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

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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 7:12AMSunset 4:35PM Thursday December 12, 2019 4:46 AM MST (11:46 UTC) Moonrise 6:12PMMoonset 8:35AM Illumination 100% Phase: Full Moon; Moon at 15 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 Nunn, CO
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location: 40.66, -104.88     debug


Area Discussion for - Denver/Boulder, CO
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FXUS65 KBOU 120236 AFDBOU

Area Forecast Discussion National Weather Service Denver/Boulder CO 736 PM MST Wed Dec 11 2019

UPDATE. Issued at 730 PM MST Wed Dec 11 2019

Satellite imagery shows the upper trough pushing through eastern colorado with some light snow continuing in the higher elevations. Subsidence seen upstream will help to reduce the snow with possibly only orographic flurries into early Thursday. With the added cloud cover provided by the enhance mountain wave overnight lows will continue to be more mild as will high temps on Thursday with values in the upper 40s to lower 50s. Only minor changes made to the forecast.

SHORT TERM. (This evening through Thursday) Issued at 335 PM MST Wed Dec 11 2019

Shortwave trough with a band of showers approaching the western Colorado border. This will move quickly across the mountains in the early evening. This should just be a band of clouds moving over the plains. There's a band of clearing, and then the warm advection clouds at mid/high levels will come into the mountains by morning and across the plains during the day Thursday. We'll probably continue to have some very light orographic snow over the ridges throughout, but limited by stability. The snow may start to pick up again later in the day Thursday.

For the plains, tonight's shortwave will just serve to weaken the inversions a bit more. The bigger effect will be the cloud cover holding up temps a bit after today's warming, resulting in another step up in our nighttime temperatures. We'll still have the cold air trapped in the valleys, but it will be a bit warmer. Likewise on Thursday, there will be less difference between the warmer and colder areas, but cloud cover will keep it from getting even warmer. Current forecast temperatures look good.

LONG TERM. (Thursday night through Wednesday) Issued at 335 PM MST Wed Dec 11 2019

Main focus is on an expected long period of light to moderate snow in the mountains from late Thursday through Sunday, combined with wind especially on Friday.

Snow should be ongoing in the mountains by early Friday as an intense Pacific jet streak moves onshore after midnight. The impacts from the jet could be felt Friday morning with northeast Colorado in the left exit region. The jet is forecast to be 150- 170kt as it enters northwest Colorado Friday morning. Would not be surprised to see an uptick in mountain snow rates as the jet moves northwest to southeast across the central part of Colorado throughout the day. Enough moisture in the NW flow will be around to keep snow going throughout the day. Models are agreeing in an uptick in rates Friday morning, but we'll have a better handle on timing of any potential moderate to heave snow bands once higher res models come in tomorrow. For now we have increased snow amounts a bit over the blended solution during this period to start the trend in the right direction for the potential of mesoscale, jet-induced band(s). A weak trough in the NW flow also moves across SE Wyoming, perhaps also leading to an uptick in snow rates Friday morning in addition to the jet streak. Once the nose of the jet streak moves southeast of us Friday afternoon, most of the forcing is via upslope as there is subsidence aloft in the wake of the first short wave trough. Snow is expected to continue in the high country through Friday into Saturday, especially the northern ranges, but should be light snow. There is enough moisture in the flow and strong lapse rates for continued snow overnight into Saturday.

Snow rates should increase once again in the mountains come Saturday morning, but only a little. Another short wave trough in the WNW flow approaches, resulting in some QG support, mainly across the northern mountains. The core of the jet is directly overhead at this time as well, perhaps resulting in enhanced snowfall, and throughout the day winds turn due west, improving upslope across many of our mountains throughout Saturday. Moisture increases early Sunday morning once again ahead of a more robust positively tilted short wave trough. Combined with west upslope, snow rates should increase to moderate once again sometime after midnight Sunday into midday Sunday, when the trough axis traverses the mountains. The last of the moisture, plus significant subsidence, should exit the high country by Monday morning. All told the mountains will be measuring snow amounts by the foot, spread out over 72+ hours. In terms of impacts, several rounds of poor travel conditions should occur, the first occurring early Friday with the jet max approaching. Brute force wind alone should result in 60-75 mph winds with possible gusts to 90 mph across high mountain passes, given 50-60 kt northwest flow at 700 mb. This will result in blowing snow and near white out conditions above 8500 feet across the mountains in wind prone areas for several hours during the strongest winds the first half of Friday. Heavier snow rates early Sunday through midday would be another period when travel conditions are expected to be poor. In between and through early Monday, snow is possible to likely, so regardless of periods of heaviest snow and wind, please stay tuned to road conditions and plan for difficult travel across the mountains Friday into early Monday. Will issue a Winter Storm Watch for the mountains above 9,000 feet east slopes, Park Range, and Summit County.

