NWS Forecast Discussion

291
FXUS63 KDTX 201751
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
1251 PM EST Sun Jan 20 2019

.AVIATION...

Cold northerly flow off lake Huron will maintain a steady stream of
lake stratus that will largely hold east of the TAF sites this
afternoon and evening. However, there remains some potential for
fragments of stratus along the western edge to drift near one or
more terminals during this time. Outgoing forecast maintains a
few/sct mention this afternoon to highlight this potential. Gusty
northwest winds during the latter half of the day - gusting 20-25
knots at times. Gust frequency and magnitude will steadily decrease
this evening. VFR conditions tonight through Sunday as building high
pressure maintains a very dry and stable environment.

.DTW THRESHOLD PROBABILITIES...

* Low for cigs aob 5kft through the evening.

&&

.PREV DISCUSSION...
Issued at 1216 PM EST Sun Jan 20 2019

UPDATE...

This morning`s update was sent with virtually no changes to the going
forecast except to account for the more northerly fetch streaming
into Huron County. Glaciation noted on channel 11 imagery and occasional
reductions to vsby, not to mention some degree of band persistence
now extending into Detroit city and Windsor, warranted an increase in
pops for today and a minor adjustment to accums. Still expecting a
1-7 inch range in the advisory area, but bled extent of higher snow
totals for today westward into the Port Austin to Caseville corridor.

Second update now forthcoming to remove any meaningful snow from the
southern Sanilac and Saint Clair County shorelines. Recent spotter
report from Port Huron confirmed that vsby reductions there are due
to blowing snow and that the band remains offshore. With tendency
toward veering wind through today/tonight, there`s no reason to wait
until the aftn package to update the forecast.

Will bump up clouds a touch elsewhere and add mention of flurries
across a chunk of the CWA. Not only are light echoes getting into the
northern metro area, but steady expansion southward growth of lake
clouds has been noted over the last hour. Impressively, lake effect
clouds are making it into the Saginaw Valley area downstream of due
northerly flow across far northern Lake Huron, sans assistance from
assistance from either Lake Superior or Saginaw Bay.

PREV DISCUSSION...
Issued at 300 AM EST Sun Jan 20 2019

DISCUSSION...

Strong high pressure will expand across the northern Great Lakes
today and tonight in the wake of an amplifying northern stream
trough rotating into the ern Great Lakes. Northerly flow between
this arctic high and the east coast storm system will sustain the
advection of polar air into Se Mi today. 925mb temps are actually
expected to drop to -18 to -20C today. Even with some daytime sun,
the degree of cold air and a fresh snowpack will support daytime
highs in the single digits to low teens. While the winds will
diminish a bit during the course of the day, wind chill readings
will hold largely at 5 to 15 below. Even though sfc high pressure
will expand into Lower Mi tonight, enhanced thermal troughing over
Lake Huron will support some light winds through the night. With
actual air temps dropping below zero, wind chill readings around 20
below look likely. This will warrant the issuance of a wind chill
advisory tonight through Monday morning for all Se Mi.

Northeast winds off southern Lake Huron and a rather slow departure
of the synoptic scale deep moisture led to some intense lake effect
snow shower activity across Sanilac County overnight. The low level
flow is now in the process of backing to the north, causing some
higher intensity snow showers to affect eastern St Clair Co early
this AM. Some additional backing by late morning should force snow
showers around Port Huron to push east to Sarnia, while additional
lake effect develops over the northern Thumb. High res guidance
suggests these will be multiple banded, thus cutting down on accums.
There is however good agreement among the 3KM NAM and RAP that there
will be a consolidation into a more dominate band later today from
just off Sturgeon Point stretching across ern Huron and ne Sanilac
County. This band is forecast to persist through a good portion of
the night. This certainly raises concerns for some locally high snow
totals. The fact that equilibrium levels are expected to hold around
5k ft, and considering the airmass will be so cold (possibly
inhibiting good dendrites) and dry, a long duration winter wx
advisory will be issued today and tonight for Sanilac and Huron
counties as opposed to a warning (with 3 to 7 inches forecast).
Gusty winds off Lake Huron will also contribute to some blowing snow.

Strong arctic high overhead amidst strongly confluent mid level flow
will support sunny but cold conditions Monday. Meanwhile, long wave
trough amplification will be underway across the Rockies. A mid
level impulse is forecast to lift out of this long wave trough and
traverse Lower Mi Tues night/Wednesday. There will be a plume of warm
moist air preceding this wave, with a 60-80 knot low level jet
aiding in the transport of this airmass into Se Mi. Precip chances
will arrive late Tuesday and continue into Wednesday due to the lead
warm air advection and moisture surge. The initial ascent is likely
to be all snow, with a transition to sleet and rain during the
course of Tues night. Model soundings suggest the low level
southerly flow will cause the strongest warming in the boundary layer,
thus mitigating freezing rain potential (although sub freezing road
temps may prove problematic). The warming profile and transition to
rain will likely keep overall snow totals in check. The progressive
nature of the system will also not keep Se Mi in the warm sector for
long, with temps likely to drop during the day Wed as the wave lifts
northeast of the region. Medium range model solutions are in good
agreement in depicting another strong arctic air intrusion into the
region by the end of the work week.

MARINE...

Northerly gales over southern Lake Huron and western Lake Erie this
morning will just slowly decrease today and tonight, with winds
quickly diminishing on Monday as high pressure arrives. Frigid
airmass will continue to cause heavy freezing spray over most of
Lake Huron, with snow squalls over the southern Basin through
tonight. Winds become southerly and strengthen on Tuesday as warmer
air moves back into the region. Gusts around 30 knots expected over
the open waters of Lake Huron, with a brief gust to Gales not out of
the question. Low pressure tracking through northern lake Huron
Wednesday morning will cause winds to become light. Winds behind the
low Wednesday night and Thursday expected to be only be around 20
knots.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...Wind Chill Advisory from 6 PM this evening to noon EST Monday for
     MIZ047>049-053>055-060>063-068>070-075-076-082-083.

     Winter Weather Advisory until 7 AM EST Monday for MIZ049-055.

Lake Huron...Heavy Freezing Spray Warning until 1 AM EST Monday for LHZ362-363-
     421-441>443-462>464.

     Gale Warning until 5 PM EST this afternoon for LHZ442-443-463-464.

     Small Craft Advisory until 7 AM EST Monday for LHZ421-441.

     Small Craft Advisory from 6 PM this evening to 7 AM EST Monday for
     LHZ442-443.

Lake St Clair...NONE.
Michigan waters of Lake Erie...NONE.
&&

$$

AVIATION.....MR
UPDATE.......JVC
DISCUSSION...SC
MARINE.......SF


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NWS DTX Office Area Forecast Discussion