Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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477
FXUS65 KBOU 260942
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
342 AM MDT Wed Jul 26 2017

.SHORT TERM...(Today and tonight)
Issued at 330 AM MDT Wed Jul 26 2017

Broad high pressure ridge aloft remains centered over North Texas
and Oklahoma today with a resultant moist, southwest flow aloft
over Colorado. As advertised, precipitable water values have
increased almost a half of an inch over past 24 hours and most
locations now ranging from 1-1.50" of PW. Water vapor showing a
weak wave over Western Colorado as there has been a uptick in
showers over West central Colorado over the past few hours and
will begin to move into our western mountains shortly. Appears
some slight drying behind this wave noted over southern Utah and
Arizona. Meanwhile a weak front and surface low pressure over
Kansas resulting in developing north to northeast winds over
eastern Colorado and a shallow upslope flow by mid morning hours.
This will help keep low level moisture in place for the rest of
today and evening and even some stratus likely to develop around
and shortly after sunrise.

So the question with these kinds of moist days over the Front
Range, can we do anything with all this moisture and turn it into
rain? Sometimes cloud cover and stability will put the kibosh on
any significant rainfall. This could be the case today at least
on the plains this afternoon as soundings show substantial 700mb
inversion through mid afternoon and then gradually erodes with
skinny CAPE profiles. Appears the focus for heavier rain will be
over the Front Range Foothills and east slopes down through
Jefferson, Park and Douglas counties in the elevated terrain
above the low level stability. See Hydrology section below to
address the heavy rain. Temperatures will be cooler today with
more cloud cover and under post frontal regime. Showers and storms
will diminish this evening with lack of any upper air support.

.LONG TERM...(Thursday through Tuesday)
Issued at 330 AM MDT Wed Jul 26 2017

Showers may still be ongoing Thursday morning over the southern
half of the forecast area including up into the mountains where
upslope flow remains. CAPE will increase to 1200 to near 2000
J/kg, focusing over the high terrain and western plains and urban
corridor - the eastern plains look too capped still on forecast
soundings to see much of a chance of anything. PWs will be
slightly less, but brief heavy rain and gusty outflow winds will
still be the main impacts.

On Friday, a shortwave will pass over the Northern Rockies. Warmer
surface temperatures will help increase CAPE, leading to the
potential for stronger storms. Once again, brief heavy rain,
strong outflow winds and even some potential for hail will occur.
The eastern plains should see a much better chance for storms on
this day.

Little change in the pattern is expected this weekend and into the
next week the upper high moves back west Saturday and Sunday then
remains nearly stationary over New Mexico through next week. Monsoonal
moisture will continue to be recycled under the upper high and
transported over the forecast area for scattered diurnal storms
each day. Temperatures will cool slightly to be below normal, and
remain that way through next week.

&&

.AVIATION...(For the 06Z TAFS through 06Z Wednesday night)
Issued at 330 AM MDT Wed Jul 26 2017

Still expecting some stratus to develop after 12z given moist,
yet shallow north to northeast winds this morning. Best chance for
storms today will be near elevated terrain around BJC/APA and
lesser chances further east like, KDEN. As a consequence will have
TEMPO grounds for TSRA at BJC/APA and just VC at Denver for now.
Could see MVFR cigs with the heavier showers.

&&

.HYDROLOGY...
Issued at 330 AM MDT Wed JTemperatures will be cooler today
with more cloud cover and under post frontal regime.
ul 26 2017

Certainly heavy rain with storms with high pw values today, but
overall flash flood threat may be more minimal as storms will be
moving with storm motions ranging from 10-18kt. Certainly bears
watching but any flooding may be very localized and confined to
burn scar areas over our southern portions. For now will not do
any Flash flood watches. Rainfall rates could easily approach 1.5
inches in less than one hour for a brief time.

Monsoonal moisture over the area will continue to bring a chance
of isolated areas of brief heavy rain that could produce localized
flooding issues. However, PW values will begin to slowly decline
Thursday from the highest values expected today. Friday`s
potential for stronger storms may present the same chance
compared to today however.

&&

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

$$

SHORT TERM...Entrekin
LONG TERM...Kriederman
AVIATION...Entrekin
HYDROLOGY...Entrekin



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