{"id":12846,"date":"2020-08-20T14:49:00","date_gmt":"2020-08-20T20:49:00","guid":{"rendered":"https:\/\/www.coloradofloodthreat.com\/?p=12846"},"modified":"2020-08-24T10:55:18","modified_gmt":"2020-08-24T16:55:18","slug":"fto-08-20-2020-a-couple-days-of-drying-before-storms-return-to-the-forecast","status":"publish","type":"post","link":"https:\/\/archive-coftb.dewberryanalytics.com\/?p=12846","title":{"rendered":"FTO 08-20-2020: A Couple Days of Drying Before Storms Return to the Forecast"},"content":{"rendered":"<p>Issue Date: Thursday,&nbsp;August 20th, 2020<br>\nIssue Time: 2:45PM MDT<br>\nValid Dates:&nbsp;8\/21&ndash; 9\/4<\/p>\n<p><img loading=\"lazy\" class=\"aligncenter wp-image-12847\" src=\"https:\/\/archive-coftb.dewberryanalytics.com\/wp-content\/uploads\/2020\/08\/FTO_20200820.png\" alt=\"\" width=\"880\" height=\"129\" srcset=\"https:\/\/archive-coftb.dewberryanalytics.com\/wp-content\/uploads\/2020\/08\/FTO_20200820.png 1154w, https:\/\/archive-coftb.dewberryanalytics.com\/wp-content\/uploads\/2020\/08\/FTO_20200820-300x44.png 300w, https:\/\/archive-coftb.dewberryanalytics.com\/wp-content\/uploads\/2020\/08\/FTO_20200820-768x112.png 768w, https:\/\/archive-coftb.dewberryanalytics.com\/wp-content\/uploads\/2020\/08\/FTO_20200820-1024x150.png 1024w\" sizes=\"(max-width: 880px) 100vw, 880px\"\/><\/p>\n<p>The stubborn ridging pattern will hang on and persist through this weekend even with a strong incoming <span class=\"glossaryLink\" aria-describedby=\"tt\" data-cmtooltip=\"&lt;div class=glossaryItemTitle&gt;trough&lt;\/div&gt;&lt;div class=glossaryItemBody&gt;An elongated area of relatively low atmospheric pressure; the opposite of a ridge.&lt;\/div&gt;\" data-gt-translate-attributes='[{\"attribute\":\"data-cmtooltip\", \"format\":\"html\"}]'>trough<\/span> from the Pacific Northwest. With the High to our west, a drier air mass will be over the state to start this weekend, so is should stay mostly rain-free tomorrow and Saturday with some <span class=\"glossaryLink\" aria-describedby=\"tt\" data-cmtooltip=\"&lt;div class=glossaryItemTitle&gt;isolated&lt;\/div&gt;&lt;div class=glossaryItemBody&gt;less than 10% areal coverage&lt;\/div&gt;\" data-gt-translate-attributes='[{\"attribute\":\"data-cmtooltip\", \"format\":\"html\"}]'>isolated<\/span> <span class=\"glossaryLink\" aria-describedby=\"tt\" data-cmtooltip=\"&lt;div class=glossaryItemTitle&gt;convection&lt;\/div&gt;&lt;div class=glossaryItemBody&gt;Refers to vertical atmospheric motion driven by buoyancy, i.e., warm air is less dense than cool air, and therefore rises. One of the primary drivers of thunderstorm development, especially during monsoon season.&lt;\/div&gt;\" data-gt-translate-attributes='[{\"attribute\":\"data-cmtooltip\", \"format\":\"html\"}]'>convection<\/span> possible over the southern mountains. By Sunday, the High moves into the 4-corners region and Genevieve moves northward. This is expected to bring some mid-level energy and slightly more moisture into the state for <span class=\"glossaryLink\" aria-describedby=\"tt\" data-cmtooltip=\"&lt;div class=glossaryItemTitle&gt;scattered&lt;\/div&gt;&lt;div class=glossaryItemBody&gt;25-40% areal coverage&lt;\/div&gt;\" data-gt-translate-attributes='[{\"attribute\":\"data-cmtooltip\", \"format\":\"html\"}]'>scattered<\/span> afternoon storms over eastern mountains and adjacent plains. This typical afternoon rainfall pattern should continue into next week with the chances for rain increasing over western Colorado after Monday.<\/p>\n<p>By mid-week, the weather gets a little more interesting as a tropical disturbance from the Gulf of Mexico could move into the High Plains and a cold front drops south. There&rsquo;s a lot of <span class=\"glossaryLink\" aria-describedby=\"tt\" data-cmtooltip=\"&lt;div class=glossaryItemTitle&gt;divergence&lt;\/div&gt;&lt;div class=glossaryItemBody&gt;This term is often used in place of &amp;quot;divergent winds&rdquo; in our discussion. When divergence occurs aloft, it promotes upward motion and increases the potential for thunderstorm development.