Easterly Flow Arriving

May 22, 2008

Snapshot A change in movement on the radar imagery the last few hours shows the change on the way the next few days.  We had "surprise" showers late this afternoon and evening that developed over the I-5 corridor and streamed down to the south and east.  These were caused by the moist marine atmosphere bubbling up with weak convection.  But between 10-11pm, showers have begun to approach from the northeast.  I see it's now raining and The Dalles and Hood River.  This is the return flow around the back side of an upper level low centered over Utah.

That upper level low retrogrades (backs up) over Oregon the next 24 hours.  This is a great setup for good soaking rain east of the Cascades.  Much better than any "wet" Pacific system in the winter.  Eastern Oregon grain growers (wheat, barley etc…) that depend on soil moisture alone…no irrigation call a good May rainfall "May Gold".  A good soaking now as the wheat is in it's most active growth is the best they can ask for.  Most years there is no significant rain in May.  We'll see how much they pick up over the next few days.

The biggest forecast problem the next few day is timing the impluses moving around the upper-level low.  One moves into Western Oregon tomorrow, giving us a good soaking.  Then another "wave" of rain/showers comes in Saturday night.  Assuming models are correct in timing, we get a break during the day Saturday.  If timing is off by 8 hours, Saturday will be a rainy day.  Obviously the forecasting is quite difficult for this holiday weekend!  Mark Nelsen


A Chilly Evening

May 20, 2008

Snapshot Quite a change the last 24 hours…during my bike ride yesterday evening (between shows), it was in the 80s and a bit sweaty. Tonight, I needed some hardware and plants, so I was shivering a bit in the chilly/breezy air. No big changes tomorrow as an upper-level low passes overhead. It is headed for Utah by early Thursday morning. This will be our first "upper level low" event of the season. A forecasting nightmare in short. The low will back up a bit and end up in S.E. Oregon by Friday morning. As a result, showers will become widespread over Eastern Oregon Friday. There is the possibility that the showers will move west over the Cascades and down into the Western Valleys. Models don't indicate too much instability, but this pattern in the past has produced thunderstorms this time of the year in this pattern for those of us west of the Cascades.

     We'll see about that, but having dry weather in the forecast Thursday-Monday (our 7 Day forecast) is a bit risky in this pattern. Hopefully I qualified that forecast well enough during the 10pm broadcast. Either way, increasing 850mb temps means a warming atmosphere Friday-Saturday for sure. That should push temps up to or above average for this time of the year. We're getting close to 70 now for our average high here in Portland. Mark Nelsen


Summer Weather Ends

May 19, 2008

SnapshotQuite a stretch of "false" summer the last 5 days.  A bit too warm for me, especially Saturday, but I sure won’t complain since I still prefer this over cold showers in May.

Well, we get those cold showers the next 2-3 days as a trough of low pressure swings inland, behind a cold front late tonight.

As of 11pm the front looks pretty vigorous, with strong echoes now moving into radar range off the North Oregon Coast.  There have been no cloud to ground (or cloud to ocean) strikes in the last 6 hours, but I wouldn’t be surprised to see a flash or hear a rumble of thunder as the front moves through late tonight.  But I sure wouldn’t stay up all night waiting for it…most likely we’ll see nothing other than brief, heavy rain towards daybreak.

I notice lifted index and instability in general is not so great behind the front tomorrow OR Wednesday.  So basically we get lots of onshore flow and frequent showers, especially near elevated terrain and up against the Coast/Cascade ranges.

Tons of uncertainty with the Friday-Monday forecast.  Latest 00z GFS has much stronger troughing with a better chance of showers, instead of an upper-level ridge approaching the Coast.  There’s always time to change the forecast the next couple of days, but my current 76-78 degree forecast is in jeopardy.

On the home front, I decided the ground was warm enough to plant more "warm weather" veggies.  Plus the rain the next few days will soak the ground nicely.  Since I live in a colder and wetter area, I’m still holding off on the real warm stuff (tomatoes, melons, squash).  AND, most important, my trees are just about done blooming and no one has left the gate open…so Bambi hasn’t visited (and mauled) anything so far…Mark Nelsen


A Historic Coastal Day

May 16, 2008

SnapshotQuite a day at the beaches…obviously the east wind had no problem making it to the beaches.  Looks like Astoria, Seaside, and Tillamook all hit all-time May highs.  Newport probably did too, the 95° here is from the Airport, which isn’t the same spot where records are kept.

Of course I was disappointed by the "cool" 92 at PDX, but the 96-97-98 at Vancouver, McMinnville, and Aurora make me feel a bit better.

Easterly flow ends soon after daybreak Saturday, replaced by a late afternoon southwesterly surge up the Valley.  I think it’ll be too late to keep PDX below 90, but it’ll be close.

No changes on the thinking Sunday…increasing marine air, but no strong trough in the upper atmosphere means a moderate amount of cooling.  This time of the year a combination of the two could drop us 25 degrees in a day!  That shouldn’t happen this time.

Have a nice weekend…looks like Summer!  Mark Nelsen


The Heat Is On!

May 15, 2008

SnapshotLots of interesting things happening this evening for temperature junkies…

First, no changes in my thinking for the next two days.  I love the consistent forecasting the last 4 days.  So according to the forecast, easterly wind should pick up (at least above the surface) overnight and tomorrow morning.  That’s obviously happening this evening…here are some highlights:
1.  Newport Airport was 61 at 9pm, is now 72.
2.  Lincoln City (on a tower above the ground) was 64 at 8:49pm, and is now 76 with a gusty east wind.  You think the easterly flow might be surfacing now along the beaches?
3.  Our TV tower temp is 78…that probably won’t change overnight as the atmosphere continues to warm.
4.  Brookings hit 101 today, and is still 90 at 11pm!

