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Area forecast discussion 
National Weather Service Grand Junction Colorado
243 PM MDT Sat Aug 27 2016

Short term...(this evening through Sunday night)
issued at 243 PM MDT Sat Aug 27 2016

Upper low is currently seen spinning over the southwest Utah and
northwest Arizona border, which is further north than the models
depicted 24 hours ago. Extensive cloud cover with some showers and
thunderstorms are seen in proximity of this low over SW Utah and
out ahead of the upper level trough in eastern Arizona and western
New Mexico. Showers and thunderstorms have developed this
afternoon over the higher terrain mainly along the bookcliffs and
southward. This upper low will track towards The Four Corners
region this evening and across The Four Corners region and rest of
the area on Sunday. Due to the track of this upper low being
further north along our southern County Warning Area border, raised pops and cloud
cover for the rest of today into much of the evening hours with
the expectation that showers and storms will increase through this
evening mainly across southeast Utah and SW Colorado. Gusty outflow winds
and brief heavy rain along with frequent lightning will be the
main concerns. Storms will become more isolated in coverage beyond
midnight but still linger through the early morning hours.

Sunday will keep our County Warning Area in the deformation zone due to the
stretching of the upper level trough with showers and storms
developing in the afternoon and continuing into the evening,
mainly over areas along and south of the bookcliffs, with better
chances in proximity of the upper low over southwest Colorado.

Long term...(monday through saturday)
issued at 243 PM MDT Sat Aug 27 2016

The upper level trough gets stretched out with the low circulation
moving onto the Front Range by Monday. This brings more of a
northeast flow over our County Warning Area with The Divide and San Juans of
western Colorado being favored for afternoon convection where
better forcing and moisture resides. Drier air will be moving in
as well in this flow pattern with eastern Utah and northwest
Colorado remaining fairly dry, with large scale high pressure
ridge over much of the central U.S.

A low pressure trough will move inland over the West Coast by
Tuesday with the first piece of energy ejecting through the
intermountain west. This will cause the ridge of high pressure to
move slightly eastward late Tuesday, allowing for moisture to
increase from the southwest. A slight increase in thunderstorm
coverage is expected Tuesday, with the western Colorado mountains
being favored. The trough will move further inland with the flow
shifting more to a southwest to northeast oriented pattern on
Wednesday into Thursday. Precipitable water values increase to
0.75 to an inch plus by Thursday with a stronger shortwave moving
through the flow. This trough is not as amplified as model runs 24
hours ago depicted, so we end up seeing a southwest flow instead
of a more direct southerly tap which would bring in more moisture.
However, sufficient jet support with our County Warning Area in the right entrance
region as well as forcing associated with the shortwave will lead
to a more active day on Thursday with more scattered to numerous
shower and thunderstorm coverage. Therefore, increased pops in
coordination with neighboring offices. A third impulse is seen
tracking across on Saturday. While details could vary on timing of
these shortwaves, it looks like a more active and unsettled
pattern will be in place from the middle to the end of next week.


Aviation...(for the 18z tafs through 18z Sunday afternoon)
issued at 1020 am MDT Sat Aug 27 2016

Showers and thunderstorms will again develop over the area today
ahead of an upper level disturbance that will shift over The Four
Corners by this evening. Southwest Colorado and southeast Utah will be
favored for the most extensive coverage of convection. However all
areas, and especially the mountains, may also see storms this
afternoon/evening. VFR will be the rule but some storms may drop
flight conditions to MVFR briefly. Expect convection to fire from
18z onwards with most coverage from 21z through 03z as has been
the case over the last few days. A few showers and storms will
persist overnight but shouldn't pose any threats to taf sites.


Gjt watches/warnings/advisories...


Short term...mda
long term...mda

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