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FXUS65 KBOU 290312 AFDBOU

Area Forecast Discussion National Weather Service Denver/Boulder CO 912 PM MDT Sun Apr 28 2024

KEY MESSAGES

- Warmer and drier conditions to start the week.

- Turning to cooler and possibly wetter Wednesday and Thursday.

UPDATE
Issued at 912 PM MDT Sun Apr 28 2024

Current radar shows the remaining cluster of covective showers moving across the east plains. Hail is no longer a likely threat; however, gusty winds near and within these showers are possible (up to 40 mph). Scattered showers are expected in the mountains tonight decreasing toward sunrise. Previous forecast is mainly on track. Made a few minor adjustments to the winds. Bumped up winds a little bit in the windy mountain spots on the Front Range as there is a very weak mountain wave signal overnight. Gusts up to 45 mph are possible. Warmer temperatures are expected tomorrow with highs in the 60s with mainly sunny skies.

SHORT TERM /Through Monday/
Issued at 255 PM MDT Sun Apr 28 2024

Convection is slow to develop this afternoon. It isn't very warm after all. The winds are pretty weak over much of the CWA The eastern third of the plains do have some northwesterlies gusting to 20-25 mph. There is pretty decent snow shower coverage in the high mountains at this time, especially north of I-70.

Models have moderately strong northwesterly flow aloft tonight, becoming zonal on Monday at 50-60 knots at jet level. Models do not have much low level moisture for the CWA; just a bit in the mountains this evening. I will lower pops a tad over the plains for early evening based on current development, current temperatures and model MLCAPE prongs. Little to no pops on Monday, maybe just 10%s over high mountains by afternoon.

For Monday's highs, thickness grids point to a 3-6 C warm-up over today's readings.

LONG TERM /Monday night through Sunday/
Issued at 232 PM MDT Sun Apr 28 2024

The focus for the extended forecast period looks to reside to our north. With multiple disturbances embedded within the upper-level flow stemming from the PNW through the week. Models are consistent with solutions for the beginning of the week, then quickly diverge come mid week.

As the weak ridging shifts east out of the region Monday afternoon, northern CO will be on the outskirts of the main QG forcings associated with an upper level low passing through Montana. A strengthening westerly jet at the base of the shortwave trough will dig southward enough to be a source of lift for the northern border of CO. A cold front associated with this system will also move into northern CO overnight, these forcings will be plentiful enough to bring some rain and snow showers to the northern Colorado Rockies into early morning Tuesday. Accumulations are expected to be light with minimal impacts.

Tuesday will be drier and slightly warmer than Monday as westerly flow aloft brings downsloping conditions to the lee side of the Rockies. With an 85-95 kt jet overhead, expect windy conditions in the typical wind prone areas in the mountains and foothills as well as the Cheyenne Ridge. Forecast soundings depict inverted V solutions with DCAPE values reaching as high as 1030 J/kg for the afternoon hours, which could bring some dry microburst potential across the plains. High temperatures will be a few degrees above normal reaching the low 70s across the plains. Overnight low temps will be similar to Monday's, albeit slightly warmer at the base of the foothills. As the upper level low shifts east across Montana through the day Tuesday, another will begin to push inland into the PNW behind it. It is with this approaching system that models begin to diverge.

From a deterministic perspective, the GFS shows the upper level low digging far more southward than the ECMWF and Canadian solutions. This would place the main QG forcings directly over the forecast area bringing more impactful weather to the area. This contradicts previous runs that had the ECMWF being the deeper trough solution. With continued uncertainties remaining, we will have to see how the models resolve future runs to have a clearer picture for the latter half of the week. For now, we should expect high temperatures in the 70s on Wednesday with increasing chances for rain showers through the day. Thursday will likely bring cooler high temperatures and some more widespread precipitation.

Ensembles show a wide spread with regards to QPF between 6 PM Wednesday and 6 PM Friday. The GFS (wettest of the bunch) shows up to an inch of QPF for some mountain locations and .75 inches for areas across the plains. The Canadian and EC are slightly more aligned, however, the Canadian is the driest showing .3 inches for the mountains and .15 inches for the plains.

After the system moves through in the Wednesday-Friday timeframe, ridging looks to build behind its exit bringing warmer and drier conditions for the weekend with a chance for Denver to see the upper 70s on Sunday.

AVIATION /00Z TAFS through 00Z Monday/
Issued at 555 PM MDT Sun Apr 28 2024

VFR conditions are expected through the TAF period.

Expected scattered showers, virga and a few storms around the terminals early this evening. Some of the more organized showers/storms nearby may result in variable outflow gusts up to 30 kts for brief periods as they move generally from NW to SE.
Shower/storm activity diminishes by 03/04Z. Winds return to southerly drainage at APA and DEN by midnight. Light winds expected Monday morning becoming light and variable around 15-16Z.
W/WNW winds for the afternoon at 05-10 kts.

BOU WATCHES/WARNINGS/ADVISORIES
None.

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