (via speakerphone) tonight…"hey mark! My web page that gives me weather forecasts says it’s going to be 51 in Reykjavik and sunny Saturday, can you believe it?". So after doing some digging I noticed how tough it is to get cold air this far south in April. Day length is rapidly increasing in the Arctic this time of year, so temps warm quickly too. In fact I see Fairbanks will be warmer than Portland Sunday as well. They have a big warm ridge on the way up there! Not so here in the Pacific Northwest.
Still no change in the remarkably accurate long range maps this week. A cold front is hard to find on the satellite picture, but observations at the Coast, including Astoria, show quickly dropping dewpoints. So the cooler/drier air is arriving tonight.
I don’t see any real organized precipitation on the maps tomorrow through Sunday EXCEPT for Saturday morning. Each model is slightly different, but It seems as though they all try to give heavier and more sustained precipitation for the central Oregon Coast and Southern Willamette Valley. That could give a "surprise" snowfall to some coastal locations, so I leaned on that bit more heavily during the 10pm show. I still think we get mainly midday-afternoon showers in the lower elevations otherwise, which means very little chance for any snow below 1,000′.
The trough should kick out of here Tuesday (or so), but it’s going to be 5-7 days before reasonable temps return…April 2008 will go down as a chilly one! Mark Nelsen
April 16, 2008
I love these graphs. The NRCS has a great SNOTEL Website where you can check out all the locations across the region. Click on the image here to get a much larger view. The blue line is current snow water equivalent on the ground. There is about 88" of SWE on the ground at the Timberline site, that compares to an average of 62" or so. The point here is that we still haven’t "peaked" with our snow totals yet. Timberline generally peaks around May 1st or so as you can see from the graph, then with quickly warming temps in May and June, the snow melts quickly. The reason we don’t get spring flooding from all that snowmelt is that we don’t get flooding rains when it’s 75 degrees in Portland. The main snowmelt occurs during the "dry" season.
Still no changes to our weekend weather. The one thing I notice is a very diurnal nature to the precipitation this weekend (at least as forecast by models). Most precipitation will fall with daytime heavy showers Saturday and Sunday. Of course a thunderstorm and hail are very likely too. I don’t see any sort of organized area of rain/snow, which MAY reduce the chances for lowland snow. I still think it’s a guarantee in the hills and more likely a "curiousity" in the lower elevations. We’ll see…Mark Nelsen
April 15, 2008
It’s been a chilly April, and apparently it’s going to get chillier yet! The maps right now for the next few days don’t really look any different than last night at this time. Brief warming the next two days is followed by a historically cold airmass for this time of year (April 18-21st) this weekend. I found the maps from April 23, 1961. That was the morning that up to 3" fell in the West Hills and dustings even in the lower elevations. The pattern was very similar to what’s coming this weekend. A quick drop of cold air down through Western Canada dug out a trough along the West Coast. The day after, the low was centered a bit more to the east of us. It may have been a "deformation zone" as steady/heavy precip. sat over us before the trough moved off to the east. The 850mb temps and upper level heights are forecast to be a bit LOWER this weekend compared to that event. I’m increasingly convinced that several inches are likely in the hills by Saturday morning and MAYBE some to the lowest elevations too. It’ll all be about precipitation intensity and timing. If we don’t get good showers at the right time (overnight and early A.M.), then no snow. But imagine if heavy/steady precip. were to arrive over the metro area at daybreak Saturday??? Mark Nelsen
April 14, 2008
Hmm…was this last weekend just a dream? I think so after the rude shock of chilly temps, hail, and snow in spots, today. Then I come in and look at model forecasts for this weekend just about fall out of the chair. Well, not really, but it sounds more dramatic that way.
First, short term: Cold trough is passing over us now. I notice it’s in the teens at Timberline and just barely above freezing at the top of our TV Tower. Some winters it barely gets that cold here! Snow COULD fall down below 1,500′ tonight, but the showers appear very weak on radar…the Coast Range is killing most of them. Showers increase tomorrow midday-afternoon as another wave moves down the backside of the upper trough.
