Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 250350

Area Forecast Discussion
National Weather Service Denver/Boulder CO
950 PM MDT Sun Sep 24 2017

Issued at 950 PM MDT Sun Sep 24 2017

Web cameras around northeast Colorado show quite a bit of drizzle
across the plains, with radars also showing rain showers over
Larimer and Lincoln Counties. Upslope low level flow is expected
to continue through the night, which should keep the drizzle
going. Only change to the forecast will be to add widespread
drizzle overnight. The airmass is expected to remain cool through
tomorrow afternoon and evening, so also removed the mention of
thunder from the forecast tomorrow night.


.SHORT TERM...(This evening through Monday)
Issued at 300 PM MDT Sun Sep 24 2017

Upper low over northeast Utah and slowly weakening and moving
slowly northeast into Wyoming. There is some weak ascent aloft
ahead of the low and this is helping to generate some very light
rain and drizzle over the Front Range and portions of the
northeast plains. This will continue through at least this evening
and most likely continue over the plains through tonight. Expect
the low stratus deck to remain anchored in place tonight and at
least through Monday morning with shallow and moist upslope flow
in place. The main trof axis will still linger over Western
Colorado through Monday with weak ascent continuing through
eastern Colorado. Subsidence and drying will be moving into the
mountains later in the day. Temperatures will be only slightly
higher than yesterday`s readings.

.LONG TERM...(Monday night through Sunday)
Issued at 300 PM MDT Sun Sep 24 2017

By Tuesday the 500mb Low is progged to be over western North Dakota
and its weakening upper trough extending back to the Desert
Southwest. This puts Colorado under a relatively light southwesterly
mid-level flow. However there`s still plenty of cold air aloft with
the 700-500mb temps over the CWA which should keep sfc temps well be
average for one more day. Meanwhile, the local airmass becomes drier
with a shift to a south-southwest low-level flow. However, a shift
to a slightly wetter southeast sfc flow on the plains, could see
isolated showers/t-storms forming late afternoon over the srn Front
Range foothills and South Park area. Overnight and Wednesday, a
shift to a southerly mid-level flow as an upper low winds up over
the Desert Southwest will advect increasing amounts moisture up into
Colorado, some of it reaching the CWA by Wednesday afternoon. Warmer
temps, increasing QG forcing and a southeasterly/upslope flow will
increase the chance of afternoon/early evening t-storms specifically
across the southwest corner of the CWA. Storms will be slow movers
with light steering winds, but rain amounts will generally be light.
Except for isolated late day storms on the Palmer Divide, the chance
for precip on the plains appears quite low.

By Thursday...models show the Desert SW low lifting newrd over the 4-
corners area, bringing with its a decent amount of moisture. Weak to
moderate QG forcing in advance of the cyclone expands over the fcst
area through the day. Furthermore, the GFS indicates a deep easterly
upslope flow on the plains Thursday, whereas the ECMWF and Canadian
models show the upslope flow no where as strong. Yet all three
models indicate areas of light QPF for most of the CWA Thursday
afternoon and overnight. By Friday, models begin diverging as the
ECMWF and Canadian models shows the upper low lifting north over
western WY, the GFS filling the low and opening the trough up over
Utah and Colorado. The GFS keeps the CWA cool and wet, the Canadian
models not quite as showery, and the EC cloudy but with lower rain
chances. Will go with a blend of these sceneries and keep temps
slightly below average. For the weekend, models show some form of
this trough passing over the state possibly giving us at least a
slight chance of showers both days. Although latest temp guidance
shows temps returning to above average.


.AVIATION...(For the 06Z TAFS through 06Z Monday night)
Issued at 950 PM MDT Sun Sep 24 2017

Low ceilings and drizzle are expected to persist overnight, with
IFR and LIFR across the Denver area airports. Should see ceilings
and visibilities increase through the late morning and early
afternoon tomorrow, but ceilings may not get much higher than 2000
feet AGL.




SHORT TERM...Entrekin
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