103 FXUS65 KGJT 201533 AFDGJT Area Forecast Discussion National Weather Service GRAND JUNCTION CO 933 AM MDT Fri Oct 20 2017 .UPDATE... Issued at 932 AM MDT Fri Oct 20 2017 Expanded the wind advisory area to include the Grand Valley, Moab and Canyonlands areas of southeast Utah, the Paradox Valley and Roan Plateau including Douglas Pass based on latest model guidance. These areas along with the valleys of northwest Colorado plateau will be more prone to reaching wind advisory criteria with gusts to 50 mph in the valley zones and gusts to 60 mph over Douglas Pass due to prefrontal southwest flow and a 90 kt upper level jet over southeast Utah through northwest Colorado. This will result in sufficient mixing of stronger winds to the surface this afternoon due to a mostly cloud free sky with a few cirrus passing overhead. The cold front associated with this upper level trough is forecast to move through this evening with gusty winds continuing until sunset. Therefore, also decided to start the wind advisory earlier at 11 am and extend it until 8 pm instead when the winds are expected to decouple after sunset and behind the cold front. See the Wind Advisory product for details on the areas included. && .SHORT TERM...(Today through Saturday) Issued at 230 AM MDT Fri Oct 20 2017 Some clouds and a few returns are showing up on radar but with cloud bases hovering around 10,000 feet, don't expect much precipitation to be hitting the ground. Clearing skies can be found just to the west of our forecast area and by daybreak, the clearing will be entering western Colorado. The main concern today will be some gusty surface winds thanks to the jet stream, approaching from the northwest, and a tightening pressure gradient. Winds will start picking up around noon, if not a bit before, and will gust between 25 to 35 mph at times. Our northern valleys will see some stronger gusts, bordering on 45 mph at times, as deep mixing taps into some stronger winds aloft. Not a slam dunk by any means but still close enough to issue a wind advisory for those two zones from noon through 6PM. As far as the cold front is concerned, timing and intensity remains the same with the front moving through after 6PM up north, 9PM for the I-70 corridor, and the rest of the CWA between midnight and 3AM. Precipitation should start around 9PM with the best coverage from midnight through 6AM Saturday. Temperatures will drop quickly as the front moves through allowing snow to fall as it does so. In fact, a quick 1 to 3 inches will occur along and just behind the front for the northern and central mountains. Snow levels will start off at 10,000 feet but will drop to mountains floors by Saturday morning. The NAM is showing some banding setting up and may cause some snow to fall for zone 2 and will need to be watched Friday night. By daybreak Saturday, the front will have scooted off to the east and with northwesterly flow setting up, expect high temps to be anywhere from 5 to 10 degrees below normal. Plenty of sunshine is also expected. .LONG TERM...(Saturday night through Thursday) Issued at 245 PM MDT Thu Oct 19 2017 Since the cold front pushed through, lows Saturday night into Sunday morning will be on the chilly side with much of the area seeing below freezing temperatures through the early morning hours prior to sunrise. Temperatures will start a warming trend Sunday as high pressure builds in from the west. Ridging aloft will continue to strengthen through the week as a few shortwave troughs slide around the periphery. Monday and Tuesday, a stronger trough should flatten the ridge somewhat as upper level flow turns more northerly. A dry cold front is expected to move through early Tuesday dropping temperatures a degree or two behind the front. Global models begin to diverge on timing and amplitude beginning on day 6 as an upper level trough is progged to move down from the NW. The GFS is considerably further east with a closed low dropping due south out of Saskatchewan and Manitoba into the Ohio Valley, as a west coast ridge intensifies. The ridging further west keeps some of the colder polar air out. The ECMWF shows a secondary shortwave feature moving over the area dragging the colder polar air further south. Regardless of the disagreement, some potential for mountain snow and a cool down appears possible in the very long range period. && .AVIATION...(For the 12Z TAFS through 12Z Saturday morning) Issued at 230 AM MDT Fri Oct 20 2017 Cloud bases between 8k to 10k feet are still being reported at this hour but will lift by daybreak giving way to mostly clear skies. Winds will start picking up around 18Z and continue through 00Z. Gusts from the I-70 corridor south will range from 25 to 35 mph while winds north will gust from 30 to 40 mph with higher gusts possible. Clouds will increase from the northwest after 00Z as a cold front moves through bringing rain and snowshowers. As the front moves through, KASE and KEGE, and maybe KRIL, may see some MVFR under rain and snow showers. Expect flight conditions to be affected by the front from 00Z through 12Z. && .GJT WATCHES/WARNINGS/ADVISORIES... CO...Wind Advisory until 8 PM MDT this evening for COZ001>003-006-020. UT...Wind Advisory until 8 PM MDT this evening for UTZ027-029. && $$ UPDATE...MDA SHORT TERM...TGR LONG TERM...ADL AVIATION...TGR |