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FXUS65 KBYZ 202129

Area Forecast Discussion
National Weather Service Billings MT 
329 PM MDT Tue Mar 20 2018

.SHORT TERM...valid for Wed and Thu...

Building ridge in advance of deepening low off the Pacific coast 
will bring a warming trend through Thursday. Warmest temps will be
along our western foothills where snow cover has diminished. 
Large area of lingering deep snow cover east of Billings will have
its usual cooling affect, especially given a trend toward 
easterly surface winds the next two days. The airmass will become 
quite warm by Thursday w/ 700mb temps above freezing and 850mb 
temps greater than +10C. This would yield temps easily in the 60s 
if not for the snow, so will be interesting to see what happens. 
Have bumped up our western foothills to the lower 60s, while 
keeping the east in the 40s. Nights will fall below freezing in 
the eastern valleys with the possible exception of Thursday night 
w/ thermal low and cloud cover in place. All of this being said, 
snow melt will be on the increase and with it will be the 
potential for ice jams and low elevation snow melt run off. Things
to watch closely if you live along a river or stream.

Atmospheric river slamming into CA late Wednesday through Thursday
will bring our SW mountains a period of rain and high elevation 
snow Thursday and Thursday night. Could see several inches above 
9kft, with snow levels falling gradually through Thursday night. 
Shortwave embedded in the SW flow aloft will bring a chance of 
mainly rain showers to lower elevations Thursday night into 
Friday. Some mixed precip (i.e. ZR-) cannot be ruled out in our 
far east if/where valleys fall below freezing.


.LONG TERM...valid for Fri...Sat...Sun...Mon...Tue...

A trend toward lower heights and overall western CONUS troffing
will occur Friday through the weekend. This will bring a gradual
cooling and and an opportunity for rain/snow showers, but models
remain highly spread in the details, especially by late weekend. 
Today's model runs show main area of baroclinicity/forcing to our
south, and a potential snow event in the central Rockies to high 
plains. The latest ECMWF brings some precip to our southeast cwa 
Sunday/Monday, but the GFS/Canadian are drier keeping us more 
under the influence of the less interesting northern portion of a 
split jet. Ensembles show a great deal of spread. Have adjusted 
pops down slightly but will keep them near climatology (15-20 pct)
as we will be under below normal heights and general troffing 
through this period. Will need to keep watch of model trends. 
Consensus is for drying by Monday/Tuesday as central Rockies 
system departs and we see a benign WNW flow for a day or two.

High temperatures will drop to the upper 30s and 40s by the 
weekend, Sunday/Monday seeming to be the coolest days, with the
onset of a warming trend by Tuesday.




Expect some light rain/snow showers over the western mountains, 
with occasional obscurations of the high terrain. Otherwise dry 
weather and VFR flight conditions will prevail across the region 
through Wednesday. There is a risk of spotty valley fog east of
KBIL late tonight and early tomorrow, but confidence is low that
fog will impact a terminal. JKL



    Wed     Thu     Fri     Sat     Sun     Mon     Tue     
BIL 028/052 032/054 039/053 031/047 027/042 025/045 027/048
    00/U    01/B    22/W    23/W    22/W    21/B    11/B
LVM 027/055 035/061 039/055 031/046 023/042 022/044 024/049
    01/B    13/W    42/W    34/W    32/W    21/B    11/B
HDN 022/052 027/053 034/052 027/048 024/043 021/045 021/048
    00/U    00/B    22/W    13/W    22/W    21/B    11/U
MLS 020/041 024/043 032/044 026/042 024/038 020/039 022/043
    00/U    00/B    32/W    12/W    22/J    21/B    11/U
4BQ 021/049 026/049 036/048 028/047 025/041 022/042 022/046
    00/U    00/B    22/W    12/W    22/J    22/J    10/U
BHK 018/040 022/043 032/044 027/043 025/037 020/039 022/043
    00/U    00/B    53/W    12/W    22/J    21/B    11/B
SHR 022/053 029/059 037/056 029/050 025/041 021/044 022/047
    00/U    00/B    23/W    12/W    23/W    21/B    11/U



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