Thursday, July 2, 2015

Record warm June

June was incredibly hot across the Inland NW, leaving us Meteorologists in awe at the numbers.  And it wasn't just Eastern Washington and North Idaho that set records.  The record warmth stretched all across Washington, Oregon, and most of Idaho as the image below shows.

See the table below for a closer look at the actual numbers.  You can see in some cities such as Ephrata and Portland, the previous records were shattered by 3 to 4 degrees.

So how much above normal was it?  Average temperatures were generally 6 to 10 degrees above normal for the month of June.  That is a huge anomaly when considering this is over a 30 day period.
See image below for the graphical depiction.

The heat wave on June 27th and 28th was exceptionally noteworthy with numerous stations setting their warmest June temperature on record.  Here is a map showing some of the observed readings, with some places such as La Crosse, Walla Walla, Lewiston, Chelan, and Omak reaching or exceeding 110 degrees!

Not only was it hot, but June was also dry which has caused elevated fire danger across the region.  See map below showing the % of normal precipitation for June

So what caused this abnormally warm and dry conditions.  An anomalous ridge was in place over the Inland NW causing the record warmth.

This past June was a month to remember.  We'll see what the rest of the summer offers, with the latest long range outlooks from the Climate Prediction Center favoring increased odds of the continued warmth.

Monday, June 22, 2015

Update to the Potential Record Heat

First, it still looks like a hot weekend coming up.  But the details are becoming a bit muddier.  In our previous blog, the computers were calling for a hot, dry, cloud-free area of high pressure to park over the Pacific NW.  Here's the GFS forecast for atmospheric moisture that was made Saturday evening that is valid for this coming Sunday.

GFS Forecast of Relative Humidity created Saturday 20 June valid Sunday 28 June
The brown color indicates low humidity, which equates to a cloudless sky, while the green is moist areas that would be cloudier.  Now here's the same forecast from the most recent run of the GFS:

GFS Forecast of Relative Humidity created Monday 22 June valid Sunday 28 June
Notice the difference?  See all that green over Washington and Oregon.  That would be a batch of clouds.  The GFS model has changed it's mind a bit.  Why the change?  In the first forecast, the GFS predicted the high pressure to be directly over the Inland NW, which would deflect any clouds/moisture around it, keeping our skies sunny.  Now, the GFS has the high pressure to our east.  Still hot, but it allows clouds/moisture from the south to move up from Mexico and California into the Pacific NW.

Here's the current forecast for Monday.  Still plenty of clouds over the Inland NW.

GFS Forecast of Relative Humidity created Monday 22 June valid Monday 29 June

So what does this mean?  If the clouds do indeed occur, that will help to keep temperatures a bit cooler than previously thought.  Also, this moisture could lead to thunderstorm development over the mountains, which might provide further cooling.  All of this is still just speculation at this time. 

So how hot will it get?  Here's our current forecast temperatures for Sunday.

If this verifies, the 102F at Spokane would not only be a record for the day.  It would be the hottest June day ever in Spokane (the current record is 101F set in 1992).  That's a significant record that could be broken.  In fact, a number of locations could set their record for the hottest June day ever.

But as is usual, the computers have some slight disagreements on the exact temperature.  Here's an example.  The table shows some computer forecasts for Spokane for the Saturday-Monday time frame.

                       Saturday                      Sunday                       Monday
Model A               102                            105                             98
Model B                 98                            103                           missing
Model C                 97                            102                             96
They're all hot, but some are a little hotter than others.

While the potential cloudiness could keep temperatures a little cooler during the day, they would have the opposite affect at night.  Clouds act like a blanket and trap the heat.  This could result in some very uncomfortable sleeping weather, especially if you don't have air conditioning.  Here's the forecast low temperatures for Sunday night. It's possible that a few locations in the Columbia Basin might not cool below 80F.

Again, the weather often comes down to the details, and the details are the hardest to predict, especially this far out.  Suffice to say, it's going to be hot this weekend and possibly the following week.  Just exactly how hot will it be?  Will there be any clouds?  Any thunderstorms?  Those details will hopefully get clearer as we get closer to this event.  We ended the last blog with a reminder:  we had a similar hot forecast for this time of year 2 years ago, and some unexpected showers resulted in cooler temperatures than forecast.

Saturday, June 20, 2015

Record Heat Returning to the Inland Northwest?

