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Area forecast discussion
National Weather Service Denver/Boulder Colorado
1131 am MDT Wed Jul 26 2017

Update...
issued at 1125 am MDT Wed Jul 26 2017

A number of minor adjustments have been made to today's and
tonight's wind, sky cover, weather and pop grids. Main changes
include adding more clouds and raising pops slightly in the high
country and across southern portions of the County Warning Area during the
afternoon and evening hours. Regional radar network is indicating
a band of light to moderate showers & a few weak T-storms
extending from Grand Junction to Cheyenne at this time. Their
eastward progress has been slow. Difficult to pin down the
forcing mechanism for this convection. Do not see a wave in
GOES-16 WV imagery and rap/NAM qg Omega fields hardly indicate any
synoptic scale ascent, except over the northeast corner of the
state. Meanwhile integrated precipitable water values on the
plains have dipped in the past few hours. For instance, the
Marshall, Colorado ipw sounder northwest of Denver is down 0.04 inch
from a peak of 1.20 inch at 12z. Ipw values at Longmont and
Greeley also down about a tenth of an inch since 13z. However,
sfc dewpoints are generally holding steady.

In the next few hours, will see the northern portion of this
shower band drifting over northern portions of the I-25 corridor.
Because of extensive cloud cover, and greater stability up there,
do not expect to see all that much T-storm development in this
part of the County Warning Area today. On the other hand, a shift to E-nely sfc-
700mb upslope flow this afternoon will concentrate low-level
moisture up against the southern foothills and along the Palmer
Divide. Should see the southern end of the high country showers
tapping into this moisture, potentially generating isolated to
multicell slow moving storms capable of locally heavy rainfall in
the area described above. Could see this happening after 21z
today. Mesocale models show this occurring at different times, but
they all show this storm development. Indicated storm total quantitative precipitation forecast
amounts anywhere from 0.25 to 1.48 inches. Could even see
T-storms in Elbert amd Lincoln counties lingering through
midnight tonight, due to a very moist sely low-level flow in place.
Will need to monitor this two County area closely as wet soils
from recent rainfall will make this area more suspectible for
flash flooding this evening.

&&

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 precipitable water. 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 1125 am MDT Wed Jul 26 2017

Low ceilings will persist for most of the day through this evening
in the Denver Metro area with the ongoing moist upslope flow.
Showers are still expected to devleop in the Denver after early
to mid afternoon. After 20z today, these showers will be
accompanied by thunderstorms, which will be capable of brief heavy
rainfall. Could see visiblities drop below 5 miles in these heavy
showers at Denver area airports. Conditions should gradually
improve through the evening with weaking of the upslope flow.
As a consequence will have tempo grounds for thunderstorms and rain at bjc/apa and
just vc at Denver for now. Could see MVFR cigs with the heavier
showers later today.

&&

Hydrology...
issued at 1125 am MDT Wednesday

Locally heavy rainfall will be possible form slowly moving
T-storms in areas rougly south of Interstate 70 this afternoon
and evening where precipitable water values and dewpoints will be
highest. Overall the flash flood threat will be low today. However,
the higher terrian of the foothills southwest of Denver and the
Palmer Divide south and southeast of Denver will have the best
chance to see isolated to scattered slow moving thinderstorms
capable of heavy rainfall. Wet soils from recent rainfall will
make this area more supectible to flash flooding late this
afternoon and evening. These storms and this area will bear
watching. Rainfall rates could easily approach 1.5 inches in less
than one hour. Elbert and Lincoln counties appear to be in the
best position to see heavy rainfall. At this time, a Flash Flood
Watch is not being considered.



&&

Bou watches/warnings/advisories...
none.
&&

$$

Update...Baker

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