Friday, June 20, 2014

Hoopfest 2014

Hoopfest 2014:  How is the Weather Looking?

Weather Outlook for June 27-29, 2014

   With Hoopfest right around corner, here is a general outlook of the potential weather for the weekend of June 27-29, 2014. 

Here is a quick look at the previous five years of max temperatures and rainfall on these dates for the Felts Airfield near downtown Spokane.  This weekend has generally been pleasant with very little rainfall and warm temperatures.



The following images are of the GFS and ECMWF 500MB Heights and 850 Temperatures in Celsius.  A quick description these can be found at the bottom of the ECMWF site.  The images are indicating a low pressure system impacting the region beginning Friday and lasting through Sunday.  The important take away from these images is the cool 850 MB temperatures over the region during the weekend.  These temperatures will be around 11°C ( 51°F).  The 925MB high temperatures for the weekend are around the Low 70’s.    


The following images are the GFS 12 hour forecast for rainfall on Saturday and Sunday.  The Low will bring a lot of moisture with it.  Rain showers can be expected throughout the weekend with an occasional thunderstorm.  Models are pointing to Friday having the most potential for thunderstorms and decreasing chances throughout the weekend.

                In Summary, this Hoopfest has the potential to be the wettest and coldest in the past few years.  Please plan accordingly when making your plans for this weekend.  As always, this outlook is subject to change as more information becomes available.  Keep track of the latest forecast at

Tuesday, June 17, 2014

When Does Summer Start in the Inland Northwest

OK, you're looking at the calendar and at the weather outside.  It's June 17, and the temperatures are in the 50s with cloudy/rainy weather.  In most locations, those weather conditions aren't typically found in mid-June.  But in the Inland Northwest, it's not that unusual.

Temperatures at 346pm on 17 June 2014

The culprit is a large area of low pressure that slowly moved across our area.  It's now east of us, but the moisture often wraps around these slow moving lows.  So our rain and clouds are actually coming from Montana.

Infrared Satellite image at 3pm 17 June 2014

This kind of weather leaves folks wondering if summer will ever arrive.  Which leads to the question:  When does summer start?

If you look at your calendar, you'll see that June 21st is the first day of summer.  But in reality, that's just the longest day of the year.  It doesn't mean that meteorological summer has arrived. Try telling folks in Phoenix, Arizona who have been seeing triple-digit temperatures since early May that it's still Spring.  It's kinda silly to think that a season will start on the same day for all locations, Miami to Anchorage.

Meteorological summer is defined as the months of June, July, and August.  This is a little better than the calendar definition.  But again, not very realistic to apply to all locations.

So how do we define summer in the Inland Northwest?  We could come up with any number of measures (e.g. average temperature, hours of sunshine, etc).  But in general, we define summer as being from the 4th of July to Labor Day.  Now of course, in any given year, we can see hot weather in May and June.  But these warm spells typically are only for a few days, and are often followed by a rather cool period.  July and August are more likely to be dominated by warm-to-hot weather, with a few cooler spells occasionally thrown in.

The chart below shows the percent of days that the daytime high temperature is colder than 70F.  As you can see, there's still a fair number of days in late June (20-30%) that don't reach 70F.  But by early July, those cool days become very rare, less than 10% of the time.  Conversely, by the end of August, we're already starting to see an increase in sub-70F days.  In other words, summer in the Inland Northwest is about 2 months long.

Percent of Days at Spokane Airport where Max Temperature < 70F

Our temperatures are going to rebound rather quickly though.  Here's the forecast for the next 7 days.  By Friday we'll be approaching 80F, and mid-80s by Sunday and Monday.  These past few cold days will be a distant memory.

7 day temperature forecast of Spokane, WA

Wednesday, June 11, 2014

Severe Weather Tomorrow??? It's a Possibility.

We have all heard of the calm before the storm, today could be just another chapter in that book. This afternoon will feature highs in the 70's and 80's under mostly sunny skies. Come tomorrow the chance for showers and thunderstorms will be on the rise as an area of low pressure approaches the Inland Northwest. Temperatures will continue on the warm side of normal, but increased moisture will push ahead of the low pressure center increasing our chances for convective activity or thunderstorms. In this post we will evaluate the chances for thunder around the region and the potential timing through various weather maps and products.

So lets start out with today and move forward from there. Our current pattern has a ridge of high pressure directly over the Inland Northwest keeping conditions calm and pleasant. The ridge also allows for warm southwesterly flow to advect into our area bringing above normal temperatures today. We will take a look at the current set up in the following image.
 11am PDT Infared satellite map with 500mb heights
From the image we can see the area of low pressure to our west and the current ridge over us. The ridge is also diverting much of the cloud cover to our north. As the low slowly moves onshore the ridge will continue to be shifted to the east allowing clouds to move east of the Cascades. Not only will this bring increased cloud cover for tomorrow afternoon, but also increased moisture through the atmospheric column allowing better instability. So lets take a look at the increased moisture moving in. This can be accomplished in a couple of manners, but we will look at Precipitable Water or PWATs in the atmospheric column.

