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000
FXUS65 KTFX 070459
AFDTFX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
1000 PM MST Thu Mar 6 2014

.UPDATE...
Made some significant changes to the forecast for tonight.
Temperatures have been running much cooler across north central
and central Montana this evening than previously expected. Have
therefore lowered low temperatures there mostly into the single
digits above zero. Models are also forecasting that the cold air
will also spread somewhat into the Helena valley area, so have
lowered low temperatures there to around 20 degrees. There is the
potential for temperatures to drop into the teens there, but it
would take an aggressive push of colder air, which seems less
likely. Have also increased the chance for precipitation overnight
(mainly after midnight) across the entire area, as precipitation
seems to be more widespread west of the Divide and into the Idaho
Panhandle. I believe that this precipitation should hold together
as it moves over the area. Am not expecting significant amounts of
precipitation, but there will likely be widespread activity. While
most of the precipitation will be in the form of snow, it will
begin as more of a rain-snow mix across southwest Montana (where
temperatures are still above freezing in many locations). Also,
the forecast model soundings keep a bit of a warm layer aloft
across central Montana (including the Great Falls and Helena
areas) so I have added a slight chance of freezing drizzle and
sleet to this area overnight. Although it will likely not be as
widespread or as accumulating as what happened last night into
this morning, it warranted a mention for the potential for slick
spots on roads come morning. However, warmer air and increasing
winds tomorrow should help melt any of these slick spots. This
period of snowfall will likely bring some additional accumulations
to the Rocky Mountain Front, so will also leave the Winter Weather
Advisory in place for tonight.
Coulston

&&

.AVIATION...
UPDATED 0500Z.
An upper level disturbance will move through central Montana tonight
and bring another period of light precip into the area. Ample low
level moisture will remain across central and northern portions of
region. This will cause areas of MVFR/IFR conditions due to cigs,
vsbys, and snow.  Weak high pressure will build Friday and gusty
west winds will develop across the Rockies and adjacent plains
during the afternoon.

&&

.HYDROLOGY...
Recent precipitation has combined with rapid snowmelt across
portions of southwest and central Montana to cause areas of
flooding. There have been numerous reports of water running over
roadways and threatening structures. In fact, the portion of U.S.
Highway 87 from Stanford to Eddie`s Corner in Judith Basin County
for much of this evening, causing traffic to be detoured. After
calls with emergency management officials, areal flood warnings
were issued for Lewis and Clark County and Gallatin County, while
areal flood advisories were issued for Jefferson, Broadwater,
Madison, and Judith Basin Counties. All of these flood statements
are in effect until at least Friday afternoon, or until the
flooding situation improves. River levels are also rising in many
of these same areas. While most are not threatening to exceed
flood stage at this time, the situation will continue to be
monitored for possible highlights for these individual river
points.
Coulston

&&

.PREV DISCUSSION...
/ISSUED 426 PM MST Thu Mar 6 2014/
Today through Saturday...A strong temperatures gradient continues
to wash back and forth across central Montana as a cold front
continues to dominate the area. Locations south of the boundary
have reported widespread snowmelt and areal flood advisories and
warnings are in place. North of the boundary freezing rain has
moved off...however untreated surfaces will remain slippery. A
second upper level disturbance will move through area and push the
cold front south well out of the area. Moist air continues to flow
over the divide...and will continue through Friday morning. Have
kept the winter weather advisory for snow and blowing snow along
the Rocky Mountain Front in effect with additional accumulation of
less than 3 to 6 inches near pass level and 6 to 12 inches above
pass level. Relatively dry conditions will persist Friday
through Saturday. However warming will return Saturday and could
cause an increase to flooding concerns as warm temperatures
continue to cause additional snowmelt. Suk

Saturday night through Thursday...Medium range models are in decent
agreement to start the period. The upper ridge gets flattened
Saturday night as short wave energy moves across the divide embedded
within the fast westerly flow aloft. The downslope winds will keep
the plains dry and confine precipitation to the western and
southwest mountains. A stronger upper trof moves to western Montana
on Monday bringing widespread mountain showers and isolated showers
over the plains. A strong upper ridge builds over the west coast on
Tuesday allowing an upper trof to slide down the front of the ridge.
The models offer differing solutions for this feature with the GFS
keeping the bulk of the precipitation across southwest Montana and
eastern Idaho. The European model has the strongest energy well east
of the area, over the upper Midwest. Regardless, both models do
paint scattered showers across the area. The upper ridge builds over
the inter-mountain west on Wednesday but a somewhat unstable
northwest flow aloft will provide isolated showers. The European
model brings another upper trof to western Montana Thursday while
the GFS maintains a somewhat dry northwest flow aloft. Have gone
with some precipitation over the southwest while keeping dry
conditions across the central and northern portions of the county
warning area. Temperatures will remain above seasonal averages
Sunday and Monday but will cool to near seasonal averages Tuesday
through Thursday.

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF   5  43  29  51 /  60  10  10   0
CTB   2  39  26  47 /  60  10  10   0
HLN  20  42  24  47 /  60  20  10   0
BZN  29  44  22  47 /  60  30  20   0
WEY  24  39  12  41 /  60  50  20  10
DLN  26  41  20  44 /  50  20  10  10
HVR   5  30  17  47 /  60  30  10   0
LWT   7  39  25  49 /  60  20  10   0

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
WINTER WEATHER ADVISORY until 5 AM MST Friday FOR ELEVATIONS
ABOVE 5000 FEET FOR Northern Rocky Mountain Front...Southern
Rocky Mountain Front.

AREAL FLOOD WARNINGS are in effect for Lewis and Clark, and
Gallatin Counties until Friday afternoon.

AREAL Flood Advisories are in effect for Madison, Jefferson,
Broadwater, and Judith Basin Counties until Friday Afternoon.

&&

$$


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