Area Forecast Discussion
Issued by NWS Billings, MT

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114
FXUS65 KBYZ 252132
AFDBYZ

Area Forecast Discussion
National Weather Service Billings MT
332 PM MDT Sat May 25 2019

.SHORT TERM...valid for Sun and Mon...

The Northern Rockies region is under a shortwave ridge today, but
strong diffluent flow aloft was slowly working into our western
zones along with a strong impulse or two. This was kicking off
some showers and thunderstorms over the higher terrain and nearby
foothills. This activity will spill over into the nearby plains
this evening before dying off after sunset. A slight chance of
showers and isolated thunderstorms expands to southeast MT as a
low-level jet develops there overnight. We do not expect much if
any chance of a severe thunderstorm this evening as helicity is
weak and CAPE marginal, but the diffluence aloft may produce some
gully-washers.

On Sunday, diffluence and large-scale ascent move over the whole
region with appreciable instability and shear in place. Helicity
bullseyes are focused over the SE corner of Montana as well as
areas from the Beartooth Foothills to Billings. CAPE values per
short term ensembles suggest chance of over 1000 J/kg is 50
percent or better around Billings and over 80 percent in Carter
County. These levels support the possibility of large hail and
damaging wind from thunderstorms. PWAT values increase across the
area as well with locally heavy downpours a good bet. If you have
outdoor plans on Sunday, please be aware of the sky and be ready
to seek shelter. The favored time frame for storms tomorrow is 3
pm to 9 pm.

A cold front looks to cross the region from north to south Sunday
evening, which will help transition the environment from one
that supports convection and thunderstorms to one that favors
more of a widespread, stratiform rain event that continues into
Memorial Day. Significant rainfall amounts are possible from this
system due to low-mid-level upslope flow combined with
instability and good moisture availability (precipitable water
values around 0.75 inches). Due to reports of some streams already
running high we have issued a Flood Watch for Big Horn County, MT
and Sheridan County, Wy. This pattern will also favor snow in the
mountains above 8,000 feet. This means that the Beartooth Highway
could be affected by snow. The heaviest snow would likely occur
early Monday through Tuesday morning. Snow levels are still in
question, but we may need to issue Winter Storm Watch for the
higher elevations on the northeast facing slopes. Future shifts
will monitor.

High temperatures on Sunday they will range from the upper 50s
near Judith Gap to the middle 70s over portions of southeast MT.
Low temperatures tonight and Sunday night will generally be in the
40s to near 50 degrees. Look for high temps about 10-15 degrees
cooler Monday. BT

.LONG TERM...valid for Tue...Wed...Thu...Fri...Sat...

Once again only minor changes to the extended forecast period.
Temperatures will be at least close to normal through the bulk of
the extended period, with highs in the 60s and 70s. Expect a
period of mainly dry weather to start the period. Pattern becomes
more unsettled again late in the week and into the weekend.

Precip will linger across the southern tier of the CWA into
Tuesday, but decreases as the upper low shifts east into Nebraska,
and northerly flow aloft brings drier air into the region.
Tuesday could be the first day where smoke from northern Alberta
wildfires becomes noticeable, but that is more likely to occur
Tuesday night into Wednesday.

Split flow over the region Thursday into Friday will allow
warmer temperatures. Some diurnal, mainly terrain oriented,
convection is possible, but may see some showers slide through
foothills and into near plains, but most locations should be dry.
Activity Friday has potential to become more widespread as another
trof moves into the region, but will need to overcome dry air in
place before can get started. This trof should keeps showers
across ther region through the weekend.

Gilstad

&&

.AVIATION...

Scattered showers and isolated thunderstorms are developing in
higher terrain in the west. Localized reduction of flight
conditions are possible in heavier showers, but mainly VFR
conditions should prevail. Gilstad


&&

.PRELIMINARY POINT TEMP/POPS...

    Sun     Mon     Tue     Wed     Thu     Fri     Sat
-----------------------------------------------------------
BIL 048/069 046/053 043/064 044/070 048/071 052/071 051/070
    25/T    88/T    72/T    01/B    12/T    22/T    22/T
LVM 043/063 044/052 039/062 038/068 044/068 046/066 046/067
    28/T    97/T    52/T    11/B    13/T    34/T    33/T
HDN 045/071 047/055 043/064 043/070 046/072 049/071 049/070
    14/T    88/T    73/T    11/B    11/B    22/T    22/T
MLS 048/073 047/058 041/067 046/072 047/073 049/073 049/071
    23/T    55/T    41/B    10/B    11/B    12/T    22/T
4BQ 047/075 049/057 042/060 043/068 046/070 048/070 047/067
    23/T    67/T    63/T    20/U    11/B    12/T    22/T
BHK 045/071 044/056 040/063 043/069 044/069 046/068 044/067
    35/T    65/T    42/W    01/B    11/U    23/T    22/T
SHR 042/070 046/055 040/057 037/066 041/068 045/067 046/065
    13/T    79/T    85/T    21/U    12/T    12/T    24/T

&&

.BYZ WATCHES/WARNINGS/ADVISORIES...
MT...Flood Watch in effect from Monday afternoon through Tuesday
      afternoon FOR ZONES 38-57.
WY...Flood Watch in effect from Monday afternoon through Tuesday
      afternoon FOR ZONES 98-99.

&&

$$
weather.gov/billings



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