Snow Totals

December 26, 2007

If you had at least 1/2", please put your snow totals only in these comments.  We need several things:

LOCATION, ELEVATION (if you know it), SNOW TOTAL

CONTINUE DISCUSSING WEATHER ON THE OTHER POSTS.


Snow Wrap-Up Christmas Evening

December 25, 2007

Whew!  I’m real happy with the forecast I put in the previous post this morning.  Models absolutely nailed the sudden drop in the snow level to very close to the surface, just as a heavy line of snow gave just about all of us in the metro area a (brief) dusting of snow that has since melted with the south wind that kicked in.  You can see below that I gave a 50/50 chance of 1/2" in the lowest part of the metro area.  Looks like some of you on the hills got that? 

At my parents home in west Gresham there was a dusting on the ground 1-2pm but it was pretty much gone when we left at 3:30pm.  Up at 1,000′ here at home I had maybe an inch or so…but it’s melting with a breezy south wind.

So what about the weather service office?  Was any snow officially recorded?   I see the PDX and TTD obs. never went to solid snowfall, but of course those are automated observations too.  Hopefully the NWS will put out a statement soon.

At 5:30pm I’d estimate the snow level to be around 1,500′ or so, it’s pretty obvious we are getting a milder onshore flow.  Of course with clearing inbetween showers temps at the surface can quickly drop to freezing, so watch out for spots of ice on roadways, mainly on the west side of town overnight.

The rest of my thoughts haven’t changed…see the previous post…Mark Nelsen


Christmas Morning Snow Update

December 25, 2007

No picture today…it’s Christmas Morning and I’m not working, so you only get the bare minimum.  Here are my latest thoughts.

CHRISTMAS DAY:  White Christmas above 1,000′!  A dusting possible anywhere early afternoon.  We’ve seen exactly the same thing several times this season, but this time it’s slightly colder.  Cold overnight airmass, then a front moves in early afternoon with precipitation.  I notice KPTV Tower temps are all at/below freezing, plus the air up above us is quite dry, which should give nice evaporational cooling up there.  Not really any Gorge effect today, so what we have right now is all we get cold-wise.  The MM5-GFS cross section shows the lowest freezing level in the next 72 hours between 1-4pm this afternoon as the precip arrives.  I would say the Gorge (east of Multnomah Falls or above 500′ west end), and areas above 1,000′ west of the Cascades will see a white Christmas today with 1-4".  But I’d put the chance of sticking snow (more than 1/2") in Portland metro area this afternoon at about 50%.  Notice this is higher percentage than what I thought two days ago.  It’s going to be close!  If we get sudden heavy precip with this front immediately as it starts falling, everyone could get a white Christmas!  This evening strong onshore flow develops behind the cold front, so the snow level lifts to around 1,500′ or higher, before dropping back to 1,000′ late tonight as the colder onshore flow works inland.

WEDNESDAY:  Possible below 1,000′ in heavy showers.  It’s ALL dependent on moisture availability.  More accumulation is likely in heavy showers at/above 1,000′.  With those heavy showers, we could get brief accumulation even down in the city.  Keep in mind though that temps in the afternoon between the showers will be up around 40 in the lowest elevations. I say maybe a 20-30% chance of sticking snow in the city

THURSDAY:  Very unlikely below 1,000′.  We do it all again with another system moving in over cooler air.  This one is slightly warmer than Christmas Day, so snow stays at/above 1,000′. 

FRIDAY-SATURDAY:  Warmer, snow level 1,500′ or higher both days…very wet.

So to sum things up…I still don’t see a GOOD chance for snow in the lowest elevations (I-5 Corridor below 1,000′) except briefly this afternoon.

Merry Christmas!  Mark Nelsen


Vacation Extra: White Christmas?

December 23, 2007

Dscf0028 I just took a very close look at the weather maps (while relaxing at home).  Someone today said "how about that white Christmas coming?".  I replied something like "that’s pretty unlikely, where did you hear that?", even though I only had a brief look at weather information the last couple of days and have seen no TV weather reports since Wednesday night.  Funny how sometimes we just spout off with very little information to back it up.  By the way, that’s my daughter Ariel getting a nice bite of snow up on Larch Mountain road Friday morning.  There was about 10" of snow at 2,000′!  Pretty impressive depth, and it’s really hard to sled off the edge of the road and into the ditch…but Daddy did some rearranging of the snow and the kids were happy in the end.

Okay, so what about snow?  Here are my thoughts, which are actually quite similar to the NWS forecast…I must be getting old and conservative, or they are much better than they were 15 years ago…most likely the latter.

