Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 151801
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
1201 PM MDT Fri Sep 15 2017

.UPDATE...
Issued at 1156 AM MDT Fri Sep 15 2017

Forecast pretty much on track. Low over northeast Wyoming has
pushed the cold air back for the moment and we will be in westerly
flow until the trough axis passes this evening. It may be slightly
windier/warmer/drier over the southern half of our area this
afternoon. Chance of mountain/northern border showers late
afternoon and evening still looks good.

&&

.SHORT TERM...(Today and tonight)
Issued at 339 AM MDT Fri Sep 15 2017

Satellite shows upper level trough lifting northeast into Wyoming
with a pronounced dry slot advancing northeast across the forecast
area early this morning. Much drier air will continue to work
across the area keeping skies mostly sunny today. The exception
will be over the far northern mountains in western Jackson county
where some wrap around moisture holds in place. This will keep a
chance of light showers in the forecast there. Convective
development this afternoon should be quite limited given the
amount of drying seen in various forecast models, and supported by
GOES 16 imagery.

By this evening, there is some hope of a few showers or storms
developing onto the northern plains. That potential is behind a
cold front that pushes quickly southward behind the departing
short wave trough. Moisture and instability is limited, and points
farther north near the Wyoming border would see the best chance.
Dry conditions will likely persist along and south of the I-70
corridor. Mountain locations mainly north of Rabbit Ears Pass will
see more widespread showers with up to 2 inches of snow above 10
thousand feet. Farther east and south toward Rocky Mountain
National Park and Summit county only scattered showers possible
with a light dusting over the higher peaks.

Late tonight, look for areas of stratus to develop across the
plains in a more moist but stable environment. Temperatures will
still be several degrees above normal today, before much cooler
air and more autumn-like air arrives behind the front early this
evening.

.LONG TERM...(Saturday through Thursday)
Issued at 339 AM MDT Fri Sep 15 2017

An upper level trough will move across Wyoming on Sat, however
there is some mid lvl ascent in the morning across nrn CO. Thus
will keep in a chc of pcpn across the higher terrain mainly north
of I-7O and across the plains near the Wyoming border. Temps will
be cold enough for some light snow accumulations abv 10000 ft. By
aftn subsidence will reside across the area with no pcpn expected.
As for temps, highs will be cooler with readings in the upper 60s
to mid 70s across nern CO.

For Sat night into early Sunday the models have been fairly
consistent the last few nights in showing some shower development
across the plains. This appears to be associated with a return of
deeper low lvl moisture and warm air advection ptrn as the low lvl
flow becomes more sely.  Thus will continue with chc pops over the
plains Sat night into Sun morning.

By Sun aftn into Sun night the flow aloft will be wsw. At the sfc,
will probably see a Denver cyclone by aftn with a convergence zone
setting up somewhere over the urban corridor. Soundings show
convective temps in the upper 70s so it`s hard to say whether cap
will be broken or not. For now will leave in low pops. With
favorable shear profile, if a few storms do develop, there would
be some potential for svr wx. Over the higher terrain will keep in
a slight chc of high based convection in the aftn. As for highs
readings will range from the lower 70s over the far nern plains
with mid to upper 70s along the front range urban corridor.

On Mon mainly dry wsw flow aloft will be over nrn CO so no pcpn is
expected.  Temperatures will be warmer as swly downslope low lvl
flow develops over nern CO.  This will allow for highs to reach the
lower to mid 80s.  For Tue a broad upper level trough will be over
the nwrn US with a continuation of wsw flow across nrn CO.  Once
again the airmass will remain pretty dry so will not much any pcpn.
Meanwhile downslope swly low lvl flow will remain over nern CO
which will allow for highs to remain in the 80s.

By Wed a broad upper level trough will extend fm the Pacific NW into
the nrn Rockies with stg swly flow aloft across the area. Overall it
will remain dry in most areas, except possibly over the higher
terrain nr the Wyoming border, where there could be a few showers
in association with the upper level jet. Meanwhile there will be
a weak cool fnt moving across the plains which will drop temps
into the mid 70s to around 80.

For Thu both the ECMWF and GFS begin to dig a piece of energy into
the Great Basin area with ssw flow aloft.  There will be some
moisture embedded in the flow which may lead to a chc of showers and
storms over the higher terrain by aftn.  Across the plains stg sfc
low pres will be over nern CO with mainly dry conditions thru the
aftn.  Current guidance temps look to cool based on 850-700 mb
temps, however, since this is way out in day 7 will follow blended
solution for now.

&&

.AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon)
Issued at 1156 AM MDT Fri Sep 15 2017

VFR through this evening. Several competing factors influencing
the wind direction in the Denver area. Southerly flow around 10
knots should prevail, though occasional eddies with light east or
northeast winds are possible. Cold front still expected this
evening with a few hours of north to northeast winds gusting at 20
to 30 knots. MVFR ceilings likely after 06z, breaking up 16z-20z
Saturday.

&&

.FIRE WEATHER...
Issued at 339 AM MDT Fri Sep 15 2017

There will be elevated fire danger today as the airmass over much
of the area will dry out some more. Temperatures will be a couple
degrees cooler, but drying and increasing winds will bring the
elevated conditions. High valleys through the southern Foothills
and Palmer Divide area will see the combination of stronger winds
and lowest humidities late this morning into the afternoon, but
parameters are forecast to be just shy of Red Flag Criteria. A
cold front will bring a period of gusty winds to all of the plains
by this evening, but humidities will improve with cooler
temperatures behind the front.

The weekend will be dry but cooler. Southwest winds aloft will
bring warm and very dry weather for the early part of next week.
Breezy conditions are likely, especially in the foothills and
west of the Front Range. A windy day is possible, more likely in
the middle of the week. Red Flag conditions are possible with the
main question mark the amount and timing of the wind. Any
thunderstorm activity should be very limited.

&&

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

$$

UPDATE...Gimmestad
SHORT TERM...Barjenbruch
LONG TERM...RPK
AVIATION...Gimmestad
FIRE WEATHER...Barjenbruch/RPK


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