&lt;\/div&gt;\" data-gt-translate-attributes='[{\"attribute\":\"data-cmtooltip\", \"format\":\"html\"}]'>divergence<\/span> in model runs, but thought it was worth mentioning and why an Elevated flood threat has been issued. It&rsquo;s likely that an Elevated threat will just be needed on one of those two days. Event #2 begins on Saturday as residual moisture is recycled and will help produce <span class=\"glossaryLink\" aria-describedby=\"tt\" data-cmtooltip=\"&lt;div class=glossaryItemTitle&gt;scattered&lt;\/div&gt;&lt;div class=glossaryItemBody&gt;25-40% areal coverage&lt;\/div&gt;\" data-gt-translate-attributes='[{\"attribute\":\"data-cmtooltip\", \"format\":\"html\"}]'>scattered<\/span> afternoon storms. The amount of residual moisture (related to the coverage of storms) will be directly tied to the tropical disturbance&rsquo;s path. So, confidence in the forecast is pretty low this far out.<\/p>\n<p><img loading=\"lazy\" class=\"size-full wp-image-12848 aligncenter\" src=\"https:\/\/archive-coftb.dewberryanalytics.com\/wp-content\/uploads\/2020\/08\/wv_20200820.png\" alt=\"\" width=\"669\" height=\"430\" srcset=\"https:\/\/archive-coftb.dewberryanalytics.com\/wp-content\/uploads\/2020\/08\/wv_20200820.png 669w, https:\/\/archive-coftb.dewberryanalytics.com\/wp-content\/uploads\/2020\/08\/wv_20200820-300x193.png 300w\" sizes=\"(max-width: 669px) 100vw, 669px\"\/><\/p>\n<p>We&rsquo;ve finally come to that time of year where climatological (average) <span class=\"glossaryLink\"  aria-describedby=\"tt\"  data-cmtooltip=\"&lt;div class=glossaryItemTitle&gt;PW&lt;\/div&gt;&lt;div class=glossaryItemBody&gt;(Stands for: Precipitable Water) The total atmospheric water vapor contained in a vertical column of the atmosphere. It is typically measured in inches, and anomalously (deviation from normal) high values of precipitable water generally correlate to heavy rainfall potential.&lt;\/div&gt;\"  data-gt-translate-attributes='[{\"attribute\":\"data-cmtooltip\", \"format\":\"html\"}]'>PW<\/span> values start to decline again. It doesn&rsquo;t mean that some late season <span class=\"glossaryLink\"  aria-describedby=\"tt\"  data-cmtooltip=\"&lt;div class=glossaryItemTitle&gt;PW&lt;\/div&gt;&lt;div class=glossaryItemBody&gt;(Stands for: Precipitable Water) The total atmospheric water vapor contained in a vertical column of the atmosphere. It is typically measured in inches, and anomalously (deviation from normal) high values of precipitable water generally correlate to heavy rainfall potential.&lt;\/div&gt;\"  data-gt-translate-attributes='[{\"attribute\":\"data-cmtooltip\", \"format\":\"html\"}]'>PW<\/span> surges aren&rsquo;t possible, but the window for the <span class=\"glossaryLink\" aria-describedby=\"tt\" data-cmtooltip=\"&lt;div class=glossaryItemTitle&gt;monsoon&lt;\/div&gt;&lt;div class=glossaryItemBody&gt;&amp;lt;!-- wp:paragraph {&amp;quot;textColor&amp;quot;:&amp;quot;white&amp;quot;} --&amp;gt;\n&amp;lt;p class=&amp;quot;has-white-color has-text-color&amp;quot;&amp;gt;a seasonal wind that brings moisture and rain to the region into which it blows; there is also a dry phase to monsoons, but popular usage refers only to the wet phase; these winds occur in many places around the world, and where they occur they are responsible for a majority of that location&rsquo;s annual precipitation&amp;lt;\/p&amp;gt;\n&amp;lt;!-- \/wp:paragraph --&amp;gt;&lt;\/div&gt;\" data-gt-translate-attributes='[{\"attribute\":\"data-cmtooltip\", \"format\":\"html\"}]'>monsoon<\/span> season rainfall is closing. Overall, not an impressive year for the <span class=\"glossaryLink\" aria-describedby=\"tt\" data-cmtooltip=\"&lt;div class=glossaryItemTitle&gt;monsoon&lt;\/div&gt;&lt;div class=glossaryItemBody&gt;&amp;lt;!