Alert archive / Idaho / Flash Flood Watches in 2018

Flash Flood Watch 1, NWS Missoula, MT

May 6, 2018Idaho County, Idaho

NWS Missoula, MT issued this flash flood watch at May 6, 2018, 3:10 PM PDT for Idaho County, Idaho. It was in force for 4 hr.

The area

The counties it named.

The facts

Issued: May 6, 2018, 3:10 PM PDT (22:10 UTC)
Expired: May 6, 2018, 6:45 PM PDT
In force: 4 hr
Issued by: NWS Missoula, MT
Flood severity: None

County Idaho County, ID

The radar

The Missoula radar (KMSX), 175 km from the middle of the area, began a volume at 22:09 UTC, the scan nearest the moment this went out.

Open the radar archive at this moment

The archived warnings, watches and discussions in force at that minute are drawn over the scan, this one among them.

The nearest sounding before it

Spokane, WA (KOTX), launched 12:00Z, 10.2 hours before the alert went out and 218 km from the middle of its area. This is the routine balloon launch nearest before it, the air the forecaster had in hand, not a measurement taken for the alert.

Skew-T log-p

Temperature in red, dew point in green, the mixed-layer parcel dashed.

Hodograph

The wind turning with height, colored by layer: ground to 1 km, 1 to 3 km, 3 to 6 km, 6 to 10 km.

Mixed-layer CAPE: 0 J/kg
Mixed-layer CIN: No buoyant parcel
Mixed-layer LCL: 1989 m above ground
0-6 km bulk shear: 22 kt
0-1 km storm-relative helicity: 55 m²/s²
0-3 km storm-relative helicity: 48 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.0

Open this sounding in Storm Lab

What forecasters said that day

The local office's own words before this flash flood watch went out, as it sent them, from the Iowa Environmental Mesonet's archive of National Weather Service text.

NWS Missoula, MT wrote its last area forecast discussion before this flash flood watch went out at May 6, 1:34 PM PDT, 1 hour 36 minutes earlier.

Area forecast discussion, May 6, 1:34 PM PDT, 1 hour 36 minutes before

Area Forecast Discussion
National Weather Service Missoula MT
234 PM MDT Sun May 6 2018

.DISCUSSION...Clear skies, warming temps, and high dewpoints have
lead to an increasingly unstable atmosphere ahead of a vigorous
cold front, expected to kick off strong thunderstorms this
afternoon through this evening. Storms have begun in eastern
Oregon and extreme west central Idaho. This area of storms will
move eastward with time, impacting Idaho and Clearwater counties
in Idaho in the next few hours. Storms will then cross into
western Montana shortly thereafter. There is a potential that
isolated severe storms will be possible, particularly across west
central Montana later this evening (around or shortly after 6pm
MDT). With as moist of an atmosphere as we have today, heavy
downpours will be the first major concern with storms. The second
will be strong outflow winds along and ahead of storms. Gusts
could reach 40 to 50 mph briefly, especially near approaching
storms. Small hail and abundant lightning will also be threats
with any storms that develop.

Northwest Montana should expect to see storms pass through a
couple hours before sunset, or around there. It's hard to pinpoint
how fast these storms will be tracking, so stay informed of
updates...especially if you have late day outdoor plans!

Rainfall will become more scattered through the night as
instability lessens, with wrap-around rainfall spreading across
northwest Montana and south into west central Montana. These
showers will linger through most of the day Monday, with cooler
temperatures expected.

Warmer and drier conditions are expected on Tuesday with high
pressure to build into the region.

The next cold front remains on track to arrive on Wednesday, so
this will be another day with high chances for showers and
thunderstorms.

For more information on flooding, please see the HYDROLOGY
portion of this discussion below.

&&

.AVIATION..Sunny conditions will give way to increasing cloud
cover and showers and thunderstorms during this afternoon and
evening. The low pressure system, that will aid in the
development of showers and thunderstorms in north- central Idaho
and western Montana this afternoon and evening, is currently
moving through eastern Oregon. Once the low moves into the
unstable environment of north- central Idaho and western Montana,
thunderstorms are expected to develop into organized clusters.
Lowered ceilings, reductions to visibility, gusty winds, moderate
to heavy rain, and hail are all threats with thunderstorms during
this evening. KSMN is most likely to see this activity between
06/2100z and 07/0100z, KMSO between 06/2300z and 07/0200z and KBTM
between 07/0000z and 07/0300z. The trough and low will remain
over the region tonight and Monday, so widespread lowered ceilings
and rain showers are expected through at least Monday morning.

