*UPDATED* Dry Thunderstorms With Strong Winds Today

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Summary | Forecast | Monitoring & Reporting | Safety

Dry Thunderstorms are expected this afternoon and evening, mainly across the higher elevations of the west early, spreading east through the afternoon and increasing in intensity after mid-afternoon. A better push of moisture arrives in the early evening, which should encourage more rain to reach the ground, especially over the higher elevations. The primary threats with these storms will be potentially damaging wind gusts over 60 MPH; also, frequent lightning over very dry vegetation sparking new wildfires is also a concern. 

 

Prepare NOW for potentially damaging winds. The atmosphere is ripe for producing strong wind gusts from storms that we can not always see on radar, therefore, some of these damaging winds could come with little to no warning.

Monsoonal moisture surging northward from the American southwest will combine with a couple of disturbances moving across the area (see animations below) to bring the potential for strong to severe thunderstorms across the state today.

 

Friday Morning Water Vapor Satellite Loop
This morning's satellite loop with lightning detections overlaid, shows today's disturbance that will be responsible for the thunderstorms early this afternoon moving into eastern Idaho and Montana. The reenforcing shot will arrive late this afternoon into the evening, this feature can be seen moving onto the Washington coast (a bulb of gray shades dropping south out of British Columbia surrounded by a horseshoe shaped pocked of dry air (orange shades). This second feature will keep some storms going into the night (ready nighttime lightning photographers?).

 

PRIMARY THREATS TODAY

  • Damaging Wind Gusts (> 60 MPH)
  • Frequent Dangerous Lightning
  • New Wildfires
  • Small Hail (<= 1" in Diameter)
  • Brief, Heavy Downpours in the western mountains in the late afternoon and evening
  •   

    Monsoonal Surge Increases Mid Level Moisture (Left), but Surface Remains Dry (Right)

    CLICK LOOP TO ENLARGE

    Time: This loop begins at Midnight Friday morning (06:00Z in the time stamp on the bottom right hand corner of the loop) and ends at Midnight Saturday Night/Sunday Morning.

    Image: The shaded portion of the image shows the layer Relative Humidity between 700MB (about 5,000 ft above the surface) and 500MB, representing the mid level moisture moving around the edge of the High Pressure center to our south (a.k.a. "Monsoon"). The orange shades show the dry areas, the blue show the moist areas, and the green shades show the wet areas that could produce heavy rain.

    Contours: The blue contours show areas where the model believes there will be some precipitation.

    Analysis:  A more robust push of moisture capable of producing some rain that will reach the surface arrives late this afternoon (at around 00:00Z Sat / 6:00pm Friday) 

     CLICK LOOP TO ENLARGE

    Time: This loop begins at Midnight Friday morning (06:00Z in the time stamp on the bottom right hand corner of the loop) and ends at Midnight Saturday Night/Sunday Morning. Every image in the loop represents a 6 hour time step.

    Image: The shaded portion of the image shows the layer Relative Humidity near the surface. The brown to orange shades show the dry areas, the blue show the moist areas, and the green shades show the wet areas that could produce heavy rain.

    Contours: The blue contours show areas where the model believes there will be some precipitation.

    Analysis:  The loop begins with very dry low levels. A more robust push of moisture capable of producing enough rain to moisten up the lower layers reducing the wind threat and increasing the chances of rain wetting the surface arrives on Friday evening (between 00:00Z Sat/ 06:00pm Friday and 06:00Z Sat / Midnight). (Note that even though the low layers are dry, the model still believes there will be precipitation (blue contours)).  So, this is the reason that we believe the thunderstorms will be dry through late this afternoon, with some rain reaching the ground in the western mountains first.

     

    Other Thunderstorms Ingredients (In Addition To Moisture)

     
     
     CLICK LOOP TO ENLARGE

    Time: This loop begins at 5:00am Thursday (12:00Z in the time stamp on the bottom right hand corner of the loop) and ends at Noon Saturday.

    Image: The shaded portion of the image shows the strength of the disturbance as it approaches the state. The purple shades show the areas where the thunderstorms at the surface will receive broad support from aloft, or an area of broad, enhanced instability.

    Contours: The yellow contours show the 400MB Height which represents the general upper level flow. At this level, there is very little interference from the thunderstorms at the surface, which can sometimes provide "convective feedback" and distort the data. If an atmospheric wave is strong enough, it will show up at this level as a "dip" in the contours - like the one that moves through Wyoming on Friday.

    Analysis:  The model is showing weak support aloft for the thunderstorms today, with very deep support with an organized wave on Friday. This is why we expect stronger winds on Friday, in addition to some hail. With increased instability, thunderstorms have stronger updrafts that are capable of keeping a hailstone aloft long enough to become large.

     CLICK LOOP TO ENLARGE

    Time: This loop begins at 5am Friday Morning (12:00Z in the time stamp on the bottom right hand corner of the loop) and ends at Midnight on Saturday Night/Sunday Morning. Every image in the loop represents a 3 hour time step.

    Image: The shaded portion of the image shows the surface based Convective Available Potential Energy (CAPE), one of the parameters used to assess atmospheric instability, a necessary ingredient for the formation of Thunderstorms. The higher the CAPE, the more unstable the atmosphere is, the more severe the thunderstorms tend to be. (Blue and Teal shades)

    Contours: The blue contours represent the numerical value of the expected CAPE.

    Analysis:  The loop shows an increase in instability on this afternoon, which co-incides with the passage of the upper level disturbance (loop on the left), further boosting confidence in the possiblity that thunderstorms will be more severe and widespread on later this afternoon...with the most severe thunderstorms in the western mountains. It also shows another wave of instability moving through on Saturday in the early afternoon, so expect more thunderstorms tomorrow, but it will be an eariler show.

     

     

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