Flash Flood Warning 5, NWS Great Falls, MT

Area Forecast Discussion
National Weather Service Great Falls MT
1140 AM MDT Sat Jun 16 2018

Aviation Section Updated.

.UPDATE...

Morning update has been published, with main adjustments confined
primarily to POPs and QPF to fine tune amounts and timing of the
precipitation. As of 9am this morning, upper level trough was
draped across the Pacific Northwest, Intermountain West, and
Northern Rockies regions, with the main upper level closed low
centered over West Central Oregon. Synoptic scale ascent was
overspreading Southwest and North Central Montana in earnest this
morning, with additional lift expected to persist into the
evening hours today. H700 closed low was located over Southwest
Montana and is expected to lift to the northeast from
approximately Butte (this morning) to Grass Range (this evening).
This track would place much of Central Montana on the preferred
northwest side of the H700 low track, which is ideal for
precipitation. Abundant moisture was also streaming northward via
isentropic upglide from the Baja of California and Gulf of Mexico,
with Water Vapor imagery clearly depicting these connections.
Strengthening mid-level easterly flow will then help to pull/push
(upslope lift) this moisture back into Central and portions of
North Central Montana through the remainder of the morning hours
and into the afternoon today. This strengthening easterly flow has
been recently noted on the KTFX radar, with northeast winds of
30kts being observed just off of the deck. Radar reflectivity has
subsequently filled in nicely over Central Montana over the past
hour, with this trend expected to continue further to the north to
around the United States Highway 2 corridor through the noon
hour. The Flood Watch will go into effect at noon today, with
rainfall amounts of 2-4" still expected over the Southern Rocky
Mountain Front/east of the Continental Divide and 1-2" expected
over the plains of Central Montana/Highwood Mountains. - Moldan

&&

.SYNOPSIS...
A slow moving upper level low will reside over the northern Rockies
region for the next several days. As a result, expect periods of
rain today over much of the region, with scattered showers and
thunderstorms expected on Sunday and Monday. Afternoon temperatures
will be below normal today, especially over the north. Expect a slow
warming trend towards seasonal normals by the middle portions of
next week.

&&

.AVIATION...
UPDATED 1740Z.
Expect IFR conditions at times, possibly LIFR at times in areas of
heavier rainfall across central MT.  Conditions will slowly improve
from south to north after 20z. Mountains/passes will be obscured at
times.

&&

.HYDROLOGY...

A flood watch remains in effect for portions of Central MT. Rain,
heavy at times is expected later today, with the heaviest
rainfall over the Rocky Mountain Front and Little Belt mountains.
The main threat looks to be the potential for small stream
flooding and poor drainage areas in urban areas this afternoon
through this evening. Adjustments to the flood watch are possible
later today should the rain not be as heavy as forecasted. Brusda

&&

.PREV DISCUSSION...
/ISSUED 500 AM MDT Sat Jun 16 2018/
Today through Sunday...Main challenge today is how much
precipitation will fall over Central MT. The latest GFS keeps the
heavier rainfall more over the Billings area, while the WRF has a
band of heavy rain over Central MT late this morning through this
afternoon. A blend of these solutions looks best, thus an average
of 0.80 to 1.30 is my thinking over Central MT. However, kept the
current internet web image of the higher forecasted rainfall, as
it matches the flood watch and potential of WRF solution, but
some adjustments to the flood watch might be needed later if
precipitation amounts are not as heavy as forecasted. Overall
expect morning rain in Southwest MT to gradually push northward
into Central MT by mid morning and into the highway 2 corridor by
mid afternoon. Snow levels will generally be above 8500 feet, so any
snow impacts should be minor in our area. Expect temperatures just
to rise a few degrees today with clouds/precip. Scattered showers
will continue Saturday night into Sunday, as the upper level low
continues to reside over the region. However, precipitation is not
expected to be as widespread or heavy. Temperatures will moderate a
bit by Sunday afternoon.

For Monday through Saturday...The main upper level low that was
over the region this weekend will slowly begin to dissipate, but
it will take several days. The GFS/EC prog another round or
rainfall over Central MT Monday afternoon into Tue. Some areas
could receive another 0.50 to 1.00 inches. For Tue through
Sat...expect a few scattered showers/thunderstorms each day as an
unstable airmass resides over the region. At this time the threat
for severe storms looks low next week. Temperatures will continue
to moderate slowly each day, possibly going above normal by next
weekend. Brusda

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  54  48  63  51 / 100  60  30  20
CTB  56  45  64  47 /  90  60  30  20
HLN  56  47  63  50 / 100  30  40  30
BZN  59  46  61  47 /  90  30  40  40
WEY  57  38  62  41 /  90  30  70  50
DLN  58  42  61  45 / 100  30  60  50
HVR  62  47  70  50 /  90  50  20  10
LWT  52  44  59  47 / 100  60  40  30

&&

.TFX WATCHES/WARNINGS/ADVISORIES...

Flood Watch from noon MDT today through this evening Cascade...
Chouteau...Eastern Teton...Fergus...Judith Basin...Southern
Rocky Mountain Front.

Flood Watch from noon MDT today through this evening Central and
Southern Lewis and Clark.

&&

http://www.weather.gov/greatfalls

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE GREAT FALLS MT
1239 PM MDT SAT JUN 16 2018

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

1230 PM     HEAVY RAIN       5 SSE ULM               47.37N 111.48W
06/16/2018  M0.50 INCH       CASCADE            MT   TRAINED SPOTTER

            RAINFALL OVER THE PAST 6 HOURS SINCE RAIN
            BEGAN FALLING.

&&

MOLDAN