Severe Thunderstorm Warning 21, NWS Grand Junction, CO

669 
WWUS55 KGJT 061743
SVSGJT

Severe Weather Statement
National Weather Service Grand Junction CO
1143 AM MDT Sat Jun 6 2020

COC029-077-085-113-UTC019-037-061752-
/O.EXP.KGJT.SV.W.0021.000000T0000Z-200606T1745Z/
San Miguel CO-Delta CO-Montrose CO-Mesa CO-San Juan UT-Grand UT-
1143 AM MDT Sat Jun 6 2020

...THE SEVERE THUNDERSTORM WARNING FOR NORTH CENTRAL SAN MIGUEL...
SOUTHWESTERN DELTA...WESTERN MONTROSE...SOUTHWESTERN MESA...
NORTHEASTERN SAN JUAN AND SOUTHEASTERN GRAND COUNTIES WILL EXPIRE AT
1145 AM MDT...
    
The storms which prompted the warning have moved out of the area.
Therefore the warning will be allowed to expire.  However gusty 
winds and brief heavy rainfall are still possible with these 
thunderstorms.

A Severe Thunderstorm Watch remains in effect until 500 PM MDT for
southwestern and west central Colorado...and southeastern and east
central Utah.

To report severe weather, contact your nearest law enforcement
agency. They will relay your report to the National Weather Service
Grand Junction.

Remember, a Severe Thunderstorm Warning still remains in effect for
to the northeast!

LAT...LON 3936 10905 3856 10814 3803 10855 3836 10895
      3870 10936
TIME...MOT...LOC 1742Z 205DEG 57KT 3909 10904 3876 10860 3849 10837 

$$

Stearns

Area Forecast Discussion
National Weather Service Grand Junction CO
544 AM MDT Sat Jun 6 2020

.SHORT TERM...(Today through Sunday)
Issued at 352 AM MDT Sat Jun 6 2020

The closed midlevel low pressure over southern California is finally
starting to lift northeastward and will track directly over the area
today. As the low approaches it will open up into a wave, but remain
negatively tilted. Ahead of the low strong southerly flow has
brought sub-tropical moisture into the region as PWATs reach 0.75 to
1.00 inches. Increased forcing and moisture is supporting scattered
showers this morning. As of now the rainfall rates are not overly
concerning, but there was a good amount of low-level dry air to
saturate. With the pump primed the potential for heavier rainfall
increases later this morning especially as the instability ramps
up ahead of the wave.

By late morning CAPE values of 1500 J/kg develop in southeast Utah
and spread northeastward in association with the steep lapse
rates. One uncertainty is that scattered showers and expansive
cloud cover will make it difficult to heat the surface and hinder
destabilization. Despite this caveat the models are remaining
pretty consistent showing these values, which is likely due to the
strong dynamics with this system. Morning showers will continue
with clearing starting in southeast Utah and moving to the
northeast, so perhaps 1 to 2 hours of surface heating is possible
before the deeper convection develops. A mid level jet looks to
strengthen over the area as the wave passes overhead. Consensus
among the CAMs is that this jet could reach 50 to 70 kt. These
wind speeds, steepening lapse rates and strong ascent could
certainly force turbulent mixing down to the surface and aid in
the convective development. Storm initiation is depicted by the
CAMs right along the leading edge of the synoptic dry slot.
Soundings show that deep layer shear is basically off the charts
with straight line hodographs, which supports the chance for
sustained and or rotating updrafts. There is slight veering in the
boundary layer causing SRH values to reach 100-200 m2/s2, which
means there is a non-zero tornado threat. Storm mode is
interesting due to the nature of the forcing. The CAMs have been
trending from semi-discrete cells to a more linear mode. This
makes sense given the modest ascent and complete removal of any
capping. Damaging wind gusts are the main threat with some
potential for large hail. This line or cluster of storms will
quickly move northeastward in the early afternoon and cover the
northwest half of the forecast area. Clearing in the dry slot will
allow mixing into the strong winds aloft, so the threat for +60
mph wind gusts exists without storms especially above the
treeline. A Wind Advisory has been issued for most of the valleys
where strong gusts are possible. Along with the wind threat PWATs
still support the chances for heavy rainfall with rates exceeding
1 inch per hour in spots, so flash flooding still looks possible.
Areas more likely to see flash flooding impacts are slot canyons
and dry arroyos in eastern Utah as well as the recent burn scars
in southwest Colorado and areas of steep terrain prone to
mudslides. Luckily the storms will be moving quickly so the
potential for training appears low.