Across the plains, confidence in snow is lower. The main story early on will be Friday morning when downslope winds are expected to be enhanced via a mountain wave. High winds from east of the Divide to west of I-25, and along the Cheyenne ridge north and northeast of Fort Collins are expected. For now, not anticipating needing highlights but in the wind prone areas of the east slopes and adjacent plains could see gusts to 60 mph, with 50 mph across the Cheyenne Ridge. Winds spread across the northern quarter of the Colorado plains throughout the day on Friday, with 30G45mph quite possible Friday afternoon. Precipitation chances are extremely low east of I-25 but not zero in case a jet-induced band forms. Even then, it's so dry in the low levels that not much precipitation will reach the ground. From the Continental Divide east, blowover showers may result in brief periods of snow in the lower eastern foothills and adjacent plains, but they will be intermittent and nor result in any significant accumulation of rain/snow below 7000 feet, or snow above 7000 feet. Close to the divide along the east slopes we do expect significant accumulation given the strength of the west winds on Friday. With the strong downslope, highs will reach the mid 40s and even some 50s across the Plains.

On Saturday PoPs increase across the plains with a short wave trough skirting the far northern parts of Colorado. A lee trough at the surface deepens south of metro Denver, resulting in increasing easterly upslope, especially for areas north of Denver. This will also help generate light precipitation across some of the plains, especially Boulder, Weld, and Larimer Counties, though there are slight chances pretty much across the plains and Palmer Divide on Saturday. With cold air aloft already in place, we expect the p-type to be snow on Saturday, but amounts across the plains should be light, with most areas getting an inch or less. Late Saturday into Sunday the positively tilted trough approaches, providing some synoptic scale lift, and a cold front crosses the plains early Sunday. The combination of weak NE upslope, synoptic support, and steepening lapse rates with really cold air aloft pouring into eastern Colorado, could result in accumulating snow for the plains and I-25 urban corridor, especially south of I-76 where the best QG forcing should be. Details are still not very clear, but accumulating snow is looking a bit more likely for Sunday, and with temperatures remaining at or below freezing, there could be travel impacts throughout the day on Sunday. Highs on Sunday should struggle to reach the freezing mark across the plains.

On Monday the coldest air aloft will be over the state through midday, and would not be surprised to see instability snow showers develop Monday morning through early afternoon, especially across the high country. Impacts should be minimal unless you drive right through one of the short-lived showers. Temperatures will remain cold area-wide, right around freezing across the I-25 corridor, mid 30s far east, and teens to around 20 degrees in the mountains.

A ridge of high pressure aloft builds to the west Tuesday and Wednesday, reaching Colorado later on Wednesday. Temperatures should moderate into the 40s across the plains by Wednesday and we should be dry areawide Tuesday and Wednesday.

AVIATION. (For the 00Z TAFS through 00Z Thursday evening) Issued at 730 PM MST Wed Dec 11 2019

VFR conditions are expected through the period. Winds will slowly switch around to drainage with light winds. With the enhanced mountain wave winds will continue to gust at BJC through 08z. There's some uncertainty about the wind pattern for Thursday afternoon, but prevailing southwest to west winds are likely. Winds may become light northeast at KDEN in the afternoon.

BOU WATCHES/WARNINGS/ADVISORIES. Winter Storm Watch from Thursday afternoon through late Saturday night for COZ031-033-034.



UPDATE . Bowen SHORT TERM . Gimmestad LONG TERM . Schlatter AVIATION . Bowen


Weather Reporting Stations
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Airport Reports
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AirportDistAgeWind ktVisibilitySky/WeatherTempDewPtHumidityPressure
Fort Collins/Loveland - Northern Colorado Regional Airport, CO16 mi51 minVar 510.00 miFair29°F21°F72%1016.9 hPa
Greeley, Greeley-Weld County Airport, CO21 mi51 minN 010.00 miFair21°F18°F88%1020.4 hPa

Link to 5 minute data for KFNL

Wind History from FNL (wind in knots)
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Last 24hrCalmCalmE3N64N3Calm3NE5CalmNE5N3W6CalmS8SE12E9S6SE3SE3SE5N3N55
1 day agoN6CalmN3S3S4S6S5S6SW3S5E3CalmSW6S3CalmSE3CalmCalmCalmN3N5CalmCalmCalm
2 days agoS6S8S9S6S8S8S8S7CalmE6SE7SE6SE5SE6N6E7N5CalmN3N5N5NE6N4N4

Tide / Current Tables for
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Tide / Current Tables for
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Weather Map
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GEOS Local Image of CentralPlains    EDIT
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 (6,6,7,8)
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Ground Weather Radar Station Cheyenne, WY
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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.