292 
FXUS65 KBOU 120832
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
232 AM MDT Tue Sep 12 2023

.SHORT TERM...(Today and tonight)
Issued at 219 AM MDT Tue Sep 12 2023

Broad weak ridging aloft over Colorado today with very 
dry airmass over northeast Colorado per water vapor imagery. There 
will be a warming trend today as 700mb temperatures warm another 3 
degrees Celsius this afternoon. This will put afternoon 
temperatures into the mid and upper 70s across the plains. 

Dry conditions will prevail on the plains today but moisture will be 
increasing over the mountains from the west and southwest, 
particularly along and south of the Interstate 70 corridor. The 
moisture increase will lead to scattered showers and thunderstorms 
this afternoon and early evening, especially over Park and Summit 
counties. ML CAPE values generally 400-800j/kg range. Expect a brief 
period of rain and gusty winds with the showers, but remaining below 
severe limits.

Early this morning, satellite imagery showing some patchy low clouds 
and fog, mainly over the Palmer divide in Elbert and Lincoln 
counties, also in Park county and a few spots over the northeast 
plains. Don't expect much fog in the Denver area due to persistent 
south-southwest winds but could see a few patches of fog developing 
just north of Denver across Larimer and Weld counties. 

.LONG TERM...(Wednesday through Monday)
Issued at 219 AM MDT Tue Sep 12 2023

There will be light flow aloft on Wednesday with weak lee 
cyclogenesis forming along the High Plains. Better moisture aloft
will be moving over our forecast area as southerly flow brings in
slightly better moisture at the low levels as well. This added 
moisture will increase the chance of showers and storms. The 
showers and storms will mainly form over the mountains and higher 
terrain due to better lapse rates. The best chance of storms 
across the plains looks like it will be to the southeast of the 
Denver metro as a modified DCVZ will setup there with weak 
instability. Overall, most places will receive little to no 
rainfall Wednesday. Highs will be near normal with partly to 
mostly cloudy skies. 

A positively tilted upper level trough will move towards Colorado on 
Thursday and into Friday. This will provide upper level forcing 
along with a right entrance region of a 250 mb jet being over 
northeast Colorado. At the surface, a cold front will move through 
Wyoming and into Colorado Thursday afternoon and evening. This front 
will provide forcing and will also provide healthy moisture with 
precipitable water values nearing 1 inch in Denver. All of these 
factors will contribute to the creation of widespread showers and 
storms from Thursday afternoon/evening through Thursday night and 
into Friday. Model data is still not locked in on rainfall totals 
for this system. The recent 00Z ensemble runs of the GFS and 
Canadian came in drier than previous runs as they have the trough 
being more progressive with drier air moving in quickly on Friday.
The ECMWF and its ensembles have a much wetter solution with the 
mean QPF in Denver of around 0.8". All three models have ensembles
that are over 2 inches of rain in Denver so there is potential 
for heavy rainfall. The ECMWF shows an MCV-like feature developing
Thursday night and into Friday which produces heavy rain. There 
is not much confidence that this feature will actually develop so 
the chances for heavy rain remain up in the air. We collaborated 
with WPC on the QPF forecast for Thursday night since they had a
forecast that was on the very high end of guidance. The decision 
was made to lower QPF more towards ensemble means and take out 
storm total rainfall totals that were approaching 2". Nonetheless,
heavy rain and minor flooding is a possibility but with cooler 
temperatures in the 50s and 60s during this event and the lack of 
tropical moisture, there is not much of a widespread flooding 
concern. Highs on Thursday and Friday will be below normal with 
highs struggling to reach 60 on Friday in Denver. 

Upper level ridging will quickly move over our forecast area on 
Saturday and will stay in place through the beginning of next week. 
This will lead to drier conditions with warmer temperatures. A few 
isolated showers and storms in the mountains may occur each day but 
the vast majority of our CWA will be dry. Highs in Denver will 
likely reach the 80s from Sunday through Tuesday. 

&&

.AVIATION...(For the 06Z TAFS through 06Z Tuesday night)
Issued at 1140 PM MDT Mon Sep 11 2023

Clear skies for tonight but there is a low chance to see patchy
fog and low stratus develop just north of the terminals after 12z.
As of now, it appears the brunt of the fog will stay north but
will leave in a temporary condition for fog in the 13-17z time
frame. Low confidence on the fog developing at DEN or BJC. APA
will remain mostly clear. Otherwise a dry day expected with any
showers/storms remaining over the mountains. 


&&

.HYDROLOGY...
Issued at 219 AM MDT Tue Sep 12 2023

There will be scattered showers and thunderstorms this afternoon
and evening over the mountains, but mainly along and south of the
Interstate 70 corridor. This means mainly dry over the burn scars
today with no flash flooding expected. With the storms that do
develop expect brief moderate rain and gusty winds. 

There will be a limited threat of flash flooding on the burn 
areas Wednesday through Friday. Showers and storms are possible 
each day but instability will be on the lower side so storms 
shouldn't be very intense. Across the rest of the CWA, there is a 
minor flooding concern Thursday night into Friday if some of the 
model solutions with heavier rain verify. Relatively cool 
temperatures and the lack of tropical moisture will keep the 
threat of flooding low.

&&

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

$$

SHORT TERM...Entrekin
LONG TERM...Danielson
AVIATION...Entrekin
HYDROLOGY...Entrekin/Danielson