Area Forecast Discussion
Issued by NWS Pueblo, CO

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FXUS65 KPUB 172222
AFDPUB

Area Forecast Discussion
National Weather Service Pueblo CO
322 PM MST Sun Feb 17 2019

.SHORT TERM...(This evening through Monday)
Issued at 317 PM MST Sun Feb 17 2019

...SNOW and COLD...

Currently...

The leading edge of the arctic front extended along the Palmer
Divide and then down towards Eads and into SW KS. North of the
boundary temps are in the 20s while south of it temps were in the
40s. Valleys at 2 pm were in the 20s, with temps well below zero
above treeline (It is already quite cold aloft).

Sat pix show lots of convection developing over the plains and quite
a bit of virga was visible looking outside the WFO.

Ridge axis was still to our west as implied by the convective cloud
streaks in the sat pix imgy as the convection was lined up NW-SE
along the greater I-25 corridor region.

Shortwave #1 that will bring snow to the region later tonight and
into tomorrow extended from NW UT down to the 4 corners. Shortwave
#2 will get us Monday night and Tuesday (long term fcst period).

Rest of today and into tonight...

All guidance indicates snow will break out as time progresses this
afternoon and into the evening. Snow showers will develop over the
contdvd by later this afternoon and rapidly increase in coverage as
the energy over UT moves east in CO. Over the plains, snow showers
will break out initially over the Palmer Divide later this afternoon
and increase over the rest of the plains later this evening and
especially tonight. At this time, it appears the heaviest snow over
the lower elevations will occur between midnight and sunrise
tomorrow. The areas down in the Spanish Peak Country/Raton Mesa area
will see the heaviest accumulations. Overall accums tonight will be
1-2" with locally heavier amounts vcnty greater KTAD area.

Over the interior mtns, San Juans will see several inches tonight,
with the best snowfall later this evening into the early morning
hours. As the short wave moves east, snowfall will decrease during
the early morning hours.

Tomorrow...

Snow should be falling over most of the plains tomorrow morning
during the 6 am - 9 am time period with the least amount over El
Paso and the most down near the Spanish Peaks Country area.

During the late morning and into the afternoon, snow will likely
decrease or end over most of the plains, with the best chances of
snow continuing down in the Spanish Peaks Country area.

The 2nd wave associated with this system will begin to affect the
San Juans by mid afternoon, and snow will be on the increase across
this region. By late afternoon all of the higher terrain will see a
chance of snow with the sw mtns being favored. Would not be too
surprised to see snow redeveloping along the I-25 corridor by late
afternoon.

It will be very cold tomorrow and max temps will be near "record low
max temps" for the date. Expect max temps only in the 10-15 F range
across the I-25 corridor region and 15-20F range farther east.
Warmest temps will likely be in the San Luis Valley were 20s will
occur. Mtn tops will be very cold with readings below 0F.

Fortunately, winds will be rather weak with this system, with winds
in the 5 - 10 mph range.


.LONG TERM...(Monday night through Sunday)
Issued at 317 PM MST Sun Feb 17 2019

Monday Night through Wednesday Morning:

At the beginning of the long term forecast period (Monday night),
the 700hPa closed low will be located near the 4 corners region
of the country with a surface high pressure system located over
the midwestern states. The largest uncertainty is over the
plains. The upslope component of the wind has become more shallow
over the last few model runs, but the warm air advection has
increased during this time period. What this says says to me is
that the main snow producer over the plains will be banded
precipitation. The location of the band will be greatly dependent
on where the surface low sets-up over New Mexico. At this time
the heaviest band of snowfall will form over Pueblo County,
eastern Fremont County, and southern El Paso County. If there is a
major snowfall forecast shift, it is because we have shifted the
location of the major snow band. A concern that is becoming more
apparent is the downslope flow over the Raton Mesa over eastern
Las Animas, Bent, and Otero Counties. New data suggests that the
700hPa winds over that region will be from the south to southwest,
which means that they may become shadowed from the Raton Mesa.
POPs and QPF grids have been updated to show the current trend.
While analyzing the forecast soundings, the majority of the low
level saturation is located in the dendritic growth zone, which
means this system is going to be an efficient snowfall producer.
The cold air keeps snow ratios around 20 to 1 during the heaviest
snowfall periods, hence the amounts we are forecasting.

