Area Forecast Discussion
Issued by NWS Grand Junction, CO

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FXUS65 KGJT 202143

Area Forecast Discussion
National Weather Service Grand Junction CO
343 PM MDT Sun May 20 2018

.SHORT TERM...(Tonight through Monday night)
Issued at 343 PM MDT Sun May 20 2018

Shower and thunderstorm activity got started during the latter
part of the morning and became more widespread in coverage as
compared to yesterday during the early part of the afternoon.
Given the relatively dry sub-cloud layer, some of this activity
resulted in wind gusts in excess of 50 MPH. The heightened
activity seemed to be driven by the broad are of
difluence/divergence ahead of a deep trough of low pressure over
the California coast. Expect the this dynamic forcing to sustain
shower and thunderstorm activity well into the evening before
diurnal cooling and waning upper level divergence sets in later

Winds pick up a bit on Monday, especially across the Four Corners
region as the trough along the West Coast closes off and moves
over southern California. A 90 knot jet at the base of the trough
will focus divergence over southwest Colorado, bringing numerous
showers and thunderstorms to the San Juan Mountains and scattered
coverage over adjoining lower elevation areas from late morning
into the evening. Areas north and west of the Four Corners region
have significantly lower chances for moist convection. Scattered
showers/thunderstorms are likely to linger over the San Juan
Mountains overnight as the low moves over Las Vegas placing the
exit region of the cyclonically curved jet over the Four Corners.

Advection of warm air will result in mild overnight lows early
this week, with a significant jump in temperatures Monday
afternoon. However, Monday`s highs won`t warm as much over
southwest Colorado where clouds and showers will hinder warming.

.LONG TERM...(Tuesday through Sunday)
Issued at 343 PM MDT Sun May 20 2018

Models were in good agreement during the medium range forecast
period and showed that the closed low will begin to fill as it
moves north of Las Vegas on Tuesday. However, conditions will
change little relative to Monday with gusty south to southwest
winds continuing over the Four Corners area. However, in the
preceding 12 hours, moisture will have spread into the northern
reaches of the forecast area. The influx of moisture should cause
shower and thunderstorms to increase over northern Colorado and
eastern Utah with the mountain areas favored during the afternoon
and evening.

The low will continue northeastward as a low amplitude shortwave
trough Tuesday night, exiting to the north of the forecast area
Wednesday afternoon. Thereafter, a ridge will build over the
western U.S. on Thursday as another low pressure system
approaches the West Coast. The ridge will then slide east becoming
quasi-stationary over the Rockies through the remainder of the
week and into the weekend. Drying beneath the ridge will limit,
but not entirely put and end to afternoon/evening showers and
thunderstorms which will favor the mountains of the Continental
Divide each day. Expect temperatures to rise to well above normal
levels from Thursday into the weekend.


.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
Issued at 1027 AM MDT Sun May 20 2018

VFR conditions are expected across the area today. Showers and
storms will slowly increase this afternoon, reaching maximum
coverage after 22Z.Gusty outflow winds will be the biggest
concern with gusts between 30 to 40 kts possible. Activity will
slowly diminish this evening.


Issued at 343 PM MDT Sun May 20 2018

Winds are expected to increase over the region Monday and Tuesday
as the pressure gradient tightens ahead of the next low pressure
system as it moves from southern California to the southern Great
Basin. Latest model guidance suggests winds and relative humidity
may reach critical levels both Monday and Tuesday afternoon for
portions of the Four Corners region. However, coverage and
duration criteria fell just shy of requirements for a Red Flag
Warning. Therefore, will not issue and fire weather highlights
with this package, though later forecasts may call for a shift in
current thinking.






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