Flash Flooding and Debris Flow in Colorado, July 24, 2018

Area Forecast Discussion
National Weather Service Grand Junction CO
1152 AM MDT Tue Jul 24 2018

.SHORT TERM...(Today through Wednesday)
Issued at 303 AM MDT Tue Jul 24 2018

The center of broad high pressure will shift from western New
Mexico to Arizona today through Wednesday, signaling the
interruption of another weak and unsatisfying monsoonal surge of
the past few days. This afternoon and evening will still see
monsoonal moisture flowing into southern CO producing showers and
thunderstorms but that flow should be interrupted by Wed. Also, a
shortwave trough in the westerlies over the Northern Rockies will
increase drying from the west and north and continue forcing the
remnants of the monsoonal moisture plume to curve to the east over
central CO. This will leave northeast UT and the northern half of
CO drier today through Wed. Wednesday will see the flow aloft
becoming more northwesterly as the high moves further west and low
pressure deepens over the midwest. There will still be showers
and thunderstorms fueled by daytime heating acting on the moisture
trapped within the high, with highest coverage over southern CO.

.LONG TERM...(Wednesday night through Monday)
Issued at 303 AM MDT Tue Jul 24 2018

Once the high pressure center migrates west it remains quasi-
stationary, centered over northwestern Arizona and southern
Nevada according to a consensus of the medium range models. In
this position moisture will slowly erode across the area as drier
air to the northwest infiltrates the region. In response, eastern
Utah and western Colorado will experience a decrease in areal
coverage of thunderstorms during the remainder of the week,
through the weekend and into early next week. Not only will
showers and thunderstorms become more scarce, they will become
higher based, producing strong outflow winds but little measurable
precipitation. Afternoon highs during this period will remain hot
with little day to day variability, while overnight lows cool
slightly as the atmosphere dries.

&&

.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
Issued at 1152 AM MDT Tue Jul 24 2018

Convection today started with an MCV across the Paradox valley
which has since weakened, but a few thunderstorms have developed
with one heading toward KTEX. Most activity should develop south
of I-70, but outflow boundaries may develop later to trigger
isolated showers and thunderstorms elsewhere. Convective activity
may continue past 06z tonight for some nocturnal activity. Gusty outflow
winds of 30 to 45 mph will be possible with thunderstorms.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...
CO...None.
UT...None.
&&

SHORT TERM...CC
LONG TERM...NL
AVIATION...JAM

Hazardous Weather Outlook
National Weather Service Grand Junction CO
223 AM MDT Tue Jul 24 2018

COZ001>014-017>023-UTZ022>025-027>029-250830-
Lower Yampa River Basin-Central Yampa River Basin-
Roan and Tavaputs Plateaus-Elkhead and Park Mountains-
Upper Yampa River Basin-Grand Valley-Debeque to Silt Corridor-
Central Colorado River Basin-Grand and Battlement Mesas-
Gore and Elk Mountains/Central Mountain Valleys-
Central Gunnison and Uncompahgre River Basin-
West Elk and Sawatch Mountains-Flat Tops-
Upper Gunnison River Valley-Uncompahgre Plateau and Dallas Divide-
Northwest San Juan Mountains-Southwest San Juan Mountains-
Paradox Valley/Lower Dolores River-
Four Corners/Upper Dolores River-Animas River Basin-
San Juan River Basin-Southeast Utah-Eastern Uinta Mountains-
Eastern Uinta Basin-Tavaputs Plateau-Arches/Grand Flat-
La Sal and Abajo Mountains-Canyonlands/Natural Bridges-
223 AM MDT Tue Jul 24 2018

This hazardous weather outlook is for eastern Utah and western
Colorado.

.DAY ONE...Today and Tonight

Scattered showers and thunderstorms will develop over the central
and southern mountains, which will drift over the valleys late in
the afternoon and early evening. Expect a slight chance of
locally heavy rain showers.

Isolated showers and thunderstorms will form over the northern
half of the area.

.DAYS TWO THROUGH SEVEN...Wednesday through Monday

A slight chance of afternoon and evening showers and
thunderstorms continues each day, decreasing Thursday through
Monday.

.SPOTTER INFORMATION STATEMENT...

Spotter activation will not be needed.

Special Weather Statement
National Weather Service Grand Junction CO
107 PM MDT TUE JUL 24 2018

COZ019-241945-
Southwest San Juan Mountains CO-
107 PM MDT TUE JUL 24 2018

...SIGNIFICANT WEATHER ADVISORY FOR SOUTHWESTERN HINSDALE...
SOUTHEASTERN SAN JUAN AND NORTHEASTERN LA PLATA COUNTIES UNTIL 145 PM
MDT...

At 107 PM MDT, Doppler radar was tracking a strong thunderstorm 10
miles south of Silverton, or 27 miles north of Durango, moving
southeast at 20 mph.

Dime size hail and winds in excess of 40 mph will be possible with
this storm.

Locations impacted include...
Elk Park.

This includes U.S. Highway 550 in Colorado between mile markers 48
and 66.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Heavy rainfall is also occurring with this storm, and may lead to
localized flooding. Do not drive your vehicle through flooded
roadways.

Frequent cloud to ground lightning is occurring with this storm.
Lightning can strike 10 miles away from a thunderstorm. Seek a safe
shelter inside a building or vehicle.

&&

LAT...LON 3763 10785 3778 10773 3760 10727 3737 10744
TIME...MOT...LOC 1907Z 301DEG 19KT 3767 10772

MDA