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Area forecast discussion
National Weather Service Grand Junction Colorado
520 PM MDT sun Sep 22 2019

Short term...(tonight through Monday night)
issued at 351 PM MDT sun Sep 22 2019

A Pacific trough moving ashore over the Pacific northwest is
expected to deepen as it moves over the western Great Basin
tonight. As this occurs, the ridge axis over the region will move
east of The Divide and southwest flow aloft develops. Some thin
cirrus was approaching from the southwest and expect this will
help moderate overnight lows just a bit tonight. Still, strong
radiational cooling will cause lows to be colder than normal and
freezing temperatures are expected across lower elevations of
northwest Colorado. However, given hard freeze at Craig, Meeker
and other areas, will not issue further warnings for Colorado zone 2.

The trough deepens further on Monday with a closed low forming
over Arizona. Latest model runs keep showers confined to extreme
southeast Utah Monday afternoon, so removed even slight chances
north and east of there. Warm air advection provided by
southwesterlies aloft should drive temperatures back above
seasonal norms. The low continues to transit southward to Mexico
Monday night taking any precipitation chances and cloud cover with
it. Expect overnight temperatures to remain unseasonably cold as
radiational cooling will be strong once again, though not quite as
cold as the past couple of nights.

Long term...(tuesday through sunday)
issued at 351 PM MDT sun Sep 22 2019

The region remains dry and warm Tuesday and Wednesday as the low
center over northern Mexico stalls early in the week. The latest
long range models showed the low drifting to the north ahead of a
shortwave trough moving across the northern rockies on Thursday.
Moisture return ahead of the southern low threatens scattered
afternoon showers and thunderstorms, mainly over the San Juans
Thursday afternoon. Precipitation chances increase across the
region Thursday night into Friday as the southern low phases with
the shortwave trough in the northern stream. Details a bit sketchy
at this point as models handle this complex interaction
differently, but all point to best precipitation chances on
Friday.

The weekend outlook was less clear. The latest GFS, European model (ecmwf) and
Canadian dig out a trough over the Pacific northwest Saturday.
However, positioning is different for each 12z/sun operational run
resulting in significant differences in quantitative precipitation forecast placement. Ec was
most progressive yielding a broad area of substantial shower
activity over much of the region. The slower GFS and Canadian
solutions had more of dry slot in place across the south with
precipitation chances largely confined to northeast Utah and
northwest Colorado. The low deepens further on Sunday and makes
no headway eastward for continued shower/thunderstorm chances
Sunday. Given model differences, let the middling nbm solution
ride this weekend.

&&

Aviation...(for the 00z tafs through 00z Monday evening)
issued at 519 PM MDT sun Sep 22 2019

With the approach of sunset any gusty winds will be subsiding and
under clear skies VFR conditions will dominate over the next 24
hours.

&&

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

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