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Area forecast discussion
National Weather Service Grand Junction Colorado
308 am MDT sun may 20 2018

Short term...(today through monday)
issued at 252 am MDT sun may 20 2018

Unsettled weather remains in the forecast through Monday thanks to
a deep trough to our west. The trough is being reinforced by the
jet stream that is dropping almost due south from Alaska along our
West Coast. This reinforcing will eventually cause a closed low to
form. However, until this happens, we'll deal with a trough to our
west with a wave moving through the trough causing an uptick in
convection. Models clearly show a line of convection forming from
Oregon through Idaho down into Nevada, Utah and then Colorado.
Like yesterday, convection will begin forming around 11am, give or
take, with coverage reaching a maximum from about 2pm onwards.
The difference today will be the southerly flow as opposed to
northerly like we saw yesterday. Models are picking up on this
shift by giving areas south of I-70 better chances for storms and
showers before shifting to the northern valleys later in the day.
As we've seen, expect some brief heavy showers and gusty outflow
winds though some small hail can't be ruled out either. Once
daytime heating ends, convection will quickly die down leading to
a quiet overnight.

By Monday, the jet will have formed the area of low pressure which
will be located over central California. As the jet is more
meridional in nature, lateral movement of this low will be quite
slow. Previous model runs kept US rather dry on Monday as we were
in the dry slot but now latest guidance suggesting some showers
and storms possible over the San Juans into the southern central
mountains. This certainly looks possible as a weak wave moves out
ahead of the closed low. Forecast follows suit with the southeast
portion of our County Warning Area favored for some convection. Remaining areas
will see variable cloudiness and an off chance for a quick stray
shower. High temperatures will inch up a few degrees each day.

Long term...(monday night through saturday)
issued at 252 am MDT sun may 20 2018

A closed low will have dropped into the southwestern Continental U.S. By Monday
night with south-southwesterly flow increasing across eastern Utah
and western Colorado. The position of the center of the low pressure
system varies from model to model at this time, impacting how early
moisture from this system will move into our area. The trend right
now seems to be for mid and high level clouds to continue to
increase on Tuesday with scattered diurnal convection developing by
mid morning. In response to the increased potential for clouds and
showers, Tuesday should be our coolest day of the week. The low
looks to transition to an open wave on Wednesday as it lifts to the
northeast, resulting in a drier southwesterly flow over our forecast

A ridge of high pressure will build to our west on Thursday and
continue to amplify overhead into Sunday. This will initiate a
gradual drying and warming trend with temperatures rising back to
above seasonal levels. However, residual moisture trapped underneath
the ridge should combine with daytime heating to produce isolated
orographic showers and thunderstorms each afternoon.


Aviation...(for the 12z tafs through 12z Monday morning)
issued at 252 am MDT sun may 20 2018

VFR conditions will be prevalent across the area today. Another
round of showers and storms is expected to fire from about 17z
onwards, reaching maximum coverage after 21z. As we've seen over
the past few days, gusty outflow winds will be the biggest concern
with gusts between 30 to 40 kts possible. As far as convection at
airports, kdro, ktex, and kguc may be under the gun today as
southerly areas are favored though did not include vcsh or thunderstorms in the vicinity
for now. Towards the afternoon and evening hours, northern
airports may be affected as well.



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