![National Oceanic and Atmospheric Administration](/build/images/header/noaa.d87e0251.png)
![National Weather Service](/build/images/header/nws.4e6585d8.png)
![United States Department of Commerce](/build/images/header/doc.b38ba91a.png)
Area Forecast Discussion
Issued by NWS Grand Junction, CO
Issued by NWS Grand Junction, CO
Versions:
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
820 FXUS65 KGJT 101206 AFDGJT Area Forecast Discussion National Weather Service Grand Junction CO 606 AM MDT Sat Aug 10 2024 .KEY MESSAGES... - Daily afternoon and evening thunderstorms with the threat of heavy rain rates, gusty outflow winds, frequent lightning, and small hail until further notice. - This uptick in available moisture will bring an enhanced threat of flash flooding and debris flows through the weekend and into early next week. - Temperatures will be near normal through the weekend cooling to below normal going into early next week with the increase in precipitation and cloud cover. && .SHORT TERM /THROUGH SUNDAY/... Issued at 422 AM MDT Sat Aug 10 2024 High pressure over Texas and low pressure along the Baja Coast keeps the door open to monsoonal moisture to flow up through Arizona and Southern California into eastern Utah and Western Colorado. Troughing/low pressure over the Pacific Northwest and southern Ontario keep the jet just to the north over Wyoming with increased shear and helicity across the northern areas, especially overnight tonight. Deep moisture with pwats at or above an inch continues across the region and will continue well into the extended forecast period (more on that below). There is currently weak convection, mostly light to moderate showers, over the San Juans that will linger into the morning hours before diurnal heating will initiate the development of thunderstorms in the late morning in the southern mountains, spreading into the central mountains and the Uintas by noon and becoming widespread over the higher terrain across the whole region in the early afternoon. Threats today will be much the same as yesterday with training storms leading to localized flash flooding, especially in the areas prone to training storms and flooding. With the lower atmosphere mostly saturated, strong winds are less of a concern, but gusts over 40 mph are still likely with the heavier rain, especially north of the I-70 corridor where the rain shafts can transport the momentum of the winds aloft down to the surface. Tonight, dynamics that can support stronger nocturnal thunderstorms moves over the northern areas generally along and north of the I-70 corridor due to a weak disturbance moving through the jet to the north. The NAM based models latch onto these dynamics, forecasting a strong nocturnal storm system moving through the northern areas overnight, but most of the other CAMS push wide spread convection through the northern region through the late afternoon and early evening, expending the energy built up form the daytime heating before the dynamics set up. This will be something to watch; should convection across the north be more widely scattered through the afternoon, then plenty of energy will be available overnight to support strong, possibly severe thunderstorm. Unfortunately, we`ll need to wait until late this afternoon to know if this will be the case. Currently leaning to the majority of the CAMS with the region getting worked over by evening and the system stratifying out to mostly showers with a few embedded thunderstorms through the overnight, much like the southern mountains had last night. The surge of monsoonal moisture pushes farther north Sunday with pwats of an inch or more through the Uinta Basin and east across northwestern Colorado. We`ll see pretty much a repeat of Saturday with thunderstorms developing in the late morning and afternoon, lasting well into the evening, with the heavier precipitation seen across the southern and central areas today spreading north to the Wyoming border. This will include the risks for training storms and localized flash flooding. && .LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/... Issued at 422 AM MDT Sat Aug 10 2024 The active weather pattern continues through early next week as monsoonal moisture continues to funnel into the area with the high pressure ridge positioned to the southeast over Texas. PWAT anomalies remain right in that sweet spot of 150 to 180 percent of normal on average. Sunday night looks to continue to be active as a shortwave moves through the flow across the south, keeping thunderstorm activity ongoing for mainly the central and southern areas, as evidenced by the latest HRRR output. PWAT anomalies are even shown to increase more heading into Monday and Tuesday as values increase up to 200 percent of normal. This is likely due to a shift from a westerly to more of a southwesterly or southerly flow, funneling the monsoonal moisture through eastern Utah and western Colorado from a deepening low pressure trough over the Pacific Northwest and the high pressure ridge still positioned over Texas. Additional shortwaves continue to move through thanks to an active northern stream, allowing for this forcing to act on the abundant moisture. Storms will be capable of heavy rain, frequent lightning and potential for flash flooding especially over more vulnerable areas like steep terrain, burn scars and already saturated soils. Given the shortwave disturbances, nocturnal activity seems like a sure bet at least through Tuesday night. The Pacific Northwest trough looks to finally push across the area by Wednesday after hanging out for a few days prior. Changes look possible late in the coming week though as high pressure builds in across the Desert Southwest following the passage of the Pacific Northwest low on Wednesday. This allows drier air to push across the Great Basin and Western Slope, with the flow shifting to a northwesterly direction, effectively shunting the monsoonal moisture tap to our south and east. PWAT anomalies drop to 60 to 80 percent of normal by Thursday into next weekend. Time will tell if this actually pans out cause models do have a tendency to dry things out too quickly. Enough remnant moisture could remain for isolated to scattered storms each afternoon mainly over the higher terrain, but the threat of excessive rainfall looks to gradually lessen late in the coming week. Given the increased clouds and showers through mid week, expect high temperatures to remain 5 or so degrees below normal with overnight lows a bit milder at 5 or so degrees above normal. Temperatures look to moderate towards near normal values by late week as drier air begins to advect in from the west and northwest. && .AVIATION /12Z TAFS THROUGH 12Z SUNDAY/... Issued at 538 AM MDT Sat Aug 10 2024 Showers and isolated thunderstorms across the southern mountains will continue for the next few hours before redeveloping into widespread showers thunderstorms after about 16Z. These storms will spread north to the Wyoming border by 20Z with periods of MVFR at times in heavier showers. Look for thunderstorms to continue through the evening, diminishing to showers after about 06Z Sunday. Winds will be gusty out of the west across the northern areas and generally light elsewhere. && .HYDROLOGY... Issued at 538 AM MDT Sat Aug 10 2024 Monsoonal moisture will keep showers and thunderstorms over the region through at least mid next week. Most of the higher terrain across the region, especially the southern and central mountains will see potential rainfall rates in excess of 1-2" per hour through this period. This will lead to increasing threats for flash flooding and debris flows across the majority of the area. Stay weather aware over the coming days, especially if recreating outdoors and in locations prone to flash flooding and debris flows, and stay tuned for forecast updates, as well as any Watches, Warnings, and Advisories over the coming days. && .GJT WATCHES/WARNINGS/ADVISORIES... CO...None. UT...None. && $$ SHORT TERM...DB LONG TERM...MDA AVIATION...DB HYDROLOGY...TGJT