-- wp:paragraph {&amp;quot;textColor&amp;quot;:&amp;quot;white&amp;quot;} --&amp;gt;\n&amp;lt;p class=&amp;quot;has-white-color has-text-color&amp;quot;&amp;gt;a seasonal wind that brings moisture and rain to the region into which it blows; there is also a dry phase to monsoons, but popular usage refers only to the wet phase; these winds occur in many places around the world, and where they occur they are responsible for a majority of that location&rsquo;s annual precipitation&amp;lt;\/p&amp;gt;\n&amp;lt;!-- \/wp:paragraph --&amp;gt;&lt;\/div&gt;\" data-gt-translate-attributes='[{\"attribute\":\"data-cmtooltip\", \"format\":\"html\"}]'>monsoon<\/span> rainfall as indicated by the worsening and large area of the drought. Over Denver and eastern Colorado, the decrease in <span class=\"glossaryLink\"  aria-describedby=\"tt\"  data-cmtooltip=\"&lt;div class=glossaryItemTitle&gt;PW&lt;\/div&gt;&lt;div class=glossaryItemBody&gt;(Stands for: Precipitable Water) The total atmospheric water vapor contained in a vertical column of the atmosphere. It is typically measured in inches, and anomalously (deviation from normal) high values of precipitable water generally correlate to heavy rainfall potential.&lt;\/div&gt;\"  data-gt-translate-attributes='[{\"attribute\":\"data-cmtooltip\", \"format\":\"html\"}]'>PW<\/span> described above can be seen over the next couple of days before <span class=\"glossaryLink\"  aria-describedby=\"tt\"  data-cmtooltip=\"&lt;div class=glossaryItemTitle&gt;PW&lt;\/div&gt;&lt;div class=glossaryItemBody&gt;(Stands for: Precipitable Water) The total atmospheric water vapor contained in a vertical column of the atmosphere. It is typically measured in inches, and anomalously (deviation from normal) high values of precipitable water generally correlate to heavy rainfall potential.&lt;\/div&gt;\"  data-gt-translate-attributes='[{\"attribute\":\"data-cmtooltip\", \"format\":\"html\"}]'>PW<\/span> returns to a more seasonal value. By the end of the forecast period, you start to see the <span class=\"glossaryLink\" aria-describedby=\"tt\" data-cmtooltip=\"&lt;div class=glossaryItemTitle&gt;divergence&lt;\/div&gt;&lt;div class=glossaryItemBody&gt;This term is often used in place of &amp;quot;divergent winds&rdquo; in our discussion. When divergence occurs aloft, it promotes upward motion and increases the potential for thunderstorm development.&lt;\/div&gt;\" data-gt-translate-attributes='[{\"attribute\":\"data-cmtooltip\", \"format\":\"html\"}]'>divergence<\/span> (indicating uncertainty) between the different model runs associated with that tropical disturbance.<\/p>\n<p>A similar pattern can be seen over western Colorado (right side). So, expecting storms (and rainfall) to increase in coverage after Monday. Until then, storms that develop over western CO with the help of passing shortwaves will produce more wind and dry lightning, which is not good with the ongoing fires and dry fuels. Really hoping the wetting rainfall in the GEFS forecast comes to be realized. The ECMWF is also showing an increase in the coverage of storms, but with less measurable rain, which is typical. It is encouraging to see an upward trend in more <span class=\"glossaryLink\" aria-describedby=\"tt\" data-cmtooltip=\"&lt;div class=glossaryItemTitle&gt;widespread&lt;\/div&gt;&lt;div class=glossaryItemBody&gt;greater than 60% areal coverage&lt;\/div&gt;\" data-gt-translate-attributes='[{\"attribute\":\"data-cmtooltip\", \"format\":\"html\"}]'>widespread<\/span> showers from both models though.