Area Forecast Discussion
Issued by NWS Great Falls, MT

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
000
FXUS65 KTFX 272358
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
558 PM MDT Thu Apr 27 2017

Aviation Section Updated

.DISCUSSION...

Tonight through Friday...Water vapor satellite and model analyses
reveal a complex pattern consisting of three shortwave features
interacting with one another over/around the forecast area.
Precipitation this afternoon has transitioned from showers to
more of a stratiform character with northwesterly upslope low-mid
level flow. Short term guidance suggests precipitation will
continue well into the evening, then gradually taper from west to
east overnight. Snow levels observed around 5000 feet today will
drop overnight, with at least rain/snow mix down below 3500 feet
overnight. Forecast snow amounts of 3-6" are possible over some of
the mountain passes, especially Marias and Kings Hill Passes. Up
to 2" may be possible over other mountain passes. Despite the
snowfall, road surfaces are expected to remain generally wet.
Observed sub-surface temperature remain well above freezing, with
METro model road surface models suggest a short period of of
slushy pre-dawn snow accumulation depending on snow intensity. We
have elected not to issue winter weather advisories for these
mountain passes, but will continue to monitor and adjust as
needed. Rain showers continue on Friday, but with much lower
spatial coverage. Partial clearing could provide sufficient
heating and instability to generate isolated thunderstorms, mainly
south of Helena. Drier air finally begins to work into the area
with height rises late Friday evening. PN

Friday Night through Next Thursday...Unsettled weather will
persist into the upcoming weekend as a longwave upper trough exits
the CWA to the east Friday night into Saturday, while a shortwave
trough dives southeastward into our area Saturday night into
Sunday. For Monday and Tuesday, flow aloft becomes northwesterly
in response to upper ridging building-in from the west, yet
multiple disturbances embedded in the flow look to traverse the
region from northwest to southeast. Thus, scattered precipitation
should persist. By Wednesday and Thursday of next week, a drying
and warming trend is expected for North- Central and Southwest
Montana as the aforementioned ridge continues to build over the
CWA. Lows will tend to be near normal throughout the period. As
for highs, values will remain slightly below normal this weekend
through Tuesday. Highs should then moderate to near or slightly
above normal by next Wednesday and especially Thursday. Jaszka


&&

.AVIATION...
Updated 2358Z.

A moist, low to mid level NW flow aloft combined with several
shortwaves in the area will keep SHRASN going into this evening for
most of the forecast area. Showers will be accompanied by lower
CIGS/VIS at times. Most terminals have seen reductions to MVFR at
times and this general trend is expected through tonight. That said,
CIGS/VIS could briefly fall to IFR/LIFR conditions with any heavier
shower that develops (note the recent VIS at KEKS that fell to 1/4SM
in a heavier snow shower). Conditions may begin to improve across
central MT by Friday afternoon as slightly drier air tries to work
in from the north. As has been mentioned in previous discussions,
this showery pattern is generally a lower confidence one as it is
more difficult to forecast aviation impacts with greater
specificity. Amendments are likely through the period. Martin

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  33  49  31  56 /  70  40  10  10
CTB  31  48  31  52 /  70  30  20  20
HLN  34  52  33  57 /  40  40  20  20
BZN  31  47  29  54 /  50  60  20  20
WEY  24  39  22  43 /  50  40  10  10
DLN  29  47  29  52 /  30  40  20  10
HVR  34  54  33  58 /  60  20  10  20
LWT  32  45  28  52 /  80  60  10  30

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
None.
&&

$$

weather.gov/greatfalls



USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.