Severe Thunderstorm Warning 28, NWS Great Falls, MT

Area Forecast Discussion
National Weather Service Great Falls MT
1131 AM MDT Thu Jun 27 2019

AVIATION SECTION UPDATED...

.UPDATE...

The morning update has been published. Grid edits were kept at
minimum as the current forecast has a good handle on the
situation. Patchy fog was extended for a couple more hours in north-
central sections and some minor edits were made to pops. Still on
track for scattered to numerous showers and thunderstorms to
develop over central and north-central Montana this afternoon and
evening. The current setup has favorable conditions for severe
thunderstorm development in terms of moisture, wind shear, and
jet dynamics. One factor that can slow things down a bit is the
presence of cloud cover this morning, which can impede daytime
heating and instability. However, there should be some periods of
sunshine to get the destabilization process going as the day
progresses and the current dynamics are strong enough to overcome
some lack in diurnal heating. Thunderstorm threats for today will
be large hail (up to the size of quarters or larger), damaging
wind gusts up to 80 mph, heavy downpours, and frequent lightning.
This shower and thunderstorm activity will likely develop over
the Rocky Mountain Front around noon or shortly after and then
spread east and northeast from there. Note that storms could
develop ahead of the main line once the activity begins to take
off. Most showers and storms should move out of the area or
diminish by late this evening.

&&

.SYNOPSIS...

Unstable southwesterly flow aloft and embedded disturbances should
affect our region through the middle of next week. Scattered to
numerous showers and thunderstorms are expected today. Some of these
storms should become severe. After today, isolated to scattered
showers and thunderstorms are possible through the middle of next
week. In addition, a few more severe storms may occur on Friday.
Temperatures should be near or slightly below-normal over the next
seven days.

&&

.AVIATION...
Updated 1130 AM MDT Thu Jun 27 2019 (18Z/27 TAF issuance)

Outside of any shower/thunderstorm activity and lingering low clouds
over KGTF and KCTB, mostly VFR conditions are expected for the next
24-hours. Disturbances embedded within the southwesterly flow aloft
along with other dynamics will produce scattered to numerous showers
and thunderstorms generally between 20Z/Thu and 04Z/Fri, while
isolated lighter showers and thunderstorms are possible before and
after that period. Note that Periods of MVFR/IFR may accompany any
shower or storm. Some thunderstorms are still expected to become
severe this afternoon and early evening, especially in central and
north-central MT. Quarter-size or larger hail and erratic surface
gusts of 50 to 70 knots are the primary severe threats, along with
the potential for heavy downpours. Regional surface winds remain
light outside outflow (i.e. precip-cooled air emanating from any
shower or storm). Lastly, patchy fog may redevelop tonight over the
the North-Central terminals again late tonight along with localized
MVFR/IFR.

&&

.PREV DISCUSSION...
/ISSUED 506 AM MDT Thu Jun 27 2019/

Today...Southwesterly flow aloft and embedded shortwave disturbances
affect our region as our CWA remains east of a longwave trough axis.
A mid- to upper-level low pressure center embedded within this
longwave trough is progged to move north-northeastward from offshore
northwestern OR to near Seattle by the end of today. The
southwesterly flow aloft remains strong over our CWA as the longwave
trough and embedded low interact with a nearly-stationary longwave
high pressure ridge over/near the central U.S. In addition, this
southwesterly flow aloft will continue to tap into abundant moisture
from the Pacific. In the low-levels, flow is expected to be
predominantly easterly, especially in north-central MT, and this
easterly flow will tap into abundant moisture originating over the
Gulf of Mexico. This pattern will contribute to the development of
scattered to numerous showers and thunderstorms, especially this
afternoon and evening, given daytime heating of higher terrain will
be a primary mechanism for initiation of showers and storms.
Unusually-high humidity will allow showers and thunderstorms to
produce downpours. Localized flash flooding may occur today,
particularly where showers and storms manage to train (i.e. follow
the same path). WPC has outlined a marginal risk of flash flooding
for all of north-central MT. However, refrained from issuing a Flood
Watch since there is much disagreement between different higher-
resolution models as to where hourly rain rates may be heavy enough
to cause flash flooding.

