Area forecast discussion...updated
National Weather Service Grand Junction Colorado
909 PM MDT sun may 19 2013
Update...
issued at 908 PM MDT sun may 19 2013
Minor upper level trough axis associated with low pressure over
the northern plains will rotate south through Colorado overnight
and Monday morning. Vorticity advection and qg forcing along and
ahead of this trough will continue the shower activity over
eastern Utah and western Colorado...and bring a more-focused area of
precipitation currently over west-central Wyoming south into northern
Colorado after midnight. 00z NAM seems to be handling this well...though
perhaps a little overdone on the quantitative precipitation forecast. Kgjt 00z sounding indicated
the snow level should already be under 9000 feet and with 700 mb
temperatures expected to drop to around -2c...expect the snow level to
get down to around 8000 feet overnight. Favored areas for the
measurable precipitation are the higher terrain and northwest
facing slopes...and perhaps some of the valleys mainly north of
I-70. With slug of moisture hitting The Flat Top mountains
overnight and our digital forecast database showing similar
snowfall amounts as the Elkhead/park/Gore ranges...went ahead and
included Colorado zone 13 in a Winter Weather Advisory as well.
&&
Short term...(this evening through Monday night)
issued at 322 PM MDT sun may 19 2013
Upper trough axis from southeastern Idaho to northestern Colorado continues to lift to the
north-NE as a shortwave disturbance entering southwestern Utah slides underneath
it. Scattered showers and isolated thunderstorms will persist into
early evening. The stronger storms could produce a period of
moderate to heavy rainfall and possibly small hail.
The focus shifts to the north tonight into Monday morning...with the
forecast challenge being snow across the northern and central mountains
as an upper low forming over Nebraska results in moist northwest orographic
flow and cold advection. Expect precipitation to be on the increase
across the northern mountains by midnight after a bit of a lull this evening.
700 mb temperatures fall to -1c to -2c across the north half of the area by
12z Monday...lowering snow levels down to around 8000 feet mean sea level there.
This would affect Rabbit Ears/Gore/Vail passes. With temperatures
running cooler today and tonight...roads may not have picked up as
much heat so would be more prone to accumulate snow or slush by
sunrise Monday morning.
Models point to 2-6 inches of wet snow for the Park Range...so will
issue a late-season Snow Advisory for Colorado zone 4 tonight through
Monday morning to capture Highway 40 over Rabbit Ears Pass. Vail
Pass could see up to 2 inches of snow/slush by midday Monday...but
expecting just 1-2 inches in general for the central mountains so no
highlight for those areas. By midday Monday...temperatures should be warm
enough for a rain/snow mix over the passes and melting on roadways.
300 mb trough/deformation axis extending back from the low lingers
across NE Utah/northwest Colorado through Monday morning before rotating south out
of our area by Monday evening. With cold air aloft...this should
some showers and isolated thunderstorms Monday afternoon
before diminishing Monday night.
Low temperatures are expected to be in the 30s from Cortez to Pagosa
Springs tonight and again Monday night...but a killing freeze
appears unlikely.
Long term...(tuesday through sunday)
issued at 322 PM MDT sun may 19 2013
Tuesday...ridge will move eastward into the area...shifting winds to
westerly then southwesterly. Ridge axis reaches central Utah by midday
Tuesday. As southwesterly flow develops...temperatures will
transition back to normal over eastern Utah/western Colorado.
Tuesday night through Sunday...dry southwest flow will remain in
place for the remainder of the week. Temperatures will climb to well
above seasonal norms throughout the week. There is little threat of
precipitation through late week with the exception of convectively
driven afternoon showers at mountain elevations. Wednesday
evening...winds are expected to pick up in eastern Utah as energy from
strong low pressure over the Pacific northwest interacts with ridge
over the County Warning Area. This tight pressure gradient will move into western Colorado
as well Thursday night. The gradient will loosen Friday as low
pressure in Pacific northwest weakens and moves north. Warm southwesterly flow
is expected to continue through the weekend.
&&
Aviation...(20/00z)
issued at 540 PM MDT sun may 19 2013
Scattered showers and isolated thunderstorms will continuethrough
03z this evening. At the taf sites...VFR conditions should be the
rule though a brief period of MVFR visible/ceilings is possible in a
shower or thunderstorm. Expect mountain obscurations as ceilings lower
in the vicinity of showers. Small hail...gusty winds...and a brief
period of moderate to heavy rain are possible from some
thunderstorms. Snow level will be as low as 8500 to 9000 feet mean sea level in
convective showers.
After 03z tonight...snow will become widespread over the northern
mountains from Vail/kccu northward to k3mw obscuring mountains. Periods
of MVFR ceilings in -ra are likely at ksbs...khdn...and kcag after 09z.
Kase could see MVFR conditions in light snow and fog during the
daytime morning hours Monday. Scattered showers and isolated
thundestorms are expected again Monday afternoon.
&&
Fire weather...
issued at 322 PM MDT sun may 19 2013
The current cool and moist pattern will last through Monday. Ridge
shifts eastward into the area pulling very dry and warm air in
from the southwest beginning Tuesday. Will need to keep an eye out
for potential critical fire conditions in eastern Utah and western
Colorado Thursday afternoon as wind picks up and very low humidity
persists.
&&
Gjt watches/warnings/advisories...
Colorado...Winter Weather Advisory until noon MDT Monday for coz004-013.
Utah...none.
&&
$$
Update...bwm
short term...jad
long term...jam
aviation...jad/bwm
fire weather...jam
