Scientific Forecaster Discussion
Area forecast discussion...updated
National Weather Service Billings Montana
950 am MST Wednesday Dec 18 2013
Only minor changes were made to today/S forecast...mainly to make
sure that highs were at least 3 degrees f warmer than the maximum
temperatures already observed as of 16 UTC. Ridgetops are already
well-mixed this morning and most valleys should mix out easily in
the pre-frontal environment today...but the thermal ridge axis at
850-hpa will be shifting east as well. Thus...there is probably a
limit to how warm we can get...though the mild start makes a case
for some cold-biased forecast busts in spots. However...the first
piece of the surface cold front will reach southeastern Montana in the
middle to late afternoon...bringing dropping temperatures along with
stratus and maybe even some flurries to Miles City and Baker.
Otherwise...our main attention today is on the coming snow event.
The cold front passed through Cut Bank at 14 UTC...and normally a
passage at Billings will be 10 hours later...meaning it should be
arriving by late afternoon or early evening. It appears snow will
develop a few hours after the initial frontal passage as the cold
air deepens and frontogenesis takes off...so snow forecast timing
looks on target. We still have high confidence in widespread 3 to
6 inch snow amounts...but one challenge today will be deciding if
any larger-scale area will end up with more than that. Schultz
Short term...valid for today and Thursday...
Several issues to deal with in the short term package. The first
involves lingering wind over the west. The second is the onset of
snow and cold with the arrival on an Arctic boundary tonight. The
third is potential blowing snow over the west with a quick return
to winds. First to winds this morning.
Winds have been hitting advisory criteria consistently at
Livingston through the night. Gradient adequately tight to keep
these winds going this morning. Models advertise a loosening
surface pressure gradient through the day...and this has been
happening over the last several hours. Surface pressure falls were
starting to slide into eastern Montana...so do expect winds to
gradually back off this morning at Livingston. Will keep advisory
in place for the morning as currently pegging advisory criteria.
Will drop the warning for southern Wheatland County. Winds have
not approached warning criteria and with gradient relaxing...not
expecting that to occur. Big Timber has shown an increase in winds
over the last several hours...but winds have still fallen short of
advisory criteria. Winds should remain up through a good deal of
the morning...but as with Livingston...should see winds gradually
decrease. Will go ahead and drop advisory for Big Timber.
A mild day in store again with downslope flow. Winds aloft
decrease as does the surface pressure gradient through the day so
am not expecting as effective mixing. That being said...are
starting out very mild this morning. Was tempted to bump highs up
a couple of degrees to account for the warm start but 850mb
temperatures support current forecast. Not expecting much warming
today with lowering middle level heights and clouds streaming across
from Washington and Oregon. The mild weather will be broken
tonight with an advancing Arctic front.
The front was sitting up in southern Canada this hour. Models
have slowed the timing a little bit but am concerned that they
have slowed it down too much. Timing looks a little off based on
surface observations at the moment. Expect the front will arrive
in Billings early Wednesday evening and clear the state overnight.
A strong period of over running snowfall will occur behind the
front and this band of snow will shift south through the night.
Models have been consistently advertising a high end advisory
event but am concerned about lift through the good dendrite growth
zone overnight. Have raised snow amounts a touch for tonight.
Decided to issue advisories for most of the area. Snow will start
north of Billings this evening...and be accompanied by gusty winds
from Wheatland to Musselshell County...especially in the Judith
Gap vicinity. Included blowing snow there. Most other locations
will have a brief period of gusty winds...but blowing snow does
not look to be a major concern. Snow amounts should fall in the 3
to 6 range for almost everyone. Could be periods of moderate snow
with the west to east snow band getting hung up and this could
allow a few sites to exceed 6 inches...but am not expecting those
type of amounts to be widespread. Will also have to watch
locations from McLeod to Red Lodge as upslope does contribute to
the ascent. Models do not have usplope flow in there tremendously
long with the progressive nature of the system...so will keep
these locations at advisory levels for now.
Snow will taper off Thursday from northwest to southeast...with
the east having light snow lingering into the afternoon. Thursday
will be much colder with highs held in the single digits to teens.
The cold surface high shifts into the Dakotas Thursday night and
this turns low levels to downslope flow over the west late
Thursday night. A Lee trough is prognosticated to deepen late Thursday
night and this may cause some blowing snow concerns from Big
Timber to Livingston. Twh
Long term...valid for Friday...Sat...sun...Mon...Tue...
Extended models in fairly good agreement late this week through
the weekend but diverge some by the beginning of next week.
Unsettled northwest flow aloft will be over the forecast area as a
couple of disturbances move across the area. A surface low will
drop south out of Canada and across eastern Montana and the
Dakotas with each of these disturbances. Lee-side troughing and
windy conditions will be ahead of each low followed by a wind
shift to the north and cooler temperatures behind the passage of
each low. The air does not look Arctic in nature as the coldest
temperatures look to stay east into the Dakotas. Each disturbance
will bring a chance for snow showers to the forecast area but
significant amounts are not expected at this time.
However...models can sometimes have a difficult time with a
northwest flow aloft so will need to watch each of these
disturbances as time gets closer. In general...temperatures will
be around normal or slightly above for the weekend into early next
week with the far east being the coolest given proximity to the
coldest air across the Dakotas. Hooley
Mixed airmass ahead of Arctic front will keep gusty winds and
unstable conditions through the afternoon. Winds will weaken and
turn easterly through the evening as the front slips into the
area. Some scattered rain or snow showers will be possible as the
front begins to move into the area. Stronger part of the Arctic
front will move into the area late this evening bringing
widespread IFR conditions by midnight. Borsum
Preliminary point temp/pops...
Today Thursday Friday Sat sun Monday Tuesday
bil 047 008/011 002/028 017/028 018/033 023/041 025/036
2/r +9/S 11/b 44/j 32/j 12/j 22/j
lvm 048 010/014 004/028 028/031 023/036 033/041 026/034
2/r +9/S 12/j 64/j 32/j 22/west 22/j
hdn 047 007/011 907/027 008/027 007/030 016/040 020/033
1/east +9/S 11/b 44/j 32/j 12/j 22/j
mls 043 000/007 910/019 008/019 000/021 013/034 020/033
1/M +9/S 10/b 34/j 22/j 12/j 22/j
4bq 050 006/010 908/024 005/026 009/024 012/038 022/034
0/b 9+/S 10/b 33/j 22/j 11/b 22/j
bhk 041 000/006 909/018 006/018 902/016 008/030 017/032
1/M ++/S 10/b 23/j 22/j 12/j 22/j
shr 052 009/013 905/025 012/027 010/031 016/042 020/035
0/north 79/S 10/b 44/j 32/j 22/j 23/j
Montana...Winter Weather Advisory in effect from 6 PM this evening to
noon MST Thursday for zones 28-29-42-63.
Winter Weather Advisory in effect from 6 PM this evening to 6
PM MST Thursday for zones 30>35-39>41-56-57-64>66.
Winter Weather Advisory in effect from midnight tonight to 6
PM MST Thursday for zones 36>38-58.
Wind Advisory in effect until noon MST today for zone 66.