Since our last mini heat wave around the 10th of June, temperatures across the Inland Northwest have generally remained above normal.  If we just focus on afternoon highs, the term "above normal" suggests that we are warming above 30-year averages which range from the lower 70s to lower 80s °F.  I think it's safe to say that the current string of above normal warmth has been manageable with highs only a handful of degrees above June's standards.  Dryness levels on the other hand, are another story, but we will reserve that for a different time.

Following that early June heat wave, a low-amplitude jet stream has been in place across the Eastern Pacific, Pacific Northwest, and Upper Midwest.  We have seen a few minor shortwaves rippling through at times but overall, no major storm systems or swings in temperatures.  Another feature of note has been a persistent area of low pressure residing over British Columbia.  

Saturday jet stream (color contours) overlaid with 500 mb heights
This low has helped the flow remain flat and as a result, prevented the dome of heat strengthening over the Desert Southwest from expanding northward.  This time of year it's not uncommon for triple digit heat in the Desert Southwest but it has been anything but normal.  Temperatures in Phoenix for mid June typically range 103-105 °F.  On Friday, Phoenix warmed to 114 °F, marking the 5th consecutive day that temperatures exceeded 111 °

High temperatures Friday 6/19

Now let's shift our focus to the forecast.  Sunday to Wednesday, only minor changes are expected. The trough currently off the coast will weaken while traversing the region.  It will increase the risk for mountain thunderstorms and deliver locally breezy winds but temperatures will generally remain steady in the upper 70s to 80s °F.  By Thursday, the pattern over the Pacific will begin to shift.  The area of low pressure currently along the western tip of the Aleutian Islands will shift east, amplify, and become the dominate area of low pressure between the Rockies and the International Dateline.  Yes, this means the persistent area of low pressure that has been lingering over British Columbia will finally depart.

Saturday morning Water Vapor satellite image with 500mb heights overlaid

If we fast forward to Sunday, here is the output from the GFS weather model: 

Sunday (June 27th) jet stream (color contours) overlaid with 500 mb heights

The GFS is indicating a ridge of historic proportions across the Western US.  Will this really pan out? Lets see how additional models stack up.

 4 different model output for Sunday (June 27th).  Jet stream (color contours) overlaid with 500 mb heights
As you can see, there is good agreement that a strong ridge will develop over the Western US but definitely some uncertainty exactly when the ridge will be strongest over the Pacific Northwest. The model output from the "less amplified" solutions did support the GFS output at one time or another but Saturday morning runs trended a bit flatter, at least for the Sunday time-frame.  When I investigated those "flatter" models a bit further, I noticed two things: 1) They eventually come into line with the GFS, just a day or two later and 2) They still indicate enough warming in the lower-levels to support 90-100s °F.

Confidence is rapidly increasing for a strong warming trend for next weekend and early next week which is likely to yield temperatures 15 to 25 degrees above normal.  

The Climate Prediction Center outlook would agree.

What are the odds we see record heat?  First lets see how this compares historically. Utilizing the GEFS (Global Ensemble Forecast System) and M-climate Return Interval, we see that 850 mb temperatures by Saturday evening are already approaching values seen once every 10 years in Southeastern WA and outside the database near the Cascades and Northern Mountains.  This particular model output does not have data for Sunday onward but I imagine a similar signal. 

M-climate return interval from GEFS mean 850mb temp

I also investigated sounding climatology from the Storm Prediction Center Page:

Example of sounding climatology from SPC.  This particular graph plots historic 700 mb temps

Of a few variables examined, output from the GFS indicated the possibility that the ridge could be of historic proportions for these dates in June.

If these numbers were to come to fruition, record temperatures are a strong possibility.  More importantly, the excessive heat will impact numerous outdoor sporting events, recreation, and festivals that are scheduled for the weekend and continue to have large impacts on outdoor activities and workers early next week.  The NWS forecast only goes out through Saturday so for the time being, here is the temperature forecast from the BCCONSALL, one of our more reliable model outputs that uses an average of medium range guidance and applies a bias correction.  In summary, highs will have the potential to soar into the 90s and 100s Saturday with many locations near or exceeding triple heat thereafter.


BCCONSALL High Temperature Forecast for Saturday 6/27



To put this into perspective, many locations could come close to breaking their all time warmest June temperature with the current records listed in the table below.


