This April will end up being the 10th coldest April ever recorded in Seattle, but in Bellingham, this will be their 5th coldest. Why have we been so cold? The answer is that instead of getting customary high pressure that settles in off the coast and allows sunshine to warm things up along with warmer air in the upper atmosphere, we have been under the influence of cold upper-level troughs continually dropping out from the Gulf of Alaska and the North Pacific. These troughs have ushered in extremely COLD air aloft as well as cool to cold temperatures at the surface. Although these troughs are fairly common for this time of year, the freqency and strength at which they have been occuring this April is practically unprecedented. Snoqualmie pass has gotten 65 inches of snow this month (and still adding on!), their highest total for the month since 1984 (and we may break that). Much of the forecast from yesterday is still on track, except things get really messy for the weekend, with the ECMWF (European) and GFS (NOAA) models giving pretty much exact opposite situations, and they haven’t shown a trace of changing.
Tomorrow will probably be the nicest day of the workweek, with highs near 60. A few showers come in on Friday.
And then the weekend… In fact, the National Weather Service office in Seattle says:
EXTENDED FORECAST IS BOOM OR BUST AT THIS POINT FOR
SATURDAY NIGHT AND SUNDAY. HUGE DIFFERENCES IN THE MODELS WITH THE
GFS BUILDING AN UPPER LEVEL RIDGE OVER THE AREA SATURDAY NIGHT WHILE
THE EURO HAS A COLD LOW OVER THE AREA. NONE OF THE GFS ENSEMBLES
HAVE ANYTHING CLOSE TO THE EURO SOLUTION. IT IS A LITTLE WORRISOME
THAT THE EURO HAS BEEN CONSISTENT WITH THIS TYPE OF SOLUTION FOR A
FEW RUNS. IF THE GFS ENSEMBLES HAD A HINT OF THE EURO SOLUTION I
WOULD BE INCLINED TO ADD A CHANCE OF SHOWERS TO THE FORECAST FOR
SUNDAY BUT FOR NOW GOING WITH THE DRY GFS SOLUTION.
So that is what I will do for now… go for highs near 60 or a little above Saturday through Monday… although this could rapidly change. Stay tuned.
Thursday: 60 45 partly cloudy
Friday: 58 42 few showers
Saturday: 60 40 partly cloudy
Sunday: 61 41 mostly sunny
Monday: 62 42 partly cloudy
Another trough of low pressure comes in next week! And by now you know what that means… 🙂
April 29, 2008
Predicted (on Thursday): 57 41
Actual: 56 41
Well, I’m back from Reno. I am sorry that I did not post a forecast yesterday, I just had too much homework.
The unsettled pattern I talked about potentially having last week is now on us. Today featured showers and sunbreaks as solar heating destabilized the cool and unstable air mass and allowed for those showers to pop up. The Puget Sound Convergence Zone (PSCZ) is causing rain north of us right now, and it should shift south and dump rain over the Seattle area.
The Puget Sound Convergence Zone is a band of rain formed by air converging over the Puget Sound region, and it usually forms in southern Snohomish County or so. When there is a northwest flow aloft, the air splits around the Olympic mountains. One part goes through the Strait of Juan de Fuca, and the other part goes through the Chehalis Gap. When these winds meet back over the I-5 corridor, clouds and rain result from the air rising as it meets each other. However, rising air some place usually means sinking air nearby, so although the convergence zone brings rain, it can clear skies around it because of air sinking.
This week we should gradually get warmer as we become less influenced by a trough of low pressure over the North Pacific and more iinfluenced by a building ridge of high pressure.
Wednesday: 55 40 showers
Thursday: 58 48 partly cloudy
Friday: 60 45 showers
Saturday: 59 43 showers
Sunday: 62 44 partly sunny
Long range: Next week looks sunny with highs in the mid 60s! For now…
April 24, 2008
IMPORTANT NOTICE: I WILL BE IN RENO FROM THE 25TH TO THE 27TH, AND THERE WILL BE NO DAILY FORECASTS DURING THIS TIME
Forecasted: 55 44
Actual: 53 44
At least I got the low temperature right!
First, before I discuss the weather today, I want to talk about La Nina. La Nina is the opposite of El Nino. In La Nina, the waters off in the equatorial Pacific off the coast of Peru cool to below-normal averages, the opposite of El Nino, where temperatures in the equatorial Pacific warm above normal. The reason why this happens is very complex and still not quite understood by scientists. Although waters in the equatorial Pacific in La Nina cool, waters north of that actually warm up. This creates a better breeding ground for the storms that wash up upon the Pacific Northwest, and during this time, the Northwest experiences above normal rainfall, below normal temperatures, and sometimes vastly above normal snowfall. 1998-1999 was a La Nina year, and Mt. Baker ski resort set the record for the most amount of snow in a year in the WORLD with 96 feet. La Nina could be responsible for the above normal snowfall and below normal temperatures we have seen this winter and spring. Snoqualmie pass has seen the most snow in April in 24 years this year!
