Scientific Forecaster Discussion
Area forecast discussion...updated
National Weather Service Glasgow Montana
848 PM MDT Tuesday Mar 11 2014
Short term...for northeast Montana...tonight through Thursday...
Made only very small adjustments to the grids for a minor update
tonight. Dropped all probability of precipitation to zero...and tweaked temperatures and wind and
clouds following latest observational and model trends. Rest of
the forecast continues to look quiet and uneventful from the
Previous short term discussion...pleasant Spring conditions
areexpected to continue. NE Montana sandwiched between two surface high
pressure systems. A low system will be moving onshore from the
Gulf of Alaska tonight and spread warmer air into the area
tomorrow with 850 mb temperatures about 6 to 8*c warmer than today. Since
the area is snow free...the stronger March sun will continue to
warm things above model guidance...as has been the case today.
Therefore went about 2 to 3 degrees above suggested numbers.
Wednesday night and Thursday...weak cold front moves in from the
northwest. 850 mb temperatures drop about 4 to 6*c. Northwest winds will be
increasing with the cold air advection. Tfj
Long term...Thursday night through Tuesday...
Little in the way of changes to the going forecast were made as
the previous thinking in the long range still holds overall.
Models are still in agreement having northwest flow aloft over the
northern plains Thursday night through Friday night with a ridge
to the north of the County Warning Area. Friday night and Saturday will yield
flattening of the ridge as a shortwave aloft and accompanying
surface cold front drops across the region. Expect a mix of rain
and snow showers along with this system. Timing/placement in
precipitation is somewhat uncertain with the GFS considerably
further south with the leading edge as compared with the European model (ecmwf).
The European model (ecmwf) also shows the heaviest precipitation on Saturday
afternoon with the best positive vorticity advection moving across...while the GFS has this
earlier in the day.
Next upper shortwave quickly follows on Sunday with potential
Chinook effects allowing for a warm March day with temperatures
soaring into the 50s and 60s. Large scale subsidence will also
dominate allowing for dry conditions and sunny skies.
Given such increasing ensemble spread later in the forecast
period...adjustments were mainly in the form of tweaks beyond
Sunday night. Maintained near climatology probability of precipitation given large uncertainties
and temperatures generally in the 40s to near 50 for highs and
20s for lows. Maliawco
Previous long term discussion...
Synoptic set up...a center of cold air lies over the Hudson Bay
with a trough spur running down through Manitoba and the Dakotas
terminating over Colorado. A ridges runs up the intermountain west
through British Columbia and into Alaska. Northeast Montana begins
between these two features with cold influence from the trough and
northwest flow aloft. Farther west... a large cold trough sets
over bearing sea and will spill out into the northeast Pacific.
Thursday night through Sunday... the large ridge to the north and
west will gain influence very slowly throughout these periods.
Broad northwest flow will be the main factor with a shortwave and
cold front Friday night/Saturday bringing rain and snow showers to
the region. Temperatures should be well above normal through out
these periods with a slight warming effect.
Sunday night Onward... model confidence begins to get fuzzy during
this time frame. Sunday night and Monday are the only exception
where a cold front and shortwave are anticipated to pass through
the area... but a up to a 24 hours phase problem for this event
is going on. Afterward... model solutions vary wildly and will
probably change within the next few runs. Cooler and seasonably
normal temperatures are anticipated here. Gah
Expect VFR conditions to continue through the overnight hours. Winds
will diminish from the northwest to around 5 to 10 kts.
Area rivers will be watched for responses for the next several
days from recent snow melt and potential ice jams. Ice jams have
been causing Rapid River rises in places...followed by rapid
declines as the jams clear. Clearing ice jams have had dangerous
rapid ice flows with them.
Ice jam Flood Warning on the Yellowstone river...a dangerous ice
jam on the Yellowstone river in southeastern Richland County is
moving toward Sidney and Fairview. Therefore a Flood Warning for
ice jam flooding has been issued for today and tonight. In
addition...with a continued threat of ice jam flooding on low
lands and nearby roads...a Flood Advisory also remains in effect
for both Dawson and Richland counties for today and tonight.
Flood Warning on the Musselshell river...there is significant
flooding upstream of Petroleum County on the Musselshell river
due to ice jam effects and snow melt runoff. Water levels remain
high above 10 feet and at minor flood stage at Mosby...where
cresting is expected to occur on Wednesday above 11 feet. Ice jams
have occurred where ice continues to move and jam along the
Musselshell river. Since water level are expected to rise
further...a Flood Warning will remain in effect through Wednesday.
Ice jams will continue on to the U L Bend later this week.
Flood Advisory for Flatwillow and McDonald creeks that are
running high and contain ice jams. Therefore a Flood Advisory
remains in effect for southern Petroleum County.
Flood Advisory for Wibaux County...an ice jam is located on
Beaver Creek about 2 miles south of Wibaux. With additional
snowmelt...and ice jamming which may cause flooding...a Flood
Advisory remains in effect today and tonight. Until ice jams melt
or push out of the area...levels will continue to remain high.
Reports of lower water upstream may provide some relief on
Big Dry Creek in Garfield County and the Redwater river in McCone
County...levels remain high but have not caused any unusual
problems. Some water-covered low water crossings are being
avoided with alternative roadways. Overnight levels on the big dry
have hold steady...while water levels were dropping on the Redwater.