Precipitable Water values from 11am today (left image) and 5pm Thursday (right image)
The images above show the increase in atmospheric moisture from today to tomorrow from the North American Model (NAM). For much of the Inland NW we will see an increase of nearly a quarter of an inch of precipitable water. Another method to address the amount of moisture would be the change in forecast soundings which show temperature and dewpoints up through the atmosphere. Next we will examine the forecast soundings to see the change in moisture from today to tomorrow.
NAM forecast soundings from 2pm today (left image) and 2pm Thursday (right image)
From the sounding you can see the major differences in the amount of moisture present. The red line would indicate the temperatures and the green indicates the dewpoint which reflects the amount of moisture in the atmosphere. For the left image a dry layer is noted around 500mb (where the green line moves away from the red) whereas for tomorrow (right image) much more moisture is present (green and red lines are closer throughout the image). So from these two examples the change in moisture can easily be noted, but will we have the instability to promote the thunderstorms? We will now at these parameters that promote thunderstorms.

For thunderstorms to occur, many things need to be present including lift (forcing), moisture and instability (atmospheric stability). We will first look at the lift for the area and the one way to do this is to compare from today's conditions to tomorrow. Below is an image looking at the Q vector convergence in the upper atmosphere or Div-Q. Div-Q is a generalized way to assess the lifting potential in a portion of the atmosphere.
Upper level Div Q from 11am today (left image) and 5pm Thursday (right image)
From comparing the images we can see the major differences concerning forcing. Tomorrow the low will move onshore bringing a good amount of forcing ultimately aiding in thunderstorm development. With the right image being for 5pm tomorrow, we will most likely be looking at a case that will unfold more in the late afternoon and evening hours rather than early in the afternoon. Would this be a good or a bad thing with it unfolding in the evening? For now it looks good. We have been hitting our high temperatures in the late afternoon/early evening which would be the best time for the stronger storms, so this would also would aid in thunderstorm development. We have already looked at the moisture profiles for the area and have concluded that higher amounts of moisture will be in place. Finally we will look at one of the convective parameters that are normally consulted to address thunderstorm potentials which is CAPE or the Convective Available Potential Energy. First we will once again look at the NAM model. It has been the most aggressive when it comes to CAPE values, but paints a similar picture to the others as to the areas with the best chances for seeing thunderstorms.

NAM CAPE values for 5pm Thursday
From the NAM we can see a broad area with values surpassing 1000J/kg and localized areas greater than 1500J/kg (blue and green shading). If you remember around a week ago on the afternoon of June 3rd we had thunderstorms for much of the area. These storms were also working with around 1000J/kg of CAPE. With the NAM being on the upper end of model perspective lets take a look at another one. Next we will examine the model often used by the Storm Prediction Center (SPC) in Norman, OK which is the SREF or the Short Range Ensemble Forecast.
SREF CAPE values for 5pm tomorrow
Although not as colorful as the NAM, the SREF is also showing higher values for eastern Washington and into the Idaho Panhandle. It also has peak values in the 1000J/kg to 1250J/kg range. So we do have some consistency among short range models of the potential for higher amounts of CAPE. So with all of this in mind, now comes the million dollar? will we see thunderstorms and if so, how strong will they be? Concerning the chance for thunderstorms, it is a given. We will see thunderstorms tomorrow. The next question is where? As we can see, the best forcing will be in the eastern third of Washington and the Idaho Panhandle so these are the locations with the best chances. We do not want to omit the chance for the east slopes of the Cascades or the Basin, but the threat will not be as great as the other locations. From the SPC, they create a calibrated outlook of the thunderstorm chances for a location so lets take a look at what they think.
SPC calibrated thunderstorm probabilities between 5am-5pm Thursday
So from the SPC, they highlight a 40% chance for much of northeast Washington into the Idaho Panhandle.  These are some of the higher values I have seen from this for our area so it would lead me to think the chance for thunderstorms is essentially a slam dunk.  Finally the big one.....will any of the storms be severe? Here at the office we seem to think the potential is definitely there for strong storms. Comparing to last week, we had similar CAPE values, but tomorrow we actually have better dynamics to support storms. The SPC also does a product for the chances of severe storms and here it is.
SPC severe thunderstorm probabilities for 5pm Thursday
While the chances for severe storms do not look very high, they still highlight the potential for portions of the area. This product usually only has slight chances for us when severe events do occur, so the potential is there. The region will want to keep an eye on the skies tomorrow as active weather looks to be a given.