TONIGHT:  No, it’s pouring right now with a cold front getting close.  By the way, I think I’ll crack 10" in my monthly rain total at home tonight.  A wet month.

CHRISTMAS EVE (Day or Night):  Very unlikely below 1,500′.  By the time the coldest air arrives tomorrow evening, we’re getting very dry.  Similar to what we saw Saturday.  I think it’s going to be very tough to get snow even at my home (at 1,000′ in the Cascade Foothills).

CHRISTMAS DAY:  Very unlikely below 1,000′.  Why?  We’ve seen exactly the same thing several times this season.  Cold overnight airmass, then a front moves in middle of the day or afternoon with precipitation.  At the same time low level wind is southerly (mainly above the surface, pretty calm down where we live.  Both NAM and GFS say slightly too warm.  MM5-GFS X-Section shows it quite well, as does the meteogram.  I would say the Gorge (east of Multnomah Falls), and areas well above 1,000′ west of the Cascades will see a white Christmas afternoon.  But I’d put the chance of sticking snow in Portland metro area anytime Christmas Day (8am-Midnight) is maybe 10-20%.  The reason I don’t see anything in the evening is that strong onshore flow develops around sunset.  At that point, and until colder air arrives Wednesday daybreak or so…forget about snow below 1,500-2,000′.

WEDNESDAY:  Possible below 1,000′ if the moisture holds up, but it’ll be tough to get snow down below that elevation.  And it’s still only maybe a 20-30% chance of sticking snow in the city.  It would only be showers, and most likely our high makes it up to 39-42 degrees in the city.  By the time it cools off in the city in the evening, we’re drying out again.  But this is probably the best chance for some widespread snow on the hilltops.

THURSDAY:  We do it all again with another system moving in over cooler air.  This one is slightly warmer than Christmas Day, so snow stays well above 1,000′.

So to sum things up…I don’t see a GOOD chance for snow in the lowest elevations (I-5 Corridor below 1,000′) the next few days. That said…lots of spots in the hills will have at least a dusting, maybe more than once, and almost all of us should at least see some snow in the air. Of course this is based on what I see as of Sunday evening.  If we get an area of low pressure that develops to our south, or a very organized system develops in the cold air Wednesday, that’s a different story..Mark Nelsen

Back to Christmas now…


Windy Start…Now the Snow

December 19, 2007

Snapshot Snapshot2I was pleased with the windspeed forecast both on the Coast and in the Valleys.  Looks like peak gusts here in the valley were near or below 40 mph (yes, I know Salem was a bit higher).
Coastal wind seems to have maxed out 50-60 mph in the cities (Newport, Tillamook, Astoria).  But the recent standouts were there once again…The hill east of Cape Meares at 1400′ hit 77, the radio tower in Lincoln City up around 200′ elevation hit 76, and the Yaquina Bay Bridge was 72 mph.

Now it’s time to talk snow…the radar is full of rain moving through the metro area at 4pm headed for the Cascades…can’t wait to see the live shots from the evening newscasts (including on FOX12).  Now that the flow at 850mb. turns westerly, the snow should really pick up in the Cascades due to orographic lifting.

About 10-13" has fallen with this current storm and another 12" or so should fall by the time things die down tomorrow evening.   The snow level dips down to around 1,500′ tomorrow afternoon, then possibly down to 1,000′ or a bit lower tomorrow night.  Unfortunately, the precipitation appears to shut off quickly around sunset, so that’s why I’ve really pooh-poohed the chance for lowland snow tomorrow night.

The next system rushed in Saturday morning; I wouldn’t be surprised to see a minor "Forest Grove Effect" if the precip arrives before 10am.  That’s due to a sharp east-southeast flow ahead of the front piling up some cold air against the Coast Range.  Just a possiblity, but something to watch for since the UW-MM5 hints at it.  That will be system #1 of the new round.  #2 comes in Sunday night and Christmas Eve morning.  #3 arrives Christmas Day late.  The 12z/18z GFS were quite cold behind each system, with snow down to 1,000′ or so Christmas Eve, then even lower the morning after Christmas.  The ECMWF was not quite as cold.  I noticed it had -5 deg temps at 850mb.  That wouldn’t bring snow as low.  So now the 00z GFS comes in with slightly warmer air behind the Christmas Eve front, and significantly more reasonable temps for the day after Christmas…plus it pushes the timing on that front a bit later too.
So…I think we’ll flirt with low elevation snow (to the foothills) both periods, but I still see no decent chance for lowland snow.  Too much westerly flow with cold fronts flying through the Northwest about every other day, not a good chance for cold air to get established.

