Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Grand Forks ND
332 am CST sun Dec 21 2014
Short term...(today through monday)
issued at 325 am CST sun Dec 21 2014
Main forecast challenge revolves around upcoming pre Christmas
snow event and expect snow amounts. Confidence rising as models coming
into better agreement and will use model blend and National
guidance for anticipated snow amounts.
Area of mainly -sn associated with current wave and zone of
isentropic lift will continue to propagate east and will monitor
for morning probability of precipitation. Once this moves through this am remainder of the
day should be mainly dry with persistent fog and low ceilings. With
southerly flow...continued warm advection and warmer start most of
the forecast area will be a few degrees either side of 32f.
Wave will drop into deepening trough tonight closing off over
South Dakota/NE region by morning. Surface inverted trough from South Dakota surface
low gradually takes shape across the central Dakotas. Lowering
condensation pressure deficits and isentropic lift confined to the
southern forecast area so have highest probability of precipitation there towards morning. Clouds will
hold temperatures up overnight.
Stacked low drifts slowly southeast Monday allowing surface inverted trough
to shift into the forecast area. Via Omega fields and 290k isentropic surface
lift increases during the day and raised probability of precipitation accordingly. Have
highest probability of precipitation associated in zone of 850mb frontogenetic forcing
although at this point banding snow potential does not look great.
Also from the 290k surface full saturation looks spotty. Based on
surface temperatures expect close to a 10:1 snow ratio.
Long term...(monday night through saturday)
issued at 325 am CST sun Dec 21 2014
Lift looks maximized Monday night and should be the favored period
for accumulating snow. Fortunately wind does not look to be a
serious issue although could see some drifting in open areas.
Low begins to fill Tuesday and isentropic lift diminishes during
the day. Still expect -sn during during the day but should
diminish from west to east during the evening. Cold advection weak
and mixed layer very shallow so winds should be manageable.
Considering headlines...based on model solutions and National
guidance feel this will be a fairly extended period of mainly
light snow. With wind also not appearing as a serious issue do not
feel watch warranted at this point although future advisories
Wednesday-Saturday...a bit of light snow could linger east of the
valley on Wednesday as the low continues to lift away from the area.
Thereafter have maintained a primarily dry forecast. The 00z
GFS/European model (ecmwf) indicate a more progressive Pacific shortwave trough
crossing the central/northern plains on Christmas...with precipitation
suppressed mainly south of the region. There will also be a few
shortwave troughs dropping southeastward in amplifying northwest
flow aloft. While any of these may produce some light snow...they
would be rather minor. Perhaps more importantly...this pattern will
allow colder air to filter southward for the latter half of the
period. The GFS/European model (ecmwf) both indicate 850 mb temperatures dropping to -20c by
next Saturday...bringing to an end our recent string of near to
above average temperatures.
Aviation...(for the 06z tafs through 06z Sunday night)
issued at 1142 PM CST Sat Dec 20 2014
Will keep IFR ceilings in through the taf period. Clearing in central ND
just about dvl to jms and hrrr indicates it likely not making it
further east. 925 mb winds are southwest in that area now and turn
more southerly again by 15z sun. Dvl Airport only spot where brief
clearing may occur...but also along the clear-cloud line that is
where the fog was thickest Friday night.