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National Weather Service Grand Junction Colorado
1252 am MDT sun Apr 19 2015

Update...
issued at 1250 am MDT sun Apr 19 2015

Updated to remove expired winter weather headlines. Significant
snowfall has ended in the northern and central mts of Colorado and only
light additional accumulations area expected.

Update issued at 744 PM MDT Sat Apr 18 2015

Upper low continues to rotate in place over the eastern plains
this evening. Wrap around moisture keeping snow going in the high
country...a mixture across The Mesa and plateau region and
thunderstorms across eastern Utah. Steep lapse rates due to
heating outside of the thicker cloud shield is aiding the weak
wave dropping through eastern Utah. Storms started out quite
robust west of the Colorado River...but as they travel southeast
across the instability gradient...they weaken over our County Warning Area. Will
loss of heating expect the coverage to slowly wane over the next
hour or so. Will be watching the affect of nightfall on eastern
passes as melting has kept roads in decent shape. May keep some
of the headlines along Divide if necessary past midnight. Lastly
dew points did creep up a bit this afternoon into the 40s over the
western valleys. Will be monitoring the threat of dense fog
as well.

&&

Short term...(tonight through Sunday night)
issued at 325 PM MDT Sat Apr 18 2015

The low pressure responsible for the much needed precipitation over the
last few days is now located over the front plains while cyclonic
flow continues to pump in moisture from the north to south. This
flow starts in northestern Wyoming and the plume reaches as far south as the
San Juans. Snow and rain has fallen much of the day under this
plume of moisture and will continue to do so through this evening.
Current winter highlights look good so no changes there. An upper
level disturbance over southern Canada is trailing a trough that is
causing the area of low pressure to keep moving ewrd. The reason
this is happening so slowly is the lack of any strong jet features
to really get this system moving. Even so...the cloud shield/plume
will bring more precipitation to the area as the attendant low pressure
meanders east. By midnight...precipitation will favor the northern and central
mountains along with The Flattops due to their favorable location so
additional accumulations still possible up there. The rest of the
County Warning Area may see an odd shower or two but nothing too significant.

By Sunday...the Canadian low will be just to the north of
Minnesota while high pressure builds into the pacnw. This will
cause our County Warning Area to be sandwiched between these two features. Weak
pieces of energy will drop down from the northwest possibly causing some
precipitation for the County Warning Area. The GFS highlighting two distinct waves...one
Sunday evening and another Monday morning. The nam12 only showing
some spotty showers at best with some convection thrown in. The
hrrr and rap showing much less in the way of precipitation. This all
means unsettled weather will continue but with much more definitive
breaks between disturbances. Forecast brings mostly benign
weather Sunday with increasing chances for precipitation from
midafternoon onwards...mainly favoring the Continental Divide.

Temperatures will warm up considerably tomorrow though still remain 5 to
10 degrees below normal.

Long term...(monday through saturday)
issued at 325 PM MDT Sat Apr 18 2015

Unsettled northwest flow is expected Monday and Tuesday. An embedded wave
should focus the best chance of showers over the northern and
central mountains Monday afternoon and evening. Daytime instability
will keep isolated to scattered showers over the mountains on Tuesday.

Temporary ridging develops over the area by midweek as a trough
forms along the West Coast...with an upper low over Southern California by Thursday
morning. Enough residual moisture lingers for a few afternoon
showers or thunderstorms. Flow aloft becomes southwest...and the
Southern California lifts across The Four Corners/Desert Southwest Thursday night
and Friday morning. Timing and track a bit different between models
but still looking like a better chance of precipitation with some
thunderstorms late next week. Boosted probability of precipitation for Thursday afternoon
through Friday over the blended forecast guidance as a result.

GFS and European model (ecmwf) solutions continue to diverge on Saturday. European model (ecmwf) more
amplified as it digs a Pacific northwest trough to the southern Great Basin by
Saturday...resulting in downstream ridging and SW flow over our
area. GFS drops some energy from the Pacific northwest trough down the West
Coast but sends more of it across the northern rockies with westerly
flow across UT/co. Will follow the blended guidance for Sat.

&&

Aviation...(for the 06z tafs through 06z Sunday night)
issued at 1040 PM MDT Sat Apr 18 2015

A high latitude system diving into the northern plains will be
kicking this storm system that has been parked over Colorado the
past several days. This will allow precipitation coverage to trend
downward over most of western Colorado and eastern Utah. The High
Divide mountains will the most likely area to keep collecting
light snow overnight and be under obscuration. The big challenge
into middle morning Sunday will be low clouds and fog due to a moist
near surface layer from recent precipitation. There is already a
hint of this at kril...kase and kmtj late this evening as cloud
cover aloft has thinned. Anticipate this will become more of a
widespread problem through the night bringing IFR/LIFR to many
valleys including the Colorado taf sites. Improvement should be
quicker Sunday morning with more sunshine available to burn off
the low level moisture.



&&

Gjt watches/warnings/advisories...
Colorado...none.
Utah...none.
&&

$$

Update...cirrocumulus
short term...tgr
long term...jad
aviation...tgjt

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