Severe Thunderstorm Warning 4, NWS Grand Junction, CO

Area Forecast Discussion
National Weather Service Grand Junction CO
1131 AM MDT Fri Jul 26 2019

.SHORT TERM...(Today through Saturday)
Issued at 350 AM MDT Fri Jul 26 2019

Monsoonal moisture wrapped around the west/northwest periphery of the
high pressure system, currently centered over western New Mexico, has
supported a few lingering showers across southeast Utah and southwest
Colorado this morning. These showers will taper off shortly after
sunrise, before the next round of precipitation builds this
afternoon.

A trough off the PacNW coast will start to squish the ridge of high
pressure to our south, forcing the center of the circulation to the
south and west. A southwesterly track of the high will transition our
CWA from southwest to westerly flow aloft, steering any storm that
develops this afternoon on a northeasterly to easterly track.
Showers and thunderstorms will develop around noon over higher
terrain, before moving over valleys later in the evening. High
PWAT values and slow moving storms are likely again this
afternoon, keeping the threat of localized flash flooding until
diminishing after sunset.

The shortwave responsible for pushing the high to our SW will cross
the CWA on Saturday. Moisture ahead of the shortwave will keep chances
for afternoon showers and thunderstorms high, with dry air filtering
in behind. Expect stronger northwest winds Saturday, as the pressure
gradient tightens. Increased sheer aloft may allow for stronger storms
to develop, mainly north of I-70.

.LONG TERM...(Saturday night through Thursday)
Issued at 350 AM MDT Fri Jul 26 2019

Upper level trough/shrtwv will be exiting the forecast area
Saturday night with ridging rebuilding across the western Great
Basin. This will bring drier, northwest flow across eastern Utah and
western Colorado as we close out the weekend. Would expect any
Saturday evening convection to be dissipating by midnight with dry
and cooler weather for Sunday morning. The center of a somewhat
broad and flat ridge will set-up west of the Four Corners on Monday
with generally dry conditions anticipated through Tuesday. The
exception may be an isolated storm or two across the San Juans.

The ridge slides east Tuesday night and Wednesday, which opens the
door once again for another push of monsoonal moisture from the
south. Precipitable water values are forecast to rapidly improve
from south to north rising from around 0.5" on Tuesday to near 1.3"
by Wednesday afternoon. Another shortwave is also advertised by the
GFS to cross eastern Utah and western Colorado sometime Wednesday.
This will be enough to get at least high chance pops back into the
forecast for Wednesday and Thursday. The GFS continues to pump
moisture northward right on into the weekend. With most monsoonal
plumes, will see focus of convection over the higher elevations
during peak heating with nighttime convection favoring the valleys.
Those detail will be worked out as the we move deeper into the
event. Temperatures will be running near seasonal norms for much of
the extended period.

&&

.AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon)
Issued at 1127 AM MDT Fri Jul 26 2019

Scattered to numerous showers and thunderstorms will occur over
the next 24 hours, with the peak period for shower and
thunderstorms expected between 18Z this afternoon and 06Z this
evening. Gusty outflow winds to 45kts, small hail and very heavy
rainfall will accompany the strongest storms. CIGS may reach ILS
breakpoints with VSBYS dipping to between 3-5 NM in heavy
rainfall associated with the stronger storms. Otherwise, VFR
conditions will prevail through the period.

&&

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

SHORT TERM...ERW
LONG TERM...JDC
AVIATION...JVC

Hazardous Weather Outlook
National Weather Service Grand Junction CO
425 AM MDT Fri Jul 26 2019

COZ001>014-017>023-UTZ022>025-027>029-271200-
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-
425 AM MDT Fri Jul 26 2019

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

.DAY ONE...Today and Tonight

Scattered to numerous thunderstorms are expected over the
high country with the southern ranges favored. Lightning, heavy
rain and gusty outflow winds up to 40 MPH are the main threats
through late this evening.

.DAYS TWO THROUGH SEVEN...Saturday through Thursday

Thunderstorm coverage will peak on Saturday, before drier
conditions move in Sunday through Tuesday. Heavy rainfall rates
will remain a significant threat through Saturday. Thereafter,
there will be a decreasing trend in thunderstorm activity from
Sunday into early next week.

Monsoonal moisture will surge back over eastern Utah and western
Colorado by Wednesday, with showers and thunderstorms returning to
much of the region.

.SPOTTER INFORMATION STATEMENT...

Spotter activation is not expected today or tonight, however
spotters are encouraged to relay rainfall amounts or any observed
flooding to the National Weather Service in Grand Junction.

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Special Weather Statement
National Weather Service Grand Junction CO
117 PM MDT Fri Jul 26 2019

COZ011-017-262000-
Uncompahgre Plateau/Dallas Divide CO-
Central Gunnison and Uncompahgre River Basin CO-
117 PM MDT Fri Jul 26 2019

...SIGNIFICANT WEATHER ADVISORY FOR NORTH CENTRAL MONTROSE COUNTY
UNTIL 200 PM MDT...

At 116 PM MDT, Doppler radar was tracking a strong thunderstorm 19
miles northeast of Nucla, or 26 miles west of Montrose. This storm
was nearly stationary.

Nickel size hail and wind gusts up to 50 mph will be possible with
this storm.

This storm will remain over mainly rural areas of north central
Montrose County.

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 3850 10843 3861 10835 3854 10814 3841 10823
TIME...MOT...LOC 1916Z 299DEG 4KT 3851 10835

JVC