Tuesday could be just as hot!  As we go into July, the outlook from the CFS does not offer much hope that the Northwest will cool off anytime soon.  Note the warm anomaly in 850 mb temperatures planted directly over the Northwestern US.

So a good blog always adds some doubt to the main argument right?  Well, we were faced with a similar scenario two years ago when forecast models advertised a major heat wave for the end of June.  This happened to correlate with a large basketball tournament held in downtown Spokane.  The weather models a week out were shouting HOT HOT HOT!  Long story short, it was warm but not unbearable as a combination of clouds and thunderstorms kept temperatures in check.  Will history repeat itself?  Stay tuned!

Sunday, May 31, 2015

Does Monday still look like a severe day?

A few days have come and gone since our last post about the potential severe weather event for the first day of June. So how are things looking now that the event is nearing? Well according to the water vapor imagery below, it's looking pretty good. See the swirl off the northern California Coast? That's the deep low-pressure system which will deliver the active weather as it moves toward the Inland Northwest. Why is this low important? Well for a good thunderstorm day we need three key ingredients: lift, instability, and moisture. The low will provide us with the first ingredient.

Animated water vapor imagery. Note the swirl off the Northern California coast. 

The models are very consistent in taking this low from its current position off the California Coast toward the Washington/Oregon border by afternoon and then toward the Washington/BC border by evening. This pattern resembles the typical negative tilted pattern we associate with severe weather in the Inland Northwest. The track of the low will ensure that the region will be subject to strong lifting potential beginning in southern Washington and central Idaho in the morning and spreading northward through the day. 

500 mb forecast with precipitable water forecast

Notice the shading in the 500 mb map above? That represents the precipitable water forecast. The greens, blues, and purples depict where the juiciest air will be located, Initially the pool of moisture, currently over far northern Oregon, will shift northward tonight and then become enhanced with even more moisture from the incoming low. How much moisture will we see? We forecast that using  a parameter termed precipitable water. Precipitable water is a figure used to represent how much water the atmosphere is holding. The precipitable water forecasts are expected to reach  values are forecast to exceed an inch over portions of the Inland Northwest by afternoon. How unusual is that? According to the graphic below, it would be placed in the 97.5-99th percentile for this time of year. So it will be far from typical. 

Precipitable Water anomaly
So with the two key pieces in place, what about the third, instability? Well it looks like that piece of the puzzle will be realized as well. If you recall our previous blog post, one of the ways to measure potential instability is looking at the lifted index values. If we see negative lifted index values, that indicates potential instability. So as early as 5 am, we begin to see some of this instability. Notice the yellow and orange shading over southeast Washington? This is enough instability to support thunderstorms even without the benefit of daytime heating. 
5am Monday Lifted Index Forecast
How about later in the day? Suffice it to say the instability will not be lacking. The entire region is expected to see negative lifted index values, with the best instability represented by the -6 to -8 values over extreme eastern Washington and north Idaho. That's about as good of a lifted index as you can expect to see over the region. 
5 pm Monday Lifted Index Forecast
So with all the pieces in place what would we expect to happen? We think there will be a band of showers and thunderstorms early in the morning spreading across the Washington/Oregon border, which should slowly work their way northward through the morning. How extensive this band will be remains rather uncertain. One of the weather models is forecasting the radar to look like the image below. Notice the nice cluster of showers and thunderstorms near the Blue Mountains in SE Washington. This coincides nicely with the good pocket of instability forecast by another model.  

7 am simulated radar image

By midday, this band is expected to drift farther north, but could lose some of its definition and strength.  
11 am simulated radar
However, the first band which moves through will further moisten and destabilize the atmosphere before the strong upper-level disturbance tracks toward our region. So what will the afternoon look like? This is far from certain, and there are as many answers as there are high-resolution models. Here's just one of the forecasts for 5 pm. 

5 pm simulated radar
That is a pretty impressive simulation with strong thunderstorms located across the northern portions of Washington as well as in the southern Idaho Panhandle. However recall that the best instability (or lifted index values) were located over the Idaho Panhandle. So we have better faith in the eastern portions of this radar simulation verifying. Another thing we can look at is an ensemble of simulated radar returns. The image below shows where the greatest risk will be for the biggest thunderstorms (chances of having a 40 dbz or stronger radar echo). The regions shaded in purple have the best chances (over 90%) followed closely by the reds (over 70%). This would highlight two areas. The Cascade crest and over the southeast corner of Washington and the southern Idaho Panhandle.
Ensemble chances for 40dbz or higher echoes
So what will the main risk of severe weather involve tomorrow? Based on the instability, the biggest risk looks to be large hail. If we look at the model soundings they are likely a little too moist to support widespread wind damage, however, we still expect to see some strong wind potential with a few of the storms. 

