Area Forecast Discussion
Issued by NWS Gaylord, MI

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FXUS63 KAPX 181612
AFDAPX

Area Forecast Discussion
National Weather Service Gaylord MI
1112 AM EST Sat Nov 18 2017

.UPDATE...
Issued at 1100 AM EST Sat Nov 18 2017

Deepening surface low pressure (991 mb) over east central Illinois
will track by to our south this afternoon and evening. Apx and
surrounding radars shows rain building in from the south. This
progression should continue over the next few hours. Colder air
moving in behind this system will likely change the rain to snow
across the higher terrain early this afternoon. Current forecast
has this progression well in hand so only a few minor tweaks
required.

&&

.NEAR TERM...(Today through Tonight)
Issued at 316 AM EST Sat Nov 18 2017

High impact weather potential: Minimal. Periods of rain, mixed with
a little wet snow in spots today, gradually turning to NNW/NW flow
lake effect snows in gusty winds.

Pattern synopsis and forecast:

Positively tilted upper troughing was across the central conus, with
several weaker shortwaves ejecting through the Mississippi valley
and Great Lakes. One of these waves was crossing us now, taking with
it, an expansive area of rain (mixed with a little snow from eastern
upper down into the higher terrain of nrn lower). Left behind was
grunge. Fairly thick low level moisture/stratus, areas of drizzle
and some light fog, all out ahead of a cold front that was pressing
into Lake Michigan. Spottier reflectivities were seen within the
weaker vorticity across WI/IL, but precipitation becomes more
expansive again out in Iowa/NE. This is associated with developing
low pressure ahead of a more pronounced shortwave coming out of
Colorado.

As the deeper moisture is stripped out aloft this morning, see no
reason why periods of light rain/drizzle will end. This light rain
will gradually increase in coverage through the day, especially in
the SE CWA, as the aforementioned developing low pressure in the
central conus, deepens while lifting through SE lower Michigan. This
low pressure will also help the cold front from over Lake Michigan
gradually sink in from the NW/NNW, which will allow for some more
wet snows mix in on the nrn periphery of the precipitation shield.
As the low pressure crosses into the eastern Great Lakes tonight,
it`ll drag the cold front over Lake Michigan through the region,
with strong cold advection and gusty NW winds developing, along with
lake effect rain and snows changing to all snow overnight. The
convective depth of the BL is not overly impressive for most of the
night, with inversion heights struggling to reach 5kft by daybreak,
but the general light lake effect will get a little bit of a boost
from a shortwave and added moisture late tonight. Can only foresee
maybe a few tenths of snow today in the higher terrain, with and
inch or two around the GTV Bay region overnight.

Highs today in the 35 to 40F range for most areas, with lows tonight
in the low to mid 20s, slightly warmer in the GTV Bay region.

&&

.SHORT TERM...(Sunday through Monday)
Issued at 316 AM EST Sat Nov 18 2017

...Snow showers Sunday will give way to a dry and milder Monday...

High Impact Weather Potential: Accumulating snow in the Lake
Superior/Lake Michigan snow belts Sunday.

Pattern Forecast: Progressive upper level pattern in place as height
falls progress eastward from western North America...with a
splitting trough on its heels over the eastern Pacific...part of a
rather unbalanced four wave hemispheric pattern.  Short wave
troughing (actually consisting of two separate potential vorticity
anomalies) will slide across the Great Lakes/Ohio Valley today and
tonight...with a secondary short wave trough zipping across Michigan
Sunday...followed by another PV anomaly Sunday night with height
rises building in for Monday.

At the surface...a cold front was advancing into the upper Great
Lakes to the north of a broad area of low pressure stretching from
eastern Colorado into western Missouri.  A consolidated surface low
will arise from this later this morning...deepening as it tracks
into the lower Great Lakes tonight and into Quebec/New England
Sunday.  Cold cyclonic flow will follow in its wake across Michigan
tonight into Sunday...before low level anticyclonic flow/warm
advection arrives Sunday night associated with developing height
rises.

Primary Forecast Concerns: Lake snow showers will be ongoing Sunday
morning...as inversion heights are given a boost by passing synoptic
wave (inversion bases in the vicinity of 750mb with a decent
dendritic growth layer).  Have boosted PoPs above what the consensus
forecast was giving (utilized SREF PoPs to account for this)...
backing winds during the afternoon expected to shift bands to a more
westerly component (and probably shift north of the M-72 corridor by
late in the day) as inversion heights drop below 800mb.  But passage
of next short wave trough will deepen the moisture profile once
again...so will need to linger snow chances into Sunday night
though expect precipitation to diminish by Monday morning.

Snowfall amounts during the day are expected to be relatively
light...though do feel that there will be some decent bands going
Sunday morning in the Lake Superior/Lake Michigan snow belts...and
can see 2-3+ inch amounts in spots over northeast Chippewa County
and along the US-131 corridor in northwest Lower by late Sunday
afternoon when snow shower intensity should lessen.  Snow totals of
3-4+ inches will be possible between tonight and Sunday in these
aforementioned areas.

Temperatures expected to return to more normal mid November levels
Monday (upper 30s-mid 40s).

.LONG TERM...(Monday night through Friday)
Issued at 316 AM EST Sat Nov 18 2017

High Impact Weather Potential: Minimal.

Temperature roller coaster will roll on during Thanksgiving
week...with another strong push of cold air expected to arrive
Tuesday (with the possibility of early daytime highs followed by
falling afternoon temperatures).  This will set the stage for more
lake induced snow showers heading into the big Thanksgiving travel
day on Wednesday (but doesn`t look like a big deal at this point).
Thanksgiving Day itself looks dry...with more precipitation possible
on Friday.

&&

.AVIATION...(For the 12Z TAFS through 12Z Sunday morning)
Issued at 703 AM EST Sat Nov 18 2017

Rain will expand across nrn lower Michigan through the day with
the best coverage expected to be along and south of a line from
MBL to APN. CIGS will be lifting out of IFR to MVFR through the
day behind a cold front, while lake effect rain and snow showers
develop late in the day and especially through the night, along
with gusty NW winds. No significant snowfall rates expected and
only an inch or two accumulation in and around TVC/MBL by the end
of the TAF period.


&&

.MARINE...
Issued at 316 AM EST Sat Nov 18 2017

Lower end gale force gusts are expected for late this afternoon and
tonight for much of Lake Michigan and Huron. This is due to a
tightening pressure gradient on the backside of developing low
pressure that crosses the srn and eastern Great Lakes. Solid
advisory winds elsewhere. NW winds taper off some heading through
Sunday afternoon and night while also backing more out of the west,
but gusty conditions still expected due to deep overlake
instability. Periods of rain today, particularly closer to Saginaw
Bay, will eventually turn to lake effect rain and snow showers
late this afternoon through tonight.


&&

.APX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
LH...SMALL CRAFT ADVISORY until 7 PM EST Sunday for LHZ345-346.
     GALE WARNING from 4 PM this afternoon to 7 AM EST Sunday for
     LHZ349.
     GALE WARNING from 4 PM this afternoon to 11 AM EST Sunday for
     LHZ347-348.
LM...SMALL CRAFT ADVISORY until 7 PM EST Sunday for LMZ341.
     GALE WARNING from 4 PM this afternoon to 7 AM EST Sunday for
     LMZ323-342-344>346.
LS...SMALL CRAFT ADVISORY until 7 PM EST Sunday for LSZ321-322.
&&

$$

UPDATE...AS
NEAR TERM...SMD
SHORT TERM...JPB
LONG TERM...JPB
AVIATION...SMD
MARINE...SMD



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