458 
FXUS65 KBOU 152056
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
256 PM MDT Mon May 15 2023

.SHORT TERM...(This evening through Tuesday)
Issued at 128 PM MDT Mon May 15 2023

A ridge of high pressure aloft will continue over the forecast 
area tonight and Tuesday. It will remain moist and unsettled under
the ridge with showers and isolated to scattered thunderstorm 
coverage. This afternoon, SPC analysis shows precipitable water 
values up to 0.60 inch, with up to 0.80 inch over the eastern 
plains. Storm motions generally northwest at 10-15 mph, with 100 
mb/sfc based CAPES 250/500 j/kg over the mountains. The models 
keep the highest coverage over the elevated terrain this 
afternoon, with some weaker showers or storms moving across the 
urban corridor through early this evening as they move into a. 
more stable environment. There will be clearing overnight with 
enough moisture over the plains to produce patchy fog late tonight
into Tuesday morning, especially over the South Platte River 
drainage north and northeast of Denver. 

For Tuesday, sunshine will return to much of the area through the 
morning, with just some patchy fog over the plains through 8 am. 
High temperatures on Tuesday will warm back into the mid 70s.  The 
warmer temperatures combined with persistent moisture under the 
ridge will allow for another round of showers and thunderstorms by 
the afternoon.  There will be better coverage across the plains in 
the afternoon, with model forecast mean layer CAPES of 400-900 j/kg. 

.LONG TERM...(Tuesday night through Monday)
Issued at 245 PM MDT Mon May 15 2023

A somewhat active weather pattern will remain over the area
through the next several days. Thursday will see the highest 
chances of rain and hydro issues.

For Tuesday evening, scattered showers and a few thunderstorms
will continue at least until mid evening, before the airmass
stabilizes with decreasing coverage and likely ending before
midnight. We can't totally rule out something lingering a little 
past midnight on the northeast plains, but overall look for 
stabilization to do its trick with gradual clearing skies 
overnight. 

On Wednesday, the airmass will further destabilize with daytime
heating and moisture building along and ahead of a developing lee
trough. At this time, the strongest low level moisture convergence
and instability should set up just east of the I-25 Corridor, so
the eastern plains would have highest MLCAPE (near 1000-1200
J/kg). 0-6 km bulk shear would be sufficient as well for a couple
severe storms over the northeast plains with large hail being the
primary threat. High temperatures will be a couple degrees warmer
with highs in the upper 70s over the plains and I-25 Corridor.  

By Thursday, ensemble members are in agreement that we'll see deep
moisture build across portions of Colorado. NAEFS percentiles show
precipitable water building to near 0.90 inch along the I-25
Corridor, which would put us near the 99th percentile. Weak
forcing is also indicated. One limiting factor is that the cold
front, or at least the first push of cooler more stable air, is 
now advertised to push southward across the plains Wednesday 
night. That would leave the airmass across the Front Range and 
plains more stable. That said, there will still be forcing aloft 
by a weak approaching trough and lapse rates (above any low level 
stable layer) would be nearly moist adiabatic. Therefore, this 
weak wave could still be an efficient precipitation producer with
locally heavy rainfall, despite the lacking instability. More in 
the hydro discussion below.

By Friday, we're pretty confident the upper level trough and
support for precipitation will be shifting to our south. We'll
still have a chance of showers and a couple storms in the forecast
in case the system slows down, but right now we think the National
Blend of Models (NBM) is holding onto to much precipitation so
we've trimmed PoPs back for this period. Mountain areas would
still be more unstable.  

Little changes for Saturday with mountain areas likely seeing the
bulk of convection. The airmass will start to destabilize again on
the plains during the weekend and into early next week, so we may
see a higher chance of showers and storms spreading into the lower
elevations, especially if we can keep the deeper moisture around.

After the cooldown for Thursday and Friday, temperatures will warm
back into the 70s in the lower elevations by the weekend. Overall
the unsettled weather will continue for many days to come but
temperatures are likely to hold above the levels observed this 
last cool, unsettled week. 

&&

.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
Issued at 1201 PM MDT Mon May 15 2023

In spite of the improvement expected this afternoon, ceilings 
will likely stay under 6000 feet through the day before scattering
by mid evening. Light E/NE winds will shift to S/SW this evening 
and continue overnight, then shift to the W/NW Tuesday morning by 
15z. I do not think any showers will impact DEN this afternoon, 
but a low probability at APA 22-01z. The models hint a lower vsbys
developing at DEN around 12z Tuesday so I did include vcfg. Also 
put vcsh in the outlook period for DEN Tuesday afternoon as more 
sunshine and warmer temperatures will equal a better chance of 
showers and thunderstorms. N/NE winds will pick up as well 10-15 
kts in the afternoon.

&&

.HYDROLOGY...
Issued at 245 PM MDT Mon May 15 2023

Scattered showers and thunderstorms this afternoon will diminish 
this evening. This will result in a limited threat of flash 
flooding in the burn scars. A similar scenario will play on 
Tuesday afternoon with another round of showers and thunderstorms,
and a limited threat of flash flooding.

On Thursday, precipitation efficiency will be driven by a deeper 
warm cloud depth (initial indications it would be close to 5,000 
feet deep), skinny CAPE profile, high precipitable water (near 
99th percentile) weak synoptic lift, and shallow upslope focusing 
heavier precipitation in/near the foothills. There is a chance 
this could all end up farther south and focused toward 
southeast/south central Colorado, but will keep an eye on this 
period as it won't take near as much rain to create hydrology 
issues. 

&&

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

$$

SHORT TERM...Cooper
LONG TERM...Barjenbruch
AVIATION...Cooper
HYDROLOGY...Cooper/Barjenbruch