Area Forecast Discussion
Issued by NWS Billings, MT

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FXUS65 KBYZ 220302
AFDBYZ

Area Forecast Discussion...Updated
National Weather Service Billings MT
902 PM MDT Wed Sep 21 2016

.UPDATE...

Backed off on PoP`s earlier this evening with some updates as
main bands of showers are basically delayed due to backing mid
level flow ahead of upper low. Satellite imagery suggest good
dynamics pushing northward across eastern Idaho at this time.
However, as flow slowly continues to back it will still take
awhile for the eastward progression of upper low to get these
dynamics and surge of Pacific moisture into our western CWA. So we
have the categorical PoP`s slowly making their way from west to
east late tonight and into early Thursday. Precip Water values are
still progged to be unusually high by late tomorrow. As much as
four standard deviations above normal and outside the 30 year
climatology record. So expecting good rain and socked in
conditions tomorrow into tomorrow night. BT

&&

.SHORT TERM...valid for Thu and Fri...

The first day of Fall is on Thursday and accordingly the forecast
through the beginning of the weekend will be cool and wet. An
upper level low will move into the Western US tonight, and deep
south and southwest flow aloft will transport rich atmospheric
moisture over the region. We have good confidence of two periods
of precipitation moving over the region with the heaviest rainfall
impacting regions north and west of Billings. The first will be
tonight as a wave of energy embedded in the low moves over the
region. The second wave will move through overnight Thursday into
Friday. Rainfall amounts will be lower with the first wave and
will be around 0.25 to 0.75 inches, with the higher amounts west
and north of Billings. The second wave on Thursday night will
yield higher rainfall totals of 0.5 - 1.25 inches as the
positioning of the upper level low places our area in a better
position for rainfall. Given precipitable waters nearly 4 standard
deviations above normal, especially in locations west and north of
Billings, I would not be surprised to see locally higher amounts
of rainfall overnight Thursday. In between these waves expect
cloudy and cool conditions in the 50s with scattered light showers.
The biggest impacts through these two days will be agricultural
interests and any outdoor activities and events. If traveling
along the Beartooth Pass the next few days, pay attention to road
closures as 3-6 inches of snow above 9000 feet is possible through
Friday morning.

By Friday morning the upper level low will begin pushing northeast
through the forecast area. Varying paths in the global models of
this upper level low will bring differing amounts of
precipitation to the region as moisture wraps around the western
side of this low. As the low slides east we are expecting another
round of precipitation around 0.25 to 0.75 inches for the region,
with the higher amounts in locations east of Billings. I should
note, however, that there is still quite a bit of uncertainty in
the rain amounts on Friday and Friday night so stay updated with
future forecasts. Dobbs

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


Still quite a bit of model uncertainty with the departure of the
closed low pressure system in the extended portion of the
forecast. Latest GFS has a weaker more disorganized system with
dry slotting across the eastern portions of the state and light
rain bands over central Montana on Saturday. The ECMWF looks
stronger with better wrapping of moisture and heavier rainfall.
Kept a blend of solutions in the forecast with best chances for
rain over the plains tapering down as you get to the foothills.
Ground will already be quite wet from rainfall on Thursday and
Friday, so outdoor activities could be impacted from wet
conditions. Anticipate a clearing of the low by Sunday with high
temps gradually warming into the 60s and low 70s by the end of the
period.

Models have started to indicate a blocking ridge of high pressure
developing over the Northeast U.S. by the mid part of the week
which may push the exiting low pressure system back over western
South Dakota. Included a mention of precip possible over the
eastern Plains at the end of the period to account for this. Walsh

&&

.AVIATION...

Areas of rain and drizzle will occur across the region
tonight through Thursday. An isolated thunderstorm is not out of
the question Thu. afternoon. Conditions will range from MVFR to
LIFR tonight, with mainly MVFR conditions on Thursday. The
mountains will be mostly obscured through the period. Arthur

&&

.PRELIMINARY POINT TEMP/POPS...

    Thu     Fri     Sat     Sun     Mon     Tue     Wed
-----------------------------------------------------------
BIL 048/061 051/057 047/059 044/062 042/065 044/067 045/070
    68/T    95/R    54/W    31/B    01/U    11/U    11/U
LVM 046/058 046/054 043/055 039/060 040/066 041/068 043/072
    98/R    88/R    63/W    21/B    01/U    11/U    11/U
HDN 050/068 051/061 046/060 043/063 041/065 043/066 044/071
    47/T    95/R    55/W    31/B    01/U    11/U    11/U
MLS 053/064 052/064 048/059 043/061 040/064 043/065 043/068
    36/T    87/R    56/W    62/W    12/W    21/U    11/U
4BQ 053/066 052/071 048/059 042/060 038/062 040/063 041/069
    34/T    74/R    46/W    41/B    12/W    21/U    11/U
BHK 049/060 049/061 047/057 041/056 040/059 041/062 041/064
    24/T    57/R    56/W    52/W    12/W    22/W    11/U
SHR 049/070 051/065 045/058 041/059 040/063 041/066 041/070
    58/T    95/R    55/W    31/B    11/U    11/U    11/U

&&

.BYZ WATCHES/WARNINGS/ADVISORIES...
MT...None.
WY...None.

&&

$$
weather.gov/billings



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