Marine Weather and Tide Forecast for Granby, CO

DISCUSSION /Through Friday/
Issued at 202 PM MDT Fri May 15 2026

Summerlike warmth and dryness will be replaced by active spring weather with a severe storm threat Saturday and potentially into Sunday, before more winterlike weather arrives Monday.

In the short term, isolated high based showers and thunderstorms are already developing over the Palmer Divide as we reach convective temperatures. Given DCAPE near 1100 J/kg, we expect the main threat outside of lightning to be gusty winds to around 40 mph. Those isolated showers and high based storms may continue this evening and overnight, especially with a little moisture advection noted from the southeast.

That moisture advection will set us up for a greater risk of a few severe storms Saturday. While the moisture advection is marginal, surface dewpoints increasing into the lower to mid 40s over the eastern plains combined with daytime heating should drive MLCAPE into the 600-1300 J/kg range for afternoon. Bulk shear increases significantly to 40-50 kts, with decently curved hodographs more than sufficient for supercell formation. The highest MLCAPE would be east of a Fort Morgan to Akron line, where the greatest risk of strong storms would be found and thus a Slight Risk over most of the plains. The most recent Storm Prediction Center increased the risk to Enhanced over the far northeast plains where storms may organize further and updraft helicity values increase. Storm Relative Helicity values are not terribly strong, with 0-1 km values mostly under 100 m2/s2 and 0-3km in the 100-200 m2/s2 range. However, those could be locally enhanced along/just ahead of a dryline expected to develop off the Palmer Divide and a warm front extending from there into west central Kansas. Therefore, while large hail to 2" in diameter and damaging winds to 60+ mph will be the main threats, one or two brief tornadoes will also be possible.

On Sunday, we're still keeping an eye on another day of severe storm potential, but signs are growing (more model agreement) that the cold front will be pushing south through most of our forecast area and taking the majority of the instability and severe weather threat with it. As discussed yesterday, however, a sharper trough digging into the Great Basin could hold the front up slightly or allow it to stall near the Palmer Divide into east central Colorado, so we'll continue to monitor this threat.

The main concern then shifts to Sunday night and Monday with high potential for accumulating snow in the mountains, and even a few snowflakes down into the lower elevations including the I-25 Corridor by Monday. Overall, ensembles have trended colder due to more agreement that the trough moving across the forecast area will be in more more organized piece. Thus, about 50% of ensembles are hinting at some snow mixing in for the I-25 Corridor. It's important to note this does not appear to be like last week's tree breaking storm, as temperatures will be several degrees warmer making it hard to accumulate any snow - even if it does mix with or turn completely over. The majority of the precipitation will also fall during the day. For the mountains, several inches if not close to a foot of snow can be expected, while foothill areas could see anywhere from a trace to 10". Those heavier amounts would be favored toward the north, including the higher foothills above 7,500 feet in Larimer County.

The heaviest total liquid equivalent precipitation from this storm system is still expected along and north of I-70 and I-76 on the plains. Ensembles have bumped up things a little, with the 25th-75th percentiles now at 0.50-1.25 inches for the Denver metro, with a floor (10th percentile) near 0.25" and a mean of 0.80-1.0 inch. From those means, add on another 0.3 to 0.5 inch for locations near the Wyoming border and take away about 0.5 inch for points farther south along the Palmer Divide.

The weather pattern settles down for much of next week. As this first trough exits and cold air lingers, some frost/freezing temperatures can be expected down onto the plains late Monday night into Tuesday morning. That, of course, depends on how much clearing and drying we see. Weak troughiness should then keep a few showers and weak storms in the forecast Tuesday and Wednesday, with temperatures gradually moderating. We'll be warming back to normal or above normal levels by the end of next week as a more zonal flow aloft develops.

AVIATION /00Z TAFS through 00Z Sunday/
Issued at 637 PM MDT Fri May 15 2026

Current radar imagery shows that the thunderstorm activity southeast of the Denver metro area has begun to taper off. However, a few 20- 25KT outflow gusts from elevated showers and virga are still possible over the next hour or two, particularly at KDEN and KAPA.
Winds this evening will remain light S-SE before weak drainage winds take over in the early morning hours.

The main concern for this TAF period will be the thunderstorm threat Saturday afternoon. Prevailing winds will turn S-SE after 18Z and begin transporting moisture into the area, which will bring the potential for scattered showers and thunderstorms. Relatively modest instability and convective dynamics may allow for a few isolated strong thunderstorms to develop, particularly in the vicinity of KDEN and KAPA, but the better storm environment will reside in the northeast CO plains. Nevertheless, wind gusts up to 35-40 KTS will be possible with any outflows and microbursts that develop over the region.

Ceilings will begin to lower after 00Z Sunday, with MVFR or IFR possibly developing after midnight, but there is still some uncertainty regarding the timing and western extent of low clouds.



BOU WATCHES/WARNINGS/ADVISORIES
None.