Longer range weather forecasters rely primarily on two models: the GFS (American) model and the ECMWF (European) model. Lately, they have not been in line, especially on Saturday and Sunday. They differ in the breaking down of the ridge of high pressure we will be under, especially on Sunday. The GFS breaks it down more quickly, and the ECMWF more slowly. The ECMWF has been more consistent with past model runs of it, so I am leaning toward it’s solution. The GFS model also showed the possibility of a bit of light rain Friday night, but it has leaned toward the ECMWF as well.
Models have generally took a turn for the sunnier and warmer.
Because of the confusion, Sunday’s highs could either be into the 70s with sun or into the low 60s with rain after noon. For now, I have split the difference and I will see how it plays out!
Friday: partly-mostly cloudy 59 42
Saturday: mostly sunny 67 45
Sunday: clouds developing 66 44
Monday: showers 56 41
Tuesday: showers 57 41
Long range: Still the same! REALLY long range, though, we might get into some warmer weather
April 23, 2008
Today generally went as planned. It was a cool and showery day, the classic “showers and sunbreaks” type of day in the Northwest. The atmosphere was cool and slightly unstable, which is what caused these random showers to pop up.
But what does instability mean?
When I say that the atmosphere is unstable, it involves two things. One is that the temperatures at the ground are much warmer than those aloft, and the second is that the atmosphere is unstable (lack of inversion, air moving all around, etc.) When the atmosphere is unstable, we get these hit-and-miss showers that pop up.
My forecast hasn’t changed much. Today was a couple degrees warmer than expected (likely due to a strong sunbreak in the middle of the day). It is tough to forecast high temperatures when the atmosphere is unstable like this because high temperatures are often determined by which places get big sunbreaks and which other ones don’t. It is practically like trying to forecast sunbreaks. Nevertheless, tomorrow should be similar to today, and Friday should be warmer with just clouds. Saturday is still on track to be pretty sunny, although the computer models show a weak warm front that might add some clouds. The cold front that was expected on Sunday is now pegged to still be offshore, stalling and weakening as it comes ashore Monday.
My forecasted high and low for today: 51 40
Actual: 55 43
Thursday: 55 44 showers
Friday: 57 44 sunny and clounds
Saturday: 64 45 partly sunny
Sunday: 65 45 partly sunny with rain late
Monday: 57 43 showers
Long range: pretty much the same as yesterday. Unstableness shall prevail. Much of this is due to La Nina (more on that tomorrow!).
April 22, 2008
My first forecast!
What a spring it has been. Record snowfall and low temperatures have occured this month, and we can expect that to continue, although to a lesser extent, over the next few days. A low pressure system currently off the Oregon coast will move east tonight, resulting in increasing periods of rain. Tomorrow, we will be under the influence of a cool “upper level low pressure system.” This type of system occurs in the upper levels of the atmosphere and is a typical occurence during spring. It will drop out of the Gulf of Alaska and stall over the region, with cool temperatures and showers resulting. The Cascades should see more snow. This pattern will continue into Thursday, but by Friday, higher pressure should build over the area, resulting in warmer temperatures and drier conditions.
Saturday should be beautiful. A low pressure system will be approaching by that time, but that will actually warm temperatures on Saturday since it is not over the area yet. This warming will occur due to offshore flow. This means that the wind will flow from the east to the west.
Wind is caused by differences in air pressure in the atmosphere, and wind is the atmosphere’s way of “leveling itself out,” as wind always flows away from high pressure to low pressure. Since there will be low pressure off the coast on Saturday, the air will flow to it. Since the air will be flowing off of the Cascades, the decrease in elevation will naturally warm it and dry it. Saturday therefore could be very warm. The low pressure system will come ashore Sunday, resulting in cooler conditions and a bit of rain.
And now… my five day forecast.
Wednesday: high: 51 low: 40 showers
Thursday: high: 52 low: 41 showers
Friday: high: 56 low: 43 isolated showers to partly cloudy
Saturday: high: 67 low: 45 partly sunny
Sunday: high: 60 low: 43 light rain
Long range: next week, models show us returning to a cooler and wetter pattern, with more upper-level low pressure system regimes. This should help build on the snowpack!
April 21, 2008
Daily forecasts (except when I can’t get to a computer) start tomorrow!