Area Forecast Discussion
Issued by NWS Billings, MT

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FXUS65 KBYZ 222051

Area Forecast Discussion
National Weather Service Billings MT
251 PM MDT Tue May 22 2018

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

Active weather ahead tonight htrough Wednesday night, with areas
of heavy rainfall likely. Stay alert if you live near a river or
stream with the potential to flood.

An upper trough of western Utah will work northeast tonight. This
process will send increasingly diffluent flow aloft into southern
Montana and northern Wyoming for ascent. Enough cape around for
storms to pulse high enough for some hail, but shear does not look
strong enough (only around 30-35kts) for organized severe storms.
As stronger lift moves in this evening, would not be surprised to
see stronger cells form over over mainly southern and eastern
locations. Will have to watch as this evolves tonight.

The bigger story will likely be heavy rain potential.
Precipitable water amounts were over three quarters of an inch for
the entire area, with amounts over an inch over southeast
Montana. Models send stronger energy into the area overnight. This
combined with surface convergence, will get strong showers going
south of Billings, with this activity spreading northwest through
the night into Wednesday. GFS, and some of the high resolution
models, were very aggressive with QPF amounts tonight and
Wednesday, putting over an inch (and in some instances near 2
inches) of QPF from Sheridan county northward into the foothills
(mainly west of a line from Roundup to Billings to Sheridan).
Given the high water levels on rivers and streams, this added
water could cause more problems with flooding. Issued a Flood
Watch for the western half of the forecast area (including
Sheridan county) for tonight through Wednesday night.

Wrap around showers will continue through the day on Wednesday
over the western zones, while a dry slot allows for some drying to
occur over parts of the central zones and the east. Cyclonic flow
will allow a few showers to develop Wednesday afternoon and
evening, before the main drying trend for Thursday as an upper
ridge builds in. TWH

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

Ridging will be brief on Friday and allow for temperatures to
reach well into the 80s. These warm temperatures will cause an
uptick in mountain snow melt again, as we head into the weekend.

Another upper low moves into position (similar to the current one)
on Saturday. This low is progged to move slowly east through early
next week. This pattern will send a series of shortwaves into the
forecast area for periods of showers and thundestorms this weekend
into early next week. Some of the storms could be strong with
locally heavy rain. There are a few differences with the strength
and position of the low between the GFS and ECMWF, and this has
big impacts on which day would be the bigger storm day. The main
story with this upper low is that it will continue to risk for
flooding through the holiday weeeknd, into early next week.

Please monitor for the latest on our streams
into early next week. The main spring runoff will likely be upon
us later this week through the holiday weekend and will need to be
closely monitored for potential flooding. TWH



Showers and thunderstorms will become more widespread this
evening. Stronger storms with some hail and wind gusts in excess
of 40kts are possible this evening. Locally heavy rain is likely
with the storms. Conditions will deteriorate to MVFR tonight with
IFR conditions expected in the stronger showers. TWH



    Wed     Thu     Fri     Sat     Sun     Mon     Tue
BIL 055/068 053/082 055/086 056/087 055/080 055/077 054/078
    79/T    52/T    11/U    11/U    23/T    54/T    53/T
LVM 049/066 049/078 049/082 051/081 052/074 052/072 050/074
    79/T    64/T    32/T    12/T    36/T    66/T    44/T
HDN 055/072 052/084 055/088 056/092 056/084 055/081 054/081
    78/T    42/T    11/U    11/U    23/T    54/T    53/T
MLS 059/075 056/081 059/087 059/091 060/086 060/083 059/082
    68/T    52/T    11/U    00/U    13/T    54/T    43/T
4BQ 057/079 055/082 057/086 057/090 059/085 058/082 055/080
    85/T    41/B    11/U    00/U    13/T    44/T    44/T
BHK 058/078 054/078 057/084 056/089 055/085 057/081 054/079
    87/T    31/B    10/U    01/U    12/T    44/T    44/T
SHR 052/074 050/079 052/083 052/087 054/079 051/077 050/075
    94/T    51/B    21/U    11/U    23/T    55/T    43/T


MT...Flood Watch in effect from 6 PM MDT this evening through late
      Wednesday night FOR ZONES 28-29-34-35-38>42-56-57-63>68.
WY...Flood Watch in effect from 6 PM MDT this evening through late
      Wednesday night FOR ZONES 98-99.


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