Snowfall totals seem on track for the San Luis Valley, an additional
5 or so inches is expected during the overnight periods between
Monday night and Tuesday morning. The valley will see winds from the
south, which will fill the valley with added moisture at the
surface. The added moisture should offset the effects of topography
over the valley, enabling mid-level synoptics, such as PVA and WAA,
to deliver some added lift. Forecast soundings indicated the low
level saturation existing in the dendritic growth zone and the cold
temperatures will make the snow ratios around 17 to 1.

Now onto the mountains... Since the 700hPa closed low is on track,
there isn`t too much change in the snowfall forecast. The eastern
San Juans will experience exceptional upslope flow throughout the
warning period, with additional snowfall amounts around the 1 foot
range. The La Garitas will be on the upstream side of the moisture
plume, but should still see an additional 6-10 inches of snow, the
Sawatch Mountains will range from an additional 10-15 inches, the
Mosquito Mountains will see an additional 10-12 inches, the Wet
mountains will see an additional 12-18 inches of snow, the southern
Sangre de Cristo Mountains 14-20 inches, and finally the big winner
of the snow event, the northern Sangre de Cristo Mountains with 16-
22 inches of snow.

High temperatures on Tuesday afternoon will be well below the
average for this time of year. The lower 20s will be observed over
the entire region, which is around 30F below average for the plains
and around 15F below average for the San Luis Valley.

Wednesday Afternoon through Friday:

Lingering snow showers will remain during the overnight hours from
Tuesday through Wednesday afternoon, but snowfall rates will be
light. 500hPa heights begin to increase through the afternoon on
Wednesday, but quickly fall again as another broad trough begins to
impact the region. At this point in time, most of the snow will fall
over the mountains, leaving the plains and the San Luis Valley dry,
but there is a lot of time for that forecast to change.

The San Luis Valley will remain around the same high temperature
through Friday and may be even cooler depending on how much snow
falls over the valley. The plains and upper Arkansas River Valley
will gradually warm during the week, but temperatures are still
anticipated to be around 10F below average through Friday.

Next Weekend:

Zonal flow returns to the region which should bring dry conditions
and the return of near average temperatures across the region. Some
embedded shortwaves may bring some light snow showers over the
mountains during this time. There is a model resolved jet streak
developing over the northern portions of the state and if that jet
streak develops further south than what is resolved at this point,
some heavier snow would be observed over our northern mountains.

~Skelly

&&

.AVIATION...(For the 00Z TAFS through 00Z Monday evening)
Issued at 317 PM MST Sun Feb 17 2019

Accumulating snow will affect all 3 taf sites (PUB, ALS and COS)
during this period. Two rounds of snow are expected...tonight and
early tomorrow, and tomorrow night into Tuesday morning. roughly 1-3
is expected with the first round and 2-4" with the 2nd round (this
snow accum fcst is subject to change!!). VFR occurring at taf
issuance time will go to mvfr/IFR by later this evening (04-06 UTC)
and likely remain there through at least tomorrow morning. CIGs may
lift somewhat tomorrow afternoon and then go to IFR once again
Monday evening into TUE morning.

Winds will generally be light so no blowing snow expected.

&&

.PUB WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory from 8 PM this evening to 6 PM MST
Tuesday for COZ058-060-061-063>067-069>071-076>078-081>086-089-
093>099.

Winter Storm Warning from 8 PM this evening to 6 PM MST Tuesday
for COZ068-072>075-079-080-087-088.

&&

$$

SHORT TERM...HODANISH
LONG TERM...SKELLY
AVIATION...HODANISH



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