So what is the typical weather we experience with this type of upper-level pattern? We can utilize a fascinating tool produced by the Cooperative Institute for Precipitation Systems (CIPS) at Saint Louis University. They created a tool that makes an analog of the 15 closest weather patterns (since 1980) to what the forecast weather pattern is supposed to be. So below we see the forecast for tomorrow in red compared to the mean of the top 15 analogs (or pattern matches). This looks like a pretty good fit.

500 mb forecast for tomorrow (red) plotted against the 15 top weather analogs since 1980
So what weather was experienced on those days? Interestingly enough, quite a bit. Of those 15 days that matched Mondays expected weather, there were widespread severe reports. Most of them were related to hail, but a good sample of the reports were related to wind as well. Also, notice there were 3 tornado reports in the Inland Northwest. We do not expect to see tornadoes on Monday, as the wind patterns are not quite right to support violently rotating storms, however, they have occurred in this weather pattern before. 
Severe reports from the top 15 analog days to Monday's weather pattern

The other risk we see tomorrow will be for flash flooding. The storms which develop tomorrow will obviously contain copious amounts of moisture. And more importantly they could be slow movers. 
The risk of heavy rains will likely continue through Monday night before tapering off. Here's a look at the 24-hour precipitation forecast from 4 different weather models.

Precipitation forecast from 11am Mon-11am Tue
That's a lot of precipitation (purple amounts are above  0.75") and there is a fairly consistent message that the bulk of it will occur across the northern quarter of Washington, the Cascade Crest, and over the Idaho Panhandle. Since much of this will be attributed to thunderstorms, there is likely to be a high variability over short distances, with some areas likely to receive much heavier amounts. 

Stay tuned for updates to the forecast as this will likely be a very active weather pattern. 

Friday, May 29, 2015

Severe Weather Monday?

You may have heard about the potential for severe thunderstorms on Monday, June 1st.  We've been talking about it in our forecasts for the past couple of days.  So how likely is this?  Let's take a look at a few things.

First, thunderstorms rely on instability.  There's several ways that meteorologists assess the instability of the atmosphere.  One of the more straightforward methods is called the Lifted Index, or LI.  There are more sophisticated methods, but we'll stick with the LI for simplicity sake.  Essentially, if the LI is less than 0, then the atmosphere could be unstable, leading to thunderstorms.  The more negative the LI value is, the stronger the thunderstorms could be.

So here's 4 LI forecasts for Monday afternoon.

Lifted Index forecasts from four models valid Monday afternoon, 1 June 2015

The yellow, orange, red, and pink colors show areas of LI less than 0, with pink showing the areas with LI less than -4.  So as you can see, these 4 models all show instability on Monday afternoon, with some areas of rather strong instability (pink shading).  The exact location varies a bit, but in general they agree on the southern Idaho panhandle.  So from an instability standpoint, Monday certainly looks favorable for strong thunderstorms.

Another parameter we look at is wind shear.  We look at this over a layer of the atmosphere, typically from the surface up to about 4 miles.  Shear measures the change in wind speed as you go up.  For strong storms, we want lots of shear.  This helps the thunderstorm develop.  Weak shear means the storms will be more vertical, which isn't as good for strong storms.

Here's the shear forecast from the GFS model (the others are similar to it)
Forecast 0-6km Wind Shear for Monday afternoon, 1 June 2015

The colors of purple indicate shear of less than 30 knots.  This isn't very strong.  The cyan color shows shear of 30-40 knots, which is moderate, but still not strong.  So the shear forecast doesn't look very promising for strong thunderstorms.  

We also need a "kicker", something to get the ball rolling so to speak.  Often times this can just be the sun warming the ground.  So let's see what the forecast looks like for clouds.

Relative Humidity Forecast for Monday morning, 1 June 2015

This is the Relative Humidity forecast from the GFS model for Monday morning.  The green shading shows the atmosphere nearly saturated, which usually means clouds.  As you can see, there's the potential for a lot of clouds Monday, which would limit surface heating from the sun, and thus diminish the thunderstorm chances.

