Thursday, December12, 2019
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Marine Weather and Tides
Sheridan, CO

Version 3.4
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10/9/2019 Updated the Marine Zones.
9/4/2019 Fixed the weather maps due to NOAA moving them.
7/25/2019 New feature in the Airports section gives a link to 5 minute updates for data reports.
6/2/2019. Many thanks to a user for reporting an error on one of the Edit pages. The switch to PHP 7.2 caused many pages that previously worked to quit working. I fixed many but I still depend on users to report ones I missed. Please report errors HERE or send an email to me at L-36.com. Allen

Sunrise 7:10AMSunset 4:37PM Thursday December 12, 2019 1:57 PM MST (20:57 UTC) Moonrise 5:16PMMoonset 7:33AM Illumination 99% Phase: Waning Gibbous; Moon at 16 days in cycle
NOTE: Some of the data on this page has not been verified and should be used with that in mind. It may and occasionally will, be wrong. The tide reports are by xtide and are NOT FOR NAVIGATION.
Marine Forecasts
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7 Day Forecast for Marine Location Near Sheridan, CO
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location: 39.68, -105.06     debug


Area Discussion for - Denver/Boulder, CO
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FXUS65 KBOU 121838 AFDBOU

Area Forecast Discussion National Weather Service Denver/Boulder CO 1138 AM MST Thu Dec 12 2019

UPDATE. Issued at 1138 AM MST Thu Dec 12 2019

We got a brief shot of moderate to heavy snow showers with the shortwave just exiting the mountains now. Showers should continue but be lighter this afternoon with just another inch or two. Deeper moisture and weak lift will arrive this evening. Despite the weak lift, there should be a hefty response as the mountaintop flow increases to 40 knots and shifts more northwesterly. There's a period this evening where model soundings show a neutral lapse rate up to 400 mb! This doesn't last too long, but this evening's batch of showers could well overproduce. After that, we settle into a long period of light to moderate orographic snow with strong winds over the rides which should continue to produce travel difficulties.

For Denver and the plains, the forecast is looking good. We'll actually warm through the shallow low level inversion with a bit of mixing as temps get into the lower 50s. We had expected southwest breezes, but the mountain wave has interfered with the winds around Denver so far. We still expect more of a west to southwest breeze to develop this afternoon. The exception of course is in the cold pool in the valleys north and northeast of Denver. There should be enough of a southwest gradient to hold this further east of the foothills than the last couple of days (out of Denver), but temperatures will struggle to get to the lower 40s there.

SHORT TERM. (Today and tonight) Issued at 405 AM MST Thu Dec 12 2019

The problem of the day this time around is the developing winter storm that is expected to move into the mountains by tonight which will then continue for several periods. Ahead of that, today should be a mild day as downsloping westerly flow continues. Moisture aloft will be increasing through the day, leading to mountain wave clouds over the plains and generally increasing clouds in the mountains. Snowfall is expected to begin in the mountains during the afternoon, but accumulation rates are not expected to increase until later tonight. When the storm arrives, abundant Pacific moisture is going to be moving over the state, being driven by a 130+ knot jet stream aloft. Strong orographic effects should produce light to moderate snowfall over west-facing exposures through tonight and Friday morning. Gusty winds are also expected due to the fast flow at mid and upper levels. Blowing and drifting snow could be a problem over the higher elevations through the duration of the storm. Will be upgrading the Winter Storm Watch to a Winter Storm Warning for tonight and Friday. The rest of the Winter Storm Watch will be left as is because of the uncertainty over how long the storm may continue. (See below) Snow accumulations with the initial surge of moisture are expected to be 12 to 18 inches by Friday afternoon. Continuing strong downslope effects in the lee of the mountains will keep the plains dry.

LONG TERM. (Friday through Wednesday) Issued at 430 AM MST Thu Dec 12 2019

Water vapor imagery shows a strong jet stream moving ashore over Oregon this morning with a plume of moisture that extends as far west as Hawaii's longitude. This jet and associated moisture plume will be responsible for the prolonged snow event across Colorado's mountains that lasts through this weekend. Global models predict this jet will enter Colorado Friday morning with maximum 300-200 mb winds of up to 180 knots. During this time, our CWA's mountains will be under the left exit region of the jet which will provide lift along with a quick moving shortwave trough. This will enhance snowfall rates to between one to two inches per hour Friday morning and create hazardous travel conditions. By Friday afternoon, the jet will move directly overhead with slight ridging building in behind the departing shortwave trough. This will decrease snowfall rates to around a half inch an hour. It is important to note that while snow rates will decrease Friday afternoon, the strong winds, gusting up to 60 mph at times, will create blowing snow and poor travel conditions. It is for this reason that the Winter Storm Warning goes through Friday evening with a Winter Storm Watch continuing immediately after the warning ends.

A secondary plume of moisture will arrive ahead of a shortwave trough Friday night. Snowfall rates will increase to one to two inches in the mountains with hazardous travel conditions. These snowfall rates will continue through the day Saturday and into Saturday evening before tapering off. The jet stream moves farther south to southern Colorado Saturday night which leads to the lull in snowfall. Models still show considerable differences for Sunday across our CWA but it appears a trough will deepen over the Four Corners region during the day. As this system moves eastward-northeastward, it will produce a swath of moderate snowfall. This swath will likely be farther south than the previous two systems and will hit the central and southern mountains harder than the northern mountains. By the time the snow ends Sunday night, we expect significant snowfall amounts especially on west facing mountain slopes. There was extensive discussion on the timing of warnings and watches for this storm as it will come in three waves. We determined that highlighting the first wave would be ideal at this time while signaling there is some uncertainty with the second and third waves. From Monday through Wednesday, a ridge will build over the western US keeping Colorado dry.

