Special Weather Statement, NWS Grand Junction, CO

Area Forecast Discussion
National Weather Service GRAND JUNCTION CO
426 PM MDT Sun May 7 2017

.SHORT TERM...(Tonight through Monday night)
Issued at 425 PM MDT Sun May 7 2017

Cutoff low over southern California will be meandering slowly
eastward over the next few days. This will keep deep difluent
southerly flow in place with ejecting waves lifting through the
forecast area. Have seen a few stronger storms today with several
reports of pea up to quarter size hail. The strongest cell popped
north of Rangely and broke from the flow, turning right toward
Blue Mountain. Storm showed some rotation with long lived and
persistent hail path per MESH products.

On that note, convection likely to persist through this evening
with HiRes models in good agreement keeping activity focused on
the northern zones. Southern zones will be more isolated in
coverage through this evening. Convection diminishes after
midnight, but not expected to totally shut down. Latest HRRR and
RAP13 showing some activity firing near the Four Corners between 3
and 6 am, although confidence no extreme. So will keep pops on the
low side for now.

Monday should be an interesting day as we see an old frontal
boundary set up along the I-70 corridor with energy rotating
northward during the morning and early afternoon hours. NAM CAPE
values in excess of 1500 J/kg by midday along and just north of
the surface front. Steep lapse rates, instability, forcing and
difluence aloft will get storms rolling early with activity
persisting through the afternoon hours. SPC currents showing this
area in marginal severe, which looks reasonable with the above
parameters in play.

Temperatures will be tricky with cloud cover from developing
convection shading some areas. This will also play a role in our
convection through the day with the strongest storms firing along
the edges of denser cloud cover.

.LONG TERM...(Tuesday through Sunday)
Issued at 425 PM MDT Sun May 7 2017

The deep upper low will be lifting toward the Four Corners Tuesday
and Wednesday with a stronger wave lifting northward Tuesday and
Tuesday night. Cooling aloft associated with the upper low should
drive snow levels down over the San Juans by Tuesday night with
showers spreading from south to north through the day. EC and GFS
have come into better agreement with this scenario with the low
arriving over the Four Corners by midday Wednesday. As with many
closed lows, the exact timing of the kick-out will play a critical
role in our precipitation forecasts, so while ramping things up,
not quite ready bite off on the heavier QPF forecasts that a few
models are showing. Influence from this system is expected to
diminish on Thursday with dirty ridge sliding into place Thursday
night and Friday with continued unsettled weather. Flow then backs
to the southwest over the weekend with drier and warmer weather
returning. Although winds will likely be picking up in the drier
air mass as we mix deeper aloft.

&&

.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
Issued at 1112 AM MDT Sun May 7 2017

Relatively moist southerly flow continues to move through the
area. The atmosphere will become unstable this afternoon
supporting showers and thunderstorms into the evening hours.
Expect gusty winds, hail and frequent lightning will accompany
these storms.

&&

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

SHORT TERM...JDC
LONG TERM...JDC
AVIATION...Larry

Hazardous Weather Outlook
National Weather Service GRAND JUNCTION CO
237 AM MDT Sun May 7 2017

COZ001>014-017>023-UTZ022>025-027>029-080845-
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-
237 AM MDT Sun May 7 2017

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

.DAY ONE...Today and Tonight

Breezy with scattered to numerous showers and a few thunderstorms,
decreasing this evening, then increasing again late tonight.

.DAYS TWO THROUGH SEVEN...Monday through Saturday

Monday through Thursday: Breezy and slightly cooler with a chance
of afternoon and evening showers and a few thunderstorms.

Friday and Saturday: a slight chance of afternoon showers and
thunderstorms mainly near the Continent Divide.

.SPOTTER INFORMATION STATEMENT...

Spotter activation will not be needed.

CJC

Special Weather Statement
National Weather Service Grand Junction CO
438 PM MDT SUN MAY 7 2017

COZ001-UTZ024-025-072330-
Lower Yampa River Basin CO-Eastern Uinta Basin UT-
Tavaputs Plateau UT-
438 PM MDT SUN MAY 7 2017

...SIGNIFICANT WEATHER ADVISORY FOR NORTHWESTERN RIO BLANCO AND EAST
CENTRAL UINTAH COUNTIES UNTIL 530 PM MDT...

At 437 PM MDT, Doppler radar was tracking a strong thunderstorm 17
miles southwest of Rangely, or 46 miles southeast of Vernal, moving
north at 25 mph.

Dime size hail and winds in excess of 30 mph will be possible with
this storm.

Locations impacted include...
Dinosaur, Artesia and Blue Mountain.

This includes the following highways...
 U.S. Highway 40 in Colorado between mile markers 2 and 12.
 U.S. Highway 64 in Colorado between mile markers 1 and 15.

LAT...LON 3983 10889 3983 10912 4026 10918 4026 10883
TIME...MOT...LOC 2237Z 178DEG 20KT 3990 10902

NL

Special Weather Statement
National Weather Service Grand Junction CO
440 PM MDT SUN MAY 7 2017

UTZ024-025-072330-
Eastern Uinta Basin UT-Tavaputs Plateau UT-
440 PM MDT SUN MAY 7 2017

...SIGNIFICANT WEATHER ADVISORY FOR SOUTHEASTERN UINTAH COUNTY UNTIL
530 PM MDT...

At 440 PM MDT, Doppler radar was tracking a strong thunderstorm 36
miles southwest of Rangely, or 46 miles southeast of Fort Duchesne,
moving north at 15 mph.

Dime size  hail and winds in excess of 30 mph will be possible with
this storm.

This storm will remain over mainly rural areas of southeastern Uintah
County.

LAT...LON 3967 10919 3967 10943 4009 10950 4009 10914
TIME...MOT...LOC 2240Z 180DEG 13KT 3976 10931

NL

Special Weather Statement
National Weather Service Grand Junction CO
537 PM MDT SUN MAY 7 2017

UTZ024-080015-
Eastern Uinta Basin UT-
537 PM MDT SUN MAY 7 2017

...SIGNIFICANT WEATHER ADVISORY FOR CENTRAL UINTAH COUNTY UNTIL 615
PM MDT...

At 537 PM MDT, Doppler radar was tracking a strong thunderstorm 27
miles southwest of Dinosaur, or 28 miles southeast of Fort Duchesne,
moving north at 20 mph.

Nickel size hail and winds in excess of 30 mph will be possible with
this storm.

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

LAT...LON 3995 10933 3994 10956 4031 10962 4031 10927
TIME...MOT...LOC 2337Z 179DEG 16KT 4002 10945

NL

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