Area forecast discussion
National Weather Service Grand Junction Colorado
1145 am MDT Monday may 20 2013
Update...
issued at 1145 am MDT Monday may 20 2013
Widespread area of precipitation with snow above 8000 feet this
morning across northwest Colorado. The short wave responsible for
this precipitation has weakened as it slides southward. Extensive cloud
cover will hamper warming today and have updated temperatures to reflect
this.
Convective potential is higher across the south and expect a few
more thunderstorms this afternoon. Due to the cooled air mass
from the widespread precipitation...destabilization across the north will
be slower but isolated storms may form by late afternoon.
&&
Short term...(today through tuesday)
issued at 340 am MDT Monday may 20 2013
Upper-level low over the northern plains will continue to remain
nearly stationary into tonight. Deformation axis wrapping around
the system in northerly flow will move south from Wyoming today
bringing an increasing threat of precipitation over the forecast
area with snow levels falling to near 8000 feet across the north.
The best focus for snowfall continues to be over the Park Range and
Flattops where a Winter Weather Advisory looks on track through
noon on Monday. Lesser amounts are expected over Vail Pass with
the best focus for the central mountains occurring later in the
morning when heating will lessen impact of snow on roads. Expect
shower activity to spread over the remainder of the forecast area
this afternoon with isolated thunderstorms possible as afternoon
heating increases instability.
Northwest flow will continue tonight with a weak
embedded disturbance passing over the north. The NAM indicates
another shot of moisture will move over northwest Colorado centered from
03z-09z... along with a weak embedded disturbance. This will allow
a few nocturnal showers to continue...favoring the north.
Otherwise showers and thunderstorms will diminish once the diurnal
element fades during the early evening. Temperatures will remain
mild due to the lingering moisture. Southern locations will see
better clearing overnight.
Long term...(tuesday night through sunday)
issued at 340 am MDT Monday may 20 2013
A drying and warming trend will begin on Tuesday as high pressure
builds in from the west. The ridge axis reaches the Utah/Colorado border
early Tuesday evening...then to the Continental Divide by midday Wednesday. As
a result the flow will weaken on Tuesday and become more westerly...then
become southwest on Wednesday. These will be benign weather periods with
afternoon convection limited to the higher terrain. Temperatures
will climb but remain shy of normal values on Tuesday...then climb above
normal on Wednesday.
A deep closed low will remain nearly stationary over the Pacific
northwest coast through the weekend. As the pressure gradient
tightens over the intermountain west...southwest flow will increase over
the region bringing breezy to windy conditions with dry and
seasonably warm temperatures through the extended period. The big
forecast issue for the extended period will be the potential for
critical fire conditions in eastern Utah and western Colorado by the
second half of the work week into the weekend as southwest flow
increases and very low humidity persists.
&&
Aviation...(for the 18z tafs through 18z Tuesday afternoon)
issued at 1101 am MDT Monday may 20 2013
Low clouds and precipitation will continue to impact the mountains
and northern valleys going into this afternoon. By late morning
most terminal forecast sites were sitting at VFR levels but some low
cloudiness and light rain was being pushed up the Roaring Fork
valley into the Aspen area. The energy driving the precipitation
looks to be weakening through the day. Heating and convection this
afternoon look to take over for the main precipitation source
which should allow many of the lower cloud bases to lift. Mountain
obscuration will still be poss bible but anticipate many of the
valleys...including the taf sites should mainly prevail and VFR
levels. Passing showers however may affect the kege and kase
terminals through sunset with temporary lowered flight criteria.
Gusty winds look to be the main threat near any shower or isolated
thunderstorms this afternoon. Clearing after sunset should leave
VFR levels in place going into Tuesday...with some lower clouds
hanging in over the northern and central mountains.
&&
Fire weather...
issued at 340 am MDT Monday may 20 2013
The current cool and moist pattern will last through Tuesday. 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 by the second half of the work week into the weekend as southwest
flow increases and very low humidity persists.
&&
Gjt watches/warnings/advisories...
Colorado...Winter Weather Advisory until noon MDT today for coz004-013.
Utah...none.
&&
$$
Update...pf
short term...eh/mpm
long term...eh/mpm
aviation...tgjt
fire weather...tgjt
