Marine Weather and Tide Forecast for Pierce, CO

DISCUSSION /Through Saturday/
Issued at 402 PM MDT Sat May 17 2025

Scattered showers and some weak thunderstorm chances will persist through the evening tonight, diminishing from west to east across the forecast area. Mild temperatures are expected across the plains tonight, ranging from the low to upper 40s, with 30s on tap for the mountain valleys.

Southwesterly flow aloft will increase overnight tonight ahead of an approaching upper-level shortwave. At the surface, lee cyclogenesis will deepen throughout the day Sunday, with it's center dropping to ~992 mb along the CO/KS border by early evening. Gulf moisture will be advected into northeastern Colorado as it wraps around the surface low, with dewpoints nearing 60F on the east side of an eastward propagating dryline by the afternoon. SPC has upgraded the northeastern corner of the state to an Enhanced Risk for severe weather for tomorrow, with large hail being the main threat, but severe winds and a few tornadoes can't be ruled out.
With forecast soundings showing MUCAPE approaching 2000 J/kg, effective bulk shear topping 50 kts, and mid-level lapse rates near 9C/km, this environment would support supercells capable of producing significant (2"+) sized hail.

Meanwhile in the mountains, winter weather will return to our highest elevations and increase in intensity through the day.
With the height of the snowfall expected in the warmest portion of the day, accumulations will likely remain on grassy surfaces, but some of the higher mountain passes may see some slick travel conditions develop during the heaviest snowfall. With 4 to 8 inches expected, mainly for elevations above 10,000 feet, we have gone ahead and issued a Winter Weather Advisory beginning Sunday at 6 AM and continuing through Monday at 6 AM for Rabbit Ears Pass, Summit County, Mosquito Range, and the Indian Peaks.

The main changes made to the NBM reside in the first half of the week. As the midnight shift mentioned, PoPs were very heavy across the plains on Monday on the latest NBM output. I went ahead and trended downward, keeping the greater chances of precipitation along the Palmer Divide where northerly flow behind a cold front will keep upslope in place, and lowered them south of the Cheyenne Ridge where downsloping conditions will reside. Should still see a chance for some rain showers and scattered storms across the forecast area as the aforementioned shortwave trough axis moves across the region.

Drier conditions are expected to return on Tuesday as some weak ridging develops over the Rockies. A disturbance just to the north may initiate some afternoon showers or storms over the northern mountains, but the plains will largely remain dry. A warming trend will also begin on Tuesday, and by mid to late week, we should see some 80s return to the lower elevations.

AVIATION /00Z TAFS through 00Z Monday/
Issued at 526 PM MDT Sat May 17 2025

Will maintain an ESE winds thru mid evening and then have SE winds by 06z. There is a low threat (10% chance) of a tstm at DIA but believe the activity will stay E and SE. Late tonight there will be some stratus just to the east. If Denver cyclone becomes more developed some of this could wrap into DIA but for now have just kept a sct deck. By 18Z Sun, should see a well developed Denver cyclone near DIA. Hi res guidance shows storms could develop by 19z along the convergence zone near DIA so will just go with a prob group. Not sure about winds due to position of cyclone but will start with an easterly component by 16z with an ENE direction by 18z. Winds may switch to NW by 22z or 23z.



BOU WATCHES/WARNINGS/ADVISORIES
Winter Weather Advisory from 6 AM Sunday to 6 AM MDT Monday for COZ031-034.