572
FXUS65 KBOU 291812
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
1212 PM MDT Wed May 29 2024

.KEY MESSAGES...

- Scattered thunderstorms this afternoon and evening. A few severe
  storms are likely with large hail and strong winds in areas east
  of I-25 the main threat.

- Scattered afternoon showers and thunderstorms Thursday-Friday. A
  few could be severe Thursday from the Palmer Divide eastward.

- Warmer and drier beginning Saturday. Hottest temperatures so far
  this year likely Sunday into Monday.

&&

.UPDATE...
Issued at 1033 AM MDT Wed May 29 2024

With dew points near the mid 40s to 50s along the urban corridor
especially north of Denver, it is possible our dryline may not
set up that far north. A few stations display lower dew points
near 35-40 west of the I-25 corridor but not as low as the HRRR.
Given models have shown weaker showers occurring first, this
outcome may keep the environment stable late afternoon to early
evening due to this early development.

With this mind, there is higher chance of showers pushing into
urban corridor today then becoming severe east of DIA. It is
possible areas along the urban corridor such as Greeley, Mead and
Firestone could receive additional rainfall from these showers
anywhere between 0.10-0.20 inches. These showers should move
quickly unlike yesterday where outflow dominated storms stalled in
certain areas.

&&

.SHORT TERM /Through Wednesday Night/...
Issued at 500 AM MDT Wed May 29 2024

Well, that was interesting. Cloud remnants of the convection that
blew up around Greeley in the late evening are moving across the
northeast corner at this hour. There`s a little pressure couplet
associated with that which has turned low level winds more SSW
across our plains for now, which could be a wrinkle in today`s
plans. The HRRR seems to have some idea of this. Its last several
runs have been really aggressive about bringing drier air into the
Denver area and setting up a sharp dryline with dew points in
Denver around 20 by noon. That seems like too much, but maybe not
since we already appear to be eroding the west edge of the richer
moisture that was coming in last evening.

The tricky part is the battle between the rate of drying and the
warming. How far north and east, and how strong, will the drying
be when we get convective initiation? I had been skeptical of the
limited amount of storms forecast for the I-25 corridor given that
today was supposed to have better moisture, but now that is
looking like it might be correct and we may even still have too
much if it`s going to dry thoroughly be early afternoon. One
question is the shape of the evolving dryline. How much will it
bend back towards Weld or even Larimer counties as SSE winds
redevelop on the plains and wrap westward north of the Palmer
Divide? Given what`s currently happening, I`m not too worried
about a big moisture recharge for Greeley/Fort Collins but they
may not dry out as much as Denver. That could keep a threat of
marginally severe hail for those areas if they can hang on to
CAPES of 800-1000 J/kg.

The HRRR has capes under 800 J/kg along and west of the dryline
with 1000-1500 J/kg east of it in the late afternoon, which looks
reasonable and matches the HREF means. There are runs with up to
3000 J/kg but that looks quite unlikely. So this may wind up
being a fairly typical late May/early June day with a few severe
thunderstorms with the main threat being 1 to 2 inch hail. We
could have heavy rain issues too as stronger low level winds than
mid levels will favor a backbuilding tendency or at least slow
storm motions. But the expected linear nature of the storms should
promote better outflow propagation. If there are hydro issues, it
would be more likely on the eastern plains in the early evening.

For now, we didn`t make too many adjustments, some minor trimming
of the PoPs in the less likely areas.

&&

.LONG TERM /Thursday through Tuesday/...
Issued at 500 AM MDT Wed May 29 2024

A cold front will push through most of our forecast area Thursday
morning, bringing with it more stable conditions and slightly
cooler temperatures. Low-level moisture will also be quite
limited behind the front. This should taper the strong
thunderstorm potential for the northern tier of the forecast area,
although isolated convection will still be possible late afternoon
and into the evening. Parameters will be more favorable for areas
from the Palmer Divide eastward into Lincoln County, where both
moisture and instability will be maximized. Storms here will
likely be better organized and could carry a severe threat, mainly
in the form of hail and gusty outflow winds.

Friday will see a weak shortwave embedded in largely zonal flow
aloft zip over Colorado, with low-level flow shifting back to a
generally southeasterly direction bringing some increase in
moisture. Unstable conditions in the afternoon look to be more
expansive compared to Thursday and would support slightly greater
coverage of afternoon convection from the mountains into the
plains.

We`ll start to transition to a drier and warmer pattern on
Saturday, with a downward trend in moisture and instability but
still some lingering potential for isolated afternoon convection.
Subsident flow becomes much more prevalent for Sunday under weak
ridging and rising 700mb temperatures, accelerating the warmup
and significantly reducing precipitation potential region wide.
Could be Denver`s first shot at 90 degrees this year. EC and
Canadian ensemble suites have the thermal ridge and downslope
flow (and consequently temperatures) peaking Monday, while the GFS
leans towards some tapering of the heat with a cold front
passage. Regardless, we`ll be staying dry Monday and likely much
warmer than average. Model spread increases quite a bit for
Tuesday with varying solutions in the upper-level pattern,
precipitation chances, and longevity of the above-normal
temperatures.

&&

.AVIATION /18Z TAFS through 18Z Thursday/...
Issued at 1209 PM MDT Wed May 29 2024

Expect VFR conditions through the TAF period.
With scattered showers developing earlier, VCTS could begin as
early as 19Z-20Z. These storms should remain weaker as favorable
conditions for severe storms remain east of all terminals. Wind
direction will likely become difficult as showers pass nearby but
generally wind speeds between 12-20 mph producing gusts up to
25-35 mph. Winds shift southwest tonight then shifting northerly
into Thursday morning. Wind speeds increase between 10-13kts
through late Thursday morning.

&&

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

&&

$$

UPDATE...AD
SHORT TERM...Gimmestad
LONG TERM...Rodriguez
AVIATION...AD