Area forecast discussion
National Weather Service Billings Montana
229 PM MDT Sat may 25 2013
Short term...valid for sun and Monday...
Tornado Watch 217 issued for Carter...Fallon...Powder River and
Rosebud counties until 10 PM MDT.
Short term models in good agreement with regard to area under the
gun today. This involves areas mainly northeast of an Alzada to
Roundup line. Cape values of 1000-2500 j/kg expected at maximum
heating with lifted indices down to -6 prognosticated. Upper forcing
upstream is subtle...but evident on 400mb vorticity proggs and
should be plenty to kick things off. However...timing of heaviest
action is inconsistent with hrr/NAM indicating 3-6 PM but BUFKIT
soundings showing cap breaking by noon today. We already have some
strong cells in the southeast zones so will lean toward a middle afternoon
initiation of surface based severe storms. The vertical wind
profile continues to show strong shear which will easily sustain
updrafts leading to hail. I am also concerned for isolated
tornadoes with the level of instability and shear. If forcing
turns out to be greater than prognosticated the environment may indeed
yield super cells capable of tornadoes. For tomorrow...proggs
indicate higher cape pushed well west into our forecast area so
the threat of super cells developing will involve most of the
lower elevations including Billings. Strong veering winds with
height will again sustain updrafts for a large hail threat with
storms initiating over the pryors and beartooths and intensifying
as they move north/northeast. Our central zones including Billings
may be the focus Sunday afternoon and then the convection moving
northeast by evening affecting the Miles City and Baker areas.
Monday...severe thunderstorm threat continues as a short wave
trough in the mean flow aloft moves over Montana. Strong
divergence prognosticated to affect our forecast area with a strong wind
shift to the west occurring. This may establish a line of
convection from just east Billings moving east into higher
dewpoints in the afternoon. Thus...best chance of severe weather
seems to be in the eastern sections while west may downslope
behind the trough passage. Lowered probability of precipitation in the west for latter
part of Monday. Bt
Long term...valid for Tuesday...Wed...Thu...Fri...Sat...
No changes planned to the extended forecast today due to early
onset of severe weather. The period Wednesday through Friday looks to be
the best time for widespread precipitation. Severe potential
appears diminished for the extended period. Temperatures will be
around seasonal values. Arthur
&&
Aviation...
Thunderstorms will continue across the entire area through this
evening. In terms of coverage...the storms will be isolated to
scattered west of Rosebud County. From Rosebud County east...expect
scattered to numerous thunderstorms. Thunderstorms could become
severe from Rosebud County east...with wind gusts in excess of 55 knots
and large hail.
Precipitation will taper off SW of a Harlowton to kbil to southern
Rosebud County line overnight. Scattered showers and a slight
chance of thunderstorms will occur east and north of kbil Sun morning.
Additional thunderstorms will move into the klvm and Harlowton
areas by 18z sun. Thunderstorms will increase in coverage across
the entire area Sun afternoon. Severe thunderstorms will be
possible from Roundup to kbil to kshr east. Conditions will range
from MVFR to LIFR in the thunderstorms through sun. Expect
scattered mountain obscuration due to the precipitation. Arthur
&&
Preliminary point temp/pops...
Sun Monday Tuesday Wednesday Thursday Friday Sat
-----------------------------------------------------------
bil 052/077 052/074 052/073 053/073 051/068 047/067 049/069
24/T 33/T 23/T 44/T 55/T 54/T 44/T
lvm 040/075 044/072 043/069 044/068 041/065 038/066 040/068
24/T 33/T 24/T 44/T 44/T 43/T 33/T
hdn 052/081 051/077 051/075 053/077 052/069 047/067 050/069
34/T 32/T 24/T 34/T 55/T 55/T 54/T
mls 055/080 055/077 055/076 056/078 056/070 051/067 052/069
44/T 54/T 34/T 44/T 55/T 55/T 55/T
4bq 053/082 050/079 050/075 052/078 052/071 047/065 048/067
34/T 44/T 35/T 34/T 55/T 55/T 54/T
bhk 054/076 052/075 052/074 052/075 055/069 050/066 049/068
54/T 55/T 35/T 35/T 55/T 55/T 55/T
shr 047/079 046/075 044/071 049/074 049/067 044/067 045/069
23/T 32/T 24/T 44/T 44/T 44/T 44/T
&&
Byz watches/warnings/advisories...
Montana...Tornado Watch 217 in effect until 10 PM MDT this evening for
zones 31>33-36-37-58.
Wyoming...none.
&&
$$
Weather.Gov/Billings
