June 09, 2023

Finally! Rain West of the Cascade Crest

After a long dry period, western Washington and Oregon are finally getting some significant rain.

The radar image at 7 AM shows a mass of precipitation extending roughly from Seattle to Portland, some of it of moderate intensity (yellow colors).   This precipitation is coming from an unusual direction:  from the east.

The infrared satellite image at the same time shows the extensive clouds over the region, some of it clearly convective.  But none of it is deep enough for lightning.

As of 8 AM, there has been significant 24-h precipitation over the Cascades and southwest Washington (see below)

The latest NOAA HRRR forecast of accumulated rain from 5 AM Friday until 8 PM tonight, predicts up to approximately half an inch from the Olympics to the south Cascades.

An Admission

    This situation has not been particularly well forecast.   On Wednesday afternoon our model prediction had the rain heading further northward (the 72h rainfall total ending 5 AM Saturday is shown below).

On Thursday morning, our prime tool for understanding forecast uncertainty...ensembles of many high-resolution forecasts, was starting to show the potential for rain with about half of the ensemble members going for significant precipitation (see accumulated precipitation plots for forecasts starting 5 AM Thursday, time increases to the right).  Each line is one model, the black line is the average of all of them.

Accumulated Precipitation at SeaTac

By last night, the ensembles were going wet (see the forecasts below).

The bottom line is that the models had problems initializing the weak disturbance associated with this modest, relatively small-scale rain area.   I will be examining this event to understand its evolution better.

Saturday will be a transition day (some clouds and showers early) and Sunday will be warmer and dry.

June 07, 2023

The Worst Air Quality in New York History?

A historic meteorological/air quality event is now occurring over the New York metropolitan area.

And as far as I can determine, this is the worst air quality event ever recorded there over the past 70 years, the result of smoke from large wildfires in northern Quebec.  

Certainly, the worse air quality ever observed during the warm season in the region.

The real-time cam image of New York City around 1 PM PDT is stunning (see below)

And the high-resolution MODIS imagery reveals the area of dense smoke over the Big Apple:

When I checked the small particulate levels (PM2.5, the concentration of particles smaller than 2.5 microns--millionth of a meter), using the PurpleAir network, I could not believe my eye..values of 300-450 micrograms per cubic meter.

And a plot of PM2.5 from an official site in Queens, NYC shows levels getting to around 800 micrograms per cubic meter...just unheard of.

The weather situation has been perfect to pull the Quebec smoke into the New York area.  Why?   Because of a strong low-pressure area just off the NE coast (see map below at around 5000 ft).  I have added a red arrow to show the low-level wind flow.

The NOAA HRRR Smoke model clearly shows the circulation of the smoke around the low:

So why have we gotten into the early season wildfire situation in northern Canada?

Because the atmosphere over North America has been in an unusual, persistent configuration, with a ridge of high pressure over Canada and a trough of low pressure over California (the figure below shows the situation around 18000 ft for the past month).  Red indicates much higher than normal heights, which are associated with warmer temperatures at low levels, blue indicates lower-than-normal pressure (troughing).

A similar pattern has been in place over the last 90 days (see below).

The high pressure resulted in unusual warmth and drying of the surface fuels.

Is there any reason to think that this configuration is the result of global warming/climate change?  Current research suggests no.

Finally! Rain West of the Cascade Crest

After a long dry period, western Washington and Oregon are finally getting some significant rain. The radar image at 7 AM shows a mass of pr...