Area Forecast Discussion
Issued by NWS Great Falls, MT

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870
FXUS65 KTFX 251601
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
1001 AM MDT Wed Apr 25 2018

.UPDATE...
Updated forecast is out. A fast moving Canadian cold front is
moving southward into North Central MT this morning. The front has
gone through Cut Bank and should arrive in Great Falls around
1130 AM. With cloud cover, lowered temperatures a few degrees
over the north, kept them the same over Southwest MT. Kept pops
out until this afternoon. Otherwise the rest of the forecast is on
track. Brusda

&&

.SYNOPSIS...
An upper level ridge of high pressure will reside over the region
for Thursday and Friday, resulting in very nice spring conditions
over the region. Afternoon highs will climb into the 70s and 80s.
However another spring storm will move into the region over the
weekend, with showers and thunderstorms on Saturday, followed by
widespread rain and high mountain snow for Sunday and Monday.

&&

.AVIATION...
Updated 1600Z.
A cold front will continue to move southward through the region.
Expect a wind shift to the north with a few scattered rain showers
this afternoon. Clearing skies with light winds and VFR
conditions are expected later tonight and through the day on
Thursday. Brusda

&&

.HYDROLOGY...
The areal flood advisory continues for Meagher/Glacier counties
and the areal flood warning for Hill/Blaine counties continue.
The water is receding in most areas outside of Blaine county, and
some adjustments are possible later today.

The point flood warnings also continue for the Milk River near
Harlem. It will take several more days before the Milk River
falls below flood stage.

Afternoon temperatures in the 70s to near 80 degrees later this week
will cause snowmelt to increase out of the mountains, which could
impact nearby creeks/streams. Scattered showers/thunderstorms are
also expected over the weekend, with the potential for a
significant spring storm early next week. This storm could produce
more widespread flooding impacts over the region. Brusda

&&

.PREV DISCUSSION...
/ISSUED 528 AM MDT Wed Apr 25 2018/

Today and tonight...main forecast concerns/impacts is a fast moving
clipper system that will bring a significant wind shift and light
precipitation to portions of the region.

Upper level ridging over the Northern Rockies this morning, will
quickly breakdown as a fast moving shortwave dives southeast from
Alberta. As the surface low moves across Southern Canada this
morning and afternoon, a cold front will drag from northwest to
southeast across Northern Central and into Southwest Montana. While
this system has favorable divergence/lift and moisture in the
mid/upper levels (PWATS of generally 0.35" to 0.55"), BUFKIT
analysis shows very dry air residing in the boundary layer
throughout the day. This dry air is due to dry downsloping
southwesterly winds, which will be experienced across most of North
Central Montana prior to the cold frontal passage. As the cold front
passes, winds will quickly turn to the northwest/north. 3hr pressure
rises 2.5mb to 5mb combined with steep lapse rates and mechanical
mixing from the passage of the front will create a period of
breezy/gusty winds. Some light rain showers will be possible with
and after the passage of the cold front, however, QPF amounts are
expected to very light.

Thursday through Saturday morning...main forecast concerns are
temperatures.

Upper level ridging quickly builds back into the Northern Rockies
during the day on Thursday, amplifying and persisting over the
region through the morning hours on Saturday. 1000mb-500mb thickness
values climb to around 5700m on Friday and Saturday, which would
result in widespread high temperatures in the 70s/80s at lower
elevations and 50s/60s in the mountains. Low temperatures Thursday
night and Friday night will be very mild, with most mountain
locations remaining at or above freezing. The combination of
bountiful sunshine and these warm temperatures, will lead to
increased snowmelt at mid-slope and possibly higher elevations (as
melting levels climb to 9500ft to nearly 11000ft). More details
regarding hydrology concerns can be found in the hydrology section.

Saturday afternoon through Tuesday night...main forecast concerns is
the potential for a significant warm and wet storm.

Large and potent upper level low moves from Northern California and
into the Northern Rockies from Saturday afternoon and through the
day on Monday. This system will have the potential to bring
significant QPF to the Rocky Mountain Front, Central Montana
mountains, and North Central Montana. Very, very preliminary QPF
totals (most if not all of which would fall in the form of rain) of
0.5"-1" appear possible across the plains of North Central Montana
and over the mountains of Central Montana, with 1" to 2" possible
along the Rocky Mountain Front/over the Continental Divide. Given
that temperatures will be warm leading up to and during most of this
event, significant hydrology concerns could arise by early next
week. Future shifts will need to closely monitor this event, as it
could bring rapid snowmelt flooding to the region. - Moldan

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  58  31  70  38 /  20  20   0   0
CTB  58  28  71  34 /  20  10   0   0
HLN  66  34  72  40 /  10  20   0   0
BZN  64  28  69  33 /  10  30   0   0
WEY  55  22  59  23 /  10  20   0   0
DLN  68  32  68  33 /   0  10   0   0
HVR  57  30  69  36 /  20  20   0   0
LWT  60  30  63  37 /  20  30   0   0

&&

.TFX WATCHES/WARNINGS/ADVISORIES...

Areal Flood Warnings continue for Hill and Blaine Counties until
further notice.

A Flood Warning remains in effect for the Milk River near Harlem
until further notice.

Areal Flood Advisories continue for Glacier and Meagher Counties
until further notice.

&&

$$

http://www.weather.gov/greatfalls



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