FXUS65 KBOU 021124
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
524 AM MDT Fri May 2 2025

.KEY MESSAGES...

- Dry and warmer through Saturday. Only an isolated shower/storm
  possible in the mountains Saturday afternoon. 

- Spring storm begins late Sunday/Monday and continues into the 
  middle of next week. Soaking rain, and heavier mountain/higher 
  foothills snow quite likely (70-80% chance). 

&&

.SHORT TERM /Through Tonight/...
Issued at 253 AM MDT Fri May 2 2025

Current satellite imagery shows yesterday's passing trough exiting 
to the east early this morning, with much drier air and quieter
weather filling in behind its departure. Some lingering low level
clouds remain in place over the southern foothills and urban 
corridor, but these are expected to clear out near sunrise this 
morning. NNW flow will be in place over the forecast area through 
the day as upper-level ridging builds over the Rockies. With ample
sunshine expected and 700 mb temperatures warming ~5-8 deg C over
yesterday, afternoon high temperatures are expected to warm by a 
few degrees over yesterday's as a result. Sunny skies and warmer 
temperatures should make for a nice day to end the work week. 

For tonight, NNW flow will decrease and dry conditions will 
persist. Near normal temperatures are expected, with 30s and 40s 
forecast for the foothills and plains, and 20s and 30s for the 
mountain valleys. 

&&

.LONG TERM /Saturday through Thursday/...
Issued at 253 AM MDT Fri May 2 2025

A large upper level ridge centers itself across the Rockies
Saturday, bringing sunshine and warmer temperatures. Temperatures 
will be around 10 degrees above normal, with highs pushing into 
the mid 70s on the plains, 60s foothills and high mountain 
valleys, and 40s and 50s above 9,500 feet. There may be just 
enough moisture building under the ridge for a slight chance of a 
late day shower/weak storm over Park/Summit County area, but 
doubtful at this point (20% chance). 

For Sunday, most of the day is shaping up to be mild and dry,
still under the influence of the high amplitude ridge over the
High Plains. That's essentially the beginning of an omega block,
with another upper low just east of that in the Ohio River
Valley. Given the proximity of the ridge, the main chance of 
showers and storms through Sunday afternoon and evening will 
remain confined to the mountains and western Colorado. 

It's not until Monday when we think the bulk of precipitation will
arrive. And even that could be a bit fast considering the omega
block. Moisture will certainly be increasing by then, given the
deep southerly flow and influx of gulf moisture. There is good
agreement in the ensembles that Monday will be the start of this
potentially long-lived precipitation event, with Tuesday being the
peak day for precipitation and lowest snow levels, and then
things winding down by Wednesday as the upper low eventually 
shifts eastward into the Central Plains. 

With regard to precipitation amounts, the ENS has backed off
precipitation amounts slightly in the latest 00Z output, with
generally 1.5-2.0 inch amounts along the Front Range and I-25
Corridor. That essentially puts it in line with the GEFS. What was
interesting to note, not surprisingly, is that ensembles have
backed off QPF amounts across the northeast plains. That would be
due to the stronger omega block holding the ridge over the 
Central Plains. There is still a slight chance (~20%) that ridge 
holds too strong and starts to impact precipitation amounts along 
the Front Range as well. But with upslope and gulf moisture plume 
that shouldn't be a problem so at this point a soaking spring rain
event it quite likely (70-80%). Meanwhile, there's a very small 
threat (<10% chance) of excessive rainfall that could lead to any 
meaningful hydrologic issues. This is noted by WPC's Marginal Risk
in the Excessive Rainfall Outlook (ERO). Finally, temperatures are
cold enough to support snow, and potentially heavy accumulations 
for the Front Range Mountains and higher foothills. A rain/snow 
mix down through the lower foothills and perhaps the Palmer 
Divide is possible by Tuesday/Tuesday night. A few of the 
individual members even brought a little snow down to the I-25 
Urban Corridor, although at this point that seems quite unlikely 
given the influx of gulf moisture and lack of cold advection. 

&&

.AVIATION /12Z TAFS through 12Z Saturday/...
Issued at 504 AM MDT Fri May 2 2025

VFR conditions expected through the TAF period. WSW winds have 
set in at all TAF sites early this morning. Expecting a westerly 
to northerly turn in winds through the morning with northeasterly 
winds expected for the afternoon. Winds should generally be light 
throughout the day, however, some hi-res guidance show a window 
of northeasterly gusts between 15-18 kts possible (~20% chance) 
between 18Z to 22Z at KDEN.


&&

.BOU WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$

SHORT TERM...Bonner
LONG TERM...Barjenbruch
AVIATION...Bonner