A Convergence Zone Snowfall As Well As Hail Over Key Puget Audio Amongst Deadly Consequences
A really potent Puget Sound convergence zone formed yesterday evening, bringing heavy rain, snow, soft hail, together with lightning inward a band from N Seattle into the Washington Cascades.
And it was a convergence zone amongst serious consequences, leading to dozens of accidents, the closure of I-90, together with the buy the farm of a adult woman together with her unborn child.
As a reminder, a Puget Sound convergence zone forms when low-level westerly/northwesterly menstruation on the Washington Coast is forced to displace around the Olympics together with therefore convergences over Puget Sound. Such low-level convergence forces upward motion, clouds together with atmospheric precipitation that stretches from the Sound to westward side of the Cascades (see figure).
Convergence zones actually rev upward when 2 things occur: (1) an unstable atmosphere, inward which temperature cools chop-chop amongst height, together with (2) an surroundings amongst upward lift.
We had both of them final time. The air aloft was really cold....in fact, the air at 5000 ft (850 hPa) was close tape levels. This is illustrated past times the figure below, which shows the climatology of 850 hPa temperatures at Quillayute, on the WA coast. The bluish business shows the tape lows for the appointment together with the gray circle was the observed value yesterday at v PM. Pretty much tied the tape mutual depression temperature for the appointment at that level!
And at that spot was really potent full general elevator from a good defined upper aeroplane trough moving into the percentage (see the 500 hPa...about 18K foot...map at 8 PM Sunday).
The visible satellite imagery at half-dozen PM yesterday showed a classic convergence zone signature. You tin see the sparse enhanced band over Puget Sound that widens together with stretches towards the Cascades. The classic clear areas to the N together with S of the band was evident-- due to sinking air inward the lee of the Cascades together with mountains of Vancouver Island. And percolating, unstable air offshore (you tin see the convective clouds). Just perfect.
The convergence zone was really evident inward conditions radar imagery. Here are some 1-h atmospheric precipitation totals based on radar data... y'all tin see the band of convergence atmospheric precipitation over the Sound together with the HUGE enhancement on the western slopes of the Cascades.
But turning 180 degrees to the N 1 was viewing the jaws of deep clouds together with heavy rain.
But amongst such a depression snowfall aeroplane together with heavy precipitation, snowfall pushed downwards to lower elevations, together with started roofing I xc downwards to North Bend (see icon from Eastside Fire Rescue). Dozens of accidents occurred, including the terrible fatality crash noted earlier.
And close body of body of water level, at that spot was a position out of heavy "soft hail" together with graupel (small piece H2O ice particle) showers that turned the Earth white inward places.
The threat of a convergence zone was clear before during the day, every bit was the depression snowfall level. Here is a forecast of the 3-h atmospheric precipitation ending 8 PM Sunday, from the UW WRF model run made v AM Lord's Day morning. Not bad.
Seeing this situation, I believe nosotros involve to unwrap a agency to furnish folks amongst ameliorate real-time warnings when this sort of province of affairs occurs, including the purpose of WSDOT reader boards to tiresome traffic agency downwards when such features occur. People tend to motion likewise fast when such inclement conditions occurs together with WSDOT together with my profession involve to construct an infrastructure that volition warn drivers together with strength them to tiresome before this hitting conditions hazards such every bit heavy rain, loss of visibility, roadway ice, together with snowfall on the roadway. Next calendar week at that spot volition move a WSDOT thought session together with I volition endeavour out some ideas amongst them.
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Announcement: The Northwest Weather Workshop is on Apr 27-28
The NW Weather Workshop is the big annual coming together for those interested inward Northwest meteorology. This yr nosotros volition get got a major session on the meteorology of NW wildfires together with others on other aspects of our regional weather. The gathering takes house at the NOAA facility inward Seattle. To persuasion the agenda together with to register, become to the meeting website. The workshop is opened upward to everyone, simply registration is required.
And it was a convergence zone amongst serious consequences, leading to dozens of accidents, the closure of I-90, together with the buy the farm of a adult woman together with her unborn child.
As a reminder, a Puget Sound convergence zone forms when low-level westerly/northwesterly menstruation on the Washington Coast is forced to displace around the Olympics together with therefore convergences over Puget Sound. Such low-level convergence forces upward motion, clouds together with atmospheric precipitation that stretches from the Sound to westward side of the Cascades (see figure).
Convergence zones actually rev upward when 2 things occur: (1) an unstable atmosphere, inward which temperature cools chop-chop amongst height, together with (2) an surroundings amongst upward lift.
We had both of them final time. The air aloft was really cold....in fact, the air at 5000 ft (850 hPa) was close tape levels. This is illustrated past times the figure below, which shows the climatology of 850 hPa temperatures at Quillayute, on the WA coast. The bluish business shows the tape lows for the appointment together with the gray circle was the observed value yesterday at v PM. Pretty much tied the tape mutual depression temperature for the appointment at that level!
The visible satellite imagery at half-dozen PM yesterday showed a classic convergence zone signature. You tin see the sparse enhanced band over Puget Sound that widens together with stretches towards the Cascades. The classic clear areas to the N together with S of the band was evident-- due to sinking air inward the lee of the Cascades together with mountains of Vancouver Island. And percolating, unstable air offshore (you tin see the convective clouds). Just perfect.
The convergence zone was really evident inward conditions radar imagery. Here are some 1-h atmospheric precipitation totals based on radar data... y'all tin see the band of convergence atmospheric precipitation over the Sound together with the HUGE enhancement on the western slopes of the Cascades.
Some lighting was produced past times the relatively deep cumulonimbus associated amongst the convergence zone. The lightning detection network showed on strike correct over Seattle (see below)
You could instruct a bang-up persuasion of the province of affairs from the Space Needle PanoCam. Looking south, the clear zone was evident.
But turning 180 degrees to the N 1 was viewing the jaws of deep clouds together with heavy rain.
With really mutual depression temperature air aloft (about -6C at 850 hPa....5000 ft), nosotros started amongst a really depression snowfall aeroplane (around grand ft). So getting snowfall inward the passes was no problem. Snoqualmie got hitting hard, amongst 16.5 inches of novel snowfall reported. The move past times unopen final nighttime together with was all the same closed....as spinning out cars together with tracks blocked passage.
The threat of a convergence zone was clear before during the day, every bit was the depression snowfall level. Here is a forecast of the 3-h atmospheric precipitation ending 8 PM Sunday, from the UW WRF model run made v AM Lord's Day morning. Not bad.
Seeing this situation, I believe nosotros involve to unwrap a agency to furnish folks amongst ameliorate real-time warnings when this sort of province of affairs occurs, including the purpose of WSDOT reader boards to tiresome traffic agency downwards when such features occur. People tend to motion likewise fast when such inclement conditions occurs together with WSDOT together with my profession involve to construct an infrastructure that volition warn drivers together with strength them to tiresome before this hitting conditions hazards such every bit heavy rain, loss of visibility, roadway ice, together with snowfall on the roadway. Next calendar week at that spot volition move a WSDOT thought session together with I volition endeavour out some ideas amongst them.
_________________________________________________________
Announcement: The Northwest Weather Workshop is on Apr 27-28
The NW Weather Workshop is the big annual coming together for those interested inward Northwest meteorology. This yr nosotros volition get got a major session on the meteorology of NW wildfires together with others on other aspects of our regional weather. The gathering takes house at the NOAA facility inward Seattle. To persuasion the agenda together with to register, become to the meeting website. The workshop is opened upward to everyone, simply registration is required.
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