But there are other ways to make thunderstorms without sunshine.  A strong low pressure system can do the trick.  And that's what is causing the spiral of green off the Oregon coast in the above image.  This low could bring enough "dynamic" lift to kick off thunderstorms.  In fact, for  strong/severe storms, we usually want both (sunshine and strong low).

Here's the model precipitation forecast from 4 models.  Again, there's fairly good agreement.  These would seem to indicate that the best activity could fire off in the Panhandle and quickly move into western Montana.

Forecast precipitation from four computer models, valid Monday evening 1 June 2015

This is still a few days away, so there's still time for the models to refine their forecast.  Timing will be critical.  If the low comes in too fast, there will be too much clouds; too slow, and the sun will be setting before things can get going.  So as always, stay tuned to the forecast.

Wednesday, May 20, 2015

Is it still looking wet for this Memorial Day Weekend?

So a couple days have passed since our last blog post about the weather outlook for the Inland Northwest for the upcoming Memorial Day weekend. Consequently, our confidence in what sort of weather to expect should be increasing. Recall that in the last post, there were suggestions that this could be a very wet weekend. In fact, perhaps the wettest Memorial Day weekend since 1997 and the second wettest on record (since 1970). So is that still the case?

Saturday 500 mb height
Above is the 500 mb map for Saturday from the GFS. This is a similar setup to the maps we explored earlier this week with a deep low centered over the Pacific Northwest. So is this GFS run an outlier or do other model agree with the solution?

4 different models showing 500 mb heights for Saturday (upper left model did not come in fully)
Here's is a look at 4 models compared to each other and they all show a low focused somewhere over the Pacific Northwest on Saturday. So where is this low on Sunday?

500 mb maps for Sunday
Again there is great agreement that there will be a low focused somewhere over the Pacific Northwest. The top 2 models take the low into southern Oregon, whereas the bottom two models drop the low into southern Oregon. Now, what the positioning of the low on Memorial Day?

500 mb maps for Monday
Again all the models keep the low over the region, however, the consensus is to drop the low south of the Washington/Oregon border.

So our confidence in this event is quite high. We are certain this low will form and move over portions of the Inland Northwest however how long it will remain over the area and where its precipitation  band will set up is the big question. Looking at the GFS for the Saturday and Sunday yields a significant northwest to southeast orientated band of precipitation.

48 hr precipitation amounts for Saturday-Sunday (latest model run )
This is quite similar to the previous model run we looked at a couple days ago(see below). Both model runs show a similarly oriented band of precipitation, however,  the latest version has the band a little farther to the west leaving places such as Sandpoint and Colville much drier than the previous forecast.

Rainfall forecast for Saturday and Sunday (Monday's model run)
Obviously wherever this band sets up will determine who gets a lot of rain and who doesn't. If we decide to consult another model solution it also shows a similar NW-SE band setting up, but this time it's displaced even further west. If this solution were to pan out even Spokane would miss out on the bulk of the rain as would the Silver Valley. 

Another Saturday-Sunday 48 hr precipitation forecast

So given these uncertainties it will be hard to pinpoint exactly where the band will take up residence. This is where ensemble model forecast can sometimes help to pinpoint the band (s) of heavy precipitation. So once again referring to the GEFS/NAEFS ensemble forecasts we see that it maintains a NW-SE oriented band of heavy precipitation as well. However the model has backed off from previous runs which suggested this would be a 99-99.9 percentile event for this time of year. Nonetheless the model still suggests this is potentially a 90-97 percentile event which is still significant. 

NAEFS/GEFS Ensemble 48 hr rainfall Sat-Sun

So what about the temperature forecast? We are holding onto our thoughts of hitting near 70° each day in Spokane this weekend, however if the band hits our area what will our temperature be? To say there is some uncertainty in this forecast would be an understatement. The 12z run of the GFS (dark blue line) has our high hitting the mid-70s that day. How about the 18z run of the GFS? A chilly mid-50s! That is about as uncertain as things can get. Its pretty much the same story for other parts of the Inland Northwest including Moses Lake (bottom meteogram)

Meteogram for Spokane
Meteogram for Moses Lake

This forecast remains a problematic one. Suffice it to say a good portion of the Inland Northwest is going to see a soggy beginning to the holiday weekend. Specifically where that will be, we still can't say with good confidence.  We expect the wettest day of the three-day weekend will be Saturday with a gradual improvement expected after that.