Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Grand Forks ND
316 PM CST Friday Nov 28 2014
Short term...(this evening through Saturday night)
issued at 316 PM CST Friday Nov 28 2014
Precipitation chances and type will be the main headaches for the period.
Positively tilted trough continues to dig onto the West Coast with
fast near zonal flow over the northern plains. Surface low pressure
continues to hang out in eastern ND with a strong baroclinic zone
stretching from northwest to southeast across North Dakota and
Minnesota. There has been a band of scattered mixed precipitation across
the central County Warning Area that fits fairly well with the 800mb frontogenesis
as seen in the rap13 analysis. This band should move northeastward
as the surface low moves out into ND tonight...with the front lifting
towards the Canadian border. Continued to keep high chance probability of precipitation
going for mainly the northern County Warning Area...with a mix of precipitation along the
southern edge of the precipitation. Will have to watch for freezing
drizzle possibilities further south...but not confident enough to
include it at this point.
The upper trough will begin to move into the northern rockies
tomorrow...with surface low pressure quickly moving off to the east.
Another cold front bringing Arctic air will plunge southward
across the County Warning Area. Think that a non-diurnal temperature pattern is
probable with rising temperatures tonight as the warm air surges north
and falling tomorrow afternoon at least in the north as the cold
front moves south. Warm air aloft will be firmly in place Saturday
morning...and with cold temperatures at the surface...some freezing rain and
sleet are possible. This mixed precipitation should move south and
eventually change over to all snow as the column cools throughout
the day on Saturday. Amounts will be very light no matter what the
precipitation type...so will include an Special Weather Statement for tonight and tomorrow
mentioning very light mixed precipitation in spots.
The upper trough will continue to dig into the northern
plains...with surface high pressure arriving in the region. North
winds should become quite breezy with strong cold air
advection. Temperatures should go down below zero in the northern
counties with the cold air even with winds and lingering clouds.
There could be some light snow in the middle level baroclinic zone
remaining over the area...but pretty scattered and light with not
Long term...(sunday through friday)
issued at 316 PM CST Friday Nov 28 2014
Sunday and Monday...cold and dry with high pressure over the area.
Highs on Sunday will struggle to get near zero and with clouds
diminishing we could again drop close to the 20 below mark in some
areas Sunday night. Warm air advection kicks in as the surface high
moves east on Monday...but with breezy winds and temperatures still in
the single digits...it will still feel very raw. Will have to
watch for wind chills approaching advisory mark but too soon to
mention at this point.
Monday night through Friday...this period begins with a departing
surface high pressure centered over Iowa and developing low
pressure over Saskatchewan. Southerly gradient becomes quite
strong...with 45 to 55 knots 850 jet and 45kt 925 jet winds
traversing County warning forecast area. Since this will occur overnight Monday/early
Tuesday do not think full gradient potential will be realized. But
it should be breezy and guidance picks up on this. Short wave
embedded in amplifying upper flow moves rapidly east along the
international border...pushing a cold front through the County Warning Area
Tuesday. As surface low forecast to track near/along Canadian
border only slight chance probability of precipitation given over eastern part of County warning forecast area.
Behind the front Tuesday night into Wednesday expect another fairly
rapid cooldown. Trajectories both surface and aloft under flatter
northwest flow with relatively higher 1000-500kpa thickness suggest
the airmass will not be quite as cold as recent intrusions.
Surface high moves rapidly east of the County warning forecast area Wednesday night into
Thursday. Temperatures moderate nicely at the end of this period
with timing differences relatively slight. At this time no
significant waves depicted by models so have kept Wednesday - Friday period
Aviation...(for the 18z tafs through 18z Saturday afternoon)
issued at 1243 PM CST Friday Nov 28 2014
Abundant moisture and weak forcing yielding areas of
IFR/MVFR ceilings/visibility this morning. Shallow low level boundary forecast
to shift slowly north through00z. Low risk -frdz/pl near the
boundary where moisture and lift are maximized. Although this
boundary should lift north during this period expect slow
improvement kdvl-kgfk-kbji line. South of boundary visibility should show
gradual improvement and decrease -sn/pl/-frdz risk. Observation and lamp
guidance suggest VFR after weak boundary lift past taf site. However
timing is very problematic as boundary will be slow to move north.