As for the metro area, we only have 2 millibars easterly flow through the Gorge, so the wind along I-84 still east of Troutdale.  I DO think it’ll push into the Troutdale/Gresham areas before daybreak, so low temp forecasts are tricky.  The rest of us drop into the 50s.

Out of time…stay cool tomorrow!  Mark Nelsen


Hot Spell Begins

May 14, 2008

Snapshot Snapshot2
I guess the graphics don’t actually say it anywhere, but these are current water temperatures on area rivers…chilly!  In fact I went down to the boat ramp on the Sandy river at Troutdale to measure the temperature today, and was surprised by how cold it was.  Because of the warm and slightly moist weather + cold water temp, you could see a condensation fog hovering over the river…kind of like when we have a flood in winter.  The chilly water is cooling the air right near the river, causing the moisture to condense out to fog.  Pretty cool…

Moving on, I was real happy with today’s weather vs. the forecast.  Nice clearing after about mid-afternoon let temps jump up into the lower 70s.  Funny how it felt a bit humid, but dewpoints were below 60 degrees the whole time, obviously we just are blessed, and spoiled, by dry air usually associating with warm/hot days.

I see the Salem sounding this evening confirmed 500mb heights of 590dm right now.  A strong upper-level ridge HAS formed directly over the top of us and the lower-level atmosphere will respond to that tomorrow.  You can see how the warm frontal clouds just evaporated this afternoon on the IR satellite picture.  By 8-11am, an easterly flow develops through the Gorge, but probably not enough to move past Troutdale even at midday.  More likely we get a breezy north wind in most of the metro area tomorrow as a thermal trough develops to our south.  I’m tempted to drop tomorrow’s high to 88 as a result. 

Then the stronger easterly flow at the surface arrives tomorrow night and Friday A.M..  By then we have several millibars of easterly gradient through the Gorge and the thermal trough is out at the Beaches.  It moves inland again by Friday evening, so Friday is that perfect setup where we get gusty east wind in the morning.  The wind pushes out towards PDX by midday, then dies down, leaving a hot & calm atmosphere by late afternoon.  You couldn’t ask for a more perfect setup any summer day.  850mb temps should be around +22 deg. C.  Assuming all this pans out as forecast, 94 is the bottom range of PDX forecast high.  The upper range is 98 or so.  We may be awfully close to our all-time May high of 100 degrees late Friday afternoon.  If the latest 00z mesoscale models say the same thing (I’m ignoring WRF-GFS sfc. temps, they were wacky with warm weather back in April), I may up the high for Friday by 10pm.

A decent, but shallow marine push later Saturday should cap us near 90 degrees (if not below), then much more significant cooling arrives Sunday for highs closer to 80.

GFS builds ridging back in over us next week, ECMWF does not…Quite a difference in models, but that’s a ways away…Mark Nelsen


Holding a Steady Course

May 13, 2008

SnapshotODOT sent out this info today in a news release.  Of course McKenzie Pass closes each winter.  It’s Highway 242 between Belknap Springs and Sisters…the most direct route between Eugene and Bend/Redmond areas.  The opening date varies from year to year.  Looks like the big snow year of 1999 was the latest opening ever, in mid summer.

Now, what about the subject for the post.  Well, as I was preparing for the 10pm show, I was thinking that I’ve reached the "info saturation stage" for our approaching weather "event".  Our hot weather has been well forecast by models, so well that only minor forecast details have changed in the last 2 days.  What can happen in these data-rich Internet days is a sort of information overload.  Every few hours new info comes in.  It could be MOS temps from 3 different models, 850mb temp forecasts, or surface temp forecasts from each different model and it’s respective runs.  For example…Thursday:  MOS from GFS, NAM, and NGM (00z) show a high of either 86, 83, or 80, respectively.  Surface temps from the GFS show 88, from NAM, 79.  So lots of numbers are always flying around in weather circles.  My special chart shows a high of 88-91.  It’s pretty reliable in general.  What’s the point?  Well, for 3 days we’ve shown a 90 Thursday and 95 Friday on our 7 Day forecast.  My theory has been increasingly one of "hold it steady" the last few years.  In my younger days (1990s), I would flip flop with each new model run, adjusting temps every 12 hours.  Now I figure there’s no need to change unless models make an obvious change.  Basically numbers are whacking you on the side of the head constantly in this business, so you need to focus your sights forward.  Pretty deep eh?  So I didn’t change the 7 day forecast yesterday or today for the Thursday-Sunday period.  If the marine push starts slightly faster Saturday evening, then Sunday may only be in the 70s, or maybe Saturday will stay in the 80s…but no need to change for now.

I did notice one thing:  It’s going to be crazy warm in the mountains Friday-Saturday.  Temps in the "free-air" at 2000′ will be above 70 degrees from Friday morning through Saturday evening!  This elevation has been in the 40s the past few days.  The snow pack is definitely going to collapse a bit, especially up on Mt. Hood where .50" of rain has fallen since this morning.

Otherwise my thinking hasn’t changed since last night’s post.  We’re going from 70 or so tomorrow to about 90 Thursday afternoon.  We start with east wind Friday and a thermal trough all the way out at the Coast, then it goes calm by late afternoon…with +22 deg C. 850mb temps, that’s the perfect setup for mid 90s.  Conceivably it could even be warmer…if it was early-mid June, 100 would be more likely…Mark Nelsen


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