Area Forecast Discussion
Issued by NWS Grand Junction, CO

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FXUS65 KGJT 061131

Area Forecast Discussion
National Weather Service Grand Junction CO
531 AM MDT Tue Jun 6 2023

.SHORT TERM...(Today through Wednesday night)
Issued at 231 AM MDT Tue Jun 6 2023

There`s no question where the closed low is this morning looking
at IR satellite. Plenty of dry air can be found under the low with
rotation around the low advecting moisture off the Pacific up and
around the low bringing some clouds to central and southeast Utah
as well as extreme southwest Colorado. PWATs over the last few
days have hovered around 0.6 inches and they look to increase some
today reaching between 0.7 to 0.8 inches. As mentioned over the
last few days, upper level support will increase as a weak jet
streak sets up and approaches the area this afternoon. Models
continue to depict stronger divergence aloft which will aid in
lift while lapse rates will reach 9 to 10 deg C/km. Looking at
surface based CAPE, values reach over 1500 J/kg this afternoon for
the Four Corners region to include Grand county UT, San Miguel
and Montezuma counties as well as the southern valleys (La Plata
and Archuleta counties). Forecast soundings are also showing DCAPE
values varying between 800 to 1000 J/kg so some stronger wind
gusts are certainly likely with storms that fire in those same
counties. Some shear also exists for those same areas indicating
some stronger storms may form this afternoon heading towards the
evening hours. Convection will start firing over the higher
terrain around noon, give or take, much like we`ve seen over the
past few days. While the closed low will park itself over southern
California, the jet streak will be rounding the area of low
pressure with the increase in divergence aloft occurring from
about mid-afternoon onwards. CAM guidance is picking up on this
detail with a line of showers and storms forming across the Four
Corners around 2PM moving northeastward through the evening hours.
By 6PM, guidance suggests this line will stretch from roughly
Moab, UT down through Nucla into Telluride and will be just south
of the Grand Valley by 9PM but by then it will have weakened
considerably leaving some showers, maybe a few rumbles of thunder.
Any showers will end by midnight.

Wednesday, the closed low will shift slightly eastward and with
the jet streak still in play, we can look for a similar day though
areas favored for convection will be from the San Juans northward.
Instability will be a bit weaker as indicated by lower CAPE and
lapse rates but not by much. Another active day in store.

.LONG TERM...(Thursday through Monday)
Issued at 231 AM MDT Tue Jun 6 2023

The persistent omega block that has setup across the CONUS remains
in place at the start of the long term but finally does break down
towards Sunday and Monday. The slowly meandering closed low that has
brought the increased moisture and convection to our CWA will start
weakening Thursday and become an open wave as it moves almost
directly north over Nevada into OR/ID. Upper level support in the
form of a weak ~50kt jet streak will follow suit though it will
move over the northern half of the CWA as it does so. No change to
models bringing in drier air to the region, especially the
southern half of the CWA, though it`s advecting this drier air in
fairly quickly...maybe a bit too quickly. Models are really
shutting off any convection due to lack of moisture and strong
forcing though the NBM is keeping some chances for showers and
storms in the forecast. Best chances are for the northern half of
the CWA though the higher terrain of the San Juans and central
mountains can`t be ruled out either. Having said that, the general
gist of convection coverage lowering and becoming less intense is

Friday looks to be mostly dry though a few afternoon showers and
quick storms can`t be ruled out as peak heating causes convection to
fire over the higher terrain. With little moisture to work with, we
can expect some gusty outflow winds from any convection that does
form. Saturday, the omega block finally starts to break down which
will cause the high pressure over Canada to drop southward across
the Plains. The remnants of the low will persist along the OR/ID
border and we`ll be between these 2 features. Impulses galore will
be moving around the area and might bring an uptick in convection.
Both the EC and GFS are hinting at this so we`ll have to see how
things shake out.

Sunday, another closed low will have set up over SoCal as our
remnant low pushes up into WA/ID and the high pressure continues to
drop southeastward. Our CWA is plum bang in the middle of these 3
features. If you follow the EC, it places a ridge over our area
which inhibits any widespread convection. Of course, the GFS isn`t
having it and wants to put widespread showers and storms across the
area. Discrepancies continue into Monday so we`ll just have to wait
and see. Looks like we`re not done with unsettled weather just


.AVIATION...(For the 12Z TAFS through 12Z Wednesday morning)
Issued at 528 AM MDT Tue Jun 6 2023

High clouds will continue to increase from southwest to northeast
FEW to SCT skies this morning with BKN skies becoming common as
the day wears on. VFR conditions will remain in place, however.
Another round of convection is expected today, firing around 18Z
when isolated to scattered showers and thunderstorms will develop
over the higher terrain. Upper level support will cause storms to
be stronger than seen recently with gusty outflow winds and some
heavy rain the biggest concerns. Put VCTS in for many TAF sites
as coverage will increase some from what we saw yesterday.




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