Cold & Showery

April 16, 2007

SnapshotSunday was a nice break from the cold & showery weather, but you knew it couldn’t last long during this cool/wet April.  A nice cold front passed overhead this evening and appears to be in the eastern 1/3rd of the state.
Behind the front, cold and unstable air is just about to move onto the Coastline.  We haven’t had many of these "episodes" this Spring season.  Lifted Index, a measure of instability in the atmosphere, goes down to right around zero by tomorrow afternoon west of the Cascades.  That plus some CAPE up to about 200 or so should give us a good chance for strong convection.  Of course this time of year that means heavy showers with possible hail or thunder too.  This cold upper-level trough coming inland tomorrow and Wednesday will sit directly over us Thursday and Friday.  Models keep just about all moisture those two days down to our south.  That seems a bit hard to believe with chilly air sitting overhead, but I’ll go with it for now.
A new trough arrives in the Pacific Northwest Saturday.  I don’t see any dramatic changes early next week.  The 00z Canadian has a bit more ridging over us, but the 00z GFS stays cool, or at most average temperature-wise over us next week…Mark

A Late Post

April 13, 2007

I’ve been a bit negligent this week with the posts.  It must be the lack of overall pattern change.  I much prefer  swings from dry to wet weather.  This constant parade of weather systems isn’t my favorite, especially since I’d like to get outside a bit more.
Speaking of this weather pattern, no model shows any dramatic change over the next 7-10 days.  Looks like April will end up wet and cool.  One trough after another drops down into the Northwest, bringing shots of rain and mountain snow.  They also bring surges of cold air well into the interior of the West, keeping the normal spring warmup at bay.
As of Friday evening, models show a brief break Sunday and early Monday, but the next system is quickly moving inland Monday evening, so I had to push rain up into Monday’s forecast.  Stay dry and warm this weekend…Mark

Strong Evening Wind?

April 11, 2007

SnapshotSnapshotInteresting development offshore this afternoon.  A clearly visible tightly wound area of low pressure is located just offshore of Newport at 3pm and headed northeast.  MM5 and our WRF model take it to Spokane by 5am, passing very near the metro area.  Our model shows 6-7 millibars pressure difference between Eugene and Portland around the 8-10pm timeperiod.  This could produce southerly wind gusts to 40 mph or so.  More interesting is the peak gust to 41 mph right at 3pm observation time at Eugene.  That’s pretty strong for Eugene.  They often don’t get gusts much more than that with the good winter storms.  I have a feeling Albany-Woodburn may see gusts over 45 mph by dinnertime.
11pm Update: 
That was a fun little system.  Peak gusts in the metro area were around 40 mph.  I see peak gust at PDX was 43 mph.  The new wind speed sensor for the ASOS system there has NOT been installed yet, although Eugene’s has.  The NWS is installing more accurate windspeed sensors at our local sites over the next few months.  It basically boils down this; the ASOS units installed in the mid 1990’s recorded a longer "peak gust", which gave us lower peak windspeeds the last 12 years.  The new instruments will take us back to the "2 second peak gust" measurement.  A prime example is that no station in the Valley recorded a peak gust above 58 mph in our big December windstorm.  Yet home weather stations recorded 60-70 mph gusts or even a bit higher in spots.
Much slower weather tomorrow and then a juicier system moves in later Friday.  The long range picture (the rest of April?) is a succession of troughs and weak ridges for plenty of showers/rain.  The dry periods will be short lived…Mark

Back on Track

April 10, 2007

SnapshotI missed a day yesterday…felt a bit uninspired with the weather pattern apparently.  But I’m back now.
The graphic to the left indicates snowpack on the ground compared to normal on this date.  It’s interesting to note after reading the Water Supply Outlook that reservoirs in the Northwest are right near where they should be this time of year…because the early Spring runoff due to warm weather in March filled them up early.  Unless we get significant snow in April, there won’t be a ton of additional runoff in many areas.

Very messy forecasting continues with systems splitting and not moving where we want them to.  Looks like tomorrow’s is moving farther north than initially expected.  Then 850mb temps are going to be cooler Thursday and Friday than expected, so I’ve had to put more rain in the forecast and cool down temps too.
The big picture over the next 7 to 10 days shows a constant parade of upper-level lows (cutoff or remaining as troughs) moving southeast from the Gulf of Alaska into the West Coast and then down into the Southern Rockies.  This is a good snow-producing pattern for the Cascades in the winter and it may be makeup time in the Cascades now for all that warm weather in March.  In my fantasy world this means a warm & sunny May.  I have no scientific reasoning for that but it sounds good…Mark

