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
044 FXUS65 KGJT 091733 AFDGJT Area Forecast Discussion National Weather Service Grand Junction CO 1133 AM MDT Fri Aug 9 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. - An uptick in available moisture starting today will lead to increased storm coverage and an enhanced threat of flash flooding and debris flows through the weekend and into early next week. - Temperatures will be cooling back toward normal with the increase in precipitation and cloud coverage through at least the middle of next week. && .UPDATE... Issued at 1133 AM MDT Fri Aug 9 2024 Confidence of heavy rainfall potential over the Grizzly Creek burn scar area today has increased enough to hoist a Flash Flood Watch for the burn scar this afternoon and evening. Model struggling with this early morning convection across the North but other parameters suggest convection should fire in the vicinity of the burn scar with the possibility of 1-2" hourly rainfall rates. Corfidi vectors suggest storm motions moving perpendicular to drainages but deep warm core storms and any training or back-building could cause some issues. There also could be a few rounds of storms move through the area with the radar currently becoming more active and then more storms forming on outflow boundaries as the high plateaus become more active. && .SHORT TERM /THROUGH SATURDAY/... Issued at 408 AM MDT Fri Aug 9 2024 An area of stratiform showers persisted across portions of SE Utah and SW Colorado early this morning due to lift provided by a mesoscale convective vortex evident in looped radar imagery. Showers were trending downward, but there`s a good chance some of this activity will persist through sunrise. Elsewhere, aside from northeast Utah and a small portion of northwest Colorado, skies were mostly cloudy under a lid of mid and high clouds streaming over the forecast area from the southwest. Winds in the 850-700mb layer indicated the movement of moisture both directly from the Gulf of Mexico and the Mexican Plateau will move into the area today. As a result, precipitable water levels will be on the rise as has been discussed over the past several days. According to the GEFS, levels will climb to around 0.8" in the north and to near 1" or more over the Four Corners region. Elevated moisture levels combined with daytime heating and dynamic forcing associated with divergence in the right entrance region of the jet moving over the Colorado`s northern border is expected to lead to numerous showers and thunderstorms from late morning through early evening. Most storms will initiate over higher terrain before moving over adjacent valleys. Localized excessive rainfall is possible, especially across the south where subcloud moisture was deeper as evidenced by dew points in the lower to mid 50s. Gusty outflow winds to 45 mph are possible with stronger cells and areas north of the I-70 corridor where there will be less subcloud moisture. Showers diminish from northwest to southeast in response to diurnal cooling tonight. However, a shallow mid-level short wave trough combined with jet divergence across the south is expected to sustain scattered shower/thunderstorm activity overnight. Moisture levels on Saturday were indicated to remain similar to those forecast for today. Meanwhile, jet divergence and another shallow, fast moving short wave trough which, when combined with diurnal warming, will bring another round of widespread shower and thunderstorm activity. The subcloud moisture should be a bit higher than today increasing the potential for excessive rainfall, especially south of the I-70 corridor. As discussed previously, afternoon highs are expected to finally fall to near normal levels today in response to increased clouds and shower/thunderstorm activity. A similar amount of cooling is expected overnight with highs on Saturday similar to those forecast for today. && .LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/... Issued at 408 AM MDT Fri Aug 9 2024 High pressure sets up over west Texas with low pressure over the Baja peninsula throughout the extended period. As a result, a monsoonal flow of mid level moisture from the Gulf of Mexico and lower level moisture off the Gulf of California will continue to advect north into the region through at least the middle of next week. This deep moisture will keep PWAT`s near, or above an inch across eastern Utah and western Colorado leading to the potential for excessively heavy rain leading to flash flooding/debris flows, especially in susceptible areas. Cloud cover from all this moisture will limit diurnal heating causing daily high temperatures to run 3 to 7 degrees below normal. Expect widespread afternoon showers and thunderstorms to develop daily over the higher terrain across the region with scattered storms rolling off the terrain and over adjacent valleys. These storms will continue through the evening before changing over to mostly stratiform showers as they diminish in the late evening and overnight. Be aware that some of these nocturnal storms could be stronger with heavy rain leading to night-time flash flooding. Stay tuned to the short term forecast for possible risks in your area. Models were hinting at a possible change Wednesday into Thursday as a trough digging south along the West Coast pulls drier air off the Pacific pushing the monsoonal flow east of the Divide. Residual moisture with diurnal heating warming the region back to near normal for mid August will keep afternoon showers and thunderstorms in the forecast through the second half of the week, though coverage will likely decrease. One concern with this pattern is the increased shear from the approaching trough and the drier airmass aloft may spawn strong thunderstorms producing large hail (>1 inch) and strong outflow winds (>60 mph). Confidence is low for this severe convective activity at almost a week out, and should the trough stay farther to the north, the deep monsoonal flow across the region could just continue. Stay tuned to see how this plays out. && .AVIATION /18Z TAFS THROUGH 18Z SATURDAY/... Issued at 1133 AM MDT Fri Aug 9 2024 The thicker cloud cover is thinning and convection beginning to bubble across the central CWA with plenty of monsoonal mositure in place. The threat of a storm in the vicinity or impacting a TAF site will not be picky today and all forecasts will have this threat through the afternoon and evening hours. Gusty outflow winds and brief heavy rainfall will be threats and this could lead to temporary MVFR conditions and a very low probability of IFR. Depending on rainfall location lower clouds could be possible by sunrise...with KEGE the most likely location going with persistence from the last few events. && .HYDROLOGY... Issued at 245 PM MDT Thur Aug 8 2024 Monsoonal moisture will be enhanced by additional moisture originating from the Gulf of Mexico increasing daily shower and thunderstorm activity over the area through next week. Areas south of the I-70 corridor and especially the southern Colorado and Utah mountains will see the most consistent activity through this period. The threat of excessive rainfall rates of 1-2" per hour increases as this moisture lingers over the area. In turn, this will lead to an increasing threat for flash flooding and debris flows across the majority of the area, potentially lasting through much of next week. Be sure to stay weather aware over the coming days, especially if recreating outdoors and in locations prone to flash flooding and debris flows. Stay tuned for forecast updates, as well as any Watches, Warnings, and Advisories in the coming days. && .GJT WATCHES/WARNINGS/ADVISORIES... CO...Flash Flood Watch until 10 PM MDT this evening for COZ008-013. UT...None. && $$ UPDATE...15 SHORT TERM...NL LONG TERM...DB AVIATION...NL HYDROLOGY...TGJT