<\/p>\n<p><img loading=\"lazy\" class=\"aligncenter wp-image-12849\" src=\"https:\/\/archive-coftb.dewberryanalytics.com\/wp-content\/uploads\/2020\/08\/PW_20200820.png\" alt=\"\" width=\"880\" height=\"295\" srcset=\"https:\/\/archive-coftb.dewberryanalytics.com\/wp-content\/uploads\/2020\/08\/PW_20200820.png 1126w, https:\/\/archive-coftb.dewberryanalytics.com\/wp-content\/uploads\/2020\/08\/PW_20200820-300x101.png 300w, https:\/\/archive-coftb.dewberryanalytics.com\/wp-content\/uploads\/2020\/08\/PW_20200820-768x258.png 768w, https:\/\/archive-coftb.dewberryanalytics.com\/wp-content\/uploads\/2020\/08\/PW_20200820-1024x344.png 1024w\" sizes=\"(max-width: 880px) 100vw, 880px\"\/><\/p>\n<h3><strong>Event #1:<\/strong> <strong>Sunday<\/strong><strong> &ndash; <\/strong><strong>Thursday<\/strong><strong> (8\/<\/strong><strong>23<\/strong><strong> &ndash; 8\/2<\/strong><strong>7<\/strong><strong>) <\/strong><\/h3>\n<p><span style=\"color: #ff6600;\"><strong>Elevated<\/strong><\/span><strong>\/<span style=\"color: #0000ff;\">No Apparent<\/span><\/strong><strong>&nbsp;<\/strong>as leftover tropical disturbances start to make their way northward and help increase moisture.<\/p>\n<p>No Apparent threat to start Event #1 as storms start to increase in coverage on Sunday. It isn&rsquo;t until Tuesday or Wednesday before the chance for wetting rainfall returns to western Colorado. Until then, above average temperatures and dry conditions are expected to continue. Possibly a slight decrease in high temperatures starting on Saturday over the San Juan Mountains and Southwest Slope. Increasing, high temperatures should be expected over eastern Colorado this next week, so it will be a bit of a heat wave. Over the mountains, daily rounds of storms will be possible favoring the southern and eastern terrains. With more northerly steering flow, storms will likely stick closer to the mountains. Lee troughs may help set up some convergence boundaries over the plains, so additional storms could fire in these areas, but warm air aloft will most likely keep <span class=\"glossaryLink\" aria-describedby=\"tt\" data-cmtooltip=\"&lt;div class=glossaryItemTitle&gt;convection&lt;\/div&gt;&lt;div class=glossaryItemBody&gt;Refers to vertical atmospheric motion driven by buoyancy, i.e., warm air is less dense than cool air, and therefore rises. One of the primary drivers of thunderstorm development, especially during monsoon season.&lt;\/div&gt;\" data-gt-translate-attributes='[{\"attribute\":\"data-cmtooltip\", \"format\":\"html\"}]'>convection<\/span> <span class=\"glossaryLink\" aria-describedby=\"tt\" data-cmtooltip=\"&lt;div class=glossaryItemTitle&gt;capped&lt;\/div&gt;&lt;div class=glossaryItemBody&gt;The area where a parcel of air has negative buoyancy or sinks. The intensity of the cap is measured by its convective inhibition. If the cap is sufficiently large, it may prevent thunderstorms from forming at all.&lt;\/div&gt;\" data-gt-translate-attributes='[{\"attribute\":\"data-cmtooltip\", \"format\":\"html\"}]'>capped<\/span>. As always, if storms do fire, they will likely have slightly higher rainfall totals and some severe storms could be possible, but those details can be found in the daily FTB as its hard to tell where the <span class=\"glossaryLink\" aria-describedby=\"tt\" data-cmtooltip=\"&lt;div class=glossaryItemTitle&gt;dryline&lt;\/div&gt;&lt;div class=glossaryItemBody&gt;A low-level, small-scale boundary that separates dry air from moist air. Storms develop along it because the dry air (behind the boundary) is less dense than the moisture-rich air (ahead of the boundary). Typically, it advances eastward during the afternoon and retreats westward at night.&lt;\/div&gt;\" data-gt-translate-attributes='[{\"attribute\":\"data-cmtooltip\", \"format\":\"html\"}]'>dryline<\/span> will set up. Higher rainfall totals and greater coverage of storms is forecast by mid-week. This would be really welcomed for the mountains, but totals are bit hard to estimate this far out.