The other concern and uncertainty today is the dry air mixing down
to the surface in portions of southeast Utah and southwest Colorado
where surface heating is maximized. In these areas Red Flag
conditions are possible, but the recent and predicted rainfall
makes it difficult to determine status of the fuels. Therefore no
fire weather products have been issued, but everyone needs to take
extra precautions and be weather aware today. It is probably a
good idea to postpone any recreational or travel plans in the
backcountry or outdoors until Sunday.

.LONG TERM...(Sunday night through Friday)
Issued at 352 AM MDT Sat Jun 6 2020

The longwave mid-level trough to the west shifts slowly eastward
on Sunday. Moisture moving northeastward on the eastern flank of
the trough is expected to generate scattered to numerous showers
and thunderstorms across northeast Utah and northwest Colorado
throughout the day. Moist convection is possible Sunday night as
the trough continues to close on the forecast area, but should be
reduced in both coverage and intensity in response to diurnal
cooling. The longwave trough sweeps over the region Monday into
Monday night and will continue to generate scattered showers and
thunderstorms, mainly across the north. Some showers may linger
into Tuesday, but conditions will largely be dry across the
region.

Dry weather is expected to persist through Thursday as flow shifts
from northwest to west, then southwest as a transitory ridge
builds to the west, then passes over the forecast area. The ECMWF
and Canadian models suggested moisture moving northward from the
Mexican Plateau will reach the Continental Divide Friday, possibly
fueling isolated thunderstorms during the afternoon. In contrast,
the GFS keeps this moisture east of the Divide. Given model
differences deferred to the national blended solution which
featured slight chances on Friday.

As mentioned previously, a longwave trough passes east of the area
Monday night. However, the cold front associated with this system
moves through the area on Monday. As a result, temperatures will
be much cooler both Monday and Tuesday with highs close to 15
degrees or more below normal. However, it doesn't take long to
moderate an airmass this time of year so by Wednesday temperatures
return to near normal levels. For the latter part of the week,
warm air advection in southwest flow will drive temperatures back
above normal with highs expected climb 5 to 10 degrees above
normal.

&&

.AVIATION...(For the 12Z TAFS through 12Z Sunday morning)
Issued at 540 AM MDT Sat Jun 6 2020

Widespread showers and embedded thunderstorms will continue across
the region today as a Pacific storm lifts overhead. Brief
moderate to heavy rain and gusty outflow winds of 35 to 55 knots
will be the primary threat with strong storms expected to quickly
move through the area around mid day. Heavier rainfall will
result in MVFR visibility at times with brief MVFR/ILS CIGS
possible. Clearing will take place this afternoon and evening once
the storms have moved through.

&&

.FIRE WEATHER...
Issued at 352 AM MDT Sat Jun 6 2020

Red Flag conditions are possible across southeast Utah and
southwest Colorado this afternoon. No products were issued because
it is difficult to determine the status of the fuels given the
recent and projected rainfall. Significantly cooler temperatures
are expected this weekend into early next week. However, afternoon
RH's will quickly bottom out again Sunday and this dry air will
spread across the southern half of the forecast area as we move
through the new week. With the strong winds and lower humidity
focused on the Four Corners region, the lower elevations of
southeast Utah and southwest Colorado will likely see critical
conditions Sunday. As such, a Fire Weather Watch has been issued
for these areas. There is some uncertainty here due to the
expected moisture in the next 24 hours. However, given the lower
forecast precipitation totals and duration in this area, fine
fuels are expected to quickly dry out.

&&

.HYDROLOGY...
Issued at 352 AM MDT Sat Jun 6 2020

The storm system moving over the area today will bring widespread
showers and thunderstorms, with increasing potential for heavy
rain. This will increase flash flooding chances especially in slot
canyon country and over recent burn scars. No changes have been
made to the existing Flash Flood Watch. By late this morning into
the afternoon, convection looks to become more robust but will be
fairly fast moving as drier air pushes in behind this trough by
late afternoon.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...
CO...Fire Weather Watch from Sunday afternoon through Sunday evening
     for COZ207-290.

     Flash Flood Watch until 4 PM MDT this afternoon for COZ018>023.

     Wind Advisory from 9 AM this morning to 9 PM MDT this evening
     for COZ001-002-006>008-011-014-020>023.

UT...Fire Weather Watch from Sunday afternoon through Sunday evening
     for UTZ490-491.

     Flash Flood Watch until 4 PM MDT this afternoon for UTZ022>025-
     027>029.

