Severe Thunderstorm Warning 23, NWS Great Falls, MT

Area Forecast Discussion
National Weather Service Great Falls MT
525 PM MDT Wed Jun 26 2019

AVIATION SECTION UPDATED...

.SYNOPSIS...

Unstable southwesterly flow aloft and embedded disturbances affect
our region through this weekend. Scattered to numerous showers and
thunderstorms are expected today and Thursday. Some of these storms
will likely become severe. Isolated to scattered showers and
thunderstorms are then forecast for Friday through this weekend.
Temperatures should be near or slightly below-normal.

&&

.DISCUSSION...

Remainder of today through tonight...After a relatively slow start,
showers and thunderstorms are beginning to develop. Moisture is still
lacking a bit, with surface dewpoints in the 40s and low 50s but this
should change as the low level easterly flow begins to advect ample
moisture into the region. At the same time, surface based cape values
and mid-level lapse rates have crept up to 1000 to 1500 j/kg and the
7 to 8 degree C/km respectively. These factors combined with good
wind shear has resulted in a severe thunderstorm watch being issued
for a good portion of our CWA until 10pm tonight, which includes
Gallatin, Jefferson, Broadwater, Meagher, Lewis and Clark, Cascade,
Judith Basin, Fergus, Teton, and Choteau Counties. Also, a flash
flood watch has been issued for the Alice Creek and Park Creek burn
scars in Central and Northern Lewis and Clark County until 11pm
tonight as there will be a potential for flooding should a storm
with heavy rain become situated over this area. Severe weather
threats include, hail to the size of a lime and damaging wind gusts
of 60 to 70 mph for this afternoon and evening. Conditions should
temporarily calm down tonight but the severe threat reemerges
tomorrow as an even more unstable atmosphere allows severe storms to
produce hail as large as quarters to perhaps baseballs and damaging
wind gusts of 70 to 80 mph or greater. A few tornadoes cannot be
ruled-out, especially during the late afternoon and early evening
hours, mostly for portions of Blaine and Fergus Counties. rcg

Friday through Sunday...Southwesterly flow aloft and embedded
shortwave disturbances continue to affect our CWA as we remain east
of the longwave trough axis. The embedded mid- to upper-level low
pressure center may eject northeastward from the Pac NW to northern
MB by the end of the period. Simultaneously, the aforementioned
longwave high pressure ridge persists over the central U.S. and
vicinity. The shortwave disturbances will assist in the development
of isolated to scattered showers and thunderstorms daily. In
addition, moderate instability and strong vertical wind shear may
allow a few severe thunderstorms to affect far-eastern portions of
north-central MT on Friday. Temperatures remain near or slightly
below-normal.

Next Week Monday through Wednesday...Compared to 24-hours ago,
ensemble means are in much better agreement that our CWA will remain
east of the longwave trough axis over/near the Pacific NW and
western Canada, allowing southwesterly flow aloft and embedded
shortwave disturbances to persist over north-central and southwest
MT. Isolated to scattered showers and thunderstorms are possible on
a daily basis, especially during the afternoon and evening.
Temperatures should remain near or slightly-below normal.
- Jaszka

&&

.AVIATION...
Updated 525 PM MDT Wed Jun 26 2019 (00Z/27 TAF issuance)

Mostly VFR conditions for the next 24-hours except during shower and
thunderstorm activity. Scattered showers and thunderstorms should
begin to diminish after 4Z although a few showers will be possible
beyond that time. Showers and storms redevelop Thursday morning into
the afternoon and some of these have the potential to become severe
once again, especially in central and north-central MT. Hail (up to
1 inch in diameter or greater)and erratic surface wind gusts of 60
knots are the main severe threats, as are heavy downpours of rain.
rcg

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  51  76  51  74 /  80  80  70  30
CTB  47  70  45  71 /  60  80  70  20
HLN  50  80  52  77 /  30  60  60  30
BZN  47  81  49  79 /  30  20  10  10
WEY  38  73  40  73 /  30  10  10   0
DLN  46  75  48  72 /  20  30  20  10
HVR  51  79  52  77 /  80  50  80  30
LWT  48  77  50  74 /  80  40  40  50

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
Flash Flood Watch until midnight MDT tonight Central and
Southern Lewis and Clark...Southern Rocky Mountain Front.

&&

http://www.weather.gov/greatfalls

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