Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 211811

Area Forecast Discussion
National Weather Service Denver/Boulder CO
1211 PM MDT Tue Mar 21 2017

Issued at 1208 PM MDT Tue Mar 21 2017

Expected weak shortwave is pushing into Utah with increasing
upward QG lift moving into the state. Cumulus and some radar
echoes showing up over the mountains and foothills. Still looking
for some weak thunderstorms potentially, over the northern
mountains, urban corridor and adjacent plains. Hires models
showing CAPE staying west of a line from mainly the CO/NE/WY state
lines down to Limon. PWATs are expected to be 0.4-0.5 inches,
which is above the 90 percentile. Expect some brief moderate rain
and gusty winds from the storms that do form. Forecast soundings
show the boundary layer cooling quickly this eveing, so shouldn`t
see much storm activity past sunset.


.SHORT TERM...(Today and tonight)
Issued at 436 AM MDT Tue Mar 21 2017

Cooler air has moved into eastern Colorado. There is more moisture
as well, but the low level air is not close to saturation. Richer
moisture has remained north and south of our area. Low level flow
will go southeasterly this morning in the break between
shortwaves. This will help increase moisture, and also help
maintain the low level inversion over the plains. Another weak
wave will bring a little lift in the late afternoon/early evening
hours. This is well timed to help convection over the mountains
where there will not be an inversion. Over the plains it may be
too cool for surface-based convection, but there will be some
showers aloft moving over, and a small chance of surface-based
convection as well. Best chances are probably near the northern
border and along and east of a Denver cyclone boundary that should
have developed by afternoon. Probably just enough CAPE to mention
thunder, but it may be mainly showers with just a few storms.

Shortwave of the day passes east this evening. There will probably
still be some mid and high level clouds, and southeast winds on
the plains should make it another mild night.

.LONG TERM...(Wednesday through Monday)
Issued at 436 AM MDT Tue Mar 21 2017

An upper level ridge axis will move into the Great Plains on
Wednesday, with an increasing southwesterly flow aloft Wednesday
afternoon and Wednesday night as the next system moves into the
Great Basin region by 12z Thursday. Models not very heavy handed
on the wind Wednesday aftn near the foothills with a weak sfc low
developing over Douglas County at that time. If this occurs then
the strongest winds may be over portions of the northeast plains
Wednesday aftn. Models are a little slower than the prvs runs
regarding this next system, so have backed off the pops for
Wednesday aftn and confined them to the mountains and foothills.
The flow aloft become more southerly on Thursday as the upper low
moves to around the Four Corners region. Southerly flow does not
benefit the north central mountains with generally rain showers in
the aftn. Stronger winds as well sfc and aloft Thu aftn with
temperatures back in the low 70s, reference the Fire Weather
Discussion below. Moderate to strong mid level qg ascent over
eastern CO by 00z Friday with pcpn quickly developing across the
cwa. Thursday night into Friday, snow in the mountains, with the
models developing a closed low over sern CO by 12z Friday. Mainly
rainfall across the northeast plains, with the snow level around
7000 ft msl at that time. Certainly some uncertainty as to where
the rain/snow line will be, but for now will keep the mention of
snow aoa this level. The combination of snow and strong winds may
likely warrant a winter weather highlight for the Front Range
mountains east facing slopes late Thu night and Friday. Deep/moist
northeasterly flow Friday between 12Z-18z, but pcpn now appears
to carryover through 00z Saturday so have extended the best pops
through the day Friday due to the slower timing. Friday night,
diminishing pops with increasing stability as a ridge of high
pressure moves over the region for Saturday. Next system that is
expected to bring more pcpn to the region will be Sunday into
Sunday night, with more inconsistencies regarding the timing of
this system as well with the upper trough anywhere from the four
corners to southeast colorado by 18z Sunday. Ridging on Monday
with drier weather ahead of another potential pcpn producer for CO
for Monday night into Tuesday.


.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
Issued at 1208 PM MDT Tue Mar 21 2017

VFR through tonight. Some uncertainty remains on the wind
direction in the Denver area as a Denver cyclone is expected to
strengthen by this afternoon. Winds will likely switch from
easterly to southeast and then south in the afternoon and evening
at KDEN/KAPA, but there is a chance they could switch to northwest
if the boundary moves across the airports. Cyclone should be
closer to KBJC, making direction there harder to predict. Hi res
models wanting to bring some showers and possible thunder near the
airports after 20z, with radar echoes already showing up
currently, this looks fine. These showers/storms could result in
a couple of wind shifts. Increased southerly winds this evening
and overnight.


Issued at 436 AM MDT Tue Mar 21 2017

On Wednesday, it will be warmer with increasing winds aloft but
not much wind at the surface as a weak area of low pressure
develops around Douglas County. Main area of concern may be fire
wx zones 241..245 and 246, but marginal regarding wind and rh in
the aftn so no highlights planned at this time. On Thursday, it
will be drier with the potential for more wind especially across
the northeast plains in the aftn. No highlights yet but if the
next mdls runs continue to advertise this trend then a Fire
Weather Watch may be needed with the main area of concern along
and south of I-76 and east of I-25 due to stronger winds, less rh
and a slgt chc of tstms.




SHORT TERM...Gimmestad
LONG TERM...Cooper
FIRE WEATHER...Cooper is the U.S. government's official web portal to all federal, state and local government web resources and services.