     Wind Advisory from 9 AM this morning to 9 PM MDT this evening
     for UTZ022-027>029.

&&

SHORT TERM...KJS
LONG TERM...TGJT
AVIATION...TGJT
FIRE WEATHER...TGJT
HYDROLOGY...TGJT

Hazardous Weather Outlook
National Weather Service Grand Junction CO
425 AM MDT Sat Jun 6 2020

COZ001>014-017>023-UTZ022>025-027>029-071030-
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 Sat Jun 6 2020

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

.DAY ONE...Today and Tonight

A system will be moving over the forecast area today bringing
rain, heavy at times, along with some thunderstorms. The heavy
rain will increase chances for flash flooding, especially over
canyon country and recent burn scars, so a Flash Flood Watch is in
effect for eastern Utah and southwest Colorado through 4 pm.
Gusty winds and hail will be possible through the day under the
stronger thunderstorms. Wind gusts could exceed 60 mph even
without a storm especially above the treeline.

.DAYS TWO THROUGH SEVEN...Sunday through Friday

Critical fire weather conditions are possible across Southeast
Utah and southwest Colorado Sunday into Monday.

.SPOTTER INFORMATION STATEMENT...

Spotter activation is needed later this morning and into the
afternoon as the chance for severe thunderstorms increases across
the area. The main threat with these storms will be damaging wind
gusts.

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE GRAND JUNCTION CO
1039 AM MDT SAT JUN 6 2020

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

1038 AM     HAIL             MONTICELLO 8E           37.86N 109.19W
06/06/2020  E0.75 INCH       SAN JUAN           UT   PUBLIC

            STRONG WINDS BUT NO NOTICEABLE DAMAGE.

&&

NL

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE GRAND JUNCTION CO
1049 AM MDT SAT JUN 6 2020

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

1007 AM     NON-TSTM WND GST ASPEN-PITKIN AIRPORT    39.23N 106.87W
06/06/2020  M48 MPH          PITKIN             CO   ASOS

&&

NL

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE GRAND JUNCTION CO
1056 AM MDT SAT JUN 6 2020

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

1042 AM     HAIL             MONTICELLO              37.88N 109.35W
06/06/2020  M1.25 INCH       SAN JUAN           UT   PUBLIC

&&

NL

Special Weather Statement
National Weather Service Grand Junction CO
1059 AM MDT Sat Jun 6 2020

COZ019-022-061745-
Animas River Basin CO-Southwest San Juan Mountains CO-
1059 AM MDT Sat Jun 6 2020

...SIGNIFICANT WEATHER ADVISORY FOR NORTHEASTERN MONTEZUMA AND
CENTRAL LA PLATA COUNTIES UNTIL 1145 AM MDT...

At 1059 AM MDT, Doppler radar was tracking a strong thunderstorm 13
miles southwest of Durango, moving north at 50 mph.

Half inch hail and wind gusts up to 50 mph will be possible with this
storm.

Locations impacted include...
Durango, La Plata, Mayday, Hesperus, Hermosa, Trimble, Breen,
Redmesa, Kline, Rockwood and Marvel.

This includes the following highways...
 U.S. Highway 550 in Colorado between mile markers 29 and 32, and
between mile markers 37 and 45.
 U.S. Highway 160 in Colorado between mile markers 61 and 82.
 Colorado 140 between mile markers 7 and 23.
 Colorado 145 between mile markers 34 and 40.

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.

&&

A Severe Thunderstorm Watch remains in effect until 500 PM MDT for
southwestern Colorado.

LAT...LON 3706 10798 3710 10824 3763 10819 3758 10776
TIME...MOT...LOC 1659Z 189DEG 46KT 3719 10809

15

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE GRAND JUNCTION CO
1106 AM MDT SAT JUN 6 2020

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0950 AM     FLASH FLOOD      VALLEY OF THE GODS      37.27N 109.92W
06/06/2020                   SAN JUAN           UT   CO-OP OBSERVER

            NORMALLY DRY ARROYOS FILLED RAPIDLY WITH
            FLASH FLOODING OBSERVED. NO KNOWN DAMAGE OR
            INJURIES.

&&

JDC

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE GRAND JUNCTION CO
1107 AM MDT SAT JUN 6 2020

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

1107 AM     HAIL             MOAB                    38.57N 109.55W
06/06/2020  E0.25 INCH       GRAND              UT   PUBLIC

            VERY HEAVY RAIN FALLING AS WELL.

&&

JDC