As for the plains and urban corridor, the westerly, downslope flow will keep conditions dry on Friday and Friday night. Strong gusts will be the biggest issue as they could reach up to 45 mph during the day. We may even see some loosely attached Christmas decorations taken for a ride if a gust gets a hold of them.

The second system will have better QG ascent aloft over the urban corridor and plains which will lead to a chance of snow. The ECMWF is the most bullish about snow amounts in the Denver area while other models keep the snow farther north along the Cheyenne Ridge. Since systems tend to come in slightly farther south and deeper than models predict, I trended the forecast toward the ECMWF and increased PoPs over much of the urban corridor and plains on Saturday.

The third system will have the best QG and frontogenesis aloft out of the three. This system appears it will hit southeastern Colorado the hardest but areas from Denver southward may still see light to moderate snow amounts. Confidence in the track and intensity of this system is still rather low but it will need to be watched closely for those traveling on Sunday. Monday through Wednesday will see dry conditions with moderating temperatures.

AVIATION. (For the 18Z TAFS through 18Z Friday afternoon) Issued at 1138 AM MST Thu Dec 12 2019

VFR through tonight. Winds are expected to become westerly between 20-22z. Gusts up to 25 knots are expected at KBJC, with speeds closer to 10 knots at KDEN/KAPA.

BOU WATCHES/WARNINGS/ADVISORIES. Winter Storm Warning from 5 PM this afternoon to 5 PM MST Friday for COZ031-033-034.

Winter Storm Watch from Friday afternoon through late Saturday night for COZ031-033-034.



UPDATE . Gimmestad SHORT TERM . Dankers LONG TERM . Danielson AVIATION . Gimmestad


Weather Reporting Stations
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Airport Reports
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AirportDistAgeWind ktVisibilitySky/WeatherTempDewPtHumidityPressure
Denver - Centennial Airport, CO14 mi64 minN 010.00 miPartly Cloudy53°F18°F25%1013.3 hPa
Broomfield / Jeffco, CO16 mi72 minN 10 G 2715.00 miMostly Cloudy50°F21°F32%1014.2 hPa
Buckley Air Force Base Airport, CO17 mi2 hrsSSW 410.00 miMostly Cloudy50°F17°F27%1013.6 hPa
Erie Municipal Airport, CO23 mi64 minWSW 510.00 miFair47°F22°F39%1015.6 hPa
Denver, Denver International Airport, CO24 mi64 minVar 610.00 miMostly Cloudy51°F19°F28%1011.4 hPa

Link to 5 minute data for KAPA

Wind History from APA (wind in knots)
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Last 24hrNW3N6N5SE5CalmE3S4S5E7SW4NW4S5S7S8SE8SE5SE6CalmS5S9S5SE4CalmCalm
1 day agoN4NW4N4NW3S4S5SE5S9SE6S10SE6S5SE5SE8SE8SE8S4S8SE6SE5W4CalmCalmNW3
2 days agoE7E6SE8SE5SE9S8CalmS6S7SE5S6S6S8SE4E5E5CalmSE3NE7NW4NW33NE3N3

Tide / Current Tables for
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Tide / Current Tables for
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Weather Map
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NOTE: East coast views moved to GEOS-16. They are experimental and not well supported by NOAA so they may not be correct so be warned. This change required redoing a large amount of the GOES code. If the image you are expecting is not showing, please let me know. You may need to use the EDIT function to update your location.
Link to Loop

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Wind Forecast for Denver/Boulder, CO (15,3,4,5)
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Ground Weather Radar Station Denver/Boulder, CO
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The information on this web site has not been checked for accuracy. It is for entertainment purposes only and should be independently verified before using for any other reason. There are five sources. 1) Documents and manuals from a variety of sources. These have not been checked for accuracy and in many cases have not even been read by anyone associated with L-36.com. I have no idea of they are useful or accurate, I leave that to the reader. 2) Articles others have written and submitted. If you have questions on these, please contact the author. 3) Articles that represent my personal opinions. These are intended to promote thought and for entertainment. These are not intended to be fact, they are my opinions. 4) Small programs that generate result presented on a web page. Like any computer program, these may and in some cases do have errors. Almost all of these also make simplifying assumptions so they are not totally accurate even if there are no errors. Please verify all results. 5) Weather information is from numerious of sources and is presented automatically. It is not checked for accuracy either by anyone at L-36.com or by the source which is typically the US Government. See the NOAA web site for their disclaimer. Finally, tide and current data on this site is from 2007 and 2008 data bases, which may contain even older data. Changes in harbors due to building or dredging change tides and currents and for that reason many of the locations presented are no longer supported by newer data bases. For example, there is very little tidal current data in newer data bases so current data is likely wrong to some extent. This data is NOT FOR NAVIGATION. See the XTide disclaimer for details. In addition, tide and current are influenced by storms, river flow, and other factors beyond the ability of any predictive program.