Hail and Damaging Winds in Montana, June 21, 2016

Area Forecast Discussion
National Weather Service GLASGOW MT
329 PM MDT TUE JUN 21 2016

.SHORT TERM...for northeast Montana...tonight through Thu...
...A few severe thunderstorms capable of producing large hail and
damaging winds are expected this afternoon and evening across
portions of northeast Montana...

Thunderstorms beginning to develop across northcentral Montana
with expectation of strengthening as they move east through this
evening. Strong east winds occurring ahead of the frontal system
associated with the thunderstorm potential. These winds will turn
west and continue to be gusty behind the front tonight.

High pressure will settle into the region for Wednesday and
Thursday bringing drier weather conditions. Ebert

.LONG TERM...Thu night through Tue...

An upper low pressure system, currently spinning in the Gulf of
Alaska will make its way to just off the Washington/Oregon Coast
Thursday evening. Anchored by a dome of hot air over the
Southwest, an upper ridge pushes north through the Plains with the
axis along the Montana/Dakota border. This will give Northeast
Montana a zonal to slightly southwest flow aloft.

By Friday afternoon the trough will have moved into the Northern
Rockies. This will establish a strong southwest flow over the
local area that will bring in moisture. The associated frontal
boundary sweeps across the area Friday evening through unstable
air. Expect thunderstorms to develop that will move into North
Dakota. Severe thunderstorms with large hail and strong winds will
be possible.

Saturday the low blows through the local area. Timing is still not
set, with the EC faster, and farther north and east, than the
GFS. The location of the low is important to the forecast, since
it will determine wind strength and rain totals. In either case
Saturday is expected to cool down to well below normal, rebounding
to near normal on Sunday. Both the EC and the GFS suggest the
storm stacking up with the closed surface low Saturday night.

Few significant grid edits were necessary, mainly for
coordination and blending in the latest guidance, mainly to
increase Friday/Saturday pops.

Templer

Previous discussion:
Upper level ridge moves to the east Thursday Night. Flow aloft
turns to the southwest as an upper low moves inland from the
Pacific. A weak frontal system moves through the area late
Thursday Night with limited moisture. Will keep forecast dry.

The upper low moves to Western Montana by Friday afternoon.
Meanwhile, a strong cold front moves through Eastern Montana
Friday evening. The system bring enough moisture and instability
for a good chance of thunderstorms.

Models differ somewhat on the movement of the upper low across
Montana and Saskatchewan on Saturday as it becomes stacked with
the surface low. ECMWF track is faster and north of the GFS track.
As a result, EC limits wrap around precip to Saturday while the
GFS extends it through Sunday Morning. There are also differences
in timing of dry slots on Saturday. Will broadbrush a chance of
showers and thunderstorms for most of the weekend and dry most of
the area out by Sunday Afternoon. Both models have a tight
surface gradient on Saturday which will result in gusty west to
northwest winds.

Surface high will move into the area Sunday Afternoon. The next
shortwave trough is expected on Monday with a slight chance of
thunderstorms. A shortwave ridge will bring mainly dry weather on
Tuesday. Forrester

&&

.AVIATION...

A quick moving trough traveling east just north of the Hi-Line
will generate rain showers and thunderstorms this afternoon and
evening. Some of the thunderstorms may become severe with large
hail and damaging winds. Expect TAF amends as storms develop with
temporary MVFR/IFR conditions. The terminals at greatest risk
appear to be KOLF and KSDY, with lesser chances for KGGW and KGDV.

The Storm Prediction Center has issued a Severe Thunderstorm Watch
this afternoon through mid evening.

The frontal passage of this storm will occur in late afternoon or
early evening, the result will be a wind shift from easterly of
15-20kt to westerly of similar strength.

Wednesday winds will veer to the north and diminish in strength
through the day. Models are showing low status clouds in the
morning that will clear in the afternoon.

Templer

&&

.GLASGOW WATCHES/WARNINGS/ADVISORIES...
Lake Wind Advisory until 4 AM MDT Wednesday For Fort Peck Lake
for Central and Southeast Phillips...Central and Southern
Valley...Garfield...McCone...Petroleum.

&&

weather.gov/glasgow

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE GLASGOW MT
322 AM MDT TUE JUN 21 2016

MTZ016>027-059>062-220930-
CENTRAL AND SOUTHEAST PHILLIPS-CENTRAL AND SOUTHERN VALLEY-
DANIELS-SHERIDAN-WESTERN ROOSEVELT-PETROLEUM-GARFIELD-MCCONE-
RICHLAND-DAWSON-PRAIRIE-WIBAUX-NORTHERN PHILLIPS-
SOUTHWEST PHILLIPS-NORTHERN VALLEY-EASTERN ROOSEVELT-
322 AM MDT TUE JUN 21 2016

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF NORTHEAST
MONTANA.

.DAY ONE...TODAY AND TONIGHT

SCATTERED SHOWERS AND THUNDERSTORMS ARE EXPECTED THIS AFTERNOON
AND EVENING. A FEW STORMS MAY BE SEVERE WITH LARGE HAIL AND
DAMAGING WINDS. LOCALLY HEAVY RAIN IS ALSO POSSIBLE WITH ANY
STORMS.

GUSTY NORTHWEST WINDS ARE EXPECTED THIS AFTERNOON INTO TONIGHT
WITH A COLD FRONTAL PASSAGE. A LAKE WIND ADVISORY IS IN EFFECT FOR
FORT PECK LAKE FROM 2 PM TODAY THROUGH 4 AM WEDNESDAY MORNING.

.DAYS TWO THROUGH SEVEN...WEDNESDAY THROUGH MONDAY

A STRONG STORM SYSTEM IS EXPECTED TO MOVE OVER THE AREA FRIDAY
AND SATURDAY. THERE IS A GOOD CHANCE OF THUNDERSTORMS FRIDAY
AFTERNOON... FRIDAY NIGHT AND SATURDAY. STRONG WEST TO NORTHWEST
WINDS ARE LIKELY FRIDAY NIGHT AND SATURDAY WHICH COULD MAKE
BOATING HAZARDOUS ON FORT PECK LAKE.

.SPOTTER INFORMATION STATEMENT...

WEATHER SPOTTERS ARE ENCOURAGED TO REPORT SIGNIFICANT WEATHER
CONDITIONS ACCORDING TO STANDARD OPERATING PROCEDURES.