<\/p>\n<p><img loading=\"lazy\" class=\"aligncenter wp-image-12892\" src=\"https:\/\/archive-coftb.dewberryanalytics.com\/wp-content\/uploads\/2020\/08\/FTO_20200820_e1.png\" alt=\"\" width=\"880\" height=\"592\" srcset=\"https:\/\/archive-coftb.dewberryanalytics.com\/wp-content\/uploads\/2020\/08\/FTO_20200820_e1.png 890w, https:\/\/archive-coftb.dewberryanalytics.com\/wp-content\/uploads\/2020\/08\/FTO_20200820_e1-300x202.png 300w, https:\/\/archive-coftb.dewberryanalytics.com\/wp-content\/uploads\/2020\/08\/FTO_20200820_e1-768x517.png 768w\" sizes=\"(max-width: 880px) 100vw, 880px\"\/><\/p>\n<h3><strong>Event #2: <\/strong><strong>Saturday &ndash; <\/strong><strong>Monday<\/strong><strong> (8\/2<\/strong><strong>9<\/strong><strong> &ndash; 8\/<\/strong><strong>31<\/strong><strong>)<\/strong><\/h3>\n<p><span style=\"color: #0000ff;\"><strong>No Apparent<\/strong><\/span> threat as residual moisture is recycled under the ridge.<\/p>\n<p>Not too concerned about this event for now. Looks like recycled moisture trapped under the ridge will continue to help trigger afternoon storms over the mountains. Currently, it is looking like this event will favor the northern mountains with more dry conditions south. Again, what happens during this period will be strongly dependent on the tropical system that moves through (or doesn&rsquo;t) later next week, so confidence is lower. A drying trend is hinted at in the models by the end of this event, hence the shortness of the event.<br><img loading=\"lazy\" class=\"aligncenter wp-image-12893\" src=\"https:\/\/archive-coftb.dewberryanalytics.com\/wp-content\/uploads\/2020\/08\/FTO_20200820_e2.png\" alt=\"\" width=\"880\" height=\"593\" srcset=\"https:\/\/archive-coftb.dewberryanalytics.com\/wp-content\/uploads\/2020\/08\/FTO_20200820_e2.png 890w, https:\/\/archive-coftb.dewberryanalytics.com\/wp-content\/uploads\/2020\/08\/FTO_20200820_e2-300x202.png 300w, https:\/\/archive-coftb.dewberryanalytics.com\/wp-content\/uploads\/2020\/08\/FTO_20200820_e2-768x518.png 768w\" sizes=\"(max-width: 880px) 100vw, 880px\"\/><\/p>","protected":false},"excerpt":{"rendered":"<p>Issue Date: Thursday,&nbsp;August 20th, 2020 Issue Time: 2:45PM MDT Valid Dates:&nbsp;8\/21&ndash; 9\/4 The stubborn ridging pattern will hang on and persist through this weekend even with a strong incoming <span class=\"glossaryLink\" aria-describedby=\"tt\" data-cmtooltip=\"&lt;div class=glossaryItemTitle&gt;trough&lt;\/div&gt;&lt;div class=glossaryItemBody&gt;An elongated area of relatively low atmospheric pressure; the opposite of a ridge.&lt;\/div&gt;\" data-gt-translate-attributes='[{\"attribute\":\"data-cmtooltip\", \"format\":\"html\"}]'>trough<\/span> from the Pacific Northwest. With the High to our west, a drier air mass will be over the state to start this weekend, so is [&hellip;]<\/p>","protected":false},"author":8,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":[],"categories":[3],"tags":[],"post_mailing_queue_ids":[],"_links":{"self":[{"href":"https:\/\/archive-coftb.dewberryanalytics.com\/index.php?rest_route=\/wp\/v2\/posts\/12846"}],"collection":[{"href":"https:\/\/archive-coftb.dewberryanalytics.com\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/archive-coftb.dewberryanalytics.com\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/archive-coftb.dewberryanalytics.com\/index.php?rest_route=\/wp\/v2\/users\/8"}],"replies":[{"embeddable":true,"href":"https:\/\/archive-coftb.dewberryanalytics.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=12846"}],"version-history":[{"count":3,"href":"https:\/\/archive-coftb.dewberryanalytics.com\/index.php?rest_route=\/wp\/v2\/posts\/12846\/revisions"}],"predecessor-version":[{"id":12894,"href":"https:\/\/archive-coftb.dewberryanalytics.com\/index.php?rest_route=\/wp\/v2\/posts\/12846\/revisions\/12894"}],"wp:attachment":[{"href":"https:\/\/archive-coftb.dewberryanalytics.com\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=12846"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/archive-coftb.dewberryanalytics.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=12846"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/archive-coftb.dewberryanalytics.com\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=12846"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}