Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 232030

Area Forecast Discussion
National Weather Service Great Falls MT
230 PM MDT MON MAY 23 2016


Tonight through Wednesday...A low pressure trof continues to affect
Central and Southwest Montana and water vapor pics show a very moist
airmass still moving across the area. Dynamics will remain weak
through Wednesday although a disturbance will rotate around the
upper level low tonight. An associated push of cool, moist air will
cross the border early this evening and some showery activity will
linger. Weak instability will develop Tuesday with afternoon showers
but any thunderstorm activity will be very isolated. Temperatures
continue to trend warmer through Wednesday and the airmass again
will become unstable during the afternoon...and with a better chance
of thunderstorms. However, CAPE and shear values indicate little
chance of severe development. Temperatures will be trending higher
through Wednesday but still remain below seasonal normals. Zelzer

Wednesday night through Memorial Day...A broad upper level trough
remains in place across western N America late this week through the
upcoming weekend. Initially, only weak shortwave energy moving
through a NW to W flow aloft Wednesday night through Thursday will
bring a chance of mainly afternoon and evening convective
precipitation with temperatures near seasonal averages Thursday.
Friday through the upcoming holiday weekend, models are in large
scale agreement to bring an upper level low south from the Gulf of
AK into the PAcific NW and gradually have this system edge east
toward the Northern Rockies late this weekend into early next week.
In general, this will bring increasing precipitation chances to the
region and somewhat cooler temperatures as the flow aloft becomes
southerly Friday and Saturday and likely continues through much of
the upcoming weekend as the upper low approaches.
Differences in smaller scale details however increase through the
upcoming weekend as the GFS keeps the upper low center farther west
over the Pacific NW through much of the weekend while the ECMWF and
CMC models take the system into northern Rockies/across MT
respectively much earlier in the weekend. Hoenisch



Latest water vapor loop shows an upper level low drifting slowly
eastward across southern Saskatchewan at this time. Low/mid level
moisture continues to pinwheel around it across our forecast area.
Within this regime, scattered showers will continue to move slowly
E/SE through this evening before a gradual decrease in coverage
occurs. Some models bring additional showers into the area again
Tuesday morning, but confidence in the location/occurrence of the
next round of showers is more uncertain at this time. Through this
evening, lower cigs/mtn obscurations can be expected. CIGS may lift
some across SW MT by Tuesday morning, but are expected to remain
lower across central MT. Instability today should be confined to far
SW MT with KBZN have the best chance of seeing a thunderstorm. Even
there, though, confidence was too low to include in the TAF for now.


Scattered showers will continue over the region for the next few
days. No new additional flooding is expected at this time as
rainfall totals generally remain less than one inch.
However...models suggest another wet system will affect the region
next weekend. Thus some hydrologic highlights might be needed for
portions of the region and an Hydrologic Outlook has been issued
to highlight this event.


GTF  39  58  40  65 /  50  30  20  20
CTB  37  57  37  65 /  50  30  20  20
HLN  41  60  43  65 /  40  40  30  30
BZN  37  60  39  61 /  40  40  30  40
WEY  30  52  34  50 /  30  40  50  60
DLN  37  58  39  58 /  30  50  40  50
HVR  40  60  41  68 /  30  30  10  20
LWT  39  57  40  62 /  40  40  30  50



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