The big picture shows an almost continuous parade of storms through the New Year…lots more weather fun.  I’ll be on vacation now through Christmas Day, so probably no blog posts until the 26th.  BUT, for those of you expecting a big weather event while I’m on vacation???  Unlikely since I will be in town taking care of Santa Claus duties for a few days.  I could be in here with a moment’s notice!  Mark Nelsen

More later…Mark Nelsen


Snowy Cascades

December 18, 2007

SnapshotThis is a graphic produced from the data output by our RPM-WRF model.  It is run 8 times a day out to 48 hours…a similar model to the UW-MM5.  It has an algorithm that converts precipitation to snow accumulation.  Makes for a nice pretty graphic, in a Joseph’s Coat sort of way.
Storm #3 for this week is rapidly moving towards the Coastline this evening.  The surface low pressure is going to pass very close to buoy #46036 soon.  Then it makes landfall on Vancouver Island midday tomorrow.  The low will be slowly beginning to fill.  Even so, this is still a pretty deep low coming relatively close to the N.W. coastline.  So gusts to 60 mph or so are likely on the Coast.  Inland, we should see stronger wind than today.  I expect more widespread gusts in the 30-40 mph range…not a windstorm, but real breezy midday.
The cold air behind the cold front pours inland tomorrow night.  Models are still insistent on bringing -6 deg. 850mb. temps over us Thursday.  Unfortunately, it sure dries out quickly by Thursday evening.  So snow in the lowlands looks like a tough order.  But read last night’s post.  The possibility in a pattern like this is always there.
After a break Friday, 00z models show the stormy pattern resuming over the weekend.  At this point  I don’t see a significant wind producer or flooding setup.  Too warm for snow through Christmas too.  However, these are relatively cold storms forecast for next week, which means the snow level could dip down pretty low at times after Christmas.  Something to keep an eye on.
A bonus to this weather pattern?  Those of you near and in the west end of the Gorge know.  A parade of weather systems moving into the Northwest keeps stagnant surface high pressure from developing east of the Cascades.  That means no long periods of east wind.  I remember going almost 3 weeks in January 1999 (I think that was the year) with no east wind in Corbett.  That was a La Nina winter too with lots of weather systems moving through constantly…Mark Nelsen


White Christmas?

December 17, 2007

Uswhitechristmas_2Don’t forget that whenever I insert images into the blog, you can click on them to get a larger view.  In this case it’s pretty important because it’s making my old eyes hurt just to squint at this image.  Notice how much company the west side of the Cascades has with the rest of the USA.  Most of the country has a pretty slim chance of seeing an inch of snow on the ground on the average Christmas Day.  And now with only 8 days to go, I think the chance for snow is VERY low for Christmas Eve or Christmas Day.  The reason is that the westerly flow with frequent mild Pacific weather systems will continue through the foreseeable future.

System #2 for this week is arriving tonight.  Earlier today it was accompanied by a 986mb (estimate) low.  That low tracks northeast into the Puget Sound area by early afternoon tomorrow.  Normally this could be a high wind threat for inland areas considering that by that time the isobars are lined up perpendicular to the western valleys.  That can be very good for accelerating wind straight up the valley.  BUT, in tomorrow’s case the low has weakened to 990-995 millibars.  You don’t get damaging, or really even strong, wind with a very weak low that’s weakening as it moves inland.  Models have been showing this for days now, so not really a surprise.

System #3 is racing across the Gulf of Alaska and will be here in 24 hours!  This one should have quite a bit more moisture with it.  Also, a much stronger surface low down around 980mb moves onshore.  This low moves into Central Vancouver Island…a bit too far north to give us damaging wind in the western valleys.  But this should give the strongest wind to the Coastline that we’ve seen in two weeks.  Peak gusts of 60-70 mph are likely out there very late tomorrow night.

A cold trough then follows storm #3 for Thursday and Thursday night.  Thicknesses drop to around 522dm and 850mb temps down to around -6 means snow will be quite close!  I put one little hidden snowflake in the 7 day forecast.   It’s cold enough for snow on the hills for sure.    00z NAM says the freezing level drops to right around 2,000′ Thursday and a bit lower Thursday night.  This pattern tends to be awfully dry, but it IS similar to the day after the big windstorm last December.  Remember what happened that day?  A line of showers in the late afternoon moved from the Scappoose/St. Helens area down through Vancouver and into outer N.E. Portland, giving those areas a good 1/2" or so of snow.  So, Thursday and Thursday night needs to be watched closely.

High pressure settles in to our east Friday for flow turning offshore and likely dry weather.

Saturday-Christmas Day returns us to frequent weather systems moving through.  It seems that the 00z models have pushed most of the action a bit farther offshore though…Christmas MAY end up being pretty quiet…(or may not)….Mark Nelsen