&&

.HYDROLOGY...Snowmelt runoff continues to cause rivers to rise
quickly with warm conditions across the region. Rain with
thunderstorms this evening has the potential to be widespread
enough to add to the rising streams and rivers. Major mainstem
rivers, such as the Clark Fork River above and below Missoula, the
Bitterroot River and the Yaak River are all forecast to see
significant rises in the next several days. Most notably, the
Clark Fork River above Missoula is forecast to approach Major
Flood Stage (13 FT) by Friday, May 11th.

Needless to say, rivers are on the rise and will continue to run
high, fast, and dangerous in the coming days across the entire
Northern Rockies region. This includes small streams and creeks as
they reach bankfull and spill over their banks. Please be alert to
your local bodies of water and ensure you have a plan in the event
of flooding.

&&

.MSO WATCHES/WARNINGS/ADVISORIES...
MT...Flood Watch through late Tuesday night Missoula/Bitterroot
     Valleys.

ID...None.
&&

In the hours before

Special weather statement, May 6, 1:47 PM PDT, 1 hour 23 minutes before

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Special weather statement, May 6, 2:21 PM PDT, 49 minutes before

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Special weather statement, May 6, 2:47 PM PDT, 23 minutes before

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Special weather statement, May 6, 2:55 PM PDT, 15 minutes before

Special Weather Statement
National Weather Service Missoula MT
255 PM PDT SUN MAY 6 2018

IDZ005>008-062315-
Southern Clearwater Mountains ID-
Lower Hells Canyon/Salmon River Region ID-
Northern Clearwater Mountains ID-Orofino/Grangeville Region ID-
255 PM PDT SUN MAY 6 2018

...SIGNIFICANT WEATHER ADVISORY FOR CENTRAL IDAHO AND SOUTH CENTRAL
CLEARWATER COUNTIES UNTIL 415 PM PDT...

At 251 PM PDT, Doppler radar was tracking several strong
thunderstorms moving north-northeast at 55 mph. The strongest storm
currently was between Riggins and Grangeville.

Pea size hail and wind gusts up to 50 mph will be possible with
some of these storms.

Locations impacted include...
Grangeville, Kooskia, Weippe, Riggins, White Bird, East Kamiah,
Lowell, Clearwater, Stites, Red River Hot Spring, Riggins Hot Spring,
Lucile, Orogrande, Copperville, Burgdorf, Woodland, Warren, Winona,
Pollock and Slate Creek.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

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 4546 11656 4550 11656 4560 11646 4568 11653
      4574 11654 4616 11621 4616 11619 4621 11614
      4621 11608 4623 11601 4629 11611 4641 11602
      4631 11515 4521 11518 4527 11667 4532 11668
TIME...MOT...LOC 2151Z 239DEG 49KT 4614 11572

The office that day

Everything else NWS Missoula, MT issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
May 6, 2:03 AM PDT	Areal Flood Warning	MSO	Lincoln	5 days
May 6, 9:24 AM PDT	Areal Flood Warning	MSO	Missoula, Powell	12 days
May 6, 10:24 AM PDT	Flood Watch	MSO	Missoula, Ravalli	24 hr
May 6, 1:47 PM PDT	Special Weather Statement	MSO	Deer Lodge	28 min
May 6, 2:47 PM PDT	Special Weather Statement	MSO		28 min
May 6, 3:52 PM PDT	Special Weather Statement	MSO	Silver Bow	23 min
May 6, 3:53 PM PDT	Special Weather Statement	MSO	Ravalli	67 min
May 6, 4:30 PM PDT	Special Weather Statement	MSO	Granite	75 min
May 6, 2:21 PM PDT	Special Weather Statement	MSO	Lemhi	24 min
May 6, 2:55 PM PDT	Special Weather Statement	MSO	Idaho	80 min

Nearby

Flash Flood Watches in Idaho, 2018 Every flash flood watch in 2018

Sources

The product and its follow-ups from the Iowa Environmental Mesonet's archive of National Weather Service and Storm Prediction Center text; the sounding from the Mesonet's radiosonde archive; radar from the NEXRAD Level II archive.