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.