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 171042

Area Forecast Discussion
National Weather Service Denver/Boulder CO
442 AM MDT Mon Jun 17 2019

.SHORT TERM...(Today and tonight)
Issued at 442 AM MDT Mon Jun 17 2019

There will be a slight risk of severe thunderstorms this afternoon
east of a line from around Greeley to Byers to Monument this 
afternoon, with a marginal risk along and west of the I25 
Corridor. The strongest storms along the I-25 corridor are 
expected to occur between noon and 3 pm, then the focus will shift
eastward across the northeast plains. The latest HRRR/RAP13 show 
a secondary wave of weaker thunderstorms develop over the Front 
Range this evening, with some lingering showers overnight. 
Forecast CAPES this afternoon around 2000 j/kg for Denver, 
2500-2900 j/kg over the northeast plains. Precipitable water 
values 1-1.1 inches as well, so locally heavy rainfall may be 
concern as well, Main issue will be large hail up to 2 inches and 
damaging wind gusts. Best wind shear profile will be around 21z. 
Storm motions around 10 kts, so leaning more towards advisory 
criteria rainfall vs flash flooding at this time. 

Models show generally weak qg ascent in the mid levels this afternoon
with a mid level trough axis brushing across northern Colorado 
around 00z. At the surface, low pressure will form over southeast 
CO by midday, allowing for a persistent east to southeast winds 
through early this afternoon, with stronger northerly winds spreading
southward into the cwa late this afternoon and evening. Isolated
thunderstorms over northeast Larimer and over Sedgwick and
Phillips counties at this time, should diminish by 12z. Patchy
fog also expected north and northeast of Denver until around 14z. 

.LONG TERM...(Tuesday through Sunday)
Issued at 442 AM MDT Mon Jun 17 2019

Pretty good model agreement through this week. On Tuesday showers
associated with Monday's little low will be moving out of the 
northeast corner in the morning while moisture ahead of the next
trough will be moving into the mountains. There should be a break
between these two systems though, so we lowered PoPs for much of
the day across the plains, with the expectation of showers/storms
spreading across the area from west to east during the afternoon
and early evening. Guidance is trending cooler for Tuesday and
depending on the clouds and showers it may stay in the 60s in the
northeast corner. This area may cool enough to be too stable for 
the second round of storms to make it that far east. 

Drier air will move in behind the Tuesday wave and it looks like
there will be enough flow for some downslope winds east of the
Front Range later Tuesday night into Wednesday. Not particularly
strong, but it will help to dry out the lower levels. There should
also be significant warming, so Wednesday looks like a day with a
pretty low level of convection and highs in the lower to mid 80s
on the plains. Thursday looks like a similar environment, except
some moisture return over the eastern part of the plains and a jet
streak could create some storms, and possibly even some marginally
severe storms near the eastern border as the wind profile will be
pretty good. There may also be a little small-scale front 
associated with the jet streak. We'll see if the moisture return 
is enough yet or if that will have to wait for Friday.

It looks like there should be an uptick in convection starting
Friday as a trough develops over the west. There is fair agreement
on a lead shortwave trough that would give some lift, and enough
flow for lee cyclogenesis around southeast Colorado that will draw
moisture westward. This may be a severe weather day with the 
moisture more than making up for a little cooling and much better
shear. For the weekend, there should be continued west to
southwest flow aloft depending on the shortwave details, but there
will likely be some cooling, a still moist airmass, and some lift
at times to provide a chance of thunderstorms. The blended model
solution looks good for this.


.AVIATION...(For the 06Z TAFS through 06Z Monday night)
Issued at 442 AM MDT Mon Jun 17 2019

Stratus/patchy fog developing around KDEN at this time, with high
resolution models showing similar development north and east of 
Denver this morning so will keep at least vcfg for KDEN and maybe 
KBJC until 14z. This could result in pockets of MVFR ceiling and 
visibility restrictions until 14z. Generally light northeast to 
easterly winds expected this morning. VFR from around 14z-20z this
afternoon until showers and thunderstorms develop, then ILS/MVFR 
restrictions again develop. The threat of showers and isolated 
thunderstorms will continue overnight, but will lean primarily to
showers vs thunderstorms in the terminals after 03z. Window for 
the strongest thunderstorms will be from around 19z-23z this 




LONG TERM...Gimmestad