Strong vertical wind shear will contribute to the potential of
severe thunderstorms today, especially in north-central MT, where
easterly low-level winds will veer to southwesterly and strengthen
with height, resulting in enhanced vertical wind shear. Some of
these severe storms will likely be supercells (i.e. rotating
thunderstorms). However, partly to mostly cloudy skies may limit
daytime heating and atmospheric destabilization. Even so, SPC still
has nearly the entire CWA highlighted in a risk of severe
thunderstorms, including an enhanced risk (level 3 on a scale to 5)
for much of north-central MT. Suspect there will be enough breaks in
the cloud cover to allow at least moderate instability to
materialize across much of our CWA during this afternoon through
early evening. Hail the size of quarters to perhaps baseballs and
damaging wind gusts of 60 to 80 mph remain the primary severe
threats. However, a few tornadoes remain possible east of I-15 in
north-central MT, especially from Hill County to Judith Basin County
and points east. Here, cumulonimbus cloud bases may be favorably-low
and low-level vertical shear may be sufficiently-strong for a
tornadic supercell or two. The late afternoon through early evening
timeframe should be the preferred window for potential tornadoes.
Temperatures will be near or slightly below-normal.

Friday through next Wednesday...Latest deterministic and ensemble
model guidance is in rather good agreement during this period. Thus,
southwesterly flow aloft and embedded shortwave disturbances should
continue to affect our CWA as the longwave trough axis remains to
our west and the longwave high pressure ridge remains essentially
anchored to our east. Isolated to scattered showers and
thunderstorms are possible daily, especially during the afternoon
and evening hours. In addition, a few severe thunderstorms may
affect eastern portions of the CWA Friday afternoon and early
evening, when moderate instability and strong vertical wind shear
may exist. Temperatures should remain near or slightly below-normal.
- Jaszka

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  74  50  74  51 / 100  70  20  30
CTB  69  45  71  45 /  90  60  10  20
HLN  77  50  77  51 /  80  40  30  20
BZN  81  48  78  48 /  20  20  20  20
WEY  71  38  73  39 /   0   0   0  10
DLN  74  46  73  46 /  30  10  10  10
HVR  80  51  76  51 / 100  90  20  50
LWT  76  48  74  49 /  50  40  50  50

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
None.
&&

http://www.weather.gov/greatfalls

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE GREAT FALLS MT
1111 AM MDT THU JUN 27 2019

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

0548 PM     HAIL             4 ESE WOLF CREEK        46.99N 111.99W
06/26/2019  E0.88 INCH       LEWIS AND CLARK    MT   FIRE DEPT/RESCUE

            FACEBOOK VIDEO OF NICKEL SIZED HAIL COVERING
            THE GROUND AT HOLTER LAKE CAMPGROUND.

&&

JAA

Special Weather Statement
National Weather Service Great Falls MT
133 PM MDT Thu Jun 27 2019

MTZ008-272000-
Beaverhead MT-
133 PM MDT Thu Jun 27 2019

...SIGNIFICANT WEATHER ADVISORY FOR NORTH CENTRAL BEAVERHEAD COUNTY
UNTIL 200 PM MDT...

At 133 PM MDT, Doppler radar was tracking a strong thunderstorm 19
miles west of Divide, or 24 miles southwest of Anaconda, moving
northeast at 55 mph.

Half inch hail and winds in excess of 40 mph will be possible with
this storm.

Locations impacted include...
Wise River.

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 4584 11325 4588 11322 4587 11319 4588 11310
      4586 11308 4581 11300 4580 11293 4569 11311
      4581 11330
TIME...MOT...LOC 1933Z 224DEG 46KT 4581 11314

Moldan

Special Weather Statement
National Weather Service Great Falls MT
141 PM MDT Thu Jun 27 2019

MTZ014-048-272000-
Southern Rocky Mountain Front MT-
Central and Southern Lewis and Clark MT-
141 PM MDT Thu Jun 27 2019

...SIGNIFICANT WEATHER ADVISORY FOR CENTRAL LEWIS AND CLARK AND
SOUTHWESTERN TETON COUNTIES UNTIL 200 PM MDT...

At 141 PM MDT, Doppler radar was tracking strong thunderstorms along
a line extending from 14 miles west of Augusta to 12 miles southeast
of Lincoln. Movement was northeast at 40 mph.

Half inch hail and winds in excess of 40 mph will be possible with
these storms.

Locations impacted include...
Augusta, Nilan Reservoir, Bean Lake and Pishkun Reservoir.

A Severe Thunderstorm Watch remains in effect until 800 PM MDT for
north central and west central Montana.

LAT...LON 4788 11239 4692 11213 4670 11253 4683 11253
      4684 11257 4753 11275
TIME...MOT...LOC 1941Z 222DEG 33KT 4749 11270 4681 11252

Moldan

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