Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 261105

Area Forecast Discussion
National Weather Service Great Falls MT
505 AM MDT THU MAY 26 2016

Updated Aviation Discussion


Today through Saturday....Mid-upper level circulation center
evident in satellite imagery this morning over NE MT will slowly
edge east into ND by tonight, maintaining a moist and somewhat
unstable cyclonic NW flow aloft across the region today with
shortwave ridging building in from the west tonight. Airmass
destabilization this afternoon will again lead to an increase in
showers and thunderstorms with models indicating greatest coverage
along a corridor from roughly Cut Bank SE to White Sulphur
Springs. Flow aloft and corresponding wind shear is relatively
weak today for primarily pulse type thunderstorms with little or
no thunderstorm organization expected. Next upper level low,
currently upstream with center near Queen Charlotte Island, will
move SE with trough axis extending S into the Pacific NW Friday.
Initial shortwave energy ahead of the trough will move into the
Northern Rockies Friday with the bulk of the shortwave energy
lifting NE across N-central MT Friday night through early
Saturday. Showers and thunderstorms will increase again Friday
afternoon in SW flow aloft with an inverted surface trough
sharpening across central MT. Opposite of today, CAPE values
appear marginal Friday afternoon with somewhat better shear as
winds aloft increase ahead of the trough for just a small chance
of any organized convection Friday afternoon and evening.
Shortwave and upper jet energy lifting NE across the region Friday
night will likely lead to an area of widespread rain across
central/eastern portions of the forecast area with drier air
working in from the west Saturday afternoon. Hoenisch

Saturday night through Thursday...From Saturday night through early
Monday morning, an upper level trof will swing through the northern
portions of the region and then gradually move east of the region.
Thus there will be a chance for showers early in the period, but
some dry conditions are possible late Saturday night and into Sunday
morning, before isolated showers/thunderstorms redevelop on Sunday
afternoon. For Monday through Wednesday, significant differences
have developed in the models from the GFS/EC. The GFS progs
moderate/heavy precipitation to move through Central MT Monday
afternoon thru Tue, while the EC is significantly less. For now, I
have blended the solutions, with more confidence given to the EC
solution. The precipitation gradually exits the region on Wednesday,
with weak upper level ridging trying to build over the region by
next Thursday. Thus precipitation chances on Thur are confined
mainly to the western mountains. Temperatures will generally be
below normal through the period, with Tuesday being the coolest day,
but temperatures will start to warm to near normal by next Thursday
as the upper level ridge starts to rebuild. Brusda


A moist and somewhat unstable NW flow aloft continues across the
region today with upper level low centered over eastern MT, drifting
east tonight. Isolated showers this morning will increase in
coverage this afternoon with a few weak thunderstorms also possible.
VFR conditions will generally prevail with some localized MVFR and
mountain obscuration in the vicinity of showers/thunderstorms. The
airmass stabilizes this evening for decreasing precipitation with
drier air moving in from the west as well. Surface winds remain
generally light and below 10kts with a few gusts in excess of 15 kts
near showers and thunderstorms. Hoenisch


Today thru Sunday...Scattered showers/thunderstorms are expected
over the region from today through Sunday, but precipitation amounts
will generally be light and no hydro issues are expected.

Monday through Tuesday...The GFS/EC show significant differences in
precipitation from Monday afternoon through Tuesday night. The GFS
progs widespread rainfall of 1 to 3 inches over Central MT, while
the EC is much lighter, generally less than 0.50 inches. In
coordination with WPC, the forecast leans towards a bend, with more
weight towards the EC model. However, continue to monitor later
forecast and updates on any changes that could lead to the potential
for hydrologic highlights early next week. Brusda


GTF  65  44  62  41 /  50  30  60  60
CTB  64  41  61  38 /  60  40  30  40
HLN  66  45  62  41 /  50  30  50  60
BZN  65  41  62  40 /  40  30  60  60
WEY  56  35  55  33 /  50  30  30  30
DLN  63  41  58  37 /  40  30  60  60
HVR  67  45  68  44 /  20  10  50  60
LWT  63  43  63  42 /  30  20  60  70



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