National Weather Service United States Department of Commerce

Forecast commentary -

Regional satellite and mesoanalysis reveals strongly confluent flow forcing a cold front southward
through the lower peninsula at press time. Surface temperatures range from the low to mid 30s ahead
of the front and immediately behind it beneath nocturnal stratus to the teens and 20s in the
unmodified airmass over Minnesota and Wisconsin. Cross-section analysis shows the lead edge of the
cold air aloft extending well ahead of the surface front, which is currently still back over
northern lower. In fact, latest rap and 06z NAM suggest 850mb front is already about halfway through
the cwa, supporting rapid boundary layer growth as soon as the surface front passes later this
morning. Deep post-frontal northwest flow will ensue with winds gusting over 20 mph and rapid
expansion of stratocu limiting temperature recovery as cold advection continues through the day.
Slight upward tick in temps is likely during peak heating simply due to mixing, but otherwise little
movement from current readings. Forecast soundings and upstream trends offer increased confidence in
persistence of stratus through tonight as moisture remains trapped beneath lowering inversion
heights. Nudged overnight low temperatures up accordingly, but there remains plenty of room for an
additional upward adjustment. Any clearing potential will likely be closer to Tuesday morning as the
surface ridge positions directly overhead coincident with maximum subsidence.


Little change for Tuesday as the mid-level thermal trough remains in place. A moderating trend will
commence Tuesday through Thursday as heights gradually build in spite of suppression due to
shortwave energy tracking across southern Canada and the northern Great Lakes. The resulting rather
flat ridge will be sufficient to allow temperatures to recover into the 40s in spite of ample
mid/high debris.


The active subtropical jet noted on full disk imagery will be key to the slow evolution of the
pattern during the week, and likely the greatest source of uncertainty. Currently supporting
broad/weak upper energy near the mexican border, this energy will essentially act as a readily
available as a PV reservoir as mid-latitude troughing amplifies over the front range in response to
strong Pacific jet energy coming onshore early this week. The resultant longwave trough is progged
by the 00z ec to extend clear to guatemala, which is guaranteed to cause a high degree of
sensitivity in the solution space. One way or another, a significant cyclone is likely to emerge
over the eastern us. Initially warm, eventual infiltration of cold air as northern stream energy
feeds into the trough will likely support rain ending as snow along the deformation zone track.


. . posted at 400 AM EST Mon Dec 17 2018



Regional satellite and mesoanalysis reveals strongly confluent flow forcing a cold front southward
through the lower peninsula at press time. Surface temperatures range from the low to mid 30s ahead
of the front and immediately behind it beneath nocturnal stratus to the teens and 20s in the
unmodified airmass over Minnesota and Wisconsin. Cross-section analysis shows the lead edge of the
cold air aloft extending well ahead of the surface front, which is currently still back over
northern lower. In fact, latest rap and 06z NAM suggest 850mb front is already about halfway through
the cwa, supporting rapid boundary layer growth as soon as the surface front passes later this
morning. Deep post-frontal northwest flow will ensue with winds gusting over 20 mph and rapid
expansion of stratocu limiting temperature recovery as cold advection continues through the day.
Slight upward tick in temps is likely during peak heating simply due to mixing, but otherwise little
movement from current readings. Forecast soundings and upstream trends offer increased confidence in
persistence of stratus through tonight as moisture remains trapped beneath lowering inversion
heights. Nudged overnight low temperatures up accordingly, but there remains plenty of room for an
additional upward adjustment. Any clearing potential will likely be closer to Tuesday morning as the
surface ridge positions directly overhead coincident with maximum subsidence.


Little change for Tuesday as the mid-level thermal trough remains in place. A moderating trend will
commence Tuesday through Thursday as heights gradually build in spite of suppression due to
shortwave energy tracking across southern Canada and the northern Great Lakes. The resulting rather
flat ridge will be sufficient to allow temperatures to recover into the 40s in spite of ample
mid/high debris.


The active subtropical jet noted on full disk imagery will be key to the slow evolution of the
pattern during the week, and likely the greatest source of uncertainty. Currently supporting
broad/weak upper energy near the mexican border. This energy will essentially act as a readily
available as a PV reservoir as mid-latitude troughing amplifies over the front range in response to
strong Pacific jet energy coming onshore early this week. The resultant longwave trough is progged
by the 00z ec to extend clear to guatemala, which is guaranteed to cause a high degree of
sensitivity in the solution space. One way or another, a significant cyclone is likely to emerge
over the eastern us. Initially warm, eventual infiltration of cold air as northern stream energy
feeds into the trough will likely support rain ending as snow along the deformation zone track.


. . posted at 400 AM EST Mon Dec 17 2018