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Area forecast discussion 
National Weather Service Great Falls Montana
351 am MDT Friday may 22 2015


Today through Sunday...a broad cyclonic circulation presently moving
ashore over Southern California is forecast to drift slowly
northeast across Utah on Saturday...and eastern Wyoming on Sunday.
The system is nearly equivalent barotropic...providing weak shear
but just enough instability to support widespread general
thunderstorms. Specific to our County Warning Area...afternoon showers and
thunderstorms will continue to remain active over the southwest
given deeper moisture and elevated heating sources over higher
terrain. Small hail and gusty winds will again be possible in a
few of these slow moving thunderstorms...especially Saturday
afternoon as middle- level lapse rates exceed 7 deg/km. Deep-layer
easterly flow continues over north central Montana. This is
associated with drier air and a middle-level inversion that will
suppress development of showers in this area. However...on
Saturday afternoon a subtle inverted shortwave trough rotates
around the parent low to help weaken the inversion and allow
showers and thunderstorms to spread into southern portions of
north central Montana including the Great Falls area. Showers will
be less widespread on Sunday as the primary trough moves further
way into the northern plains. Nutter

Sunday night through Friday...models continue to be in agreement in
a general sense with precipitation trends at least into midweek.
That is shower activity should be mainly isolated Sunday night and
Memorial Day then pick up some into midweek. Within a particular
model there is general consistency from run-to-run but the GFS and
European model (ecmwf) continue to exhibit differences between each other with their
forecasts aloft. Like last night the European model (ecmwf) takes an upper low near
Vancouver Island Sunday night southeast and weakens it as it moves
into central Montana by mid-week. The GFS takes the upper low
southeast ever so slowly and then for a period has it quasi-
stationary before weakening it and moving it into Montana on Friday.
Due to model differences with details of their precipitation
forecasts will go with the broadbrush idea from Tuesday on of
scattered showers except isolated showers towards the Canadian
border. Over the forecast area there will be isolated thunderstorms
during the late afternoon and early evening but do not anticipate
any severe storms at this time. Blank


Aviation... updated 0430z.

Earlier scattered -shra and isolated -tsra from khln to kdln have
dissipated. Not expecting any precipitation at khln/kbzn overnight
though a new round of -shra may develop overnight from kdln
southward as next swath of moisture pushes north from Idaho. Central
Montana will see mostly clear skies tonight and through Friday morning.
East to southeast surface winds will continue through tomorrow and
may be locally gusty at times at the klwt and khvr terminals. Area
of moisture/instability spreads further north Friday afternoon with
scattered showers/isolated thunderstorms possible further north into
north central Montana by Friday evening.


Preliminary point temps/pops...
gtf 69 46 66 43 / 10 20 40 20
ctb 69 41 68 38 / 0 10 20 10
hln 71 47 67 46 / 20 20 70 40
bzn 68 42 63 41 / 30 20 60 40
wey 60 35 58 35 / 50 50 60 30
dln 66 44 64 43 / 30 30 40 30
hvr 73 42 73 41 / 10 20 20 10
lwt 67 45 63 42 / 30 40 50 20


Tfx watches/warnings/advisories...



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