Then it’s on to milder weather for Wednesday and Thursday. Temperatures should be closer to normal. Somewhere near 60. Probably dry both days too.
The big story is the agreement by all models on an unusually cold trough dropping in over the Western USA Friday-Monday. Latest 00z runs of GFS continue VERY cold airmass forecast…just about as cold as what we just saw two weeks ago (4-5 days of snow at 1,000’+). Since it’s mid April, it’s very unlikely we could see snow on the Valley floor unless everything lines up perfectly. However, I have a feeling that 850mb temps of -6 to -8 and thicknesses of 516-520 will bring several inches of snow to those spots at/above 1,000′. My trees about to bloom are toast aren’t they? But, to borrow from one of my favorite TV shows "this has all happened before and it will happen again". April 23rd 1961 brought 3" of snow to the West Hills, but none in the city. The high at PDX that day was 43 degrees. As far as I know, that’s the latest that snow has been seen in the immediate metro area. Mark Nelsen
April 11, 2008
I’m torn this evening; which is better, a beautiful sunny day tomorrow, or a brand new episode of Battlestar Galactica on at 10pm? At least in this case I can have both. Well, obviously I’ll be recording episode #1 & #2 of this final season since I have a little job to get done from 10-11pm. I screwed up last week when I forgot to set the VCR to Daylight Time. Amazing that I can get a weathercast together isn’t it?
A nice warm 69 degrees at PDX today, the warmest so far this season and right around the 68 I forecast for today. We did this without much of any easterly flow, some light easterly drift down the Gorge, but that was it. Quite a change by morning though. Mesoscale models say up to 5 miliibars easterly gradient in the 7-10am timeframe. This gives us much better mixing of the warm/dry atmosphere above. According to the April "Magic Chart", offshore flow+850mb temps 11-12 deg = a maximum as high as 80 tomorrow at PDX, with 75-78 most likely. So I’ve bumped up the high temp forecast to 77, assuming that we’ll be between 74 and 80 (I consider a 3 degree margin of error acceptable). Whew…lots of numbers. For the regular person, it just means a perfect mid-June day is on tap for Saturday!
Models are all in agreement in bringing a dying cold front inland Sunday. Our model here holds off rain until the evening. Then it’s back to cool, showery, and "troughy" weather the rest of next week. The big picture looks like this: the weekend will only be a brief intermission in our cool & wet spring so far. Mark Nelsen
April 9, 2008
Well, a few days off in a nice warm place, I come back and it’s still chilly and drippy. Okay, there were 2 days last week that were nice, but in general it’s been a long 4 weeks of rain, snow, and "general unpleasantness". That’s going to come to a quick end Friday-Sunday as we get a first taste of May-June weather.
I boosted high temps up a bit Friday-Saturday based on good offshore flow and a thermal trough developing west of the Cascades. 850mb temps support 74-78 degrees with offshore flow. So of course, I went wild and shot for the moon (78 degrees Saturday). It may only be 75, but nice and warm either way. Do you realize we haven’t even made it to 66 so far this season? And we’re heading into the middle of April!
The 00z GFS & GEM (Canadian) both show the cool troughiness returning quickly on Monday, so this may only be a temporary break in our cool spring so far. More tomorrow…By the way, the comments on posts automatically shut off after 1 week, so apparently you’ve been unable to comment for the last 26 hours. I’m sorry if anyone experienced withdrawal, things are back to normal now..Mark Nelsen
April 1, 2008
I was checking out snowfall totals again this evening. Looks like Government Camp is nowhere near a record, but the lower elevations are. The numbers speak for themselves. That winter (1968-1969) was one of the snowiest in recorded history for many areas in the Northwest.
A short post tonight, because I’m getting ready to take 5 days off. Next post won’t be until next Wednesday. Considering the weather pattern, I have a feeling it’ll be pretty quiet on this blog anyway. Nice warm sunshine the next two days is followed by a new stretch of westerly flow and cool temps from Friday through early next week.