Scientific Forecaster Discussion
Area forecast discussion...updated
National Weather Service Billings Montana
922 PM MDT Monday Jul 27 2015
Thunderstorm activity has exited stage right into northeastern Montana
and the western Dakotas as of 03 UTC...so we cancelled the rest of
the Severe Thunderstorm Watch. Cooler and much more stable air has
followed the convection and cold front into the area...and evening
radar trends suggest only a few light showers will occur the rest
of the night. Humidities are climbing too...so we cancelled the
red flag warning a few hours early despite continued gusty winds.
Previous update...issued at 651 PM MDT Monday Jul 27 2015...
We removed another row of counties from the Severe Thunderstorm
Watch...including Yellowstone...as the main threat of strong to
severe storms is quickly shifting more deeply into southeastern
Montana. We also decreased probability of precipitation for the rest of the evening in south
central Montana behind the main complex of storms. Schultz
Previous update...issued at 554 PM MDT Monday Jul 27 2015...
We cancelled the Severe Thunderstorm Watch early for Stillwater...
Carbon...and Golden Valley counties as deep convection is east of
there as of 2345 UTC. We will likely be able to cancel the watch
for Yellowstone and Musselshell counties by about 01 UTC /7 PM
MDT/...but need to hang onto it for a bit longer given strong
storms observed on radar over far eastern parts of those counties
at this time. The threat for severe weather is over with in the
Billings metropolitan area though. Schultz
Short term...valid for Tuesday and Wednesday...
At 19z...cold front was from klwt S to Nye. Frontogenesis was
accompanying the front. Vorticity was rotating NE into the area
from Idaho per water vapor imagery...and jet divergence was over
western areas per the rap. Despite temperatures in the 50s and
60s...little cape and weak lapse rates...storms were strengthening
over the western forecast area...which showed the strength of the
dynamics. Have received some reports of half inch hail. Other
convection was slow to get going in the inverted trough over far
southeast Montana. Radar showed other storms approaching from Wyoming. Consensus of
latest models brought the cold front to kmls by 00z Tuesday. Meanwhile
convective available potential energy over the east half of the area ranged from 1000 to 2000
j/kg...and shear over central parts of the area was 40-50 knots.
The jet divergence and q-vector convergence will lift north of the
area before 06z...so strong dynamics will last into the early
evening hours. The best chance for severe weather will remain over
the east due to the high convective available potential energy...but a strong to severe storm cannot
be ruled out anywhere over the area. Will adjust probability of precipitation to go with
highest values central and east due to a generally slower system
movement. Had chance probability of precipitation over the west and kshr area. Precipitation
chances will decrease from S to north after 06z. Strong pressure rises
will follow the front this evening allowing for windy conditions.
Will continue red flag warning through 06z. Doubtful that
humidities will be very low due to dewpoints in the 50s to around
60...but dangerous fire conditions will exist due to warm
temperatures...the wind shift and increasing winds with frontal
passage and increasing thunderstorms.
Upper low/trough will move out of east Montana on on Tuesday. Showers may
linger across the north and mountains. The strong pressure gradient
behind the departing low will create windy conditions...especially
from Rosebud County east with models showing 850 mb winds from 45 to
55 knots and good mixing. Will issue a High Wind Warning from 12z to
03z for these areas. GFS looked warmer and drier than the WRF...so
went with a compromise for temperatures and relative humidities.
Humidities ended up above 20 percent so will not issue a red flag
for Tuesday. Future shifts can watch precipitation trends to get a
better handle on how humidities will behave on Tuesday.
Flow aloft becomes flat northwest Tuesday night through Wednesday night bringing
dry and warmer weather with less wind. Arthur
Long term...valid for Thursday...Fri...Sat...sun...Mon...
After a great relief from the summertime heat in the short
term...things will be warming up as we enter mostly zonal flow
aloft. Temperatures will remain just above normal as chances for
rain will be greatly reduced. Little pieces of energy could rotate
around the Desert Ridge on Friday and Saturday afternoons which
could help generate isolated thunderstorms...mainly over the
mountains. Weak piece of energy on Sunday in the northern stream
could produce a weak backdoor cold front. This should push
temperatures back to normal on Sunday and Monday.
Gusty west-northwest winds...a few showers or an isolated storm...
and possible local MVFR ceilings are expected tonight and Tuesday.
Winds will be strongest during the day Tuesday with gusts to 40 knots
in south central Montana and north central Wyoming and gusts to around 50 knots
in parts of southeastern Montana. Schultz
Preliminary point temp/pops...
Tuesday Wednesday Thursday Friday Sat sun Monday
bil 050/075 053/085 057/092 060/094 061/091 061/090 060/088
22/west 00/u 00/u 01/u 11/u 11/b 11/b
lvm 046/073 047/083 051/089 053/092 054/089 054/086 054/085
42/west 00/u 00/u 01/u 11/u 12/T 21/b
hdn 049/076 051/087 054/094 058/096 060/092 061/091 060/090
32/west 00/u 00/u 01/u 11/u 11/b 11/b
mls 053/072 053/087 057/093 061/095 062/091 063/089 062/088
83/T 10/u 00/u 01/u 11/u 11/u 11/u
4bq 052/073 052/086 055/093 060/095 061/093 062/091 062/090
31/north 00/u 00/u 01/u 11/u 11/b 11/b
bhk 053/070 052/084 055/090 057/092 060/088 060/085 059/085
83/T 10/u 00/u 01/u 11/u 11/u 11/b
shr 046/072 048/083 052/091 055/093 056/091 058/089 057/086
21/north 00/u 00/u 00/u 01/u 12/T 21/b
Montana...High Wind Warning in effect from 6 am to 9 PM MDT Tuesday for