Scientific Forecaster Discussion

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Area forecast discussion 
National Weather Service Great Falls Montana
950 am MDT Thu Apr 24 2014

Update...
a weather disturbance and diffluent southwest flow aloft will
overspread the area this afternoon. Widespread showers will push
onto the Continental Divide and over the mountains of southwest
Montana. Moisture and instability will work against downsloping
effects to bring some showers into the plains and valleys this
afternoon. Have adjusted probability of precipitation up over the mountains and southwest
valleys today. Also have expanded mention of precipitation across
the plains and increased probability of precipitation over the High Plains. The rest of
the forecast looks on track for today with temperatures warming to
near seasonal averages. Langlieb

&&

Aviation...
updated 1135z.
Weak ridge over the region will move east today as shortwave energy
moves toward the northern rockies today. Increasing mid and high
level clouds are expected through the morning hours with isolated to
scattered showers develop over southwest Montana and southern
portions of central Montana after 18z. Showers will diminish after
00z Friday with skies clearing over north central Montana. Mpj

&&

Previous discussion...
/issued 535 am MDT Thu Apr 24 2014/

Today through Saturday...an active westerly flow aloft continues
over the region with water vapor satellite imagery this morning
showing a shortwave trough moving into the Pacific northwest coast with
additional shortwave and upper level jet energy upstream of this
trough over the eastern Pacific. Trough along the West Coast this
morning will weaken as it moves across a weak ridge in place over
the northern rockies this afternoon, but will bring increasing
cloud-cover to the region this morning with good chance for
showers this afternoon as the upper level energy and Pacific
moisture move across the area. A drier period is expected tonight
before the previously mentioned upstream trough digs into the
western US and amplifies Friday and Saturday. Flow aloft turns to
the SW ahead of the trough on Friday with moisture and instability
increasing by Friday afternoon. The first piece of energy rotates
north across across Montana late Friday/Friday night with another
lifting north through the area on Saturday. Showers and possibly a
few isolated thunderstorms develop over SW Montana Friday afternoon
which evolves into an area of widespread precipitation that lifts
north across central and north central Montana Friday night. A brief
period of little activity is expected Saturday morning before the
second wave moves through the region later on Saturday, taking a
slightly more eastern trajectory through central Montana. Hoenisch

Saturday night through Thursday...medium range models are in good
agreement for the early portion of the forecast period. Southern
portion of an upper level trough over the western USA is expected to
move slowly east-northeast Saturday night through Monday night and
gradually forms a cutoff low over the Great Plains. However, the
northern portion of this trough remains anchored along the British
Columbia coast forming a negative tilt trough that keeps the
northern rockies in an unsettled northwesterly flow aloft. This
pattern is expected to keep temperatures generally near seasonable
averages with showers lingering over the forecast area. Have updated
the forecast to increase pops for Saturday night and Sunday then
kept isolated to scattered pops in place through Tuesday. By Tuesday
night models begin to inch the closed low further east and build a
positive tilt ridge into the northern rockies. This is similar to
what was shown by the European model (ecmwf) for early to mid week last night but
models are now showing more of a dry northeast flow transitioning
into a better likelihood for western Montana to come under the
influence of the ridge axis. Have gone with a somewhat drier
forecast for Tuesday night through Thursday with model guidance in
better agreement in a slow warming trend. Mpj

&&

Preliminary point temps/pops...
gtf 57 35 58 39 / 30 10 50 80
ctb 56 31 56 35 / 40 10 10 80
hln 58 37 58 39 / 50 20 60 80
bzn 59 35 59 37 / 40 20 50 60
wey 48 32 49 32 / 50 50 60 60
dln 55 35 55 37 / 50 30 50 60
hvr 62 34 63 39 / 20 20 10 70
lwt 57 32 56 37 / 30 20 40 80

&&

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

$$



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