639 
FXUS65 KBOU 051617
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
1017 AM MDT Tue May 5 2020

.UPDATE...
Issued at 1017 AM MDT Tue May 5 2020

Temperatures have quickly climbed this morning under sunny skies 
after a chilly start to the day. Will see some cumulus clouds form
over the higher terrain and drift eastward this afternoon. 
Otherwise, sunny skies will continue. Temperature forecast of 
upper 60s and lower 70s over northeast Colorado still look on 
track. No changes to the current forecast planned.

&&

.SHORT TERM...(Today and tonight)
Issued at 435 AM MDT Tue May 5 2020

An impressive early May ridge builds north and shifts east
throughout the day today. The axis is still west of us so we will
be under northwest flow. The atmosphere will continue to be bone 
dry at all levels, with 0.25" PW across the I-25 urban corridor 
and all of the high county, and just 0.40" near the KS/NE border.
Winds will be downslope from near the surface to above ridgetop,
leading to even more drying close to the surface. Dewpoints
tomorrow across the plains and I-25 urban corridor may dip below
20 degF. Same for the high country. Needless to say no
precipitation and only a few clouds are expected through tonight.
With mixing, winds will pick up again this afternoon though not 
as strong as yesterday, with 15-25 mph across the plains expected 
out of the NW. Temperatures should be in the low 70s at 
elevations below 6000 ft elevation, and mid 50s to low 60s up to 
9500 ft elevation.

The only expected wx impacts are from frost before sunrise this
morning, and again early Wednesday morning. With current temps in
the low 30s and light winds across the advisory area, frost 
development is ongoing right now and should end once the sun hits 
those surfaces a few hours from now. One limiting factor to frost 
development early Wednesday morning may be the very dry air (since
you need some moisture to generate it, either the air just off 
the surface or after a recent rainfall). Nevertheless, east of 
the Denver metro area and Fort Collins-Greeley metro areas there 
could be enough moisture around for frost, especially in the low 
lying river valleys and areas closer to KS/NE. The temperatures 
will be cool enough to support the development of frost, with 
lows between 32-36 early Wednesday morning. It looks both too dry 
and too warm across the urban areas for frost Wednesday morning.

.LONG TERM...(Wednesday through Monday)
Issued at 435 AM MDT Tue May 5 2020

Wednesday looks like a quiet warm day with the ridge axis passing
and low level flow turning southerly on the plains in the 
afternoon. It looks like there will be some high cloudiness
associated with some warm advection aloft, but low levels will
remain quite dry. Previous forecast looks pretty good here.

There's decent agreement on the timing and location of a sharp
shortwave trough focused northeast of Colorado late Thursday.
There are still model differences in the intensity though,
including the strength of the winds and the amount of cold
advection Thursday and Thursday night. We'll compromise between
the MOS winds that are stronger than the previous forecast and 
show some cooling in the afternoon. The more aggressive NAM 
solution has 32 knot sustained winds at Akron at noon Thursday and
keeps highs in the 50s across the plains. We'll have to watch to 
see if that looks more likely. Either way, there's not much
moisture. The stronger solution has more cloud cover but the low
levels are still dry. There may be fire weather issues for
Thursday. The strongest winds behind the front on the plains
should come with cooler temperatures and higher humidities. Closer
to the mountains, and especially in the mountain parks and
foothills southwest of Denver, humidities will be lower in the
warmer air but it should still get windy in the afternoon. The
main concern is South Park and the foothills south of I-70 where
it has been drier recently. 

Lighter northwest flow continues Friday with drying behind the 
shortwave. There are discrepancies here in both the amount of 
cooling and moisture to start the day which is later reflected in 
prospects for a round of diurnal convection. With cool
temperatures and drying, intensity should be low. Cooler solutions
could have a minimum of convection along the east slopes, where
warmer solutions might have a more typical spring day. There would
also be some frost/freeze potential on the plains but the cooler
solutions would also likely hang on to some wind in most places
overnight, so the threat might be limited to low spots.

For the weekend, we're on the edge of the northwest flow as a
ridge builds over the west. Some models keep the ridge far enough
west that we get a little impact from another shortwave passing
across the plains late Saturday or early Sunday. This would
probably just be some more clouds and a little puff of cool air to
keep us around 60 degrees Sunday, though an isolated shower would
be possible. Other models have this wave weaker with the ridge
edging over us and a sunny day around 70 on Sunday. By Monday, we
should be under the ridge. There are conflicting signals here as
there should be some warming aloft, but a little increase in low
level moisture from a surge behind the early Sunday shortwave
could lead to increased shower activity along the Front Range. The
blended low PoPs and a little warming seems appropriate.

&&

.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
Issued at 1017 AM MDT Tue May 5 2020


VFR conditions will prevail through Wednesday. Light winds this 
morning will become a northerly direction around 18Z. Gusts to 25 
knots will be possible after 21Z. Winds decrease after 01Z, but 
remain a northerly direction most of the night. Eventually winds 
will turn a southerly direction after 09Z. 

&&

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

$$

UPDATE...Meier
SHORT TERM...Schlatter
LONG TERM...Gimmestad
AVIATION...Meier