Severe Thunderstorm Warning 65, NWS Great Falls, MT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
503 PM MDT Wed Jul 17 2013

.DISCUSSION...

Tonight through Friday...Convective activity getting started this
afternoon with thunderstorms rapidly developing over west and
southwest Montana in response to an upper trof moving across
northwest Montana and into southern Alberta along with jet streak
energy. Convective parameters are not overly impressive but strong
to severe storms are possible. Additionally, precipitable water
values are very high across the area and may translate to heavy rain
with some storms. Convective activity should end after midnight with
an upper ridge rebuilding over the area Thursday. With a stronger
westerly flow aloft on Thursday, along with favorable mixing,
surface winds will become breezy during the afternoon. As the ridge
axis retrogrades a little to the west on Friday, northwest flow
aloft will develop over the area but conditions will remain dry.
Temperatures will warm to above seasonal averages through the
period. Emanuel

Friday night through Wednesday...Models appear to be in decent
agreement for the early portion of the medium range period. The
weekend starts off with a broad upper level ridge centered over
Nevada and the associated ridge axis extending into British
Columbia. Models indicate that the core of the high pressure system
will move to the California coast while shortwave energy moving over
the top of the ridge brings a dry west to northwest flow aloft to
Montana by Sunday night. Models differ on the strength of this
shortwave but both agree that the airmass will remain dry during
this period. Model solutions diverge beyond the weekend with the GFS
rebuilding the ridge over the Northern Rocky Mountains while the
ECMWF keeps high pressure over the Eastern Pacific and nearly zonal
flow aloft over Montana. Despite these differences in upper air
patterns both models remain dry and warm through the middle of next
week. Have made only minor temperatures to the going forecast for
what appears to be shaping up as a relatively quiet mid summer. mpj

&&

.AVIATION...
UPDATED 2302Z.
Scattered showers and thunderstorms will move east and diminish
during the evening...most storms should be east of KLWT by 08z. Some
storms could have large hail and gusty winds. Dry conditions will
continue through Thursday. MVFR conditions are possible near showers
and thunderstorms this evening...elsewhere VFR conditions will
prevail through the next 24 hours.

&&

.FIRE WEATHER...
Widespread rain and thunderstorms are possible this afternoon and
evening as ample monsoonal moisture, instability and wind shear
combined with an upper-level disturbance move over the forecast
area. Some storms may be strong to severe with strong erratic
winds, hail and locally heavy rainfall, however confidence remains
low with regards to heavy rainfall location and coverage. Over
recent burn areas, heavy rain could cause rapid runoff and/or
debris flows. With better chances of widespread thunderstorms, the
threat for lightning- induced fire starts will increase with
holdover ignitions possibly triggering some fires later in the
week.

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  58  89  54  89 /  40  10   0   0
CTB  56  83  52  84 /  20  10   0   0
HLN  59  90  56  90 /  50  10   0   0
BZN  55  88  51  89 /  40  20  10   0
WEY  45  82  42  83 /  40  20  10  10
DLN  56  87  51  88 /  40  10   0  10
HVR  60  85  55  88 /  20  10  10  10
LWT  57  84  53  84 /  50  10  10   0

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
SEVERE THUNDERSTORM WATCH until 10 PM MDT this evening
Beaverhead...Broadwater...Cascade...Central and Southern Lewis
and Clark...Chouteau...Eastern Glacier...Eastern Pondera...
Eastern Teton...Gallatin...Hill...Jefferson...Judith Basin...
Liberty...Madison...Meagher...Northern Rocky Mountain Front...
Southern Rocky Mountain Front...Toole.

&&

weather.gov/greatfalls

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE GREAT FALLS MT
416 AM MDT WED JUL 17 2013

MTZ008>015-044>055-181030-
BEAVERHEAD-NORTHERN ROCKY MOUNTAIN FRONT-EASTERN GLACIER-HILL-
CASCADE-CHOUTEAU-CENTRAL AND SOUTHERN LEWIS AND CLARK-MADISON-
TOOLE-LIBERTY-EASTERN PONDERA-BLAINE-
SOUTHERN ROCKY MOUNTAIN FRONT-EASTERN TETON-JUDITH BASIN-FERGUS-
JEFFERSON-BROADWATER-MEAGHER-GALLATIN-
416 AM MDT WED JUL 17 2013

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF CENTRAL
MONTANA...NORTH CENTRAL MONTANA AND SOUTHWEST MONTANA.

.DAY ONE...TODAY AND TONIGHT

STRONG TO SEVERE THUNDERSTORMS WITH STRONG TO DAMAGING WINDS...HAIL
AND LOCALLY HEAVY RAIN ARE EXPECTED THIS AFTERNOON AND EVENING.

.DAYS TWO THROUGH SEVEN...THURSDAY THROUGH TUESDAY

THE PROBABILITY IS LOW FOR WIDESPREAD HAZARDOUS WEATHER.

.SPOTTER INFORMATION STATEMENT...

ANY REPORTS OF STRONG WINDS...HAIL AND/OR STORM DAMAGE WOULD BE
GREATLY APPRECIATED AND CAN BE RELAYED TO THE NWS GREAT FALLS OR
LOCAL LAW ENFORCEMENT.

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