Area forecast discussion...updated
National Weather Service Billings Montana
1000 am MDT Sat may 25 2013
Update...
upper disturbance moved across eastern Montana this morning
producing some showers and thunderstorms...even some large hail in
Wibaux County just north of our forecast area. Satellite shows
some clouds continuing to stream across the southeast section of the
state which look convective in nature. Atmosphere is primed with
already 1500 j/kg in southeast corner...but there is some cloud cover
there to delay heating and thus deeper convection. I expect some
convection to develop in cloud free areas around midday to early
afternoon and become most of it surface based by 3 PM. Southeast
zones have a good chance of being placed in a watch box later
today. Have adjusted a few probability of precipitation for the evening based on latest
NAM. Rest of forecast on track. Bt
&&
Short term...valid for today and sun...
Very active weather setting up over southeast Montana today with
the potential for severe thunderstorms. Severe weather will again
be possible on Sunday for all of southeast Montana and portions of
south central Montana.
Today and tonight...low level jet setting up over southeast
Montana and will advect low level moisture into the area. Dew
point temperatures will increase through the day and will be in
the middle to upper 50s by afternoon from Forsyth east to Baker.
Afternoon heating will allow surface based convective available potential energy to range from
1500 to 2500 j/kc this afternoon and evening with lifted index
values of a -7c. BUFKIT soundings indicate strong directional and
speed shear across southeast Montana. 0 to 6 km effective shear
prognosticated at 35 to 40 knots. Models are indicating several short waves
to move across the region this afternoon and tonight. Upper jet
will also bring qg forcing over the forecast area. Forecast models
are also indicating preciptable waters over the southeast today
will reach around 1 inch. Upper air sounding in Rapid City had
0.75 pwat's at 00z last evening. The area most likely to see
severe weather this afternoon and tonight will be along and east
of line from Miles City to Broadus and have increased probability of precipitation to high
scattered for Custer and Powder River counties and likely for
Fallon and Carter. The main threat from these storms will be large
hail...damaging winds and very heavy rain. Cannot rule out an
isolated tornado given the strong wind shear over the area.
Scattered showers and thunderstorms will be possible west of
Forsyth to Billings to Livingston this afternoon and tonight. A
few storms could have strong wind gust given inverted vee type
soundings...but a middle level cap will be in place which should
prevent any wide spread outbreak of sevre weather over the western
and central zones.
Sunday and Sunday night...weak low level jet will persist over
the area and will advect low level moisture from southeast Montana
to as far west as Billings. Afternoon heating into the lower 80s
will cause surface based convective available potential energy to reach near 1000 j/kg near
Billings to around 3000 j/kg near Alzada. Upper trough to the west
of Montana will continue to rotate energy across the forecast area
along with maintaining a strong diffluent flow aloft. Effective
wind shear over the are will be lesser than today with around 25
to 30 kts expected. Threat from strong thunderstorms will be large
hail. Have added severe weather wording for the zones from
Billings west Sunday. Richmond
Long term...valid for Monday...Tue...Wed...Thu...Fri...
Little change again for the extended period...with persistent wet
and unsettled pattern. Models continue to have difficulties with
the details of the pattern...but remain in general agreement as to
the large scale pattern...and dominance of broad trough across the
region. Models diverge more significantly about Tuesday
evening/night. Southwest flow aloft will prevail through this
point...with multiple shortwaves radiating through the flow. Trough
begins making way across the region thereafter.
The extended period begins Monday...which looks like another day
for strong to severe storms across much of the region...but
especially in the east. Theres plenty of moisture and instability
available...with precipitable waters approaching an inch...lifted indices
ranging for -6 c to -10 c depending on your model...strong
convective available potential energy...and a strong shear profile.
As mentioned...models diverge with regard to the details from
Tuesday Onward...but agree on continued unsettled weather with
good moisture and some strong waves into the region. Have stuck to
inherited numbers at this point as uncertainty remains as to
specifics..but influence of broad trough remains evident.
Temperatures will be around seasonal average for this time of
year...a bit warmer to start the period...and generally cooling
gradually through the period toward slightly below normal by next
weekend. Aag
&&
Aviation...
There will be a slight chance of showers and thunderstorms with
associated MVFR/IFR conditions from kmls S and east late this
morning. Thunderstorms will develop across the entire area this
afternoon and persist 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. Conditions will range from MVFR to LIFR in the
thunderstorms this afternoon through Sun morning. Expect scattered
mountain obscuration due to the precipitation. Arthur
&&
Preliminary point temp/pops...
Today sun Monday Tuesday Wednesday Thursday Friday
-------------------------------------------------------
bil 076 052/080 053/075 052/073 053/073 051/068 047/067
2/T 23/T 34/T 43/T 44/T 55/T 54/T
lvm 073 040/078 043/074 043/069 044/068 041/065 038/066
2/T 23/T 34/T 34/T 44/T 44/T 43/T
hdn 080 052/082 053/076 051/075 053/077 052/069 047/067
2/T 33/T 35/T 44/T 34/T 55/T 55/T
mls 079 056/081 058/076 055/076 056/078 056/070 051/067
5/T 45/T 45/T 44/T 44/T 55/T 55/T
4bq 080 054/082 052/079 050/075 052/078 052/071 047/065
3/T 34/T 45/T 55/T 34/T 55/T 55/T
bhk 075 054/077 056/074 052/074 052/075 055/069 050/066
6/T 45/T 45/T 55/T 35/T 55/T 55/T
shr 077 047/081 048/076 044/071 049/074 049/067 044/067
2/T 23/T 35/T 44/T 44/T 44/T 44/T
&&
Byz watches/warnings/advisories...
Montana...none.
Wyoming...none.
&&
$$
Weather.Gov/Billings