Record Highs Broken

April 6, 2007

SnapshotI feel very good about the forecast for today.   Easterly gradient from PDX-DLS was over 6 millibars this morning, which is unusually strong for the warm season.  But, just as models had predicted, the gradient backed off quickly and at 5pm is down to just 2 millibars.  It was a perfect set up…warming from the downslope wind overnight and this morning, then the wind shuts down just in time for peak heating so we don’t get too much mixing.  The final highs for the metro area are to the left.  Portland, Hillsboro, and Vancouver all set new record highs for the date.
This is all real nice, but unfortunately the weekend forecast needs some major invasive surgery this evening.  That "cutoff" upper level low that was scheduled to harmlessly track through N. California has decided to remain a bit more attached to the trough moving by to the north instead.  This allows a somewhat organized frontal band sitting offshore to pass overhead as it’s dying tomorrow.  Lots of clouds and off/on showers is now the forecast for Saturday.  And instead of 70’s, we’ll be in the mid 60’s or so.  By evening a strong onshore (southwesterly) push has begun too.  That brings in cooler air for Sunday.  The only good news is that we wait until sometime Sunday afternoon for the next system to move inland.  We get a dry window from Saturday night through early Sunday afternoon, then the chilly rains return.  As for thunderstorms…the southeasterly flow is always good for storms in the warm season, even when models aren’t too keen on the idea west of the Cascades (as they are tonight).  However, I notice both the MM5 and our own 21z RPM model just out show a sudden "blowup" of moisture moving up the Valley from 3am-8am.  The look of it on the two models looks "thundery" to me, so there is a chance later tonight.  Tomorrow though should just be plain old showers after 10am…I’ll post later if anything changes, otherwise enjoy the Easter Weekend…Mark

11pm Update:  Forecast (unfortunately) appears to be on track with IR satellite and radar showing things beginning to fill in across Western Oregon.  Some nice pulsing storms moving up the east side of the valley too.  Looks live movement is due south or beginning to turn slightly southeast.  That’s exactly what the MM5 and our own RPM model show…lots of showers and the flow turning southeast by daybreak overhead.  Looks like a good morning to sleep in…after hopefully some lightning sometime after 1am???

Very Warm Friday

April 5, 2007

SnapshotA very nice warmup today with perfect offshore flow conditions.  In fact there was just a bit too much easterly wind along the Columbia River from PDX to Troutdale.  Highs in that area were only 68-73 degrees.  Those were the coolest spots in the metro area.  Other areas made it to 76 (at official stations).  We should see just slight warming tomorrow in those areas, but as the east wind dies down tomorrow afternoon near the Gorge, more warming there.  Basically I expect more even temperature coverage for Friday.
There is a problem with my currently rain-free temperature forecast for the weekend.  GFS and WRF now have the upper-level low a bit closer to us Saturday.  It could be a good convective day across the central and southern parts of Oregon.  Both of those models have some rain showers by afternoon over even Northwest Oregon though.  Past experience tells me that’s unlikely, but possible.  I’m also concerned that we will see a major marine push on Saturday night, which could keep Sunday cooler and cloudier than my forecast currently indicates.  I may make a change for the 11pm newscast.  Next week is easy…typical clouds and showers. 

Enjoy Friday, I think Clinton Rockey at the Portland NWS captured the mood well with his Aviation Discussion Haiku:

I’m not nearly as creative as those guys, but…


A Taste of Summer

April 4, 2007

SnapshotIt was interesting to go back and check Easter weather for the last 30 years or so.  I thought I remembered one where I could see snow very low on the Cascade foothills in the late morning.  At the time I lived near Mt. Angel and I clearly remember seeing snow to the east around Scotts Mills.  Apparently I wasn’t crazy.  It was early April 1980.  Heavy and steady precipitation fell at PDX during the morning hours, dropping the temperature down to 38 by 10am, then it jumped into the 40’s by early afternoon.  I’m pretty sure that was the day since 38 degrees at PDX and steady rain with onshore flow should put sticking snow down close to 1000′.  Anyone else remember that?
But lets focus on our warm weather moving in for a few days.  Looks very nice through Saturday now.  No changes in the thinking for tomorrow or Friday (see previous discussion).  GFS MOS (model output statistics) show only 71 the next 2 days at PDX.  The same MOS shows 76 tomorrow at TTD.  Even more interesting is the just-out 00z MM5 from the UW.  It shows around 72 tomorrow, 75 Friday, and 79 or 80 Saturday.  So I’m sticking with my 78 for Friday with good easterly flow through at least the first half of the day.  I bumped up Saturday due to the weak upper low moving in to our south.  That prolongs the ridging overhead and should keep the onshore (cooler) flow from kicking in until Saturday night…Mark