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Area forecast discussion 
National Weather Service Great Falls Montana
520 PM MDT sun Apr 20 2014

Update to aviation

Discussion...

Tonight through Tuesday...weak instability and isolated showers
are possible this afternoon in hill and Blaine counties behind
the shortwave trough that moved across the area last night.
Otherwise, dry conditions are expected through Monday as an
upper-level ridge builds into the area. Temperatures will continue
warming on Monday with highs 5 to 10 degrees above seasonal
averages. West-southwesterly winds will remain breezy this
afternoon, however the potential for high winds has diminished
along the Rocky Mountain front and adjacent plains so have
cancelled the High Wind Warning. Winds will diminish tonight. The
ridge axis will shift east Monday night as a deepening Pacific
trough of low pressure pushes into the Pacific northwest. As this
trough moves inland, shortwave energy coupled with an upper-level
jet will push into the northern rockies on Tuesday yielding
increasing Pacific moisture and instability. Have increased pops
along the Continental Divide Tuesday afternoon with showers
developing and becoming widespread by Tuesday evening. Isolated
thunderstorms are also expected with the best chance over central
and southwest Montana. Mlv

Tuesday night through Sunday...the main message during the period is
models have gotten into better agreement with the midweek system in
comparison to a day ago. The latest European model (ecmwf) run is much stronger with
the system than previous runs and is more like what the GFS has been
advertising as far as strength GOES. On the other hand the GFS is
farther north with the system and is more like the European model (ecmwf) in this
regard. Models forecast a weather disturbance aloft to lift
northeast through the area Tuesday night as a surface cold front
moves east. As has been advertised this period should see the
greatest precipitation. An upper low will develop over southeast
Alberta or southwest Saskatchewan by late Wednesday though the GFS
is a little farther south. The westerly flow aloft and at the
surface on the south side of the upper low will lead to downslope
effects and have lowered chances of precipitation for some areas as
well as precipitation amounts. Then for Wednesday night the
circulation on the back side of the upper low should spread
precipitation south into north central and central Montana and have
increased the chances of precipitation for those areas.
Precipitation should then diminish as an upper ridge moves into
central Montana Thursday night. Thereafter southwest flow aloft will
develop and moisture will increase. Due to model differences with
regard to precipitation details did not go real high with the
chances of precipitation but did raise inherited values a little.
Blank

&&

Aviation...
updated 2320z.
VFR conditions will prevail for the next 24 hours. Winds will be
gusty across the area through the evening hours. Winds will
gradually decrease after sunset. Light winds will develop tonight
and will remain in place through much of Monday as a ridge of
high pressure moves into the area. Suk

&&

Hydrology...
expect increased snow melt Monday through Tuesday as snow levels
rise to between 7500 and 8500 feet by Tuesday. With better agreement
amongst the models regarding precipitation details it now looks like
most lower elevations will receive from 0.4 inch to 0.7 inch
precipitation with mountains receiving from 0.7 inch to a little
over an inch with the bulk of the precipitation falling Tuesday
afternoon and Tuesday night. The convective nature of precipitation
Tuesday evening could result in localized heavier amounts than those
listed above. The threat for flooding will increase early next week
with increased snowmelt followed by widespread precipitation Tuesday
afternoon and night. For Wednesday and Thursday, cooler temperatures
and lower snow levels should reduce runoff from snowmelt at higher
elevations. Blank

&&

Preliminary point temps/pops...
gtf 34 69 45 69 / 0 0 10 70
ctb 31 66 39 64 / 0 0 10 60
hln 37 70 44 66 / 0 0 10 70
bzn 32 71 41 69 / 0 0 20 60
wey 30 60 36 57 / 0 0 30 70
dln 33 69 42 62 / 0 0 20 70
hvr 31 70 41 75 / 0 0 0 20
lwt 31 66 42 70 / 0 0 10 40

&&

Tfx watches/warnings/advisories...
none.
&&

$$



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