Preview of NWS' New Version of Forecast
This preview is not operational and should not be used for support decisions.

Area Forecast Discussion (AFD)

Issued by Denver/Boulder, CO (BOU)

FXUS65 KBOU 192037

Area Forecast Discussion
National Weather Service Denver/Boulder CO
237 PM MDT Mon Aug 19 2019

.SHORT TERM...(This evening through Tuesday)
Issued at 237 PM MDT Mon Aug 19 2019

The record high of 97 has been broken with the max at 98 so far. 
There is still enough time to add another degree or two the 
record. If it reaches 100, that would be the latest for so late in
the year. Generally light winds across the forecast area this 
evening. Too much of a mid level cap around 500 mb to produce 
thunderstorms, only chance could be over the far northeast corner 
with ML 100 CAPE around 1000 j/kg over the far northeast plains at
00z so will add isolated thunderstorms there until around 02z. 
Latest HRRR suggests the cap could be broken with the potential 
for one or two strong storms between 23-02z. The upper level ridge
will bring another day of hot temperatures to the region on 
Tuesday. In the mountains, dry conditions will persist with rh 
values in the teens North and Middle Parks. Across the northeast 
plains, low level moisture will gradually increase from east to 
west as a weak front pushes into the urban corridor and northeast 
plains late in the afternoon. The forecast soundings keep much of 
the Front Range dry for most of the day with ML 100 mb CAPES 
around 200-300 j/kg. The instability will increase dramatically 
over the northeast plains with the NAM12 indicating ML 100 mb 
CAPES over 4200 j/kg with precipitable water values around 1.35 
inches. SPC has the northeast corner under a slight risk, so 
strong to severe will be possible after 22z.

.LONG TERM...(Tuesday night through Monday)
Issued at 237 PM MDT Mon Aug 19 2019

The threat for storms will continue through Tuesday evening and 
even after midnight. Easterly low level flow behind the cold front
will continue to transport moisture westward. A short wave trough
will be tracking over the ridge and will help produce storms 
through the evening hours. Storms will likely survive after 
midnight as they slowly track east across the Colorado. Increasing
easterly winds over northeast Colorado may result in enough shear
for severe storms over northeast Colorado. Heavy rain, large 
hail, and strong winds will be possible with the storms over the 
northeast plains through the evening hours. 

Cooler airmass will be over the area Wednesday with highs in the 
80s across northeast Colorado. Airmass will be moist with 
precipitable water values around an inch across northeast 
Colorado. Surface based CAPE climbs to 1200-2200 J/kg. Winds aloft
will be weak, so there is uncertainty if there will be enough 
shear for severe storms. Heavy rainfall will be the main threat if
there isn't enough shear. Because of the weak winds aloft, storms
will be slow moving. 

On Thursday and Friday, the upper level ridge will be over the 
Southern Rockies. This will result in a westerly flow aloft across
Colorado. A lee side surface trough will act as a dry line. This 
is expected to be set up near the foothills on Thursday and keep 
the chance for thunderstorms in the forecast for much of northeast
Colorado. The surface trough shifts eastward on Friday, reducing 
moisture over the and the chances for thunderstorms. 

For the weekend and next Monday, models still having issues 
resolving the large scale patterns. The GFS shows the upper level 
ridge remaining over the Central Rockies. The ridge retrogrades 
over the western U.S. if the ECMWF pans out. Will keep the 
forecast mainly dry with temperatures above normal. If the ridge 
retrogrades to the west, northwest flow could bring cooler air and
low level moisture to eastern Colorado. 


.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
Issued at 237 PM MDT Mon Aug 19 2019

VFR through midday Tuesday with light winds expected.


Issued at 210 PM MDT Mon Aug 19 2019

On Tuesday, fire danger will remain elevated in the high country
especially North and Middle Parks. RH values will drop below 15
percent but only light winds expected. Not as hot over the
northeast plains but will still be in the low to mid 90s. Low 
level moisture however will improve from east to west in the 
afternoon behind a cold front that will start to push into 
forecast area late in the afternoon.