Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 08/02/23

Area Forecast Discussion

National Weather Service Denver/Boulder CO

 944 PM MDT Tue Aug 1 2023

.UPDATE...
Issued at 924 PM MDT Tue Aug 1 2023

The main convection for the evening is exiting the CWA to the
east. There is still scattered light rain falling over over the
mountains, foothills and northeastern corner. Will make some
minor pop, sky and wind GFE grid updates with current conditions
in mind. Will end the Flood Watch in most areas, with the
exception of the far northeastern CWA where it is still raining.

&&

.SHORT TERM...(This evening through Wednesday)
Issued at 1252 PM MDT Tue Aug 1 2023

...Flash Flood Watch remains in effect through midnight...

On the synoptic scale, the upper level ridge will be centered
Texas with a moist south/southwesterly flow over Colorado. A
combination of a very moist airmass, slow storm motions and moist
soils in areas already flooded from yesterday`s rainfall have set
the table for another day for potential flash flooding. Storms
have been slow to develop over the higher terrain so far this
afternoon, but the HiRes models and the latest radar scans show
the coverage increasing then shifting east late this afternoon and
evening. SPC analysis show precipitable water values around one
inch in the foothills, 1.1 to 1.5 inch across the plains. Both
factors elevate the risk of flash flooding so the current flood
watch will remain in effect until midnight. WPC keeps most of the
forecast area in a marginal risk of excessive rainfall, with a
slight risk over Larimer County. There is a slight risk of severe
storms over the northeast plains as well, with MLCAPEs 1000-2000
j/kg this afternoon. Strong/severe wind gusts 55 to 65 mph most
likely but can`t rule out hail to one inch in diameter possible.
Both of these have occurred up near Cheyenne a short time ago.
Most of the activity should taper off after midnight. On
Wednesday, there should be a slight decrease in MLCAPE and
precipitable water values, at least from the urban corridor
westward. MLCAPE values around Denver of 600-800 j/kg. Both values
still pretty high across the plains, PWAT of 1.2-1.3 inch with
MLCAPE of 1400-1800 k/kg. SPC still has areas east/southeast of
Denver in a marginal risk of severe on Wednesday. No Flash Flood
Watch planned for Wednesday, but that can be reassessed once
today`s watch has expired.

.LONG TERM...(Wednesday night through Tuesday)
Issued at 1252 PM MDT Tue Aug 1 2023

The focus of convective activity shift primarily to the eastern
plains for Thursday as an upper-level shortwave clips northeastern
Colorado. Increased instability with MLCAPE values locally
exceeding 1,500 J/Kg and PW values ~150% of normal will support
a few strong afternoon/evening thunderstorms, especially in the
rural plains with parameters most favorable in the far NE corner
of the state. Steering level flow should be a little stronger and
keep storms moving, but with ample moisture still available and
some question as to preceding soil conditions, localized flooding
wouldn`t be out of the question with the stronger storms, nor some
larger hail between 1-2" in diameter.

There`s quite broad consensus in transient ridging for Friday and
a notable reduction in thunderstorm coverage. Nonetheless, at
least isolated afternoon showers and thunderstorms will remain
possible for most, and a little greater coverage over the higher
terrain. Temperatures will hold mostly steady with highs in the
upper 80`s to near 90F for the lower elevations.

The break in our active pattern looks short-lived, as the upper
level pattern becomes much more supportive for stronger
thunderstorms by Saturday afternoon or evening. A more pronounced
shortwave and robust surface front will push south into Colorado
later in the day, with more favorable shear and an approaching jet
providing an additional dynamic boost under its left exit region.
Conditions should therefore be supportive of more widespread
thunderstorm coverage over the plains, with potential for several
severe storms and large hail.

We`ll likely be a little drier by Sunday, and considerably cooler
in the post-frontal environment. Latest guidance has continued
the downward trend in temperatures, with increasing likelihood of
highs remaining in the 70`s, well below normal.

Details are fuzzier for next week but big picture seems to suggest
general northwest flow aloft with ridging to our southwest, and
thus support at least isolated to scattered afternoon PoPs,
highest in the high country.

&&

.AVIATION...(For the 06Z TAFS through 06Z Wednesday night)
Issued at 945 PM MDT Tue Aug 1 2023

Normal drainage winds should kick in at DIA no later than 06Z.
There should not be any ceiling issues overnight.

&&

.HYDROLOGY...
Issued at 1252 PM MDT Tue Aug 1 2023

Very moist airmass in place with storms developing over the higher
terrain this afternoon. Slow storm motions coupled with high
precipitable water value around 1.10 inch according to the latest
ACARS sounding this afternoon. No changes to the burn areas in
the forecast matrix this afternoon/evening with a moderate risk
of flash flooding. The threat may be slightly lower on Wednesday,
but a moderate risk still looks reasonable for Wednesday as well.
The threat of flash flooding is not confined to the burn areas as
the Flash Flood Watch will remain in effect for much of the
forecast area through midnight tonight.

Depending on how precipitation plays out through tomorrow, some of
the stronger storms over the eastern plains Thursday evening could
carry the potential for localized flooding for areas that received
antecedent rainfall, despite slightly faster storm motions.

Friday looks drier with more isolated thunderstorm coverage, but
likely still enough to warrant an isolated threat of flash
flooding for the burn scars.

Some strong to severe thunderstorms will be possible late on
Saturday, with greater overall coverage and an increase in
localized flood potential.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
Flood Watch until midnight MDT tonight for COZ049>051.

&&

$$

UPDATE........RJK
SHORT TERM....Cooper
LONG TERM.....Rodriguez
AVIATION......RJK
HYDROLOGY.....Cooper/Rodriguez