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Area Forecast Discussion
Issued by NWS Grand Junction, CO
Issued by NWS Grand Junction, CO
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558 FXUS65 KGJT 150527 AFDGJT Area Forecast Discussion National Weather Service Grand Junction CO 1127 PM MDT Sun Jul 14 2024 .KEY MESSAGES... - The desert valleys of eastern Utah and the Grand Valley in western Colorado remains hot today with temperatures well above normal. Heat Advisories remain in place through this evening. - Widely scattered to scattered thunderstorm coverage and dry low levels will carry the elevated risk of fire starts. A Red Flag Warning remains in effect through this evening for areas where fuels are critical and better storm coverage exists. - Temperatures remain seasonably warm with daily thunderstorm chances through the seven day forecast as moisture continues to filter in around the high pressure. && .UPDATE... Issued at 854 PM MDT Sun Jul 14 2024 A few storms persist at this hour but lightning strikes have diminished greatly. This trend will continue over the next few hours so the Red Flag Warning for dry lightning will be allowed to expire. Also, temperatures have dropped below heat advisory criteria so that advisory will also be allowed to expire. Outflow boundaries continue to move across the area this evening bringing some wind gusts of 35 to 45 mph. These winds will diminish over the next few hours as convection winds down. && .SHORT TERM /THROUGH MONDAY NIGHT/... Issued at 302 PM MDT Sun Jul 14 2024 High pressure appears centered somewhere around Farmington near the southwest Colorado and northwest New Mexico border in a broad circulation area you can see on satellite with more widespread thunderstorm activity developing over the high terrain. Storms today have popped over all higher terrain so more widely scattered to scattered nature as anticipated. There is a bit of shear in this environment as evidenced by the southwest low level cloud movement and the storm tops taking a different direction based on the upper level flow around the high. Storms are fairly pop and drop at this time, especially over the San Juans where the upper level flow is opposite that of the low level flow, likely resulting in these storms getting sheared out and being fairly short lived. The area where the upper level flow is helping and not hindering is southeast Utah where storms are a bit more prolific. Dry thunderstorms still remains a concern given the dry low levels of the atmosphere and potential for fire starts, so the Red Flag Warning remains in effect for those more prone areas with dry fuels and more widely scattered or greater storm coverage. However, cannot rule out locally moderate to heavy rain in a few cells, especially across the south and southeast Utah where storms are training a bit. Gusty outflow winds 40 to 50 mph and small hail also remain a concern. Our precipitable water (PWAT) on the 12Z GJT sounding did climb up to 0.73 inches so the moisture is increasing around the high, but with DCAPE of 1400 to 1500 J/kg and an inverted V sounding, gusty outflow winds are the main concern. However, the environment will eventually adjust to the moisture increase heading into Monday, with less of a dry thunderstorm concern and better potential for measurable rain, especially in the higher elevations. Expect more storm coverage and more cloud cover on Monday. With the moisture increasing as PWAT rises to 0.75 to 1 inch across the area (about 150 percent of normal), opted not to extend the Red Flag Warning for dry thunderstorms into Monday. In terms of temperatures, the cloud cover has had a bit of an impact on the heat today and forecasted highs, which are currently running a few degrees below the forecasted highs thus far. While above normal temperatures will still remain, the temperatures do look to cool a bit more heading into Monday. Therefore, opted not to extend the Heat Advisory as well for the eastern Utah valleys and Grand Valley in west-central Colorado. Yes, it will still be very warm but increased moisture and therefore, cloud cover and storm activity should help provide slightly cooler temperatures that an extension of the Heat Advisory does not appear warranted. The current Heat Advisory remains in effect for the remainder of the day through 9 pm MDT this evening. && .LONG TERM /TUESDAY THROUGH SUNDAY/... Issued at 302 PM MDT Sun Jul 14 2024 The center of high pressure oscillates around the Four Corners through the first half of the long term period. While the positioning of said high doesn`t appear to fall into the ideal location for a direct plume of monsoon moisture into the CWA, the rotating high will still provide an uptick in moisture across the region. Precipitable water anomalies ramp up to 150 percent of normal by Tuesday, with remnant moisture rotating overhead through Thursday. Expect a chance of showers and storms to remain in the forecast each afternoon, favoring high terrain on the Divide. Ensemble guidance demonstrates a shift in high pressure, back west of the Divide, by the end of the week. If the high retrogrades back over to the Great Basin, GJT may tap into supplementary moisture sources driven by low pressure systems deepening along the lee of the Northern Rockies. PWAT anomalies spike to 200 percent of normal over the weekend, which improves the chance of wetting rain (i.e. measurable precipitation) across the Western Slope. Even if desert valley floors don`t end up seeing a lick of rain this week, increased cloud cover will at least relax daytime highs, 3 to 8 degrees cooler. Much closer to those seasonal norms for mid July than what we`ve experience thus far this month. && .AVIATION /06Z TAFS THROUGH 06Z TUESDAY/... Issued at 1127 PM MDT Sun Jul 14 2024 A few lingering showers were ongoing over the forecast area just before midnight. This activity is unlikely to bring showers to TAF sites before Monday afternoon. Expect showers and thunderstorms to develop over higher terrain similar to Sunday with showers in the vicinity of most TAF sites during the afternoon and evening Monday. PoPs are too low to include TEMPO groups which is not to say that it`s not possible that showers/thunderstorms will occur. That said, expect continued VFR conditions with no ceilings below ILS breakpoints at all TAF sites through the next 24 hours. Winds will generally be light and terrain driven, though outflow wind gusts to 45 mph are possible. && .GJT WATCHES/WARNINGS/ADVISORIES... CO...None. UT...None. && $$ UPDATE...TGR SHORT TERM...MDA LONG TERM...ERW AVIATION...NL